Acidification Research: Evaluation and Policy Applications : Proceedings of an International Conference, Maastricht, the Netherlands, 14-18 October (Studies in Environmental Science)

ACIDIFICATION RESEARCH: EVALUATION AND POLICY APPLICATIONS

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Studies in Environmental Science 50

ACIDIFICATION RESEARCH: ETVALUATION AND POLICY APP LICAT10NS Proceedings of an International Conference, Maastricht, The Netherlands, 14-1 8 October 1991

Edited by

T. Schneider Rijksinstituut voor Volksgezondheid en Milieuh ygiene (RIVM), 3720 BA Bilthoven, The Netherlands

ELSEVIER Amsterdam - London - New York - Tokyo 1992

ELSEVIER SCIENCE PUBLISHERS B.V. Molenwerf 1 P.O. Box 21 1,1000 AE Amsterdam, The Netherlands

@ 1992 Elsevier Science Publishers B.V. All rights reserved.

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher, Elsevier Science Publishers B.V., Copyright and Permissions Department, P.O. Box 521, 1000 A M Amsterdam, The Netherlands Special regulations for readers in the USA - This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the publisher.

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Studies in Environmental Science Other volumes in this series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Atmospheric Pollution 1978 edited by M.M. Benarie Air Pollution Reference Measurement Methods and Systems edited by T. Schneider, H.W. de Koning and L.J. Brasser Biogeochemical Cycling of Mineral-Forming Elements edited by P.A. Trudinger and D.J. Swaine Potential Industrial Carcinogens and Mutagens by L. Fishbein Industrial Waste Management by S.E. Jergensen Trade and Environment: A Theoretical Enquiry by H. Siebert, J. Eichberger, R. Gronych and R. Pethig Field Worker Exposure during Pesticide Application edited by W.F. Tordoir and E.A.H. van Heemstra-Lequin Atmospheric Pollution 1980 edited by M.M. Benarie Energetics and Technology of Biological Elimination of Wastes edited by G. Milazzo Bioengineering, Thermal Physiology and Comfort edited by K. Cena and J.A. Clark Atmospheric Chemistry. Fundamental Aspects by E. MBszbros Water Supply and Health edited by H. van Lelyveld and B.C.J. Zoeteman Man under Vibration. Suffering and Protection edited by G. Bianchi, K.V. Frolov and A. Oledzki Principles of Environmental Science and Technology by S.E. Jergensen and I.Johnsen Disposal of Radioactive Wastes by Z. Dlouhq Mankind and Energy edited by A. Blanc-Lapierre Quality of Groundwater edited by W. van Duijvenbooden, P.Glasbergen and H. van Lelyveld Education and Safe Handling in Pesticide Application edited by E.A.H. van Heemstra-Lequin and W.F. Tordoir Physicochemical Methods for Water and Wastewater Treatment edited by L. Pawlowski Atmospheric Pollution 1982 edited by M.M. Benarie Air Pollution by Nitrogen Oxides edited by T. Schneider and L. Grant Environmental Radioanalysis by H.A. Das, A. Faanhof and H.A. van der Sloot Chemistry for Protection of the Environment edited by L. Pawlowski, A.J. Verdier and W.J. Lacy Determination and Assessment of Pesticide Exposure edited by M. Siewierski The Biosphere: Problems and Solutions edited by T.N. VeziroQlu Chemical Events in the Atmosphere and their Impact on the Environment edited by G.B. Marini-Bettblo Fluoride Research 1985 edited by H. Tsunoda and Ming-Ho Yu Algal Biofouling edited by L.V. Evans and K.D. Hoagland Chemistry for Protection of the Environment 1985 edited by L. Pawlowski, G. Alaerts and W.J. Lacy Acidification and its Policy Implications edited by T. Schneider Teratogens: Chemicals which Cause Birth Defects edited by V. Kolb Meyers Pesticide Chemistry by G. Matolcsy, M. Nhdasy and Y. Andriska Principles of Environmental Science and Technology (second revised edition) by S.E. Jorgensen and I.Johnsen Chemistry for Protection of the Environment 1987 edited by L. Pawlowski, E. Mentasti, W.J. Lacy and C. Sarzanini Atmospheric Ozone Research and its Policy Implications edited by T. Schneider, S.D. Lee, G.J.R. Wolters and L.D. Grant Valuation Methods and Policy Making in Environmental Economics edited by H. Folmer and E. van lerland Asbestos in the Natural Environment by H. Schreier

38 39 40 41 42 43 44 45 46 47 48

49

H o w t o Conquer Air Pollution. A Japanese Experience edited by H. Nishimura Aquatic Bioenvironmental Studies: The Hanford Experience, 1944-1984 by C.D. Becker Radon i n the Environment by M. Wilkening Evaluation of Environmental Data for Regulatory and Impact Assessment by S.Ramamoorthy and E. Baddaloo Environmental Biotechnology edited by A. Blazej and V. Privarovh Applied Isotope Hydrogeology by F.J. Pearson, Jr., W. Balderer, H.H. Loosli, B.E. Lehmann, A. Matter, Tj. Peters, H. Schmassmann and A. Gautschi Highway Pollution edited by R.S. Hamilton and R.M. Harrison Freight Transport and the Environment edited by M. Kroon, R. Smit and J. van Ham Acidification Research in The Netherlands edited by G.J. Heij and T. Schneider Handbook of Radioactive Contamination and Decontamination by J. Severa and J. BBr Waste Materials in Construction edited by J.J.J.M. Goumans, H.A. van der Sloot and Th.G. Aalbers Statistical Methods i n Water Resources bv D.R. Helsel and R.M. Hirsch

vii

Fomword SESSION A

xii Opening session

1

Acidification: a n international problem J.G.M .Alders

3

Acidification as an example of the link between science and policy G.J.R.Wolters and H.Marseille

7

Acidification research and policy in the province Limburg H.W.Riem, B.R.Pasma and D.van Nierop

SESSIONB

State-of-the-artof acidificationresearch

17

25

Forest vegetation and acidification: a critical review RSchlaepfer

27

Global environmental change: implications for acid deposition research D.J.Waters and P.G.Whitehead

45

The role of ammonia in acidification: perspective for the prevention and reduction of emissions from livestock operations A.A.Jongebreur and J.H.Voorburg

55

Emissions of acidifying components M.Amann

85

Acidification of forests and forest soils: current status E.Matzner

77

Stress combinations in forests J.L.Innes

87

Effects of increasing nitrogen deposition and acidification on heathlands J.A.Lee, S.J.M.Caporn and D.J.Read

97

The interaction of forest vegetation and soils with the aquatic environment; effects of catchment liming on lakes T.R.K.Dalzie1, G.Howells and R.A.Skeffington

107

...

vlll

Higher order effects L.Reijnders

127

Acidifying effects on groundwater JSoveri

135

Monitoring for the future: integrated biogeochemical cycles in representative catchments T.Paces

145

The critical loads concept for the control of acidification J.-P.Hettelingh, R.J.Downing and P.A.M.de Smet

161

SESSIONC

175

AcidXcation policy

Canadian acid rain policy S.Milburn-Hopwood and K.J.Puckett

177

Acidification policy in Finland E. Lumme

185

Acidification policy - control of acidifying emissions in Germany B.Schtirer

191

Acidification policy in Hungary E .KovBcs

203

Acidification abatement policy - The Netherlands experience G.J.A.Al and V.G.Keizer

211

The convention on long-range transboundary air pollution: its achievements and its potential H.Wuster

221

Acidification policy - Sweden K.LGvgren, G.Persson and E.ThornelSf

241

Air pollution control policy in Switzerland B.C.Galli Purghart

247

Acidification research: evaluation and policy applications; a United Kingdom policy response R.G.Derwent and R.B.Wilson

253

Acidification policy in the United States D.Leaf

257

ix

SESSIOND

New mstxmh d t s on the acidBcation problem

263

Setting priorities for the measurement of acid aerosols and gases: 3 examples for Switzerland P.A.Alean-Kirkpatric and J.Hertz

266

High resolution assessment of acid deposition fluxes W.A.J.van Pul, J.W.Erisman, J. A.van Jaarsveld and F.A.A.M.de Leeuw

277

Measuring and modelling atmospheric dry deposition in complex forest terrain G.P.J.Draaijers, R.van Ek, W.Bleuten and R.Meijers

285

The transplantation of four species of Lobaria lichens to demonstrate a field acid rain effect A.M.Farmer, J.W.Bates and J.N.B.Bel1 Acidification research activities in Poland W.A. Mill

301

Critical loads for Dutch forest soils W.de Vries, J.Kros, R.M.Hootsmans, J.G.van Uffelen and J.C.H .Voogd

307

Scenario analysis with the Dutch Acidification Systems (DAS) model; an example for forests and forest soils A.Tiktak, A.H.Bakema, K.F.de Boer, J.W.Erisman, J.J.M.van Grinsven, C.van Heerden, G.J.Heij, J.Kros, F.A.A.M.de Leeuw, J.G.van Minnen, C.van der Salm, J.C.H.Voogd and W.de Vries

319

Acid rain abatement in Belgium: lessons of cost-effectiveness studies C.Cuijpers and S.Proost

341

Base content in soil and problems arising in connection with acidification L.Werner

349

Measurements of tree growth and health in the Liphook Forest Fumigation project: an evaluation of large scale open air fumigation experiments M. R. Holland and P.W. Mueller

357

SESSIONE

Results &om national research programmes

The United States national acid precipitation assessment program P.M.Irving

363

366

X

The United Kingdom research programme and its implications for policy, now and in the future R.B.Wilson

375

Research into forest decline and air pollution in France; major findings and relevance for policy applications G.Landmann

383

Background, results and conclusions of the Dutch Priority Programme on Acidification G.J.Heij and T.Schneider

397

Acidification research in Sweden H.Staaf and U.Bertills

415

Finnish research programma on acidification (HAPRO) 1985 - 1990 P.E .Kauppi

431

Status of acidification research in Czechoslovakia and its relationship to politics and economics in Europe T.Paces

443

The Swiss national research program “Forest Damage and Air Pollution” F.Haemmerli, N.Kriiuchi and MStark

449

SESSIONF

461

Closing seasion

A comparison of some national assessments J.Nilsson and E.Cowling

463

po6TFIRSESSION

519

The Dutch Acidification Systems (DAS) model: the emissions and air transport modules K.F.de Boer, J.W.Erisman, F.A.A.M.de Leeuw, T.N.Olsthoorn and R.Thomas

521

The relationship between research and policy on acidification impacts in the nature conservation agencies of Great Britain A.M.Farmer

523

The Dutch Acidification Systems (DAS)model: the forest module SOILVEG J.J.M.van Grinsven, C.van Heerden and J.G.van Minnen

525

A modelled assessment of critical load exceedences for sulphur over the United Kingdom G.W.Campbel1 and J.G.Irwin

527

xi Dry deposition over grassland: seasonal influences, chemical equilibria and surface wetness M.A.H.G.Plantaz, A.T.Vermeulen, P.J.de Wild, G.P.Wyers and J.Slanina

529

The Dutch Acidification Systems (DAS) model A.Tiktak, A.H.Bakema, K.F.de Boer, R.M.Kok and T.N.Olsthoorn

531

Long-term impact of three deposition scenarios on Dutch forest soils W.de Vries, J.Kros, C.van der Salm and J.C.H.Voogd

533

Soil and soil solution composition of 150 forest stands i n The Netherlands i n 1990 W.de Vries, E.E.J.M.Leeters, C.M.Hendriks, W.Balkema, M.M.T.Meulenbrugge, R.Zwijnen and J.C.H.Voogd

535

Automated denuder systems for dry deposition studies of acidifying compounds G.P.Wyers, A.T.Vermeulen, R.P.Otjes, A.Wayers, J.J.Mo1 and J S l a n i n a

537

AQUACID: modelling the acidification of shallow heathland lakes in The Netherlands; the aquatic systems module of DAS F.G.Wortelboer

539

An international research program on acid rain and emissions i n Asia W.K.Foel1

541

Deposition of acidifying compounds D.Fowler, J.N.Cape, M.A.Sutton, R.Mourne, K.J.Hargreaves, J.H.Duyzer and M.W.Gallagher

553

List of plu-ticipanb

573

xii

The International Conference on ACIDIFICATION RESEARCH, EVALUATION AND POLICY APPLICATIONS, organized by the Ministry of Housing, Physical Planning and Environment, was held in Maastricht, The Netherlands, from 14 - 17 October 1991. A first Conference of this kind was held in Amsterdam, from 5 - 9 May 1986. During that Conference 24 official delegations from ECE member countries discussed the available results of Acidification Research Programmes and Projects and evaluated these results with regard to the implications for Policy Actions. In 1986 already a number of results indicated the need to study and describe the (mostly negative) effects of acidification. More substantial evidence for the relative importance of acid deposition in the whole field of environmental stresses on the endangered ecosystems or environmental compartments however, surfaced during the execution of nationwide coordinated research programmes. Examples of such a programme could or still can be found in the USA,Canada, Finland, France and The Netherlands. A number of individual research results have been reported and discussed already in the Glasgow Conference held in 1990. The relation between scientific results of integrated research programmes and policy actions to prevent, reduce and limit the widespread damage caused by acidification was, however, not presented as yet. In cooperation with the members of the MARC group (Meeting of Acidification Research Coordinators) the Organizing Committee therefore suggested a programme for the Conference containing several types of presentations: - thematic reviews on specific topics of acidification research by invited key speakers; - summaries of national research programmes by programme coordinators; - overviews of acidification policy plans and actual abatement programmes by national or supra-national representatives; - selected poster presentations or short papers on recent research results. The Proceedings of the Conference contain the opening statements by J.C.M.Alders, Minister of Housing, Physical Planning and Environment; G.J.R.Wolters, Conference Chairman and W.H.Riem, Deputy Commissioner of the Queen in the Province of Limburg. After the Opening Session three half day sessions were devoted to the stateof-the-art presentations of key elements within the Acidification Research Programmes. In parallel sessions these were followed by presentations on: 1. Acidification Policy by national representatives 2. Results from National Research Programmes and 3. Recent Research Results on the Acidification Problem. During several days of the Conference also a Poster Session was held. A t this Session detailed information was given on results from specific (sub) items out of the research programmes.

...

Xlll

The final Session consisted of the presentation and discussion of a paper on “A comparison of some national assessments”. This comparison comprised an “all out effort” by two senior experts (Jan Nilsson and Ellis Cowling) in the field of Acidification Research. They succeeded in evaluating and comparing research results from a number of different national research programmes. A work of quality, carried out in a (relative) brief period before, during and shortly after the Conference. The editor would like to express here his admiration for this outstanding effort. The successful conduct of a meeting between research scientists and policy makers from a large number of countries, depends on the dedication of numerous individuals. As editor and Chairman of the Organizing Committee I would like to acknowledge here all those who have contributed to the organization of the Conference and the associated events. The preparation of the final programme, and the selection of the invited speakers, was carried out with the support of the members of the National Advisory Committee, listed in this volume. Members of this Committee also acted as chairmen of the individual conference sessions. I also would like to recognise the excellent work performed by my Organization Committee: Joop van Ham of SCMO-TNO who served as scientific secretary together with Bert Jan Heij who also organized the Poster Session. Ottelien van Steenis not only performed the secretarial work of the Committee but also formed with the excellent help of Nel Venis-Pols and Marianne Vonk the Registration and Information Centre, and last but not least she also took care of all the preparations for these Proceedings. I am grateful for the, as usual, excellent organization of the programme for accompanying guests by Mini Schneider. I would also like to thank the Burgomaster and Aldermen of the City of Maastricht for their welcome reception in the Town Hall of this most bourgondic town of The Netherlands. Finally thanks are due to the members of the MECC Conference and Hotel Services for their expert performance and good standard of Dutch hospitality. I hope that these proceedings, published by Elsevier Science Publishers in their usually rapid and professional way, will be used as a work of reference, both by research scientists as well as by policy makers.

T.Schneider Chairman Organizing Committee

xiv

CONFERENCE CHAIRMAN Ministry of Housing, Physical Planning and G.J.R.Wo1ters Environment

ADVISORY COMMITTEE G.J.R.Wolters, chairman J.van Ham, secretary G.J.Heij B.A.Kleinbloesem L.Koster L.Reijnders T.Schneider K.Verhoeff G.H.Vonkeman

Ministry of Housing, Physical Planning and Environment TNO Study and Information Centre for Environmental Research National Institute of Public Health and Environmental Protection Dutch Electricity Generating Board Shell Nederland B.V. Netherlands Society for Nature and Environment National Institute of Public Health and Environmental Protection Ministry of Agriculture, Nature Management and Fisheries Committee for Long Term Environmental Policy

ORGANIZING COMMITTEE TSchneider, chairman Mrs.O.van Steenis, secretary J.van Ham G.J.Heij PARTN'JZRSPROGRAMME Mrs.M.Schneider - Ferrageau de St.Amand scientxcsecxt2tariat

J.van Ham

Registration and Information Centre Mrs.O.van Steenis

SESSION A OPENING SESSION

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T. Schneider (Editor). Acidification Research. Evaluationand Policy Applications 1992 Elsevier Science Publishers 0 . V .

3

ACIDIFICATION: AN INTERNATIONAL PROBLEM J.G.M. Alders Minister of Housing, Physical Planning and Environment, P.O. Box 20951, 2500 EZ Is-Gravenhage, The Netherlands

Mr. Chairman, Ladies and Gentlemen, I would like to start by welcoming you here at this conference in Maastricht and I wish you a useful and pleasant stay. Undoubtedly, you are all familiar with the problems caused by acidification. These problems are emerging nowadays in all industrialized countries and have a wide variety of effects on our ecosystems. Therefore, acidification is an example of the type of problem that can be dealt with effectively only by international measures. Of course, national efforts are indispensible, but because of the transboundary aspects of the problem, only a co-ordinated international abatement strategy can effectively address this problem. Acidification is a complex scientific problem. A large number of specialist fields are involved and, hence, international cooperation is also needed in scientific research. A conference, such as this one, can play an important role in facilitating the exchange of the latest information on acidification: not only with respect to research results but also with respect to the development and implementation of abatement policies. It is very useful for all countries to be informed about each other's results: this prevents overlap in research and has a steering and stimulating effect. In the Netherlands a national research programme on acidification was set up to study the effects of the emissions of sulphur oxides, nitrogen oxides and ammonia. The most important results of the second phase of this programme are presented during this conference. The international aspects of acidification are obvious. In most countries the share of emissions from neighbouring countries in the total deposition is significant. Not only in small countries like the Netherlands, but also in large countries with relatively low emissions, a high percentage of the acid deposition can be traced to foreign origin.

4

Foreign contribution is for example very high in Norway, Sweden and the Netherlands. Spain and Great Britain however, are to a large extent responsible themselves for the SO,-deposition in their countries. The first step in an international abatement strategy was the United Nations Convention on Long Range Transboundary Air Pollution, signed in Geneva in 1979, in which countries declared their firm intention to reduce emissions that contribute to depositions in other countries. This convention, once considered a paper tiger, already provides a basis for coordinated SO,- and NO,-abatement. A VOC Protocol will be signed next month and there is still more to come. For use in international negotiations, the UN-ECE is developing the so called "critical loads concept". In this concept the maximum deposition of sulphur and nitrogen on a specific area is determined, below which no negative effects will occur: the critical load. To stay below this critical load, emission reductions of 80 to 90 percent are needed. In a step-wise approach towards this critical load, target loads will be determined. This concept creates an unique opportunity for an abatement strategy as effective as possible and will lead towards international agreements with differentiated obligations. From our experience with modelling, we know that dramatic reductions are necessary. Some people experienced this as a shock after years of belief that severe abatement measures could be avoided. Once more this is an example that a good judgement comes from experience, but that experience comes from bad judgement

.

It is not likely that the required reductions will be realized in the short term. A comparison of the emission reductions, needed to reach the target loads, with the reductions foreseen in the current policies of European countries demonstrate that considerable supplementary efforts are needed. At this moment we are confronted with a related problem that should get all of our attention. From the point of view of cost effectiveness, measures taken in countries in Central and Eastern Europe should have priority. However, most of these countries do not have the financial means to actually take these measures. The need for creative international solutions becomes more and more urgent and maybe we should adjust the "polluter pays principle" to the new situation. The countries in Western Europe should assist countries in Central- and Eastern Europe that lack both technical and financial means. The European Energy Charter offers a good possibility to turn this idea into action, if it is used to improve the energy infrastructure in the East-European countries.

5

Negotiations on reduction percentages will play an important role during the coming years: an international abatement scheme has to be developed. The considerable costs involved in reduction measures are increasing the hesitation to really take these measures. Hopefully this will be avoided by a step-wise approach. In view of the seriousness of the effects, this development of an international abatement policy cannot await still more scientific certainty. Yes, there are still gaps in our knowledge, but knowledge alone will not solve our problems. To conclude, I can state that the Netherlands is supporting the critical loads concept and has accepted the resulting necessary emission reductions. A first step to reach our critical loads has already been taken. I would like to invite other countries to do the same. Furthermore, it is clear that the West-European countries have to assist East-European countries in order to reach our common targets as soon and as effectively as possible. I thank you for your attention.

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T Schnetder (Editor), Acidification Research Evaluationand Policy Applications

0 1992 Elsevier Science Publishers E V All rights resewed

I

ACIDIFICATION AS AN EXAMPLE OF THE LINK BETWEEN SCIENCE AND POLICY G.J.R. Wolters (Conference Chairman) and H. Marseille Ministry of Directorate Directorate, Netherlands.

Housing, Physical Planning and Environment, General for Environmental Protection, Air P.O. Box 450, 2260 MB Leidschendam, The

Ladies and gentlemen, I am very pleased to welcome you all at this international conference about acidification research, evaluation and policy application. Modern environmental issues, like acidification, depletion of the ozone layer and climate change, ask for an approach in which a close link is made between science and policy. In the past, when the first environmental problems became evident, we only had the possibility to treat the problem by using a technology based approach. Emission reduction by applying best available technology was the most reasonable thing we could do. Nowadays our knowledge about the whole chain from emissions to environmental effects has increased in such a way that scientific information about the seriousness and urgency of the environmental problem can give us accurate guidance in policy development. This means that, if the problem is very urgent and application of best practicable technology is insufficient to avoid irreversible changes in ecosystems, science provides a sound basis for the additional structural measures that have to be taken eventually. For example, measures to change production processes or reduce energy use or car use could be applied. "No effect levels", or "critical levels and loads", can be used to establish a policy objective. The time scale in which the policy objective should be reached, depends on the sensitivity of the systems. If the ecosystems concerned have a large buffer capacity so that they can stand a higher level of pollution than the "no effect level" for a certain period, it could be possible to prolong the time scale. But with this we should be careful because scientific information always deals with uncertainties. Even if science tells us that an ecosystem is less sensitive than we thought, and even if we are not 100% sure of serious ecological impacts, this could never be an excuse to do less than use the Best Available Technology and to produce more pollution than necessary. Mr. Joris Al, who will speak on the acidification policy of the Netherlands (tomorrow

8 or Thursday), will explain this two-track approach, based on effect-oriented environmental quality objectives on the one hand and source-oriented Best Available Technology on the other hand. International agreements tend to reflect the close relationship between science and policy more and more. I only have to refer to the speech of Minister Hans Alders, who told you about the critical loads approach, being used for international negotiations about further reductions of nitrogen and sulphur emissions. In my opinion, the acidification policy in the Netherlands is a good example of the link between science and policy, and I will try to tell you in short how acidification policy has developed on a dynamic scientific and technical basis. The purpose of presenting these developments is to give you food for thought on the various ways science and policy may be linked with respect to acidification. Possibly our experience could be of help for policy development in other countries. I will especially try to clarify how we translated scientific information into policy goals and how we dealt with uncertainties and changing insights. Approach The process of setting policy goals for the acidification theme is given in fig. 1. The theme "acidification" was recognized in Dutch environmental policy from 1976 onwards. Swedish data about acidification of lakes had caused concern about the situation in the Netherlands, but in fact very little was known about the damaging effects of acid on ecosystems and the first document handling this theme did not set air quality objectives as a policy goal for reducing the problem. A big change however occured when photographs of dying forests in Germany appeared in our newspapers. Questions in parliament and pressure from NGOs led to the first deposition objectives in the Indicative Multi-year Programme for Air '84-'881, based on Swedish and Canadian studies of the acceptable levels of sulphur and sulphate deposition. The Swedish and Canadian critical loads were translated into a preliminary critical load of 1800 acid equivalents per hectare per year for combined deposition of SO,, NO, an NH,. Complete conversion of these compounds into acid was assumed and a rough estimate of soil sensitivity in the Netherlands was made. An emission reduction factor of 3 to 4 for total acidifying emissions on a European scale was calculated to be necessary to reach the critical load for the Netherlands. Based on the approach of equal emissions per capita, the necessary reductions of SO,, being rather mild, were assumed to be possible, but the necessary technology for reducing NO, and NH, emissions was very inadequate. Interim emission ceilings for SO, and NO, were established on the same level as the current emissions, and the intention of lowering the emission ceilings on a European scale was mentioned.

9 Start of the research programme The questions from parliament, asking for abatement measures and a research programme, also led to an overview of current scientific knowledge in the Netherlands and to the memorandum "the problem of acidification' ", after which a large national research programme, the "Dutch Priority Programme on Acidification", was started. It was financed by several ministries as well as by the Electricity Generating Board and the Oil Companies. The first phase of this programme lasted until 1988.

SOCIETY

POLICY GOALS

SCIENCE

Questions in Parliament1 Pressure from N G O s

--

International Data

Survey of Current Knowledge Acidification Problem ( ' 8 4 )

AIR '85-'89 ( ' 8 4 )

,d."

9"'

AcidificatiOn Research Programme I ( ' 8 5 - ' 8 8 )

~

'

--

Environmental Policy Plan ('89)/

Acidification Abatement Plan ('89)

4'

Fall o f

*

*l/

Acid Res Prog II

('88-'90)

,

Environmental Pollcy Plan PLUS ('90)

Acid Res

; ; ; : : ;p

\

Environmental Policy Plan # 2 ('93)

fig.1: flow chart with the interactions policy goals and society.

between

science,

10

In 1984, in the Indicative Multi-year Programme for Air '85'89,, the deposition objective was changed. On the basis of an extensive inventory of available scientific knowledge, nitrogen deposition below 1600 equivalents per hectare per year was no longer considered to be acidifying. With unaltered assumptions of sensitivity of the Dutch soils, compared to the Swedish, a deposition of 3000 equivalents, of which 1600 in the form of nitrogen, was now considered to be the critical load for our ecosystems. Emission reductions of 70% for SO,, 33% for NO, and 50% for NH, were calculated to be necessary for the Netherlands to reach this deposition level, under the condition of comparable SO, and NO, -reductions in the neighbouring countries. The first comprehensive abatement programme was drawn up. The abatement technology for ammonia still had to be developed. Little was known about ammonia emissions and a decision about additional reduction measures was planned for 1988, when final deposition objectives should be established. In 1987, the first results of the research formed the basis of the "Interim Evaluation of Acidification Policy in the Netherlands'". Ecosystems appeared to be more sensitive for acidification than formerly was assumed and the effect of the measures appeared to be overestimated. A number of additional measures was described to attain at least the original 1984emission reduction targets. Final deposition objectives After the final report of the Dutch Priority Programme on Acidification was completed in 19885, final deposition objectives were established in 1989 in the National Environmental Policy Plan6 and in the Acidification Abatement Plan'. Because of the high sensitivity of ecosystems, the available abatement technology was inadequate to attain the necessary emission reductions in a short period. For that reason a set of deposition objectives was developed, based on critical loads, with a different time scale (table 1). year

acid load (eq./ha,yr)

N-load (eq./ha,yr)

ozone (1 hr./gr.s) ( w / m 31

400

-

120/50

I2010

1400

1000

240/100

2000

2400

1600

240' /lo0

middle of next cent

I

max. number of exceedances per year: 2 table 1:

policy goals for the acidifying components and ozone in the Acidification Abatement Plan and the National Environmental Policy Plan, 1989.

11

For the acidifying components, a true critical load or no effect level of 400 acid equivalents was set as a target level, to be reached around the middle of the next century. This will require more than 95% reduction of emissions in all European countries, attainable only on the basis of completely new technology and fundamental changes in industrial production, agriculture and transport. An objective of 1400 acid equivalents was set for 2010, to be reached as a mean deposition on Dutch forests, in order to safeguard the forests against the most serious adverse effects. From this 1400, a maximum value of 1000 equivalents of nitrogen was established, to prevent nitrogen accumulation in soil and vegetation and to prevent exceedance of the target value for nitrate in groundwater used as drinking water. These objectives will require an 80-90% emission reduction in Europe, which will require extensive energy conservation, decrease of car use and structural changes in agriculture. Abatement measures will be decided upon in the second National Environmental Policy Plan, which will be drawn up in 1993. An interim target load of 2400 acid equivalents, including 1600 equivalents of nitrogen at most, was established for the year 2000. This value would protect, according to the scientific knowledge at that moment, the less sensitive parts of the ecosystems in the Netherlands, for example the continuous forest areas on richer soils. It would also prevent heathland from changing into grassland (with some management measures) and groundwater under forests and nature reserves would satisfy the standards set for the preparation of drinking water. Emission reduction objectives To reach the interim deposition objective for the year 2000, emission reduction percentages (relative to 1980 emission levels) of 80% for SO,, 50% for NO, and 70% for NH,, have been established for the Netherlands, based on Best Available Technology and additional structural measures such as energy conservation and reduction of car use (table 2). The measures are described in detail in the Acidification Abatement Plan. For the neighbouring countries comparable reductions for SO, and NO, are required, and a 25% reduction of NH,. EMMISSION REDUCTION OBJECTIVES (2000):

so*: NO,: NH,: VOC:

80% 50%

70% 60%

table 2: Emission reduction objectives for the acidifying components and VOC in the Acidification Abatement Plan and the National Environmental Policy Plan, 1989.

12

Though the uncertainty regarding current deposition and the formulated critical loads was rather great, the emission reduction objectives were rather easily accepted by all the emitter-categories. The gap between both was so big that for the period until the year 2000, the uncertainty was overshadowed by the necessary reductions to reach the critical loads. The present acid load and the development in the last ten years are presented in next table. 1980

1981

1982

1983

1984

1985

1986

1987

1988 1989

6800

6900

6500

6300

6400

6300

6200

5900

5000

table 3:

4800

Deposition of total acidifying components (acid equivalents per hectare per year) from 1980 to 1989. (source: RIVM)

The decline in deposition results mainly from the decrease in SO,-emissions in the Netherlands and neighbouring countries. However, meteorological conditions are responsible for fluctuations. Ozone

(see table 1 and 2)

In order to reduce the role of ozone in the effects of acidification on nature to such an extent that it becomes negligible, the ozone level, averaged over the growing season, should not exceed 50 pg/m3. The harmful effects on humans would be negligible when ozone levels would not exceed 120 pg/m3 as an hourly average. These values can be approached only during the course of the next century, requiring more than 9095% reduction of NO, and VOC emissions in Europe and a large reduction in carbon monoxide and methane emissions over the whole world. For that reason they are referred to as final goals. Most serious effects of ozone on nature and humans can be prevented at the values which are chosen as objectives for the year 2010: 100 pg/m3 averaged over the growing season and 240 pg/m3 as a maximum hourly average. Drastic structural measures f o r NO, and VOC are needed in an international context to reach those objectives. A s an interim objective for the year 2000, the same values are established, but the hourly average of 240 pg/m3 is alowed to be exceeded twice a year. Additional to a NO, reduction of 50%, VOC emissions will be reduced with 60% in order to reach the interim objectives f o r the year 2000.

13

Further developments

(see fig 1)

A political discussion about the structural measures in traffic caused the fall of Dutch cabinet just after the National Environmental Policy Plan was decided upon. The new government decided that the present plan was not strong enough and announced the National Environmental Policy Plan - "Plus' ' I , in which, one year later, the emission reduction objectives for SO, and NO, for the year 2000 were accelerated with several years. For NH, , extra attention to local peaks of deposition was paid by "object oriented policy", protecting sensitive ecosystems from extremely high ammonia loads. In April this year the second phase of the Dutch Priority Programme on Acidification was finished9. Important conclusions are that the deposition of NH, appears to have been underestimated and the NOI deposition overestimated. The contribution of ammonia and ammonium compounds to total acid deposition in the Netherlands is almost 50%. By the enlarged contribution of ammonia, the Dutch contribution to the deposition in our own country is also enlarged. It is now more than 50%, while we formerly thought it to be about 40%. This means that our policy of emission reductions will be more effective than we thought to reduce the deposition in the Netherlands, especially for ammonia. This is one of the reasons that, in spite of a higher present load than presumed, the prognosis for the year 2000 is that the interim deposition goal will be attained if the proposed abatement measures would have their expected effects on national emissions and if neighbouring countries would reduce according to expectations. However, a recently published evaluation study by RIVM concludes that the abatement programme is less effective. This was based on an analysis of the proposed measures in so far as effectuated hitherto or considered suitable to be effectuated well before 2000. Also the level of reduction in neigbouring countries in 2000 was concluded to be insufficient. Although part of the proposed national measures was not taken into account and further international abatement is still being negotiated, the conclusions of the study are alarming. Its policy implications will be thoroughly analysed. The new deposition figures also have implications for regional differences within the Netherlands. In regions which used to be relatively heavily polluted, acid deposition has increased more (compared to former insights) than in the less heavily polluted regions. So the problems in the southern half of the Netherlands, where deposition is relatively high, are greater than we presumed. In fig. 2, the deposition in the year 1989, according to the latest insights, is shown. The deposition varies from 3000 acid equivalents per hectare per year in the north to more than 8000 in the south. Another change in scientific insights concerns the values of the critical loads. A level of 2400 acid equivalents per hectare per year is no longer considered as a critical load for certain types of forests. For all types of forests on sensitive soils the critical load is now established to be about 1400 equivalents.

14

Model calculations show us that an abatement policy resulting in a deposition of 1400 equivalents as an average on forests in the year 2010 will in the long term give complete protection to the forests as far as the critical Al/Ca-ratio in the soil solution is concerned, and that irreversible effects like depletion of the aluminum hydroxide buffer will be prevented. Evaluation of the present acidification policy will take place in 1992 and will be partly based on the results of the research programme. But we can already conclude that the deposition objective of 1400 equivalents has a stronger basis now. A second National Environmental Policy Plan will be drawn up in 1993. This autumn the third and last phase of the Research Programme will start. The final results will be used after 1994.

fig. 2: Total potential acid deposition in 1989 (mol H+ ha- yr-’ ) (source: RIVM9 )

15

Conclusion Concluding I can say that, during the last eight years acidification policy has developed in a consistent way. Present measures are derived from the most recent scientific insights with respect to critical loads. It was a challenge for scientists to help the policy makers in setting environmental objectives. The interaction between science and policy has been very fruitful and stimulating to both sides. Though it takes some time to give answers to urgent political questions, finally it is very satisfactory to have a policy which is based on the best available knowledge. Changing scientific insights and uncertainties have not kept us from adopting far reaching emission reduction measures. Nowadays we are at the eve of deciding upon even more drastic measures, concerning structural changes in production, extra measures for regions which are heavily polluted and reduction of volume of various activities. Those measures will only be acceptable when grounded on a firm scientific basis. I hope that this international conference will promote scientific understanding and will contribute to further agreements about the reduction of emissions, not only in this country but also in the rest of Europe.

References 1. Parliamentary Documents 11, 1983/84, 18 100, nr. 7. 2. Parliamentary Documents 11, 1983/84, 18 225, nrs 1-2. 3. Parliamentary Documents 11, 1984/85, 18 605, nrs 1-2. 4. Parliamentary Documents 11, 1987/88, 18 225, nr. 22. 5. Dutch Priority Programme on Acidification: Summary Report Acidification Research 1984-1988, Publication 00-06, November 1988, RIVM. 6. Parliamentary Documents 11, 1988/89, 21 137, nrs 1-2, issued to Parliament May 25th, 1989. 7. Parliamentary Documents 11, 1988/89, 18 225, nr. 31, issued to Parliament July 20th, 1989. 8. Parliamentary Documents 11, 1989/90, 21 137, nr. 20, issued to Parliament June 14 th, 1990. 9. Dutch Priority Programme on Acidification: Final Report second phase Dutch Priority Programme on Acidification, report no. 200-09, G. J. Heij and T. Schneider (eds), April 1991, RIVM.

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17

ACIDIFICATION RESEARCH AND POLICY IN THE PROVINCE LIMBURG

H.W. Riema, B.R. Pasmab and D. van NieropC a Deputy of Environment in the Province of Limburg, P.O. Box 5700, NL 6202 MA Maastricht, The Netherlands and Department of Environment in the Province of Limburg, P.O. Box 5700, NL 6202 MA Maastricht, The Netherlands

Abseact Acidification is an important environmental problem in The Netherlands. Both national and provincial government have tasks in the prevention of further damage due to acidification and the reduction of emissions. In this paper it is shown how a policy on acidification is formulated in th e province of Limburg. The national deposition targets have been adopted. Feasibility studies were carried out to establish the emission reduction necessary to reach th e deposition targets. These studies also show what emission reduction is feasible in a cost-effective way and how cost-effectiveness decreases as reduction targets a r e set higher. Thus emission reduction targets were set and a provincial abatement strategy, including measures to be taken by various target groups, was formulated. 1.

NATIONAL AND PROVINCIAL ACIDIFICATION POLICY Provincial governments play an important role in Dutch environmental policy. Provinces a re administrative bodies, controlled by elected administrators, and take in an intermediate position between national and local government. Provinces have several tasks in maintaining air quality and emission control. One of t h e most important tasks is the issuing of licenses t o companies tha t cause air pollution. Furthermore provinces have to report to national authorities on (trends in) air quality. In this paper i t is shown how a higher scale (national) policy is used to formulate a lower scale (provincial, regional) policy. In figure 1 i t is shown how the province of Limburg is situated in The Netherlands.

Figure 1. Limburg is the southernmost Dutch province.

18 Acidification is an important environmental problem in the province of Limburg. Due t o high Ht and N-deposition levels severe damage is already visible in different parts of Limburg. The damage known a t present is listed in table 1. Table 1. Damage due to acidification in Limburg [ l ] Crops and wood (harvest losses) Buildings, materials, monuments Forest Heathlands, nature Heathland pools

DFL 30 million (13 million ECU) DFL 3,5 - 5 million (1,5 - 2 million ECU) 40 % of the forests is damaged or dying; in North-Limburg 75 - 90 % damaged > 60 % severely damaged 90 % severely damaged

The Limburg policy on acidification is of course based on the national acidification policy. The main strategic goal of this policy is the prevention of the most severe damage t o forests and nature in 2010. The national policy sets well defined deposition and emission reduction targets and has identified so called target groups. Target groups for acidification policy in t he Netherlands are: power plants, industry, agriculture and traffic. This approach is translated t o the provincial scale. The first s t e p in translating national policy to the provincial scale consists of determining the most important sources of acid emissions and the actual level of deposition throughout the province. The second step consists of a study of possible measures and their cost and effectiveness for each of t h e target groups. These studies give insight in the decrease of cost-effectiveness as t h e goals for emission reduction a re set higher. An economic evaluation of the policy showing costs and effects can thus be made. This paper describes t h e results of t h e application of this method in Limburg. 2.

MO!3 IMPORTANT SOURCES

The most important sources of acid emissions in Limburg a re shown in figure 2. I t is clear that power plants and industry a r e the most important contributors to SO2 emissions. For NO, th e largest sources a r e power plants, industry and traffic. NHY is mainly emitted by agricultural activities, while the most important VOC-source is traffic. Insight in the contribution of sources to t h e emission of the various components is needed for an effective abatement strategy. The large differences in contribution of various types of sources to emissions of acid compounds is obvious but the regional differences in contribution t o the acid emissions is also very important. In Limburg this regional differentiation is large. In the south of the province t he contribution of NO, is 62 %. In the north NH3 is the most important component: 46 %. In all of Limburg S02-emissions play a minor role. These figures a r e illustrated in figure 3.

19 Traffic 5%

SO,

;

28.9ktonly

Various 5%

NO, : 61.8kton/y Industry 7%

Various 21%

NH, : 19.4 ktonly

Traffic 49%

VOC : 2 4 . 7 ktonly

Figure 2. Contribution of different sources to emissions of SOP, NO,, NHy and VOC in Limburg (1988)

\ Region I

I Total

NO,

0

NHy

1

1

382 5 (62%) 119.6(19%)

I 1

360.2 (26%) 169 9 (22%)

552.4 (40%)

360.3(46%)

479.9 (34%)

Figure 3. Regional differentiation in contribution of various components to acid emissions in Limburg (kg H+/ha/y, 1988)

20 In the north of Limburg ammonia plays a major role in acidification. Emissions of over 200 kg/ha/y are common in this region [2, 31. Most ammonia evaporates directly from stables and manure storages, particularly from poultry sheds and storages. (figure 4) The second important source is the application of manure on fields, while relatively little emission is caused by animals in pastures. The contribution of different agricultural sources is shown in figure 4. Cattle

Pigs

0 manure storage 53%

39%

/

Figure 4. Contribution of different agricultural sources to ammonia emission in northern Limburg (1988) In the southern part of Limburg the most important sources of acidification are power plants and industry. Considerable transboundary transport from sources in Belgium and Germany occurs, but sources in Limburg have an even greater influence on foreign air quality and acidification. Limburg appears to be a net exporter of acid components (see figure 5).

.....

Figure 5. Acidification balance in Limburg (1988) 3.

DEPOSITION

In the National Environmental Policy Plan [4] t h e deposition goals for the Netherlands are set. These targets are based on critical loads for sensitive forest and heather vegetations. The Limburg targets a r e set according to this national approach.

21 The main goal of acidification policy is to prevent occurance of the most severe damage due t o acidification in the year 2010. Therefore the mean deposition levels of H+ and N have t o be reduced as quickly as possible t o the following levels (table 2). Table 2 Deposition targets in Limburg (mean values in eq.H+/ha/y and eq.N/ha/y) year

2000

H+ deposition 2.400 N deposition 1.600

2010 1.400 1.000

To reach these targets a reduction in deposition of 70 - 75 % (relative t o t h e level in 1988) is needed in the next 20 years. The Dutch strategy for the reduction of acidifying components is published in several documents 14, 5, 61. These national documents give a set of measures that should lead to the mentioned targets. This national acidification policy will reduce the mean Dutch depositionlevel, which was 4.900 equivalents H+/ha/y in 1988, to an average of 2.200 equivalents H+/ha/y in the year 2000 (71. Thus i t seems that the national deposition goal of 2.400 equivalents H+/ha/y will be realized on a national scale. If one takes a closer look a t the calculations however, the distribution of deposition over the country appears to be inhomogeneous. In the northern provinces the depositionlevel is lower than 2.400 eq.H+/ha/y and in the south i t is considerably higher. Table 3 shows deposition levels in the Netherlands and in different parts of Limburg.

Table 3 Mean deposition levels in the Netherlands and in Limburg in 1988 and 2000 (equivalents H+/ha/y). Scale

1988

2000

The Netherlands Limburg North-Limburg South-Limburg

4.900 5.360 5.590 4.860

2.200 2.960 3.060 2.750

Implementing t h e national emission policy in the province of Limburg therefore is insufficient t o reach th e deposition goals. Calculations show that in all of Limburg acid deposition remains about 25 % above the target levels. In the north of Limburg this is even more: 30 %. These figures show that important natural values will remain threatened if the national abatement strategy is implemented in Limburg. For the protection of these values a more stringent povincial policy is needed. Therefore the province of Limburg has decided on a complementary policy [ I ] . This policy includes limitation of emissions per component and per targetgroup.

22

EMISSION TARGETS IN LIMBURG

4.

Emission targets in Limburg are primarily based on the need to protect natural values and on technical and economical feasibility of measures. In order t o establish the latter several feasibility studies were carried out 12, 8, 9, lo]. The studies identified technically possible measures for each target group and determined the attainable reductions and their cost. Thus cost-effectiveness of the measures could be determined. From these studies conclusions were drawn regarding the targets for emission reductions by each target group and a set of cost-effective measures was determined. The emission reductions aimed a t a r e illustrated in figure 6. Emissions for traffic are not included in this figure, because the provincial administration has very little influence on them. For reduction of traffic emissions the national policy is carried out.

t

L

k tonly

.--. 0-0 A-A

*-*

SO, : Industry

+ power plants

+ industry + power plants

NH, : Agriculture NO, : Industry VOC : Industry

Figure 6. Targets for t he reduction of emissions of S02, NO,, Limburg.

NHy and VOC in

Table 4 shows for the different target groups and components the relation between national and provincial emission targets and the technically maximum reduction. From this table i t is obvious that the provincial government of Limburg aims a t a further reduction of ammonia emission. I t was found tha t because of the enormous acid load in t h e north of Limburg, which is primarily caused by agricultural ammonia emissions, a further reduction of ammonia emissions is needed and feasible for both industry and agriculture [2, 81. They both have to bring down emissions with an extra 5 % in 1994 above national policy. In t he north of the province agricultural emissions of ammonia have t o be reduced by 80 % relative to the emissions in 1980. Though the technical means ar e not fully available a t present i t is thought that their development can be completed in time. Although an extra effort in reducing ammonia emissions is found feasible not all farmers will be able to finance measures. I t is estimated tha t maybe 40 % of the farmers have insufficient financial means to invest in environmental measures [2]. Therefore a regional ammonia abatement program is required. SO2 emissions of industrial sources can be reduced in a cost-effective way by an extra 15 YO above national policy in 1994 [8]. On the long te rm the national target of 85 % reduction has t o be reached.

23 SO2 emissions in power plants will be reduced by 99 % in 2000 through the closure of several older units. This is more than national policy requires and therefore i t is allowed that in 1994 the emission will still be well above national targets. NO, and VOC emissions will be reduced according to the national policy.

Table 4 Goals for the reduction of emissions in Limburg per target group and for various components (% and kton/y; emission 1980 = 100 %) Target group and component

National targets

Technical maximum

Targets in Limburg

Emission (kton/y)

1994

2000

1980

1994

2000

1994

2000

voe

50 40 50 35

85 60 60 65

90 60 80 50

65 40 55 35

85 60 60 65

16.7 29.1 2.4 7.3

5.6 17.2 1.0 4.7

2.5 11.6 0.8 2.5

Power plants SO2 NO,

85 30

285 > 50

95 40

70 30

99 60

29.1 10.2

7.9 7.2

0.3 4.0

30

70 - 90

50 - 70

40 45

75 80

17.4 13.0

10.0 7.2

4.4 2.6

Industry SO2

:OH.

Agriculture

NH3 North-limburg

5.

IMPLEMENTATION OF THE LIMBURG ACIDIFICATION POLICY

As stated before Dutch provinces have important tasks in air quality control. Several instruments a r e available for the implementation of acidification policy (permit, subsidy, information). Measures that a r e found to be most cost-effective a re effectuated first. The priority ranking is based on feasibility studies 12, 8, 9, lo]. When carrying out t h e measures however sometimes further and more detailed study appears to be necessary and shall be carried out. Emission reducing measures have already been agreed upon with the power production board. These measures will result in a decrease of NO, emission of 80 - 90 % to a remaining 1.3 - 3.1 kton/y and of 99 % for SO2 in 2000. The remaining emission of SO2 by power plants will be 250 kton/y. An additional stimulation program for energy saving will be formulated in 1992. For the industrial sources a program for revision of permits will b e carried out. Furthermore there is a program for stimulating the development and use of new abatement techniques in industry and agriculture. A communication program will be developed in which the importance of action and possibilities to solve the acidification problem will be shown. With respect t o the transboundary aspects international cooperation is sought, primarily with adjoining provinces in Germany and Belgium.

24 6.

POLICY AND RESEARCH

When formulating a regional policy which is more stringent then national and supra national policies the necessity of a solid scientific basis is strongly felt. Target groups have t o make a tremendous effort to reduce their emissions and always ask for motivation for further measures. Although i t is not always possible to present realistic figures, t h e feasibility studies have provided a basis for this motivation. Policy makers in Limburg need however more study yet on two subjects in particular: i.e. on methods for monitoring t he effects of measures taken and on abatement strategies and techniques on a more detailed level. Particularly proces-integrated techniques or - if yo prefer - clean technology needs further development. With respect to monitoring the effect of measures on a regional scale methods are needed, t h a t a r e far more precise then those using general models and those following trends on a national scale. For monitoring the effectiveness of a provincial cornplementory policy more exact information is needed. Policy on a provincial scale regards saving regional natural values. Therefore i t is needed tha t critical levels a re reached a t the right places, which is primarily on acid sensitive natural values themselves. A monitoring method has to be exact enough for this scale. Regarding abatement strategies and techniques information is needed on technical options for emission reduction in various processes. This includes effects and side effects of measures in terms of environmental effectiveness and in terms of cost effectiveness. Being the licensing authority the provincial government needs t o know what emission reduction is possible in specific situations. When working out concrete measures i t appears in some cases th a t the recommended techniques, studied in feasibility studies, supply no solution in a specific process or a re far more expensive than estimated. More detailed study on various processes has to supply t h e information needed in t h e governmental licensing activities. Research and policy will have to work together t o find solutions for the problem of acidification. Policymakers have t o learn from science and vice versa. Cooperation between research and policymakers on an international scale will enhance the solution of the acidification problem on an international, national and regional scale. References 1 Province of Limburg, Environmental Policy Plan 1991 - 1994 (1991). 2 Heidemij, Haalbaarheidsstudie reductie NH3-emissie landbouw, Eindrapport; Province of Limburg (1989). 3 Heidemij, Haalbaarheidsstudie reductie NH3-emissie landbouw, Aanvulling 1989 t o t en m e t 1991; Province of Limburg (1990). 4 Ministry of Housing, Physical Planning and Environment, National Environmental Policy Plan, Second Chamber, session 1988 - 1989, 21137 nos 1-2. 5 Ministry of Housing, Physical Planning and Environment, Bestrijdingsplan Verzuring, Second Chamber, session 1988 - 1989, 18225 no 31. 6 Ministry of Agriculture, Nature and Fishery and Ministry of Housing, Physical Planning and Environment, Plan van aanpak beperking ammoniak emissies van d e landbouw, Second Chamber, session 1990 - 1991, 18225 no 43. 7 G.J. Heij and T. Schneider (eds), Final report second phase Dutch priority program on acidification (1991). 8 Badger, Onderzoek emissiebeperkende maatregelen in de industrie, Province of Limburg (1989). 9 Badger, Verkennend onderzoek naar de mogelijkheden voor het opwekken van schone energie, Province of Limburg (1989). 10 Grontmij, Haalbaarheidsstudie beperking emissies verkeer, Province of Limburg

SESSIONB STATE-OF-THE-ARTOF ACIDIFICATIONRESEARCH

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T Schneider (Editor). Acidification Research Evaluation and Policy Applications 0 1992 Elsevier Science Publishers B V All rights reserved

27

ION AND ACIDI FICATION: A CRITICAL REVIEW

Rod01 p h e S c h l aepfer

Paper presented at the International Conference ACIDIFICATION RESEARCH, EVALUATION AND POLICY APPLICATIONS, Maastricht (NL), October 14-17, 1992

Abstract The objective of this paper is to present a review of the most important scientific knowledge and uncertainties concerning forest vegetation and acidification, and to draw some conclusions for research policy. Forest vegetation and acidification are considered as parts of a global environmental system. The phenomenon of "Forest Decline" is introduced. The methods used for causal research and monitoring are presented, as well as their related difficulties. The scientific knowledge gained from epidemiological approaches (forest damage inventories), experiments and mechanistic studies are evaluated. The paper ends with some conclusions for research policy and emphasizes the need to intensify the use of integrated approaches in environmental sciences.

Contents 1. Introduction 2.

Forest vegetation and acidification as parts of a global environmental system

3.

Methodological considerations

4.

What do we know about forest damage?

5.

What do we know, at an epidemiological level, about the association between defoliation and its hypothetical causes?

6. Can we reproduce experimentally the observed symptoms?

7. Can we explain the mechanisms leading to forest decline? 8.

Summary and conclusions

9. Bibliography

28 1. INTRODUCTION

A large number of contributions concerning forest vegetation and acidification have been published. Many papers and books are available which give good reviews about the known facts as well as about of what is known, as well as about the existing gaps and uncertainties. Examples of these are:

-

The annual Reports on the Forest Damage Survey in Europe [Anonymous, 1991 a]

-

Air Pollution and Forest Health in the European Community, an Assessment of the Current Scientific Evidence [Ashmore, M.R., Bell, J.N.B. and Brown, I.J., 19901

-

Interim Report on Cause-Effect Relationships in Forest Decline [Anonymous, 1990 a]

-

Proceedings of the 5th Meeting of Acidification Research Coordinators [Anonymous, 1990 b]

-

Different reports on national research programmes about forest decline and pollution in France, Germany, Netherlands, Finland, Switzerland, US etc. [see Bibliography Nos 3, 5, 7, 9, 10, 12, 13, 15-17, 20-22, 241

The term Ifforestdeclineffis usually used to describe a decrease of the vitality in the forest ecosystem which can lead in some cases to the death of the stands. The most important criterion used to describe the phenomenon is crown defoliation. There are some generally accepted ideas about forest damage in Europe and in North America. It is clear that a number of different types of decline are present, each being spatially delimited, characterised by a specific set of symptoms and resulting from a certain combination of climate, soil and pollution. Every country has accepted the idea that forest decline is due to a complex set of factors. However, some countries differ over the interpretation of the role of air pollution. This paper is based on the assumption that our society is interested in understanding the phenomenon of ffforestdeclinef1. My objective is to draw conclusions for future research concerning forest vegetation and acidification. For this purpose, I will try to analyse the available information and to discuss how far they allow us a) to evaluate the normality of the situation, b) to describe the evolution of the damages and c) to explain the causes. The problems of global change and critical loads will not be discussed.

29 2.

FOREST VEGETATION AND ACIDIFICATION AS PARTS OF A GLOBAL ENVIRONMENTAL SYSTEM

Difficulties in discussions and decision-making in environmental sciences and policy sometimes come from a biased and narrow-minded view due to ideological thinking or a lack of understanding of the need for a global approach to the problem. We scientists can contribute towards minimizing these difficulties by presenting our results as impartially as possible and by integrating our research topics within higher order systems. In this sense it should be remembered that the forest vegetation is only a part of the forest ecosystem, that acidification is only a part of the pollution problem and that both forest ecosystems and pollution are parts of a global environmental system (Figure 1).

Forest ecosystem .............._.. ..............._. ____________._._. ~

Vegetation Fauna Mlcroorganlsms Soil Water Air

Figure 1: Global environmental system

30

The forest ecosystem is composed of the interacting elements of vegetation, fauna, microorganisms, soil, air and water. It itself interacts with other systems like llClimate*f, "Management practices" , ltPollutionlland l1Pathogensl1. The word Ilacidification" can be divided into two parts: tfacidll and "ficationll In order to understand the relationship between forest ecosystems and acidification we have to consider both parts. The vtacidlt part is the input into the ecosystem of compounds which release protons. The second part, flficationll, is the effects of acid deposition. The term "acid depositionll is often used as a synonym for "acid rain" or "acid precipitationll. Historically, these expressions have been repeatedly used as "forerunnersttin discussions and research on atmospheric pollution. They are thus frequently applied in a non-specific manner to various kinds of emissions, especially in political discussions and as titles for research programmes and conferences. In a more narrow sense, the term "acid deposition" can today be defined as the input of all components into an ecosystem which determine the net proton flux into the system. Acid rain in this context is only a part of acid deposition. For the determination of total acidity input, the interception of sulfur- and nitrogen-containing particles as well as the dry deposition of nitrogen dioxide, nitric acid, sulfur dioxide and ammonia have to be included.

.

3.

THOD DO LOGICAL CONSIDERATIONS

Ecosystems usually vary in time and in space. The changes can be normal or abnormal, compared to a defined standard. Abnormal changes are closely related to diseases, damage, decline or a decrease of vitality. We are therefore interested in the importance, the dynamics, the spatial variation and the causes of changes in the forest ecosystem. This information can serve as basis for decision making. The certainty of existing information about changes depends on the magnitude of the changes, the complexity of the processes involved, the natural variability of the system studi.edand the methods used to obtain the information. Causal research is relatively easy when the effects are due to a single factor. In ecological studies, the situation is generally more complex. Rothman (1986) presents a model of causation which helps the conceptualization of epidemiological problems like forest decline. In his view, a disease is produced by a constellation of components that act in concert. He defines the "sufficient causeu1as a set of minimal conditions and events that inevitably produce disease. ltMinimalll implies that none of the conditions (components) are superfluous. Two component causes in a "single sufficient cause" are considered to have mutual biological interaction. A component is considered as a "necessary cause" if without this component there is no

31

disease. Research indicates that it is reasonable to assume that forest decline is also produced by a constellation of components that act in concert. These components may be certain constellations of climate, soil, pollution, species and management practice. One objective of research could be the identification of the set of minimal conditions that produce forest decline. Other interesting tasks are to find out if there is a "necessary cause" without which there is no forest decline and to understand the mechanisms leading to changes. Methodological aspects of causal inference in epidemiology and ecology have caught the attention of many authors (for example: Koch, R., 1884; Mosteller, F. and Tukey, J.W., 1977; Rothman, K.J., 1986; Schlaepfer, R., 1988; Oren, R., Werk, K.S., Meyer, J. and Schulze, E.-D., 1989 or Ashmore, M.R., Bell, J.N.B. and Brown, I.J., 1990, Innes, J., 1991). Based on their contributions we can describe an integrated and iterative approach for forest decline research which should give us information about the magnitude, dynamics and variability, as well as about causes of the phenomenon: 1. Detection and definition of the problem. We have first to

detect if there are abnormal deviations and to find out their symptoms (y) and hypothetical causes (x). 2. Description of magnitude, dynamics and variability of the

phenomenon. In this step, the spatial distribution and the evolution in time of the symptoms and the hypothetical causes are described. Surveys are used to do this, the best being an integrated forest damage survey. 3.

Detection of associations in space and in time between the symptoms and the hypothetical causes (epidemiological approach). When causality exists and when other variables are equal, the relationship between the symptoms and the causes is consistent across comparable populations in direction and perhaps in amount. We can verify the consistency of relationships by using surveys. The data are analysed using multivariate techniques such as multiple regression. The results of the analysis are used to formulate hypotheses about the form and the intensity of the cause-effect relationships. The multivariate technique has the advantage of giving information about effects as well as about interactions between causal agents.

4. Experimental reproduction of the observed symptoms. Experi-

mentation is the only scientific method which allows an unequivocal assessment of the impact of a pollutant. An experiment allows us to study, under given conditions, the response of the research object when submitted to a controlled change of a parameter of interest. If the relationship between the symptoms and the hypothetical causes is indeed causal, we can, by intervening and changing the level of the hypothetical cause, reproduce experimentally the observed

32

symptoms. This step allows us to test hypotheses about the cause-effect relationships which are suggested by research or by other sources of information (i.e. surveys and case studies) and to quantify the relationships. A limiting factor in forest decline research is that experiments are difficu1.t to perform with mature trees. 5. Explanation of the mechanisms. In this step, models are pro-

posed to explain the processes by which the causes produce the symptoms of the different types of forest decline, in particular defoliation and discoloration. The hypotheses about the mechanisms are based on an integrated analysis of all the information available about the phenomena (basic research in physiology and biochemistry, surveys, experiments, field studies). 6. Validation of the models. Are the proposed models about the

mechanisms leading to the observed symptoms reasonable? The most important method used to answer this question is to verify if the models match available data derived from field studies, surveys or experiments. It is important to realise that confirmation of the importance and the causes of a particular type of forest decline should be the product of a global evaluation of the results of all the steps mentioned above. Such an integrated approach is a guideline for ecological research and helps us to recognise the difficulties of Ifprovingvv the causal nature of an association, as well as the limitations of surveys and experiments.

4.

WHAT W WE KNOW ABOUT FOREST DAMAGE?

There are numerous symptoms associated with forest decline. They usually vary in importance from region to region and from species to species. Examples of symptoms related to forest vegetation are:

-

crown defoliation, i.e. changes in the density and the size of leaves and needles and their premature senescence and abscission,

-

discoloration, for example the yellowing of spruce needles,

- changing in the branching structure of trees,

-

increment change,

-

root damage,

- increased sensitivity to stress,

33

-

nutrient deficiencies,

- degradation of surface wax structure. The International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) annually publishes a report on the forest damage survey in Europe. These surveys started in 1986, and are based on guidelines laid down in a Manual on 94ethodologies and Criteria for Harmonized Sampling, Assessment, Monitoring and Analysis of the Effects of Air Pollution on Forestsv1.31 countries participate in the programme. The most important criterion used in the surveys is the defoliation of the crown.

Conifers

Broadleaves

% of trees with needle loss >25%

% of trees with leave loss >25%

60

50

50

40

30

-----------I--

86

87

-------.-I ........

............

88

89

Austria Czechoslovakia Finland Germany

90

86

1

1

I

87

88

89

Netherlands ....-.. .- Sweden -- - - - - Switzerland United Kingdom " . . " I . "

Figure 2: Forest Damage in Some European Countries

90

34 conifarm 86

87

88

89

Broadlaavam 90

n

86

87

88

89

90

1990

Aumtria Czachoelovakia

UK

4,5

3,5

4,0

n 1990

5,5

4,l

3,3

3533

16,4

15,6

27,O

32,O

50,3

10505

-

-

23,O

27,O

34,O

43,O

1036

-

7,s

3,5

6,7

6,9

79'1

-

29,l

37.0

33,9

3056

10,O

20.0

21,O

28,s

635

Source: International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests: Report on the 1990 Forest Damage Survey in Europe (Draft) Table 1: Forest damage in some European countries from 1986 to 1990, defoliation classes 2-4 ( % trees with more than 25 % defoliation)

Table 1 and Figure 2 present for some countries, from 1986 to 1990, the percentage of trees, with more than 25 % defoliation.

The results show that the level and the course of defoliation can be very different both between countries and between conifers and broadleaves. One question is whether the observed differences are due to different assessment methods or to possible causes like climate, soil, pollution and management practices. We see from this example that an important problem related to the forest damage surveys is the interpretation of the results. It is now accepted that despite the progress made in recent of years, many uncertainties and gaps remain which make it difficult to draw conclusions from the data:

-

The nature and extent of the differences in the manner in which defoliation is being assessed by different countries have not been quantified. Comparisons between the results obtained are therefore invalid (Anonymous, 1990 a).

-

Little is known about defoliation in stands under different natural conditions. The estimates of defoliation alone provide only a little information about the severity of the damage.

- Average estimates of defoliation for countries provide no information on the different$ypes of forest decline in Europe.

35

-

In view of the difficulty of applying a standard assessment of defoliation across a wide range of growth habits (Ashmore, Bell, Brown, 1990), comparisons of the health of individual species must be made with extreme caution.

-

The observed trends in defoliation are difficult to interpret because we know little about the evolution of defoliation over the last 50 years.

-

Defoliation is not a cause-specific symptom. Estimates of defoliation alone give nearly no information on its causes.

-

There is no evidence of a widespread decline in the growth of European forests associated with the widespread reports of defoliation, although reductions have been demonstrated at a local or regional scale (Anonymous, 1990 a).

These gaps suggest some recommendations for the execution of future surveys:

-

-

Quantify the uncertainties of forest damage surveys and improve the harmonization of assessment methods in different countries. Develop criteria for the evaluation of the severity of damage. Present results according to the type of forest decline rather than by individual countries. Establish whether an observed form of damage is unprecedented or whether it has existed for some time. Incorporate other indices of tree condition into large-scale surveys (for example increment, better use of tree mortality, branching, nutrient content in needles and leaves).

5. WHAT DO WE KNOW, AT AN EPIDEMIOLOGICAL LEVEL, ABOUT THE

ASSOCIATION BETWEEN DEFOLIATION AND THE HYPOTHETICAL CAUSES?

Ideally, the data necessary for a multivariate approach to the study of associations in forests between the observed damage and hypothetical causes are given by a sampling survey, in which not only the damage, but also the levels of the hypothetical causes like climate, soil, pollution, pathogens and management practices are observed at each point. Such an integrated survey does not exist in Europe. Separate long-term monitoring programmes with no interconnection have been run for air, forest or soil. These separate programmes enable conclusions to be known concerning the variations in time of individual variables. If a high enough number of observation

36

points is used, it is possible to obtain information about the spatial distribution of the variable. There are also many integrated descriptive case-studies in Europe. Examples of these are given by the three field studies Lageren, Alptal and Davos in Switzerland (Stark, 1991). A case-study enables a detailed description of variables and relationships between variables in time to be made, but gives no information about the spatial association between defoliation and causes. Theoretically, it is possible to use the data from other monitoring programmes to estimate the value of variables of interest (for example pollution or meteorological data) which are not measured on the forest survey plots. The success of this will depend on the density and the reliability of the networks involved. In relation to pollution, it is difficult to obtain reliable monitoring data of a consistent quality from different European countries (Ashmore et al., 1990). Because of this, the European Monitoring and Evaluation Programme (EMEP) was created. The EMEP is a coordination centre which is linked through the UNECE Convention of Long-Range Transboundary Air Pollution to international agreements on pollution reduction. The EMEP network is based on a 150 km grid and therefore cannot identify particular concentrations in localised areas. The spatial distribution cannot be mapped with great certainty. However, the EMEP data provide a broad picture of the main features of the distribution of sulphur and nitrogen pollutants across Europe. Because of the above problems, it is difficult to study the relationship in the forest between damage and its hypothetical causes, especially pollution, in Europe. The available information does not show a general association between defoliation and pollution in Central Europe (Rehfuess, K . E . 1991). There are even contradictory results at the regional scale. We do not know if this situation is due to an absence of a real association or to the inadequacy monitoring methods. To fill this gap we have to support any effort which is made in Europe to:

-

create an integrated large-scale survey, including observation of forest damage criteria as well as the hypothetical causes like climate, soil, pollution, pathogens and management practices:

-

improve and apply simple field methods for air pollution monitoring:

-

improve the existing long-term monitoring programmes (more reliable data, higher density of the network);

-

improve the coordination between the existing long-term programmes for monitoring soil, air and vegetation.

37 6. CAN WE REPRODUCE EXPERIWENTALLY THE OBSERVED SYMPTOMS?

Different experimental techniques are used in forest decline research. The most important are open- and closed-top chambers, controlled environmental chambers, laboratory based experiments and field experiments. Much of the work done is based not on experiments, but on observations of forest stands, or analysis of collected material, usually making comparisons between healthy and damaged stands. Ashmore et al. (1990) give a useful picture of the current emphasis of research on air pollution and forest decline in Europe. They point out that of all work reported, approximately 75 % is on coniferous species and only 25 % is on the broadleaves. Nearly 70 % of work using coniferous species is devoted to only one species, Norway spruce, and 60 % of work using broadleaves is devoted to beech (Fagus sylvatica). They also found that the majority of experimental work has been carried out using either ozone ( - 30 % ) or simulated acid deposition (-25 % ) . The majority of studies only use single pollutants. There is little work on nitrogen pollutants. A considerable number of experiments have used pollutant concentrations in excess of those expected in ambient air across Europe. Ashmore et al. identified nine main categories of processes that have been studied:

- leaf metabolism

-

-

-

(-

30 % )

nutrient balances (-15 % ) leaf surfaces ( * 10 % ) growth/biomass ( - 10 % ) root/mycorrhizal responses (5-10 % ) water relations (5-10 % ) reproductive processes and genetics (0-5 % ) response to secondary stresses (0-5 % ) soil chemical changes (0-5 % )

It is impossible to summarize in this paper all the important experimental results obtained over the past few years. I will simply mention some conclusions reached by Ashmore et al. (1990):

- "It is clear that disruption of the processes of photosynthesis, carbon metabolism and transport is observed frequently in damaged stands of Norway spruce and other species. Similar disruptions have been demonstrated in some experiments with air pollutants, but this does not prove that direct impacts of air pollutants are responsible for the effects observed in the field. It seems more probable that nutrient deficiencies are the prime cause of loss of chlorophyl, reduced rates of photosynthesis and disrupted translocation patterns on many sites.

38

- "There is evidence that exposure of conifers to air pollutants or wet deposition can lead to changes in epicuticular waxes similar to those observed in declining stands. .. However, some experiments at realistic, or above ambient, levels of exposure have not reported significant effects on leaf surface properties."

-

IIPollutant deposition may affect soils in three major ways: by increasing acidity, by decreasing nutrient availability (either as a result of leaching or competitive inhibition of uptake), and by increasing the solubility of toxic ions such as aluminium. It

- "There is evidence that fine root and mycorrhizal vitality may be affected by both above- and below-ground pollutant impacts. It is not clear which of these is of greatest significance in different field situations, or, indeed, whether damage to the root system is necessarily associated with forest decline.

- "It seems likely that foliar leaching of mineral nutrients due to acid deposition or other pollutants is not a key factor in the development of the mineral deficiencies associated with forest decline. Rather, the supply of mineral nutrients from the soil is the critical factor."

-

"There is clear evidence that atmospheric pollutants may affect the water relations of a tree. However, the lack of consistency in the experimental data makes it difficult to generalise about the significance of this factor in forest decline.

-

"It is impossible to assess whether current levels of pollutant deposition are increasing, decreasing, or having no effect on tree growth: it is likely that all three possibilities exist on different species in different regions of the CEC .

-

"It is clear from experimental studies that air pollutants at realistic concentrations may have quite subtle effects on the pattern of seedling growth and development."

-

"Evidence suggests that pollution may enhance tree sensitivity to other environmental stresses - the most studied example being winter damage. There is a general concensus that exposure to pollutants increases the susceptibility of trees to low temperatures. This has been demonstrated for summer pollutants, such as ozone, as well as those more prevalent during the winter.

In the conclusions from Ashmore et al. the words llrnayll or Ilcan" appear frequently. The reason for these cautious formulations certainly lies in the limitations of the available experimental works, for example:

39

-

Most experiments are performed with young trees and fail to simulate field conditions.

- Often, higher concentrations of pollutants are used than are normally found in areas with forest decline.

-

Most experiments consider the effect of a single pollutant and therefore do not give information about combinations of pollutants or interaction between pollutants and other factors of influence.

- Few experiments are performed with the aim of studying directly the main symptom observed in the forest damage survey, i.e. defoliation.

- The main effort put into experimental work has been for Norway spruce and beech. It follows from these conclusions and the limitations listed above that the main symptoms of forest decline can only be partially reproduced experimentally. This situation could be improved if we encourage the following steps:

-

more emphasis on field experiments, especially those involving field manipulation,

-

more emphasis on experiments with more than one pollutant, and on experiments designed for the study of interactions between pollutants and other hypothetical causes,

-

better coordination of the objectives of experiments with the identified types of forest decline.

7. CAN WE EXPLAIN THE MECHANISMS LEADING TO FOREST DECLINE?

Ten years ago, many people attributed forest decline mainly to air pollution. The research efforts of the past decade give us a more complicated picture of the phenomenon. Different models are now proposed to explain specific processes or the whole mechanism leading to forest damage. For example, canopy photosynthesis is a well explained process. However, much has to be learnt about the processes which control the water and nutrient balances of trees, and the partitioning of carbon and other essential elements. Unfortunately, those processes for which the fundamental understanding necessary for successful modelling is poorest are precisely those which appear to be the most important in terms of pollutant impacts (Ashmore et al., 1990).

40

We also know that at the cellular or leaf level in seedlings and trees, the same basic processes occur (photosynthetic pathways, respiration, conversion to metabolites, translocation to other organs). However, due to different heterogeneity and proportions of leaf, wood and root tissue, the relationship and balance between these processes differs. It is therefore likely that differences between the responses of seedlings and mature trees to the factors of influence, particularly pollutant stress, are important. This means that experiments with seedlings may be useful for our understanding of individual processes, but are unreliable as an aid to understanding the forest ecosystem as a whole. An interesting example of an explanation of a particular type of forest decline is given by the Fichtelgebirge study (Schulze et al., 1989). In this study, a decline was recognized only if needle-yellowing was accompanied by reduced stand growth rate per ground area. Schulze et al. deduce that direct effects of air pollutant are not of major importance, that stemwood growth is most closely related to the supply of magnesium from the soil and that the symptoms of needle yellowing reflect a complex balance between the uptake of base cations from the soil and nitrogen compounds from both the soil and the atmosphere. The authors also mention that the conclusions of the study must be considered only as a set of plausible hypotheses which can best explain the patterns in the data without major contradictions. Large-scale weather stress is also considered as a inciting factor (Landmann, G., 1991) or as the possible cause of the synchronization of different disease types in coniferous stands during the period 1980-1985 (Rehfuess, K.E., 1991). Most of the proposed explanations of the mechanisms remain hypotheses and models which have still to be tested and validated in the field. Many of them were elaborated for very special situations and cannot be easily generalized. The ways in which all the key factors interact to produce the symptoms of forest decline (defoliation, discoloration) and to produce different suites of symptoms on different species, different soils and different pollution situations are unclear. This conclusion shows that a great research effort is required if we wish to have a better understanding of the mechanisms. For example, it is necessary to intensify:

-

basic research, especially in tree physiology and biochemistry,

-

the use of modelling as an approach allowing us to integrate the information coming from the different methods used in forest decline research.

41 8.

SUMMARY AND CONCLUSIONS

I will try to summarize and to draw the conclusions by answering three questions: What do we know? What are the gaps? What should we do? What do we know? The most important agreements among scientists about forest decline in Europe are:

-

There are different types of forest decline characterised by defoliation. Each of these types is associated with different sets of additional symptoms with different sets of plausible stress factors.

-

Most of the types of forest decline are multiple-stress phenomena in which climatic factors, soil conditions, pollution, pathogens and management practices may be components which act together.

-

No general spatial or temporal association between defoliation and pollution has been observed in Europe.

- There is no evidence of a widespread decline in the growth of European forests.

-

There is much experimental evidence about the form of the cause-effect relationships between pollutants and their impacts on specific processes. Unfortunately, these results cannot be easily extrapolated to field conditions.

-

There are only a few cases of forest decline for which a plausible explanation of the mechanisms exists. One of them is the yellowing of Norway spruce at higher altitudes on acidic soils in Germany. Nutrient imbalances are associated with the decline. Changes in soil chemistry seem to be a major cause of nutrient disharmony.

-

Although the direct effects of pollution on forest vegetation are not so important as was thought some years ago, they, together with the long-term impacts of acid deposition (including nitrogen) on forest soils, have to be considered as a potential threat to the forest ecosystem.

What are the gaps in our knowledge?

-

Because of our lack of knowledge about the ffnormalfl situation, we do not know how severe the observed levels of defoliation are.

42

-

The results of the forest damage surveys in different countries are not comparable.

- We do not know if the non-observed association between defoliation and pollution is due to an absence of such an association or due to the inability of existing methods to detect it.

- We do not know how far the results of chamber experiments can be extrapolated to field conditions.

-

We have only an incomplete picture of the importance and the dynamics of different types of forest decline.

- For most of the types of forest decline the mechanisms with which the influencing factors affect the ecosystem are unknown.

- We do not know the interactions between the different possible causes, in particular between pollution and climate factors. What should we do?

An important duty of research is to improve scientific knowledge concerning forest decline. As scientists, we see that the methods used have their limits. We see also that, despite of the efforts that have been made, the lack of international coordination remains an important problem. We should therefore encourage:

-

the elaboration of large-scale and regional integrated multifactorial monitoring;

-

a better coordination of experimental work with the observations in the field,

-

mechanistic studies to improve our knowledge about processes in the ecosystem, and

-

the intensification of the use of multi-disciplinary modelling techniques for explaining the phenomenon.

I believe that better progress can be made if more of the national ambitions and efforts in research are put into international projects. Only a European approach to the problem will allow monitoring and causal research in forest decline which is based on ecological realities rather than artificial spatial units like countries. In this sense, the participation of non member countries to research programmes of the European Community should be facilitated.

43 Forest decline has scientific, psychological, economic and political implications. Decision-makers in many fields have to take account of the problems related to forest vegetation and acidification. It is therefore important that scientists provide impartial information about the existing facts, gaps and uncertainties. This information should be intensified and presented in languages which can be understood by the audience. We should also make it clear that the existing knowledge about the risks facing forests is enough to justify any effort to reduce air pollution in Europe. We also have to point out that the available information about the cause-effect relationships in forest decline does not allow us to give useful advice for fixing the priorities of a European pollution control policy.

9.

BIBLIOGRAPHY

Anonymous: Interim Report on Cause-Effect Relationships in Forest Decline. Convention on Long-Range Transboundary Air Pollution, International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (1990 a). Anonymous: MARC V. 5th Meeting of Acidification Research Coordinators, Nancy, September 25-27 (1990 b). Anonymous: NAPAP Annual Report 1989 and Findings Update. National Acid Precipitation Assessment Program, Washington DC (1990 c). Anonymous: Report on the 1990 Forest Damage Survey in Europe. Convention on Long-Range Transboundary Air Pollution, International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (1991 a). Anonymous: 7. Statuskolloquium des PEF (Projekt Europaisches Forschungszentrum fiir Massnahmen zur Luftreinhaltung) vom 5. bis 7. Mlrz 1991 im Kernforschungszentrum Karlsruhe. Kernforschungszentrum Karlsruhe (1991 b). Ashmore, M.R.; Bell, J.N.B.; Brown, I.J.: Air Pollution and Forest Health in the European Community: An Assessment of the Current Scientific Evidence. Commission of the European Communities, Air Pollution Research Report 29 (1990). Haemmerli, F.; Schlaepfer, R.: Forest Decline in Switzerland. In: Huettl, R.F.: Forest Decline in Atlantic and Pacific Region, Springer Verlag, Berlin, New York. (Paper submitted: June 1991). Hauhs, M.; Wright, R.F.: Regional Pattern of Acid Precipitation and Forest Decline Along a Cross Section Through Europe. Water, Air and Soil Pollution 31 (1986). 463-474, D. Reidel Publishing Company. Innes, J.L.; Boswell, R.C.: Monitoring of Forest Condition in Great Britain 1989. Forestry Commission. Bulletin 94 (1990).

44 10

11

Innes, J.L.: The Application of Cause-Effect Criteria to the Relationship between Air Pollution and Forest Decline in Europe. In: James W.S. Longhurst (ed.): Acid Deposition, Springer Verlag, Berlin (1991). Kauppi, P.; Anttila, P.; Kenttamies, K. (eds.): Acidification in Finland: Finnish Acidification Research Programme HAPRO 1985-1990. Springer Verlag, Berlin, Heidelberg (1990).

12 13

14 15 16

17 18 19 20 21

Koch, R.: Die Aetiologie der Tuberkulose. Mitt. Kaiserl. Gesundheitsamt, 2: 1-88 (1884). Krause, G.H.M.; Prinz, B.: Experimentelle Untersuchungen der LIS zur Aufklarung mdglicher Ursachen der neuartigen Waldschaden. Landesanstalt fur Immissionsschutz, NordrheinWestfalen, Bericht Nr. 80 (1989). Landmann, G.: Les recherches en France sur le deperissement des for&ts. Programme DEFORPA, 28me rapport. Ecole nationale du genie rural, des eaux et des forkts, Nancy (1991). Mosteller, F.; Tukey, J.W.: Data Analysis and Regression. Addison-Wesley, Reading, Massachusetts (1977). Oren, R.; Werk, K.S.; Meyer, J.; Schulze, E.-D.: Potentials and Limitations of Field Studies on Forest Decline Associated with Anthropogenic Pollution. In: Schulze, E.-D.; Lange, O.L.; Oren, R. (eds.): Ecological Studies, Vol. 77, 23-36, Springer Verlag Berlin, Heidelberg (1989). Orthofer, R.: Effects of Air Pollutants on Ecosystems: Research Experiences and Future Strategies in Austria. Oesterreichisches Forschungszentrum Seibersdorf (1990). Rehfuess, K.E.: Review of Forest Decline Research Activities and Results in the Federal Republic of Germany. J. Environ. Sci. Health. A26 (3), 415-445 (1991). Rothman, K.J.: Modern Epidemiology. Little, Brown and Company, Boston, Toronto (1986). Schlaepfer, R.: Waldsterben: Eine Analyse der Kenntnisse aus der Forschung. Eidg. Anstalt fur das forstliche Versuchswesen, CH-8903 Birmensdorf, Bericht Nr. 36, (1988). Schlaepfer, R.; Haemmerli, F.: Das "Waldsterben" in der Schweiz aus heutiger Sicht. Schweiz. Z. Forstwes. 141 (3); 163-188, (1990).

22

23

24

25

Schneider, T.; Heij, G.J.: Dutch Priority Programme on Acidification: Thematic Reports. National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands (1990). Schulze, E.-D.; Lange, O.L.; Oren, R.: Forest Decline and Air Pollution: A Study of Spruce (Picea abies) on Acid Soils. Ecological Studies, Vol. 77, Springer Verlag, Berlin, Heidelberg (1989). Schulze, E.-D.; Oren, R.; Lange, O.L.: Processes Leading to Forest Decline: A Synthesis. In: Schulze, E.-D.; Lange, O.L.; Oren R. (eds.): Ecological Studies, Vol. 77, 459-467, Springer Verlag Berlin, Heidelberg (1989). Stark, M. (ed.): Luftschadstoffe und Wald: Ergebnisse aus dem Nationalen Forschungsprogramm 14. Lufthaushalt, Luftverschmutzung und Waldschaden in der Schweiz, Programmleitung NFP14. Verlag der Fachvereine, Zurich (1991).

T Schneider (Editor), Acidification Research Evaluation and Policy Applications @ 1992 Elsevier Science Publishers B V All rights resewed

45

Global E n v i r o n m e n t a l Change: Implications for Acid Deposition Research D. J. Waters and P.G. Whitehead

Institute of Hydrology, Wallingford, Oxon, OX10 SBB, UK Abstract Global environmental change has implications for acid deposition research. Many of the complex processes underlying acidification are also influenced by climate change and land use. It will be very difficult to attribute any perturbation in the ecosystem t o any specific factor, i.e acid deposition, climate change or land use. The following paper attempts to summarise the impact and interactions between climate change, land use and acidification processes and suggests key areas for research.

1. I n t r o d u c t i o n Research into the effects of acid deposition has received a relatively high profile over the last twenty years, However, increasing media awareness i n recent years has diverted some of o u r attention to affects on materials, e.g. historic and cultural monuments, health effects (i.e. increasing concern of high photochemical oxidant concentrations) and quality of life related parameters, e.g. visibility. Knowledge concerning primary pollutant emissions, atmospheric transport and chemical transformation and deposition has improved enormously. The resultant effects o n ecosystems particularly soils, surface waters and flora and fauna has progressed such that the ability for models to predict the environmental impacts has improved. Spatial variability often complicates model prediction and long term monitoring must proceed so that complex processes can be refined and improve our chances of model extrapolation. Temporal variations i n atmospheric pollutant concentrations mean that many processes are dynamic and not in steady state, e.g. sulphate adsorption. Relative contributions of acidic pollutants and their impacts o n ecosystems have changed, systems which were dominated by sulphurous compounds are feeling an increased impact of nitrogen. Our understanding of the effects of nitrogen are less well understood. However, it is clear that once concentrations exceed the biological requirements, this highly mobile anion has an acidifying effect. Other atmospheric gas concentrations have

46

changed, particularly ozone and ammonia and present research needs to incorporate their synergistic, additive or antagonistic effects. Increased emission of greenhouse gases and the resultant implications for climatic change has ramifications for acidification research. Changing temperatures will affect evapotranspiration and the rate of biochemical reactions in soil and water. Changing seasonality and volume of rainfall will effect the flushing and leaching of soils as well as the frequency of acid episodes and perhaps dilution effects. The implications for soil moisture and perhaps water pathways and, therefore, mixing will control inputs t o the surface water system. It is quite clear many of these climatic changes will have resulting implications for acidification studies. Land use change has other obvious implications for acidification research. Natural vegetation succession and colonisation might arise from climate changes. However, it is the land management practice that will have the greatest effect. Afforestation or deforestation have well documented effects as well as the implications of fertiliser and pesticide usage under more intensively managed systems. It is quite clear that environmental change has implications for many of the processes important in acidification studies. This paper attempts to summarise the implications of environmental change and perhaps suggest future approaches to continue acidification research per se and incorporate other modifications to the ecosystem.

2. Global Environmental Change

2.1 Atmospheric Pollution Trends in atmospheric pollution will have direct effects on ecosystems. However, assessing the immediate influence of changes in deposition will be complicated due to the ecosystem response time. National policies for pollution abatement differ and the resultant local deposition pattern will still be influenced by long range transport. Much time and expense has been dedicated to sulphur emission reductions and more recently abatement strategies for nitrogen emissions have been set. This reflects the increasing importance of nitrogen and its increasing contribution to the total acidic input to catchments. Policies for ammonia emission reductions is still largely a national rather than international problem. Photochemical oxidants such as ozone concentrations have also been rising, and its implicated impact on human health, materials and vegetation might see future protocols for emission control. To date most protocols for the reductions of sulphur emissions have been based on linear changes, i.e signatory to the 60% club, which requires EEC countries to reduce emissions by 30% of the 1980 levels by 1993 and 60% by 2005. Recent research into critical loads of sulphur to ecosystems has provided an alternative strategy for sulphur emission abatement. With the use of critical and target loads, various emission reductions and their total environmental resource impact can be assessed. Using this technique national policies can be equated to reflect direct ecosystem benefits. Of course reductions in emissions will not yield

47

a linear decrease in deposition but the critical loads approach is much more scientifically valid. It is, however, more complex requiring a n understanding of processes so that critical loads can be evaluated. Reductions in sulphur loadings to ecosystems will be beneficial but the magnitude and speed of response will depend on the timescales to reach new equilibrium concentrations as well as the total reduction in sulphur deposition. For example, predictions of future acidification trends using the MAGIC model (Figure I), suggests very large emission cuts are needed in some catchments if the acidification status is t o improve (Cosby et al., 1986; Whitehead et al., 1988a; Whitehead et al., 198813). I t is clear however, that as sulphur emissions and, therefore, atmospheric concentrations are reduced nitrogen will assume the role as the dominant acidic pollutant. 6.0

5.5

5.0

4.5

4.0

1840 1880 1920 1960 2000 2040 2080 2120

-Historical levels to 1984 and constant 1984 levels thereafter

..... Historical levels to 1984 and 1984 levels reduced by 50% by the year 2000 and constant thereafter - - - Historical levels to 1970 and constant 1970 levels thereafter Figure 1

Simulated historical and future pH at Dargall Lane (SW Scotland)

Abatement strategies for nitrogen are much less stringent. To date protocols concerning the control of emissions of nitrogen oxides or their transboundary fluxes commit national emissions a t 1987 levels by 1994. As our knowledge of the effects of nitrogen increases, no doubt greater control measures will be required. In some of our research programmes the role of nitrogen has attained a higher profile as rising surface water concentrations have been observed. Nitrate is a highly mobile anion and is as efficient as sulphate in leaching base cations from the soil. It is, therefore, a n acidifying agent. It is also extremely important as a nutrient source for algae and increased levels of nitrogen will lead t o more eutrophic conditions in upland streams and lakes. The

48 increasing importance of nitrogen has resulted in greater modelling effort but understanding the processes controlling nitrogen dynamics is still rather limited. Critical loads of nitrogen have not been attempted in many countries and, therefore, critical loads of acidity are preliminary. Of course increasing nitrogen deposition will not be detrimental for all areas and for all parts of the ecosystem, for example, in nitrogen deficient areas increased deposition might increase forest growth. As nitrogen is a very important nutrient it is difficult to predict when saturation will commence and, therefore, when it will act as an acidifying agent. Ammonia emissions have also been rising, particularly in regions of high livestock density. The importance of this acidifying and fertiliser compound varies nationally, for example, it requires a high priority in the Netherlands where its contribution to total acidity is greater than 45%. The highest ammonia sources are from intensively managed livestock systems, particularly from manure, land spreading and housing systems. Trends in these activities will have implications for the increasing importance of ammonia emissions. The Dutch government have already imposed an ammonia emission reduction of 30% by 1994 and a further reduction of 70% by the year 2000. In a future environment where nitrogen species are liltely to increase in importance other national abatement strategies must adopt more stringent protocols for nitrogen species. There has been increasing interest in levels of secondary pollutants, i.e. photochemical oxidants over the last two decades. In particular tropospheric ozone concentrations have been monitored and it has been implicated that elevated concentrations have a direct affect on human health, materials and vegetation. Although there are a number of factors which control the sensitivity of vegetation to ozone it has been shown that if concentrations are maintained at 50 ppb for several weeks adverse affects on plant growth have been observed. The forest decline experienced in the Federal Republic of Germany has been attributed to elevated ozone concentrations. Mean ozone concentrations recorded at these high elevation sites are comparable with areas of the USA where ozone is known to damage the forest. The main effect is the impact on cellular permeability which allows occult deposition to leach key nutrients at an accelerated rate. Changes in the concentrations of acidic pollutants will have obvious ramifications for acidification research. However, there is increasing evidence that the scientific community is targeting nitrogen species, as their relative importance is increasing. In addition, although not a primary or secondary pollutant the deposition of base cations provides an important neutralisation source and should not be ignored. Estimates of critical loads would change if there was a n increasing trend in base cation deposition to catchments. The rest of the paper deals with other global environmental changes and considers the indirect implications for acidification studies. 2.2 L a n d Use Change

Although natural changes in vegetation succession and colonisation might arise from other global environmental changes this section will consider the politically driven changes in land management, particularly, afforestation, deforestation and agricultural practice and the implications for acidification research. Land use change has already formed and integral part of acidification

49

studies. Many comparative studies have implicated the exacerbating effect of coniferous a f k e s t a t i o n on stream water quality. Similarly modelling approaches have been employed, to predict future changes in the acidification status of the water under a number of land use change scenarios. MAGIC has been used at a number of sites to predict the impact of afforestation, deforestation and replanting under a number of deposition scenarios (Figure 2) and has recently been used to investigate the influence of land use an critical load estimation (Whitehead et al., 198813, Jenkins et al., (in Press)).

7 6

5

5 4

3

1840

1900

1960 2000

21 00

0.8

0.6

-

a

0.4

0.2

18.40

=1900- 300 ml). Samples are analysed at the ScottishPower chemistry laboratory at East Kilbride for conductivity, pH, sodium, potassium, ammonium, calcium, magnesium, chloride, 1991). sulphate and nitrate. Details of analysis methods can be found in Stewart

u.(

Sub-catchments IV, VI and VII each have a distinct drainage stream (Figure 1). Automatic flow monitoring equipment, employing either v-notch weirs or trapezoidal flumes connected to stilling wells, was established on these streams and on the loch outlet stream. Water sampling sites, from where samples for chemical analysis are collected daily, were established adjacent to the flow monitoring points. Details of sample 1991a). collection and analysis can be found in Dalziel

u.(

Data on deposition inputs to the Loch Fleet catchment and on runoff outputs from the monitored sub-catchments and from the whole catchment have been collected since April 1985, one year before liming. In addition to collecting these data, a separate study was carried out between February and December 1985 by members of the Macaulay Land Use Research Institute, Aberdeen, to investigate, in more detail, the interactions between deposition, vegetation and soils. Experimental plots were established in afforested parts of the catchment below the two main species of conifer, lodgepole pine and Sitka spruce, from where data on vegetation throughfall, stemflow, soil water drainage and ditchflow were collected. A separate bulk deposition collector was used in this study, located in a forest fire break between sub-catchments I1 and 111 (Figure 1). In addition, a further deposition collector was deployed, termed an "interception gauge", which was designed to capture cloud water, mist and fog (collectively known as "occult deposition") as well as true rainfall.

112

4. MODELLING

Modelling, using the MAGIC (Modelling of Acid Groundwaters In Catchments) model (Cosby 1985), modified somewhat to allow more flexible run periods and to incorporate liming, was employed to answer some questions concerning the effects of forests on surface water acidification and the ways in which deleterious effects might be minimised. The runs were performed to simulate the response of a Norway spruce forest

u.,

&\

LOCH FLEET

A "/

OUTFLOW FROM

0

-

-

WATERSHED REASONABLY WELL DEFINED WATERSHED LESS WELL DEFINED LOCH EMBAYMENT ......... SmEAMS ... .,.,... ...... . .. . CONIFEROUS TREES 0 '4-NOTCH WEIR/TRAPEZOIDAL FLUME

I -

Figure 1. The Loch Fleet Catchment

500 METRES

113

growing on poor soil overlying a substratum with a low weathering rate. Excess base cation uptake by trees varies widely with species, growth rate, site conditions, life-cycle stage etc. For Norway spruce in southern Sweden Nihlglrd (1970) gives a rate of 97 mEq m-2-year; Norway spruce in central Germany took up 93 mEq m.'-year and Binkley and Richter (1987) quote a figure of 90 mEq m.'-year for a forest in the USA. The model runs used 90 mEq m"-year, divided 54:21:15 in equivalents between Ca2+:MgZ+:K+.The forest was modelled as growing on an acidic soil with a base saturation of 13%, on a substratum with a weathering rate of 11.3 mEq m-'-year.Charlson and Rohde (1982) estimated that the pH of pristine precipitation was between 4.5 and 5.5, taking into account natural emissions of S and N compounds. In order to predict whether forest growth could, in principle, acidiij surface water if there was no anthropogenic acid deposition a "background deposition" run was carried out using precipitation at p H 5 with an excess (or non-sea salt) sulphate concentration of 11.8 pEq 1.'. Data input for this run simulates the presence of mobile anions from only natural S and N emissions. To investigate what effect deposition containing mobile anions&o from sea salt would have, a run was carried out with no excess sulphate and a precipitation p H of 5.78. The p H is higher than the theoretical 5.65 because of a slight excess of Ca2+ and K', but essentially this is sea salt pH. A third run employed the same input data as used in the "back round deposition" run, but incorporating forest soil liming. The dosage was 25 tonne ha- of limestone (CaCO,), which was assumed to dissociate over 4 years.

B

5. RESULTS 5.1 Loch Fleet Project Data

Table 1 shows volume-weighted mean ion concentrations for major ions in bulk precipitation and in stream water runoff from sub-catchments IV (afforested) and VI (moorland) over the period 1985 to 1991. The considerable maritime influence on the precipitation inputs at Loch Fleet, due to the site's proximity to the Irish Sea, is clear from the high sodium and chloride concentrations recorded. These are particularly noticeable between October and March each year due to the quite severe westerly and south-westerly winds associated with high rainfall over this time. The precipitation volume-weighted mean pH between 1985 and 1991 was 4.72 (19 pEq1-I). Less than 4% of the rain events had pHs less than 4 and more than 50% exceeded p H 5. As would be expected, because of evapotranspiration, there is a greater water deficit on sub-catchment IV compared with that on sub-catchment VI. The effects of catchment liming in April 1986 on runoff water quality can be clearly seen by the decrease in Hf and increase in Ca2+ concentrations from 1986-87 onwards. Over 1985-86, prior to liming, however, the acidity of the runoff from both sub-catchments was significantly greater than that of bulk precipitation; runoff from the afforested sub-catchment IV being slightly more acidic than that from sub-catchment VI. Sodium, magnesium, sulphate and chloride concentrations were all elevated in sub-catchment runoff compared with those in bulk precipitation and in all cases concentrations from sub-catchment IV were greater than those of subcatchment VI.

114

Table 1. Volume weighted mean concentrations of major ions in bulk precipitation and in runoff from sub-catchments IV and VI at Loch Fleet, 1985-91. Units are pEq 1-1

19t15-91

M48

177

1

50

97

22

206

115

Table 2 shows the volumes of precipitation and concentrations of major ions collected by a bulk precipitation collector and an "interception gauge" between February and December 1985. The gauge was designed to capture more effectively occult deposition", in a way similar to coniferous trees. The results show that the bulk collector underestimated deposition and ion inputs considerably. The volume collected by the "interception gauge" was more than double that of the bulk collector, indicating the high incidence, at this upland site, of wet deposition other than rainfall. Sea salt ion inputs were increased fourfold in "interception gauge" samples, and non-sea salt concentrations were doubled, compared with samples from the bulk collector. Figure 2 shows the amount of bulk precipitation compared with throughfall recorded beneath lodgepole pine and Sitka spruce stands between February and December 1985. Interception loss was greater in lodgepole pine canopy (35%) compared with that in Sitka spruce (15%). In the same way as shown by the "interception gauge" samples, the throughfall below the forest canopy produced considerably enriched ion concentrations due to foliage-captured inputs of mist and fog (Figure 3). In most cases, ion enrichment was greater in Sitka spruce than in lodgepole pine.

Collector

volm, mn

H+/~H

~ a +

ca2+

ng2+

K+

Bulk collector

2004

29.5/ 4.53

73.5

13.0

16.5

3.8

25.0

"Interception gauge"

4735

37.2/ 4.43

353.0

30.9

56.4

8.4

44.3

NH,,+-N

so4*-s

CI-

19.3

56.7

65.4

45.7

101.6

341.4

N+--N

i

The effects of catchment liming on surface water chemistry are shown in Figure 4, for runoff from sub-catchment IV. Calcium concentration and pH increased rapidly following liming with a dosage of 24 tha-'. Although the calcium concentration has declined since the maximum reached soon after liming, it is predicted that the runoff water quality from this sub-catchment in addition to that from sub-catchments VI and VII, which were limed at the same time, will maintain satisfactory conditions for trout survival within the loch 1991b). at least until the end of the century (Dalziel

a,,

5.2 Modelling The results of the "background deposition" run, in which the effects on surface water acidification of a forest subjected to precipitation of pH 5 and only 11.8 pEq 1.' non-sea salt sulphate are modelled, are given in Figure 5. The results suggest that forests can indeed acidify waters significantly by base cation uptake alone, even in the absence of "acid rain". Over the 60 year growth period, stream water pH declines, aluminium concentration rises to potentially toxic levels and calcium concentration falls steadily as the soil cation exchanger becomes depleted of calcium.

116

0

_i L/POLE

SITKA

Figure 2. Amount of bulk precipitation (BP) compared with throughfall recorded beneath lodgepole pine (LPOLE) and Sitka spruce (SITKA) stands between February and December 1985. (Data of Nisbet and Nisbet, 1991) The results of this run indicate that in spite of the lack of excess strong acid anions in precipitation the trees, by sequestering base cations, effectively create them and the stream water pH falls as a consequence. At these pHs there will be some contribution from HCO, as a mobile anion. There is no aluminium present at these pHs. From this run it seems clear that tree growth can acidify surface waters in the absence of acid precipitation. Figure 6 shows the results of the run which employed a precipitation input of sulphate derived only from sea salt.

117

A c i t l i I,y

200

Ammoniuni

Sodium

61

30

5c 25

150 4C

20

100

30

15

20

10

50 10

5

0

0 L/POLE

S17K4

BP

L/POLE

SITKA

Nitrate

bO

Chloride 701:

00 150

30

100

20

50 10

0

0 L/POLE

SITKA

L/POI.E

SI I K A

BP

L/POLE

SIIKA

L/P0LI

SIlUd

Figure 3. Volume weighted mean concentrationsof major ions in bulk precipitation (BP) and in throughfall under lodgepole pine (LPOLE) and Sitka spruce (SITKA) between February and December 1985. Units are pEq1-l. (Data of Nisbet and Nisbet, 1991)

118

Figure 7 shows the effects of forest liming at 25 tha-' to alleviate the effects of excess base cation uptake by a forest. The improvements in water quality parameters appear dramatic and long-lasting. In the real situation, of course, the other acidification mechanisms would also be operating, so liming would not have such a lasting effect.

"$

I

45

1 Jan86

1 Jan87

1 Jan@

1 Jan89

1 Jan90

1 Jan91

9 1

I

Liming

Figure 4. Calcium concentration and pH of stream water draining sub-catchment IV, 1986 to 1991, showing the effects of catchment liming in April 1986

119

5.0

5.b

2.5

2.0

Stream

1.5

[a3+] 0.5

0.0

//

-------

1990

2000

2010

2020

2030

2040

2050

YEAR

Figure 5. Results of MAGIC modelling of the effects on surface water quality of forest growth with deposition pH 5 and containing 11.5 pEq1-l non-sea salt SO:.

120 6. DISCUSSION

6.1 Loch Fleet Project Data Sub-catchment runoff data prior to liming, compared with bulk deposition inputs, show considerable increases in acidity from both forested and moorland sub-catchments. Surprisingly, runoff from the forested sub-catchment (IV) is only slightly more acid than that from the moorland sub-catchment VI. Some of the increased acidity from the two sub-catchments can be attributed to acid generating processes within the catchment vegetation and soils, but it should be remembered that, as demonstrated by the "interception gauge", the bulk collectors underestimate ion inputs, including acidity, quite considerably.

Stream [ca2+] FEq 1.'

7.0 b.8

b.b

Stream

pH

b.4

6.2

b.0 1

1990

2000

1

1

1

l

,

2010

I

x

2020

,

1

~

2030

2040

' r 2050

YEAR

Figure 6. Results of MAGIC modelling of the effects on surface water quality of forest growth when deposition contains only sea salt derived SO-:

1

121 l0Oj

Stream

[Ca''] pEq I''

Stream

PH

1

5.0

2.0

1.5 1 .o

0.5

0.0 1990

I

2000

"

?

,

,

201 0

~

~

~

2020

I

I

,

*

I

1

203C

.

, I

.

,

I

2040

?

,

,

.

,

2050

YEAR

Figure 7. Results of MAGIC modelling of the effects on surface water quality of forest liming

122 The data on forest throughfall collected in 1985 by members of the Macaulay Land Use Research Institute (Nisbet and Nisbet, 1991) show more clearly the effects of the forest vegetation at Loch Fleet on modifying deposition inputs. Over February to December the canopy increased deposition acidity, in contrast to results from other coniferous throughfall sites elsewhere in the UK, where rainfall, particularly in summer, was effectively neutralised within the canopy. The Loch Fleet results may be due to the nutrient-poor status of the trees. During the winter and spring it is believed that the main acidifylng processes are canopy interception of cloud water and subsequent washout of this deposited acidity in association with sulphate and nitrate. Other factors may also contribute to the increased acidity of bulk deposition beneath the forest canopy such as canopy leaching of sulphate which may make a significant contribution to sulphate deposition in throughfall, particularly in summer, when the trees are metabolically most active. The foliar utilisation of ammonium ions in deposition as a source of nitrogen at this nutrient-poor site may also be acidifying, since this involves an exchange of H+ ions for ammonium.

6.2 Modelling It may be argued that the attempts to model the effects on surface water acidification of base cation uptake by trees are crude. The importance of the results, however, is that they demonstrate that water acidification due to this process alone, is, in theory, possible taking into account known processes parameterized in a realistic way. None of the other potential effects of forest growth are included in the model runs; it is exclusively base cation uptake. The soil is assumed to start in equilibrium with deposition, so in the absence of forest base cation uptake there would be no change. Thus, it appears that on poor soils forestry will exacerbate acidification. It seems necessary, therefore, to consider the policy implications of this. To not plant forests in these areas is one solution being seriously considered in the UK. However, forestry has other functions which are considered socially beneficial, such as timber production, soil protection, recreation etc. An alternative approach might, therefore, be to modify the effects of sylvicultural practice, for example by liming, to replace lost base cations as demonstrated both by modelling (Figure 7) and from the results of catchment liming at Loch Fleet (Figure 4). One disadvantage of liming which was identified in the model run is that Mg2+ and K+ are displaced from the soil exchange surfaces and may become too low for effective forest nutrition. This, however, may be correctible by fertilisation. Overall, the policy implications seem to be that reductions in acid deposition alone will not be enough to alleviate acidification in areas of slow weathering geology and forest growth. Replacement of base cations taken up by the growing forest and critical thought about other sylvicultural practices will be necessary. Liming is one option that should be considered.

7. CONCLUSIONS There is considerable evidence of adverse effects of afforestation on surface water quality.

123 A number of possible mechanisms can be invoked to account for these effects. These include pollutant capture, but also factors intrinsic to forest growth and to sylvicultural practice. Base cation uptake by trees can be modelled and, even in the absence of inputs of strong acid anions derived from combustion, can be shown by modelling to cause surface water acidification. Liming is a possible measure which may need to be considered in some instances in addition to emission controls.

8. ACKNOWLEDGEMENTS The authors would like to thank Katharine Paterson of ScottishPower and Margaret Proctor of National Power for their invaluable efforts in Loch Fleet data collection and processing, respectively. The authors are grateful for permission to publish this paper from the Loch Fleet Project Management Committee and the Joint Environmental Programme jointly undertaken and funded by National Power plc and PowerGen plc.

9. REFERENCES

(m

Adamson, J.K. & Hornung, M. (1990). The effect of clearfelling a Sitka spruce sitchensis) plantation on solute concentrations in drainage water. Journal of Hydrology, 116, 287-297 Berner, R.A. (1984). Sedimentary pyrite formation: an update. Geochim. Cosmochim. Acta 48,605-615 Binkley, D. & Richter, D. (1987). Nutrient cycles and H + budgets of forest ecosystems. 1-51 Advances in Ecological Research

s,

Brown, K.A. (1985). Acid deposition: effects of sulphuric acid at pH 3 on chemical and biochemical properties of bracken litter. Soil Biol. Biochem. l7,31-38 Calder, I.R. and Newson, M.D. (1979). Land use and upland resources in Britain strategic look. Water Res. Bull. 16,201-211

-a

Charleson, R.J. & Rodhe, H. (1982). Factors controlling the acidity of natural rainwater. Nature 295, 683-685 Cook, J.M., Edmunds, W.M. and Robins, N.S. (1991). Groundwater contribution to an acid upland lake (Loch Fleet, Scotland) and the possibilities of amelioration. J. hydrol. 125, 111-128

124 Cosby, B.J., Hornberger, G.M., Galloway, J.N. & Wright, R.F. (1985). Time scales of catchment acidification. Environmental Science and Technology, l9, 1144-1149 Dalziel, T.R.K., Proctor, M.V. & Paterson, K. (1991a). Water quality of surface waters before and after liming. In: Howells, G. and Dalziel, T.R.K. (Eds.), "Restoring Acid Waters: Loch Fleet 1984-1990', Elsevier Applied Science, London and New York Dalziel, T.R.K., Dickson, A. & Proctor, M.V. (1991b). Calcium flux calculations and predictions of catchment liming effectiveness at Loch Fleet, Galloway, Scotland. Lake and Reservoir Management, In Press Department of the Environment (1991). Forests and surface water acidification. Department of the Environment, London, UK Egglishaw, H., Gardiner, R. & Foster, J. (1996). Salmon catch decline and forestry in Scotland. Scottish Geographical Magazine, 102,57-61 Feger, K.H., Brahmer. G. and Zottl, H.W. (1990). Element budgets of two contrasting catchments in the Black Forest (Federal Republic of Germany). J. Hydrol. 116,85-99 Forestry Commission (1988). Forests and Water Guidelines. Forestry Commission, Edinburgh, 28pp Fowler, D., Cape, J.N. & Unsworth, M.H. (1989). Deposition of atmospheric pollutants on forests. Philosophical Transactions of the Royal Society of London, 247-265

m,

Hall, R.F. (1987). Processes of evaporation from vegetation of the uplands of Scotland. Trans. Roy. SOC.Edinburgh (Earth Sciences) 28, 327-334 Harriman, R. & Morrison, B.R.S. (1982). Ecology of streams draining forested and nonforested catchments in an area of central Scotland subject to acid precipitation. Hydrobiologia, 88, 251-263 Howells, G. & Dalziel, T.R.K. (Eds.) (1988). The Loch Fleet Project. a Report of the Intervention Phase (2), 1986-87. CEGB, SSEB, NSHEB, British Coal Huet, M. (1951). Nocivite des boisements en Epiceas pour certain cours d'eau de Ardenne Belge. Verh. Int. Verein. Theor. Angew. Limnol. lJ, 327-334 Irwin, J.G., Campbell, G.W., Cape, J.N., Clark, P.A., Davies, T.D., Derwent, R.G., Fisher, B.E.A., Fowler, D., Kallend, AS., Longhurst, J.W.S., Martin, A., Smith, F.B. and Warrilow, D.A. (1990). Acid Deposition in the United Kingdom, 1986-1988. Dept. of Environment, Warren Spring Laboratory, 124pp Jenkinson, D.S. (1970). The accumulation of organic matter in soil left undisturbed. Rothamstead Report 1970 (2), 113-137

125 Jones, H.C., Noggle, J.C., Young, R.C., Kelly, J.M., Olem, H., Ruane, R.J., Pasch, R.W., Hyantis, G.J. and Parkhurst, W.J. (1983). Investigations of fish kills in fish rearing facilities in Raven Fork Watershed. Tennessee Valley Authority Report TVA/ONR/WR8319, 60pp b u g , E.C. (1991). Review of acid deposition-catchment interaction and comments on future research needs. J. Hydro]. 128,1-27 Likens, G.E., Bormann, F.H., Pierce, R.S., Eaton, J.S. and Johnson, N.M. (1977). Biogeochemistry of a Forested Ecosystem. Publ. Springer, New York, 146pp McLeod, A.R., Holland, M.R., Shaw, P.J.A., Sutherland, P.M., Darrall, N.M. & Skeffington, R.A. (1990). Enhancement of nitrogen deposition to forest trees exposed to SO,. Nature, 347, 277-279 Nihlgdrd, B. (1972). Plant biomass, primary production and distribution of chemical elements in a beech and planted spruce forest in South Sweden. Oikos, 23, 69-81 Nisbet, A.F. & Nisbet, T.R. (1991). Interactions between rain, vegetation and soils. In: Howells, G. and Dalziel, T.R.K. (Eds.) "Restoring Acid Waters: Loch Fleet 1984-1990". Elsevier Applied Science, London and New York Nisbet, T.R. (1990). Forests and surface water acidification. Forestry Commission Bulletin, 86, Her Majesty's Stationery Office, London, UK Pennington, W. (1981). Records of a lake's life in time: the sediments. Hydrobiologia 79, 197-219 Skeffington, R.A. (1983). Soil properties under three species of tree in southern England in relation to acid deposition in throughfall. In: Ulrich, B. & Pankrath, J. (Eds.), "Effects of Accumulation of Air Pollutants in Forest Ecosystems". Reidel Publishing Co., Netherlands Skeffington, R.A. (1987). Soil and its responses to acid deposition. CEGB Research, 20, 16-29 Stewart, B.R., Paterson, K., Dalziel, T.R.K. and Proctor, M.V. (1991). Deposition input considerations. In: Howells, G. & Dalziel, T.R.K. (Eds.), "Restoring Acid Waters: Loch Fleet 1984-1990'. Elsevier Applied Science, London and New York Stoner, J.H., Gee, AS. and Wade, K.R. (1984). The effects of acidification on the ecology of streams in the upper Twyi catchment in west Wales. Environmental Pollution A, 3, 125-157

126

Sullivan, T.J., Christopherson, N. Muniz, I.P., Seip, H.M. and Sullivan, P.D. (1986). Aqueous aluminium chemistry response in episodic increases in discharge. nature 223, 324-327 Sverdrup, H. and Warhinge, P. (1990). The role of weathering and forestry in determining the acidity of lakes in Sweden. Water Air Soil Poll. 2, 71-78 van Breeman, N. ,Driscoll, C.T. and Mulder, J. (1984). Acidic deposition and internal proton sources in acidification of soils and water. Nature 307,599-604

T. Schneider (Editor), Acidification Research. Evaluation and Policy Applications 1992 Elsevier Science Publishers B.V.

127

HIGHER ORDER EFFECTS

L. Reijnders: IVAM Universiteit van Amsterdam; Stichting Natuur en Milieu. Utrecht. Abstract Acidification has indirect or higher order effects that seem to be less well studied than direct or first order effects. High order effects may be based on the direct interdependence of species. Such effects may result in the increased or decreased viability of species. This in turn will reverberate in foodwebs and ecosystems to which the affected species belong(s). There may be consequences for geochemical cycles. Higher order effects may also go beyond the direct interdepence of species. Two examples of such effects are discussed. One linking high N-depositions with increased concentrations of the greenhouse gas N,O and associated temperature forcing and another potentially linking acidification with increased deposition of oxidized S-compounds. Introduction Direct or first order effects following from the acidification of waters and soils are by now relatively well researched. However acidification has also higher order or indirect effects that seem to be less well studied. This may mean that effects on higher trophic levels, reverberations in food webs, and effects on fluxes of substances are currently underestimated. In this contribution I will outline a number of potential and all-to-real higher order effects of acidification and related atmogenic changes. In doing so there is no pretence of being exhaustive. My aim is primarily to point out that there are higher-order effects, and that such effects may have wide ranging consequences. Hiaher order effects based on interdependence of species Acidification of soils and waters, combined with associated atmogenic stress-factors like high deposition of N-compounds, leads to many changes in the presence and speciation of substances in soils and waters. These changes have direct (first order) effects on a number of species. First order effects, influencing for instance viability or content of trace elements, may in turn cause higher order effects on other species. These effects will in principle reverberate in food webs and ecosystems to which the affected species belong(s). Such higher order effects often follow from the direct interdependence of species. Interdependence of species may take several fo m s . In line with this there are several types of higher order effects. Table 1 briefly summarizes known types of second order effects associated with different types of interdependence.

128

Table 1. Types of second order effects caused by acidification based on direct interdependence of species. first order effect

second order effect

stress effect on, or decreased viability of, one (or more) species

increased success of (an)other species decreased viability of (an)other species

I

increased viability of (or more) species

ecreased viability of (an)other species

increased viability of (an)other species

changed concentrations of trace compounds in one (or more) species

decreased health or viability in (an)other species

Firstly stress effects on, or the decrease of viability in, one (or more) species due to air pollution, may lead to increasing populations of (an)other species. Stress induced increases in seed production by spruces have benefited the cross bill (Loxia curvirostra) and the citril finch in Germany (1). Populations of woodboring birds have (temporarily) increased parallel with the increase in standing dead trees. These include the white breasted nuthatch (Sitta carolinensis) in Canadian maple forest and the three toed woodpecker (Pircoides tridactilus) in Germany (1). We also see increased success of species, as a second order effect in the transition of heath land (dominated by Scotch heather, Calluna vulgaris) to grassland (dominated by wavy hair grass; Deschampsia flexuosa). This follows from the increased vulnerability of heather to frost, drought and heather beetles, caused by a combination of acidification and high N-deposition. This gives Deschampsia a competitive edge (2). Even more dramatically we see such changes in advanced cases of forest dieback, such as have occurred in the Harz (Germany) and Bohemia. Here one finds the replacement of forest by open woodland. And this in turn has higher order effects, as is clear from large changes in bird populations. In Bohemia and the Harz populations of robin, chaffinch, firecrest and blackbird have plummeted, whereas the number of willow warblers, tree pipits, redstarts and the rare ring ouzels have increased (3). Secondly the decline of one (or more) species may cause the decline of associated species. The association may be based on relations such as providing water, food or cover. A first example of such a second order decline relates to the association between Douglas fir (Pseudotsuga menziesii) and mycorrhiza fungi. The

129

latter are probably essential for an adequate water supply to the fir. Because mycorrhiza are negatively affected by acidification, vulnerability of the Douglas fir to drought tends to increase when soils become acidified ( 2 ) . The changed availability of food for other species associated with species decline has been shown to be a major cause of second order effects. In Scandinavia populations of piscivorous birds like red throated divers and mergansers underwent a marked decline due to reduced fishstocks in acidified lakes ( 4 ) . Similarly in the Netherlands there has been a decline of the great crested gerbe in (the vicinity of) small acidic lakes (5). Ospreys dependent on acidified lakes produce fewer young ( 4 ) . Birds (e.g. dipper populations) that feed on semi-aquatic insects have been found negatively affected by acidification, due to reduced insect abundance in Scotland and Wales ( 4 ) . Another interesting second (and higher) order effect follows from changes in cover. There is suggestive evidence that in Canadian maple woods populations of Vireo olivaceous and Epidonax minimus have decreased due to loss of cover caused by atmogenic stress (5). Loss of needles is implicated in the decrease of large (2.5 mm) spiders in Swedish and Danish forests. This decrease may in turn negatively affect the goldcrest (Regulus regulus) that is dependent on the availability of such spiders ( 4 ) . Because of the negative effects of acidification on overall productivity of plant and animal life, increased success of a species is much less common as a first order effect than decreased viability. However there are cases of increased success and these may in turn have higher order effects. An example thereof may be found in Scots pine forests. Here soil acidification and N-deposition have led to a massive increase of wavy hairgrass (Deschampsia flexuosa) (6). This in turn benefits some aphid and caterpillar species ( 4 ) . However the success of wavy hairgrass is probably the reason for the decrease of red ants. Red ants need bare soils to build their mounts. The reduced presence of red ants in turn is probably the cause of population decline of the green woodpeckers in Dutch forests subject to high N-deposition (6). A further category of higher order effects based on the direct interdependence of species is associated with changed levels of trace-elements such as calcium, aluminium and heavy metals. In acidified soils one may note a major loss of cations from the upper strata, and this is reflected in the biota on such soils. In acidified waters one may find the mobilisation of aluminium and heavy metals and a decrease of Ca- and Mg-concentrations and this in turn influences species dependent on those lakes (7). Preliminary research in Scandinavia ( 4 ) suggests a decrease in diversity and abundance of snails in acidified areas. This is probably caused by reduced amounts of calcium in plants eaten by snails. Kingbirds in acidified Canadian wetlands and dippers breeding near streams with a low pH have been reported to lay eggs with thinner shells (8). Again the probable cause is lowered calcium-levels in food.

130

Reduced numbers of snails carrying houses and/or reduced levels of calcium in insects have been identified as the probable cause of a reduced reproductive success of great tits in acidified Dutch woodlands. The birds concerned have been found to lay fewer eggs. Moreover an increasing percentage of their eggs was found to have thin and porous shells (6). There is suggestive evidence that increased levels of aluminium in insects may be linked to a decrease in the populations of some insect eating birds (9). Increased amounts of heavy metals accumulating in food chains have been correlated with acidification. In Canada increased levels of metals linked to acidification have been found in Ontario mink (Mustefa vison) and otter (Lutra Canadensis) (18). In acidified wetlands in Sweden mercury levels in juvenile Goldeneyes were found to be so high that effects on behaviour were not unlikely (11). Increased mercury levels in great northern divers breeding in acidified lakes may have been the reason for lowered reproductive success (12).

All changes in the relative abundance and viability of species caused by acidification may have reverberations in the foodwebs and ecosystems, to which these species belong. It is clear that this will have an impact on ecosystem composition. A matter arising in this context is whether acidification-induced change in ecosystems also influences the non-living environment. This pertains to among other things the ability of living nature to correct major man-made perturbations in the environment and possible effects of acidification on geochemical cycles in which living nature participates. The first matter will be dealt with in another paper at this conference. A s to the second matter, it may be noted that there is suggestive evidence that acidification may influence geochemical cycles. It is known that acidification does negatively affect lichens involved in nitrogenfixation (4) and this in turn will have an impact on the nitrogen cycle. Another impact will emerge later in this paper, where among other things the impact of the deposition of N-compounds on the release of N,O is discussed. In both cases first order effects on species are involved. However, there is no obvious reason why higher order effects on species may not lead to changes is the non-living environment. Hiaher order effects beyond the direct interdeDendence of sDecies So far higher order effects described were tied to the direct interdependence of species. However, there are also other ways in which acidification and associated atmogenic stresses may cause higher order effects. In such cases effects go beyond the direct interdependence between species. Research on such higher order effects is very limited. Nevertheless I would like to discuss two examples. A first example is schematically outlined in figure 1.

131

Figure 1. Schematic representation of higher order effects of acidification and associated atmogenic stresses linked with increased release of N,O. soils subject to depositions of high amounts of N-compounds

I I

1 increased release of N,O 1 increased temperature forcing

r

1

changes in rainfall

I

I

1

1

increased temperature stress on species

1

sea level rise

1 water related stresses on species This example includes both effects on species that go beyond direct interdependence between species and effects on the nonliving environment. There is suggestive evidence that high depositions of nitrogen containing compounds due to their impact on (de)nitrification may significantly increase the emission of N,O (nitrous oxide) (13). Nitrous oxide has an estimated atmospheric lifetime of 170 years. Its atmospheric concentration currently grows with a yearly rate of 0 , 2 - 0,3 per cent. N,O is a 'greenhouse gas'. Increasing atmospheric concentrations thereof will have a temperature forcing effect. N,O emissions between 1950 and 1990 contributed about 5 per cent to the overall temperature forcing effect by increased concentrations greenhouse gases over that period (13). To stabilize atmospheric concentrations, worldwide emissions of N,O should probably be reduced by 70 - 90 per cent (14). Acidification however probably has the opposite effect increased emissions of N,O. This will increase and may accelerate temperature forcing by greenhouse gases. There is a time delay between increased atmospheric greenhouse gas concentrations and actual temperature increases at the earth surface (15). However there is no serious doubt that (ceteris paribus) in due course such temperature increases will occur (16). These in turn may have a multitude of effects, including sea level rise, changes in precipitation patterns, and water- and temperature related stresses on natural species (16). Species that may be affected by increased temperatures do overlap species that are currently affected by high N-depositions. Thus for instance higher order effects of N-deposition may increase atmogenic stress on species such as trees (15). Moreover increases in temperature may also influence the microbial production of N,O, thereby giving rise to a cyclic relation.

132 A second example of higher order effects that go beyond the direct interrespondence between species is essentially speculative. Part of it consists of a hypothesis advanced by Sangfors (17) linking acidification with eutrophication. This example is schematically represented in figure 2.

Figure 2. Hypothetical cyclic higher order effects of acidification. acidification of soils

-

increased leaching of cobalt

I

?

increased cobalt levels in coastal waters

I

f

I

-

incieased deposition of oxidized sulphur compounds

increased production of dimethylsulfide by algae

2

1

2

I

increased primary production of algae, due to increased availability of vitamin B12

This hypothetical case of higher order effects builds on the increased leaching of cobalt from acidified soils (18). Increased leaching of cobalt is supposed to lead to increased levels of cobalt in coastal waters and in turn to increased availability to algae of the cobalt-containing vitamin B 12. This is hypothesized to induce increased primary production of algae. A s this is potentially associated with an increased generation of dimethylsulfide (la), it is hypothesized that following atmospheric oxidation (18) this may add to the deposition of oxidized sulfur compounds, which in turn may contribute to (further) acidification of soils. I have chosen this example because it exemplifies a cyclic relation in which acidification may induce further acidification. Such an acidification-cycle would by highly worrying indeed, and this provides a good reason for a serious test of the hypothesis advanced. Conclusion In the foregoing it has been demonstrated that acidification and the related phenomenon of high N-deposition do have real and potential higher effects. This demonstration has been based on limited research. Much more research is needed to obtain a more complete and less hypothetical picture of these higher order effects. In the field of effects research this is probably the major challenge of the nineteen nineties.

133 Des Granges, J.L.; in The Value of Birds, IBCP Technical Publication 6 (1987) 249-257; also in Mens en Vogel, (mei 19891, page 87-92 Eerden, J.M. van: IPO Annual Report, Wageningen, (1990), page 9 -17 Oelke, H.; Beitr. Naturk. Nieders., 42 (1989), page 109 128; Stastny K., V. Bejek; in Birds Census Work and Atlas Studies, Taylor, K. et al. eds; BTO Publications, page 243-253

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Toarstensson, P., L.E. Liljekind; Flora- och faunafBrkindringar i terrestra miljber, Rapport 3604, Naturvdrdsverker, Solna, Sweden, 1989 J. Graveland; Experientia 46 (1990), page 962-970 Schuurkes, R., P. Sturmans; Vogeljaar 1 (1987)' page 57-64 Graveland, J.; Experientia 46 (1990). page 462-970 Heij, G.J., T. Schneider; Acidification Research in the Netherlands, Elsevier, (1991) Omerod, S.J., K.R. Bull, C.P. Cummins, S.J. Tyler, J.A. Vickery; Environmental Pollution 55 (1988), page 10-121 Glooschenko V., P. Blancher, J. Herskowitz; Water, Air Soil Pollution 30 (19861, pages 353-367 Nyholm, N.E.I.; 371

Environmental Research 26 (1981), pages 363-

(10) Wren, C.D., P.M. Stokes, K.L. Fisher; Canadian Journal Zool, 64 (1986), pages 2854-2859 (11) Ericksson, M.O.G., L. Hendrikson, H.G. Oscarson; Arch. envir. contam. Toxic. 18 (1989), page 155-160 (12) Barr, J.F.; ( 1986 )

Canadian wildlife Service ,Occasional Paper 56,

(13) Robertson, K.; Ambio 20 (1991), page 151-155; Magaritz, M.; in International Environment Reporter 0149-8738, (1991), page 47 (14) Reijnders, L., C. Kroeze; in CLTM, Het Milieu, Kerkebosch, Zeist, (1990), page 285-304 (15) Krause, F.; Energy Policy in the Greenhouse, IPSEP, El Cerrito, (1989) (16) UNEP/WMO; Climate Change - The IPCC Scientific Assessment, Cambridge University Press, (1990) (17) Sangfors, 0.; Ambio 17, (1988). page 296 (18) Reijnders, L.; H,O 23, (1990), page 430-432

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ACIDIFYING EFFECTS CN GFCUNWATER

Jouko Soveri National Board of Waters and the Environment P.O. Box 436, SF-00101 Helsinki, Finland Abstract

In recent years, several reports concerning the utilization of acid groundwater, in water supply have emphasized corrosion and health aspects. Acid rain may dissolve harmful elements from soils and indirectly affect water supply distribution systems. Groundwater acidification occurs also in areas where lake acidification is reported. Acid groundwater is encountered with increasing frequence in Scandinavia, northwestern Europe and in the northeastern parts of the American continent, where the bedrock and the soil mainly consist of acidic crystalline rocks, such as granite and gneiss. In these catchment areas, the buffering capacity is generally low and the sensitivity to acidification rather high. The extent of groundwater acidification is still largely unknown. 1. INTRODUCTION

Acidification of groundwater and surface water has been considered to be one of the most serious environmental problems of the future. Waterway acidification is already a generally recognized phenomenon in almost every region where fossil fuels are used. Air pollutants have been shown to cause significant changes in the state of the environment over extensive areas in Scandinavia, Canada and North America. Future prospects also appear depressing unless we can decisively reduce sulphur and nitrogen emissions. We can assume that acidification will further increase in certain areas despite the reduction of emissions. Acidification has been shown to have affected the ion ratios of groundwater. Special concern is being expressed about the increasing mobilization of toxic metals (Pb, Cu, Cd and Al) from both soil and drinking water pipes, as well as their possible harmful effects on health. And in the future, the water supply will be obtained, to an ever-increasing extent, from groundwater sources. The greatest threat of groundwater acidification is in shallow groundwater aquifers. The water supply in rural areas is often derived from such sources especially in the Nordic countries and in Canada. Groundwater constitutes normally about 30-70% of the municipal mains water in Europe. In Denmark, however, the amount is almost loo%, but in Norway less than 10%.

136

Signs of the acidification of groundwater have been reported by many authors, for example in Norway (l), Finland ( 2 1 , Germany (3), Sweden ( 4 ) , England ( 5 ) and in Canada (6). 2. AREAS SUSCEPTIBLE TO ACIDIFICATION The risk of groundwater acidification is strongly related to acidic and intermediate bedrock and soil type composed of acidic hard rocks, such as granites, gneisses, sandstones and quarzites. These rocks and soil types are rather resistant to weathering. Which means that the buffering capacity in such catchment areas is generally low and the sensitivity to acidification rather high. The susceptibility of groundwater to acidification is therefore closely associated with the acid neutralizing capacity (ANC) of the soil. In glaciated regions with thin soils, the location of sensitive groundwater can roughly be determined from bedrock geology maps e.g.,in Europe (Figure 1 and 2). As can be seen, nearly all of the aquifers in the Nordic countries are categorized as highly sensitive. Other regions of high sensitivity include northern Scotland, northwestern Spain, and parts of Central Europe. Northern and mountainous regions with thin soils and low weathering capability are more sensitive to groundwater acidification, whereas deep-soiled agricultural areas show the least sensitivity.

Figure 1. Acidic and intermediate acidic hard rocks in parts of Europe (7).

Figure 2. Qualitative indication of groundwater sensitivity in parts of Europe after Holmberg et.al. (8).

137

At the International Institute for Applied Systems Analysis (IIASA), a method for evaluating the sensitivity of European groundwater to acidification, using aggregation matrices was developed by Holmberg et. al., (8). Various factors important to groundwater acidification are compiled on a European grid: soil type, depth, and texture: aquifer size; mineral composition: and water available for recharge. The risk of groundwater acidification is evaluated by assessing to what extent physical and chemical soil and aquifer properties of a certain region will contribute to the neutralization of acid deposition. (Figure 3).

Figure 3. Aquifer sensitivity or risk and assessed indicators after Holmberg et al. (8). Groundwaters differ from surface waters as they have normally longer residence times in soil. These combine to make solid/solution reactions which are of major importance in determining groundwater acidity and alkalinity. The presence or absence of carbonates affects the susceptibility of an aquifer to acidification. The pH in carbonate-containing aquifers rarely falls below 6.5. The buffering in these aquifers is mostly due to the presence of solid calcium carbonate rather than the dissolved bicarbonate. Groundwater in regions with granitic bedrock, thin soils and a humid climate, may show comparatively high concentrations of hydrogen ions. In Nordic countries no decreasing trends in the pH-values have been observed, although changes in bicarbonate, calcium, magnesium and sulphate concentrations have been noticed. In general, the groundwaters in the Nordic countries have relatively low pH-values in the small aquifers of glaciofluvial and till deposits.The reason for this is partly the composition of the bedrock and the overburden, and the shallowness of the aquifers. The shallow groundwater is poorly protected by the overlying soil and its residence time in soil is short. The groundwater therefore reacts easily to changes in the environment.

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3. SUBSOIL PROCESSES AND GROUNDWATER ACIDIFICATION

Groundwater acidification may be caused by both natural and manmade processes. Gradual acidification of the environment has been taking place for thousands of years as a result of natural processes. However, man's activities have clearly speeded up acidification during the past few decades. Groundwater quality is determined by the geohydrological conditions prevailing in the area where it is formed and hence the composition of the groundwater usually also reflects the mineral composition of the soil and bedrock in the area. Acid rainwater and meltwater effectively dissolve out those materials in the soil which slowly change the mass balance of the groundwater. 3.1 Impact of Acid Deposition on Groundwater

The consequences of acidification of soils and groundwater are threefold. Acidification is considered to begin when the base cations on the exchange sites of the soil particles are replaced by hydrogen ions. During the first stage small amounts of ions such as calcium, magnesium, potassium, sodium and sulphate are leached out into the groundwater (Figure 4 ) . At this time there are still large amounts of buffering material present and the pH remains stable or may even increase. A slight increase of this sort thus often indicates the onset of acidification.

Figure 4 . Sum of cations (broken line) and anions (full line) during the period 1975-1988 at a groundwater monitoring station in Finland (9). In the second stage the amount of available buffering material decreases and acidification increases. In the third stage the buffering capacity has disappeared completely (alkanity=O) and the pH has fallen below 5. Dissolution of aluminium increases sharply at this stage (Figure 5).

139

O

0

O

0

0 0

O

800-

oooo

0

-

0

0 0

400 -

0

-

0~

I

O Q

Figure 5. Aluminium concentration and pH in groundwater in Finland in area with high sulphate deposition (10). Areas northern winters. The most

-

affected by acidic precipitation are often located in latitudes where snow accumulates during long, cold Soil acidification may be caused by several processes. important ones are the following:

acid rain, in the form of wet and dry deposition, nutrient uptake by vegetation, oxidation of sulphur and nitrogen compounds in the soil, oxidation and hydrolysis of ferrous iron in the soil, soil respiration giving carbonic acid (11).

3.2 Soil Processes and Leaching

Many of the processes are reversible, hydrogen ions secreted to the soil solution when plants take up cations, are neutralized when the plant is decomposed. Likewise the reduction of sulfate and nitrate is a sink for hydrogen ions. However, in general, these processes tend to be more acidifying than neutralizing (11). Nature is able to protect itself from acidification because the mineralogy of the soil plays an important role in regulating the acidity balance. As the acidity of the soil increases, the amount of hydrogen ions in solution increases and the amount of base cations decreases. The length of time through which exchangeable ions can maintain a state of equilibrium depends on the buffering capacity of the soil. Base cations in the soil are transferred, as a result of ion exchange reactions, from exchange sites to the soil solution, and from there into the groundwater. The pH of the groundwater may even rise in the initial stages, and only start to fall when the alkalinity decreases. Leaching of metals increases as the rate of chemical weathering of minerals speeds

140

up. Reactions of heavy metals and aluminium in both the waterways and the soil are an important aspect of acidification because they frequently have a toxic effect on organisms. The capacity of soil to neutralize hydrogen ions can be estimated using the so-called acid neutralization capacity (ANC) method. The effects of natural and anthropogenic influences on acid-base chemistry can be described using the def inition of ANC (12): ANC

=

2Ca2+ + 2Mg2* + K+ + Na+ + NH,+

+2Fe + 2Mn + 2A1

-

2S0,'-

-

NO3- -C1- -F-

(1)

From this equation, it follows that reactions or processes that reduce the concentration of the cations listed without an equivalent reduction in the anions will reduce the ANC of water: processes that decrease the anions without a concurrent decrease in the cations will increase the ANC.The buffering capacity can also be determined as the difference between the basic and the strongly acidic components present in the soil. The reactions in the soil which involve the formation and consumption of hydrogen ions have an effect on the buffering capacity (13). The exchangeable base cations, mainly C a 2 + , play a deciding role in buffering acidification pushes, which are caused by the temporal discoupling of the ion cycle. The mobility of different weathering products in soil and in the soil water system may vary considerably. Calcium is mobile to some extent, and sodium is considerably more mobile than potassium, although both occur in almost equal amounts in the primary igneous material (14). The reactions between the soil and the soil water system depend above all on the mineral composition of the soil, the specific surface of soil particles and the infiltration rate. The dark minerals formed at high temperatures, such as olivine, pyroxene or hornblende are more easily weathered than for example K-feldspar, quartz or muscovite, formed at lower temperatures. One typical reaction in Precambrian bedrock and in Quaternary deposits is the disintegration and transformation of calcium silicate (15). CaAl,Si,O, =

+ 2H' +H,O

Al,Si,O,(OH),

+Ca3' (2)

If strong acids such as sulphuric or nitric acid prevail in meltwater, the weathering reactions rain water or in snow proceed as (16): H,SO, + Ca-silicate =

Ca2+ + SO,,- + CO, +H,O + A13*

(3)

Percolating water and dominating natural acids dissolve base cations from the surfaces of the soil minerals, and transport the ions to the groundwater. The weathering of cations and their exchange with hydrogen are the main reasons why the pH of the infiltration water and o f the groundwater is higher than that of the rainwater and meltwater. According to the results of lysimeter and percolation experiments, the pH of meltwater changes from 4.7 to 5.8 and to

141

6.2 (without organic topsoil) when passing through 60-110 cm of organic and mineral soil. The mean level of nitrogen compounds in percolation water samples was much lower than that in the meltwater in areas with organic subsurface matter. The loss of nitrogen was due mainly to its uptake by vegetation. There is a continuous turnover of inorganic compounds into organic compounds and vice versa. On the other hand, in areas without organic topsoil the nitrate concentrations were clearly much higher than in meltwater and in rainwater (17). Nitrogen leaching from natural forest soils is usually small. Inorganic nitrogen is mostly in the form of NO, - , because unlike NH, - , it is not adsorbed on soil particles. If NO, from soils results in a loss of NO,into aquatic systems and, if this is accompanied by H' or A 1 3 ' , acidification will occur (13). The sulphate ion is dominant in the acidification process. It is termed a mobile anion, which means that all the sulphate ions which reach the ground in one area will appear in the runoff water and groundwater in the course of time. When this occurs equivalent amounts of cations must be transported through the same areas. These are ions with the opposite charge, mainly hydrogen, aluminium, calcium and magnesium. Hydrogen and aluminium ions cause acidification of water. The major N compounds present in the atmosphere are nitrogen oxides (NO. ) and ammonia (NH,). Normally,most of the nitrogen compounds added to the soil via precipitation and dry deposition will be taken up by trees and plants. If more nitrogen compounds are deposited via precipitation than the vegetation can utilize then the surplus will seep through the topsoil and overburden into the groundwater. The nitrate ion will then have the same acidifying impact as sulphate. Nitrogen saturation of soils has already been observed as a growing problem in central parts of Europe. The significance of nitrate in the acidification of watercourses may be illustrated by the ratio of nitrate concentrations and the sum of the concentrations of sulphate and nitrate, expressed as ueq/l. This ratio expresses the contribution of the nitrate ion to the acidification of water. For example in Norway the ratio is relatively low at present, from approxmately 0 to 0.2 (18), while after assessments relatively large areas of southern Sweden will be nitrogen saturated within 10-25 years, unless the input of nitrogen is continued (19). There are also many signs in southern Finland of increasing nitrate and sulphate trends in natural groundwater areas, which are not affected by fertilization. In one undisturbed forested catchment in southern Finland, the same type of increase in nitrate has been noticed during the low flows in the years 1966-1988 (20). In the Figure 6, for example, we can see how the sulphur content has increased up till 1987 at the groundwater monitoring station in southern Finland. After this time, the concentration leveled off. This is due to sulphur emissions decreasing significantly in western Europe (more than 50% in Finland) during the last 10 years. On the contrary the nitrate content of the groundwater has dramatically increased towards the end of the 1980s and the beginning of the 1990s. At the same time, nitrogen emissions have also increased. Also groundwater acidity has been seen to be slowly increasing during this time period.

142

PH SO4-S

0

Figure 6. pH-values and increased sulphate and nitrate at a groundwater monitoring station in southern Finland during the years 1975-1991.

4.CONCLUSIONS 1.Acid groundwater occurs in the same geological environment, where acidified lakes appear and are often located in northern latitudes. 2.Acid deposition of nitrogen and sulphur compounds have an impact on the elements of groundwater and are the main cause of groundwater acidification. 3.Groundwater acidification may be caused by both natural and manmade processes. 4.Groundwater in regions with granitic bedrock, shallow soils and humid climate may show comparatively high concentrations of hydrogen ions. 5.The most important ions in buffering acid rain are calcium, magnesium, carbonate and bicarbonate. 6.Changes in bicarbonate, calcium, magnesium, aluminium, sulphate, nitrate concentrations and slowly increasing trends of groundwater acidity have been observed in Nordic countries. 7.Changes in the chemical properties of soils and groundwater and signs of acidification have been reported in Northern Europe, in Canada and in northeastern United States.

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5.REFERENCES

10 11 12

13 14 15 16 17

18 19 20

A. Henriksen and L.A.Kirkhusmo. Acidification of groundwater in Norway. Nordic Hydrology, 1982. J. Soveri. Influence of meltwater on the amount and composition of groundwater in quaternary deposits in Finland. Publ.of the water research institute, 63. Helsinki 1985. P. Benecke. Process of acidification in soil and groundwater. Air Poll. Research Report 13, United Kingdom 1988. M. Aastrup and G. Person. Utbredning och tidstrender avseende surt grundvatten i Sverige. In: Konferens luft och milje) 84, 1984 Sweden. W.M. Edmunds and D.G. Kinniburg. J. Geol. SOC. London 143, 707. D.J. Bottomley, D. Craig and L.M. Johnston. Neutralization of acid runoff by groundwater discharge to streams in Canadian Precambrian Shield watersheds. J Hydro1 75:l-26,1984. U.V. Bremssen. Acidification Trends in Swedish Groundwaters. Review of time series 1950-1985, SNV Report 3547, 1989. M, Holmberg, J. Johnston and L. Mare. Mapping Groundwater Sensitivity to Acidification in Europe. Impact Models to Assess Regional Acidification, IIASA,1990. J Soveri and T. Ahlberg. Effects of Air Pollutants on Chemical Characteristics of Soil Water and Groundwater. Adidification in Finland. HAPRO 1990. J. Soveri Influence of Air Pollutants on Groundwater Acidification in the Porvoo area, southern Finland. Publ. of the Water and Environm. Institute,Finland, 8.( 1991). G. Jacks, G. Knutsson, L. Maxe and A. Fylkner. Effect of Acid Rain on Soil and Groundwater in Sweden. Pollutants in porous media, 1984. T.J. Sullivan, C.T. Driscoll, S.A. Gherini,R.K. Munson, R. Cook, D.F. Charles and C.P. Yatsko. Influence of aqueous aluminium and organic acids on measurements of acid neut ralizing capacity in surface waters. Nature, 1989. NAPAP, Acid Deposition: State of Science and Technology, Report 10, 1990: G. Matthes, G. The properties of groundwater.USA 1982. G. Jacks. Groundwater chemistry at depht in granites and gneisses. KTH, Stockholm,l978. C.F. Elder. Chemistry of precipitation: Its importance to eastern Canada.ASCE 1981. J. Soveri. Acid percolation and disintegration, transformation and mobilization of some substances in Finnish quaternary deposits. Groundwater Contamination, IAHS, Baltimore, 1989. B. Kvaven and T. Syversen.The Contribution of Nitrogen to Acidification. The National Environmental Monitoring Programme,Report 408/90, Norway. B. Aniansson. The situation surpasses our worst fears. Acid magazine, NEPB. Stockholm 1988. A. Lepiste) and P. Seuna. Hydrological Characteristics Af fecting the Runoff Water Acidity. Acidification in Finland, HAPRO 1990.

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MONITORING FOR THE FUTURE: INTEGRATED BIOGEOCHEMICAL CYCLESINREPRESENTA~CATCHMENTS

T.Paces Czech Geological Survey, Czechoslovakia 1. INTRODUCTION Chemical elements and compounds move through environmental "compartments" such as atmosphere, surface water, soil, groundwater, oceans, sediments, rocks and living matter. These fluxes take the form of a cycle. The cycling processes proceed with variable rates. The slowest cycle is the geological cycle, a medium rate is shown by the hydrological cycle and the fastest rate is found in the biological cycle. All together, these three cycles compose the biogeochemical cycle. Within this cycle a chemical composition in the environmental compartments is found that allows man to live on the earth. The economic and population growth after the Second World War has changed the natural fluxes and has introduced new man-made chemicals into the environment. Such changes have been monitored for a long time in the separate parts of the environment. Monitoring of pollutants in the atmosphere, surface water and groundwater a t international, national, regional and local level has demonstrated, that man is changing the chemical properties of air, water and soil to such an extend that it endangers the future development of mankind. With the predicted population and economic growth, the adverse changes in the chemical composition of the environment will become, next to nuclear war, the most dangerous factor in the human existence. In spite of recent improvements in environmental quality i n the richest industrial countries, the global environmental deterioration and the deterioration in the third wold countries and the communist and postcommunist countries does not show signs of change for the better. Or does it? Our data and predictive models are not always sufEcient to answer this question conclusively. More and more politicians and industrialists realise, that environmental deterioration is a major factor in their decisionmaking. For this purpose they need precise and objective information that is also understandable to the general public, To obtain such information and to gain reliable knowledge on causes and consequences of environmental deterioration is not a trivial task. It is a n expensive and long-term scientific exercise. The reason is th a t environmental deterioration is a multi media, long-term phenomenon with many, as yet unknown feedbacks which often have the character of a n environmental time bomb. Physical, chemical and biological changes in the environment can proceed for a long time unnoticed without obvious harmful effects to become later an irreversible mechanism for a series of environmental changes. The most obvious changes are the influence of acidic atmospheric deposition on terrestrial and aquatic ecosystems, depletion of stratospheric ozone, accumulation of greenhouse gases and release of man-made toxic

146

compounds from river sediments and from sediments in estuaries. Such complicated environmental changes cannot be fully understood when we monitor only concentrations of a single compound in a single environmental compartment. The principles of ecology describing the interrelationships between living communities and their environment teaches us that we have to monitor behaviour rather than parameters, or more precisely, we should monitor behaviour through the integrated monitoring of ecological parameters. 2. HISTORY OF INTEGRATED MONITORING A research and monitoring concept which comes nearest to the integrated monitoring of biogeochemical cycles in representative catchments was introduced by G.E.Likens and F.H.Bomann in 1963 when they started a biogeochemical monitoring system within small hydrological watersheds of Hubbard Brook Valley, New Hampshire, USA (Bomann and Likes, 1967 and Likens e t al., 1977). This type of research was inspired by the concepts of modern ecology as was stated by E.P. Odum (1953).This approach was used by other researchers too. Two most comprehensive studies which use integrated monitoring to explain the functioning of forest and lake ecosystems were conducted in Coweeta watersheds, North Carolina, US (Swank and Crossley, 1988) and in lake Garsjon, Sweden (Andersson and Olsson, 1985). The first description of a n integrated monitoring programme was presented by Barnes et al. (1986). In 1987, an International Workshop on Geochemistry and Monitoring in Representative Basins (GEOMON) in Czechoslovakia brought together many researchers whose methods of investigation were very close to the integrated monitoring concept (Moldan and Paces, 1987). In the same year, the executive body for the Convention on Long-range Transboundary Air Pollution under the UN Economic Commission for Europe initiated a n international Pilot Programme on Integrated Monitoring. The Programme started in 1989.Two international workshops on integrated monitoring were organised in Sweden in 1987 where general outlines of the Programme were decided and in Finland in 1988 where the field, laboratory and data handling procedures were agreed upon. The results of all these international activities were published in the Field and Laboratory Manual, in a Manual for Input to the E C MM Data Bank (Anonymous, 1989)and in the Annual Synoptic Report 1990 (Anonymous, 1990).

3. PFUNClPLES OF INTEGRATED MONITORING Integrated monitoring of the environment is a system of objective measurements which yield data on the state of a selected ecosystem and its temporal development. An important characteristic of integrated monitoring is that it yields information on temporal and spacial fluxes in natural systems. It is not enough to measure concentrations of chemical compounds in individual parts of ecosystem or a distribution of plant species. The goal of the integrated monitoring is to determine the fluxes of matter, their influences on the development of living organisms and the feedbacks between environmental properties and the activity of these organisms. The results of integrated monitoring describe a n ecological metabolism. As in a human body, the metabolism of a healthy ecosystem, maintains a steady state or homeostasis

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which is reflected by the chemical composition of the individual parts of the system. Atmospheric deposition, weathering of rocks and fertilization represent the 'food" of the ecosystem. Runoff of water and gaseous emissions carry away 'waste". Integrated monitoring is a scientific method to detect not only an illness of the system by also the rules for "a healthy diet" by studying the ecological metabolism. Integrated monitoring of biogeochemical cycles should be carried out in a representative part of the countryside over a long enough period of time to yield reliable and comparable results. Two basic types of representative parts of the countryside are a pristine and a polluted hydrological catchment. The period of observation should not be less than seven years. This number comes from our experience, that such a period usually includes some wet years and some dry years and that the final result is close to a n average climate for a selected ecosystem. 4. BIOGEOCHEMICALCYCLES AND BUDGJiXS OF ELEMENTS

Global cycles of biologically essential elements, such as 0, C, S, N, P and Ca have been investigated by geochemists for the last twenty years (Garrels et al., 1975, Moldan, 1983). These studies showed that "industry man" became a geological factor. His activities have reached such a size that he influences global cycles of many elements, including metals which may be toxic to living organisms (Stumm, 1977,Bolin, 1981). The global cycles integrate the fluxes and reservoirs of chemical elements over the whole earth. The basic data which enable us to put together such a global cycle for a chemical element come from geochemical studies of geospheres and from inventories of natural and anthropogenic processes which produce or consume the element. In table 1, there is a n example of the natural and anthropogenic fluxes which together structure the global cycle of sulphur. In order that we learn more about continental, regional and local segments of the global cycles, we investigate local cycles by measuring the fluxes of elements in well defined smaller parts of nature. An example of local fluxes of sulphur measured and calculated for a less polluted forested catchment and for a catchment with an extensive dieback of forest is given in table 2. While the global cycles are expressed by fluxes which describe cycling in the whole globe (in terragrammes per year), the local cycles are usually expressed in specific fluxes per unit earth's surface (in kilograms per hectare per year). The specific fluxes can be compared for different types of ecosystem, climatic zone, morphological and geological structure, land use, state of biological cover etc. The cycles in a n ecosystem consists of inputs and outputs which link the system with its surrounding and of sources and sinks which represent the internal fluxes of matter. The sum of all the fluxes compose a budget or mass balance of the ecosystem. By comparing local budgets we can make a judgement about status and development of an environment under stress.

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Table 1 Fluxes within the global biogeochemical cycle of sulphur, in Tg/yr., data by Ivanov, 1983

Nature of flux

Natural flux

Continental part of the cycle: Emissions to the atmosphere from fuel combustion and metal smelting Volcanic emissions Aeolian emissions Biogenic emissions Atmospheric transport of oceanic sulphate Deposition of large particles from atmosphere Washout from the atmosphere, surface uptake and dry deposition Transport to the atmosphere over the oceans Weathering of rocks River runoff to the oceans Subsurface runoff to the oceans River runoff to continental water bodies Marine abrasion of shores and glacier abrasion Pollution of rivers with fertilizers Emuents from the chemical industry Acid mine waters Oceanic part of the cycle: Volcanic emissions Biogenic emissions Marine spray to the atmosphere Washout, surface uptake and dry deposition Burial of reduced sulphur in sediments Burial of oxidized sulphur in sediments

Anthropogenic flux

113 14 20 17.5 20

12 25

47

34.5 114.1 104.1

66 104

9.2

35

6.8 28 28 1

14 23

140

258 111.4 27.8

149

Table 2 Budget of sulphur in two forested catchments with a different level of atmospheric pollution in Czechoslovakia, fluxes in kg.ha-1.yr-1, data by Paces (1985)

Q p e of region

Rural, forested

Industrial, dieback of forest

Wet precipitation Surface runoff by streams Biological output due to lumbering of timber Weathering of bedrock Aeolian deposition Deposition of dry SO2

10.5 9.0

Accumulation in soil and biota

13.0

0.61 1.2 3.3 7.6

19.6 96.0 0.3 3.8 0.2 88.6 15.9

5. SllES FOR INTEGRATED MONPrORING Integrated monitoring is carried out in hydrologically well defined drainage basins (catchments), o r plots. Whenever it is possible, natural catchments are used. The size of the catchment should be between 0.5 to 5 km2. The catchment must be representative of the surrounding countryside. Its geology should be simple with one type of bedrock. Special care should be taken to determine the subsurface flow. It is easier if the subsurface flow is negligible with respect to the surface runoff. Otherwise, its velocity and chemical composition has to be continuously monitored together with the surface runoff. The site should be protected from land use changes so that the monitoring can continue in unchanged setting for at least 7 hydrological years. When no hydrological catchment is available a hydrological plot may be selected. This is usually more costly because a n artificial drainage has to be build into the plot in a way that all discharges from the plot are measurable. Usually, integrated monitoring of forested and lake ecosystems is carried out in artificial plots. However, we have been monitoring two agricultural natural catchments for 15 years with accurate mass balances for the major chemical elements (Paces, 1985,1991). 6. METHODS USED FOR INTEGRATEDM0"ORING

The methods cover chemical and biological monitoring. It is not possible to monitor all inputs, outputs, sources and sinks in the catchments and plots. Some of the fluxes can be measured continuously, some fluxes are determined periodically and some fluxes have to be calculated or modelled.

Table 3 Chemical and biological parameters monitored in Swedish catchments; the figures refer t o the number of measurements made per year; ’Y5” indicates that analyses are made every fiRh year; parentheses indicate limited number of catchments where this observation is made (Barnes et al., 1986)

Precipitation Moss Spruce Mor Enrichment Other soil Soil Ground Running Reindeer/ Rabbits Starlings Fish needles horzion horizons water water water moose absorbance conductivity redox potential

I2

PH Na K Mg Ca A1

I2 I2 I2 I2 I2

HC03

I2

total C NH4-N NO2-N NO3-N organic N total N PO4-P other P total P

(6-8) 1 4 1-4 1/2

m

1/10 1/10 1/10 1/10 1/2 1/2

u2

m m m

1/10 1/10

1/10 1/10 1/10 1/10 1/10 1/10

(6-8) (6-8) (6-8) (6-8) (6-8) (6-8)

1-4 1-4 14 14 14 14 14

(6-8) 1 4 14 (6-8) 1-4

I2 1/10 1/10 1/10 1/10

1/10 1/10

Si

F

1224 1224

1224 1224 1224 1224 1224 1224 1224

14

02

SO43 totals

1224 12-24 1224 1224 12-24

1/10

I2

I2

1224 1224

I2

(6-8) 1-4 V2-3 Y2-3

V5

14

1224 1224

+ v,

Precipitation Moss Spruce Mor Enrichment Other soil Soil Ground Running Reindeer/ needles horzion horizons water water water moose

c1 As V Cr Mn Fe Ni

cu

Zn Cd Hg

w

COD

1/2-3 1/2-3 Y2-3

Y2-3 1/2-3

(12)

14

1/10

1/10

14 14

14 1/2-3 1/2-3 1/2-3 1/2-3 1/2-3 1/2-3

V2-3 Y2-3 Y2-3 1/2-3 Y2-3 1/2-3

1224

U5 1/10

(12) (12) (12) (12) (12)

(6-8)

1/2-3

12

Rabbits Starlings Fish

1/5 1/5 1/5 1/5 1/5 1/5

1/10 1/10 1/10 1/10

14 14 14 14 14

1224 1224 1224 1224 (1)

1

(1)

1

1224

DDT

(1)

FJCB

(1)

1 1

1

1

152

Table 4 Chemical and biological parameters monitored in the integrated monitoring programme of UN ECE (Anonymous, 1989)

Frequency Variables

x 3 6 5

Deposition and litter-fall: Bulk precipitation Precipitation chemistry Metal deposition (mosses) Throughfall (+ chemistry) Stemflow (+ chemistry) Litter-fall (chemistry)

x 52(365) I2 x 1 x I2 X I2 x l(4)

03

Total NOr and total N H 4 +

X

x 52 (365) x (hourly) x 52 (365)

Soil and groundwater chemistry: Soil water chem., B/C-hor x Soil water chem., A/B-hor Groundwater chem., springs x Groundwater chem., tubes x Surface water chemistry: Runoff Vertical lake gradients Runoff water level Bottom fauna, fresh water Soil variables: Nutrient chemistry of soil (0-10 cm) Nutrient chemistry of soil (below 10 cm) Heavy metals of soil (0-10 cm) Heavy metals of soil (below 10 cm) Soil physics Soil temperature

(yr-1)

(yr-1)

General meteorology

Air chemistry (EMEP): Gasses 602,NO,, m03)

Extended programme frequency

X

lJ5

X

52

X

12

X

l/2

I2 I2

l/2

x 1224 x 68 x (contin.) x 1

X

X

x (some metals)

1 v5 X X

x

52-l/2

X X

1

lJ5 l/5 365

153

Variables Biological variables: Epiphytic lichen vegetation Field layer vegetation Bush and tree layer veg. Canopy cover of trees Biomass of the tree layer Nutr. chemistry of needles Micro-nutrients of needles Enzyme monitoring (soil, leaves) Mycorrhiza + fine roots Decomposition Misc.biol.monitoring

Frequency (P-1) X

x X X X

X

Extended programme frequency (yrl)

m lt5 lt5 1 X

5

X

1 1 1 1

1 1 X X

X

Hydrological inputs (precipitation, throughfall) and outputs (runoff, infiltration) should be monitored continuously. Samples for chemical analysis are collected periodically. Electric conductivity and pH of water samples and concentrations of atmospheric gasses (S02,NO,, 03) are sometimes monitored continuously to determine episodical variations in general long-term trends. There are two examples of sets of monitored data, one by Barnes et al. (1986) applied in Sweden (table 3) and another introduced by the International Cooperative Programme on Integrated Monitoring within the Convention on Long-Range Transboundary air pollution of ECE, Anonymous (1989) (table 4). There a r e not too many catchments t h a t are monitored today i n full accordance to the table 4 because of insufficient funding which would be needed to guarantee a long-term monitoring programme. Results of partial monitoring, where only selected parameters are measured, indicate that complete integrated monitoring is necessary in order to understand local, regional and global biogeochemical cycles, in order to determine the effect that human activities on them.

7. R . E S U L ~ O F I " E G R A T E D M O ~ F U N G In general, integrated monitoring should yield information on any influence of a chemical substance on functions of an ecosystem. Today, most information comes from research onto acidification of surface water and soil. Acidification is caused by flux of protons. This flux is the end result of all acidobasic biogeochemical reactions in an ecosystem and the flux of chemicals which yield or consume hydrogen ions. An example of hydrogen - ion production and consumption in two monitored catchments in Czechoslovakia is given in table 5. The proton budgets in mmo1.m-2yr-1 indicate quantitatively how fast individual biogeochemical processes proceed. These rates can be

154

compared i n catchments (ecosystems) under different environmental stress. When integrated monitoring continues for a longer period, the changes in the proton budget indicate causes and consequences of environmental changes. Finally, when biological monitoring is conducted together with the chemical one, changes in proton budget and budgets of biological essential and toxic elements are the most reliable indicators of the stresses on the particular ecosystem. A comparison of the data for the healthy forest and forest damaged by acidification in table 2 and 5,indicate that the dieback of spruce (Picea abies) is related to acidification due to the anthropogenic input of SO2 and NO, . When the budget of nitrogen in the catchments is studied (table 6) however, it appears that the input of NO, and the consequent transformation of nitrogen compounds is not the cause of the acidification. The transformation of nitrogen compounds is a result of the dieback of trees and their inability to fix nitrogen. These two nitrogen budgets indicate that our knowledge of denitrification a ndor accumulation of nitrogen in soil is inadequate and th a t the more complete monitoring of the nitrogen budget is needed. The input of acidifying gases is going to decrease due to the international effort to reduce industrial emissions and car exhausts. Only a long term integrated monitoring system will give us a reliable database to study the possible improvements of representative ecosystems. Even monitoring of simple input - output budgets in forested and lake catchments indicate that the reduction in emissions of SO2 and NO, reduces environmental acidification considerably. However, without the integrated monitoring which includes biological as well as chemical monitoring it will be very difficult to evaluate the economy of such %on-market" environmental effects. Present results of integrated monitoring in Europe are rather incomplete in spite of the fact that 14 countries take part in the ECE programma (figure 1, Anonymous, 1990). An experience of several teams that conduct long-term biogeochemical monitoring is th at such programmes, i n order to be successful, require a single or only a few researchers who keep the programma going through their sheer enthusiasm. As stated by Swank and Crossley (1988)Th ese individuals are the fabric of and provide the continuity of any successful long-term field research program, but they seldom receive credit for their valuable contribution". It will be very useful not only to future generations of scientists but also for the general public if funding and political support is granted to such individuals who wish to carry out a n integrated monitoring system to describe quantitatively the evolution of biogeochemical systems under anthropogenic stresses in separate European countries. Integrated monitoring of pristine ecosystems is necessary for comparative studies. We have learned how valuable early chemical analyses are of rain, of runoff in rivers and of soil analyses which we can compare with present data (Hanamann, 1898 in Paces 1982,Pelisek J., 1984,Kazay, 1904 in Horvath, 1983, Malmstrom and Tamm, 1925 in Tamm and Hallbacken, 1988,Hofman - Bang, O., 1905 i n Lofirendahl, 1990,Schindler, 1988,Gorham, 1982). Such historical data enable us to evaluate environmental changes today. However, it is not enough for setting standards for sustainable development. We need to carry out integrated monitoring of biogeochemical cycles in representative catchments in order to understand anthropogenic effects on nature in future.

55 I

Table 5 Hydrogen-ion production and consumption by known geochemical, biological and anthropogenic processes, mmo1.m-2.yr-1 of H Type of region

Rural forest

37.3 Input of H30+ by wet precipitation -0.01 Output of H30+ by runoff Hydrolysis reactions involving aluminium 7.3 Oxidation by pyrite calculated from the rate of release of S from bedrock according to 3.9 stoichiometryFeS2 + 3.5 0 2 + H B = F e h + 2 SOs4 + 2H+ Precipitation of femc hydroxide calculated from input andoutputs of Fez+ and the amount of Fez+ released from oxidation of pyrite Fe2+ + 0.250 2 + 2.5 H20 = 3.7 Fe(OH)3 + SH+ Dissolution and dissociation of C02 according to stoichiometry COP + H2O = HC03-+ H+ 52.5 Biological fixation of cations and anions (except nitrogen 59.6 species) in biomass removed by harvesting Transformation of nitrogen species according to stoichiometry NH4+ + ROH = RNH2 + H f l + H+;NO3- + ROH + H+ = RNH2 + 202; N&+ + 2 0 2 = NO3-+ H20 + 2H+ where R is 12.7 organic matter Atmospheric deposition of dry SO2 and oxidation according to stoichimetry SO2 + H2O + 0.5 02 = SO$- + 2H+ 47.5 Release of cations and anions by hydrolysis of bedrock and depletion of exchangeable cations in soil calculated from budgets of Na, K, Mg, Ca, C1 and P -151

Z ("excessn production of protons)

74

Industrially damaged forest

45.7 -5.4 -13.0 11.8

11.6 0.0

100 554 -609

116

157

Table 6 Budget of nitrogen in two forested catchments with different levels of atmospheric pollution in Czechoslovakia; fluxes in kg.ha-1.yr-1 of nitrogen derived from data by Paces (1985)

Type of region

Rural, forested

Wet precipitation N-NO3

N-NH4 Surface runoff N-NO3 Biological output due to lumbering of timber Weathering of bedrock Deposition of dry N-NO, Denitrification or unknown accumulation

8. CONCLUSIONS

3.7 4.9 0.58 8.7

Industrial, dieback of forest 5.5 7.5

I2

0 5

2.5 0 15

4.32

13.5

Results of measurements of input - output budgets in small hydrological catchments yield useful data on the metabolism of ecosystems. Such measurements should form a long-term programme in order to determine significant trends in the changes of the biogeochemical cycling of elements. The simple input - output budgets, however, are not enough to evaluate the influence of environmental changes on the performance of living communities. Such a n evaluation can only be made through integrated chemical and biological monitoring. Historical data on the concentrations and fluxes of elements in environmental compartments are used today by scientists to evaluate the longterm trends in the evolution of the environment. These environmental trends have influences on economic and political decisions (The World Commission of Environment and Development, 1987). Such data, which are usually based on concentrations of major chemical elements only, are not sufficient however, for the evaluation of the state of ecological metabolism a t local, regional and continental level. Politicians and industrialists will need more complete data sets in future, when environmental conflicts a t all these levels may be even more severe than today. Results of the integrated monitoring of ecosystems carried out under the auspices of the Convention on Long-Range Transboundary Air Pollution within UN Economic Commission for Europe (Anonymous, 1990) indicate that support given to this programme is not adequate to establish a reliable network of monitoring sites. Many researchers today agree that a comprehensive

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integrated monitoring of biogeochemical cycles in small catchments will yield a set of data that is essential for the establishment of guidelines for a sustainable development. 9. REFERENCES

Andersson F. and Olsson B., 1985,Lake Gardsjon, An acid forest lake and its catchment, Ecological Bulletins 37,Publishing House of the Swedish Research Council, Stockholm, 336 p. Anonymous, 1989,Field and Laboratory Manual and Manual for Input to the ECA/IM Data Bank, Programme Centre EDC, National Board of Waters and Environment, Finland Anonymous, 1990, 1 Annual Synoptic Report 1990, Environmental Data Centre, National Board of Waters and Environment, Finland Barnes C., Giege B., Johansson K. and Larsson J.E., 1986, Design of integrated monitoring programme in Sweden, Environmental Monitoring and Assessment 6,113- 126,D, Reidel Publ.Corp. Bolin B., 1981, Changing global biogeochemistry, Report CM 52, Dept. Meteorology, University of Stockholm Bomann F.H. and Likens G.E., 1967,Nutrient cycling, Science 155,427-429 Garrels R.M., Mackenzie F.T. and Hunt C., 1975,Chemical cycles and global environment, W.Kaufmann, Los Angelos Gorham E., 1981, Scientific understanding of atmosphere - biosphere interactions: a historical overview, In: Atmosphere - Biosphere Interactions: towards a better assessment of the ecological consequences of fossil fuel combustion, Chapter 2, National Academy Press, Washington D.C. Hanamann J., 1988,Die chemische Beschaffenheit der fliessenden Gewasser Bohmens, II., Theil, Hydrochemie der Elbe, Archiv der naturwissenschaftlichen Landesdurchforschung von Bohmen, vol. 10, Kommissions Verlag von Fr.Rivnac, Prag. Horvath L., 1983,Trend of the nitrate and ammonium content of precipitation water in Hungary for the last 80 years, Tellus, 35B, 304 - 308 Hofman - Bang O., 1905, Studien uber schwedische Fluss und Quellwasser, Bull. Geol.Inst.Uppsala 6,101- 159 Ivanov M.V., 1983,Major fluxes of the global biogeochemical cycle of sulphur, Chapter 7 in: The Global Biogeochemical Sulphur Cycle, (M.V.Ivanov and J.R.Freney, eds.), SCOPE 19,449- 463,John Wiley & Sons, Chichester Kazay E., 1904,Chemical analysis of atmospheric precipitations, Idojaras 8, 301 - 306 (in Hungarian) Likens G.E., Bomann F.H., Pierce R.S., Eaton J.S.D. and Johnson N.M., 1977, Biogeochemistry of forested ecosystem, Springer-Verlag, New York, 147 p. Lofvendahl R., 1990,Changes in the flux of some major dissolved components in Swedish rivers during the present century, Ambio 19,210- 219 Malmstrom C. and Tamm O., 1926,The experimental forests of Kulbacksliden and Svartberget in north Sweden, Skogsforsoksanstaltens exkusionsledare XI, Stockholm Moldan B., 1983,Cycle of matter in nature (in Czech), Academia, Praha, 171 p. Moldan B. and Paces T. (eds.), 1987, GEOMON, Extended abstracts, International Workshop on Geochemistry and Monitoring in Representative Basins, Geological Survey, Prague, 253 p.

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Odum E.P., 1953,Fundamentals of Ecology, W.B.Saunders, Philadelphia Paces T., 1982,Natural and anthropogenic flux of major elements from central Europe, Ambio 11,206- 208 Paces T., 1985, Sources of acidification in Central Europe estimated from elemental budgets in small basins, Nature 315,31-36 Paces T., 1991, Changes in rates of weathering and erosion induced by acid emissions and agriculture in central Europe, In: Land Use Changes in Europe (Brower F.M., Thomas A.J. and Chadwick M.J., eds.), Chapter 15,317323,Kluwer Academic Publishers Dordrecht Pelisek J., 1984,Changes in the acidity of forest soils of the Orlicke Mts. caused by acid rains, Lesnictvi 30,955- 962,Praha (in Czech) Schindler D.W., 1988, Effects of acid rain on freshwater ecosystems, Science 239,149- 156 Stumm W., 1977,Global chemical cycles and their alteration by man, Dahlem Konferenzen, Abakon, Berlin Swank W.T. and Crossley D.A. (eds.), 1988,Forest Hydrology and Ecology a t Coweeta, Ecological Studies 66,Springer-Verlag, 469 p. Tamm C.O. and Hallbacken L., 1988, Changes in soil acidity in two forest areas with different acid deposition: 1920s to 19808,Ambio 17,56- 61 The World Commission on Environment and Development, 1987, Our Common Future, Oxford University Press, Oxford

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T. Schneider (Editor). Acidification Research. Evaluation and Policy Applications 1992 Elsevier Science Publishers S.V

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The critical loads concept for the control of acidification Jean-Paul Hettelingh, Robert J. Downing, and Peter A.M. de Smet Coordination Center for Effects, National Institute of Public Health and Environmental Protection, P.O. Box 1, 3720 BA Bilthoven, The Netherlands

Abstract "Critical loads" have been defined as the highest deposition of compounds that will not cause chemical changes leading to long-term harmful effects on ecosystem structure and function. European maps of critical loads of acidity, sulphur and nitrogen have been produced to assess the sensitivity of forest soils and surface waters. These maps can be compared with present and projected levels of pollutant emissions, allowing assessment of the effects of various emission abatement strategies. Parts of central and northwest Europe currently receive 20 times or more acidity than their critical loads, thus affecting the long-term sustainability of these ecosystems. It is shown that stringent emission reductions are needed to protect large parts of European forests and surface waters against acidification. 1. INTRODUCTION

The reduction of acidifying emissions of sulphur and nitrogen are the subject of international negotiations in the United Nations Economic Commission for Europe (UN ECE) under its Convention on Long-Range Transboundary Air Pollution (LRTAP). These negotiations have led to international agreements ("protocols") on reducing the emissions of sulphur [l]and nitrogen oxides [21. The sulphur protocol, which took effect in 1987,commits participating countries to reduce sulphur emissions by a t least 30 percent as soon as possible and a t the latest by 1993. A nitrogen protocol in effect since early 1991 requires that by 1994,annual national emissions of nitrogen oxides should not exceed 1987 levels. The protocol also requires that average annual emissions of NO, between 1987 and 1994 should not exceed the 1987 emission level. Both protocols are similar in that they do not explicitly include quantitative considerations about environmental effects. The abatement intentions are based predominantly on technical and economic considerations related to emission reductions. The renewal of these sulphur and nitrogen protocols, in 1993 and 1994, Note: The policy examples presented in this paper do not necessarily reflect the views of the National Institute for Public Health and Environmental Protection but have been introduced by the authors for illustrative purposes only.

162

respectively, will also include consideration of the effects of deposition reductions on European ecosystems. Critical loads provide a measure of the relative sensitivity of ecosystems on a large scale, and thus can serve as a means by which to assess the environmental effects of such deposition reductions. The general definition of a critical load is "a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge." 131 (See also [41 for a general overview of critical load definitions.) In other words, a critical load is a maximum "no-effect''level of a pollutant. If an ecosystem has limited natural capacity to absorb or neutralize pollutants, then the critical load for that ecosystem would be low. Areas which are more able to withstand pollutant deposition have correspondingly higher critical loads. The pollutants considered in this paper are acidity and one of its major components, sulphur. "Harmful effects" are defined as chemical changes in forest soils and surface waters which may cause damage to an ecosystem, and a limited number of key parameters and values have been used for this mapping exercise. The use of critical loads as a measure for assessing the effectiveness and efficiency of emission abatement strategies constitutes the "critical load concept". However, this basic concept gives rise to different interpretations. The critical load concept from a policy point of view includes setting "target loads", which are desired levels of pollutant deposition which consider not only the sensitivity of a n ecosystem, but also other technical, social, economic and political considerations. In theory, these target loads should gradually be reduced to become equal to critical loads in order to prevent continued damage to sensitive ecosystems. The critical load concept, from an environmental point of view, consists of defining the critical loads and includes the estimation of the long-term effects of pollution levels which are higher than critical loads. These "exceedances" of critical loads may induce chemical changes which deplete an ecosystem's capacity to buffer acidity, leading to toxic concentrations of (e.g.1 aluminum in forest soils or to the excess of acceptable soil or water acidity. This process may take many years and can be demonstrated using dynamic models which describe chemical processes in soils and surface waters. Such models may also be used to describe ecosystem recovery once acidification is alleviated 151. This paper emphasizes the critical load concept from a policy point of view. The paper first describes the methods used to obtain European maps of critical loads of acidity, sulphur and nitrogen. Maps of critical loads of acidity and sulphur are then compared with abatement strategies for acidity ("maximum reductions"), and the achievement of nationally specified sulphur target loads. 2. CALCULATION AND MAPPING OF CRITICAL LOADS

The UN ECE Task Force on Mapping developed a Mapping Manual [6] in 1988 to provide guidance in national efforts to calculate critical loads. The RIVM Coordination Center for Effects in the Netherlands produced a Mapping Vademecum [71 and held workshops for national mapping experts to address more specific mapping issues as the work progressed.

163

The European map of critical loads of acidity was obtained by incorporation of data on critical loads for surface waters and forest soils of 14 European countries'. Critical loads for 11other countries were computed using European data on forest soils. Details on national and European critical load mapping can be found in [81, The Steady State Mass Balance (SSMB) method was predominantly used for the computation of critical loads of acidity. This method assumes a timeindependent steady state of chemical interactions involving an equilibrium between the soil solid phase and soil solution [9,101. Similar assumptions apply to in surface and groundwater chemistry. The SSMB method computes the maximum acid input to the system that will not cause excess of the critical alkalinity value. The latter value has been computed from average thresholds for chemical values: pH, aluminum concentration, and aluminum to calcium ratio [8]. A simpler, qualitative method (the "Level 0" approach) was used by the United Kingdom, Ireland, Czech and Slovak Federal Republic, and the Soviet Union, to calculate critical loads. This method uses existing geographical data bases on four ecological factors (bedrock lithology, soil type, land use and rainfall) to assess the sensitivity of ecosystems to acidic deposition to which critical load values may be applied [81. 2.1. Critical loads of acidity The primary equation used to compute the steady-state critical load of actual acidity in forest soils is as follows [8, 91:

CL'(Ac,,)

= BC, - Alkl(,t)

(1)

where: CL'(Ac,,,) = critical load of actual acidity for forest soils BCW = base cation weathering rate Alk,,,,, = critical value of alkalinity leaching All of the above terms are expressed in moles of charge per hectare per year (mol, ha.' yf'). The critical value of alkalinity leaching is defined from critical hydrogen leaching and critical aluminum leaching as follows: AlkI(m0 = - HI(,,, - All,,,,

(2)

where: All(,,)

= critical value of hydrogen leaching (mol, ha.' yr.') = critical value of aluminum leaching (mol, ha.' yr.')

The two exogenous variables in Equation 2 are defined as a function of net precipitation3, base cation deposition (as an approximation of the calcium concentration), base cation weathering, and base cation uptake as follows:

Hl(kt)

= Q * [HI,,

(3)

164

where:

[HI,,

= critical value of hydrogen concentration (= 0.09, approximately

Q

= net precipitation

equivalent to pH=4.0)

and

where: = critical value of aluminum concentration (= 0.2 mol, m-3) R(Al/Ca),, = critical value of the aluminum to calcium ratio (= 1.5 mol, mol;') = seasalt-corrected deposition of base cations (mol, ha" yr-') BC,' = base cation uptake (mol, ha.' yr.') BC,

[MI,,

In Equation 4 the minimum is taken from a function of aluminum concentration and a function of the aluminum to calcium ratio. The critical values assigned to the exogenous variables of Equation 4 are further elaborated in [8,91. Substitution of Equations 2 through 4 into Equation 1yields the following final expression used to compute the critical loads of acidity for forest soils in Europe: CL'(Ac,,,)

+ 0.29.Q ; 2.5.BC, + 0.09.Q

= min ( BC,

+ 1.5.BC,' - 1.5. BC,

1

(5)

The critical load of acidity for surface waters [9, 111 is computed by:

where: CLw(Ac,,) = critical load of actual acidity for surface waters = seasalt-corrected original base cation concentration (mol, ha-' yf') BC,' 2.2. Critical loads of sulphur

The computation of the critical loads of acidity using Equations 5 and 6 does not, however, provide European policymakers with s f i c i e n t tools for evaluating required emission reductions, because current UN ECE protocols are designed to control individual acidifying compounds; i.e., sulphur and nitrogen oxides, rather than on acidity as a whole. Therefore it was necessary to derive a "sulphur fraction" by apportioning the critical load of acidity between the acidifying share of sulphur and the acidifying share of nitrogen. This fraction was obtained using the following assumptions: (a) The share of present sulphur deposition in total acidic deposition is used as a surrogate of the portion of the critical load of actual acidity which can be attributed to sulphur. (b) The share of present nitrogen deposition in total acid deposition contributes to acidification only when it is not taken up or immobilized by the ecosystem.

165

In other words, nitrogen is assumed to be acidifying when the ecosystem is unable to use nitrogen as a nutrient. Assumptions (a) and (b)lead to the definition of the sulphur fraction: Sf =

PL(S0,) PL(S0,) + PL(N0,) + PL(NHJ - Nu - N,(&t)

(7)

where:

Sf PL(S0,) PL(N0,) PL(NH,) NU

= sulphur fraction (mol, ha.' yi') = present load of sulphur (mol, ha.' yf') = present load of nitrogen (mol, ha'' yf') = present load of ammonia and ammonium (mol, ha.' yr-') = nitrogen uptake of managed forests (mol, ha.' yr-') = critical value of nitrogen immobilization (mol, ha.' yi')

Equation 7 has been applied for areas in which the total present load of nitrogen (PL(N0,) + PL(NH,)) exceeds the nitrogen uptake capacity (Nu). The sulphur fraction is assumed to be equal to 1 when nitrogen uptake exceeds the total nitrogen load. In that particular case the critical load of acidity becomes equal to the critical load of sulphur. This is always assumed to be the case in watersheds. From Equations 5 and 7, the critical load of sulphur on forest soils is calculated by multiplying the critical load of acidity by the sulphur fraction: CL(S) = Sf*CL*(Ac,,)

(8)

As sulphur and nitrogen are complementary in the definition of acidity, a derivation of the critical load for nitrogen is obtained from Equation 8: CL(N) = Nu + (1-Sf).CL(Ac,,)

(9)

From Equation 9 it can be seen that the critical load of nitrogen is equal to the nitrogen uptake only when the critical load of sulphur is equal to the critical load of acidity (i.e., when S, = 1). In that case the critical load of nitrogen becomes consistent with its original definition as "the maximum deposition of nitrogen compounds that will not cause eutrophication or induce any type of nutrient imbalance in any part of the ecosystem or recipients to the ecosystem" E91. The relationship between the acidifying and eutrophying potential of nitrogen is not covered in this definition, although described in existing literature (see for example [12]). In fact, Equation 9 states that nitrogen will lead to acidification when a n ecosystem is subject to a supply of nutrients which exceeds its demand. The validity of the assumptions used to derive the sulphur fraction have not been verified in the field and should be made subject to further work. For example, the drawback of assumption (a) is that the relative contributions of sulphur and nitrogen compounds to total acidity in deposition is not constant over time, since these are dependent on national emissions of sulphur dioxide, nitrogen oxide and ammonia.

166

One of the drawbacks of assumption (b)is that it assumes nitrogen uptake to be constant over time. Some indications exist that the ability of vegetation to take up nutrients is dependent on the acid stress 1123. 2.3. Exceedances of critical loads Abatement strategies can be evaluated by comparison of the deposition to the critical loads. However, this comparison does not simply consist of subtraction of critical loads from deposition. The computation of exceedances needs to include chemical compounds in the air and in the soil which affect the level of acidity of deposition. These chemical compounds are (1) base cation deposition, nitrogen uptake and nitrogen immobilization which decrease the exceedance, and (2) base cation uptake which increases the exceedance. Using the definitions of critical loads from Equations 5 and 8, the inclusion of these variables lead to the following formulation of the exceedance of critical loads of acidity: CL(Ac),,

+ PL(N0,) Nu Ni(crit1

= PL(S0,)

+ PL(NHJ - CL(Ac,) + BC, - BC,' (10)

The difference between present load and critical load leads to the exceedance of the critical load of sulphur:

Equations 10 and 11 do not consider the effects of processes (such as forest filtering and throughfall) which tend to produce higher levels of acidic deposition in forested areas as compared to open land (lakes and agricultural areas). These factors have been excluded from the present exercise since available data on a European scale are very preliminary. Results of exceedance calculations which consider such effects can be found in 191. 2.4. Mapping critical loads and exceedances To allow direct comparison between maps of critical loads and present loads of pollutant deposition, the geographic resolution of the two maps must be similar. The Co-operative Programme for the Monitoring and Evaluation of the LongRange Transmission of Air Pollutants in Europe (EMEP), one of the first programs initiated under the LRTAP Convention of the UN ECE, operates a monitoring network over a European grid of approximately 150 x 150 km2 grid cells. Modeling work conducted by EMEP [13] to compute emissions and deposition of pollutants in each grid cell is used in negotiations on emission reduction by parties of the LRTAP Convention. Thus, critical loads have been mapped on the EMEP grid system to achieve consistency with the practice of deposition mapping. The size of an EMEP grid cell is such that it contains many ecosystems with a range of critical load values. In mapping critical loads for each EMEP grid cell, a decision is needed about which value best represents the range of ecosystems contained in it. A cumulative frequency distribution (CDF) of critical loads in each EMEP grid cell has therefore been calculated. A critical load value is calculated for each ecosystem in a grid cell, and a CDF is constructed indicating the

167

percentage of a particular grid cell which has a critical load lower than or equal to a particular value. For instance, if half of a grid cell area has a critical load of 1000 acid equivalents per hectare per year or lower, then the 50-percentile value of the grid cell is 1000 eq ha.' yf'. The critical load of the lowest (i.e., most sensitive) 1 percent of the grid cell area is called the "1-percentile critical load". A level of acidic deposition equal to the 1-percentile critical load of acidity protects 99 percent of the EMEP grid cell area. In this paper the 1-percentile critical load values (which reflect the most sensitive ecosystems) have been used to calculate the exceedance of acidity and sulphur by deposition patterns computed from national emissions. 3. ASSESSING EUROPEAN EMISSION ABATEMENT STRATEGIES

National emissions are linked to grid cell deposition using the Regional Acidification INformation and Simulation (RAINS) model [141 which uses the EMEP source-receptor relationship. RAINS enables the comparison of deposition patterns resulting from a variety of emission abatement options. In this paper, current levels of acidic deposition and sulphur deposition El31 are used as reference scenarios and compared, respectively, with two abatement strategies: Maximum feasible reductions of emissions of acid precursors: In this scenario it is assumed that removal efficiencies of 90 to 98 percent are achieved by applying flue gas desulphurization to large boilers in refineries, power plants and industry. It is also assumed that small boilers are supplied with low-sulphur fuels, and best available techniques are applied to reduce NO, emissions. Achieving target loads for sulphur: Table 1lists the countries which have formulated preliminary target loads for sulphur deposition. National emission reductions for all European countries needed to achieve these target loads a t minimum costs have been calculated using the RAINS model's optimization module. These optimized emissions are then used to calculate sulphur deposition patterns for Europe. While some countries have set specific target loads for individual EMEP grid cells, only the total national ranges are shown here. As mentioned above, these target loads include environmental, political, socioeconomic, and other national considerations. Austria, France, Switzerland, and the Soviet Union have set their target loads for sulphur to be equal to the 5-percentile critical load for sulphur. The resulting effects of these two strategies on critical load exceedances have been evaluated by analyzing deposition patterns in contrast to the references cases of current patterns of exceedances of acidity and sulphur, respectively. 4. RESULTS

Exceedance of the critical load of acidity: The exceedance of present loads of acidity over critical loads under current conditions has been calculated using Equation 10. Values for present loads of sulphur and nitrogen compounds are

168

Table 1 National target loads for sulphur deposition' Target load Country (range) Units' Remarks Austria

161 - 393 eq ha" y i ' 0.71 - 1.21 g m-' yr"

Preliminary target load for sulphur Preliminary target load for sulphur corrected for base cation balance

Denmark

0.5

g m-' yr-'

Preliminary target load for sulphur

Finland

0.2 - 0.5

g m-' yr"

Preliminary target load for sulphur

200 - 2000 eq ha.' yr.'

Unofficial preliminary target loads for sulphur

2400

eq ha" yf'

1400

eq ha" yr.'

For 2000. Target load for acidity of which a maximum of 1600 eq ha.' yr-' is attributed to nitrogen For 2010. Target load for acidity of which a maximum of 1000 eq ha.' yr-' is attributed t o nitrogen

Norway

0.5

g m-' yr"

Unofficial preliminary target loads for sulphur

Sweden

0.3 - 0.5

g m.2yr"

Unofficial preliminary target loads for sulphur

Switzerland 0.71 - 0.94

g m-' yr.'

Preliminary target loads for sulphur corrected for the base cation balance

France Netherlands3

United Kingdom

200 - 2300 eq ha.' yr.'

For 2005. Target loads are set equal to critical loads where they can be achieved by 2005

USSR

3.0 - 20.0 kg ha.' yr.'

Preliminary target loads of sulphur for forest and water ecosystems

1. Adapted from UN ECE, 1991. The critical load concept and the role of best available technologies and other approaches (EB.AIR/WG.5/R.24/Rev.l).Convention on Long Range Transboundary Air Pollution, Working Group on Abatement Strategies, Geneva. 2. eq ha" y i ' = acid equivalents per hectare per year;

g m.* yr" = grams per square meter per year. 3. The Netherlands has specified a target load for total acidity, with allowed maximum values for nitrogen, the remainder being sulphur.

169

based on 1990 EMEP emissions and deposition data C131. At current levels of acidic deposition in Europe, critical loads of acidity are exceeded in approximately three-quarters of the European area under consideration (Figure 1). Areas of the greatest exceedance (more than 2000 eq ha.' yf'), account for approximately 20 percent of the land area and occur primarily in central Europe. Under this scenario, all European countries have some areas in which critical loads are exceeded. Figure 2 shows the expected pattern of exceedances resulting from the implementation of "maximum feasible reductions" of emissions of sulphur and nitrogen. Under this scenario, the area in which deposition is estimated to be less than critical loads increases (from 25 percent in Figure 1) to 68 percent. Generally, the pattern of critical loads exceedance is similar to the current conditions depicted in Figure 1: the areas of highest exceedances occur in central Europe and the United Kingdom. However, the magnitude and scope of the areas receiving deposition higher than critical loads is reduced significantly. The maximum exceedance for a grid cell under this scenario is 2144 eq ha" yf', as compared with a maximum of over 10,000 eq in the current base scenario. European emissions of SO, and NO, are reduced by 81 and 57 percent, respectively, from the levels used to calculate the exceedances shown in Figure 1.

Exceedance of the critical load of sulphur: Figure 3 shows the current pattern of exceedances of the critical load of sulphur, based on the calculations of Equation 11. These exceedances are derived from subtracting critical loads of sulphur [9] from the present deposition of sulphur [13]. Approximately 25 percent of the area receives sulphur deposition less than critical loads. The area of maximum exceedance, covering roughly 10 percent of the area under consideration, is centered in north-central Europe (eastern Germany, Poland, and Czechoslovakia), but also includes large parts of the United Kingdom, the Netherlands and Belgium. Figure 4 shows the expected pattern of exceedances resulting from emission reductions which are optimized to achieve target loads for ten countries. In this sulphur target loads scenario, both the magnitude and geographic extent of critical loads exceedances are reduced significantly. European emissions of SO, are reduced by approximately 60 percent from the levels used to calculate exceedances in Figure 3. The area in which sulphur deposition is less than critical loads increases to 61 percent. The areas of greatest exceedance shift eastward and slightly southward, reaching a maximum of 2144 eq ha" yf' in eastern Yugoslavia. These shifts reflect the uneven geographic distribution of countries, primarily in north and northwest Europe, which have identified target loads for sulphur deposition. Additional countries which identify national target loads in the future would of course change this distribution. 5. CONCLUSIONS

The critical loads concept provides an environmentally based measure by which to optimize the environmental benefits of future emission reductions within

Figure 1. Exceedance of the critical load of acidity due to present emissions of acidic precursors. (1 percentile).

F'igure 2. Exceedance of the critical load of acidity after maximum feasible reductions of SO2 and NOx emissions in Europe (1 percentile).

Figure 3. Exceedance of the critical load of sulphur, due to present patterns of sulphur emissions (1 percentile).

Figure 4. Exceedance of the critical load of sulphur a h r reductions of SO2 emissions to achieve target loads in 10 European countries (1 percentile).

-

4

*

172

Europe. By classifying the relative sensitivities of different ecosystems and relating these values to patterns of pollutant deposition, areas which are most affected by current and projected levels of pollutant deposition can be identified. The scenarios presented here compare the current patterns of exceedances of critical loads of acidity and sulphur with the results of two different emission reduction scenarios: maximum feasible reductions (of acid precursor emissions), and achieving sulphur target loads. The results indicate that even under these stringent pollution control policies, the geographic area in which acidic deposition exceeds critical loads is reduced, but that large parts of central Europe and most of Scandinavia would still receive more acidic deposition than these ecosystems can safely absorb in the long term. Large parts of Scandinavia have critical loads which are close to zero; i.e., these ecosystems can absorb little or no additional acidity without harm. Since a "zero deposition"level could never be achieved practically, different methods to evaluate and protect these areas should be addressed. The efficacy of other options, such as liming, to ameliorate these ecosystems should be further investigated. A number of national considerations influence the calculation of critical loads, target loads, and exceedances. Important factors t o be considered in applying the critical load concept include: Choice of "most sensitive/valuable" receptor. For this first attempt to map critical loads on a European scale, the selection of receptors was limited to forest soils and surface waters. Critical loads for forest soils were mapped for all countries in mainland Europe, while Scandinavian countries mapped surface waters or a combination of the ecosystems. Definition of "harmful effects". The guidelines developed for calculating critical loads for forest soils included a limited number of critical chemical values to be used as cutoff points in defining a harmfbl effect. Selection of percentiles. Use of higher percentile maps (e.g., 5 or 10 percentile) leads to lower exceedances, but at the cost of greater risk to the most sensitive ecosystems in each grid cell. Some countries are now investigating in detail the ramifications of exceedances on individual ecosystems. Definition of target load. Many countries have set target loads based on critical load value; for example, a target load equal to the 5-percentile critical load for a grid cell. This assumes that (roughly) 5 percent of the area within the grid cell would remain above critical loads. Most nationally set target loads exceed critical loads. Current policies and negotiations do not specify for how long target loads will remain operational, which could lead to loss of ecosystems over the long term. While the current critical load mapping effort has been successful in preparing maps for Europe, the preliminary data will be revised in the future as new and better data becomes available. Future work will include the consideration of more chemical criteria and ecosystem receptors. In the present exercise, no biological effects have been considered, but only chemical balances in forest soil and surface water systems. In addition, there is a need to investigate synergies among different pollutants (e.g., acidity and heavy metal leaching). In spite of these uncertainties, the ability to compare and assess projected ecological effects of various emission reduction strategies is important. The

critical loads approach in designing international emission reduction agreements can be more effective than flat-rate "30%"protocols, since emission reductions can be targeted to achieve the most environmental benefit. In combination with various computer models of pollutant transport and deposition in Europe, the critical loads concept offers a method by which to analyze options for national and multilateral pollution control schemes. For example, it may be more effective (and economical) for some countries to provide economic and technical assistance to other countries to reduce their sources pollution. Different types of these "burden sharing" mechanisms are now being examined within the UN ECE framework. While no analysis has been made in this paper concerning the costs associated with such emission reductions, there is a large body of research underway within the UN ECE and elsewhere to assess the economic implications of such Europewide emission reductions. These economic aspects of emission reductions play a key role in the assessment of future European emission control strategies. Using critical loads as an environmental indicator of ecosystem sensitivity to acidifying deposition has gained much support in recent years. While elements of the scientific principles and assumptions and their implementation are undergoing continued refinement, the basic concepts of defining and mapping critical loads on a European scale are the result of a broad scientific consensus among the countries involved. The application of the critical loads concept as a tool for designing and implementing strategies to reduce pollutant emissions on an international scale has also gained widespread support. Critical loads offer a yardstick to measure the efficacy of multilateral pollution abatement strategies, and thus can serve as a usehl tool in international fora such as the UN Economic Commission for Europe's current negotiations. 6. ACKNOWLEDGEMENTS

This research was funded by the Air Directorate of the Ministry of Public Housing, Physical Planning and the Environment of the Netherlands. The work of the National Focal Centers which collaborated closely in the development of the methodologies, data collection and processing, and mapping of European critical loads is gratefully acknowledged. 7. NOTES

1. Austria, Bulgaria, Czech and Slovak Federal Republic, Denmark, Finland, France, Germany, Ireland, Netherlands, Norway, Sweden, Switzerland, Soviet Union, and United Kingdom. 2. Base cations considered include calcium, magnesium and potassium. 3. Net precipitation in soils is defined as precipitation minus evapotranspiration minus surface runoff. Surface runoff is not included for the computation of net precipitation in watersheds. In this paper net precipitation is denoted by Q for both soils and watersheds for notational simplification.

174

8. REFERENCES 1 United Nations Economic Commission for Europe. 1985. Protocol to the 1979

Convention on Long-Range Transboundary Air Pollution on the Reduction of Sulphur Emissions or their Transboundary Fluxes by at least 30 per cent. U.N. ECE, Geneva. 2 United Nations Economic Commission for Europe. 1988. Protocol to the 1979 Convention on Long-Range Transboundary Air Pollution concerning the Control of Emissions of Nitrogen Oxides or their Transboundary Fluxes. U.N. ECE, Geneva. 3 J. Nilsson and P. Grennfelt (eds.). 1988. Critical Loads for Sulphur and Nitrogen. Report from a workshop held a t Skokloster, Sweden, 19-24 March 1988. Nordic Council of Ministers, Milj~rapport1988:15, Copenhagen. 4 K.R. Bull. 1991. The Critical Loadfievels Approach to Gaseous Pollutant Emission Control. Enuiron. Pollut. 69:105-123. 5 J.-P. Hettelingh, R.H. Gardner, L. Hordijk. In press. A Statistical Approach to the Regional Use of Critical Loads. Environ. Pollut. 6 UN ECE. 1990. Draft Manual on Methodologies and Criteria for Mapping Critical Levelfioads and Geographic Area Where They Are Exceeded. Convention on Long-Range Transboundary Air Pollution, Task Force on Mapping, Geneva. 7 Hettelingh, J.-P. and W. de Vries. 1991. Mapping Vademecum. National Institute of Public Health and Environmental Protection, Bilthoven, The Netherlands. 8 J.-P. Hettelingh, R.J. Downing, P.A.M. de Smet (eds.). 1991. Mapping Critical Loads for Europe. National Institute of Public Health and Environmental Protection, Report 259101001, Bilthoven, The Netherlands. 9 H. Sverdrup, W. de Vries, and A. Henriksen. 1990. Mapping Critical Loads: A Guidance Manual to Criteria, Calculation, Data Collection and Mapping. Nordic Council of Ministers, Miljerapport 1990:14, Copenhagen. 10 W. de Vries. 1991. Methodologies for the Assessment and Mapping of Critical Loads and Impacts of Abatement Strategies on Forest Soils. Winand Staring Center Rep. 46. Wageningen, The Netherlands. 11 A. Henriksen, L. Lien, and T.S. Traaen. 1990. Critical Loads for Surface Waters: Chemical Criteria for Inputs of Strong Acids. Norwegian Institute for Water Research Rep. 0-89210, Oslo. 12 T. Brydges and P.W. Summers. 1989. The acidifying potential of atmospheric deposition in Canada. J. Water Air Soil Pollut. 43:249-263. 13 T. Iversen, N.E. Halvorsen, S. Mylona, and H. Sandnes. 1991. Calculated Budgets for airborne acidifying compounds in Europe, 1985,1988,1989,1990. Cooperative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air Pollutants in Europe (EMEP), MSC-W Report 1/91. Norwegian Meteorological Institute, Oslo. 14 J. Alcamo, R. Shaw, and L. Hordijk (eds.). 1989. The RAINS Model of Acidification: Science and Strategies in Europe. Kluwer, Dordrecht.

SESSIONC ACIDIFICATION POLICY

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T Schneider (Editor). Acidification Research Evaluation and Policy Applications 0 1992 Elsevier Science Publishers B V All rights reserved

I77

CANADIAN ACID RAIN POLICY S. Milbum-Hopwood and K.J. Puckett

Atmospheric Environment Service Environment Canada, 4905 Dufferin Street, Downsview, Ont. M3H 5T4, Canada

INTRODUCTION On March 13 of this year, the Prime Minister of Canada, Brian Mulroney and the President of the United States of America, George Bush, signed an Agreement on Air Quality [l]. This agreement enshrines Principle 21 of the 1972 Stockholm Declaration which states that countries are to ensure that activities within their jurisdiction do not cause damage to the environment of another country. This agreement also includes provisions for controlling acid rain. The Agreement on Air Quality followed 11 years of discussion between the two countries and is a significant milestone in the history of Canadian acid rain policy. This paper will begin by describing Canadian acid rain policy and its evolution. The paper will also outline the Canada-United States Air Quality Agreement and the effect of the acid rain provisions on deposition in Canada. Finally, it will consider the future work that must be undertaken to further resolve the acid rain problem. CANADIAN ACID RAIN POLICY Damage due to acid deposition in Canada is most severe in the eastern part of the country, in the provinces of Ontario, Quebec, New Brunswick and Nova Scotia. The extent of the acid sensitive land mass is shown in Figure 1. Approximately half of the 800,000 water bodies greater than .18 hectares in size, in the areas east of the Manitoba-Ontario border and south of James Bay are sensitive to the effects of acid deposition. It is estimated that more than 3 1 ,000lakes greater than 0.18 hectares in size and 14,000 lakes greater than 1 hectare in size are acidic [2]. The damage is mainly caused by sulphur dioxide emissions from smelters and fossil-fuelled power plants in eastern Canada and from power plants in the midwestem and northern United States (see Figure 2). Emissions of nitrogen oxides contribute to the acidity of precipitation; however, they are not currently a major cause of surface water acidification in eastern Canada. The Canadian sulphur dioxide control policy consists of two components: (1) an environmental objective or target loading to protect a specified component of the environment, which in this case is moderately sensitive aquatic systems; and (2) the emission reductions required to achieve the target loading. The target loading was established in the early 1980s, based on the limited information

178

Areas most sensitive to acid deposition

Figure 1. Areas of Canada most sensitive to acid deposition available at that time on aquatic effects [3]. The value chosen was 20 kilograms of sulphate in precipitation per hectare per year (kg/ha/yr) as a maximum deposition level and it was seen to be protective of moderately sensitive aquatic ecosystems. It was realized at the time, that very sensitive basins would not be protected by this loading and that further evaluation would be needed when more information was available. The Canadian federal and provincial environment ministers adopted the 20 kg/ha/yr of sulphate in precipitation target loading as the objective of their control program. To attain this target loading, it was agreed that a 50 percent reduction in emissions was required since the maximum deposition being observed was approximately 40 kg/ha/yr. It was also recognized that emission reductions in the U.S. would be required to achieve the target loading. In 1985, the Canadian sulphur dioxide control program was established, whereby the seven eastern provinces agreed to achieve, by 1994, a 50 percent reduction in annual sulphur dioxide emissions from the 1980 allowable base case value of 4,516 kilotonnes. As part of the 1985 agreement, each province was responsible for passing the necessary legislation or establishing the necessary programs to ensure that the emission commitments would be achieved. The specific reduction requirements for each province are shown in Table 1. The approach taken by the provinces was not to specify the type of control technology required but rather to allow industries and utilities to determine themselves how

179 to achieve specific control orders or objectives. This approach allowed the industries and utilities the flexibility to choose the most cost-effective approach to emission control. Table 1 Provincial SO, emission reduction commitments 1980 Base Case

Reduction

(tonnes)

(tonnes)

Newfcundland

738,000 2,194,000 1,085,000 215,000 6,000 219,000 59,000

188,000 1,309,000 485,000 30,000 1,000 15,000 14,000

mtdl

4,516,000

2,042,000

Province hnitoba

mtario Quebec New BrunsWick EX1

Nova w t i a

Still to be apportioned: 174,000 tonnes 1994 SO, emission objective for eastern Canada: 2,300,000 tonnes Although the 1985 emission reduction requirements focused specifically on eastern Canada, the distribution of emission sources in Canada was such that the 50 percent reduction in emissions in eastern Canada translated into a more than 30 percent reduction in 1980 national sulphur dioxide levels, permitting Canada to sign the Helsinki Protocol of the Economic Commission for Europe's Convention on Transboundary Pollution. The major emitters of sulphur dioxide in eastern Canada are six large copper, zinc and nickel smelters, one iron ore sintering plant and three provincially owned electrical utilities. Between 1987 and 1994 the major emitters will invest about $1,500 million (U.S. dollars) in capital projects to reduce their sulphur dioxide emissions. The average annual investment over the period is $220 million (US.dollars) per year but, during the final four years, the investment in capital projects will be higher at approximately $312 million (U.S. dollars) per year [4]. Some of the companies involved in the control program have indicated that they may be able to further reduce emissions after 1994. In 1990, the federal and provincial environment ministers agreed to expand the acid rain program to all of Canada and permanently cap sulphur dioxide emissions at 3.2 million tonnes by the year 2000 [5]. In implementing this program, the governments will consider the feasibility of using emission trading as a means of controlling emissions in both eastern and western Canada.

180

Figure 2. Eastern North America Sulphur Dioxide Emissions

CANADA-UNITED STATES AIR QUALITY AGREEMENT The main text of the "Agreement between the Government of Canada and the Government of the United States of America on Air Quality" provides a framework for addressing transboundary air pollution problems. Additional annexes dealing with other transboundary air quality problems, such as ground-level ozone and air toxics, will be added in the future. The first annex of the agreement specifies the targets and timetables for the reduction of acid rain causing emissions. Highlights of the annex follow:

181 -annual sulphur dioxide emission will be permanently capped to approximately 13.3 million tonnes in the United States and 3.2 million tonnes in Canada; -emissions of nitrogen oxides from power plants and factories will be reduced over the next ten years in both countries; -standards for new motor vehicles will be further tightened in both countries; -emissions of sulphur dioxide and nitrogen oxides will be closely monitored; -specific actions will be taken to protect pristine wilderness areas in both countries from transboundary air pollution. The second annex of the agreement deals with cooperative scientific activities between the two countries. These activities will assess the effectiveness of the acid rain controls described in the agreement and will provide information for addressing other transboundary air pollution problems. Canadian scientists have undertaken a preliminary analysis of the effect of the combined Canadian and U.S. control programs on sulphate loadings in eastern Canada. Atmospheric models were used to compare sulphate deposition for the period 1982-1986 with predicted sulphate deposition when the Canadian and U.S. control programs are fully implemented. The models are better at predicting relative changes in deposition under different emission conditions than quantifying the actual deposition levels. For this reason the percentage change between the 1980 wet deposition and the future deposition conditions, as predicted by the models, were applied to the observed mean excess sulphate deposition for the period 19821986, in order to prepare a map showing future deposition conditions (see Figures 3 and 4) [6]. The models predict that when the control programs in both the U.S. and Canada are fully implemented, the sulphate load in eastern Canada will drop below the 20 kg/ha/yr target over virtually the entire region.

FUTURE WORK The Canadian acid rain research and monitoring program will continue for an additional 6 years as announced by the Minister of the Environment in September 1991 [7]. The main goal of the program is to assess the effectiveness of the Canadian and US.sulphur dioxide control programs in reducing acid deposition below the target loading to protect human health, forests and very sensitive aquatic systems, and assess the need for further reductions. A significant fraction of the Canadian population resides in areas where some of the highest levels of acidic air pollution have been observed in eastern North America. Within this general population, there is clear evidence from other air pollution studies that there are subpopulations (i.e. children, asthmatics) which can be expected to be sensitive to elevated levels of air pollution, including acidic pollution. Evidence of increased hospital admissions and visits to emergency departments have been correlated with air pollution levels. In addition, transient but statistically significant decreases in the lung function of children have been observed during and after air pollution episodes. Currently there is no air quality objective or critical load for acidic sulphate aerosols. Although national objectives exist for the precursors of acid rain, SO, and NO,, there are insufficient data on dose-response relationships to properly determine the human health risk posed by acidic sulphate aerosols. A comprehensive health research and assessment program is underway to determine the magnitude of the effects, and necessity and extent of a

182

kglhalyr Figure 3. Observed 5 year (1982-86) mean excess sulphate deposition

Figure 4. Model projections of deposition under condition of full implementation of the SO2 control programs in eastern Canada and the United States of America

I83

mitigative program. Since the Canadian Acid Rain Policy came into being, new information gathered over the past few years has been analyzed to determine the "critical load" for aquatic ecosystems. The critical load is the highest deposition of acidifying compounds that will not cause chemical changes leading to long-term harmful effects on the overall structure or function of the aquatic ecosystem. Critical load information can be used along with information on economic and social concerns in the selection of target loads and the design of control programs. Recently, the criterion of pH26 needed to protect aquatic systems, has been used in aquatic models to predict critical load values for the different regions of eastern Canada. These values range from less than 8.0 in Atlantic Canada to more than 20 kg/ha/yr in some of the less sensitive regions of Ontario and Quebec (see Figure 5) [8].

I

Critical Load Values (kg/ha/yr of sulphate in precipitation)

12-16

Figure 5. Critical load values for eastern Canada

184 However, given the uncertainty in the predictions of the effect of the Canadian and U.S. sulphur dioxide controls on acid deposition levels and the critical load values themselves, modifications to the current control programs will not be made at this time. Nevertheless, specific projects will be carried out to monitor the rate and response of aquatic recovery in eastern Canada following sulphur dioxide controls and substantiate the critical load estimates for aquatic ecosystems. Changing air quality has been implicated in forest declines of maple and birch forests in eastern Canada. The complexity and variability in the forest ecosystem and the lack of information on the history of both air pollution and natural stresses makes it extremely difficult to establish cause-effect linkages. The current Canadian acid rain control program is based on the need to achieve a "target" acid loading to provide protection for moderately sensitive aquatic ecosystems. To date there has been insufficient information to develop target loadings to protect Canadian forests. Research will continue to determine the causes of the observed forest decline, to develop critical loads for forest ecosystems and to assess the need for further controls. In summary, the extended acid rain research and monitoring program is designed to assess the adequacy of the Canadian and U.S. acid rain control programs, to determine the rate and extent of aquatic recovery and to develop criteria for protecting forests and human health. The results of this program will be reviewed in the mid 1990s to determine the need for refinements to the control program.

REFERENCES Agreement between the Government of Canada and the Government of the United States of America on Air Quality. Federal/Provincial Research and Monitoring Coordinating Committee, The 1990 Canadian Long-Range Transport of Air Pollutants and Acid Deposition Assessment Report, Part 4, Aquatic Effects, 1990. Bangay G.E. and Riordan C., Impact Assessment-Work Group 1, Final Report, United States-Canada Memorandum of Intent on Transboundary Air Pollution, 1983. Federal/Provincial Research and Monitoring Coordinating Committee, The 1990 Canadian Long-Range Transport of Air Pollutants and Acid Deposition Assessment Report, Part 7, Socio-Economic Studies, 1990. Canadian Council of Ministers of the Environment, Information Release, November 29, 1990. FederallProvincial Research and Monitoring Coordinating Committee, The 1990 Canadian Long-Range Transport of Air Pollutants and Acid Deposition Assessment Report, Part 1, Executive Summary, 1990. Government of Canada, News Release, Green Plan provides $30 million to Acid Rain Controls, Sept. 23, 1991, PR-HQ-091-32 Federal/Provincial Research and Monitoring Coordinating Committee, The 1990 Canadian Long-Range Transport of Air Pollutants and Acid Deposition Assessment Report, Part 4, Aquatic Effects, 1990.

T Schneider (Editor) Acidtfication Research Evaluation and Policv Applicat ons

@ 1992 Elsevrer Sc<encePLblishers 8 V All rights resewed

185

Acidification policy in Finland E. Lumme

Ministry of the Environment, Air Pollution Control and Noise Abatement Division, P.O. Box 399, SF-00121 Helsinki, Finland

INTRODUCTION

Finland is a Nordic country. Nature in Finland is very sensitive to the effects of environmental pollutants. Our climate aggravates any natural stress on the ecosystems. Acidification is still the most serious regional air pollution control problem in Finland. A special national research project on acidification, HAPRO, was finished in 1990. This programme gave a lot of information to Finnish decision-makers. Some facts about the state of our water and forest ecosystems were quite obvious. A certain amount of damage has already been found in our water ecosystems: till date the harmful effects of lake acidity on fisheries are concentrated to the southern part of the country, but areas sensitive to acid deposition occur throughout the country. Changes in soil chemistry threaten the growth and health of our forests. Some negative effects on trees are already visible. Acidification may become an extremely serious threat to the forests of Finland especially in the future, if emissions are not curbed. The acidifying deposition exceeds the critical loads for forest and water ecosystems in nearly all parts of the country. A remarkable part of the deposition is long range transported. It has been calculated that e. g. in 1980 about 35 per cent of the sulphur deposition in Finland was coming from national sources and, correspondingly, in 1987 about 25 per cent. From the beginning of the 1970's, Finland has actively participated in international co-operation, because exclusively Finnish emission control will never be enough to guarantee a healthy future to the different ecosystems in Finland. During the 1980's the Council of State of Finland has given high priority to the reduction of emissions of acidifying compounds in our own country and to negotiations on the reduction of emissions in our neighbouring countries. Finland has supported the critical loads approach as an acceptable basis for further air pollution abatement strategies. Many kinds of emission reductions have been based on the use of the best available technology *

186

EMISSIONS AND EMISSION REDUCTIONS The major cause of acidification in Finland will for a long time continue to be sulphur emissions. In 1980 o u r sulphur emissions were 292 000 tonnes (S) per year, which was about 1 per cent of the total European emissions. Finland signed the minus 30 per cent sulphur reduction protocol in 1985, but two years later the Council of State set the reduction goal at 50 per cent by 1995. The Finnish sulphur emissions have already been reduced by about 55 per cent since 1980 (in 1990 they were about 0,5 per cent of European emissions). Emissions have been reduced by renewals of process technology and structural changes. In the near future fuel gas desulphurization will further reduce the emissions of sulphur dioxide. In 1987 the Council of State made seven decisions on sulphur emissions. They cover the sulphur content of oil products and hard coal, sulphur dioxide emissions from new and old coal fired power stations, sulphur emissions from oil refineries and sulphate cellulose and sulphuric acid plants. At the beginning of 1991 the Council of State made a decision in principle to reduce sulphur emissions by 80 per cent from the 1980 level by about 2000. In 1980 the Finnish emissions of nitrogen oxides were about 260 000 tonnes ( N O 2 ) per year (about 1,2 per cent of the total European emissions). The annual emissions have increased slightly during the 198O's, as they have done in many other parts of Europe. It has been estimated that in Finland, nitrogen oxides emissions can be reduced by 15 per cent by 1998 by applying, in addition to the exhaust regulations for new private cars, the following measures: development of combustion techniques in new and existing energy generation units and flue gas cleaning in new ones: a 50 per cent cut in exhaust emissions from new heavy diesel vehicles. Structural means will at least in theory make it possible to reduce the emissions to the target level (reduction by about 30 per cent) by the year 2000. Until now the Council of State has limited the emissions of vehicles and energy generation plants (the latest decision was made in March 1991). Ammonia emissions in Finland are about 43 000 tonnes (NH,) per year (about 0,5 per cent of the total European emissions). Nearly 70 per cent of the Finnish emissions are due to cattle breeding. It has been estimated that about 20 per cent of the acid deposition in Finland is caused by ammonia emissions. In Finland the acidyfing potential of ammonia emissions is at present approximately on the same level as that of nitrogen oxides. An ammonia working group has recently (report in March 1991) investigated technical ways and means of reducing ammonia emissions and the costs thereof. N o decisions have as yet been made on how to reduce ammonia emissions in the future.

187 CRITICAL LOADS

Finland has actively participated in the recent European work to produce the first maps of critical loads. Mapping critical loads has been and will continue to be an important area of Nordic co-operation under the Nordic Council of Ministers. According to the available maps Finland and the other Nordic countries belong to the most sensitive areas in Europe. In the whole of Finland the load of actual acidity or sulphur should not exceed 20 milliequivalents per square meter per year. The critical loads for Finnish lake and forest ecosystems have also been illustrated in smaller grids, corresponding to three by three subdivisions of the EMEP grids used in the European work. These more detailed maps give more information on the distribution of sensitive areas and on the differences in sensitivity of lakes and forests. In a number of grids throughout Finland the critical load of potential acidity for lake ecosystems ( 5 percentile) is less than 20 meq/m2, but for forest soils the critical load of potential acidity is 50 - 100 meq/m2 in large parts of the country. The European maps of critical loads of actual acidity show that critical loads are exceeded in all parts of Finland. The critical load of actual acidity ( 5 percentile) is exceeded by 100 - 200 meq/m2 in parts of southern Finland and by 20 - 100 meq/m2 in the central parts of the country. The critical sulphur load (5 percentile) is exceeded in quite large parts of southern Finland by 20 - 50 meq/m2 (even over 50 meq/m2 ) . According to the current European reduction plans the critical sulphur load would still be exceeded in the southern part of the country in about 2010. POLICY AND STRATEGIES

In 1984, when issuing air quality guidelines, the Finnish Council of State defined the long-term goals of air quality policy: to protect conifers in wide forest and agricultural areas or nature conservation areas: the annual sulphur dioxide levels outside towns and bigger villages should not be more than 25 ug/m3: and in order to avoid acidification effects the total sulphur deposition should be under 0,5 grams sulphur ( S ) / m 2 . For most of Finland this still seems to be a reasonable goal. On the basis of the national critical loads mapping programme the Ministry of the Environment identified, in May 1991, preliminary national target load values for sulphur. In the most sensitive regions in the arctic and subarctic areas of Finland, the sulphur load should not exceed 0,2 g S/m2/a. In some areas in the western part of Finland the sulphur load should not exceed 0,4. For the rest of the country the target load was set at 0,5, the earlier value for the whole country. When setting these target loads it was realized that for many aquatic ecosystems the critical sulphur load will still be exceeded. For forest ecosystems these values should ensure that the

critical load according to the present knowledge will not be exceeded. Studies on critical loads and levels and on the state of the environment will be continued. Although Finland has been able to cut certain emissions, there is still a lot to be done. In January 1991 the Council of State made the decision in principle that Finland will further reduce the acidifying sulphur emissions by 80 per cent (from 1980 level). Before the decision was made it was estimated that if the other countries also reduce their emissions by about 80 per cent the critical loads would not be exceeded. The Ministry of the Environment has set up a sulphur committee to prepare a ten year programme on how to achieve the 80 per cent reduction in sulphur emissions. The first proposals given by the committee in last September concern the increased use of heavy fuel oil with less sulphur. Finland will also study further possibilities to reduce emissions of nitrogen oxides and ammonia. The Finnish Carbon Dioxide Commission (report dated June 1991) has recently investigated alternative strategies and measures for limiting and reducing the emissions of carbon dioxide and other greenhouse gases. It concluded that it is possible to reduce greenhouse gas emissions by increasing the use of carbon dioxide free forms of energy and natural gas and by more efficient energy generation. It is obvious that the future policy in reducing greenhouse gases will also influence some emissions of acidifying compounds. These policies will be reconsidered in the future. The effects of an 80 per cent reduction in sulphur dioxide emissions, a 30 per cent reduction in emissions of nitrogen oxides and a 25 per cent reduction in emissions of carbon dioxide will be estimated in terms of their influence on Finland's energy policy. The parliamentary energy policy council has presented a report on Finland's national energy strategy at the beginning of October 1991. The most essential goals set to energy policy are to guarantee availability of energy sources and economical energy generation while taking environmental demands into account. Until recently, the general promotion of environmental protection in Finland has relied largely on legal controls. However, additional financial controls (like environmental taxes) have also been introduced during recent years. A working group on environmental taxes presented its report in April 1991. Finland tries to encourage saving and to reorient consumption in a direction more conducive to sustainable development by means of tax reforms. It is believed that if sufficiently high taxes and charges are levied on operations causing pollution, this will guide development in a less polluting and environmentally sound direction more effectively than would laws and statutes alone. Some financial controls were included in the state budget as early as in 1990. It is obvious that the 1993 budget will include more measures aimed at influencing e. g. the emissions of carbon dioxide and nitrogen oxides. The Ministry of the Environment has, in October 1991 set up a high level project to study and to make concrete proposals on the use of economic instruments in promoting environmental protection. Special attention will be given to the demands of international development. The work is leaded by the ministers of the environ-

ment, finance, agriculture and forestry, trade and industry, transport and communication. Finland will also continue to participate in international co-operation to negotiate efficient emission reductions for the whole of Europe. The co-operation between the Nordic countries will be continued. Moreover, Finland has bilateral co-operation with those neighbouring countries which contribute most to our acidifying load. The Finnish Government has drawn up a plan of action concerning co-operation with Eastern Europian countries in the near future. Co-operation in the field of environmental protection occupies a central position. In connection with the plan, e. g . an Environmental Review and Priority Action Programme for St. Petersburg, the St. Petersburg region, Karelia and Estonia has been made (report dated September 1991) to determine the main environmental problems and the main measures to reduce them. Significant air pollution projects are included in the project priority list. To achieve concrete results the Ministry of the Environment has set up a special East-Europe project in 1990. Solving the problems of transboundary pollution calls for deviation from the polluter pays principle, which is a commonly accepted means of promoting generally sustainable development.

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T Schneider (Editor). Acidification Research Evaluation and Policy Applicatlons @ 1992 Elsevier Science Publishers B V All rights reserved

ACIDIFICATION POLICY GERMANY

-

191

CONTROL OF ACIDIFYING EMISSIONS IN

Bernd Scharer Umweltbundesamt, Bismarckplatz 1, 1000 Berlin

33,

Germany

Abstract Since the mid-eighties total annual acidifying emissions have started to decline in West Germany. There was considerable impact on this positive trend in air pollution by the control of SO2 and NO, emissions from large boilers, which were reduced by more than 8 0 % . Corresponding control programmes have been established for other groups of sources as well as other pollutants and - with unification - for East Germany. The driving force behind this development was and still is first of all the legal principle of anticipatory action or precaution which means in practical terms “emission minimization“. This cornerstone of German clean air legislation is the most powerful component of Germanyls “acidification policyt1,as it requires policy-makers to draw up new or review existing regulations for emission reduction based on requirements according to the state of the art and forces operators to apply the most modern ways and means of operation. This paper, as point of departure, describes the system used in Germany to deal with air pollution, with the emission minimization strategy in the center, and the actions against acidifying emissions based thereon. In addition, an outlook on what might be necessary to cope with the challenges of a sustainable development concerning acidification is given. 1. INTRODUCTION

Is there a German acidification policy? Acidification policy is understood to mean here the activities of the political decision-making bodies, the parliament and the government, which have as their aim the improvement of the initial acidification situation by the use of specific measures. This includes the generation of information on the initial situation (pollution) and its assessment, the fixing of goals as well as the adoption and implementation of measures which are suited to bringing about a change in the initial situation and contributing to achieving the goals.

192

German environmental policy evolved in the late sixties. At that time policy-makers were already aware of an acidification problem in Germany: Concern was directed at the llsmoke-induced damage near the emission source1', which one attempted to counteract more by a high-stacks policy than by reducing emissions. Largely constant pHs in precipitation in the seventies prevented the development of comprehensive reduction programs. An acidification policy developed in Germany mainly against the background of dying forests, receiving important impetus from that direction. The warnings and calls for help from Scandinavia, prompted by the acidification of otherwise nonpolluted lakes, observed there as early as the beginning of the seventies, had not yet managed to awaken a specific acidification policy in Germany. It was with reserve that Germany contributed to the political activities launched thereafter on the international level - initially within the OECD, later at the UN Economic Commission for Europe (ECE) in Geneva. And also the findings on problems caused by the acidification of German forest soils, which, as from the mid-seventies, were obtained as a by-product, so to speak, of research into the question of "what forests feed onll, still required some time to gain political relevance. Then, however, with rapid acceleration in the late seventies and early eighties, awareness of the dying of forests - in officialese: new forms of damage to forests - among the public, the media, and policy-makers became so high as to effect tremendous pressure for a change towards a solution to the acidification problem. In 1982/83, within a short time, the Federal Government - initiated systematic surveys of forest damage to be conducted at regular intervals (as from 1982); - convened the Interministerial Working Group "Forest Damage/Air Pollution1@(1983); - initiated a research programme to study damage to forests (1983)

- submitted the action programme IISave the Forests1' (1983); and last, but not least - took effective actions against the air pollutants considered

the cause of the problem, which in terms of the reduction of relevant emissions have met with considerable success. Also in its foreign policy, the Federal Government gave a clear indication of its active role in the solving of transboundary environmental problems by sponsoring a I1Multilateral Conference on the Causes and Prevention of Damage to Forests and Waters by Air Pollution in Europet1(Munich, June 1984). Given the successes achieved by policy-makers in pushing through emission reduction programmes and the reductions in acidification causing emissions already obtained except for NH3, on which attention did not focus until later an assessment of German acidification policy in the eighties would have

-

193

to be quite favourable. It should, however, be borne in mind in such considerations that a basic set of legal instruments to combat acidification processes and the dying of forests did not have to be conceived, but was already on hand, when the acidification problem became apparent. The basis for the measures was the strategy of anticipatory action which was incorporated into German air pollution control law (Federal Immission Control Act) as early as 1974 and which in practice is a requirement for all emission sources to minimize emissions. The emission minimization requirement was the main driving force of German air pollution control policy in that it provided the decisive justification for the further development of control technologies and the establishment of emission limitation requirements. It thus gave impetus to measures aimed at combatting acidification and damage to forests. Due to the fundamental importance of the emission minimization requirement, this basic conceptional element of the Federal Immision Control Act is explained in more detail in the following section before moving on to the description of various emission reduction programmes. 2. CONTROL OF ACIDIFYING EMISSIONS 2.1 The Technology-based Concept of Emission Control

In the beginning of the eighties, Germany systematically started to establish comprehensive cleanup programmes for existing emission sources. Up to that time, mainly new plants had been controlled and existing plants only in areas where ambient air quality standards were exceeded. The new regulations required both new and existing sources to control their emissions according to the state of the art, irrespective of whether air quality standards had been exceeded. The most important driving force behind air pollution control actions was and still is the legal principle of I'anticipatory action1' (Vorsorge) based on the Federal Immission Control Act (Bundes-Immissionsschutzgesetz - BImSchG). In practical terms, anticipatory action means minimizing emissions from all sources as far as technically reasonable. Air quality conservation (principle of protection), which is likewise founded on the BImSchG and aims at maintaining certain immission standards which may not be exceeded (ambient air quality standards AAQS), practically only plays a minor role as immission standards usually are not exceeded. Anticipatory action and conservation form a double-track strategy, that aims at the maintenance of a certain air quality and, independently thereof, at minimizing emissions. To implement the principle of anticipatory action, the Federal Immission Control Act exacts highest standards with respect to a) the development of emission reduction regulations, and b) the responsibility of the sources to be in compliance.

194

Emission standards and other requirements for emission reduction are principally based on technical feasibility, i. e. they have to reflect the state of the art. State of the art in this context means that emission standards must reflect the development of advanced processes, installations or operation practices, which have the practical potential of reducing emissions efficiently and to the greatest extent possible. This legal definition of the state of the art is intentionally directed at pushing technology forward, it thus illustrates that environmental policy tends to be technology-driven. The emission standards, referenced to the state of the art, must always be attained by the regulated party and facilities must be fitted with the appropriate technology, even if emissions do not result in Ambient Air Quality Standards being exceeded in the affected area or even if the measured air quality lies well below AAQS. The instruments designed to implement the state of the art at stationary sources in the Federal Republic of Germany are - construction and operating licenses for new or significantly altered plants, subsequent orders issued by the competent authorities for existing plants, and - ordinances containing provisions that operators have to comply with directly. Installations subject to licensing under the Federal Immission Control Act are all plants with a certain emission relevance. For example, all boilers with a thermal capacity of more than 1 MW require licenses €or both their construction and operation. Larger plants are required to monitor their emissions continuously. The results have to be made available to the responsible authorities for review. Small plants are normally not subject to licensing in accordance with the Federal Immission Control Act, they have to undergo plan approval. However, the requirement of "state of the art1*also applies to small plants. The ways and means of ensuring compliance of stationary sources are based on - ambitious obligations directly imposed on the operators, as well as - a differentiated implementation and enforcement infrastructure. The law imposes ambitious obligations on the operators, which are specified in Article 5 of the Federal Immission Control Act. According to these provisions, sources have be established and operated in such a way that the following four requirements are met: (a) attainment of ambient air quality standards (b) compliance with emission standards according to the state of the art, and regular monitoring (c) prevention, utilization, or at least harmless disposal of residual substances and (d) use of produced (waste) heat.

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195

While (a) is to ensure that certain ambient air pollution thresholds are not exceeded, (b), (c) and (d) require plant operators to use progressive technologies while taking crossmedia aspects into account, and they thus promote the use of integrated technologies. With respect to automotive emissions, however, the BImSchG is overruled by relevant provisions agreed upon within the Commission of the European Communities; but also in this sector, national efforts are aiming at the introduction of state-of-the-art technology. The following section describes the measures taken to implement the state-of-the-art concept.

Action against Acidifying Emissions

2.2

stationary sources An all-encompassing system of emission standards exists in Germany, covering boilers, waste incineration plants, all relevant industrial processes and smaller area sources. Concerning stationary sources subject to licensing table 1 gives a summarizing overview of important emission standards for NO, and SO2 for new and old plants. These emission standards have been promulgated in the Ordinances on Large Combustion Plants ( 1 3 . BImSchV) and Waste Incineration ( 1 7 . BImSchV) and last but not least in the Technical Instructions on Air Quality Control (TA Luft), an administrative regulation binding on the authorities responsible for implementing legislation. 2.2.1

Table 1 Important emission standards for stationary sources subject to licensing in Germany w/m3 MWth Heat and power generation

> 300 > 50 1

-

-

-

300

50

-

300

100

< 10

Waste incineration Industrial processes

9

50

200 400 500 4001) 8003) 1000 2000

15D 3 00 450 so2 4001) 680 8503) 17004)

SO2

200

5 0 0 2 ) SO2

100 200 200 352) 352) 352) 352)

NO,

5002) NOx

solid fuel; 1: liquid fuel; g: gaseous fuel and 1 5 % max. emission rate for all plants; special regulations for special processes required in implementation and enforcement practice for plants < 5 MW use of light heating oil is required

X) s:

l) 2) 3) 4)

1

No,

> 300 > 100 10

sx)

196

At large combustion plants, the main source of SO2 and NO,, the practical implementation of the emission standards has been effected without any problems within a period of six years, as a result of which power plants operated by public utilities, for example, achieved emission reductions of 8 8 % for SO2 and 73% for NO,. The trends of these emissions, which follow that of the application of FGD and SCR technology in Germany, are shown in figure 1.

1.4

.......................................................................

......................................................................................................................... .........................................................................................

........................................................................................ ...............................................................................

a

Figure 1. Trend in

SO2

and NO, emissions from power plants.

For smaller plants (< 1 m t h ) not subject to licensing under the Federal Immission Control Act, the Ordinance on small combustion plants (1. BImSchV) lays down emission reduction requirements with respect to fuels and combustion technology. Another regulation that is particularly applicable here is the Ordinance on the sulphur content of light heating oil and diesel fuel (3. BImSchV) , which limits the sulphur content to 0.2%.

Ammonia emissions in Germany are roughly estimated at 1 million t NH3/a. 90% thereof originate from agriculture, of which two-thirds arise from the application of manure to farmland. An ordinance is currently being prepared, which prescribes requirements for workha the manure directly into the sail during application 85 well a s for stabie design. In addition, large stables have been included in the list of installations subject to licensing.

197

Mobile Sources As the main sources of NOx emissions, motor vehicles are an important target of acidification policy. In Germany in 1 9 8 3 , the Federal Cabinet adopted a policy goal, according to which emission standards were to be based on the three-way catalyst, which at that time had already been in use in the USA and Japan. It was then decided, however, to agree to the decisions adopted within the EC, in order to promote an EC-wide regulation and to prevent a split of the automobile market. To still be able to achieve emission reductions immediately, that is, before the EC emission standards went into effect, t a x privileges were granted in Germany for environmentally friendlier cars, both for new cars and retrofitted cars in traffic. Thus, with financial support by the government, some 0 . 5 million cars in traffic had been retrofitted with catalytic converters or primary measures and some 4 million environmentally friendlier new cars had been put into traffic before the corresponding emission standards became effective, these numbers accounting for approx. 15% of the vehicles in Germany. A s for heavy-duty vehicles, emission control requirements for NOx will not become effective until model year 1 9 9 2 / 9 3 , with a second stage effective as of 1995/96. Emissions will thereby be reduced by 4 0 % and 2 0 % , respectively, versus previous levels. 2.2.3 Cleanup of E a s t Germany A s a result of German unification, West Germany's environmental regulations are now also applicable in East Germany. This means that new plants there can only obtain a license if they comply with the current emission limits and that existing plants will have to be retrofitted within certain transitional periods, comparable to those applicable for West German installations, or be shut down. The S O z - and NOx-relevant restructuring and retrofitting of East Germany's industry is expected to be completed to a great extent in the second half of the nineties. An earlier date is envisaged for the conversion of small combustion plants to fuels low in sulphur. The renovation of power plants, industrial boilers and heating stations currently underway in eastern Germany comprises shut-downs, conversion to low-sulphur fuels and retrofitting with effective flue gas cleaning systems. Some lignitefired power plants and industrial plants have already been shut down. According to the power industry, the first 3 , 0 0 0 MWel will be retrofitted with flue gas desulphurization systems as early as 1 9 9 3 / 9 4 . 2.2.2

2.3 Efficient use of energy

The energy sector accounts for more than 9 0 % of acidifying and NOx emissions. Efficient, economical use of energy therefore is an essential component of acidification policy. A high standard of energy efficiency has already been attained in West Germany in comparison with many other industrial nations. Specific energy use by the West German economy as related to the gross domestic product dropped by more than 20% over the past 15 years. In addition to price SO2

198

increases for energy and advances in energy technology, a number of regulations and support measures to promote efficient use of energy, e. g. cogeneration of electricity and heat, use of renewable energy sources, provided important impetus in this direction. An ordinance on heat utilization is currently being prepared, which is designed to minimize the heat generated by installations subject to licensing and ensure that the heat, whose generation cannot be avoided, is utilized. Due to the necessity of climate protection, the intensity of energy-related measures has taken on a new dimension. The Federal Government, in a decision adopted by the Cabinet on 13 June 1990, pledged to reduce energy-related C02 emissions versus 1987 levels by 25% in western Germany, and even more in eastern Germany, by the year 2 0 0 5 . Preliminary estimates show that corresponding measures will result in a further reduction in emissions by approx. 20% for SO2 and approx. 7% for NO, versus the levels already reached in 1 9 8 9 . Trend in aaidifying pollution Acidifying emissions as a whole have been on a downward trend since the early eighties. However, considerable differences exist among the various pollutants and, above all, between the trends in eastern and western Germany. Drastic reductions of about 70% were achieved for SO2 in western Germany in the eighties, with an 88% reduction in the emissions from power plants (see figure 1). The reduction of NO, emissions was likewise considerable in this sector, amounting to 74%. Due to an increase in traffic emissions, however, total NOX emissions decreased only slightly. The emissions of N H ~ ,the third major acidifying component, are roughly estimated at 1 million t/a, of which 90% originate from agriculture. According to the latest emission projections of the Federal Environmental Agency as presented in table 2 , the future will bring further emission reductions. For example, the application of West German air pollution control legislation in eastern Germany will effect a 95% reduction in SO2 emissions there. The measures taken to protect the climate ( 2 5 % reduction in C 0 2 emissions by the year 2 0 0 5 ) as well as the increased use of catalyst-equipped vehicles will also bring about reductions in emissions. For the united Germany SO2 emissions are projected to decrease by 88% and NO, emissions by 50% comparing 1989 with 2005 figures. 2.4

199

5 1

Table 2 Trend in acidifying emissions in Germany Year

1980

4300

500

1000

-

1000

2700

1989 5250

Projection W without W with no data

2005

E without E with

no data

W: West Germany; E: East Germany; without: without climate protection measures: with: with climate protection measures The decrease in SO2 emissions has had an effect on pollution levels. Since 1988 , the measurements taken by the Federal Environmental Agency's air pollution monitoring network have shown a marked decrease in the concentration of sulphur dioxide versus the levels ascertained in the years prior to that time. The reductions range from just below 30% in the eastern part of the pre-unification Federal Republic of Germany to 70% in the west, averaging about 5 0 % . This development, however, benefitted from relatively mild winters in the course of which stagnant weather conditions and winds from the east rarely occurred. The decrease in SO2 concentrations is even more pronounced if the times of transport from emitting regions further to the east are excluded from consideration. The drastic decline in economic activity, which occurred in eastern Germany after the Itchangett, is now also becoming apparent in the available air pollution measurement data. Regrettably, for NO, there is no reduction in pollution levels, since the successes achieved in reducing emissions at combustion plants have so far been cancelled out by additional NOx pollution from traffic. The situation will only improve over a longer term, as a result of the emission reductions that are expected for the future. An improvement is also expected for NH3, however it has not yet been quantified. Acid deposition, too, has decreased in Germany in recent years. To deal with this in detail would, however, go beyond the scope of this paper, as the situation is complex and therefore differs greatly, especially because of the great influence of weather conditions.

200

Whether these successes in reducing emissions in Germany are sufficient to ensure effective protection of the environment and restore to health those components of nature that have been damaged, increasingly depends on the extent to which pollutant exports to Germany can be reduced. Recently, in scientifically determining and justifying effect thresholds below which adverse effects are not expected to occur, it was found that the llcritical loads" cannot be complied with in large parts of Germany. To be able to do so, much further-reaching emission reduction measures would be required. These would have to be taken above all in countries exporting acidifying pollutants to Germany. 3. FUTURE CHALLENGES

SUSTAINABLE DEVELOPMENT BY CRITICAL LOADS AND LEVELS?

Critical loads and levels are scientifically founded effect thresholds below which environmental damage is not expected to occur according to present knowledge. The critical loads/critical levels concept would thus meet the demands of a sustainable development and would be in accordance with the principle of protection (hazard prevention) which is incorporated in the Federal Immission Control Act. Compliance with the critical loads as specified in the report "Mapping Critical Loads for Europelll) will not be possible in Germany in a timeframe used in relevant projections. This holds true even if critical loads were applied which would allow the respective area or reference values of an EMEP grid to be exceeded by 10% and even if all countries "exportingn SO2 to Germany were to take measures according to the state of the art, although the latter would of course result in a marked reduction of pollution levels. Scenario calculations have been performed using RAINS (IIASA). In this work, the respective 99%, 95% and 90% critical load values were compared with the deposition levels obtained - when the ECE countries! current reduction plans are implemented ; - if measures according to the state of the art (maximum feasible reduction) were performed throughout the ECE. A comparison with the deposition levels resulting from the "current reduction plansr1 scenario shows that even the 90% critical load values are drastically exceeded in all EMEP grids. A comparison with the deposition levels of the !!maximum feasible reductionll scenario still shows exceedances of the 99% critical load values for large parts of Germany, whereas the 95% values are exceeded only in the EMEP grids along the border to the Netherlands, the North Sea coast and along the border to

l)

United Nations Economic Commission for Europe, Convention on Long-Range Transboundary Air Pollution CCE Technical Report No. 1, July 1991

201

the CSFR in the EMEP grids Chemnitz, where the deposition level is greatly in excess of the critical load, and Fichtelgebirge (mountain range near Bayreuth, Bavaria) with only slight exceedance. For all other German EMEP grids, the application of state-of-the-art technology would result in compliance with the 95% critical load values. Based on the RAINS calculations the Federal Environmental Agency has proposed that the 9 5 % critical load values be used as target loads for Germany. These are attainable (except for a few grids), if measures based on the state of the art are implemented in the countries emitting to Germany. For all other grids, the deposition levels attainable by using measures according to the state of the art are proposed as target loads. The Federal Environmental Agency considers these targets to be realistic. They are not only necessary, but also feasible, and do not amount to asking too much of neighbouring countries. As for Germany itself: As described above, the philosophy of German air pollution control law is to actually accomplish feasible emission reductions (emission minimization requirement). In conclusion, mention should be made of the planning currently underway to clean up an area known as the "black triangle1I, which comprises parts of northern Bohemia, Silesia and Saxony. This region has the highest emissions of acidifying pollutants in Europe. Within the framework of the *@Working Group for Neighbourly Co-operation on Environmental Issuesl@, the Environment Ministers of the CSFR, Poland and Germany initiated an analysis of the current situation and the development of a Ifrecovery and development plan". This hopefully is the beginning of the solution and thus the beginning of the end to the acidification problem.

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203

@ 1992 Elsevier Science Publishers E.V. All rights raseNed

A d i c i f i c a t i o n p o l i c y i n Hungary

E . KovAcs I n s t i t u t e f o r E n v i r o n m e n t a l P r o t e c t i o n , Aga u . 4 . B u d a p e s t , H-11U Hungary

Abstract

A N a t i o n a l Conference on t h e A c i d i f i c a t i o n o f t h e Environment gave t h e framework o f t h e l a t e s t r e v i e w .

A i r p o l l u t i o n abatement

i s a m a j o r e l e m e n t i n a c i d i f i c a t i o n p o l i c y . A r e m a r k a b l e reduction of

SO2 a n d N O x e m i s s o n s h a s b e e n a c h i e v e d i n t h e l a s t d e c a d e .

I n s p i t e o f t h i s f a c t s o i l s h a v i n g a pHKC1C5,5 i n c r e a s e d t h e i r s h a r e b y 6 % .New l e g s l a t i o n o n a i r p o l l u t i o n a b a t e m e n t comprises i m p o r t a n t e l e m e n t s t o c o n t r o l t h e e m i s s i o n o f a c i d i f y i n g compounds.

1. INTROOUCTION I n 1985 t h e N a t i o n a l A u t h o r i t y f o r E n v i r o n m e n t a l P r o t e c t i o n and N a t u r e C o n s e r v a t i o n a n d t h e H u n g a r i a n Academy o f S c i e n c e s i n i t i a t e d

a r e v i e w c o v e r i n g t h e t o p i c s o f a c i d i f i c a t i o n . E x p e r t teams p a r t i c i p a t e d i n t h e work a i r quality, waters,

c o v e r i n g emission o f p o l l u t a n t s , ambient

d e p o s i t i o n o f a c i d i f y i n g compounds,

s o i l and f o r e s t ,

h e a l t h and on s t r u c t u r e s ,

acidification in

t h e i m p a c t o n t h e e c o s y s t e m , o n human r e s p . h i s t o r i c a l monuments.

The r e p o r t

One o f t h e f i n a l f i n d i n g s o f t h e r e p o r t was i s s u e d i n 1 9 8 7 [I]. was t h a t f u r t h e r c o - o r d i n a t e d r e s e a r c h s h o u l d b e c a r r i e d o u t t o d e s c r i b e t h e v a r i o u s phenomena, t o r e v e a l t h e p o s s i b l e c a u s e s g i v i n g a f i r m background t o t h e measures t o be t a k e n .

Primary i n t e r e s t

s h o u l d b e p a i d a n d f i n a n c i a l means s h o u l d b e a l l o c a t e d t o i m p l e m e n t a t i o n o f c o n t r o l measures.

the

204

In November 1990 a National Conference on the Acidification of the Environment gave the framework of the latest review on that topic. Some 6 0 papers were presented covering the fields ofresearch as follows: modelling; emission of pollutants; ambient air quality; dry and wet deposition of acidifying compoundsat different energy scenarios; emission control of S O x and NOx; correlation between emission, depositions and acidification; aquatic ecosystems;data and the causes of acidification of soils; puffer capacity of soils; mobility of toxic ions in soils; chemical treatment of soils; the impact of fertilizers; forest damages due t o air pollution; impact of acid rain on structures and historical monuments; impact of salting on roads and structures [ 2 ] . It seems to be difficult to give a comprehensive review of this broad field of reserach. However, some results will be presented here.

2 . E M I S S I O N S , CONCENTRATIONS AND D E P O S I T I O N S OF A C I D I F Y I N G CWOUNDS

Acidification policy is overlapping with air pollution abatement, however, it covers a wider range of topics. Nevertheless, the reduction of the emission of acidifying compounds is of primary interest. The main targets guiding the national policy for abatement of air pollution comprise the elements as follows

-

t o reduce air pollution in the heavily polluted regions of the country, as in the capital and in some industrialized areas, with an emphasis on improving ambient air quality in the big cities, - to maintain the ambient air quality of the relatively "clean" regions, - to fulfill the obligations due to international agreements, a s of the protocols on SO2 and NOx. The first target is clearly human health oriented because there exists evidence that serious damages to human health occurs in regions where people suffer expositon to excessive air pollution. Even in terms of financies, damages to human health expressed in

205 e x p e n s e s l e a d s t h e l i s t b e f o r e damages o f s t r u c t u r e s ,

s o i l s and

f o r e s t s due t o a c i d i f i c a t i o n . The i m p r o v e m e n t o f u r b a n a i r q u a l i t y r e q u i r e s t h e r e d u c t i o n o f p o l l u t i o n generated mainly by road t r a f f i c , hydrocarbons,

carbon monoxide, s o o t ,

such as n i t r o g e n o x i d e s ,

l e a d and s u l p h u r d i o x i d e .

The s e c o n d a n d t h i r d t a r g e t s a r e c l o s e l y r e l a t e d t o r e d u c t i o n o f p o l l u t a n t s c o n t r i b u t i n g t o a c i d i f i c a t i o n . However,

interrelation

between t h e s e elements c l e a r l y e x i s t s . E m i s s i o n s o f s u l p h u r d i o x i d e a r e shown i n T a b l e 1. H u n g a r y i s P a r t y t o t h e C o n v e n t i o n on l o n g - r a n g e

transboundary a i r p o l l u t i o n

and t o t h e P r o t o c o l s on t h e c o n t r o l o f SO2,

r e s p . NOx e m i s s i o n s .

The P r o t o c o l on t h e r e d u c t i o n o f SO2 e m i s s i o n s i m p o s e s t h e b a s i c o b l i g a t i o n o f a 30 % r e d u c t i o n o f e m i s s i o n s b y 1 9 9 3 b a s e d o n 1 9 8 0 emission values.

Thus,

SO2 e m i s s i o n s o f 1 . 6 3 3

kt/year

i n 1980 s h o u l d

be r e d u c e d t o 1.143 k t / y e a r b y 1993. T h i s r e q u i r e m e n t w i l l be met due t o s t r u c t u r a l changes i n f u e l m i x , t h e economic r e c e s s i o n .

r e s p . i n t h e i n d u s t r y and

However, measures a r e t o be t a k e n i n t h e

f u t u r e c o n s i d e r i n g t h e p r e d i c t a b l e economic e x p a n s i o n and t h e i m p l i c a t i o n s o f a second s u l p h u r p r o t o c o l based on t h e c r i t i c a l l o a d s a p p r o a c h . Means o f f u r t h e r r e d u c t i o n o f SO2 e m i s s i o n s a r e a s follows:

f u r t h e r s t r u c t u r a l changes i n f u e l m i x ,

e n e r g y conservation

measures, t h e i m p l e m e n t a t i o n o f f l u i d i z e d bed c o m b u s t i o n methods

i n power g e n e r a t i o n on a l a r g e s c a l e and t h e i n t r o d u c t i o n o f f l u e g a s d e s u l p h u r i z a t i o n f a c i l i t e s i n some p o w e r p l a n t s .

The c o s t

e f f e c t i v e i m p l e m e n t a t i o n o f t h e a b o v e m e n t i o n e d m e a s u r e s may r e d u c e c a p i t a l i n v e s t m e n t n e c e s s a r y and o p e r a t i o n a l c o s t s i n a r e m a r k a b l e r a t e . I n v e s t i g a t i o n s i n t h i s m a t t e r h a v e shown t h a t t h e r e a r e r e s e r v e s i n energy u t i l i z a t i o n which s h o u l d be e x p l o r e d f i r s t . The P r o t o c o l o n t h e c o n t r o l o f NOx e m i s s i o n s i m p o s e s t h e b a s i c o b l i g a t i o n o f an e m i s s i o n f r e e z e b y 3 1 December 1 9 9 4 b a s e d o n 1987 e m i s s i o n v a l u e s . Thus,

t h e e m i s s i o n o f 280 k t / y e a r

i n 1987

s h o u l d n o t b e e x c e e d e d a f t e r 1 9 9 4 . The e m i s s i o n s o f NOx a r e shown

i n Table 2.

E m i s s i o n s o f power p l a n t s and o f i n d u s t r y d e c r e a s e d

i n t h e l a s t years,

however,

t h e amount o f t r a f f i c g e n e r a t e d n i t r o g e n

o x i d e s r e m a i n e d p r a c t i c a l l y unchanged. T h i s i s due t o t h e f a c t t h a t t h e i m p a c t o f g r o w i n g c a r f l e e t h a s b e e n c o m p e n s a t e d b y decreasing c a r use.

206

T h e reduction of nitrogen o x i d e s emission i s envisaged o n mobile sources. T h e catalyst p r o g r a m m e planned will reduce emissions o f N O x , HC and CO by a r e m a r k a b l e r a t e . O E N O X equipments for power plants have not b e e n c o n s i d e r e d s o f a r . The ammonia e m i s s i o n s a r e i n t h e range o f 160-180 kt/year. T h e emission o f volatile organic c o m p o u n d s i s in t h e range of 2 0 0 - 2 1 0 kt/year. At three background monitoring stations located in ecological basis a r e a s measurements of t h e l a s t 3 y e a r s have shown results concerning acid deposition a s f o l l o w s [ 3 ] : - dry acid depositions were 7 5 , 1 0 9 and 147 mgH+ /in2. year in hidrogen ion e q u i v a l e n t , - in dry acid d e p o s i t i o n s S O 2 and N O 2 g a s e s h a v e a dominating role. Yearly a v e r a g e s a r e w e l l below t h e l i m i t values considered 3 damaging for f o r e s t s ( S O 2 = 30 )g/m , NO:, = 30 p g / m 3 ) , - wet acid d e p o s i t i o n s a r e in t h e same magnitude (110, 9 2 , 2 1 5 2 mgH+/rn .year) a s dry a c i d d e p o s i t i o n s , - in wet acid deposition s u l p h u r and nitrogen c o m p o u n d s have a 40 % , resp. 60 % s h a r e , - in total acid d e p o s i t i o n t h e s h a r e o f d r y acid deposition i s bigger in winter, r e s p . wet acid deposition i s bigger in summer. T h e yearly a v e r a g e values o f S O 2 and N O 2 concentrations o n a regional s c a l e , their o r i g i n , t h e d e p o s i t i o n s o f sulphur and oxidized nitrogen c o m p o u n d s a n d their acidifying potentialaccording to model c a l c u l a t i o n s a r e s h o w n in T a b l e 3 [4].

3. ACIOIFICATION OF SOILS

According t o investigations [5] there a r e some 2 , 3 million hectares o f acidic s o i l s in Hungary. Out o f t h i s total t h e r e a r e - 300.000 ha s t r o n g l y acidic (pHKC1 70% covered by heathland species), about one third contains large amounts of grass and will probably change into grassland within the next 3-5 years, and about one third has already changed into grassland. So, the Dutch heathland is rapidly changing into grassland. Although many possible causes of this degradation are reported (such as ineffective management, lowering of groundwater levels and stress from excessive recreation), it is obvious that air pollution and the resulting soil acidification and N eutrophication are key factors in this process. The research carried out as part of the Dutch Priority Programme on Acidification was focused on direct and indirect effects of SOx, NO,, and NH, on udominantnheathland species (Calluna and grasses) and on urare” species (Arnica montana, Viola caninae). No research was carried out on the effects of ozone on heathland vegetation. The most important findings of the heathland research are:

-

At the ecosystem level, nitrogen input ultimately leads to the elimination of slow-growing species by fast-growing species, but Calluna will not be crowded out by grasses at nitrogen deposition levels up to 150 kg N ha-lyr-1if its canopy remains closed. Opening of a Calluna canopy can be caused by stress factors such as frost, drought, heather beetle plagues, or by natural ageing. Under normal conditions in The Netherlands, the canopy will hardly ever be opened by natural ageing. The critical nitrogen load for replacement of open Calluna canopy by grasses is about 10-15 kg N ha-lyr-1 (700 - 1100 mol, ha-lyr-1). At this critical deposition level, vital heathland can be maintained with a sod-cutting frequency of once every 50 years. Both experimental research on Calluna and modelling work on Calluna (in competition with Deschampsia) and Erica (in competition with Molinia) indicate the same critical load of 10 - 15 kg N ha-lyr-1.This is illustrated in Figure 10. With grazing and very frequent sod-cutting (once every 10 years) a vegetation of Calluna or Erica, though without rare species, can be maintained at nitrogen deposition levels up to about 30 kg N ha-lyr-1. (Present N deposition on Dutch heathland is approximately 35 - 40 kg N ha-

412 1yr-1.).

- At the individual plant level, nitrogen input (as NH3 or (NH4)2S04) causes growth stimulation even at low dosages. In rare heathland species however, changes may occur that make them more sensitive to frost, drought, and plagues. A critical level of N H 3 cannot be exactly defined, but is probably in the range of 5 - 10 pg.m-3 (long-term).

- The decline of rare heathland species is probably due to direct effects of gaseous SO2 and soil acidification. Adverse effects of SO2 on more than 5% of th e heathland species can be expected a t long-term average concentrations above a critical level of 8 pg.m-3. Effects on dominant species (Calluna and grasses) will probably not occur at the current SO2 levels in The Nether1ands.Crowding out of Violion caninae by grasses can also take place, but is probably only important at nitrogen deposition levels above the current ambient level in The Netherlands. However, this level may affect the reproduction or establishment of Violion caninae.

atmospheric nitrogen deposition 20 k~ N ha ' y r

C'D=5:1

5 60 8 a-D

.

40 20

0

0

--4

#

8

12

yea,

IS

20

40 r.

20

\

24

0

1

8

22

. IS

20

2,

YBBl

Figure 10.Model results of interaction between Calluna and Deschampsia at two levels of atmospheric nitrogen deposition. C:D=ratio between Calluna and Deschampsia at the start of the simulation.

413

7.

FINAL CONCLUSIONS

The impact of acidification on forest ecosystems in The Netherlands cannot directly be expressed in terms of (a percentage of) forest decline; there is no monocausal relationship between acid load and forest vitality in terms of needle loss and discolouration. Acidification plays a certain role (a role that is very difficult to quantify) but it is not the only factor. In general, its impact is a weakening of the resistance of the tree, making i t more vulnerable to other stress factors. Changes in the nutrient status of the tree play also a key role here. Consequently, in the Dutch situation the occurrence of visual damage related to acidification has to be expressed in terms of risk and cannot be predicted with dose response relationships. Abiotic changes in forest ecosystems in The Netherlands have been demonstrated, but its resulting impact on forest health is a risk problem. The greater the exceedance of the critical loads of the ecosystem and the longer it lasts, the greater the risk of damage by attack of traditional stress factors like frost and drought, pests and plagues. 8.

LITEXATURE

Schneider T. and Bresser A.H.M., 1988 Summary report; Acidification research 1984 - 1988, Report nr. 00-06 Winkel Kde, 1988 Ammoniak-emissiefactoren voor de veehouderij Publikatiereeks Lucht, nr. 76, Ministerie VROM, 1988 Annual Air Quality Report, 1989 (in Dutch) Rapport nr. 222101006, Laboratory for Air Research, National Institute of Public Health and Environmental Protection, 1990

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T. Schneider (Editor). Acidification Research. Evaluationand Policy Applications 0 1992 Elsevier Science Publishers B.V. All rights reserved

415

ACIDIFICATION RESEARCH IN SWEDEN HBkan Staaf and Ulla Bertills Swedish Environmental Protection Agency, Research Department, S-171 85 Solna, Sweden

Abstract A number of acid rain research programmes have been conducted in Sweden since 1978. The total cost for these programmes has amounted to about 250 million SEK, and during this period an additional 950 million SEK has been used to finance practical countermeasures, mainly lake liming. Acid deposition has caused damage to soils, lakes, groundwater, flora & fauna, buildings and materials. The role of acid rain in causing forest damage is not yet fully elucidated. However, there is strong evidence suggesting that ongoing soil acidification and nutrient imbalances associated with it pose the major threat to Swedish forests. Current ozone levels are damaging trees on the physiological level, but the effects of ozone on forest production is unknown. Liming is an efficient means of counteracting the negative effects of acidic deposition on forest soils, lakes and watercourses. 1. BACKGROUND

Acid rain research in Sweden has played a n important role in Swedish environmental history. Swedish scientists identitied the acidification problem a t an early stage, and the political system responded quickly. The connection between emissions of acidic substances and effects on the environment was established as early as 1967-68. As a result, environmental authorities took steps for reducing sulfur emissions, starting in 1969. Initially, most research was directed towards surface water acidification, since it caused obvious damage in the form of declining fish populations. Studies made between 1970 and 1975 showed that liming could counteract surface water acidification. Thus, in 1976 a large-scale lake liming experiment was started. Since 1982 a liming programme for lakes and watercourses f h d e d by state grants has been fully operative. The first integrated acidification research programme, started in 1977178, dealt with ecological effects on soil, surface water, forest, flora and fauna. Since then, several other programmes have been initiated. The total expenditure for these programmes during the period 1977178-1990191 has amounted t o about 250 million SEK (40 million US$). During this same period a n additional 950 million SEK has been spent on monitoring and countermeasures, notably lake liming. Research programmes are currently running in the following fields:

416

* * * * *

*

Ecological effects; soils, groundwater, forests, crops, flora & fauna Surface water acidification - effects and remedial measures Corrosion of underground structures and installations Liming and revitalisation of forests Protection and restoration of historical monuments Effects of soil and water acidification on human health

PO

Foresl.soi1 and groundwalel

H Surface water H Ljming experiments0-0

- 14

soil and groundwater

Buildings and maleria1s

/I / I / I

..i\ I

I

79

81

-8 -6

c77

:lo

I -

83

85

87

89

9lyear

Figure 1. Allocation of funds to W e r e n t areas of acid rain research in Sweden, 1978-1990. 2. DEPOSITION OF ACIDIFYING SUBSTANCES

Sweden stretches about 1 500 km from north to south and represents a considerable deposition gradient. Wet (bulk) deposition of H varies from about 0.05 keqhdyr in the far north to 0.5 keqhayr in the southwestern part. Dry deposition of sulphur and nitrogen compounds to different ecosystems has been mapped using EMEP-data, calibrated against throughfall measurements from about 80 forest sites. GArdsjon, a mixed deciduous forest area on the Swedish west coast, represents an area with high deposition load in Sweden. Here, the deposition of potential acidity is 2.8 keqhdyr, divided on the following components: - SO&30, 1.4 keqhdyr (48%) - NOx/NO, 0.7 " (26%) -" H i 0.7 " (26%)

417

An analysis of air and rain chemistry recordings made a t five EMEP stations in Sweden showed that from 1979 t o 1987 concentrations of sulphur dioxide and particle-bound sulphate generally decreased and NO, concentrations remained about the same, while the wet deposition of sulphate, ammonia and nitrate increased. Although total sulphur deposition seems to have decreased during the 1980s) a t least in southern Sweden, unfavourable climatic conditions counteracted the positive effects of reduced emissions (Figure 2). Throughfall measurements in southern Sweden have revealed a considerable spatial variation in the deposition of sulphur and nitrogen compounds. Exposed hills and forest edges receive the highest loads. Nitrogen deposition has been found to decrease markedly when moving inland from coastal areas. For sulphur, geographic gradients are less steep. Instead, tree stand characteristics are important in determining deposition rates. Thus, the total deposition of sulphur in deciduous forest and Scots pine stands generally increases by a factor 1.2-1.5 in relation to wet deposition, while for Norway spruce the corresponding factor is 2-3. Foreign sources play a major role in both sulphur and nitrogen deposition. On a national level, the Swedish contribution is 10-15%. In southwestern Sweden the domestic contribution to nitrogen deposition is higher (20-25 %) and is mainly in the form of ammonidammonium (Table 1). Table 1 Deposition of acidifying substances in the southernmost part of Sweden (province of SkAne), in 1988, according to EMEP data (Anonymous 1990) Total sulphur Deposition, kg N h d y r

Total nitrogen

NHJNH,

17

11

5

10

10 16

20 19 17 10 7 6 4 4 10 3

38 9 24 4 5 5 2 3 10

100

100

100

Proportion contributed by countries (%) Sweden Germany, West Denmark Great Britain Germany, East Poland France The Netherlands Others Unattributed Total

9 23 8

17 7

0

418

20

-

10

-

RORVIK 20

BREDKALEN

-

10 -

2 1

2 ' -

-

0 1979

1981

1983

1985

1987

0 1979

1981

1983

1985

1987

Figure 2. Estimated sulphur deposition at two Swedish EMEP stations from 1979 to 1988 at Riirvik (southwestern Sweden) and Bredkalen (north-central Sweden). Estimates were made with the EMEP model based on the following assumptions: 1) actual emissions, identical climate every year 2) actual climate, constant SO, emissions in Europe (After Lovblad 1990) 3. ENVIRONMENTAL EFFECTS

3.1. Soil acidification National Forest Survey data for 1983-1987 show that forest soils are least acid in northern Sweden and that the degree of acidity increases southwards. Analyses show that large areas of forest in southern Sweden have a pH value in minerogenic soil under 4.4,i.e. the level at which free inorganic aluminium begins to appear in large quantities in soil water. In total, the area affected is around 650,000 ha, of which approximately 300,000 ha is found in southwestern Sweden. We now have clear evidence that uncultivated soils in southern Sweden have become acidified t o a considerable extent over the last few decades. The strongest evidence for this has been obtained from studies where previously examined soil profiles have been re-examined. Reported reductions in the pH of forest soil over the last 10-55 years in southwestern Sweden are mostly around 0.3-1.0 pH units, but in individual cases, reductions as high as 1.5-2.0 pH units have been observed (Figure 3). In other parts of southern and central Sweden the reductions have been lower and in the northernmost parts of Sweden no acidification caused by air pollution has been found. Soils with a high pollution load seem to be sulphate-saturated to great depth, and leaching of sulphate has resulted in a 30-70% decrease in exchangeable stores of base cations in southernmost Sweden over the last four decades. Chemical balance calculations also suggest that easily available stores of calcium and other base cations are decreasing by 1-2 per cent annually.

419 p l i chunge

0

o &ech forest Other deciduous forest A Noway spruce forest

0

.

h.0: 0 0 0

0 0 0 0

*no0

0 .

I

Figure 3. pH changes in the A horizons of 104 forest and pasture soils in the southernmost part of Sweden over a period ranging from 14 to 35 years. The final sampling was made 1984 or 1985. (After Falkengren-Grerup 1987) The greatest pH reductions have been found in soils of medium fertility with relatively high original pH values, i.e. in the ion-exchange buffer range. The acidification front currently lies a t several meters depth in calcium-poor moraine soils in southwestern Sweden, where it has reached superficial groundwater. Further to the north and to the east, acidification is more superficial. About half of the acidification of the surface layer of forest soils that has occurred since the 1920s can be attributed to biological acidification caused by forest growth and timber harvesting. Acidification of deeper soil layers can only be explained by the deposition of acid, mainly sulphuric acid. Thus far, nitric acid has contributed only slightly to acidification of mineral soil, groundwater and surface water in Sweden. Nitrogen leaching from Swedish forest soils is generally low, normally below 1 kg Nhdyr. Long-term monitoring of watercourses has not revealed any increase in nitrate leaching in northern Sweden during recent decades. However, increases in nitrate concentrations in soil water and small streams have been recorded a t forest sites where nitrogen deposition in throughfall exceeded 10 kg NO,-Nha'yr, indicating that nitrogen saturation is approaching in certain areas in the southernmost part of Sweden. The reasons for the increased nitrate leaching are still unclear. Nitrification in the soil profile of a spruce forest a t SoderAsen (province of SkPne) that showed extensive nitrate leaching was very low. Thus direct leaching of deposited nitrate would appear to be the most probable mechanism.

420

3.2. Groundwater Acidified groundwater has been reported from large parts of Sweden throughout the 1980s) particularly in areas where soils and lakes are acidified. Acidification is usually worst in shallow groundwater and diminishes with depth of the water table. Shallow wells are particularly affected in calcium-poor areas of southern Sweden and in certain coastal areas in the north. The problems are most pronounced for private water supplies. About 400,000 wells are used by permanent residents, and from 1985 to 1988 government grants were available for de-acidifying household water from private wells. Evidence that acidification is increasing has been obtained from inventories of private water supplies carried out between 1984 and 1986 and from data on municipal water supplies, as well as from groundwater measurements made by the Swedish Geological Survey and the Swedish National Monitoring Programme. We now foresee an increase in the acidification of groundwater in large areas of Sweden. Particularly in areas receiving a heavy load of acidifying substances, markedly increased aluminium levels appear in shallow groundwater. As soils are acidified to greater depth, an increase in the transport of aluminium and cadmium to the groundwater can be expected. As a result of the corrosion of plumbing systems, sharply raised levels of copper have been found in drinking water from many private wells throughout Sweden. During the last decade, copper in drinking water has been suggested to be a cause of diarrhoea in small infants and children in Sweden. However, the relationship is still unclear, and further studies in this field are underway. 3.3. Lakes and watercourses

Biological and chemical analyses of water have shown that most Swedish lakes and watercourses have been affected by acidification. About 16,000 of Sweden’s 85,000 lakes are so badly affected by acidification that sensitive species have drastically declined in number or disappeared completely. Almost 6,000 of these lakes have been limed. The acidification situation for Swedish watercourses is less well known. Estimates suggest that at least a quarter of the total length of watercourses would be seriously damaged by acidification if it were not for liming. The acidification of lakes and watercourses takes place primarily as a result of chemical and physical changes in the catchment area. A good general understanding of acidification history has been achieved by combining results from long-term monitoring of individual lakes, paleolimnological studies and modelling. The biotic changes associated with acidification have also been reasonably well documented. This is especially true for the inhabitants of open water and associated food chains. The response of littoral communities in lakes has been less well studied. Large areas in southern Sweden have chronically acidified surface waters with low pH, no alkalinity and high aluminium levels the year around. Here, soil acidification has penetrated so deeply that even deep-flowing groundwater supplies very little alkalinity to the waters. In northern Sweden numerous watercourses are periodically acidified - usually after heavy

42 1

rainstorm events in autumn and during snow-melt in spring. Results from a catchment study in northern Sweden indicate that dissolved organic acids can play a major role in these acid events, and that this acidity originated within a few meters from the stream. Most small streams in northern Sweden are surrounded by moist, humus-rich zones which appear to be important for short-term surface water acidification in northern, humid areas. Acid events can be very pronounced even if the soils are largely unaffected by acid rain. The acidification situation in the southern and coastal parts of northern Sweden has not changed to any great extent since the mid-1970s. By contrast, in mountain and submontane regions in northern Sweden, it has continued t o deteriorate over the last 10-15 years. Damage to minor watercourses in the southern part of the mountain region and in adjacent areas increased considerably in the 1980s. Both low pH and high aluminium concentrations seem t o be harmful to biota in acid lakes and streams. For benthic invertebrates the pH itself seems to be more important than aluminium concentrations in explaining the response and distribution patterns, but species resistant t o low pH generally tolerate elevated aluminium concentrations as well. However, for certain fish species, e.g.salmonids, aluminium is considered to be a main factor limiting their survival in acid waters, Generally, it appears as though biotic changes in response to surface water acidification can be ascribed to biotic interactions in the food-chains combined with abiotic stress on a long-term or short-term basis, giving different physiological and behavioural disturbances, but also favouring certain species. Nu mr d species

m a

60 50

0

40

30 20

'

10 '

o

h

I 1

4.5

.

I

.

5.0

5.5

6.0

6.5

7.0 pH

Figure 4. Number of phytoplankton species in lakes in southwestern Sweden in relation t o their pH (summer values) (After Eriksson et al. 1983)

422 3.4. Forests

Forest damage, in the form of needle loss and crown thinning, became noticeble in southern and central Sweden in 1983, particularly in coniferous trees. In national inventories made between 1984 and 1990 crown thinning (more than 20% needle loss) was evident on an average of 24 per cent of the Norway spruce trees and 13 per cent of the Scots pine trees. Only about 1 % of the trees were classified as seriously damaged (suffering more than 60 per cent needle loss). Birch, oaks and beech also showed considerable crown thinning. An analysis of the various surveys made show that forest damage varies considerably a t both regional and local levels. The degree of damage increases with stand age, but in most cases no straightforward relationships have been found between forest damage and emission sources or soil conditions. In the case of Norway spruce, the most extensive damage is found in inland areas of northern Sweden, probably because these forests tend to be very old and the climate is harsh. Differences between northern and southern Sweden are considerably smaller for Scots pine. The causes of forest damage in Sweden are still uncertain, but most scientists favour the multi-stress hypothesis. Mean monthly concentrations of sulphur dioxide and NOx in background areas of southern Sweden are generally below 5 ug/ms air, even in winter, which is considerably below damaging levels.

1

.\

\

*

'\

-NPK

\: \

.

11

0

300

kg H,SO,

600

900

. ha-'

Figure 5. Basal area growth of young Scots pine forest from 1972 to 1984 in plots given different doses of sulphuric acid. A field experiment in central Sweden (After Tamm and Popovic 1989)

423

Ozone concentrations, on the other hand, are near the critical level thoughout Sweden. Studies on Norway spruce subjected to different ozone levels in open-top-chambers for 5 years showed that the current ozone level in southern Sweden causes ultrastructural damage to needles and reduces the rate of photosyntesis. Indirects effects of acid deposition, especially soil acidification and nutrient imbalance, are probably the most severe threats to the long-term vitality of Swedish forests. Long-term studies indicate that nutrient concentrations in conifer needles in southwestern Sweden have changed over the last twenty years - i.e. nitrogen concentrations have increased while those of most other nutrients have decreased - which might be indicative of an approaching nutrient imbalance. Low base cation stores and increasing concentrations of Al3+ in the soil solution might impair the uptake of phosphorus, potassium, calcium and magnesium, and eventually some of these elements could become limiting for forest growth. However, there is still no example of tree growth responding to a supply of any of these nutrients in a Swedish fertilizer experiment, unless added together with nitrogen. The initial response of forest trees to soil acidification may be an increase in growth. This is suggested by two acidification field experiments in which sulphuric acid was added to the soil for eight years. Plots given moderate doses of acid (up to 600 kg H,SO,/ha) showed increased tree growth, while higher doses of sulphuric acid did not result in a growth increase. These experiments were performed in north-central Sweden, where the acidic load is relatively low, and although the treatments caused losses of available calcium and magnesium from the soil they did not induce any nutrient changes in the trees. To study how trees growing on an acidified soil respond t o stress, a long-term field experiment was started a few years ago at Skogaby in southwestern Sweden. Thus far, both drought stress and the addition of ammonium sulphate have resulted in slightly reduced growth. We do not know the extent t o which air pollution contributes to the forest damage observed in Sweden. Air pollution affects the forest both positively and negatively, and to date it seems as if heavy nitrogen deposition has increased forest growth. However, it seems probable that soil acidification and ozone have been partly counteracting this growth-enhancing effect.

3.6. Crops Crops may be affected directly by gaseous and particulate air pollution and indirectly via soil acidification. Ozone is probably the atmospheric pollutant causing the greatest damage. Levels of ozone in Sweden during the summer months commonly approach or exceed threshold concentrations above which crop damage can occur. Field studies have shown that current ozone levels reduce the yield of spring wheat by approximately 10 per cent in western Sweden, whereas barley seem to be less sensitive. Economic losses associated with anthropogenic ozone-caused yield reductions have been estimated to be 1.4 billion SEK per year for the period 1986-88. Injury to ley, oats, potatoes, winter wheat and spring wheat accounted for most of the losses. Air pollution in the form of acid deposition, together with harvesting, fertilisation and leaching, contributes to the acidity of agricultural land. The

424

relative contributions of these acid sources to acidification have been estimated to be: acid deposition 12 %, harvesting 20 %, use of fertilisers 32 %, and leaching 36%. Compilations of land survey data from the National Board of Agriculture (1958-1961) show that the acidity of soils has not changed much in recent decades. The optimal pH value for arable soils is usually 6.0-6.5, which is considered to provide satisfactory protection against absorption of heavy metals, particularly cadmium, by crops. About 45 per cent of the arable hectarage in Sweden has a pH lower than 6.0 and approximately 15 per cent has a pH value lower than 5.5. These acidity levels are not strongly related to the amount of acid deposition, since the worst lime/calcium situation is found in the two northernmost counties, where deposition is low. The pH of arable land is determined primarily by the type of soil, the crops grown and the amount of liming carried out. 3.6. Flora and fauna It has long been known that acidification of lakes and watercourses causes great changes in aquatic plant and animal life. Knowledge of the effects of air pollution on terrestrial flora and fauna is, however, still very patchy. Air pollution has afTected plant and animal life directly through the effects of gases, acid rain and acid water, and indirectly as a result of changes in nutrient availability and elevated levels of toxic metals in the ground. In addition, secondary effects have resulted from changes in competition, food availability and physical properties of the habitat. Extensive changes in epiphytic mosses and lichens have been observed in southern Sweden. Many species have disappeared over the last 40 years, while others are presently endangered. Nitrogen-f~ng lichens containing blue-green algae are most threatened. This group comprises about 130 species, or 6 per cent of all Swedish lichen species. Lichen disturbances can be ascribed mainly to the direct effects of nitrogen compounds and acid rain. The vascular flora in southernmost Sweden, including trees, herbs, grasses and ferns has changed over the last 15-35 years, particularly in deciduous forests. Populations of many species preferring neutral or only weakly acid soils have declined, while others with a preference for nitrogen-rich environments have tended to increase. The same tendency has been observed for hngi. These changes are probably due to soil acidification and increased nitrogen deposition. Air pollution effects on the terrestrial fauna are of an indirect nature and are generally most pronounced for species preying on aquatic organisms or reproducting in aquatic habitats. This category includes many insect species and some species of birds. As acidification increases, the amount of available calcium in the soil is reduced. This has had severe effects on populations of land snails in several parts of southern Sweden. There are also signs that the number of overwintering coniferous forest birds has diminished in areas of damaged forest in southwestern Sweden. This decline may be linked to changes in spider populations (a source of food for the birds) resulting from the the thinning out of tree crowns. Thus, it appears as though plant and animal life in the forests of southern Sweden, as well as in marshes and in other uncultivated areas are

425

changing as a result of acidification. The terrestrial fauna is probably changing more slowly, with the exception of species dependent on lime-rich environments. Air pollution mainly affects the fauna by causing reproductive disturbances, and such effects take a long time to surface in the form of population changes. There is therefore a significant risk that faunal changes are taking place, even though we have not yet detected them.. 3.7. Human health Air pollution poses a threat t o human health in two quite different ways: First, potential risks arise when people are exposed directly, by inhaling acid air pollutants. Second, acidification will change the level of exposure of several metals and metaloids via food and drinking water. In the latter field, only limited research has been performed. However, these aspects are currently included in two research programmes that started earlier this year (1991). One of these aims a t developing models and methods for evaluating health risks caused by air pollution. The other programme will focus on the indirect effects, mainly via effects on solubility of metals in the environment. 3.8. Buildings and materials The first integrated research programme with the aim of studying the effects of acid rain on Swedish cultural heritage was started in 1988. First, surveys were performed t o estimate the extent of damage to various objects, notably stone buildings, bronze statues and monuments, mediaeval glass paintings, sensitive textiles, runic stones and bronze age rock-carvings. Thereafter the restoration and conservation of threatened objects in all the above mentioned categories is t o begin. Projects of more basic character have also been initiated. The largest of them concerns weathering mechanisms in sandstone and limestone materials. Other projects are directed towards the study of mineral weathering in granitic rocks and the effects of lichens on decomposition of rock material. Lichen growth on rock-camings and runic stones appears to be an increasing problem: Research is also underway on corrosion of installations in contact with acid soil and water. Corrosion affects the longevity of pipes, cables, cisterns, foundations and other structures in the ground. Zinc is the metal most sensitive to acidification, and corrosion of zinc strucures increases as the pH and alkalinity of water decreases. Lead is also considered to be sensitive to acidification, as are copper, cast-iron and carbon steel. Among other materials, concrete is affected negatively by acidification, whereas plastics generally resist acidification well. Water pipes and road culverts, etc., are often exposed simultaneously to acid soil and acidified water. Approximately 60 per cent of the municipal water supply network is made of cast-iron, while copper is the most common material used for pipes in indoor plumbing systems. The occurrence of corrosion damage in water pipes in Sweden is generally most serious in acidified areas. The Corrosion Institute carried out a study on the situation in the early 1980s, a t which time it was estimated that approximately one third of all indoor corrosion damage was due to acidification. It is not

426

possible at present to estimate the total economic loss resulting from such acidification-caused damage. 4. AMELIORATION OF

DAMAGE

4.1. Forest liming

A Swedish programme to counteract forest soil acidification was started in 1983. Initially a number of old liming experiments were reinvestigated and evaluated. In addition, a new set of field experiments on forest liming were started. Tree growth, soil chemistry and soil biology, as well as effects on surface water and flora & fauna, are being monitored in these experiments. Results of the old experiments demonstrate that the application of 5-10 tonnes limeha to forest soils results in long-lasting (more than 50 years) effects on pH, base saturation, exchangeable base cations and aluminium concentration. In the new experiments about 3 tonnes limeha was added in most cases. As a result many large soil animals, such as earthworms, molluscs, diplopods and isopods, were favoured while small ones, e.g. mites, nematodes and enchytreaeids, decreased in number. Active hngal hyphae and bacteria were not affacted to any great extent nor was any damage to mycorrhiza noted. On dry, nutrient-poor soils liming led to a depression in tree growth lasting 10-20 years, followed by a slight enhancement of growth. On more fertile sites this initial growth reduction did not take place, and in some cases a positive growth effect was noted soon after applying the lime. Laboratory studies on soils with different nitrogen contents were set up to explain these observations. These studies showed evidence that the growth response of the trees was determined mainly by the effect of lime on nitrogen mineralization. In nitrogen-poor soils liming induces a decrease in net nitrogen mineralization, thereby reducing the nitrogen supply to trees. A single lime dose of 2-5 tonnesha is recommended for acidified forest soils, but the knowledge base needed for making detailed recommendations is still incomplete. Liming is considered as a long-term measure for soil amelioration. Thus far, Swedish experiments have only produced a few results indicating that tree vitality can be improved by treating soil with limestone, dolomite, wood ash or industrial slags. Additional field experiments have recently been established to evaluate combinations of lime and various fertilisers in terms of their potential for counteracting future acidification-induced nutrient imbalances in trees. 4.2. Liming of wells and groundwater supplies

Different methods for neutralizing acid groundwater supplies have been tested in practical experiments. Good results have been obtained for; (i) recirculating well water over a bedding of sand and lime placed in the ground near the well, and (ii) placing a mixture of lime and sand in a ditch around or beside the well. With these methods positive changes of the well water with regard t o pH, alkalinity and content of iron and aluminum were generally achieved within one year. Other methods have been less successful, e.g. placing lime on the ground

427

over all or part of the watershed of the well. About 10 experiments of this type have been performed, and although large doses of lime were used, up to 50 tonnesha - sometimes applied as a slurry, the lime apparently penetrated the soil very slowly. Although the water quality in the wells has been monitored for up to 7 years after treatment no great effect has been noted so far. 4.3. Liming

of surface waters The Swedish liming programme is practically oriented. Thus, much of the research activies have been directed towards follow-ups to see if the practical liming operations gave the desired positive effects on water quality and aquatic life. Research on mechanisms have thus far been rather limited. Most liming operations are performed by applying finely ground calcium carbonate from a helicopter o r boat directly to the lakes. This procedure is often supplemented by wetland liming and installations of dosers in streams. Generally the desired chemical targets for surface water, i.e. pH above 6, alkalinity above 0.05 meq/L, and reduced levels of toxic aluminium, are easily achieved by lake liming using fine-grained limestone. In addition to these changes, colour increases in limed clear-water lakes and increases in phosphorus levels often occur. Thus, liming results in increased nutrient supply and detoxification of the water. Improvment of the chemical conditions in limed lakes and watercourses generally results in great changes in the lake biota. Although there is often initially a drastic rise in the abundance of certain opportunistic species, biological diversity soon increases. A progressive increase in populations of acid-intolerant species, followed by recolonization, generally takes place. However, certain relatively immobile species like crayfish, snails and mussels normally recolonize very slowly, and this is sometimes also true of fish. Reintroduction of fish species may be necessary in severely acidified areas where acid-sensitive species have been eliminated over large areas or whole water-systems. 5. CRITICAL LOADS

The critical acid load for surface water in Fennoscandia has been determined using the steady-state water chemistry method (Henriksen et al. 1990). In Sweden the mapping was based on data from 4 018 lakes sampled during a national lake survey made in 1990. Although a wide variation exits in sensitivity both within and between mapping grids (50x50 km) it is clear that the present deposition exceeds the critical load of the most sensitive lakes throughout the country. The critical load, based on a n ANC limit = 0.50 meqil, is exceeded for 46% of all lakes in the country. In southwestern Sweden the critical load is exceeded for up to 75-100% of the lakes, while the correspondig figure for the northern part is around 25%. The results also show that even with a 50% reduction of the acid deposition, about 15% of the lakes, mainly in southern Sweden, would still remain acidified, and that a reduction of more than 80% is needed to protect more than 95% of the lakes.

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The critical acid load of forest soils has been determined for 1392 individual sites in Sweden using the PROFILE model (Sverdrup et a1 1990) based on geochemical data from soil samples collected by the Swedish Forest Survey. The results of the calculations confirm that Swedish forest soils are very sensitive to acid deposition. Of the Swedish forest area with moraine soils, 85% receives acid deposition in excess of the critical load, and sensitive soils occur throughout the country (Figure 6). A minimum deposition reduction of 83% is required to protect 95% of the forest area from being damaged in the long run. Such substantial reductions in acid deposition imply that both sulphur and nitrogen deposition must be reduced.

Figure 6. Critical load of acidity and exceedance of critical load for moraine forest soils in Sweden (5 percentile). The calculations were made with the PROFILE model and mapped using 50x50 km grids (Sverdrup, Warfvinge, Ros6n and Melkerud, unpublished).

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6. REFERENCES

Anonymous. Air Pollution '90. Swedish Environmental Protection Agency Informs. Solna. (1990). Eriksson, F., Homstrom, E. Mossberg, P. and Nyberg, P. Ecological effects of lime treatment of acidified lakes and rivers in Sweden. Hydrobiologia 101 (1983) 145-164. Falkengren-Grerup, U. Long-term changes in pH of forest soils in southern Sweden. Environmental Pollution 43 (1987) 79-90. Henriksen, A., Kiimiiri, J. Posch, M., Lovblad, G. Forsius, M. and Wilander, A. Critical loads t o surface waters in Fennoscandia. Nordic Counsil of Ministers, Copenhagen. Environmental report 1990:17.(1990). Lovblad, G. Concentrations and deposition of air pollutants in back-ground areas - temporal and spacial variations. Swedish Environmental Protection Agency, Solna. Report 3812. (1990). (In Swedish) Sverdrup, H., de Vries, W., Henriksen, A. 1990. Mapping critical loads. Nordic Counsil of Ministers, Copenhagen. Environmental report 1990:14 (1990). Tamm, C.O. and Popovic, B. Acidification experiments in pine forests. Swedish Environmental Protection Agency, Solna. Report 3589. (1989).

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T. Schneider (Editor). Acidification Research. Evaluation and Policy Applications 1992 Elsevier Science Publishers B.V.

43 1

Finnish Research Programme on Acidification (HAPRO) 1985-1990 Pekka E. Kauppi Finnish Forest Research Institute, Unionink. 40 A,

SF-00170Helsinki. Finland (Director of HAPRO in 1984-1990 a t the Ministry of the Environment, Finland)

Abatxact A programme for research on acidification in Finland (HAPRO) was organised in 1985-1990.Sulphur deposition, estimated using a n atmospheric transport model a n d checked a g a i n s t m e a s u r e m e n t s , decreased from s o u t h to north. The same spatial gradient was observed for sulphur concentrations in lake water samples. This spatial correlation indicates a causal link between (European) sulphur emissions and t h e presence of excess s u l p h u r i n t h e Finnish environment. Nitrogen concentrations in lake water were insignificant indicating uptake of nitrogen in terrestrial systems. Various biological effects were detected in aquatic ecosystems and in forests. However, forest resources in terms of growing stock and wood growth were not affected. Policy implications of the programme with regard to the use of natural resources, air pollution abatement and research management a r e discussed in this chapter. 1.INTRODUCTION Before 1985,there had been little research in Finland on acidic deposition, in comparison to t h e neighbouring Nordic countries Norway and Sweden [see, however, 1-31. A reason for this was t h a t there were no alarming large scale impacts similar to, for example, t h e fish kill in Soerlandet in Norway. The F i n n i s h t o p o g r a p h y i s s m o o t h , w i t h o u t s i g n i f i c a n t m o u n t a i n ranges. Upstream lakes which are sensitive to acidification have only sparse and scattered trout populations. Other fish species are less interesting to the fisherman and, moreover, a r e more tolerant of acid conditions. In Finland, as in Norway and Sweden, fishing is popular and important but is practised almost exclusively in large downstream lakes and in the Baltic. These ecosystems are relatively insensitive to acidification damage. Forests and forest industries are of the utmost importance in Finland and much information about forests has been collected through the decades, especially a s regards timber production and utilization [4].About one half of the ex-

432

port revenue of t h e Finnish economy is from t h e forest sector. Forests and lakes are the main characteristics of the Finnish landscape. In 1983-1984the impacts of acidic deposition on aquatic ecosystems in southe r n Scandinavia were thoroughly understood. The role of t h e long range transport of sulphur compounds had been established. Alarming news were released on the status of German forests. There was much concern in Finland a s in many other countries on t h e s t a t u s of t h e environment. There were widespread opinions urging additional research. 2.

THE HAPRO PROGRAMME

In April 1984 t h e government of Finland decided to s e t u p a special programme for acidic precipitation research. A time frame and a budget plan were established. A General Plan for the programme was released in early 1985,with objectives a s follows 151: "The programme is concerned with the development of acidification caused by sulphur and nitrogen emissions and, more generally, with t h e problems associated with air pollution. The aim of t h e HAPRO programme is to study cause-and-effect relationships in air pollution and, on that basis:

-

-

to determine the extent of regional effects of air pollutants in Finland to study whether the harmful effects of a i r pollutants are on the increase to determine which a r e a s and components of t h e environment are being especially threatened t o assess what measures would most effectively, and a t the lowest cost, reduce the harmful effects of air pollutants."

Only a short time was allowed for establishing t h e research, and in 1985 about 50 full-time and 100 part-time scientists were already engaged in 38 individual projects. The volume of the work remained approximately a t this level until the year 1990. The programme secretariat consisted of the director, three members of the professional staff and two members of the technical staff. The government established a n advisory board which, assisted by a technical ad hoc group, supervised t h e programme, examined and confirmed t h e major decisions, especially those concerning finances. The main programme report, t h e book "Acidification in Finland", was released in August 1990 [61. There are 62 individual research articles by a total of 145 authors contained in one volume of 1237 pages with 440 figures. An international committee of experts reviewed all t h e material offered for the book during a one-week meeting in June 1989.The members of the programme secretariat, on the basis of this material, prepared a n assessment report in collaboration with two programme scientists [71. T h e m a i n outcome of t h e HAPRO programme is summarised i n this chapter.

433

3. PRINCIPAL FINDINGS

3.1. Pollution climate Annual mean concentrations of sulphur dioxide in rural areas were 6 to 12 pg/m3 in southern Finland a n d 2 to 6 pg/m3 in northern Finland. Seasonal peaks occurred in winter, when the concentrations in southern Finland were 5 to 10 times higher than the lowest values measured in August. Monthly mean concentrations during the growing season were between 1 and 2 pg/m3. Three quarters of the sulphur in the air was in the form of S 0 2 , the rest being sulphate. The concentrations of NO2 in the rural parts of southern Finland varied between 4 and 7 pg/m3 i n winter a n d between 2 and 4 pg/m3 in summer. Ozone concentrations peaked in March-April ( a t 70 to 90 pg/m3) and were the lowest in December-January (35-50 pg/m3). In southern Finland, high concentration episodes of all the pollutants were mainly associated with south-easterly, southerly or south-westerly winds [81. The deposition of sulphur varied between 0.7 to 1.2 g/(m2a) i n southern Finland and 0.2 to 0.4 g/(m2a) in northern Finland according to measurements taken by monthly sampling of bulk deposition collectors [91. The same deposition gradient but slightly higher absolute values were estimated using atmospheric transport models [ l o ] . The impact of two large smelters in t h e Kola a r e a in Russia on t h e pollution climate was observed in north eastern Finland [lo, 201. The deposition on deciduous forests was roughly the same a s on the bulk collectors. However, on conifer stands it was up to twice a s much 1111. The deposition of Ca was substantially higher in south eastern Finland than in other parts of the country. This was largely because of the use of oil shale for energy production in Estonia about 100 kilometres south across the Baltic sea 1121, and was from 0.5 to 0.8 g/(rn2a) 191. It thereby had the potential of buffering 50 to 70 per cent of the acidifying impact of sulphur deposition, assuming no limitations in the chemical contact and reaction kinetics.

3.2. Aquatic effects A synoptic survey of lake water chemistry was carried out during t h e autumn overturn in 1987, following an objective sampling scheme [131. The measured sulphate concentration in 70 % of t h e lakes was higher t h a n 50 peq/l. However, in the northern subregion of the country, covering about one third of the land area, measured sulphate concentrations were above 50 pgA in only 22 % of the lakes [141. Many Finnish lakes a r e humic, "brown water" lakes. High concentrations of organic carbon were found in lakes throughout the country, but especially in lakes in southern and central Finland where the median total organic carbon was 14 mg/l. The organic anions, with a median concentration of 89 peq/l slightly dominated over sulphate, t h e second-most important anion. The median concentration of sulphate was 71 peq/l. I n acidic lakes which have lost their acid neutralisation capacity (ANCeO) organic anions dominated (with a median 88 peq/l) over sulphate (median 54 peqll). The contribution of nitrate in

434

acidic lakes was only 0.8 peq/l [14]. The lakes dominated by organic anions were mostly located in central Finland, on t h e west coast, and in eastern Finland. In the south the lakes were mainly dominated by sulphate and in the north by bicarbonate. The concentrations of organic anions and sulphate were slightly lower in acidic t h a n in other lakes. This indicates t h a t acidity occurs in oligotrophic lakes and is associated with the scarcity of bases rather than with an exceptionally high contribution of acids. I t was estimated that 1300 to 3100 lakes in Finland are acid because of anthropogenic sulphur deposition [ 141. Lake acidity affects biological organisms directly through the low pH and the associated increase of mobile inorganic aluminium. I t can also have a n indirect effect through responses in the food web. Biotic effects were studied in detail within HAPRO in 140 survey lakes, mostly acid lakes located in southern Finland. The species composition of macrophytes, phytoplankton, zooplankton, diatoms and benthic invertebrates were correlated with lake acidity [151. Acidification therefore affected the whole ecosystem. Fish species were ranked in terms of sensitivity t o acid conditions [16].Direct toxicity was observed, especially in the reproductive phase [171. A slow decline of fish populations rather than an abrupt fish kill was the observed response to acidification both in demographic [161 and in experimental 1171 investigations. The synoptic lake survey and diatom investigations on acidification history 1181 were used t o generalize fish investigation results. On this basis, it was estimated that 300-700 lakes have lost one or more fish populations. In addition, acidification has had a significant impact on the structure of fish populations in 800-1600 lakes, i.e. 1.4 to 2.8 % of the total of 56,000 lakes.

3.3. Forest effecte The sampling grid of forest research investigations was linked with t h a t of t h e forest inventory, a national system for monitoring forest resources. The synoptic survey grid was used t o measure soil, vegetation and tree characteristics. Experimental and modelling research was carried out in addition t o the survey approach. The growing stock and t h e growth in Finnish forests have increased substantially in recent decades [4]. Changes in the structure and age distribution of forests have been the primary reasons for this. Acidifying deposition or other forms of air pollutants have not had a significant negative effect on wood production. Early warning signals of potential future damage were investigated in terms of changes in sensitive vegetation and in soils.

A widespread decline of sensitive epiphytic lichens was observed in southern Finland, where the deposition and concentration of air pollutants is highest. Long term monitoring of canopy litter indicated t h a t there has been a gradual decline since the mid 1960s [19]. Elevated concentrations of heavy metals were observed in lichen vegetation in rural forest areas over large regions [20]. Similar patterns were observed in a Nordic study on heavy metal concentration in mosses [21]. Hypotheses of the mechanismk) of the lichen decline were developed but remained untested. Sulphur and heavy metal pollution can

435 induce toxic effects. Nitrogen loading can alter t h e species competition relationships. Despite the lack of direct experimental evidence it is apparent t h a t the change in the chemical composition of the atmosphere has been the major cause of the observed change in lichen vegetation. A link was established between diameter growth and defoliation of individual trees [22]. However, no spatial correlation was observed between defoliation and pollution load on a regional scale [231. The time series of systematic defoliation observations were too short to allow trend analysis and will remain so for a t least five more years. Hence there were no firm observations of trees or tree populations which, on a large regional scale, could be interpreted a s early warning signs of a productivity decline. In experimental research, links were established between the gas exchange of trees and the levels of nutrition and inorganic aluminium in soils [241. Scots pine trees on extreme oligotrophic, dry sites showed adverse nutrition effects in terms of discoloration and growth decline [251. Tree damage was also observed on ordinary soils in the vicinity of heavy metal [261 or ammonium [27] sources. Hence there is evidence of air pollution damage of trees on a restricted geographic scale. The most widespread effects were those caused by ammonium emissions in f u r farming regions 1271. Model calculations indicated leaching of base cation nutrients from the top soil [281, a phenomenon which was also firmly established on the basis of lake survey results 1141 and ground water observations 1291. Air pollutants thus affected tree nutrition over large regions, although marginally, since t h e r e were no major responses in terms of productivity or canopy characteristics. Unfortunately, present models of stand development and growth are insufficient for predicting possible future responses. 3.4. Other individual findings

Agricultural soils, sampled in 1974 and resampled i n 1987, were analysed for their chemical characteristics. Both soil pH and the concentrations of most macro nutrients were higher in 1987 than in 1974 because of liming and the application of fertilizers. The deposition from the atmosphere had a n effect on t h e cadmium concentration in soils [301. Anthropogenic deposition from the air was the main source of heavy metals (Cd, Hg and Pb) in t h e sediments of forest lakes [311. The waste problem of coal fired power plants was studied a s a separate issue. Desulphurization, which will be implemented on a large scale to combat acidic deposition, produces gypsum waste. The amount of wastes will increase significantly in Finland by the year 2000. The largest utilization potential is within geotechnical construction, although there a r e environmental concerns 1321. The potential impacts of forest decline on the international market of forest products was also a subject a r e a within HAPRO. Model scenarios indicated t h a t t h e market mechanisms a r e fairly robust. Only extreme decline, e.g. in central Europe, would have effects on trade flows and prices of Finnish products [33].

436

4. INTERCOMPARISONS AND CONCLUSIONS

H A P R O was a n interdisciplinary programme and yielded particularly valuable results because many research fields were involved. For example, the results of the lake survey were used in order to draw conclusions about the status of forests. The smooth and consistent gradient of sulphate concentrations in lake water followed the spatial distribution of sulphur deposition, a s estimated with the atmospheric transport model (Fig. 1).This is a n important finding for the following reasons. Firstly, it gives credibility both to the lake survey and t o the atmospheric deposition model. Secondly, it indicates the dominance of anthropogenic deposition, since there are no natural sulphur sources that could possibly generate the observed spatial pattern of sulphur concentration in lakes. Thirdly, forests are probably subject to the same spatial pattern of sulphur load because in the Finnish landscape most of the water entering the lakes has percolated through the forest. Finally, as the deposition is described with a model, it is feasible to compute deposition scenarios in order t o evaluate and assess various emission reduction measures. Sulphur deposition in 1987 g/(m' a) Sulphate in lake water

1.2

'

Figure 1. Sulphur deposition (contour lines) and lake water aulphate concentration in 1987 (dot symbols). Each dot represents five lakes.

431

The Finnish research programme was, a s far a s we know, the only national programme where a consistent spatial correlation was established between the model estimated s u l p h u r deposition and t h e spatial pattern of sulphur in ecosystems. This was feasible because of t h e clear gradient of sulphur from south t o north. Moreover, t h e smooth topography of t h e country is a n asset when constructing and testing atmospheric transport models. In addition, the uniform patterns of bedrock and land use facilitate interpretation of synoptic inventories such as the lake chemistry survey (Fig. 2 ) .

Figure 2. Forests, lakes and typical Finnish topography. Photo: Jyrki Luukkonen. The change in lichen vegetation in forests followed the same geographic pattern [19]. I t is unclear whether sulphur deposition has directly affected t h e lichen vegetation. Nitrogen loading and the atmospheric deposition of most heavy metals followed similar geographic patterns. The causal relationships, therefore, remained unclear and should be studied by using an experimental approach. However, i t is apparent t h a t , one way or the other, a i r pollutants have been the cause of a substantial change in lichen vegetation. Measurements on deposition were compared with those on surface water chemistry in order to estimate the role of the different chemical compounds in

438

surface water acidification.The contribution of nitrogen deposition was estimated to be insignificant. The impact of sulphur deposition was quantified against that of the natural sources of surface water acidity. It was established t h a t sulphur deposition affects aquatic biota in various ways especially in southern Finland. One of the specified research objectives was "to study whether the harmful effects of air pollutants are on the increase". For lakes, it was established, firstly, t h a t fish populations in acidified lakes continue t o deteriorate. Secondly, new lakes are being acidified at the current rate of (sulphur) deposition. However, the rate of increase in the number of acidified lakes was estimated a s low. Less than 100 lakes were estimated to bypass zero alkalinity over the next ten years. Mass balance calculation was the method used to estimate responses in forest soils. Comparing input (deposition) with output (leaching), it was shown that K, Ca and Mg are being depleted from forest soils [361. Nitrogen, on the other hand, accumulates in vegetation. Given the role of the different elements in limiting growth, it is possible t h a t the present deposition mix tends to increase rather than decrease forest growth. Silviculture, climatic variability, changes in the structure of forests, and other factors, however, obscured the potential general impact of air pollutants on forest growth. In average conditions in Finland, the change in plant nutrition is a threat t o forests not in the short but in the long term (> 60 years). I t was established t h a t the main body of natural resources have remained intact both in lakes and in forests. Forest growth and tree survival have not been affected. Large rivers and lakes are strongly buffered and have been only marginally acidified. It was concluded t h a t there i s no reason for concern about existing, large scale ecological damage but one should be aware of the possibility of future damage. Pollution abatement thus aims to prevent damage rather than t o restore ecosystems. In the process of programme assessment, critical loads were estimated [34]and integrated assessment models were used in order to compare options of pollution abatement [351.

Loss of genetic diversity has taken place in lakes and in forest with respect to certain species and populations. Pollution abatement cannot bring back those genotypes. This can be judged to be a serious, irreversible consequence of air pollutants. Changes in soils and in the frequency of biotic organisms are reversible and will respond to pollution abatement. Nitrogen deposition has not so far caused significant adverse effects. Because of the increasing trend of nitrogen deposition, as demonstrated in [ 101, detailed evaluation of whether the situation is changing is necessary. 5. POLICY IMPLICATIONS

5.1. Utilization of natural resources

Renewable natural resources, especially forests, are vital to the national economy. It was an important finding that trees in Finland have not shown signs of decline on a large geographical scale. On the other hand, there are signs indicating ecosystem responses in terms of changes in soils and in sen-

439

sitive vegetation. Stand rotation on certain sites in Finland can be as long a s 160 years. Observations of gradual changes in the ecosystems therefore create genuine concern about the future of the resource. Sustainable forestry has been the "trade mark" of Finnish forestry policy. The industrial products are exported mainly to central Europe and t o the United Kingdom. Consumers in those countries are environmentally aware, creating an additional incentive for the Finnish forest sector to maintain and develop acceptable forestry practices. This has brought the sector into a new situation. Sustainability, both in the narrow sense referring t o wood production and in the broad sense referring t o biodiversity, is a vital goal even from the viewpoint of direct business interests. The standing stock of Finnish forests, about 1900 million cubic metres, is equivalent to harvest for over 30 years a t the present rates. The annual growth a t present is 1.3 times higher than the harvest. In the worst case imaginable, a horror scenario, growth would be radically reduced and trees would start dying. Even then it would be logical to maintain forest industries until the standing stock has been exhausted. This kind of exploitation is business-as-usual in the utilization of oil and natural gas, but is ruled out a s an acceptable practice in forestry. Fortunately, the probability for such a scenario in Finnish forests is practically zero. Given the amount of wood t h a t already exists in forests, acidic deposition can not affect the availability of timber within the next 20 to 30 years. Concern about the environment is viewed a s a long term potential for the Finnish economy, in particular for the forest sector. The largest environmental problems, like acidic deposition and the threat of the greenhouse effect, are consequences mainly of the utilization of non-renewable resources. The forest sector draws upon a renewable resource base. Productivity can be maintained without decreasing the potential for future generations to enjoy the benefits from the resource. 62. Air pollution abatement and liming

Sulphur emissions have been successfully reduced in most European countries. If this development can continue for another 10 to 20 years, sulphur deposition will not threaten Finnish ecosystems apart from exceptional and insignificant cases. The remaining impacts can be taken care of by liming and other related measures. This optimistic scenario has been the basis for recommendations about large scale liming. To ensure the potential for future action, HAPRO urged a continuation of liming experiments. If, however, emission reduction can essentially solve the problem, there is no need for large scale liming. Liming, after all, adds to the material fluxes from the industrial system t o the environment. The guiding principle of environmental protection is t o decrease those fluxes. In addition, liming is costly and has negative side effects L371. The total annual costs of reducing sulphur emissions in the near term in Finland were estimated a t 1.3 billion FIM (about 300 million U.S. dollars). If 1.9 billion FIM are invested annually in Russia and in Estonia, and if the emissions elsewhere in Europe are reduced by 60 % from the level of 1980, sul-

440 phur deposition in Finland would be less than 0.5 g/(m2a) [7].This would solve the major part of the problems caused by sulphur deposition. It remains to be seen whether the expenditure is economically and politically acceptable in these countries. Nitrogen deposition has so far been rather insignificant in Finland in terms of acidification, aquatic effects, and adverse responses of vegetation. Nitrogen deposition is a potential future threat to ecosystems, for example to the Baltic sea.

6.3. Research management HAPRO was a unique exercise and many lessons were learned about research management. I t proved effective to have t h e programme secretariat as a n independent unit located a t t h e ministry, i.e. a t a n administrative level above research institutes and universities. This made it possible to make direct contacts to research groups without complicating interventions by the administration of different institutes. The rapid beginning of t h e programme meant t h a t there was a shortage of time for screening t h e projects. The topic was politically so interesting that postponing research was not an option. It was possible to some extent to adjust the programme during the second and the third year. In retrospect, the advantages of the quick s t a r t outweighed the disadvantages. The budget framework and the time schedule of the programme were met. I t is understandable, given the size of the programme that pressure developed towards the end of it. Voices were raised in favor of continuation. However, it was necessary to keep to the original plan. Firstly, this was the first programme of this size in the country and it was important to maintain the credibility of its management. Secondly, having a fixed time frame was i m p o r t a n t f o r creating t h e momentum: I t would otherwise have been difficult to organize joint reporting by more than a hundred authors. Thirdly, it was estimated that the best way of promoting fut u r e projects was to r u n t h e existing project according to the predetermined schedule. This strategy was partly successful, although a well-justified proposal for a continuation programme on critical loads was rejected. HAPRO gave new insight in the process of environmental research probably to all participants. My initial perception of the role of research in environment a l protection was a s depicted in Fig. 3a. New information according to this model emerges from individual research projects. Review papers organize and evaluate t h e information and serve a s t h e basis for environmental assessments. Alternative policy options are prepared. The options are internally cons i s t e n t a n d u n d e r s t a n d a b l e to policy m a k e r s a n d t o t h e g e n e r a l public. Politicians then choose between t h e options, modify them, and transform them into legistlation and statutes. This chain of activity existed in HAPRO but was not the only important channel for preparing decisions. Frequently, a case was met a s depicted in Fig. 3b. The media picks u p a n individual scientist describing individual research findings, often direct measurements with concrete interpretation. The public responds to the media report, starts t o discuss and make contacts with politicians. Ministers and other high ranking politicians react and, first, a s k t h e best experts to prepare a statement on the issue. Policy decisions are then taken to achieve an improvement.

44 1

a Primary

measurements * Report

Scientific

Policy

Political * Improvement in the environment

* review * Assessment *options * choise

b

Primary measurements

1

Assessment

4t

Press Public * Political Polrtical * Improvement release * concern reaction * decision in the environment

Figure 3. Linkage between research and improvements in t h e environment: (a) through review and assessment; (b) through media. The latter chain of events has the disadvantage of being ineffective. I t can focus on random problems a s i t circumvents t h e review and assessment processes. I t tends to omit t h e deep understanding of causal linkages. However, this "mediacratic" line of events strengthens democracy over the alternative, potentially bureaucratic procedure. Recognition of t h e mediacratic line of events (Fig. 3b) may have implications for research management. I t is important in this situation that a large number of scientists is available for making initiatives and giving statements. In this way environmental issues can be illuminated from many different angles by small, concrete pieces of information. A balance between the two approaches might serve society best. Anyway, the support of t h e general public is the only solid basis both for research and for the management and protection of environmental resources.

Reprints: Reprints of individual HAPRO publications, a s given in t h e reference list, can be ordered from the author of this chapter. 6. REFERENCES

1

2 3 4

5

J. Merilainen, Ann. Bot. Fenn. 4 (1967) 51. S. Huttunen, In M. Treshow (ed.) Air Pollution and Plant Life, Wiley, New York, 1983. H. Arovaara, P. Hari and K. Kuusela, Commun. Inst. For. Fenn. 122 (1984) 1. E. Tomppo and M. Siitonen, Paper and Timber 73 (1991) 2. Finnish Research Project on Acidification (HAPRO), General Plan, Ministry of the Environment, Ministry of Agriculture and Forestry, Helsinki 1985.

442

6 7

8 9 10 11 12 13 14 15

16 17 18 19 20 21 22 23 24 25 26 27 28 29

30 31 32 33 34 35 36 37

P. Kauppi, P. Anttila and K. Kenttamies (eds.), Acidification in Finland, Springer-Verlag, Berlin, Heidelberg, New York, 1990. P. Kauppi, P. Anttila, L. Karjalainen-Balk, K. Kenttamies, J. Kamari, I. Savolainen, Forsurningen i Finland, HAPROs slutrapport, (available in Swedish and in Finnish), Ministry of the Environment, Report 90,1990. S.M.Joffre, T.Laurila, H.Hakola, V.Lindfors, S.Konttinen and P. Taalas, in ref. 6, p. 43. 0.Jarvinen and T.Vanni, in ref. 6, p. 151. J.-P.Tuovinen, L.Kangas and G.Nordlund, in ref. 6, p. 167. A.Hyvarinen, in ref. 6, p. 199. P.Anttila, in ref. 6, p. 111. M.Forsius, V.Malin, I.Makinen, J.Mannio, J.Kamari, P.Kortelainen and M.Verta, Environmetrics l(1990) 73. M.Forsius, J.Kamari, P.Kortelainen, J.Mannio, M.Verta and K.Kinnunen, in ref.6, p.759; J.Kamari, M.Forsius, P.Kortelainen, J.Mannio and M.Verta, AMBIO 20 (1991) 23. L.Heitto, in ref. 6, p. 963; P.Kippo-Edlund and A.Heitto, in ref. 6, p. 973; P.Eloranta, in ref. 6, p. 985; P.Huttunen and J.Turkia, in ref. 6, p. 995; J.Sarvala and S.Halsinaho, in ref. 6, p. 1009; J.J.Merilainen and J.Hynynen, in ref. 6, p. 1029. M.Rask and P.Tuunainen, in ref. 6, p. 911. P.J.Vuorinen, M.Vuorinen a n s S.Peuranen, in ref. 6, p. 941. P.Huttunen, K.Kenttamies, A.Liehu, M.Liukkonen, T.Nuotio, 0.Sandman and J.Turkia, in ref. 6, p. 1071. M.Kuusinen, K.Mikkola and E.-L.Jukola-Sulonen, in ref. 6, p. 397. E.Kubin, in ref. 6, p. 421. A.Riihling, L.Rasmussen, K.Pilegaard, A.Makinen and E.Steinnes, NORD 1987:21. P.Nojd, in ref. 6, p. 507. E.-L.Jukola-Sulonen, K.Mikkola and M.Salemaa, in ref. 6, p. 523. H.Arovaara and H.Ilvesniemi, in ref. 6, p. 715. H.Raitio, Acta Universitatis Ouluensis, Ser. A 216 (1990) 1. K.Heliovaara and R.Vaisanen, in ref. 6, p. 447. A.Ferm, J.Hytonen, P.Lahdesmaki, P.Pietilainen and A. Patila, in ref. 6, p. 635. M.Johansson and I.Savolainen, in ref. 6, p. 253. J.Soveri and T.Ahlberg, in ref. 6, p. 865. R.Ervio, R.Makela-Kurtto and JSippola, in ref. 6, p. 217. M.Verta, J.Mannio, P.Iivonen, J.-P.Hirvi, 0.Jarvinen and S.Piepponen, in ref. 6, p. 883. J.Ranta, in ref. 6, p. 1209. H.Seppala, RSeppala and M.Kallio, in ref. 6, p. 1217. A.Henriksen, J.Kamari, M.Posch, G.Lovblad, M.Forsius and A.Wilander, NORD 1990:124. M.Johansson, J.Klmari, R.Pipatti, ISavolainen, J.-P.-Tuovinen and M.Tahtinen, in ref. 6, p. 1171. K.Kallio and L.Kauppi, in ref. 6, p. 811. J.Derome and A.Patila, in ref. 6, p. 1093.

T Schneider (Editor). Acidification Research Evaluation and Policy Applications 1992 Elsevier Science Publishers B V

443

STATUS OF ACIDIFICATION RESEARCH IN CZECHOSLOVAKIAAND ITS RELATIONSHIPTO POLITICSAND ECONOMICS IN EUROPE T.Paces Czech Geological Survey, Czechoslovakia Acidification of water and soil is related to political and economic systems. Data from 1987 (Anonymous, 1990a, 1991a) indicate that the socialist countries with centrally planned economies show large differences with the democratic countries with market economies. The socialist countries a s a group have similar values for environmental and economic parameters that are inferior to those of the other group. This is documented by statistic data on acidic emissions, consumption of energy and gross national products of selected European countries, USA, Japan and China (figures 1 and 2). Czechoslovakia, after 42 year with a planned economy, is approximately in the centre of the cluster and represents a country with very serious acidification problems in relation to its economic status. High consumption of energy per gross national product causes the country to use local soft coal with a high sulphur content. The existing power plants do not have any desulphurisation devices and emit large quantities of SO2 into the atmosphere. This is the major cause of environmental acidification (Paces, 1985). This acidification is most severe in the western part of the country - Bohemia. This part is drained by the Elbe river. In this river the acidification is partly responsible for the increased concentration of strong acid anions and a decrease in concentration of weak acid anions represented by bicarbonates (table 1).Also soils are acidified (table 1) a s well as lakes (table 2). Acidification is held responsible for the fast increase in the damage and dieback of forests (figure 3) and the changes in the rates of weathering and erosion (Paces, 1991). Acidification, in spite of all the evidence, was virtually ignored by the socialist government and environmental information was either classified o r its dissemination was suppressed. Within the Geological Survey of Prague (present title is Czech Geological Survey), it was claimed that acidification is a geochemical process and we started to investigate this phenomenon in 1978 by monitoring a small catchments in the northern Bohemia near Chomutov. This is a n area hardest hit by industrial emissions from power plants and the local chemical industry. A comparison with monitoring results of the mass balance of sulphur, nitrogen, chloride, base cations and hydrogen ions in a catchment located in less polluted region of the Bohemian - Moravian Highland near Pacov indicate how serious the biogeochemical cycles of elements are affected by acidification (Paces, 1985). Later, data from studies of other catchments and lakes were published in a volume of the International Workshop on Geochemistry and Monitoring in Representative Basins (Moldan

444

and Paces, eds. 1987) organized by the Geological Survey in Prague. After the political changes in 1989, environmental issues became priorities to be solved by the present federal and republic governments. Present research of acidification includes: (1)monitoring of input and output in 6 small representative catchments and lysimetric measurements in the soil of the severely acidified Krusne hory mts., less acidified Slavkovsky lea mete. (Kram and Hruska, 1991), and the least acidified Bohemian-Moravian Highland. A project GEOMON will start in 1992. This project, headed by the Czech Geological Survey will include monitoring of input and output of chemical elements in 14 catchments in the Czech and Slovak Federal Republic; (2) evaluation of hydrochemical and sedimentary records in acidified lakes of the Sumava mts.; (3) mapping of critical loads (Hettelingh et al., 1991) and integrated monitoring of small catchments (Anonymous, 1990b, 1991b) within the framework of the Convention on Long-Range Transboundary Air Pollution (UN-ECE). Air pollution emission and acidification by industrial sourcea is monitored and made public through daily announcement of critical concentrations of SO2 and NO, by the Czech and Slovak Hydrometeorological Institutes. Ecological impacts of acidifying emissions are studied by the Czechoslovak Academy of Sciences and the Department of Forestry at the T.G.Masaryk University a t Brno. Local forest authorities are responsible for reforestation of damaged areas after the dieback of the spruce. Czechoslovakia will not be able to reduce acidification rapidly because it will require fundamental changes i n energy consumption, installation of expensive desulphurisation equipment and modernisation of the chemical industry. These changes will come with the privatisation of state-owned industries and with the political changes that take place in central and eastern Europe.

445

Table 1 Changes in the acidification status of Elbe river and the soil of the Orlicke hory mountains, data by Paces, 1982 and Pelisek, 1984

Elberiver

1982

1976 mmo1.m-?yr-1

36

NOSHCOr

170 40 252

5.6

330 Czech soil

1953

1981 pH H20

A0 Hh

B

3.6 3.8 4.9

4.2 4.7 5.2

Table 2 Acidification of Cerne (Black) lake in Sumava mountains in Czechoslovakia, data by Vesely, 1987

Depth of lake m

Acidity* p o l H+.rl

1936 0 5

50-70

15

90-135

25

30

160 - 180

m 215 210 1% #I5

215

* titration with NaOH with phenophtalein indicator

446

40

-

DDR

30-

P'

a

5

R'

&

g

20-

g 10 -

0

USSR' ' 0 DDR BRD s 0 0 8 j

A.

'USA us$/c

441 60-

-

f

-o-

Czech republic

-m-

Slovak republic

40-

1

-5

10

-

0 1960

1970

1980

1990

time in years

Figure 3. Development of forest damage in Czechoslovakia, data from "blue book" of Czech Ministry of Environment, 1990 REFERENCES

Anonymous (1990a1, World Resources 1990 - 1991, Oxford University Press, Oxford Anonymous (1990b1, Pilot Programme on Integrated Monitoring, 1 Annual Synoptic Report 1990, Environmental Data Centre, National Board of Waters and the Environment, Helsinki, 88 p. Anonymous (1991a1, Data by PlanEcon, USA, published in Lidove Noviny, March 14,1991, Praha Anonymous (1991b), Pilot Programme on Integrated Monitoring, 2 Annual Synoptic Report 1991, Environmental Data Centre, National Board of Waters and the Environment, Helsinki, 200 p. Hettelingh J.P., Downing R.J. and De Smet P.A.M. (eds.1 (19911, Mapping Critical Loads for Europe, CEE Technical Report no. 1, RIVM report no. 25910001, National Institute of Public Health and Environmental Protection, Bilthoven, 79 p. Kram P. and Hruska J. (19911, Hydrogeochemical balance of acidic catchment Lysina (Slavkovky lea mnts.1 with extremely high content of aluminium in discharge, Casopis pro mineralogii a geologii, v. 36, No. 4, Prague Moldan B. and Paces T. (eds.1 (19871, Extended Abstracts, GEOMON, International Workshop on Geochemistry and Monitoring in Representative Basins, Geological Survey, Prague Paces T. (19821, Natural and Anthropogenic Flux of Major Elements from Central Europe, Ambio, vol. 11, pp. 206 - 208

448

Paces T. (19851,Sources of Acidification in Central Europe Estimated from Elemental Budgets in Small Basins, Nature, vol. 315,pp. 31 - 36 Paces T. (19911,Changes in rates of weathering and erosion induced by acid emissions and agriculture in central Europe, In: Land Use Changes in Europe, F.M.Brouwer et al. (eds.1, Chapter 14,pp. 317 - 323, Kluwer Academic Publishers Paces T. and Pistora Z. (1979),Antropogenni Ovlivneni Chemickeho Slozeni Labske Vody, Vodni hospodarstvi, B., vol. 11,pp. 305 - 307, Praha Pelisek J. (19841,Changes in Acidity of Forest Soils of the Orlicke Mts.caused by Acid Rains, Lesnictvi vol. 30,pp. 955 - 962,Praha Vesely J. (19871,The development of acidification of lakes in Bohemia, In: GEOMON, Extended Abstracts, pp. 80 - 82,Geological Survey, Prague

T Schneider (Editor). Acidification Research Evaluation and Policy Applications All rights reserved

0 1992 Elsevier Science Publishers B V

449

S w i s s National Research Program "Forest Damage and A i r Pollution" (NFP 14+)

The

Frank Haemmerlil, Norbert Krauchil, Martin Stark2 1 Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf.

Switzerland 2 Program Management NFP14+, Sigmaplan, Zihringerstrasse 61. CH-3012 Bern. Switzerland

Abstract The ohjective of this paper is to present a review of the NFP 14+. The studies of this multidisciplinary research program were carried out hetween 1985 and 1989. They were concentrated on three forest sites at different altitudes, one in the densely populated Mittelland, one in a protection forest in the Prealps, and one in the Alps proper. All sites are dominated hy Norway spruce (Picea ahies). The main goal of the case studies was a comprehensive characterization of the sites, giving the opportunity to evaluate the role of air pollution in forest health. The program included various ecological investigations as well as measurements of meteorological parameters, gaseous pollutants and atmospheric deposition. The results indicate neither a temporal nor a spatial dependence of crown defoliation on air pollution for the study sites. Nevertheless, there is experimental evidence that the presentday ozone levels in Switzerland have to he considered as a risk factor for more sensitive tree species.

1 MAIN OBJECTIVE AND CONTENTS OF THE RESEARCH PROGRAM ~

In 1980 the Swiss National Science Foundation got the order from the Executive Federal Council to conduct a National Research Program about 'Air Cycle and Air Pollution in Switzerland' (NFP 14). Because of the general impression that the crown defoliation of trees had increased hetween 1982 and 1984, the program was extended hy a supplementary program called 'Forest Damage and Air Pollution' (NFP 1 4 t ) . The projects of this multdisciplinary research program were conducted hetween 1985 and 1989. They were concentrated on one case study in the densely populated Mittelland, and two in protection forests, one in the Prealps, one in the Alps proper (Figure 1). The main goal of the program was a comprehensive characterization of these three sites, giving the opportunity to evaluate the role of air pollution in forest health. More than 20 different scientific groups from several research institutes were integrated in the research program, which included various forest ecological studies. Four towers were installed at different altitudes on the Laegeren ridge, another tower was erected in the Alptal, and another in Davos to measure the air chemistry and meteorology of the sites. Table 1 gives a general account of the focal points of this research program. The program was completed this year with the publication of six partial synthesis reports - three of them concerning forest relationships. A comprehensive report will he puhlished in 1992.

450

Figure 1 The geographical situation of the study sites

Table 1 Focal points of the NFP 14 + tree and stand vituliry

- crown condition (terrestrial and aerial inventory)

- growth - nutrient supply of spruce needles

- mycology of spruce needles

meteorology and uir chemistry - climate and weather conditions

- air pollution situation (gaseous pollutants, atmospheric deposition above and below the canopy of spruce and beech, stemflow of heech) - fog chemistry

physiology und biochemistry of trees under the influence of guseous pollutants

- photosynthesis and stomata hehaviour of spruce needles

- condition of the wax layer of spruce needles - fumigation experiments in the laboratory and in the stands

soil ecology - water balance - nutrient and heavy metal contents

- condition of root mycorrhizas

- litter input and litter decomposition

45 1

2. ECOLOGICAL CHARACTERISTICS OF THE STUDY SITES

Topographic, climatic and soil specific requirements for plant growth are extraordinarily varied in a mountainous country like Switzerland. Considering these circumstances the three study sites were chosen in three distinct regions differing greatly in altitude. Since Norway spruce is the most widely spread species in Swiss forest, the main analyses were made for spruce. The study site in the Mittelland is situated at 685 m a.s.1. on the southern slope of the Laegeren; it belongs ecologically to the heech forest area (Galio odoratio-Fagetum typicum & Pulmonario-Fagetum typicum). Today, it is a mixed spruce-fir stand with beech. The dominant spruce is between 100 and 150 years old. The geological subsoil is either moraine and sandy molass or, rarely, clay-rich molass marl. The acidity of the surface layer varies from acid over moderately acid to slightly alkaline since different soil types occur: cambisol. luvisol and pararendzina (Tahle 2). The soil is rich in clay and silt. The study site in the Prealps is situated at 1185 m a.s.1. on the western slope of the Alptal. The spruce-fir forest is based on natural regeneration (ecologically: Veronico urticifoliae-Piceetum to Sphagno-Piceetum typicum). It mainly consists of 120- to 150- year-old spruces. The soil is rich in clay, often saturated and partially moving. The surface layer of this gleysol is of moderate to high acidity. Finally, the study site in the Central Alps is situated at 1660 m a.s.1. in the high valley of Davos. A characteristic of the natural spruce forest (Larici-Piceetum)is the wide age range of the trees which varies between 120 and 370 years. An acid iron-humus-podsol has developed on the gneiss crystalline subsoil. Climatologically the sites Laegeren and Alptal are intluenced hy a maritime climate. Davos, on the other hand, is already continentally intluenced resulting in a rougher climate and a high radiation intensity (Table 2). Typical for the Alptal is a high annual level of precipitation due to blocked air masses on the northern side of the Alps. Special, climatically induced stress situations occur from time to time in Davos and in the Alptal due to the Fiihn, an alpine wind which causes abrupt air temperature changes. In relation to the air quality situation none of the study sites was close to major emission source. The sites may therefore be considered as representative for pollution situations covering large areas. Table 2 Climatic and soil-specific characteristics of study sites (from Stark et al. 199I , Liischer 1991) Characteristics (1987188189) temperature [“C] precipitation [mml

Laegeren

Alptal

Davos

7.2 18.3 18.5

5.7 16.7 17.1

2.9 13.8 14.2

1084 I1017 I866

2600 12300 I2150

986 I809 I671

gleysols

humus form

cambisol, luvisol pararendzina mull

iron-humuspodsol raw-humus

rooting depth permeability acidity (surface layer) nutrient supply

60 - 90 cm slighlty reduced pH 4.5-7.5 normal

SQU

soil type

raw-humus, anmoor 30 60cm poorly permeable pH 3.6-5.4 normal

-

-

10 30 em

excessive pH 3.5-4.5 normal

452

3. VITALITY OF TREES ON THE STUDY SITES The condition of the tree crowns on the three sites changed only minimally between

1986 and 1988. This was demonstrated by a low needle loss level on the Laegeren, and

essentially higher needle loss values in the Alptal and in Davos. Figure 2 shows further that the extent of crown defoliation on the sites Alptal and Davos is distinctly higher than the comparative value of the large scale forest damage inventory for the regions Prealps and Alps. According to the internationally approved definition, trees with more than 25 per cent foliage loss are considered to be damaged. About the half of the trees in the stand Alptal and about one third in the stand Davos fell into this category. Therefore, it might be expected that this high needle loss level would be reflected in the growth behaviour of spruce. As Figure 3 shows, this is not the case. The average development of radial growth does not exhibit an unusual decrease in the eighties on both sites. It is therefore difficult to denote the observed level of spruce defoliation as new and abnormal. On the other hand, we notice on the Laegeren a growth depression of spruce since the sixties, even though the actual needle loss level is relatively small. These apparent contradictions show that a clear picture of stand vitality can only be obtained through the combined observation of crown defoliation and growth. Despite all its drawbacks, crown defoliation still remains a measure of vitality; significant correlations have been found between needle loss and radial growth of spruce (Keller L Stark 1991). Table 3 shows that the nutrient supply of young spruce needles on all sites varies between sufficient and optimal with a few exceptions. Using the threshold values of Bergmann (1988) and Anonymus (1987) no distinct deficiencies have been noted. The spruce collectives on all sites did not show any relation between the observed crown transparency and the nutrient supply of needles. Taking the growth depression of spruce on the Laegeren into consideration, it may be that on1 these trees are in a critical situation. Growth depression may be related to the barely suficient content of magnesium in the needles. On acid soils in the Fichtelgebirge (Germany) and in the Vosges, needle yellowing has been detected as symptom of magnesium deficiency. No such yellowing was observed on the Laegeren site. As the soil here is well supplied with magnesium, there is the hypothesis that root uptake is hindered by the high level of calcium.

4. GASEOUS POLLUTANTS AND THEIR INFLUENCE ON TREE CROWNS

In order to evaluate the air quality situation on a specific site the Swiss Clean Air Act (LRV 1985) provides threshold values for air pollutants. These lawful limits, which should guarantee an overall protection for man, plants, animals and environment, are based upon a great number of scientific studies and mostly concur with the recommendations of recognized technical organizations (WHO,VDI, UN-ECE). As shown in Table 4, the levels on the sites due to primary pollutants such as sulfur dioxide and nitrogen dioxide are usually small, especially at Alptal and Davos, where the daily average limits of the Swiss Clean Air Act were never exceeded. On the other hand the secondary pollutant ozone has to be considered as a serious stress factor. It is striking to see how many times the highest allowed hourly average of 120 pg/m3 ozone was exceeded each year on the Laegeren and in the Alptal.

453 Percentage o f trees with defoliat. 1 2 5 % 100

Lageren-Midland

Alptal-Prealps

Davos-Alps

80 60

858687888990

858687888990

=

NFP14*

858687888990

Region

Figure 2 Crown defoliation in the stands of NFP 14+ and in the comparative regions ofthe Swiss forest damage inventory (ohserved trees: Laegeren 214, Alptal 240, Davos 519) (from Keller &stark 1991)

4

rniII Imet re I

3

2

A

L D

1

I

Davos (D) 01

t

1 - L L I . J

---I&

IIU

LLILUJ,

1

LA

+

,LL+-LLdLl

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990

Figure 3 Average development of radial growth of dominant and co-dominant spruces hetween 1890 and 1989 (Observed trees: Laegeren 16, Alptal 20, Davos 17). These collectives are slightly more defoliated than the whole stands (from Joos 1991).

454

Table 3 Nutrient supply in 6 month old needles of older spruces (from Stark 1991)

Element N

Laegeren

Alptal

Davos

+

0

0-

P

t

0 -

t+

Mg Ca K Zn B Fe

0

+ ++ ++

++

t+

++ ++ 0-

+t

0

t+

++ ++

++ +

++

0

Table 4 Annual mean concentrations (AM, pg/m3) of S 0 2 , NO2 and 0 and number of exceedences (NE) of the short-time threshold values of the Swiss Clean Air Act ( V 1985) [from Star in pressl. Maximum I-day average concentration for SO : 100 pg/m , tor N02: 80 pg/m , maximum I-hour average for 0 3 : 120 pg/m3. The Act &Crees that these limits may only be exceeded once a year.

Y

5

455

The influence of gaseous pollutants on tree crowns was examined in three projects. The first project dealt with the question of whether significant alteration in gas exchange of spruce needles under the influence of ambient air pollutants could be measured (Hlsler 1991). To this end, the gas exchange of the two youngest needle age-groups of older spruces was measured at 5-minute intervals for 3 years on the southern slope of the Laegeren and at Davos. Measurements were conducted with branch chambers made by Walz (Germany). Considering the available results, the hypothesis of a direct and immediate influence of air pollutants on the gas exchange of needles cannot be completely excluded, but it is certain that meteorological conditions were the determining factors for net photosynthesis and stomatal behaviour of young needles during the study period. It was further established that photosynthetic activity, as measured some 30 years ago, does not differ significantly from toda 's measurements. Nothing can be said about the question as to whether photosynthesis in order needles, which have been exposed for several years to today's air quality conditions, has k n chronically affected. If so, it would not be too detrimental for the photosynthetic performance of the whole tree, since 80 per cent of the photosynthesis occurs in the two youngest age-groups of needles. The wax layer of needles builds a barrier between the plant and the atmosphere. The goal of a second project was to figure out whether the wax layer changes under the influence of air pollution (Giinthard-Goerg 1991). To this end, 1-, 3- and 5- year old needles of 6 mature spruces from Laegeren and Davos, as well as 6-month-old needles of 4-year-old spruce seedlings were used for the analyses. The seedlings were exposed to different doses of ozone, sulfur dioxide and ambient air. The results show that exposure to ambient air did not lead to any deterioration in wax structure. The condition of the wax layer was always mainly determined by the expos' 'on to weather conditions. Only an experimental exposure to a high level of ozone (300pg/m ) led to retardation in the development of the wax layer. The third project dealt with the question as to what extent ozone concentrations such as occur in Switzerland may negatively effect forest plants (Landolt & Luthy-Krause 1991). To determine this, various I- to 5-year-old forest plants were fumigated in the closed-top chambers of the Swiss Federal Institute for Forest, Snow and Laryiscape Research in Birmensdorf for a maximum of 20 weeks with 0, 100 and 200 pglm ozone. Supplementary fumigations with ambient air were conducted in open-top chambers on the Laegeren and in Davos for a maximum of 2 years. As a measure for the evidence of pollutant effects either visible symptoms or biochemical parameters in needles/leaves were used. As shown in Table 5 , Scots pine (Pinus silvestris) was most sensitive to ozone in the classic gas exposure experiment. Needle yellowing occurred after only three weeks of 100 pg/m3 ozone exposure. Within the concentration range of 200 pg/m3 ozone European beech (Fagus silvatica) reacted after 6 weeks with brown necrotic spots on leaves. In the same concentration range Norway spruce (Picea abies) showed visible symptoms too, but much later or even several weeks after the fumigation had ceased. The symptoms were also hardly or not at all reproducible for spruce. Finally, Silver fir (Abies aha) never reacted with visible symptoms. Regarding the biochemical changes induced by ozone, pine was established as the most sensitive species of those tested. During fumigation with ambient air on the Laegeren and in Davos, only the well known bio-indicators red clover (Trifolium pratense var.'lucrum') and a poplar hybrid (Populus euramericana var.'Dorskamp') exhibited any symptoms. In the study on pine and spruce in ambient air compared with controls in filtered air, no obvious reactions were observed. In conclusion, these experiments demonstrate the sensitivity of various plants to ozone exposure is very different.

P

456

experimental fumigation with ozone

100 d m 3 Pinus silvestris Fagus silvatica Picea abies Abies alba

I

zoo pg/m3

BC

VS

+

+

+

-

.

-

(-)

VS

-

I

BC

experimentalfumigation with ambient air Lawren

VS

+

-

+

+

nl

-

+

-

I

BC

-

Davos

VS

I

BC

nt

nt

nt

nt

nt

-

?

.

?

nt

nt

nt

nt

5. ATMOSPHERIC DEPOSITION

Results about atmospheric deposition are available for the wet deposition above and below the canopy of spruce and beech (Table 6). Figure 4 shows the annual load of protons, nitrate and ammonium above and below spruce canopy for all three observation sites. The load of protons above the canopy of the Laegeren and Alptal is comparable to the average value measured in Germany (032 kg/ha*year, Fuhrer et al. 1988). At the alpine site Davos it falls well below that value. For the Laegeren and Alptal the load below spruce is higher than that in the open field. In the beech crown cover instead it seems that protons are buffered, since the acid deposition onto the soil below beech is very small (Table 6). The wet deposition of nitrate and ammonium in the open field is for the two sites Laegeren and Alptal on a similar level to the mean values found in Germany (6,7 kg nitrate/ha* ear; 9.0 kg ammonium/ha*year ; Fuhrer et al. 1988). On the alpine site Davos it falls signif;Ycantlybelow these values as already for the proton load. Figure 4 shows further that the nitrogen deposition below spruce is notably high on the Laegeren. For this site it is clearly shown that measuring precipitation in the open field comprises only a part of nitrogen deposition onto the soil in spruce stands. An essential part is probably due to dry deposition of nitrogen compounds to the tree crowns during p o d s without rain. Regarding the role of the observed deposition for the investigated sites, there is currently no evidence for existing problems for tree vitality. It does not Seem that the nutrient supply is limited on any site by the proton load. The two sites Laegeren and Alptal, which are more affected by acid deposition, show a sufficient supply of calcium, magnesium, potassium and manganese in the soil solution. A critical situation for the fine roots cannot be deduced from the calcium/aluminium-ratio in the soil solution. Regarding the actual load of atmospheric nitrogen on the Laegeren and in the Alptal, neither site exhibits signs of a fertilization overdose. The nitrogen content in spruce needles is on all sites below the optimal range. The atmospheric deposition of such metals as lead, cadmium and zinc seems to he harmless for all three observation sites. There is no evidence of disturbance of litter decomposition or of the release of nutrients in the soils. Regarding the Swiss Clean Air Act (LRV 1985), the deposition of these metals measured by Bergerhoff method does not exceed the threshold values.

451

Table 6 Wet deposition of selected chemical constituents (from Klijti et al. 1991, Keller & Klijti 1988).

nitrate

ammonium

20 15 10 5

0

A d -

LA AL

DA

~~

LA AL

above canopy

DA

L A AL

DA

below canopy

Figure 4 Wet deposition above and below the canopy of spruce (observation period: 1986/87; LA: Laegeren, AL: Alptal, DA: Davos) [from Kloti 1991, Keller & Kloti 19881.

45 8

6. SUMMARY AND CONCLUSIONS The National Research Program NFP14+ was based on three case studies in different parts of Switzerland. The observation period was rather short. Therefore, the results cannot be unreservedly generalized. Nevertheless, some valuable conclusions can be drawn. Assessment of crown condition alone is insufficient for the estimation of stand vitality. The condition of the mountain forest in Davos and in the Alptal is considered normal based on several indices (e.g. growth. nutrient supply), even though the actual needle loss level is high. About a third to a half of the trees on these sites have more than 25 per cent crown defoliation. The internationally used damage limit would consider all these trees as damaged. This general damage definition for all ecological zones of Europe and for all tree species should therefore be critically examined. Nevertheless, the crown defoliation remains a measure of vitality. The investigations indicate neither a temporal nor a spatial dependence of crown condition on air pollution. It can be concluded for the study sites that air pollutants have hardly affected the crown condition of spruce within the observation period. In a spatial point of view, the pollution on the alpine site Davos is generally low, while the needle loss level is high. On the other hand the pollution on the Laegeren, in the densely populated lowland, is relatively high whereas the extent of crown transparency is small. On all sites the actual levels of gaseous pollutants such as sulfur dioxide and nitrogen dioxide as well as the loads of metals such as lead, cadmium and zinc do not exceed the lawful threshold values in the Swiss Clean Air Act (LRV 1985). This is, however, not the case for ozone. There is experimental evidence that the current ozone levels have to be considered as a risk factor for more sensitive tree species. The margin existing between the present-day ozone concentrations and those which have been experimentelly shown to produce damage to Scots Pine is on a toxicological scale small. On the other hand, the assumption that ozone is damaging to Norway spruce and Silver fir should be critically questioned, as sensitivity to ozone varies greatly between species. Acid and nitrogen deposition onto forest soils is distinctly higher on the Laegeren and in the Alptal than on the alpine site in Davos. Nevertheless there is currently no evidence of an existing problem for the tree vitality due to this deposition on all sites. The long term risk of this factor for the different forest types in Switzerland is, however, unknown. Another long-term risk can be the potential climate change by the emission of greenhouse gases. Even if, or perhaps just because, these potential risks due to our modern civilisation are so difticult to assess, it is more than sensible to pursue efforts to reduce air pollution.

7. BIBLIOGRAPHY

1 Anonymus: Grundsatze f i r die Dungung im Wald. Bayerisches Staatsministerium fiir Erntihrung, Landwirtschaft und Forsten, Munchen (1987) 2 BergmaM, W. : Erniihrungsstorungen bei Kulturpflanzen. 2. Auflage. Fischer Verlag, Stuttgart (1988) 3 Fuhrer, H.W.; Brechtel, H.M.; Ernstberger, H.; Erpenheck, C.: Ergebnisse von neuen Depositionsmessungen in der Bundesrepublik Deutschland und im benachbarten Ausland. BOM, Mitt.Dt.Verb.Wasserwirt und Kulturbau, 14 (1988) 4 Gunthard-Goerg, M.: Die Einwirkung von Luftschadstoffen und Klimafaktoren auf die Wachschicht von Fichtennadeln. In: Stark, M. (4s.): Luftschadstoffe und Wald (1991) 5 Haemmerli, F.; Schlaepfer, R.: Forest Decline in Switzerland. In: Huettl, R.F.: Forest Decline in Atlantic and Pacific Region, Springer Verlag. Berlin, New York (paper submitted: June 199 I 1.

459 6 Hasler, R.: Vergleich der Gaswechselmessungen der drei Jahre (Juli 1986 - Juni 1989). In: Stark, M. (eds.): Luftschadstoffe und Wald (1991) 7 Joos, K. : Jahrringanalysen auf den Beoabchtungsflachen Davos, Alptal und LIgeren. In: Stark, M.(eds.): Luftschadstoffe und Wald (1991). 8 Jutzi, W. (eds.): Luftschadstoffe und ihre Erfassung. Ergehnisse aus dem Nationalen Forschungsprogramm 14 "Lufthaushalt, Luftverschmutzung und Waldschiden. Teil 1 . Verlag der Fachvereine an den schweizerischen Hochschulen und Techniken, Zurich ( 1 991). 9 Keller, H. M.,Kliiti, P.: Teilprojekt Bestandesniederschlag, Schlusshericht zu Handen der Programmleitung NFP14+. Eidg. Forschungsanstalt fLir Wald, Schnee und Landschaft, Birmensdorf (1988). 10 Keller, W.;Stark, M.:Wachstum und Kronenverlichtung auf den Beohachtungsflachen Ligeren, Alpthal und Davos. In: Stark, M . (eds.): Luftschadstoffe und Wald (1991). 1 I KWi, P.; Gehrig, R.; Portmann, W.: Depositionen. In: Schuphach, E. (eds.): Meteorologie und Luftchemie in Waldhestinden ( I 99 I ) 12 Landolt, W. ; Luthy-Krause, B. : Wirkungen umweltrelevanter Ozon-Konzentrationen auf verschiedene Pflanzen. In: Stark, M. (eds.): Luftschadstoffe und Wald (1991) 13 LRV: Luftreinhalte-Verordnung des Schweizerischen Bundesrates, EDMZ, Bern (1 985). 14 Luscher, P. : Gesamtschweizerische Einordnung der drei Beohachtungsflachen aus physiographisch-hodenkundlicher Sicht. In: Pdnkow, W. (eds.): Belastung von Waldhoden (1991). 15 Pankow, W. (eds.): Belastung von Waldhiiden. Ergehnisse aus dem Nationalen Forschungsprogramrn 14 "Lufthaushalt, Luftverschmutzung und Waldschiden, Teil 6 . Verlag der Fachvereine an den schweizerischen Hochschulen und Techniken, Zurich (1991). 16 Schlaepfer, R.; Haemmerli, F.: Das "Waldsterhen" in der Schweiz aus heutiger Sicht. Schweiz. Z. Forstwes. 141 (3): 163-188 (1990). 17 Schupbach, E. (eds.): Meteorologie und Luftchemie in Waldbestinden. Ergehnisse aus dem Nationalen Forschungsprogramm 14 "Lufthaushalt, Luftverschmutzung und Waldschaden, Teil4. Verlag der Fachvereine an den schweizerischen Hochschulen und Techniken, Zurich (1991). 18 Schiiphach, E.; Wanner, H. ( 4 s ) : Luftschadstoffe und Lufthaushalt in der Schweiz. Ergehnisse aus dem Nationalen Forschungsprogramm 14 "Lufthaushalt. Luftverschmutzung und Waldschaden, Teil 2. Verlag der Fachvereine an den schweizerischen Hochschulen und Techniken, Zurich (1991). 19 Stark, M. (eds.): Luftschadstoffe und Wald. Ergehnisse aus dem Nationalen Forschungsprogramm 14 "Lufthaushalt, Luftverschmutzung und Waldschaden, Teil 5. Verlag der Fachvereine an den schweizerischen Hochschulen und Techniken, Zurich (1991). 20 Stark, M.; Primault, B.; Schupbach, E.: Die Beohachtungsflachen an der Ggeren, im AIptal und Davos. In: Stark, M. (eds.): Luftschadstoffe und Wald (1991)

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T. Schneider (Editor), Acidification Research. Evaluation and Policy Applications 1992 Elsevier Science Publishers E.V

463

A comparison of some national assessments J a n Nilssona and Ellis Cowlingb aswedish State Power Board, S-162 87 Vallingby, Sweden bNorth Carolina State University, Raleigh, North Carolina 27695 USA

Abstract During the past two years, several countries in Europe and North America completed major scientific research and assessment programs on acidification and related air-pollution problems. Most of these programs culminated in publication of detailed documents which summarize the results obtained in each national program. In this paper we have tried to compare these national documents for similarities and differences in six specific features: 1) natural, cultural, and economic resources a t risk; 2) pollutant emissions of concern; 3) research and assessment approaches used; 4) scientific findings obtained; 5) policy options considered; and 6) use of research and assessment findings in making environmental decisions within each country. Based on these comparisons, we have drawn a few generalizations about the impacts of acidification and air pollution on soils, crops, forests, surface waters, fish, wildlife, engineering materials, cultural resources, public health, and visibility. We have also described a few lessons learned in various countries about the interface between science and environmental decision making. 1. INTRODUCTION This paper was prepared as a summary contribution for a n International Conference entitled Acidification Research: Evaluation and Policy Applications. This Conference was held 14-17 October 1991 a t the Maastricht Exposition and Congress Center (MECC) in The Netherlands. It was sponsored by The Netherlands' Ministry of Housing, Physical Planning and Environment and its National Institute of Public Health and Environmental Protection. The Conference was organized in four sections: 1) New Research Results on the Acidification Problem; 2) Results from National Research Programmes; 3) State-of-the-Art of Acidification Research; and 4) Acidification Policy. This summary paper was designed t o compare and contrast several of the recently completed national research and assessment documents with regard to six specific features: 1)natural, cultural, and economic resources a t risk; 2) pollutant emissions of concern; 3) research and assessment approaches used;

464 4) scientific findings obtained; 5 ) policy options considered; and 6) use of research and assessment findings in making environmental management decisions within each country.

Based on these comparisons, we also have tried to draw a few generalizations about both the scientific facts and also about public perceptions in various countries about impacts of acidification and air pollution on soils, crops, forests, surface waters, fish, wildlife, engineering materials, cultural resources, public health, and visibility. Finally, we have described a few of the lessons learned in various countries about the interface between science and environmental decision making. The national documents used a s the primary focus for comparison in the present paper include the following: The Netherlands -- Acidification Research i n The Netherlands (Heij and Schneider, 1991); Sweden -- Air Pollution '90 -- Action Programme for Air Pollution and Acidification ( S N V , 1990) and Mercury i n the Environment: Problems and Remedial Measures ( S N V , 1991); Finland -- Acidification in Finland (Kauppi, Antilla, and Kenttamies, 1990); United Kingdom -- Review Group Reports on: Effects of Acid Deposition on the Terrestrial Environment, (DOE, 1988); Effects of Acid Deposition o n Buildings and Building Materials (DOE, 1989a); Acidity in United Kingdom Fresh Waters (DOE, 1989b);Acid Deposition in the UK 1986-1988 (DOE, 1990a); Oxides of Nitrogen in the UK (DOE, 1990b); Acidity in Scottish Rivers. A Chemical and Biological Survey (Doughty, 1990); Critical and Target Loads Maps for the United Kingdom (DOE, 1991); Canada -- The 1990 Canadian Long-Range Transport of Air Pollutants and Acid Deposition Assessment Report including its Executive Summary and its separate components on: Emissions and Controls, A t m o s p h e r i c Sciences, Aquatic Effects, Terrestrial Effects, Human Health Effects, Socio-Economic Effects, and Quality Assurance Studies (FPRMCC, 1990); and United States -- State of Science and State of Technology Reports including four volumes: Emissions, Atmospheric Processes and Deposition; A q u a t i c Processes and Effects; Terrestrial, Materials, Health, and Visibility Effects; and Control Technologies, Future Emissions, and Effects Valuation (NAPAP 1991a). The national documents for the USA also include: the 1990 NAPAP Integrated Assessment Report (NAPAP,199lb); and a report by a n Oversight Review Board entitled The Experience and Legacy of NAPAP (NAPAP, 1991~). As a stimulus for further thought, we also have made some comparisons between the major scientific and assessment findings in these recent national

465

documents with: 1) some related observations in one east European country -Czechoslovakia (Thomas Paces, Personal Communications); and 2) the conclusions drawn more than ten years ago in the final report of the Norwegian Joint Research Project (SNSF project 1972-1980) -- A c i d Precipitation -- Effects on Forest and Fish (Overrein et al, 1981). Readers with an interest in other aspects of the history of acid deposition research may wish to examine an earlier review paper by Cowling (1982). In this paper, we have used the term national document to include both research documents (reports dealing with scientific findings) and assessment d o c u m e n t s (reports dealing with policy options o r management recommendations). This was done whether o r not these different types of reports were published separately (as in the cases of the United Kingdom and the United States) o r published in the same document (as in the cases of the national documents for The Netherlands, Sweden, Finland, Canada, and Norway). To save space in the paper we have often used the following abbreviations: NL = The Netherlands, S = Sweden, SF = Finland, UK = United Kingdom, CS = Czechoslovakia, CAN = Canada, and USA = United States. In comparing the several national documents we have used two general approaches -- a rough numerical approach, and a more detailed narrative approach. The rough numerical comparisons take the form of tables in which we have used numbers to indicate our judgement of relative importance within a given national document: 3 = major matter of concern; 2 = moderate matter of concern; 1 = minor matter of concern; 0 = matter not dealt with so far as we could tell. The narrative comparisons are simply that -- a few sentences (sometimes quotations from the documents themselves) describing our judgement about the features of the national documents being compared. Before beginning the comparisons, a few acknowledgements and disclaimers may be in order: We are grateful for advice and counsel received from many colleagues prior to, during, and following the Conference in Maastricht. We have tried our best to study the national documents thoroughly and objectively. In spite of our best efforts, however, we are sure t o have overlooked o r misunderstood some important aspects of these sometimes very long documents. For this reason, we look forward eagerly to both personal communications and published reactions to our efforts from colleagues in all countries who are willing to help improve our collective understanding of these important environmental problems.

466 2. COMPARISON

OF NATIONAL RESEARCH AND ASSESSMENT

DOCUMENTS 2.1. Who Prepared the Documents? What Methods Were Used?

Table 1 contains a very brief overview of the duration of research efforts, management approaches, and types of documentation developed in each national program. In most cases, some type of international peer review was used in addition to the within-country efforts to insure that high standards of scientific quality and integrity were maintained in developing the national documents.

Discussion In The Netherlands and Sweden, the assessment documents were prepared by a relatively few persons within o r with close connections to the federal government. Scientists who played important roles in writing research documents also played important roles as advisors in evaluating alternative policy options and occasionally in formulating national environmental goals. In the USA, a very large number of scientists and policy analysts from different disciplines and geographically distant regions were involved. This was also but somewhat less true in Canada, where most assessment team members were from Environment Canada or other federal and provincial bodies. These differences seem to reflect various "cultures": In The Netherlands and Sweden, a high degree of consensus existed between the government and the scientific community. Thus scientists had a relatively strong influence on decision making because the process called for policy analysts and scientists to work closely together. In the USA, greater separation was maintained between the persons involved in the research program and those involved in developing the assessment document. Also, many different federal agencies were involved. This sometimes led to compromises in interpreting scientific results. To some extent these differences in ways of conducting national research and assessment programs can be explained by differences in starting points. In most of Europe and Canada, there was a higher degree of public and scientific consensus about the seriousness of impacts and the need for international cooperation in limiting emissions than was true in the UK and the USA. The smaller scientific and policy-analysis communities in The Netherlands, Sweden, Finland, Norway, and Canada also made i t more necessary for scientists involved in research also to be involved in policy analysis.

Table 1 Management of the assessments in various countries

The Netherlands Duration of Research Program Management of research and assessment program

EuroDe Sweden

Finland

United Kingdom

First phase (198588) Second phase (1988-90) Small assessment team worked closely with research scientists

Three phases (1976-88) Fourth phase (1988-93) Main work done by staff a t Swedish EPA & collaborating scien-

Book. Part 1: Results and conclusions relevant for policymaking.

Three basic Book on primary reports on: scientific Consequences findings in of deposiEnglish. tion of sulphur and Assessment nitrogen, Air pollureport in Finnish and tion in Swedish urban areas, Mercury problems and environmental goals

(1985-90) Small assessment team worked closely with research scientists

Part 2: Thematic reports with summary of scientific results.

North America United States

(198590) Scientific review groups covenng various fields

tiStS

Documentation

Canada

Reports on Acid Deposition, Acid waters, Terrestrial effects, Nitrogen deposition, Photochemical oxididants, Buildings, Critical loads

Eight assessment teams mainly from Environment Canada and provincial orpanizations Eight separate reports: Executive summary; Emissions and control; Atmospheric sciences; Aquatic effects; Terrestrial effects; Human health effects socioeconomic studies

First phase (1980-90) Second phase (1991-) Ten task groups prepared 27 State of Science/ Technology &DO&

Integrated assessment document prepared in policy questiodanswer format: Effects of concern? Related to acid deposition? Sensitivity to change? Possible control scenarios?

P 4

m

468 2.2. PollutantEmissions of Concern

Significant differences in the pollutant emissions of concern were evident among the various national documents:

EuroDe nts of Concern

SO, emissions NOx role in acidification NO, rolein 03 formation NHx emissions

NL

S

SF

UK

CS

3 3 2 3

3 3 2 2

3 2 2 1

3 1 3 2

3 1 1 1

North h a a k a CAN USA

3 1 3 0

3 1 3 1(0F

a In the USA, NHx emissions were dealt with only in the NAPAP State of Science reports, not in the Integrated Assessment. In addition to this rough numerical comparison we found i t useful also to examine the amounts of emissions in each country in the several ways shown in Table 2. Table 2 Emissions of sulfur dioxide-S, nitrogen oxide-N, and ammonia-N in some countries (In Canada and the USA, emissions are shown only for the eastern parts of each country, roughly east of the 103rd meridian).

ElXOQ€!

Eastern North America CAN USA

S

SF

UK

CS

Emissions of sulfur dioxide-8: 125 loo Total, ktondyr Density, kg/ha/yr 35 3 Per capita, kg/yr 8 1 2

165 5 33

1900 74 32

1200 93

120 3 14

76 2 15

750 29 l3

250 19 16

298 0.7

60

35 1 7

450

160 12 10

66 0.2 4

NL

Total, ktondyr Density, kg/ha/yr Per capita, kg/yr

165 46 11

Fmissions of ammonia-N: Total, ktondyr 1% Density, kghafyr 55 Per capita, kg/yr 13

2

7

18 8

77

1915 3 94

20

m 17 52 4702 9 25 984 2

5

469

Discussion Globally, natural emissions of sulfur and nitrogen oxides are significant. In Europe and North America, however, natural emissions are small (10% or less) compared to anthropogenic emissions. Emissions densities in the various countries varied over a very wide range -by a factor of 35 in the case of sulfur oxide emissions, by a factor of 70 in the case of nitrogen oxide emissions, and by a factor of more than 200 in the case of ammonia emissions. The large differences i n human population density between most of central Europe and the UK compared to the Scandinavian countries are reflected in the much larger emission densities for The Netherlands and the UK compared to those for Sweden and Finland. Similar differences in population density are apparent between Canada and the USA. In The Netherlands and Sweden, per capita emissions of sulfur were very low (8 and 12 kg/yr) in comparison with eastern Canada (94 kg/yr), Czechoslovakia (77 kg/yr), and the USA (52 kg/yr). Finland and the UK showed intermediate figures (33 and 32 kg/yr). Per capita emissions of nitrogen oxides were much more similar in all countries with only a factor of 2.5 separating the values for the lowest country (The Netherlands) and the highest country (USA). The ratios of SOx/NOx (on an elemental weight basis) were less than one in the Netherlands (0.76)and Sweden (0.831, but vaned from two to six in other countries (2.17 in Finland, 2.53 in the UK, 4.80 in Czechoslovakia, 6.33 in eastern Canada, 2.04 in the eastern USA). These figures are reflections of differences in rates of energy use, dominant types of industries, and the strength of control measures used in various countries. Emissions of sulfur dioxide, and to a lesser extent, nitrogen oxides, have been the dominant pollutants of concern with regard to acidification problems in both Europe and North America. In The Netherlands, however, emissions of ammonia are now recognized as the emission of concern -- with larger total emissions, a larger emissions density, and even a larger per capita emissions rate for ammonia than for either sulfate sulfur o r nitrate nitrogen. The importance of total nitrogen deposition also has risen in important as nitrogen saturation and eutrophication as well a s acidification of ecosystems has become more common in Europe. These developments also have led to some important changes in the language of air pollution discussions, especially in Europe, where the terms acidification, acidifying deposition, total potential acidity, total nitrogen deposition, nitrogen saturation, and eutrophication all are growing in frequency of use and concern in both scientific debates and public discussions. In North America, both nitrogen oxide emissions and ammonia emissions were not considered to be a s important as they were in Europe. Although emissions inventories for ammonia were included in the scientific reports for

410

the USA,the major regions of ammonia emissions were considered too distant to be important in areas where significant effects of acidification had been observed. We could find no mention of ammonia emissions in the assessment document for the USA.

As discussed in a later section of this paper, we found the emissions data in Table 2 to be important also in understanding some of the conclusions drawn and the management strategies suggested in the national documents. 2.3. Domestic and InternationalPollutantSources of Concern

In all countries, only a fraction of the total deposition within the country originated from emissions sources within the country itself. Table 3 shows the distribution between domestic and foreign sources to the extent that this is discernible from the national documents. Table 3 Origin of the deposition from sources within each country itself, % of total deposition

EuroDe NL S ~

-N

SF

UK

CS

CAN

USA

10 25 4 0 1 0 1 5

70 60 70

50 XI 40

50 35

80 96

~

Origin of SO, Origin of NO, Origin of NH,

30

804030

--

--

The extent of transboundary exchange of pollutants is a very complex function of the atmospheric half-life of the pollutant, the relative size of the country, location of emission sources within the country, the relative magnitude of domestic sources and sources outside the country, the strength and direction of dominant winds, and many other factors. 2.4. Depositionof Acidification-Relevant Substanw

Rates of deposition varied greatly within all countries. Within Sweden, for example, the areal deposition of sulfur in the north is only about 10% of that in the south. Also, within a given region, differences in type of vegetation, topography, and other landscape and climatic factors influence the rate of deposition. The deposition to a coniferous forest edge is sometimes five times larger than that t o the interior of a forest or to a typical agronomic crop. Because of these large variations within countries, we have presented in Table 4 the estimated mean regional deposition in the most affected regions within various countries. Still higher deposition values were reported in close

47 1

proximity to large point sources, in cloud-impacted forests, and other areas with special conditions. Table 4 Deposition of some acidification-relevant compounds. The values shown are estimates of regional mean values in acidification-affected areas within each country, k g k d y r

NL

S

Euro~ea SF UK

CS

North Arne* CAN USA

..

osition of sulfur oxides-& 24 25 Total, kg S k d y r 8 I2 Wet, kg S k d y r

16 10

30 10

160 100

10

Denosition of n itroven oxides-N: Total, kg N h d y r 19 10 Wet, kg N k d y r 5 5

6 4

10 4

18 10

10 5

f ammonium -N and ammonia-N: 6 30 Total, kg N/ha/yr 60 10 Wet, kg N k d y r 14 5 4 5

-_

_-

16

5

--

14

4

5

..

ition of Ca Wet, k g k d y r

+ MP:

9

3

5

5

13

17 10

l5 8

--

~~

a In the national document for Norway (SNSF report), wet deposition was estimated to account for about 70% of the total s u l h r deposition.

Discussion The data in Table 4 show several intriguing similarities and differences in areal rates of deposition in the most-affected areas within each country: As expected, total (wet plus dry) deposition is greater than wet-only deposition. In Europe, however, the tota1:wet deposition ratio usually was greater than in North America. In the most-affected areas within Europe, for example, total (wet plus dry) sulfate deposition was usually 2-3 times greater than that for wet-only sulfate deposition -- 3.0:l in The Netherlands, 2.1:l in Sweden, 1.6:l in Finland, 3.0:l in the UK, and 1.6:l in Czechoslovakia. By contrast, in North America, the tota1:wet ratio for sulfate deposition is only 1.3:l in eastern Canada and 1.7:l in the eastern USA. Regional estimates in Canada indicate that total sulfate deposition is only about 15%greater than

472

wet sulfate deposition, except for areas near large point sources of sulfur dioxide emissions. The distinctions among the most-affected regions of Europe and North America is less striking with regard to nitrate deposition. The tota1:wet ratio for nitrate deposition was -- 3.8:l in The Netherlands, 2:l in Sweden, 1.5:l in Finland, 2.51 in the UK, 1.8:l in Czechoslovakia, 2.0:l in Canada, and 1.9:l in the USA. The deposition data in Table 4 for the UK refer primarily to Scotland and Wales which contain the most-affected regions. In some parts of southern England, however, the total deposition of sulfur and nitrogen is much greater than in the more acid-sensitive regions of Scotland and Wales (as much as 60 kg of SOX-sulfurhdyr and 70 kg of total nitrogenihdyr (NOxN plus NHx-N). The tota1:wet ratio for deposition of ammonia was sometimes higher than for either sulfate or nitrate deposition -- 4.2:l in The Netherlands, 2.0:l i n Sweden, 1.5:l in Finland, and 6 : l in the UK. Neither total nor wet deposition data for ammonia were found in the national documents for Canada and the USA. In the national documents for Canada and the USA, expected rates of acidification usually were evaluated in terms of wet sulfate depositionihdyr rather than in terms of total (wet plus dry) sulfate deposition, total sulfur deposition, or total sulfate plus nitrate depositionihdyr. I n Europe, total deposition of sulfurlhalyr o r total deposition of sulfur plus nitrogedhalyr (sulfate ion + sulfur dioxide + nitrate ion + ammonia + ammonium-ion/ha/yr) were more commonly used. In the national document for The Netherlands, these ideas were extended further in two closely related concepts called potential acid deposition and actual acid deposition which are defined as follows: "Various substances are considered to contribute to acidification: - the deposition of oxidized sulfur compounds (SOX) includes dry deposition of S02, and sulfate aerosol (SOe), a s well as wet deposition of sulphate (SO4).1mol SOx can lead to the production of 2 mol H+; - the deposition of oxidized nitrogen compounds (NOy) includes the dry deposition of NO, NO2, HN02, HNO3, and nitrate aerosol (NOg), a s well as wet deposition in the form of NO3. 1mol NOVcan lead to production of 1mole H+; - the deposition of reduced nitrogen compounds (NHx) includes the dry deposition Of NH3 and NH4 aerosol, as well a s dry deposition of NH4.- 1 mol NHx can lead to the production of 1mol H+. It should be mentioned t h a t these figures indicate the maximum (potential) contribution. The actual acid load (H+) depends on what happens to the compounds [the chemical and biological processes taking place in ecosystems1 after deposition." [In many ecosystems, especially

473

those deficient in nitrogen, the difference between potential and actual acid deposition can be quite large].

As also shown in Table 4, regional average wet deposition of base cations (Ca

+ Mg) in the most-affected regions does not vary much from country to country.

Nevertheless, base cations can influence the acidity of air and precipitation and sometimes even its acidifying effects in ecosystems. In both Europe and North America, the main sources of Ca and Mg are dust from arable land. In southeastern Finland and some areas of central Europe, however, the amounts of basic cations in dust from some combustion sources in eastern Europe sometimes are so high that they effectively neutralize the sulfate and nitrate in wet and dry deposition. In the most-affected regions of the northeastern USA, wet deposition of nitrate nitrogen seems to be larger than in the most-affected regions of some other countries. As shown in Table 4, the total deposition of nitrate nitrogen is somewhat larger in The Netherlands and the USA than in Sweden, Finland, the UK, and Canada. It is striking that gaseous ammonia and ammonium-ion deposition are considered major air-pollution problems in the national documents for most European countries. But these pollutants are dealt with only very briefly in the national documents for Canada and the USA. Why is this so? We speculate a s follows: The importance of these pollutants derives from three closely related concepts which have gained general scientific acceptance only recently (last 5-8 years): 1)the concept of acidifying deposition (as opposed to acidic deposition). This concept includes the notion of gaseous ammonia and ammonium ion a s acidifying nutrients rather than j u s t a s acidneutralizing constituents in wet and dry deposition; 2) the concepts of nitrogen saturation and optimum nutrition of ecosystems (as opposed to wide-spread nitrogen deficiency in ecosystems); and 3) the concept of nitrogen-induced (as opposed to phosphorus-induced) eutrophication of large lakes, estuaries, and even ocean waters. Much more evidence for these concepts was accumulated in Europe, and especially in The Netherlands and Sweden, than in North America. Manures from large populations of domestic livestock have been regarded a s the largest source of airborne ammonia and ammonium ion in Europe. In central Europe, large domestic animal populations exist in close proximity to areas sensitive to acidifying deposition. In the assessment documents for Canada and the USA, however, these distances apparently were regarded as too long for ammonia to be contributing significantly t o acidification impacts. 2.5. Effects on Surface Waters

Much of the original impetus for development of national programs of research and assessment on the acid-deposition problem derived from

414

discovery during the late 1960s and early 1970s of linkages between: 1) pollution-induced changes in the chemistry of precipitation; 2) concomitant changes in the chemistry of lakes and streams; and 3) changes in fish populations. The original focus of concern was on emissions of sulfur dioxide which led to changes in the sulfate content and therefore the sulfuric-acid content of rain and snow. Later, concerns were broadened to include: Dry deposition of acidic aerosols and gases; Emissions of nitrogen oxides which led to formation of nitric a s well a s sulfuric acid; The concept of acidifying as well a s acidic deposition and thus the inclusion of ammonia and ammonium ion a s part of the several causes of acidification of soil and surface waters; The discovery of episodes of acidic stream water a t times of spring snow melt and after prolonged summer droughts; The acidification of soils and eventually ground water; and The effects of the changing acidity and alkalinity of surface waters on the productivity, health, and reproductive capacity of fish, amphibians, aquatic insects, benthic invertebrates, and other aquatic organisms. Through this series of discoveries relating to the effects of acid deposition on surface waters and aquatic ecosystems came much of our present understanding of the acid deposition issue. It is interesting t o compare the recent national assessment documents in the context of this series of unfolding discoveries and concepts:

Eurom Concern about effects on surface waters

NL

S

Sl?

UK

1

3

3

3

North Amen= CAN USA 3

3

The Netherlands The national document for The Netherlands contains no significant discussion of acidification effects on surface waters and aquatic biota. There are two major reasons for this: 1) there are very few natural lakes or streams in the country. Although a high fraction of the total surface area is surface water, almost all such waters are either highly polluted rivers o r man-made canals with a n extremely high water table; and 2) the subject of surface water effects (mainly focused on small ponds) was discussed in the assessment document completed earlier in 1988 by the Dutch Priority Program on Acidification.

Since Swedish research scientists and their colleagues in Norway have been (and remain) in the forefront of studies of the effects of acid deposition on

475

aquatic ecosystems since the mid-l960s, it was not surprising that the current national document for Sweden contained significant reports of progress in understanding air pollution and acid deposition effects on aquatic ecosystems. "About 16,000 of Sweden's total of around 85,000 lakes are so seriously affected by acidification that sensitive species had greatly declined in number or disappeared completely. Areas where more than 25 per cent of all lakes and watercourses are seriously affected [now cover more than half the total land area of southern Sweden]. The situation of the flora and fauna in 6,000 of these lakes has been markedly improved by means of liming. At least a quarter of the total length of watercourses would be seriously harmed by acidification if i t were not for liming." "Water chemistry studies indicate that the acidification situation for surface waters in Gotaland (southern Sweden), Svealand (central Sweden) and coastal areas of Norrland (northern Sweden) in general has not changed to any great extent since the middle of the 1970s. On the other hand, acidification in the mountains and adjacent areas in northern Sweden has continued to worsen over the last 10-15 years. Deleterious biological effects due to acidification of minor watercourses have increased considerably in the 1980s. Iron, aluminum and manganese are dissolved out of the ground and then precipitated in the water. Fish and many bottom-dwelling animals have decreased in number."

United Kingdom Many studies have shown that streams draining from forest plantations are more acidic and contain higher concentrations of aluminum than streams draining from grassland and moorland. The major factors appear to be the increase in strong acid anions in the drainage water caused by the "airfiltering" effects of the tree canopies and the production of organic compounds in the soil as a result of drying. Sediment core studies have shown that lakes with pH less than 5.0 became common only during recent decades and only in areas of high acid deposition. The downward trend in pH generally began around 1850 and typically involved a decline of 0.5 to 1.5 pH units. All studies point to atmospheric deposition of acidic and acidifying substances as the major causal factor. The ecological effects of acidification are of fundamental importance in the

UK. Populations of salmon and brown trout show evidence of decline, as do several species of frogs. The dipper, an insectivorous riparian bird, has been shown to decrease in abundance along streams in both Scotland and Wales.

A report on Acidity in Scottish Rivers summarizes effects on surface waters a s follows: "In recent years, evidence has been accumulating of the acidification of rivers and lochs in parts of Scotland. In the mid-l970s, a number of lochs in southwestern Scotland with granite catchments were found to be acidified.

476

Several of these lochs were fishless and others supported only sparse fish populations. Subsequent studies in Central Scotland showed that streams draining base-poor catchments with large areas of mature coniferous forest were particularly susceptible to acidification and had impoverished fish and invertebrate communities. More recent work has provided further evidence of acidification and its effects on fish populations, particularly in Galloway. Paleoecological studies have shown that lochs here and in other parts of Scotland (Arran, Rannoch Moor, and the Cairngorms) are acidified." Canada

"Forty-three percent of Canada's land area is sensitive to acidic deposition. Sensitive terrain generally has non-carbonate bedrock and coarsely textured, shallow surface deposits ...The coincidence of sensitive terrain and acidic deposition defines the damage area of concern for aquatic effects. In eastern Canada these conditions occur in an area east of the Manitoba-Ontario border and roughly south of James Bay." "An inventory of lakes with an area slightly smaller than the region of concern described above...found almost 800,000 water bodies greater than 0.18 hectares in area. A special data base has been compiled that contains physical and chemical information for 8,505 lakes across eastern Canada." "The regional acidification of eastern Canadian lakes is primarily due to the deposition of atmospheric sulphate rather than to nitrogen deposition or to natural acidifying agents, such as organic acids or sulphide minerals in the bedrock. Acidification arising from land use changes is not considered to be important." "Apart from the long-term acidification of waters, temporary episodes of acidification may also produce conditions that are lethal to aquatic biota. Storage of acids within the winter snowpack can lead to the release of exceptionally high concentrations of sulphate during early melt stages that may cause short-term acidification of surface waters. Acidification episodes can also be caused by temporary storage of sulphate in the catchment, particularly in wetlands, during dry seasons. Release of sulphate at the onset of the next period of wet weather causes short term acidification of the runoff water."

USA "Within acid-sensitive regions of the United States, 4% of the lakes and 8% of the streams are chronically acidic. Florida has the highest percentage of acidic surface waters (23% of the lakes and 39% of the streams). In the MidAtlantic highlands, the mid-Atlantic Coastal Plain, and the Adirondack Mountains, 6%-14% of the lakes and streams are chronically acidic; about three times that many become temporarily (days to weeks) acidic during storms and snowmelt conditions in these regions. Virtually no (~1%) chronically acidic surface waters are located in the Southeastern Highlands or the mountainous West."

411

"Acidic deposition is the dominant source of acid anions, excluding chloride, in about 75% of the acidic lakes and 50% of the acidic streams in the National Surface Water Survey (NSWS). Most of these have probably become more acidic (declined in pH) because of acidic deposition. These acidic surface waters are found primarily in the mid-Atlantic Highlands, the Adirondacks, New England, the mid-Atlantic Coastal Plain, Florida, and the eastern portion of the upper Midwest." "Natural organic acids are the dominant source of acid anions excluding chloride, in about 25% of the acidic lakes and streams in the NSWS, and these are found in Florida, the mid-Atlantic Coastal Plains, the upper Midwest, and New England." "Acid mine drainage is the major source of acid anions in about 25% of the acidic streams in the NSWS. These acidic streams are located in the midAtlantic and Southeastern Highlands."

26.Ef€ectson Forests The assessment documents for all European and North American countries contained significant sections on the effects of air pollutants and acid deposition on forests: EuroDe Concern about effects on forests

NL

S

SF

UK

3

3

3

2

North Amerka CAN USA 2

2

In the national documents for all six countries, several general conclusions were drawn: Airborne gases and aerosols as well as precipitation, cloud water, and fog were recognized a s significant sources of several of the 16 essential elements needed for plant growth and development, and, most notably, as significant sources of nutrient sulfur and nitrogen; The cumulative atmospheric deposition of acidic and acidifying substances (including sulfate, nitrate, and ammonium ions a s well a s gaseous ammonia, amines, and other nitrogen compounds) were recognized as potential causes of increased acidity and decreased fertility of forest and other wildland soils; Forest trees and other natural vegetation were recognized to be subject to a wide variety of natural and human stress factors. These include natural competitive stresses, natural climatic stresses such as drought, frost, and wind, natural nutrient stresses such as nutrient deficiencies and excesses, natural biotic stresses -- especially insects and fungal diseases, human disturbance stresses, and air pollutant stresses. Thus, it was

47 8

always difficult to reliably distinguish between the individual and combined effects of airborne chemical stresses and other natural or human stress factors acting singly or in various combinations; Ozone was recognized as a significant stress factor for forest trees and other natural vegetation in many parts of Europe and North America. The emphasis given to these several generalizations varied considerably in the national documents from each country in Europe and North America.

The Netherlands The major conclusions regarding effects on forests in The Netherlands include the following: "Increasing nitrogen deposition over a period of several decades has led, first of all, to a removal of nitrogen deficiencies and increased growth, and secondly, to nutrient imbalances as a result of magnesium, potassium, and phosphorus deficiencies. More and more forests are moving from a situation of nitrogen deficiency to a situation of nitrogen saturation. At the moment [1990]about 15% of the Dutch forest soil is saturated. At the same time, the nitrogen input, together with SOX deposition, is causing considerable soil acidification. The present contribution of nitrogen to actual soil acidification is about 35%, and that of sulfur about 65%. The combined action of increased nitrogen availability and soil acidification has led to a decline in cation availability (nutrient deficiency). This is resulting in a greater risk of damage to forests by pests and plagues, frost and drought." "In The Netherlands, soil acidification is the greatest risk factor. The research carried out in the context of the second phase of the Dutch Priority Program on Acidification has confirmed the hypothesis that Dutch forest soils are degrading (radical physico-chemical changes in the long run) by deposition of acidifying substances. This hypothesis was proposed about five years ago on the basis of various measurements and data from other countries. Confirmation of this hypothesis was obtained from input-output budgets and model analyses, and through nation-wide monitoring of soil solution chemistry. A major concern are virtually irreversible changes in the soil caused by depletion of the aluminum buffer, and the consequences of a decline in pH (to between 2.8 and 2.9) associated with aluminum depletion, which in the event of unchanged deposition) is the expectation for Dutch forest soils. In any case, large changes in the soil and thus in the conditions of forests stand locations, are to be expected. This could lead to changes i n vegetation and soil fauna."

Sweden The assessment document for Sweden is less worrisome with regard to effects on forests in large part because of lower rates and cumulative amounts of deposition of sulfur and nitrogen compounds, and lower ozone concentrations

479

than in The Netherlands. Nevertheless, the document contains the following statements regarding effects on forests:

"A considerable portion of Swedish forest is suffering from impaired vitality. Approximately 20 per cent of spruce trees and 14 per cent of pine have abnormal needle loss (more than 20 per cent of needles). Deciduous trees such as beech, oak, and birch display more extensive damage than spruce o r pine. Such damage is manifested in the form of thinning and a n altered growth pattern in the crown. It is not possible to distinguish a clear trend in the damage caused to spruce and pine over the last six years [198419901". "Increasing soil acidification and the impoverishment of forest land thereby caused appear to be the greatest long-term threat to Swedish forests". "Uncultivated [mostly forest] land in the south of Sweden has been acidified to a considerable extent over the last few decades. Acidification of soils in Skdne and Halland, as well as in southern Smdland (all provinces situated in Gotaland) has penetrated to a depth of several meters, where i t affects the superficial ground-water. This acidification has meant that the easily available store of nutrients such as calcium and magnesium in the soil has diminished between 30 and 70 percent in southernmost Sweden. A t the same time metals such a s aluminum are liberated. Such metals are poisonous to plants and animals." "There are strong indications that forest soils in southern Sweden are approaching nitrogen saturation, with resultant acidification, nitrogen leaching and nutrient imbalance in the trees. Large areas of southern Sweden may be suffering from nitrogen saturation within 10-20 years unless nitrogen deposition can be reduced."

United Kingdom Surveys of the health of forests in the UK suggest that significant changes in crown density have taken place in sitka spruce and scots pine. Beech forests are not in good health in some parts of the UK. Air pollution cannot be excluded as a contributing stress factor. There is no direct proof of pollution-related decline of forest trees in the UK. But some forests are subjected t o pollution climates which probably cause stress. There is good evidence that air pollutants decrease the frost resistance and winter hardiness of forest trees. Damage by some fungal diseases and insects seem to be increased by exposure to air pollutants. Canads

"In Canada, most of the forests exposed to high levels of acid deposition and ozone are those close to populated areas. These forests are some of the most productive in the country and the most heavily utilized. Typical uses include

480

recreation, tourism, wildlife habitat, aesthetics and forest products activities (woodlots, maple syrup, quality softwood and hardwood lumber)." "There is general agreement that the current episode of maple decline in Canada is more severe and more extensive than those which have occurred in the past. Although no current evidence currently exists for a direct (foliar/airborne) o r single component causal role for acidic deposition o r ozone in any of the current tree declines i n eastern Canada, studies conducted in Ontario and Quebec indicate that acidic deposition and other long range transported air pollutants may be indirect (soilhutrient) o r contributing (pre-disposing) factors in sugar maple decline. The role and importance of these additional stresses on the trees already under natural stresses such as climatic extremes (drought, temperature), or attack by insects and disease, remains unknown but must be viewed with concern." "Symptoms of maple decline and tree mortality have continued to increase in severity and extent. Other species in the same stands have also been affected. In many areas subject to acidic deposition and experiencing tree decline, soils have become deficient in several essential nutrients. Nutrition research has indicated that soil chemistry is a n important factor in the decline syndrome and that in the short term, forest fertilization can provide a n effective ameliorative treatment." "Dendrochronology data from Ontario maple decline studies also indicate that significant growth reductions have occurred in declining a s well as outwardly healthy trees since the mid-1940s to mid-1950s in regions experiencing moderate to high levels of acidic deposition and ozone." "Research a t New Brunswick has circumstantially linked the white birch deterioration along the Bay of Fundy with exposure to acidic marine fog."

USA "Ozone is important in a decline of pines in southern and central California and is the pollutant of greatest concern with respect t o possible regionalscale impacts in North American forests." "Within the Los Angeles Basin and the southern and central Sierra Nevada Mountains, ozone has been documented to contribute to decline in the health of mixed conifer forests in the San Bernardino Mountains. There is evidence for alteration of productivity, ecosystem dynamics, and physiological processes of ponderosa and Jeffrey pines by ambient levels of photochemical oxidants. Field studies support the occurrence of these alterations in time and space with patterns of oxidant occurrences. "Controlled exposure studies with a wide variety of forest species have shown either no effect, mixed results, o r negative effects on growth a t ambient levels. As a result, quantitative, reproducible exposure-response functions are not as available for tree species as they are for crop species."

48 1

"There is no conclusive evidence of widespread forest damage from current ambient levels (pH 4.0-5.0) of acidic deposition in the United States". "Although crop production rates are high and most forests appear healthy, acidic deposition and associated air pollutants affect some terrestrial ecosystems." "There are indications that acidic deposition and associated pollutants have contributed to growth reductions and mortality of red spruce a t high elevations in the northern Appalachians and to growth reductions in red spruce in the high elevations of the southern Appalachians." "Long-term changes in the chemistry of some sensitive soils are expected, but it is uncertain whether these will result in reduced forest health, how the effect would be manifest, how much of the forest resource would be affected, o r how long it would take for such effects to occur." 2.7. Effects on Agriculture

-

Significant differences in concern about effects of acidification and air pollutants on agricultural crops were evident among the various national documents:

Concern about effects on agricultural crops

NL

S

SF

UK

0

2

1

1

North A& CAN USA

3

3

The national documents for the European countries, include only very brief statements about the effects of gaseous air pollutants and acid deposition on agricultural crops and none about effects on domestic livestock. By contrast, the assessment documents for Canada and the United States, deal both explicitly and a t length with effects of gaseous air pollutants and acid deposition on agricultural crops. But they too contain no information about effects of ozone or acid deposition on animal agriculture. Sweden

"Ozone levels in Sweden during the summer months are near or above the levels which, in the short or long term, harm crops. In western Sweden the present ozone levels reduce the crop of spring wheat by around 10 percent, while barley seems to be less susceptible. Crops such a s meadow grass, oats, and potatoes are also affected".

United Kingdom Ambient concentrations of ozone are known to decrease yields of some sensitive crops in some areas of the UK. Interactions between pollutant

482

stresses and other stress factors such as diseases and insects also have been demonstrated in various locations. Current concentrations of sulfur dioxide and nitrogen oxides in the UK usually are too low to cause significant harm by either pollutant acting alone. Increased damage by ozone has been observed when ozone and sulfur dioxide o r ozone and nitrogen oxides occur concurrently. Canada

The Canadian assessment document on Terrestrial Effects includes a chapter on effects of acid deposition and other air pollutants on agriculture crops. Ozone is the major air pollutant of concern to agriculture in Canada and critical levels for foliar injury are included in the assessment document. A significant reanalysis was made of the adequacy of Ontario's present ambient air quality standard for ozone (80 ppb for one hour) to protect agricultural crops and ornamental plants from harm. The conclusion was that attainment of this standard would provide economic benefits to agriculture in Ontario alone of between $170 million and $1.9 billion per year. Effects of sulfur dioxide on crops is not discussed but effects of peroxyacetyl nitrate (PAN) and nitrogen oxides are mentioned as potential causes of direct effects and of interactive effects with ozone. Field experiments in Canada and the United States have shown no significant direct effects of acid deposition on yields of crop plants (with the exception of a single variety of soybean (Amsoy). Also, no important interactions between acid deposition and ozone were reported.

USA The United States assessment document also includes a section dealing with effects of acid deposition and other air pollutants on agriculture. Although sulfur dioxide is reported to cause occasional damage to crops in the vicinity of major point sources of pollutants under unusual meteorological conditions, ozone is the major air pollutant of concern to regional crop production. A major study called the National Crop Loss Assessment Network (NCLAN) provides a very thorough analysis of ozone impacts on the yield of agricultural crops. The important crops found to be damaged by ozone include alfalfa, corn, cotton, soybeans, sorghum, forage, rice, and both spring and winter wheat. These nine crops account for 75% of the value of total crop production in the United States. The NAPAP assessment document contains estimates of the potential changes in wheat, corn, soybean, and sorghum production in each of the 10 major agricultural production areas of the United States. The document contains two major conclusions about agricultural effects: "Ozone represents a significant stress factor in agricultural crop production in the United States. Depending on species, location, and exposure, yield reductions in crops have been estimated to range from 2% to 56% a t ambient ozone concentrations"; and

483

"Acidic deposition a t ambient levels is not responsible for regional crop yield reduction." NCLAN provided estimates of the range of economic impacts of ozone on crop production in the United States ($1 to $5 billion per year). The NAPAP assessment document concluded that: "Substantial increases in tropospheric ozone levels above background level [approximately 30 ppbl, can be expected t o cause biological damages or crop yield reductions. However, an evaluation of economic effects requires a n allowance for the action of market forces..." These market forces were not considered in developing the NCLAN estimates of economic impacts. 2.8. Effects on Natural Terrestrial Flora and Fauna

Relatively few studies have been made of the effects of air pollutants on terrestrial fauna and flora (non-tree species). This topic has played a minor but recently growing role in most national research programs. It has rather strong implications for the air pollution policy especially in some European countries:

EuroDe N

L

S

S F U K

North America CAN USA

Overall impact'concern

3

2

2

2

1

0

Vascular plants Lichens, mosses Birds Heavy metals in moose Land snails

3 2 2 0 0

2 2 2

2 2 0 0 0

2

1 2

0 1 1 0 0

3 2

2

2 0 0

2

3 0

The Netherlands Increasing atmospheric deposition of total nitrogen strongly stimulates growth of nitrogen-loving grasses (e.g. Molinia caerulea and Deschampsia flexuosa) and herbaceous plants (e.g., Urtica sp. and Rubus idaeus) over large forest areas. Heathlands in The Netherlands are being rapidly transformed into grassland, mainly due to acidification and excessive inputs of nitrogen. About one third of the heathland is still healthy, about one third contains large amounts of grass and will probably change into grassland within 3-5 years, and one third has already changed into grassland. Some rare heathland species have almost disappeared, probably due to direct effects of gaseous sulfur dioxide coupled with soil acidification. The critical

484

level for sulfur dioxide impacts on heathland in The Netherlands is estimated to be about 8 pg sulfur dioxidelcubic meter -- a n amount which is frequently exceeded. The main cause of these vegetational changes is excessive deposition of nitrogen. The changes are o r major interest i n policy-making. Separate critical loads for nitrogen have been established based on the criterion of “vegetation changes” in both heathlands and well-drained sandy forest soils. Changes in lichen populations also have been observed in The Netherlands -decreases early in this century, probably caused by sulfur dioxide, followed by increases in recent decades probably caused by ammonia which now neutralizes the harmful effects of sulfur dioxide.

Sweden Vascular flora, particularly in deciduous forests in southern Sweden, have changed over the last 15-35years. Species which prefer only weakly acid soils have declined while species with a preference for nitrogen-rich environments have increased. The same tendency may be seen for fungi. Even larger changes in fungal flora are expected by the year 2000. Extensive changes in epiphytic mosses and lichens have been observed in southern Sweden. Approximately 130 species are affected. Many species have disappeared or become threatened during the past 40 years. These changes are believed t o be caused by changes in both nitrogen and acid deposition. Effects on birds are seen especially among species (such as osprey) that feed on aquatic organisms. There also are signs that populations of overwintering coniferous forest birds have decreased in areas of damaged forests in southern Sweden. Acidification causes decreases in available soil calcium. These changes have had severe effects on populations of land snails i n several parts of southern Sweden. Strong accumulation of cadmium in kidneys and livers of moose has been established in a gradient from south to north. These organs have been declared unfit for human consumption in affected parts of the country. United Kingdom

In the northern and western UK, semi-natural vegetation covers a large proportion of the total land surface. Few data exist on the impact of air pollutants on natural vegetation other than some bog plants that are known to be affected by acidifying deposition. Little is known about effects of increased deposition of nitrogen compounds, including ammonia, on a wide array of plants species. Nitrogen deposition has caused some changes in vegetation that affect grouse habitat.

485

Many species of birds live near lakes and streams, with some totally dependent on fresh waters for food. Osprey and other fish-eating birds have been adversely affected. Effects on dipper populations have been studied in some detail. Both in Wales and Scotland, dippers are scarce on streams with pH less than 5.5 to 6.0. On a Welsh river, abundances of breeding dippers declined by 80 to 90% between the 1950s and 1980s a t the same time that the pH of the river water decreased.

Food chain effects through lichens and some other forage organisms, have resulted in accumulation of cadmium in kidneys and livers of moose and deer living in poorly buffered areas. These organs have been declared unfit for human consumption in several provinces. Defoliation in declining maple stands has been shown to decrease populations of some birds. Increased acidity in deposition results in decreased growth, size, and ground cover by some cryptograms, including several species of Cladonia and the feather moss, Pleurozium Schreberii. Rainfall events of pH 3.5 or lower pose a threat t o some species of herbs and lichens. This might have serious wildlife implications, since lichens are an important winter food source for ungulates. Wetland birds, e.g., the common loon and osprey, are affected, probably through changes in quantity and quality of their food supply in acidified lakes.

OthercoUntries In contrast to the situation in several countries in Europe, impacts of air pollution on terrestrial fauna and flora were not identified a s a n effect of concern in the 1980 Norwegian assessment document o r the 1990 assessment document for the USA. In many European countries, impacts on natural flora and fauna now play a n important role in establishing environmental goals. These differences with Norway and the USA might be due to: Significant differences in the magnitude of effects, perhaps because nitrogen deposition impacts are greater in some parts of Europe. Possible differences in societal and government attitudes between 1980 and 1990 or from one country to another. Changes in natural fauna and flora and disappearance of species are now matters of major concern in public discussions of the environment in some countries. 29. Effects on Soils

Results Acidification of soils can be expressed in various ways. It is often defined as a decrease in acid neutralizing capacity (ANC) or sulfate absorption capacity

486

(SAC). The soil solution characteristics are of key importance in evaluating the effects of acidifying deposition. Effects on forest soils were of great concern i n many of the national documents, especially those for European countries:

EuroDe N Overall impact/concern

3

L

S 3

S F U K 2

3

North America CAN USA 1

1

The Netherlands In The Netherlands, acidification of forest soils by airborne sulfur and nitrogen compounds has led to rapid depletion of base cations and increasing soil-solution concentrations of aluminum in the root zone of trees. A1uminum:calcium ratios are very high and aluminum concentrations frequently exceed the critical value of 2 lg/l for damage to tree roots. Mobilized aluminum is currently the main buffer system i n sandy soils. Mathematical models of these soils indicate th a t current rates of acid deposition will cause the exhaustion of the aluminum buffer system within 10 to 100 years. These acidifying effects are attributed primarily to total sulfur deposition (65%) and total nitrogen (35%)deposition. Sweden

Acidification of forest soils has increased dramatically during the past 50 years. The extent of these effects is most pronounced in southern Sweden and decreases progressively to the north. No acidification of soils has been detected in Norrland. Decreases in pH of 0.5 to 1 pH unit (and sometimes even 2 pH units) have been observed in large parts of southern Sweden. At present, the total land area with a pH of mineral soil below 4.4 is about 650,000 hectares. In this area, soil acidification has penetrated to a depth of several meters. Also, the easily-available base-cation content of these soils has decreased by 30-70% since 1950. About half of the acidification of superficial layers of forest soils results from natural processes, especially growth of forests and timber harvesting. Acidification of deeper layers of forest soils cannot be explained by natural processes. These deep-soil effects can only be explained by the cumulative deposition of acidifying substances from the atmosphere. About 90% of current changes in soil acidity are attributed to sulfur deposition, the remainder to nitrogen. Finland

Time-series data on soil acidification are not available from Finland. But mass balance calculations indicate similar extent and distribution of soil

487

acidification a s in Sweden. In southeastern Finland base cations often neutralize the strong acid anions in precipitation and thus minimize soil acidification.

United Kingdom As in other European countries, atmospheric deposition of sulfur from anthropogenic sources superimposed on already substantial deposition of sulfur from marine sources are believed to cause changes in the chemistry of terrestrial ecosystems and soils in the UK. Acidification of some sensitive soils also has been demonstrated in several areas of the UK. The extent to which acidity of upland peats has increased is not clear. Large inputs of nitrogen, especially ammonia, may have significant impacts in some sensitive soils. Long-term changes in soil acidity are suspected to decrease rates of litter decomposition and subsequent release of nutrients and to affect mycorrhizae on forest trees. The Critical Loads Advisory Group for the UK has recently published a series of maps showing the geographical distribution of critical loads for acidity and sulfur deposition into soils. These maps were then combined with maps for non-marine sulfur, nitrogen, calcium, and magnesium deposition in order to identify regions where critical loads for deposition of acidity and sulfur are exceeded. These maps show that large areas of west-central England and of west-central and northern Scotland are receiving total loads substantially in excess of the critical loads for both sulfur and acidity.

Canada Impacts of acid deposition on forest soils in Canada have not been well documented. But nutrient deficiencies have increased in recent years and decreases in soil pH have been detected. These changes in properties are thought to be contributing factors in the current changes in condition of maple and birch forests in southern Ontario and Quebec.

A recent analysis based on known soil properties and bedrock geology in eastern Canada indicates that 46% (400 million hectares) of the land surface mapped is considered sensitive, 21% moderately sensitive, and 23% less sensitive to acidification. The proportion of total land area considered sensitive was 82% for Quebec and 34% for Ontario. It is considered unlikely that current rates of nitrogen deposition to forests in Canada will produce nutrient imbalances in the short-term. Thus, sulfur deposition is considered the dominant cause of soil acidification in Canada.

USA Most soils in the eastern USA, where emissions and deposition of sulfur and nitrogen, and emissions of volatile organic compounds are concentrated, are inherently less sensitive to acidification than those in large parts of eastern Canada. Model simulations suggest that most soils in the eastern USA will not

488

experience large changes in chemical properties a t current rates of sulfur deposition. Even if sulfur deposition were increased by 30%, base saturation of most forest soils is expected to decrease by only 2-4% in a 50 year period. If sulfur deposition were decreased by 50%, base saturation is estimated to increase by 1-2% in 50 years. In eastern spruce-fir forests, especially at high elevations above cloud base, however, some changes in soil chemical properties and significant changes in rates of growth, susceptibility to winter injury, and rates of mortality of the trees have been detected. Regardless of region or elevation, soils within sprucefir forests are by nature strongly acidic (pH 3.5-4.5) and have mineral horizons with low base saturation (3-15%). Peak soil aluminum concentrations and aluminudcalcium ratios a t several sites in the southern Appalachians approach o r exceed the toxicity threshold for red spruce seedlings. Values in the northeastern USA typically have remained below this threshold. The total nitrogen content of spruce-fir soils is especially high in the southern Appalachians. Under current rates of sulfur and nitrogen deposition, the combination of large soil nitrogen pools and low carbodnitrogen ratios are expected to result in increased nitrate and aluminum concentrations in the soil solution. Discussion

The national documents for several countries suggest that biological processes and intensive forest management are of substantial importance in the acidification of humus and the upper-most portions of the mineral soil. I n deeper horizons, however, it appears that atmospheric deposition is the principal cause of acidification. Soil acidification is a matter of major concern in most of the national documents for European countries. Dramatic changes have been demonstrated in soil acidity, buffering status, ion exchange capacity, sulfate absorption capacity, weathering rates, and most importantly, nutrient supply and availability. These processes are thought to pose a threat to the long-term productivity and both the natural function and structure of terrestrial ecosystems in Europe. Impacts on soil chemistry do not seem to be very obvious in North America. In some areas, especially in eastern Canada, however, it appears that soil aluminum concentrations exceed critical levels. Also, essential nutrients in some soils are near or below suggested critical levels. These differences between Europe and North America might be explained by: Real differences in intensity and duration of land use. The landscape of Europe has been under intensive management by humans for many centuries. As a result, essential nutrient reserves have been depleted through erosion, intensive cropping and grazing, litter removal, treecutting, burning, and other land-use practices.

489

More intensive study of soil processes in Europe. Studies of the impact of airborne chemicals on soils were given very high priority i n many European countries. Detailed studies of soils early in this century also made it possible to remeasure soil properties on the same plots after time periods of 10 to 70 years. There are few places in North America, where reliable remeasurements of soil properties can be made over these time scales. In part this reflects differences in approaches in earlier forestry research. Detailed characterization of soils on fixed plots is more common in Europe than in North America. The 1981 final report of the SNSF project in Norway, included the following statement about acidification of soils: "Acid precipitation may result in changes in the properties of the soil. At present it is difficult to draw any definite conclusions in the time required. Severe effects can hardly be expected to be observed. Some land use changes (spreading of coniferous forests) have for a long time been known to affect acidity of the soil. Acidification may affect micro-organisms and invertebrates. The ecological importance of this is uncertain." 2.10. Effects on Groundwater

Acidification and other changes in groundwater and drinking-water quality were of some concern in most national documents: N Overall impactlconcern Major changes of concern

L

2

pH NO2 Al-

Euro~e S S F U K

th A m e d CAN USA

3

1

1

1

1

pH Cu Cd

pH

pH

PH

PH

Pb cu A1

Pb Pb

"he Netherlands

In a study a t 150 locations, the nitrate content of groundwater exceeded the drinking water standard (50 mg/l) in 30% of the coniferous forest sites and 13% of deciduous forest sites. The aluminum content of shallow groundwater exceeded the drinking water standard (7 pmoV1) in 90% of the coniferous forest sites and 70% of deciduous forest sites investigated.

490

Sweden

Groundwater accounts for about 50% of the municipal water supply i n Sweden. Approximately 1.1 million permanent residences and 2 million temporary residences (summer houses) use groundwater from their own wells. Acidified groundwater is found in most areas where soils and lakes are acidified; this is especially true of shallow groundwater. Acidification during the past 40 years has been the primary cause of changes in groundwater quality. Alkalinity in groundwater has decreased over large areas. Acid well water sometimes results in corrosion of household plumbing systems with resulting costly damage and dissolution of heavy metals, especially cadmium and copper. Very high concentrations of copper have been found in drinking water from many private wells. In a study of 300 households in western Sweden more than 25% had copper concentrations greater than 3 pgA.

Finland Acidification of groundwater has been documented and this has enhanced public understanding of the acidification issues in Finland. Groundwater is a significant source of drinking water especially in the countryside. The general public and policymakers, however, appear less concerned about human health effects than about ecological effects of acidification.

United Kingdom Groundwater acidification is not dealt with in the national documents for the

UK. Canada

Groundwater sources make up a significant proportion of all drinking water used in Canada. Twenty-six percent of Canadians use groundwater from domestic wells and approximately 38% of municipalities rely entirely or partly on groundwater. The overall rate of groundwater acidification in Canada is unknown. Short term acidification of shallow groundwater has been reported in association with large acid-loading events such as spring snow melt. If acidic deposition continues, the frequency and duration of near-surface pH depressions in the groundwater are expected to increase.

USA Acidification of groundwater is not specifically addressed i n the NAPAP Integrated Assessment report. Lead and methyl mercury are the only substances that are considered likely to pose increased health risks due to acid deposition. Discussion

Acidification of groundwater is generally regarded a s a slow process that results from the cumulative effects of acidifying deposition over decades of

49 I

time. Short-term acidification of shallow groundwater has also been reported, usually in association with acid-release episodes such as spring snow melt. Acidification of groundwater has been observed in large parts of Sweden. Here, groundwater is a n important source of both municipal and household water supplies. Acid well water results in corrosion in household plumbing systems, with resultant damage caused by leaks. Sharply increased concentrations of copper pose potential health risks. In The Netherlands, groundwater is strongly acidified and contains high concentrations of nitrates. Since groundwater from individual wells is not so widely used, however, these effects are of only moderate concern. Parts of southeastern Canada and the northeastern USA may experience groundwater acidification in the future. The 1980 Norwegian assessment document does not specifically address groundwater acidification. 2.1 1. Effects on Human Health

Results Air pollution can affect human health both directly and indirectly -- directly when people inhale toxic gases o r aerosols, and indirectly when acidification causes mobilization and/or dissolution of toxic metals that are then ingested with drinking water or foods. Mobilization of lead from soldered joints by acidified drinking water and accumulation of mercury in fish from acidified lakes are examples of indirect effects. Considerable variation in concern about these two types of effects on human health were evident in the various national documents: NL Direct health effects Indirect health effects

0 0

EuroDe S SF

UK

0 1

0 1

1 2

North A m x i ~ a CAN USA

2 1

3 1

The Netherlands Human health effects are part of another research program and hence not evaluated in Acidification Research in the Netherlands. Effects of long-term exposure to ozone are of concern. Acid aerosols are under suspicion. All drinking water is treated and meets EEC-standards. Sweden

The ambient air quality standard for ozone is exceeded in large parts of Sweden. Acidification of ground water is a matter of great concern because of increased risk to human health due to increased intake of heavy metals. Several studies have shown a connection between copper in drinking water and diarrhea in infants. A possible connection between copper toxicity and

492

cirrhosis of the liver is currently being debated. Although a causal linkage between aluminum and cadmium in drinking water and human health has not been established, their presence in drinking water from private wells is a matter of concern. Accumulation of methyl mercury in fish from acidified lakes has been demonstrated repeatedly. The guideline of 1 p g k g in pike is exceeded in thousands of lakes. The livers and kidneys from moose have been declared unfit for human consumption in many acidified regions of Sweden.

United Kingdom Effects of acidification and air pollution on human health is not dealt with specifically in the review group documents for the UK. The potential risk to humans from acidification is discussed briefly in the report on fresh water. Most of the surface water used for domestic water supplies receive treatments that do not include adjustment in pH or other measures to decrease metal solvency or corrosivity. Thus, soft acid waters may dissolve copper and lead from plumbing systems.

Canada Although a great deal remains to be learned about the health effects of air pollutants, there is now incontrovertible evidence that ozone and other pollutants are contributing to observed effects on human health i n Canada. In many Canadian cities, current peak ambient concentrations of ozone a r e sufficient to cause transient respiratory effects in healthy people. There is strong evidence that human health also is impaired by exposure to acid aerosols. The combination of ozone and acid aerosols is suspected to increase individual susceptibility to respiratory disease. An estimated 300,000 people in acid-sensitive areas obtain their drinking water from unregulated sources that may be affected by acidic and acidifying deposition. More monitoring of such water supplies for the presence of toxic metals is required before the risk to public health can be evaluated.

In some acid-sensitive areas in Canada, moose, deer, and caribou accumulate such high concentrations of cadmium in liver and kidneys that these organs have been declared unfit for human consumption.

USA Ozone and other photochemical oxidants are the most significant air-pollution threats to public health in the United States. About 145 million people live in areas that exceed the national air quality standard for ozone -- 0.12 ppm for one hour. The annual ambient air quality standard for sulfur dioxide (0.03 ppm) is attained virtually everywhere in the USA. A similar situation exists for nitrogen oxides. A t present, only the Los Angeles area exceeds the 0.053 ppm annual average air quality standard for nitrogen oxide. There is an emerging

493

database on the effects of acute (1-2 hour) exposures to nitrogen oxides on the lungs of some sensitive asthmatics. The databases on health effects and exposures to acidic aerosols have major uncertainties that preclude quantitative risk assessment. However, the information available justifies concern over the potential for health effects a t high ambient concentration of acid aerosols, especially for acid sulfate particles. Preliminary sensitivity analysis suggests that continuing acid deposition could significantly increase drinking water lead exposures. In the eastern USA, the population potentially a t risk because they obtain drinking water from shallow wells includes about 18,000 children and 7,000 women. Methyl mercury exposure due to acid deposition is not thought to be a significant problem, except for individuals who consume substantial amounts of fish from acidified lakes and streams. People who consume typical amounts of wild game are not likely to have significantly increased exposure to toxic metals due to acidic deposition.

Discussion Human health effects of air pollution and acidification were not discussed in the national documents for The Netherlands, Norway, or Finland. The direct health effects of ozone and acidic aerosols were of major concern in the national documents for Canada and the USA. By contrast, indirect health effects of acidification were not well quantified in the documents for either country. In Sweden, indirect health effects of acidification via drinking water and food are judged to be a substantial future health risk. Increased methyl mercury in fish is a large problem today. The widely varying attention given to health effects of air pollution and acidification in the national documents from different countries may be explained in part by the following: Real differences in human exposures. Almost all drinking water in The Netherlands is chemically treated. In Sweden and Finland, however, ground water from wells is commonly used. Soils and ground waters in Sweden are more strongly acidified than in North America and thus cause more obvious indirect effects. The high population density in urban areas in North America leads to high concentrations of ozone and other oxidants as well as acid aerosols. Different research priorities. In Europe, indirect health effects generally have had high priority, while direct health effects are of greater concern in North America. Similar differences in priority also are evident in the case of research on terrestrial effects.

494 2.12. Effects on Visibility

-

The most striking of all differences in concern about effects of air pollutants among the various national documents was the complete absence of discussion about pollutant-induced changes in visual range in Europe and its substantial emphasis in the documents for the USA:

Concern about effects on visibility

NL

S

SF

UK

CAN

0

0

0

0

1

America USA 3

The national document for the USA included substantial emphasis on both the fundamental physics of haziness in the atmosphere and the quantitative anaIysis of relationships between particulate matter in air and the quality of scenic vistas in parks and rural areas. A unique computer-assisted method for analysis of visibility effects is presented in the State of Science document on visibility. We infer from the complete absence of discussion of visibility impacts of air pollutants in the national documents for European countries that Europeans generally must have come to accept loss of visual range in scenic vistas and in rural and urban areas. They apparently regard it a s a n unfortunate (but unavoidable) consequence of the high population density and style of modern life in Europe. Apparently, both the public and federal and state government agencies in the USA continue to regard scenic vistas a s a n important part of the natural and cultural heritage of the nation. 2.13. Effects on Engineering Materials and Cultural Resources Significant differences were evident among the various national documents i n degree of concern about effects of acid deposition and air pollutants on engineering materials and on cultural resources such a s monuments, statuary, and historical buildings: EuroDe Concern about effects on engineering materials and cultural resources

NL

S

SF

1

2

1

UK 3

North America CAN USA 2

3

The Netherlands

In the national document for The Netherlands, we could find no discussion about effects of acidification on engineering materials or cultural resources. We are aware that effects on buildings and water works are,of concern within the country, however.

495

The national document for Sweden emphasizes the effects of acidification on underground installations and constructions: "One effect of acidification is that installations in contact with soil and water corrode more quickly than they otherwise would. ...Waterpipes, road culverts and similar constructions are affected both via the ground and via acidified water. 'I

"Zinc is the metal most sensitive to acidification, and corrosion of zinc constructions increases with falling pH and alkalinity in water. Lead is also considered to be sensitive to acidification, as are copper, cast-iron and carbon steel." "There is a certain correlation between the occurrence of corrosion damage in water pipes in Sweden and acidified lakes. The Swedish Water and Waste Water Works Association has estimated the total cost of corrosion damage to the water supply network throughout Sweden amounts to approximately 1 billion kroner per year. The Corrosion Institute carried out a study on the situation a t the beginning of the 1980s, in which i t was estimated that approximately one third of indoor corrosion damage has been caused by acidification."

United Kingdom Laboratory studies have shown clearly that air pollutants can damage most building materials. There is increasing evidence t h a t pollutants act synergistically. Commonly used damage functions usually do not take account the complex interactions among environmental variables t h a t affect the stability of building materials (e.g., the chloride content of air, synergism in the effects of nitrogen and sulfur oxides, the role of moisture in both vapor and liquid forms). There is no unequivocal evidence that present rates of weathering of stone and most metals in the structure of historic buildings are significantly different from those in the recent past. Different materials show different sensitivities to air pollutants. Various types of stone and metals interact strongly with sulfur and nitrogen oxides. Concrete shows reaction to carbon dioxide, while paints, plastics, and organic materials show greatest sensitivity to photochemical oxidants. It has so far not been possible to determine with confidence, relationships between pollutant exposure and rates of weathering or damage including the effects of present exposures and future changes in exposures which might result from changes in pollutant emissions. Thus, i t is not possible to develop reliable estimates of the costs of damage to buildings in the UK.

496

Canada In the national document for Canada, we could find no discussion of effects of acidification on engineering materials and cultural resources. But we are aware of concern within Canada about accelerated weathering a n d deterioration of buildings in urban areas -- especially buildings of special historical value.

USA The national documents for the USA include three separate State of Science and Technology reports dealing with materials: Effects of Acidic Deposition on Materials, Processes of Deposition to Structures, and Distribution of Materials Potentially at Risk from Acidic Deposition. There is also a n extensive discussion about materials damage in the 1990 NAPAP Integrated Assessment. Emphasis is given to three broad categories of materials mainly in urban environments: 1) functional construction, 2) structures with unique artistic qualities, and 3)structures with historical value. A few excerpts and conclusions drawn in these reports are instructive:

In functional construction, the following materials may be listed in order of decreasing sensitivity to acidic deposition: galvanized steel > marble > painted steel and limestone > painted wood > bricwmortar > copper > aluminum concrete. "The key concern for construction materials is additional public and private expenditures to maintain an acceptable level of fbnctionality and appearance for the duration of the structure's economic life. This can involve using more durable materials or stricter design standards as well a s maintenance actions on existing structures...Aesthetic and safety concerns may exist if maintenance does not always occur promptly in response to physical damage." "Marble stone statuary ranks high in terms of sensitivity, lack of protective options, and irreplaceability but is not exceptionally prevalent. Other statuary (e.g., bronze) is less sensitive and is possible to protect, reducing the importance of damages that otherwise would be irreversible." "Important historical buildings in the United States are listed in the National Register of Historic Places. This source indicates that there are over 275,000 historic buildings in an 18-state region of the Northeast, about 35,000 of which are constructed partially o r wholly of stone. All but 3% of the properties are located in urban areas. Five percent of the registered historic structures are of special value [and are] listed a s National Historic Landmarks." "The value of cultural resources derives from their symbolic a s well a s from their practical functions in society. ...Since the early 1980'9, annual expenditures for rehabilitation of existing structures have equaled or

497

exceeded investment in new construction (in the range of hundreds of billions of dollars), a n unknown portion of which was performed on historical structures. ...It is important to bear in mind, however, that not all of these expenditures are due to air pollution. ...Future incremental damages due to sulfur-related acidity will be smaller, even without further controls on SO2 emissions." 3.0. THE CRITICAL LOADS APPROACH -- IN WHAT COUNTRIES IS IT

USED?

Results Many nations are looking for more effective and scientific means for assessing the expected effects and comparing the benefits and costs of various types of emissions controls. Many would prefer an alternative to mandating arbitrarily defined percentage decreases or use of best available technology (BAT). The critical loads approach is an alternative concept that has some promise both nationally and internationally. Despite many differences in definitions and approaches, critical load calculations in different countries have so far yielded similar answers. This has led to increased confidence in the critical load concept as a method for developing pollution control policy. The critical load approach is used a s the basic tool in the current negotiations to reach international agreements in Europe on control measures to decrease emissions of sulfur and nitrogen under the Convention on Long-Range Transport of Air Pollutants within the UN-ECE. Readers with an interest in the origins of the critical loads approach may find i t useful to review the volumes edited by Nilsson and Grennfelt (1988) and Malanchuk and Nilsson (1989). The extent to which the critical loads approach has been used in the national documents for various countries is illustrated below: Euro~e Pollution issue of concern Acidification Nitrogen deposition Ozone

North America

NL

S

SF

UK

3 3 3

3 3 3

3 1 1

3 1 3

CAN

USA

2 0 3

0 0 3

The Netherlands The critical loads approach has been used extensively in both scientific discussions and in formulating environmental policy goals for The Netherlands. A set of concrete examples are given in Tables 5-8. The critical loads for various effects of total acid deposition on forests and surface waters are presented in Table 5. Similarly, the critical loads for

498

various effects of total nitrogen deposition on forests and heathlands are presented in Table 6. Table 5 Average critical loads of total acidifying deposition on terrestrial ecosystems on well drained sandy soils and surface waters in the Netherlands, mol/ha/yr Effects

Coniferous forests

Deciduous forests

Root damage Aluminum depletion Aluminum leaching to groundwater Decline of fish populations

1100-1400'

1200

1400-17OOb 1500

500

300

Surface waters

400

aThe first value is related to a critical aluminum concentration of 0.2 moVm3 and the second value to a critical aluminudcalcium ratio of 1.0. bThe first value is related to a critical aluminudcalcium mol ratio of 1.0 and the second value to a critical aluminum concentration of 0.2 moVm3.

Table 6 Average critical nitrogen loads for terrestrial ecosystems on well drained sandy soils in The Netherlands, molkdyr

Vegetation changes Elimination by grasses Frost damagelfungal diseases Nutrient imbalances Nitrate leaching to groundwater

Coniferous forests

Deciduous forests

400-1400

600-1400

Heathlands

700.1100 1500-3000 800-1250a 900-1500

1700-2900

aThe worst case would be total inhibition of nitrification.

2000-3600

499

These two sets of scientifically determined critical loads were then used by the Parliament of The Netherlands to establish target loads for both total acidifj6ng deposition and total nitrogen as described in Table 7. These politically determined target loads for various years were then translated into specific emissions-reduction targets for the years 1994 and 2000 a s outlined in Table 8. By fulfilling these targets leading up to the year 2010, The Netherlands will do its part (together with other nations of Europe) in attaining the objective of keeping atmospheric deposition below scientifically determined critical loads and thus avoid o r minimize harm to the forests, heathlands, and surface water of The Netherlands.

As indicated by the percentage changes in emissions outlined in Table 8, achievement of these environmental quality objectives will require rather drastic measures which will require that abatement strategies be developed for various categories of sources including agriculture, industry, households, etc. Table 7 Comparison of scientifically determined critical loads and politically decided target loads for total acidifying deposition and total nitrogen deposition in The Netherlands, molshdyr Scientific estimate gf critical load

Politically decided tarFet loads Year 2000 Year 2010

Total acidifvinv deDositiou: Forests and soils

1200 - 1700

2400

1400

1600

loo0

Total n i t r a n deDosition: Forests Heathlands

400 - 1500 700 - 1100

Table 8 Emissions reduction targets for The Netherlands, percentage change relative to 1980 emissions

Ammonia emissions Nitrogen oxide emissions Sulfur dioxide emissions

Year 1994

Year 2000

Year 2010

30

70

80-90

20

50 80

80-90 80-90

60

500

Sweden As shown in Table 9, similar use has been made of the critical loads approach in setting environmental goals for Sweden.

Table 9 Critical loads, target loads, current (1990) deposition, and percentage decrease in emissions of total sulfur and total nitrogen in various parts of Sweden a s specified in Parliament-approved environmental goals for Sweden, k g h d y r Critical load

Target load

Deposition in 1990

Reduction required (%I

5 5 3

10-20 5-10 3-5

75 50 40

10 8 6

10-20 5-10 25

50 20 0

Total sulfur deDosition: Whole country Gotaland Svealand Norrland

3-8

Total nitroTen denosition: Whole country Gotaland Svealand Norrland

5-15

The critical load for sulfur in the major provincial areas of Sweden vary from 3 kg sulfurlhdyr in the north to 8 k g h d y r in a few parts of southern Sweden. Thus, the target load for sulphur deposition is set a t 5 kg sulphudhdyr in Gotaland and Svealand (southern and central Sweden) and a t 3 k g h d y r i n Norrland. The target load value of 3 kg sulfurhdyr in Norrland is justified by the fact that a great deal of acid accumulated in the snow pack during winter is released during spring snow melt. Similarly, the critical load for nitrogen varies from 5 kg nitrogen/ha/yr in lowproductive ecosystems mainly in the north to 15 kg nitrogenlhdyr in highly productive ecosystems in the south. Thus, the target load for nitrogen deposition is set a t 10 kg nitrogenhalyr in Gotaland, 8 k g h d y r in Svealand, and 6 kghalyr in Norrland, since growth and accompanying uptake and utilization of nitrogen is smaller in the north.

50 I

These target loads for sulfur and nitrogen have now been accepted by the Parliament as environmental goals for Sweden. Progress toward these target loads is planned by the years 1995 and 2000 as outlined in Table 10. Table 10 Emission reduction targets for sulfur, nitrogen compounds, and volatile organic compounds in Sweden by the years 1995 and 2000

Pollutant

Reference year

Total sulfur Nitrogen oxides Ammonia Volatile organic compounds

1980 1980 1990 1988

Emission reduction target pe reduct&: Year 1995 Year 2000

65 30 25b

80 50a 50b 50

aParliament has ordered a further evaluation of this target load. bThese reductions in emissions will apply mainly in southern and southwestern Sweden. Alternative strategies for achieving these reductions are currently being evaluated.

Finland The first critical loads maps for acidity, sulfur, and nitrogen and their exceedences were published in the national document for Finland. The Finish Council of State decided in 1991 to decrease sulfur emissions by 80% by about 2000. According to model estimates, the critical load for sulfur will be achieved if Finland and other countries decrease their emissions by this amount. If so, only very small areas in Finland will still be threatened by acidification. The possible continuing effects of nitrate and ammonium deposition are causing some uncertainty about this optimistic scenario.

United Kingdom Drawing on the work of various review groups in the UK, critical load maps have been prepared for acid deposition effects on soils. Similar maps also have been prepared for acidification of fresh waters, so far only for Scotland. National surveys are currently in progress throughout the UK. Generally, critical loads for soils are lower than critical loads for fresh waters. Critical load exceedence maps also have been prepared for much of the UK. There is generally good agreement between the areas where exceedences are shown on these maps and areas where acidification impacts have been reported.

502

Provisional maps of target loads for sulfur have been prepared by the government. Abatement actions are being taken t o meet the requirements of the European Community's emissions standards. Even though sulfur deposition will have been reduced by the year 2005, some of the more sensitive ecosystems in the UK will still be sustaining damage. These still-unprotected areas with regard to soil acidification constitute about 8% of the area of the UK. Catlilda

In order to protect surface waters from acidification, the critical loads approach was used in establishing the agreement among the provinces that sulfur dioxide emissions in Canada should be decreased by 50% by 1994. The critical load for sulfur in all of eastern Canada was estimated to be 20 kg sulfatehdyr (7 kg sulfurhdyr). Integrated atmospheric, water quality, and aquatic biota models were used to establish emissions reduction targets and to identify the least-cost means by which these targets could be achieved. A variety of federal, provincial, international political, engineering, and social factors were considered in reaching the final emission control decisions shown in Table 11. Table 11 Reductions in sulfur emissions in various Canadian provinces intended to meet the target of a n overall 50% decrease in sulfur emissions in eastern Canada by 1994, % reduction in each province

Province Manitoba Ontario Quebec New Brunswick Nova Scotia Newfoundland Prince Edward Island

Based on 1980 regulated emissions 25 83 45 14 7 2A 17

Based on 1980 actual emissions 0

50 45

16 0

20 0

The critical loads approach has not been used for other pollutants and/or resources a t risk in Canada although some effort has been made with respect to sulfur-induced changes in soil chemistry.

USA The concepts of critical loads and target loads have not been addressed in the national document for the USA.

503 4.0. USE OF EMISSIONS-REDUCTIONSCENARIOS

-

Many of the national documents used emissions-reduction scenarios a s a technique of assessment, but the extent of use varied from country to country:

Use of scenarios in assessment

NL

S

3

1

S

F

U

3

K

1

North A m e m CAN USA 2

3

The Netherlands In the national document for The Netherlands, long-term potentials for management of acidifying deposition were explored using the Dutch Acidification Systems Model (DAS). To illustrate this approach, the results of three illustrative scenarios are presented in Table 12. The deposition targets presented in these scenarios are derived from explorations of possible emissions decreases in The Netherlands and other countries in Europe. Four features of these three scenarios are important: Changes in amounts of deposition. In all three scenarios, a 54% decrease in potential acid deposition is proposed by the year 2000. This probably would be achieved mainly by decreasing emissions of ammonia. In scenario 2, further decreases totaling 71% and 75% are proposed In scenario 3 further decreases totaling 75% and 85% are proposed by 2010 and 2050. Expected changes in forest soils. Significant decreases in amounts of acidifying deposition generally lead to rapid improvement in the soilsolution chemistry of forests. Change from a n average annual deposition of 4800 to 2200 mol H+/hafyr are expected t o decrease the area exceeding the critical aluminum concentration and the aluminudcalcium ratio from about 75% of the forest soil area to 40%. In scenario 2 the exceedence is expected to be negligible by the year 2050 and thus depletion of the aluminium buffer system probably would be prevented. Expected changes in forest trees. The most significant positive effects on forests are expected to be lower nitrogen content of leaves and decreased leaching of nitrate, both of which probably will make the trees less susceptible to frost, insect pests, and fungal pathogens. Increased growth of trees (compared to unchanged deposition) is also expected in the southeastern part of The Netherlands. Decreasing deposition before the year 2000 is expected to have larger beneficial effects than decreases after the year 2000.

504

Expected changes in heathlands. According to the DAS model, scenario 1 offers no prospect for the continued existence of typical dry heathland vegetation, while scenario 3 does. Wet heathland vegetation is expected to be successful under scenarios 2 and 3 if sod-cutting also is applied. Table 12 Three possible scenarios of change in management of acidifying deposition and expected effects on forest soils in The Netherlands. Part 4:Potential acid deposition targets set by the government. Part 8: Changes in percentage of forest land area where critical soil-solution concentrations probably would be exceeded, 1990-2050. Current vear 1990

h€tA Scenario 1 Scenario 2 Scenario 3

Scenario 1 Scenario 2 Scenario 3

Future Years

m

2010

2050

(Target potential acid deposition)a 4800 2200 2200 2200 4800 1400 1200 2200 4800 2200 1200 700 (Percentage of forest land area where critical soil-solution concentrations would be exceeded$ 75 40 40 25 75 40 a0 0 75 40 ? 0

apotential acid deposition includes SOX + NOx + NHx (mols H+/ha/yr). bThe critical soil-solution concentrations selected for this analysis included aluminum concentration, calciudaluminum ratio, ammoniudpotassium ratio, and nitrate concentration. These estimates were based on calculations using the Dutch Acidification Systems Model (DAS).

Sweden The national document for Sweden contains no systematic analysis of alternative emission or deposition scenarios. Environmental goals for the nation have been established mainly through consensus-forming processes by scientists and policy experts assembled by the Swedish Environment Protection Board. Mathematical models have been used for analysis of effects on surface waters. These models indicate that a 50% decrease in acid loading beginning in the year 2000 and continuing to 2030 would be required to bring about half the

505

acidified lakes in southern and central Sweden to pH 6.0 or higher. In order to achieve the same effect in the most sensitive parts of southern Sweden, a decrease in acid loading of at least 80% would be required beginning in the 1990s. These forecasts mean that liming of acidified lakes must continue for several decades. If present rates of sulfur and nitrogen deposition are not decreased, acidification and associated depletion of base cations in forest soils are expected to continue for several decades. This is projected to cause long-term decreases in productivity of large areas of forest in southern and central Sweden. In addition to decreases in deposition, both liming and nutrient supplementation are expected to be necessary to avoid impoverishment of forest soils. Also, a t present rates of deposition, substantial areas of southern Sweden are projected to suffer from nitrogen saturation within 10-20 years. This would result in continuing soil acidification, leaching of nitrate, nutrient imbalances in forest trees, and major changes in species composition of natural flora and fauna. Continuing acidification of soils and surface and ground waters also is expected to pose a continuing threat to human health. But much more research is needed to improve present understanding of these possibilities.

Finland Finland developed a n integrated acidification assessment model called HAKOMA. The model was then used to evaluate alternative energy-use and specific emissions-control scenarios. Both basic scenarios for Finland are adaptations of the present energy system. The first involves only the current emissions-reduction plans. The second involves maximum feasible reductions in emissions. Specific methods by which to decrease emissions of sulfur dioxide, nitrogen oxides, and ammonia also have been explored. Increasing use of natural gas and enhanced energy conservation are among the options studied. The RAINS model also has been used to analyze the effects on Finland of similar emissions-reduction options in the rest of Europe. More detailed analyses have been used to estimate changes in deposition within Finland that might result from different energy-production options in the Russian Republic and the other Baltic States including Estonia, Latvia, Lithuania, and Poland. Analyses of relative cost-effectiveness also have been made for various methods of decreasing emissions. The following conclusions were drawn from these scenario analyses in Finland: The critical loads for forest soils and lakes are presently exceeded in large parts of Finland; Maximum feasible reductions in emissions both in Finland and elsewhere in Europe will be necessary t o substantially decrease total acid deposition in Finland;

506

Even maximum feasible decreases in emissions of sulfur in Finland would not be sufficient to stop acidification of forest soils in Finland; The critical load for forest soils could be achieved in most areas of Finland if maximum feasible reductions were applied both in Finland and abroad; Uncertainty about NHx emissions in Finland and abroad are the principal causes of uncertainty in estimates of future acidifying deposition in Finland.

United Kingdom There is no comprehensive analysis of future emissions-reduction scenarios for the UK. Modeling of future trends is an important part of the Review Group Report on Acidity in Fresh Waters, however. These models indicate that: Restoration of most surface waters to their pristine state probably would require a decrease in sulfur deposition of about 90%. Within a few years, many waters would be expected t o respond positively to such a drastic change. A few waters, however, are almost certainly irreversibly acidified. A decrease in emissions of about 50% would be required to prevent further biological changes in many moorland surface waters in Wales.

Because of the "air-filtering" effect of forest canopies, forest cover increases the total transfer of acidifying deposition from the atmosphere by about 30%. For this reason, the effect of planting new forests in a n upland moorland catchment is a sensitive region is equivalent to a 30% increase in acidifying deposition. Canada

In the national documents for Canada, four scenarios were compared. We describe two of0.2 keq ha-'. 4. REFERENCES

1 Heyes CA, Irwin JG, Pemn DA (1991) Modelling sulphur concentrations and depositions in the UK in 1987 and 1955. Stevenage: Warren Spring Laboratory, LR 772. 2 Stedman J (1991) Measurements of background sulphur and scavenging ratios at a site in the west of Northern Ireland. Amos Environ, 25A, 699-708. 5. ACKNOWLEDGEMENT

The funding of this work by the United Kingdom Department of the Environment within their air pollution research programme (contract no PECDI7I 10/29) is gratefully acknowledged.

T Schneider (Editor). Acidification Research Evaluation and Policy Applications 1992 Elsevier Science Publishers 8 V

529

DRY DEPOSITION OVER GRASSLAND: SEASONAL INFLUENCES, CHEMICAL EQUILIBRIA AND SURFACE WETNESS M.A.H.G.Plantaz, A.T.Vermeulen, P.J.de Wild, G.P.Wyers and J.Slanina Netherlands Energy Research Foundation ECN, The Netherlands

Dry deposition of NH3, NH4NO3 and HNO3 over flag, homogeneous grassland will be measured under different atmospheric and surface conditions. Special attention will be paid to periods with dew occurrence. The measurements will cover a period of one year (four seasons) and will be continuous and automated up to a high degree. The aim is to provide the modelling of dry deposition with respect to influences: - of meteorological and seasonal conditions; - of the presence of water layers on the surface; - of chemical equilibria. Deposition fluxes of the target components will be derived from vertical concentration profiles (1 and 5 m measured by thermo denuder systems), using both the gradient method and a modified Bowen-ratio technique. Therefore, profiles of temperature, windspeed and moisture are also measured, besides radiation (netto and global), soil heat flux and soil heat storage. From these, fluxes of sensible and latent heat and of momentum are calculated, and by combination with the concentration profiles-, the component fluxes. Under dew conditions, dew samples are also taken and analyzed, and dew volumes per square meter are measured. As profile-related methods fail under such stable conditions, fluxes of target components are estimated by supposing an analogous exchange behaviour with H20(,); therefore fluxes of H20g) (and of sensible heat and momentum) are also measured directly using the eddy-correlation technique. This combination of atmospheric flux estimates and dew water analysis will yield information on the effects of water layers on deposition of HN3, NH4N03 and HNO3 and on the equilibria that are involved in different stages of the deposition process. The allseason coverage and the combination of methods will improve knowledge and modelling of meteorological (seasonal) influences. The experiment is planned for 1992; until then, the set up will be tested at Schagerbrug, near ECN. Preliminary data, obtained during the testing period, will be presented.

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53 I

The Dutch Acidification systems (DAS) model A. Tiktak, A.H. Bakema, K.F. de Boer, R.M. Kok and T.N. Olsthoorn National Institute of Public Health and Environmental Protection, PO Box 1, 3720 BA BILTHOVEN, The Netherlands

Abstract The Dutch Acidification Systems (DAS) model is presented. The model aims a t evaluating the long-term effectiveness of acidification abatement strategies on soils, forests, heathlands, aquatic systems, agricultural production, monuments and construction materials in a regionalized way. Some results for the soil, forest and heathland modules are presented. Within the framework of the Dutch Priority Programme on Acidification, the Dutch Acidification Systems (DAS) Model has been developed. The model aims a t evaluating the long-term effectiveness of acidification abatement strategies on a number of receptor systems in the Netherlands and describes the entire causality chain from emissions to effects in a regionalized way. The time-span for the model is one hundred years, starting in 1950. DAS contains modules for the calculation of emissions, air transport and effects on soils, forests, heathlands, aquatic systems, agriculture, monuments and construction materials. Each module can be run independently. The individual modules are described in detail in accompanying posters. The air pollution components included are the acidification agents NH,, NO, and SO,. As some of the effect modules use additional components, such as ozone, the base cations (Ca'', M e and K') and the anion Cl-, these components have also been included. Results are presented using emission data for the past (1950-1990) and the near future (1990-2000). Future emission data are based on acidification abatement strategies as announced in the National Dutch Environmental Policy Plan Plus (NEPP'). No information about emissions is available for the period after the year 2000. Instead, three deposition targets, which aim a t an acid deposition of 2200 (scenario l), 1230 (scenario 2) and 700 (scenario 3) mol,.ha-'.yr-' have been formulated for the year 2050. The air transport and transformation module SRM calculates the deposition and concentration of the acidifying components by means of transfer matrices. The matrices include a linear relationship between emissions and concentrations or deposition of a compound. Different matrices are available for compounds from low (lo0 meters) sources. The module generates depositions for an average Dutch landscape. However, the dry deposition to forests is about 20% higher than the average deposition. To account for this, the average dry deposition is multiplied

532

by compound and region specific correction factors which are derived empirically. Using the emission and air transport modules of DAS, the average potential acid deposition to the Netherlands will be 2200 mol,.ha".yr-' in the year 2000, which is a reduction of more than 50% compared to the deposition in 1989 (which was 4800 rnol.ha".yr-'). The strong deposition reduction up to 2000 is caused by a dramatic reduction of the NH, emission in the Netherlands, but considerable reductions are also expected for NO, and SO,. The soil module of DAS is the process orientated REgional Soil Acidification (RESAM) model. RESAM describes changes in soil chemistry, both in the solid phase (minerals, Al-hydroxides and adsorption complex) and in the liquid phase. Processes included are weathering of primary minerals and Al-hydroxides, cation exchange reactions, nitrogen transformations and nutrient cycling by the vegetation. The model includes the major components in A13+,Ca", M P , K+, Na+, NH,+, NO,', SO:., Cl, HCO; and forest soils, i.e. H+, RCOO-. Deposition reduction leads to a fast improvement in soil solution chemistry, i.e. a n increase in the pH value and a reduction in A13+and NO, concentrations and the A13+/Ca2+and NH,+/K+ratios. The exceedance of the critical A13+ concentration from about 75% of the forest soil area (the current situation) reduces to 40% in the year 2000, the exceedance of the critical A13+/Ca2+ ratio reduces from about 65% to 40%. Deposition reductions according to scenario 2 and 3 cause a decrease in the exceedance of these parameters to negligible values for the year 2050. In scenario 1, the critical A13+concentration and A13+/Ca2+ ratio will still be exceeded in a considerable area of forest (25 and 10%) respectively) a t that time. The forest module of DAS is the model SOILVEG. This model predicts growth and phenology of Douglas fir in relation to the availability of carbon from photosynthesis and N, Ca, Mg and K from atmospheric deposition and soil processes. Indirect and direct effects of acid deposition are included. The model has been parameterized for Douglas fir stands on four sandy soil types. The scenario analysis for these forests indicates that the nitrogen content of needles is reduced significantly. As a result, the sensitivity of Douglas for plagues, frost and drought stress will reduce. In the South-Eastern part of the Netherlands the increase of nitrogen and total acid deposition between 1970 and 1990 leads to a net decrease of needle mass and wood production. In relatively clean areas, however, there is a positive effect of enhanced nitrogen deposition on needle mass and wood production. The reduction of photosynthesis by direct impact of SO, and 0, will not exceed 5%. However, additional reduction of M e uptake by roots, due to low pH can amount to 15% and reduction of M e uptake due to high aluminum concentrations can amount to 20%. The heathland module CALLUNA simulates the nitrogen cycle and the competition between Calluna vulgaris and Deschampsia flexuosa for nitrogen. Simulations indicate that scenario 1 does not offer any prospects for the continued existence of dry heathland vegetations, whereas scenario 3 offers good prospects for such vegetations.

T Schneider (Editor). Acldlflcatlon Research Evaluatlon and Pol~cyAppllcatlons 1992 Elsevier Science Publishers B V

533

LONG-TERM IMPACT OF THREE DEPOSITION SCENARIOS ON DUTCH FOREST SOILS W. de Vries, J. Kros, C. van der Salm and J.C.H. Voogd DLO The Winand Staring Centre for Integrated Land, Soil and Water Research (SC-DLO), P.O. Box 125, 6700 AC Wageningen, The Netherlands

The long-term impact of three deposition scenarios on Dutch forest soils has been evaluated using the model RESAM (Regional Soil Acidification Model). RESAM describes changes in the chemical composition of the soil solid phase (minerals and adsorption complex) and soil solution due to natural and maninduced processes. The model is part of the overall Dutch Acidification Systems model (DAS). Deposition scenarios for total acidity (SO,, NO, and NH,) have been generated by the DAS air transport model for the period 1990 to 2050 based on expected emissions in the near future (1990-2000) and deposition targets (2000-2050) as shown in Table 1. Table 1 Average deposition trends of total acidity for the Netherlands for three scenarios during the period 1990-2050. Scenario

1 2 3

Acid deposition (mol, ha-' yr-') 1990

2000

2010

2050

4420 4420 4420

2240 2240 2240

2240 1400 1230

2240 1230 700

The regional application of RESAM has been restricted t o seven tree species and fourteen non-calcareous sandy soil covering about 65% of the Dutch forest area. The Netherlands has been subdivided in twenty deposition areas. Presentation of the model results is restricted t o pH, A1 concentration, AVCa ratio and NH,/K ratio in the topsoil (top 20 to 30 cm) and to pH, Al, NO, and SO, concentration in the subsoil (at the bottom of the rootzone). The parameters in the topsoil are important indicators of forest stress, whereas the parameters in the subsoil are important indicators of potential groundwater pollution. In order to gain insight in the reliability of the model predictions, model results of the soil solution chemistry were compared with soil solution

534

measurements in 150 forest stands during the period March to May 1990. The model results and field data agreed well for pH and SO,; they were fair for the A1 concentration (topsoil), AWCa ratio and NO, concentration and unfavourable for the NH4/K ratio and A1 concentration (subsoil). Future trends in soil solution parameters in response t o three emissiondeposition scenarios for the period 1990-2050, showed that deposition reductions generally lead to a fast improvement of the soil solution chemistry. It leads to an increase in pH and a decrease in A1 and NO, concentration and AUCa and NH,/K ratio. However, for the NO, concentration and NHJK ratio there was a clear time lag between deposition reduction and concentration reduction which is mainly due t o N mobilization from the litter layer. The effect of deposition reductions according to scenario 2 in some relatively densily forested deposition areas is shown in Table 2. Table 2 Decrease in areas exceeding a critical A1 concentration (0.2 mol, m-,) and a critical Al/Ca ratio (1.0 mol mar') in response to scenario 2 during the period. Deposition area

Area exceeding critical [All

Area exceeding critical AYCa

(%I

(%I

1990 2000 2010 2050

1990 2000 2010 2050

Drenthe Noord Overijssel Twente Veluwe Achterhoek Eindhoven Venray

98 62 86 69 87 98 61

50 40 64 21 70 70 40

15 17 46 1 60 27

1 5 23 0 30 14 12

84 56 90 65 88 79 59

Netherlands

80

45

23

8

70

32

-_ 51 62 38 81 69 35

4 19 48 6 62 33 23

0 0 3 0 4 0

51

22

1

33

3

Table 2 shows that a deposition reduction to 2240 mol, ha-' yr" in the year 2000, will reduce the exceedance of a critical A1 concentration and AVCa ratio from 80% and 70% of the forest soil area (current situation) t o 51% and 45% respectively. Reductions up to 1400 mol, ha-' yr-' in 2010 will reduce t h e exceedance of a critical A1 concentration and Al/Ca ratio in the topsoil to less than 25%. However, there are large differences in the various areas. In 2050 t h e exceedance of these criteria will be almost negligible.

T Schneider (Editor). Acidification Research Evaluationand Policy Applications 1992 Elsevier Science Publishers B V

535

SOIL AND SOIL SOLUTION COMPOSITION OF 150 FOREST STANDS IN THE NETHERLANDS IN 1990

W. de Vries, E.E.J.M. Leeters, C.M. Hendriks, W. Balkema, M.M.T. Meulenbrugge, R. Zwijnen and J.C.H. Voogd DLO The Winand Staring Centre for Integrated Land, Soil and Water Research (SC-DLO), P.O. Box 125, 6700 AC Wageningen, The Netherlands

During the period March to May 1990, the chemical composition of the humus layer, the mineral topsoil (0-30 cm) and the mineral subsoil (60-100 cm) has been determined for 150 forest stands. All stands were part of the national forest vitality inventory. They were all located on non-calcareous sandy soils. Tree species included were Scotch Pine, Black Pine, Douglas Fir, Norway Spruce, Japanese Larch, Oak and Beech. Measurements for the humus layer and mineral topsoil included total contents of C, N and P and exchangeable contents of H, Al, Fe, Ca, Mg, K, Na and NH,. Soil solution measurements in the mineral soil included the cations mentioned before and NO,, SO,, C1, HCO, and DOC. An important aim of the research was to assess the effect of deposition levels, tree species and site characteristics on the level of A1 mobilization (acidification) and N accumulation (eutrophication) in the soil. Important characteristics of the chemical composition of the humus layer and mineral topsoil are shown in Table 1. Table 1 Median values for the N contents in organic matter and exchangeable base cation and A1 contents in the humus layer and mineral topsoil of 150 forest stands Tree species

Scotch Pine Black Pine Douglas Fir Norway Spruce Japanese Larch Oak Beech All species

N contents (%) _______ humus topsoil layer

Base saturation (%)

A1 saturation (%)

humus layer

humus layer

2.0 1.9 2.4 2.2 2.1 2.6 2.4 2.2

34 36 38 38 42 46 34 38

1.9 2.0 2.2

1.9 1.8 2.4 2.0 2.0

-__

topsoil

topsoil

6 5

69

7

67 63 68 43 64 66

6

5 17 6 6

70

536

The N contents in the organic matter of the humus layer were somewhat higher than in the mineral topsoil. Values in the humus layer were much higher than in relatively unpolluted areas, where the N content was generally less than 1.5%.This suggests N immobilization caused by high N deposition. In the humus layer, base saturation was high (about 30-70%)and A1 saturation was low (about 3 t o 13%) compared t o the mineral topsoil. This is due to base cation mineralization and a negligible A1 mobilization in this layer. In the topsoil, base saturation was low (often below 20%) whereas A1 saturation was high (about 30 t o 80%). This implies that acid input is hardly buffered by exchange with base cations. Except for the Oak, the variation between tree species appeared to be small. Important characteristics of the soil solution composition of the mineral topsoil are shown in Table 2. Table 2 Median values of important soil solution parameters in the mineral topsoil of 150 forest stands __-__

Tree species

Scotch Pine Black Pine Douglas Fir Norway Spruce Japanese Larch Oak Beech All species

___

Concentrations ( m ~ l , . m ' ~ )

Ratios (mol.mo1-l)

__

pH

A1

Ca

SO,

NO,

NH,/NO,

NH,/K

AVCa

3.60 3.67 3.41 3.43 3.55 3.70 3.67 3.59

0.81 0.62 1.43 1.16 0.81 0.40 0.52 0.69

0.39 0.36 0.90 0.58 0.47 0.51 0.31 0.45

1.09 0.80 2.56 2.04 1.02 0.83 0.65 1.03

0.56 0.27 0.92 0.50 0.71 0.54 0.33 0.55

0.35 0.75 0.70 1.18 0.46 0.25 0.60 0.45

1.oo 1.19 2.56 2.36 1.67 0.54 0.60 1.12

1.22 1.27 1.42 1.38 1.15 0.63 1.09 1.13

Low pH values and high concentrations in NO,, SO, and A1 occured below all tree species, especially below Douglas Fir and Norway Spruce. Most probably this is due to a high dry deposition on - and a high evapotranspiration of these tree species. The ratio of NH, t o NO, was generally below 1.0, indicating a reasonable rate of nitrification. Consequently, the ratio of NH, to K remained below a critical value of 5. The ratio of A1 to Ca was generally above 1.0, which is considered a critical value. The median NO,/SO, ratio was about 0.6. In the Netherlands, the N/S ratio in the input is a t least 1.0. Assuming that SO, behaves a s a tracer, this implies that a considerable amount of nitrogen is fixed or disappears as a result of uptake, immobilization and/or denitrification.

T Schneider (Editor). Acidification Research Evaluation and Policy Applications 1992 Elsevier Science Publishers B V

531

AUTOMATED DENUDER SYSTEMS FOR DRY DEPOSITION STUDIES OF ACIDIFYING COMPOUNDS G.P.Wyers, A.T.Vermeulen, R.P.Otjes, A.Wayers, J.J.Mols and J.Slanina Netherlands Energy Research Foundation ECN, The Netherlands

Sampling of atmospheric trace gases using conventional denuders is a laborious task. Since it involves many manipulations in the field and the laboratory, the precision of this technique is limited. Automation of the technique increases its precision and offers the possibility to perform measurements over a long period which allows a study of seasonal and daily influences on concentrations and fluxes. Initially, emphasis was placed on the development of thermodenuders. Thermodenuders for ammonia, in which N H 3 is collected on a V205 coating and, partly, converted to NO, by heating and detected by an NO, monitor, were used to study dry deposition over a forest (Speulderbos) for a period of five months. The relative precision of these instruments is 5% for concentrations of 1-20 g/m3. Another line of development involved the so-called wet denuders, in which trace gases are collected in a solution film on the walls of an annular, rotating denuder. The denuder is automatically emptied and refilled. The samples are stored by a fraction collector and analyzed off-line for N H 3 , HNO3, HN02, HCl, H202 and S02. One of these instruments was used to measure the concentrations of these trace gases for a full year. A major advantage of wet denuders is that they feature quantitative collection of trace gases over a large concentration range. Recently a wet denuder has been constructed in which the absorption solution is continuously refreshed and on-line analyzed for ammonia. With the continuous-flow rotating denuder a very high precision can be obtained (better than 1% for 20-minute measurements) which makes it well-suited for measurement of, usually very small, concentration gradients for dry deposition studies. In a recent joint field experiment at a heather field (Leenderheide), organised within the framework of the EUROTRAC-subproject BIATEX, three of these instruments were used to measure profiles of ammonia above the field. Preliminary results will be presented.

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539

AQUACID: Modelling the acidification of shallow heathland lakes in The Netherlands. The aquatic systems module of DAS. F.G. Wortelboer Laboratory for Water and Drinking Water, National Institute of Public Health and Environmental Protection, P.O. Box 1,3720 BA Bilthoven, The Netherlands. The model AQUACID describes the changes in the ecosystems of shallow heathland lakes in The Netherlands as induced by high levels of atmospheric deposition. The characteristics of the lakes themselves led to the formulation of a new model, instead of using one of the more widely known models. Most important factor was the complete hydrological isolation of these lakes from surface water and groundwater, the lakes receiving atmospheric input only. Furthermore, changes in the macrophyte vegetation and accumulation of organic matter in the sediment, along with acidification, were recognized as important aspects of the lakes and should be described by the model. For this, the inclusion of various biological and biochemical processes into the model was needed. The heathland lakes are found in sandy soils with low calcium contents. Low amounts of nutrients and organic material used to be the normal situation. They are therefore weakly buffered and acid-sensitive. The surface area ranges from 1 to 100 ha, with a n average depth of 1m. The heathland lakes formerly had a very low production of biomass. Deposition only brought minor amounts of nutrients. Vegetation was dominated by submersed plants, such as Littorella uniflora,Lobelia dortrnanna, Isoetes lacustris. Due to acidification, the pH ofthe water dropped from about 6.5 to less than 4, the lakes showing an increase in concentrations of carbon dioxide and the nutrients nitrate and ammonium, and an accumulation of organic matter in the sediment. The vegetation has become dominated by Juncus bulbosus and Sphagnum spp. Acidification is seen as a balance (whether or not disturbed) between acidity and alkalinity producing processes. These processes are regarded the most important with respect to the ability of these aquatic systems to recover from acidification. The model simulates the competition between the characteristic submerged macrophyte species Littorella uniflora and Juncus bulbosus. The modelling is based upon the ecophysiology of the species themselves, which differ in their productivity, the site of CO, and nutrient uptake (sediment vs. water), the source of nitrogen (nitrate vs. ammonium; Wortelboer, 1990). Because of differences in the degradability of the organic matter produced by the macrophytes species, four organic matter fractions were distinguished: of each species, both a labile and a refractory fraction. Other processes included in the model are aerobic mineralization, denitrification, sulphate reduction, methanogenesis, oxidation of ammonium, sulphide and methane. Interaction with the lake surroundings takes place through exchange with the atmosphere, wet and dry deposition, and the input of allochtonous organic matter. A schematic representation of the model is given in Figure 1.(See also Wortelboer, 1992.)

540

Figure 1.Scheme representing the main characteristics of the model AQUACID. The model, consisting of a set of non-linear ordinary differential equations, was implemented using the interactive modelling environment FAME (Wortelboer & Aldenberg, 1992), in which the chemical equilibria calculations were incorporated into the integration algorithm. Calculations were performed over simulation periods of 100 years. The input of allochtonous organic matter is necessary to refrain the system to become carbon deficient, as the carbon dioxide is continuously depleted by exchange with the atmosphere. The presence of macrophyte vegetation depends on carbon dioxide levels in both water and sediment. The speciation of nitrogen in the system (and thus in the deposition) is important in determining the species composition of the vegetation. Furthermore, the results indicate the importance of the mineralization processes in neutralizing the acidifying effect of the primary production by the macrophytes. Results of scenario analyses to establish the critical deposition levels will be published elsewhere.

References Wortelboer, F.G., 1990. A model on the competition between two macrophyte species in acidifying shallow soft-water lakes in The Netherlands. Hydrobiol. Bull. 24:91-107. Wortelboer, F.G., 1992. AQUACID: Acidification model of shallow soft-water lakes in The Netherlands. National Institute of Public Health and Environmental Protection, Bilthoven, in prep. Wortelboer, F.G. & T. Aldenberg, 1992. FAME: Friendly Applied Modelling Environment. Version 3.0 User Manual, National Institute of Public Health and Environmental Protection, Bilthoven, report no. 779200001.

T. Schneider (Editor). Acidification Research. Evaluation and Policy Applications

0 1992 Elsevier Science Publishers B.V. All rights reserved

AN INTERNATIONAL RESEARCH PROGRAM ON ACID RAIN AND EMISSIONS IN ASIA Wesley K. Foell Resource Management Associates of Madison, 520 University Avenue, Suite 300, Madison, Wisconsin, 53703. U.S.A. FAX: (608) 283-2881. Abstract Strong economic and population growth will accelerate the rapid development of fossil fuel energy systems throughout Asia. If the present trends continue, by early next century Asian emissions of SO, will exceed the present emission levels in North America and Europe combined. In response to the concern that these emissions have the potential to cause significant damage in Asia, a group of international specialists has established a project on Acid Rain and Emissions in Asia. In the initial phase of this project, work is underway to develop an integrated assessment model to assist policy makers in evaluating options to reduce precursor emissions and to catalyze the process of international policy dialogue on acid rain in Asia. 1. INTRODUCTION

Fossil fuels are now used in large quantities throughout Asia. These present systems, however, are dwarfed by the substantial fossil fuel systems planned in many Asian nations over the next two decades. The accelerated development of these energy systems is propelled by the very high economic and population growth rates of the AsiaPacific region. The vast expansion of these energy systems combined with plans for a major fuel shift to coal in a number of predominant countries, will result in greatly increased atmospheric emissions of a wide range of substances of concern, including most prominently, acidifying compounds and greenhouse gases. In addition to their global implications, the long-term and regional/local implications of these atmospheric emissions touch not only the natural environment, but also have far-reaching implications for important commercial and cultural activities such as forestry, agriculture, and tourism. In response to the growing concern about acid rain and emissions of other atmospheric pollutants, a group of international specialists convened a workshop on this topic in Bangkok in 1989. In November 1990 in Bangkok, an expanded group of prominent experts attended a second workshop under the broader sponsorship of the World Bank, the United Nations Environment Program (UNEP), the Economic and Social Commission for Asia and the Pacific (ESCAP), and the US. Dept. of Energy (DOE). The participants had the objective of reviewing the problem in more depth, and if

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appropriate, to lay out a detailed program and plan of action'. As a result of the current and future situation in Asia, the Workshop concluded that acidifying compounds and other related emissions from energy facilities have the potential to cause (and in some locations are already causing) significant damage in Asia. In China for example, there already appears to be considerable evidence of the effects (Zhao et al., 1988). The participants were greatly concerned by the implications of the planned initiatives for accelerated development of massive fossil-fuel energy systems in many Asian nations, which could entail greatly increased emissions of acid deposition precursors. Because these would likely be emitted from large energy faculties with high stacks, they could increase the transport of these acidifymg substances to sensitive geographical areas. Developing and implementing approaches to reduce anthropogenic emissions will require the efforts of many organizations, both public and private. Currently, there is little regional coordination. However, as national regulators and the development community become increasingly aware of this issue and the consequences of no action become clear, sound programs and projects could be developed in the region. In order to reduce the emissions of acid precursors, the Asian countries will have to shift their energy policy through: Expanded use of cleaner fuels and renewable energy sources 0 0 Upgrading of older inefficient facilities 0 Instituting energy efficiency measures Industrial restructuring for regional energy efficiency 0 Installation of pollution control devices 0 Strategies to reduce acidifying emissions will also result in reduction of other pollutants such as greenhouse gases. There are two international initiatives under way to address greenhouse gas emissions: the Intergovernmental Panel on Climate Change (IPCC), under the auspices of UNEP and World Meteorological Organization (WMO); and the Global Environmental Facility (GEF), administered by the World Bank in association with UNEP and UNDP. Similar initiatives for acid rain in Asia may be needed because of the regional and global implications and to obtain regional agreement. Based on this conclusion, the Workshop recommended the development of a specific research project and plan of action. In addition the Workshop strongly recommended that an integrative program be developed for the purpose of formulating and assessing long-term strategies to confront the emerging problems of acid rain and the anthropogenic atmospheric emissions of a wide range of substances of concern at both the national and Asia-wide levels. 2. NEED FOR AN ACID RAIN PROGRAM IN ASIA

Our concern about the acid rain problem in Asia is heavily influenced by

'The Third Annual Workshop on Acid Rain and Emissions in Asia was held in Bangkok at the Asian Institute of Technology from November 18-22, 1991. Although the detailed output from that workshop has not been incorporated into this report, a few of the more general programmatic ideas regarding the future direction of the project's collaborative efforts have been noted in this paper.

543 consideration of Asia's population, its growing economy, and the associated systems of energy consumption and production. Growth of both population and economy are powerful driving forces behind the rapidly growing use of fossil fuels whose combustion is ultimately responsible for the emissions leading to acid deposition. Both the size and the growth rates of Asia's population and economy intensify this concern. Asia currently accounts for more than 55% of the world population and by the year 2010, according to United Nation scenarios of population growth rates, could be close to four billion people. The economic growth rate of Asia is far higher than for any other world region. Japan is currently responsible for more than half of the region's income. However, as is well-known, the economic growth rates of several of the industrializing countries of the region are extremely high and it is quite likely that several countries will establish developed industrialized economies early in the next century if not before. If current trends continue through the end of the century, the Western Pacific countries would have an economy comparable in size to those of North America or Western Europe. The acid rain impact in Asia may already be significant (Rodhe et ul., 1988; Bhatti et aL, 1990). The expansion of these energy systems, propelled by the very high economic and population growth rates of the region, combined with a major fuel shift to indigenous coal, will result in increased atmospheric emissions of acidifymg compounds and greenhouse gases. The total projected SO, emissions for the Asian countries in year 2010 of 76 million tons exceed the current emissions of North America and Eastern/Western Europe combined. Table 1

Emissions of SO2 in million tons per year Region/Country 1985* Europe 53 U.S.A. 21 Asia 28 China 19 India 3 * 1986 estimates for Asia

1990 50 24 35

2000 39 25 53 34 5

2010 39 21 76 49 9

Europe: Based on RAINS "currentreduction plan" scenario U.S.A.: Based on NAPAF' Integrated Assesrnent, Draft Sept. 1990 Asia: Base case scenario, Foe11 and Green, 1990.

An overview of key elements of the acid rain situation in Asia has been briefly sketched in Figure 1 (Bhatti et ul., 1990). Relative sulfur dioxide emissions in 1985 by country or region are indicated by vertical bars. Emissions are significant in China, India, Japan, and the Koreas, and are small but very rapidly growing in several other

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countries of south and southeast Asia. Deposition patterns of emissions are largely determined by wind flow patterns, shown by arrows in the figure. In winter (January) the flow is generally from the land mass to the ocean, while in summer (July) the reverse is true. Typical monitored values of pH are shown in the circles. Low pH values (4.5) occur in Japan and southern China where emissions are large; elsewhere the pH values are 6 to 7. Because of the paucity of monitoring sites, we cannot discount the possibility of low-pH at other unsuspected locations. In Asian countries where the recognition of this phenomenon is just beginning, there is very limited information available on the possible consequences of acid deposition. Some of the ecosystems of the Asian region are very similar to those found in areas of North America and Europe where the majority of the research on acid deposition impacts has been conducted. Thus, in some cases it should be possible to extrapolate the potential effects found in these western nations to the corresponding ecosystems of Asia. However, many other environments in Asia are very different from those for which acid deposition impacts have been studied, and research will have to be conducted to analyze and assess the relative vulnerability of these various anthropogenic and natural environments to acidic inputs. Nevertheless, based on knowledge of the various components (i.e., soils, flora, fauna, climate, etc.) of the ecosystems in question, their relative vulnerability to acidic inputs and their distribution in the Asian region, it is possible to attempt to predict the potential effects of acidic deposition (Bhatti et al., 1990). For a given area to be at high risk from acidification, a number of conditions must be present simultaneously. First, the area must be receiving or at risk of receiving high levels of deposition. Second, the soils of the area must be sensitive to acidification, and the area must have vegetation, fauna, aquatic organisms, man-made materials and/or large human populations vulnerable to increased inputs of acidity. In light of the present and future situation in Asia, the time has come to develop an integrated program of assessment and policy analysis for the purpose of analyzing long-term strategies for acid rain problems at national and at Asia-wide levels. A key component of such a program entails the application of the analytic and policy development experience gained in the West to this emerging issue in Asia. A predictive tool could be built to help decision-makers project future trends in emissions, estimate the regional consequences for acid deposition levels, evaluate the vulnerability of natural and artificial systems, and determine the costs and effectiveness of alternative mitigative actions that might be taken. Such a policy analysis exercise can start to raise environmental awareness in the region and begin a dialogue that could help ameliorate (or prevent the worsening of) an environmental problem in the early stages. 3. ENERGY AND EMISSIONS 3.1 Current Situation

The current energy system which has evolved to fuel Asia’s economic development is striking in many respects. First, it is almost completely dependent on fossil fuels (more than 95% of its commercial energy). Second, approximately 60% of the consumed fossil fuel is in the form of coal, with most of the remainder being fuel oil. Both of these fuels contribute significantly to the emissions of acid rain precursors

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in Asia. Equally important from an environmental perspective are the extremely high growth rates of Asian energy systems. During the past decade these annual rates have greatly exceeded (by factors of 2 to 4) those in Western industrialized countries, which are now relatively stable at a few percent or less. There is little reason to expect that per capita energy use in the developing countries of Asia will stabilize anywhere near its present level of approximately 0.5 tons of oil equivalent per year, which is approximately ten percent of the per capita use in North America and Europe. If the Western experience can be used as a guide, even with strong conservation measures we can expect continued very high energy growth in Asia for many years. Of particular concern is the continued growth of coal use. Coal use in the region in 1987 was approximately 1360 million metric tons with the three largest users being China, India, and Japan. Preliminary data and estimates presented at the 1989 Workshop indicated that regional coal use in the year 2000 could be as high as 2,300 million metric tons, with very large growth increments in China and India, and significant growth rates in several other countries, including Indonesia, Thailand and the Koreas. In addition to the concern about the level of total emissions early in the next century, we anticipate increasingly serious problems associated with the high density of emissions sources from a number of localized areas. Among those areas of concern are eastern and central India, northeast and southwest China, the Korean peninsula and Japan, northern and possibly southern Thailand, and western Java. The majority of these emissions would likely result from uncontrolled coal combustion and/or motor vehicle use. 3.2 Framework for Emissions Analysis Described briefly below, is a framework developed by Foe11 and Green to calculate a range of emissions scenarios for 13 developing Asian countries for a range of energy scenarios based on a variety of socio-economic and technical assumptions. From these energy scenarios, national values for sulfur emissions from fossil-fuel combustion were calculated, based on fuel characteristics, combustion technology, and emission control assumptions. The objective of the analysis was to calculate SO, emissions resulting from fossil fuel consumption in a base year (1986) and two future years, 2000 and 2010. Energy use in the scenarios is disaggregated into 5 sectors (industry, residential/commercial/agricultural, transportation, energy sector energy use, and other) and three fuel types (coal, oil, and natural gas) for each country. A uniform emission factor for SO, is applied to each fuel type in each sector. Such methodology is often adopted in national studies to account for the variations in sulfur, ash, and energy content within fuel types and differences in combustion technology. Additionally, the emission factor used will be influenced by the control strategy adopted for each sector. The resultant emissions are then summed to give the total SO, emissions for each country. The energy consumption scenarios which were developed for this analysis were in general based upon scenarios taken directly from the literature, e.g., from a countryreport developed by an energy agency in the country of interest. This approach was used as much as possible for the so-called base case scenarios. Wherever possible, both the assumptions and the resulting energy consumption patterns were compared with

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available related studies. In essentially every case, the "alternative scenarios" required a considerable amount of supplementary analysis because of the need to introduce different assumptions on a sectoral or fuel-by-fuel basis. The general scenario assumptions are described below. (For a more detailed description, see Foell and Green, 1990). 3.3 Scenario Assumptions Four main scenarios were developed. s1: Bme Case Scenario. s2: EfFciency Case: Energy improvements are introduced by sector into the residential, industrial, and transportation sectors as well as the electricity distribution network. Significant improvements over the base case values were introduced progressively in 2000 and 2010. These improvements were in general on the order of 15 to 30 percent depending on the country and sector involved and were assumed to be in part price-induced and in part through other interventions. A further assumption, probably reasonable in comparison with the gross assumptions made for such a long time horizon, is that these efficiency improvements occur equally across all industrial fuels, i.e., they are fuel independent. s3: Low Carbon Emission Care: This scenario combines the energy efficiency improvements of S2 and shifts to fuels with low carbon and acid-precursor emissions. The study examined the availability of natural gas, and where judged appropriate, assumed substitution for a fraction of the coal or oil used for electricity generation in the year 2010. In addition, new and renewable electric generating sources which are free from all precursor emissions were introduced in that year to a small degree. s4: Control Scenario: Sulfur controls were assumed to be implemented on electric power plants in a phased approach. In this approach, 50 percent of all new power generation between 1986 and 2000 was assumed to have 90 percent sulfur removal; all new power generation between 2000 and 2010 was assumed to have 90 percent sulfur removal. The controls were assumed to be applied to the Base Case energy and emission figures. 3.4 Scenario Results Of particular interest in the results of this analysis are the continued high growth rate of primary energy consumption and the continued dependance on fossil fuel energy sources, particularly coal and oil. In aggregate, commercial energy consumption for the region as a whole in the Base Case scenario is expected to grow at above 4.5 percent per year from 1986 through 2000 and only slightly less than 4.5 percent per year from 2000-2010. As a result, primary commercial energy is expected to reach approximately 2000 million tons of oil equivalent (MTOE) in 2000 and 3000 MTOE in 2010. Even when considering significant improvements in energy efficiency, energy growth in the region remains at relatively high levels. Efficiency improvements assumed in S2, the Efficiency Scenario, result in a net savings of about 250 MTOE in 2000 and 600 MTOE in 2010 from the base case. However energy growth rates for both periods remain at about 3.5 percent per year, still far higher than those of industrialized western countries.

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Also of interest is the continued dominance of China’s energy use in the regional totals. In 1986, China was responsible for nearly 55 percent of the region’s total primary energy, Despite the assumption of a significant decrease in China’s overall growth rate for energy (from 5.2 percent in 1980-1987 to 3.9 percent in 2000-2010), China is expected to comprise 48 percent of the region’s total energy use in 2010. Coal has supplied about 75 percent of China’s commercial energy needs during the 1980’s, and this situation is not expected to change during the 1990’s or into the next century.

ASIA REGION SO2 EMISSIONS 8o 70

8

Ease Case S1

Effie. Case 52 Low Carbon 53

Control S4

1

l1 o09 8 5

1990

1995

2000

2005

2010

Figure 2 Projected SO, emissions for the Asia Region The regional sulfur dioxide emissions are shown in Figure 2 for the Base Case and for the three alternative scenarios. The total emissions for 1986 are approximately 28 million tons of SO,. For comparison, the estimated U.S. sulfur dioxide emissions in 1985 were 21 million tons. Notable in 1986 were the emissions of China (19 million tons), India (3.2 million tons), and the Republic of Korea (1.2 million tons). By far the largest portion of the 1986 emissions is from coal-based facilities. The base scenario shows very high growth rates of the emissions, as might be expected from the scenario assumptions described above, and in particular the continued or growing reliance on coal in several of the major countries. Coal is responsible for the largest part of the emissions and, in both the base year and in 2010, accounts for approximately two-thirds of the total, followed by petroleum which accounts for around thirty percent. The contribution of natural gas is very small. By the years 2000 and 2010, total emissions for the 13 countries have grown to 53 and 76 millions tons respectively. Annual growth rates of SO, are 4.6 and 3.7 percent in the periods 1986-2000 and 2000-2010, respectively. Of this total, coal is responsible for 35 million tons in the year 2000 and 50 million tons in the year 2010; nearly 65 percent of

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the total emissions by 2010. The sulfur control strategy, S4, leads to a reduction of 3 million and 12 million tons in 2000 and 2010, respectively. Interestingly, this pollution control strategy, although quite ambitious in its rate of implementation, does not ultimately lead to the magnitude of reduction achieved by efficiency improvements and fuel shifts. Of course, the economics of these alternatives need to be investigated in some detail. If efficiency improvements, fuel shifts, and emissions controls were all implemented, it appears that the emissions could possibly be stabilized between 2000 and 2010. However, reduction in the absolute level would require more drastic measures. 4. DESIGN OF A RESEARCH PROGRAM

Environmental problems that have emerged in the last two decades can be characterized by two important factors: they are triggered by rapid socioeconomic development; and the spatial resolution of their impacts is usually well beyond the local and often even the national scale. These two important factors strongly influence the basis for building an analysis and policy framework for problems such as acidification and global climate change. In addressing the first factor, socioeconomic development, attention should be paid not only to the costs of abating but also to the costs of not abating. Especially in the developing countries of Asia, it is important to point out that benefits of abatement do exist. Concurrent with the explicit recognition of these benefits has been the emergence of the concept of sustainability, as introduced by the World Commission on Environment and Development. Development policies, which in the long run are not sustainable because of their increasingly negative impacts on the productivity of human and natural systems, are proving extremely costly for industrialized countries. The second factor, namely, the increasing tendency of environmental impacts to extend their domain to points at greater distances from the pollution source, has been strongly demonstrated by the nature of the acidification problems in Europe and North America. In North America, the acid precursor emissions of the midwestern industrial heartland of the U.S. inflict their damage on the states of the northeastern part of the U.S. or on Canada, hundreds or even a few thousand kilometers distant. In Europe some 30 countries influence each others environment to such a degree that national solutions are not adequate. An environmental decision in one country can greatly influence the situations of its neighbors. Because of the importance of the above factors, any attempt to develop approaches to avoid the emerging problems of acid rain and emissions in Asia need be comprehensive in scope. That is, the analysis should take into account the entire cause-and-effect chain of events which leads to the damage. This would include the energy supply/utilization system, its consequent emissions of precursors, emission control measures, transport and transformation of pollutants, acidic deposition, and the spectrum of impacts. These factors are shown schematically in a sequential systems diagram in Figure 3. As shown by the feedback loop, the analysis should also include the effects of various strategies and interventions to address the problem, including the economic consequences. For example, an analysis would examine the entire chain of

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consequences of a planned action such as expansion of the coal-fired electricity generation system over a long-term time horizon, as well as the consequences of alternative measures such as emission control, alternative fuel choices, and technology choices.

'igure 3 The Cause-Effect Chain for Acid Rain, Including Feedback to Policy Decisions

Approaches should also be comprehensive in the geographical sense. With increasing socioeconomic and industrial development, we are observing in Asia, a shift from small-scale (domestic) uses of fossil fuels to large-scale, tall-stack emissions associated with power plants and industrial facilities. This is increasing the propensity for long-range transport of pollution. Transboundary transport and deposition are inevitable, with, increasingly, damage to sensitive ecosystems in regions or countries far removed from the sources. Thus, mitigation strategies involving regional compacts or international agreements may be necessary. In recent years, integrated assessment models have been utilized for international negotiations on acid rain. The purpose of these models is to provide negotiators or regulators with a full regional picture of the problems associated with the entire causal process from energy systems and emissions through to the ultimate impact on natural and man-made systems. The model user can analyze the regional and national implications of various scenarios, which include options for energy use, control strategies, and mitigation policies. Such an effort for the acid rain problem in Europe has led to the Regional Acidification, INformation and Simulation (RAINS-EUROPE) model (IIASA, 1990). The RAINS model has been developed as a tool to assist policy advisors in

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evaluating options to reduce acid rain in Europe. The model can be used for both scenario analysis and optimization analysis. The optimization analysis can assist with questions such as: maximum SO, reduction for a given budget; reductions needed for a specific deposition target; or minimum cost to achieve specified deposition target. RAINS-EUROPE consists of sub-models (modules), each describing various aspects of the acid rain system. The user is guided through the model via a set of menus and options. A first set of sub-models deals with pollution generation and cost of abatement. For scenario analysis, users can select one of several preset energy use scenarios or can create their own, based on expectations of fuel use. The technical constraints (such as power plant efficiencies) are shown, and the user is warned when these constraints are violated. The user can then pick an abatement strategy for each country. The second set of sub-models deals with atmospheric transport and deposition of acidifying compounds. Calculations are based on a sub-model that consists of a transfer matrix for long range transport of pollutants in Europe, developed under the cooperative program for the Monitoring and Evaluation of Long-Range Transmission of Air Pollutants in Europe (EMEP). The outputs from the first set of sub-models are taken as inputs and transformed into deposition patterns for Europe. Comparisons between scenarios and abatement strategies can also be carried out. The third set of sub-models includes regionalized environmental impact models for forest soil acidification, lake acidification, susceptibility of groundwater, and direct effect of SO, on forests. All of these models are driven by the deposition patterns calculated by the second set of sub-models. The outputs from this module allows the user to compare scenarios and abatement strategies. In Europe, the Critical Loads Approach is being used in the negotiations for a new Sulfur Protocol. For this approach, knowledge of the sensitivity of ecosystems is necessary to derive national emission reductions. This knowledge is available in the form of critical loads maps for Europe (Hettelingh et al., 1991) which can be connected to RAINS-EUROPE to calculate the difference between deposition patterns and critical loads. The international collaborative Project on Acid Rain and Emissions in Asia has established as its initial objective the adaptation of the RAINS-EUROPE model to the Asia region. RAINS-ASIA will be developed by integration of the following modules applied to the Asian situation: (1) Energy and Emission Module Atmospheric Transport and Deposition Module (2) (3) Ecosystem Sensitivity Module Initially, RAINS-ASIA will be used to conduct a preliminary analysis of different energy and emission scenarios. The impacts of these energy and emission scenarios consist of (a) acid deposition and (b) comparison of acid deposition to the best estimates for sensitivity of ecosystems in Asia based on the European and North American data. The subsequent phases of this project will allow for refinement of the impact data based on specific work on critical Asian ecosystems, more detailed scenarios analysis, and inclusion of other pollutants. A specific sub-objective of this initial project phase is to involve scientists and policy makers from Asian countries and development institutions in all aspects of the project, to increase their awareness, and to transfer the model RAINS-ASIA and

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associated technologies to participating Asian governments and organizations.

5. SUMMARY AND CONCLUSIONS As a result of the present and future socio-economic and energy situation in Asia, emissions of acid precursors are likely to reach levels that could have far reaching implications for human and environmental systems throughout the region. To address this emerging problem, a group of specialists from Asia, North America, and Europe has established a project on Acid Rain and Emissions in Asia. The broad goals of this international collaborative project are to: develop approaches that assist in deriving regional and sub-regional 0 policies to avoid the rapidly emerging problems of atmospheric emissions in Asia; provide preliminary basic assessments needed to catalyze the process of 0 inter-governmental policy dialogue on acid rain precursor emission control in the Asia Region; and, develop basic strategies for policy advice, institution building, and 0 investment initiatives in countries of the Asia Region to deal with the problem of acid rain precursor emission control. Although the initial focus of the project will be limited to acidification, the overlap with several related issues of concern (e.g., emissions of greenhouse gases and other pollutants) is recognized. Later phases of this project must therefore address some of these related issues as well. 6. REFERENCES 1.

2. 3. 4. 5. 6.

7. 8.

Zhao Dianwu and Xiong Jiling: 1988.”Acidificationin Southwestern China,” In: Rodhe, H.and Herrera, R. (Eds) Acidification in Tropical Countries. SCOPE Report 36, pp. 317-376,John Wiley and Sons, Chichester, U.K. Rodhe, H. and Herrera, R. (Eds): 1988.Acidification in Tropical Countries. SCOPE Report 36, John Wdey and Sons, Chichester, U.K. Bhatti, N., Streets, D.G., and Foell, W.K.: 1990 “Acid Rain in Asia,” In: Foell, W.K. and Sharma, D. (Eds) Proceeding of the Second Annual Workshop on Acid Rain and Emissions in Asia. pp. 533,Asian Institute of Technology, Bangkok, Thailand. Foell,W.K., and Green, C.W.: 1990. “Acid Rain in Asia: An Economic, Energy and Emissions Overview,” In: Foell,W.K. and Sharma, D. (Eds) Proceeding of the Second Annual Workshop on Acid Rain and Emissions in Asia. pp. 123-145,Asian Institute of Technology, Bangkok, Thailand. International Institute for Applied Systems Analysis: 1990. The Rains Model of AcidiJication: Science and Strategies in Europe. Alcamo, J., Shaw, R., and Hordijk, L. (Eds). Kluwer Academic Publishers, Dordrecht, the Netherlands. Hetteligh, J.-P., Downing, R.J., de Smet, PAM., (Eds): 1991. Mapping CriticalLoadsfor Europe. Coordination Center for Effects Technical Report No. 1,RIVM Report No. 259101001,Bilthoven, the Netherlands. Workshop on Acid Rain in Asia: November 13-17,1989.“Report of the Workshop on Acid Rain in Asia,” Asian Institute of Technology, Bangkok, Thailand. Second Workshop on Acid Rain in Asia: November 19-22,1990.“Report of the Second Workshop on Acid Rain in Asia,” Asian Institute of Technology, Bangkok, Thailand.

T Schneider (Editor). Acidification Research Evaluationand Policy Applications 1992 Elsevier Science Publishers B V

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DEPOSITION OF ACIDJFYING COMPOUNDS D. Fowlercr, J.N. C a w , M A Suttona, R Mourn@ K.J. Hargreavesa, J.H. Duyzerb, M.W. GallagheF

eInstituteofTemsttd * Eoology Bush Estate, Pdcuik Midlothian,EEI26 OQB, United Kingdom bTN0

PO Box6011,2600 JA Delft The Netherlands cunivemity ofManchester Institute of Science& Technology Sackville,Manchester U60 lQD, United Kingdom Abstract Inputs of acidifying compounds to terrestrial ecosystems include deposition of the gases NO2, NO, HN02, HNO3, PAN,NH3, SO2 and the ions NO3-, NH4+, SO$-and H+ in precipitation, cloud droplets and particles. Recent research has identified particular ecosystems and regions in which terrestrial effects are closely linked with specific deposition processes. The air pollution related forest health problems at high elevation in the Appalachian mountains for example are primarily due to the cloud water deposition while the health of Dutch heathlands appear to be linked primarily with inputs of ammonia. Areas of large wet deposition in northern Europe show large spatial gradients in inputs and peak values up to a factor of 2 in excess of those provided by long range transport models as a consequence of seeder-feeder scavenging. Aerosol fluxes t o shoot vegetation a r e small relative t o gaseous deposition and seldom provide deposition velocities larger than 2 mms-1. There is also evidence of aerosol production in the few metres of the boundary layer close to the surface. Dry deposition rates for gases onto vegetation are controlled by atmospheric processes for the very reactive gases HNO3 and HC1. For NO2 uptake has been shown to be entirely stornatal with deposition increasing from zero a t night to 6 mms-1 over rapidly growing vegetation during the day. Rates of SO2 deposition are also regulated by stomatal uptake in the absence of surface water or ammonia. In the presence of NH3 (rc 0-200 sm-1) rates of deposition may reach the upper limit set by turbulent exchange processes (Vg = (r, + %)-I but the chemistry of NH3 and SO2 interactions on natural surfaces and its dependence on surface condition has not been quantified. Ammonia exchange over natural plant communities has been shown to

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be bidirectional, with NH3 emission over polluted Dutch heathland in dry conditions and deposition in wet conditions and is very similar to agricultural surfaces. For the cooler, wetter, less polluted regions such ecosystems represent a very efficient sink for NH3. Mechanistic models of deposition processes to extrapolate to regional scales have now been developed for S02, NO2, cloud droplet and wet deposition processes, but they do not satisfactorily incorporate NH3, SO2 co-deposition and are not yet adequate to extrapolate NH3 fluxes to the landscape scale. INTRODUCTION The atmospheric trace gases and particles which contribute t o acidification of ecosystems include the primary emitted pollutants SO2 and HCI,the secondary pollutant gases N02, HNO3 (and possibly HN02) and the SO$-, N o s - and H+ ions in aerosols and precipitation. Some of these components are not acidic directly and only lead to acidification as a consequence of chemical or biochemical processes within plants and soil (van Breeman and van Dijk, 1988). A notable addition to the list of acidifying compounds in recent years has been NH3, emitted largely from agricultural sources (Apsimon et al. 1987) and present close to sources in gaseous form and as the NH4+ ion in aerosols, cloud droplets and precipitation after a few hours in the atmosphere. The acidification resulting from NH3 or NH4+ deposition results from the microbial nitrification of NH4+ to NOS-. The physical and biological fate of deposited NO2, NOS-,NH3 and N H 4 + is not fixed or unique for each compound. For example an ammonia molecule may dry deposit t o a leaf surface into a water film and be washed by rain into a soil where it is nitrified and leached as NOS- from the soil profile. OR the same NH3 molecule may following deposition be taken up by a plant directly or the root system as NH4+ following its transfer to the soil. Such complications mainly with deposited nitrogen compounds lead to considerable difficulty in quantifying the actual acidification resulting from k n o w n deposition rates. For the purposes of this review the biological or chemical processing of deposited gases or ions will not be considered beyond the initial sites of uptake. For the sites of uptake it is clear that initial chemical processing may influence the deposition process directly and will be considered further especially under the subject of dry deposition of gases. This paper is not a review in the conventional sense as it does not provide a uniformly detailed consideration of the entire subject. It does however identify areas of the subject in which important developments have occurred during the last 5 years and an attempt is made to show which aspects of the subject are most important for the policy makers (i.e. what do we most need to get right). This necessarily requires us to identify particular components of the pollution climate which cause the largest acidification or impact and as such components are now always the dominant feature it is necessary to identify specific ecosystems and pollutants which are considered to be particularly sensitive.

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Wet deposition The chemical composition of precipitation is extensively monitored and there are networks on regional scales for Europe and North America (EMEP, NADP) and global background stations (BAPMON) Iversen et al. 1991 (Fig. 1). Such networks are not uniform and within the regions there are areas with intensive detailed networks e.g. the Netherlands and areas in which monitoring is not adequate to define the inputs to sensitive ecosystems, e.g. in many of the acid sensitive high altitude regions of Europe and North America. While interest and field measurements in wet deposition is growing in countries with rapid industrial development it is likely that the detailed networks to establish the scale and intensity of acidic input will follow the identification of damage rather than precede it. 1.5

Figure 1

Non-marine sulphate concentrations (mgl-1)in precipitation in North America and Europe (1990)

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The process of wet deposition scavenging of pollutants is reasonably well understood and has been recently reviewed as a part of the National Acidic precipitation assessment programme of the USA (NAPAP, 1990). This understanding is sufficient to explain observed wet deposition of aerosols and gases and the concentrations of major ions SO$-, Nos-, NH4+ and H+ at sites where the concentration of aerosol and gaseous precursors are known. The major limitation in the modelling of wet deposition processes on regional scales lies in the other processes; in quantifying the oxidation rates of sulphur and nitrogen oxides, in dry deposition and in describing the local variability in wet deposition scavenging due to orographic effects. The latter process is very important to the current discussion because many areas experiencing acidification effects from wet deposition lie in uplands with complex terrain on which the inputs show a very considerable spatial variability. The importance lies in identifying sensitive areas which receive wet deposition smcient to induce biological effects or in excess of a critical load yet which may be smoothed out of regional deposition estimates as a result of being sub-grid scale. The effect results from two different (though related) processes, the seeder-feeder enhancement of wet deposition with altitude (Fowler et al. 1988)and the turbulent deposition of cloud droplets (occult deposition) Dollard et al. 1983. The seeder-feeder process has been shown to increase wet deposition at an upland site by a factor of 4 relative to an adjacent lowland site. As rainfall amount was increased by approximately a factor of 2 any model which used only the spatial rainfall field would underestimate inputs at such sites by a factor of 2. The process of seeder-feeder scavenging illustrated in Fig. 2 results from the incorporation of aerosol SO$-, NOS-, NH4+ and H+ into orographic cloud above hills and the scavenging of the hill cloud droplets by rain droplets falling from a higher level cloud. FRONTAL CLOUD ( SEEDER)

TYPICAL CONCENTRATIONS (ueq 1-1 )

1

Cap cloud

Rain 200m 800m

I

WIND DIRECTION

A

(FEEC

-

VALLEY

200m

Figure 2

The seeder-feeder scavenging process by which wet deposition on elevated topography is enhanced by scavenging of polluted orographic cloud

557

The process necessarily leads to large spatial gradients in wet deposition and in complex terrain the measurement of such gradients is a difficult task and requires a large array of collectors (Dore et al. 1992). Even with such detailed measurements the physical difficulties in operating high altitude precipitation collectors precludes long term large area measurements of wet deposition using conventional techniques. Alternative techniques have been applied to estimate the inputs in complex terrain. The measurements of 210 Pb deposition from soil inventories by Graustein and Turekian, 1986 show the effect of altitude on wet deposition. These methods provide a longterm (- 1OOy) estimate of the scavenging of submicron aerosol by precipitation and dry deposition and have been further developed by Mourne et al. (1992). He has shown that the lead 210 Pb inventory averaged over the Pennine ridge a t Great Dun Fell increases from the valley to the ridge by a factor of 4 and that the point of maximum deposition lies l k m downwind of the summit a s predicted from the more detailed event studies (Fig. 3). Such methods applied to other sites in more complex terrain have quantitatively demonstrated the scale of this enhancement at a range of sites. Clearly the detailed monitoring of a n entire region o r country is prohibited by cost and practicality. With a n understanding of the seederfeeder process it has been possible to develop a simple model of the process and to generalize over regional scales. For the UK such a model has provided a revised wet deposition map and in the high rainfall areas of northern and western Britain the inputs have been increased by up to 70% (Dore et al. 1992). The same exercise should be extended to other regions. In Scandinavia, for example, the coastal mountains of Norway in particular are subject to very similar meteorological conditions, and close to the coast the seeder-feeder scavenging process contributes significantly to the total input.

-

Altitude (rn) A.S. L.

NE

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6 f-

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”

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EDEN VALLEY

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Figure 3

Lead 210 inventories on a transect a t Great Dun Fell showing the point of maximum deposition and the degree of orographic enhancement (from Mourne et al. 1992)

558

For other upland areas of Europe and in E. North America the above generalizations do not apply quantitatively because a much larger proportion of the wet input occurs through convective storms rather than frontal rain. In these circumstances, and with the much greater variability in topography and altitudes there is a requirement for more field study. The modification of wet deposition processes by snow at much greater altitude have been studied by (Ronseaux and Delmas, 1988) but the effect on annual inputs at sites where most wet deposition falls as snow remain poorly understood.

~udandfbg~~tdepoeition Work in Europe and N. America during the last six years has provided a mechanistic understanding of the cloud droplet deposition process and has quantified the dependence of this process on the physical properties of the underlying surface and atmospheric conditions. The main emphasis in this work has been on the 'interception' of cloud or fog droplets by vegetation which for high altitude or coastal vegetation may represent a large input which is not detected by precipitation collectors (and hence was the origin of the term occult (Kerfoot, 1968). Equally important are the chemical characteristics of hill cloud and fogs. Droplets are activated on aerosols, and in a polluted atmosphere the ionic composition of aerosol is dominated by SO$-, NOS-,NH4+ and H+. Following activation the droplets may grow as the air cools, in the case of hill cloud by lifting the air further up a hillside, or in the case of fog, following radiative cooling at the surface. The concentrations of the above ions in hill cloud and fog lie in the range 20 to 2000 peq 1- (Saxena et al. 1991) and generally exceed the concentrations in rain (Fig. 2). The largest concentrations to which hill vegetation is exposed (10002000 peq 1-1)are very much larger than those in rain and have been identified as an important mechanism by which high elevation forests may be damaged by pollutants (Johnson and Siccama, 1983, Leith et al. 1989, Fowler et al. 1989). Hill cloud and lowland fog droplets generally have diameters between 3 and 20 pm, and it is the dependence on the droplet size of deposition rates on a range of vegetation that has been obtained from process studies. The major limitation on estimating inputs by the cloud droplet deposition process is the lack of monitored cloud water composition. The rates of turbulent deposition vary with windspeed, droplet size and the aerodynamic roughness of the vegetation. The maximum rate of droplet deposition is provided by the rate of transfer of momentum (vm)so that the ratio of deposition velocity of cloud droplets V&m provides a good illustration of the efficiency of the deposition process. The results from measurements by Gallagher et al. (1988) (Fig. 4) show that over the most common drop size range for hill cloud droplets (radius 4-12 pm) the rate of deposition is approximately equal to that for momentum. In these conditions the forest or moorland surfaces are efficient sinks for the droplets and rates of deposition can readily be calculated for a range of surface and atmospheric conditions. To model the inputs satisfactorily it is necessary to know the land use, windspeed, concentration of major ions in cloudwater and cloud liquid water content. A substantial collection of data for Eastern North America has been provided by the mountain cloud chemistry programme (Weathers et al. 1988) and 'campaign' data exist for 5 sites in the UK and 6 sites in Germany. These

559 10'

1

lo-' 0

Moorland

lo-* 0

2

4

6

8

10 12

14

16

Droplet radius (urn )

Figure 4

The variation with particle size of the ratio of turbulent deposition rate for cloud droplet deposition Vt to that for momentum (from Gallagher et al. 1990)

consistently show the large concentration of ions in cloudwater to which vegetation is exposed but are not adequate for precise estimates of inputs. In the absence of such monitoring data it is possible to provide a n estimate of the lower limit of cloudwater deposition by assuming that the concentrations of major ions in cloud are on average proportional to their regional average concentrations in rain, and using field data to establish the constant of proportionality. From precipitation and cloud composition studies a t Great Dun Fell, Fowler et al. (1988) estimated the mean ratio of concentrations of major ions in cloud and rain during precipitation. Such data provide much smaller concentrations than the median for cloudwater from all events and are therefore likely to be an underestimate. Using these data cloudwater deposition has been modelled for the UK incorporating observed cloud frequency land use and wind speed data (Fowler et al. 1992). Alternative methods for modelling cloud droplet deposition have been adapted for individual sites in N. America by Lovett et al. 1983 using a n empirical model and a much more detailed mechanistic approach over areas of complex terrain has been used by Gallagher et al. (1992). Although differing in detail, similar conclusions are drawn by all authors on the importance of the deposition process for upland forests. For high elevation forests in Europe and N. America cloud water deposition has been estimated to contribute up to 75% of the total atmospheric inputs of S and N. Even a t modest altitudes of lOOOm in N. Britain the input by this process may be as much as 40% of total wet deposition. Fog water deposition at low elevation sites has only been shown to contribute significantly to the hydrological input at coastal sites (e.g. California and Japan). However, the concentrations of major ions during

-

560

winter months in radiation fogs in parts of Europe (e.g. the Po Valley, Fuzzi, 1988) are large enough to represent a potential threat to some sensitive tree species and merit further investigation. If the total regional amounts of acidic pollutants deposited in cloud or fog droplets were expressed as a fraction of the total deposition this deposition mechanism would be dismissed as irrelevant. However the importance of this process for inputs on hills, the implications for land use and critical loads, and the mechanism for exposure of vegetation to damaging concentrations of pollutants, highlight the need t o know more about the composition of hill and mountain cloud.

Dryde~tionofparticles The subject of particle deposition has received little attention during the last 5 years but remains an area of substantial controversy. On the one side, wind tunnel and field micrometeorological methods have consistently reported small rates of aerosol deposition on vegetation, with deposition velocities in the range 0.1 to 1 mm s-1. Such small values for the deposition velocity are consistent with the gradual accumulation of aerosol during dry weather and with the known particle size dependence of impaction efficiency for particles in the size range 0.1 to 1.0 pm (radius), (Chamberlain 1975). However there have also been measurements using surrogate surfaces and a range of leaf washing techniques (Lindberg et al. 1990) which imply rather larger rates of particle deposition, especially for coarse particles (radius >> 1 pm). Further, the modelling studies of Wiman (1988) also suggest larger rates of particle deposition close to a forest edge. Thus the forest present in areas of southern Sweden for example, with large edge perimeter of forest areas. may be much more important as a sink for aerosols than the wind tunnel studies suggest. Recent measurements of particle deposition rates have provided the particle size dependence of aerosol deposition using micrometeorological techniques (Fig. 5). These results, from measurements by the eddy covariance method using a sonic anemometer and an active scattering aerosol spectrometer probe (ASASP) above a heather dominated heathland in the Netherlands, show apparent emission of particles smaller than 0.1 pm and deposition of particles in the size range 0.1 to 0.5 pm increasing to 5mm 5-1 at 1pm. The process responsible for the apparent upwind fluxes are not known but such fluxes of very small particles are not consistent with the literature on resuspension of particles from foliage (Slinn 1983). At this early stage an analysis and interpretation of the field data no quantitative explanation of the results has been provided and the only plausible mechanism advanced has been the possibility of rapid gas to particle conversion. Such rates of deposition to short vegetation make the aerosol dry deposition pathway a small component of the annual budget. For forests however with much larger leaf area and smaller characteristic dimensions in the case of conifers, together with larger windspeeds, the question is still open and detailed measurements of the kind made by using ASASP methods over forests are necessary to address this question.

561

26th April 1991

30

tt

-30

0 0.05

0.1 0.3 0.8 1.0

ptle radius (pm) Figure 5

The size dependence of aerosol particle deposition onto heathland during the Leende experiment in 1991

DRY DEPOSlTIONOFGASES

H N a and HCl These very reactive gases are deposited on vegetation as rapidly as they can be transported to the foliar surfaces by turbulent transfer. Rates of deposition are therefore large and are determined by windspeed and the aerodynamic roughness of the surface. Recent measurements, reported by Dollard et al. 1987 and early measurements by Hubert 1983 consistently reported canopy resistances (re) close to zero. The only measurements in which non-zero surface resistances have been detected a r e those of Johannson and Granat (1986) for measurements of HNO3 deposition to snow a t temperatures below -543. NQa Stomata represent a n important sink for pollutants and in many circumstances are the major sink. For Nos, field data over rapidly growing cereal crops show rates of NO2 deposition very close to those expected for stomata1 uptake, and no leaf surface uptake, a s shown in Figure 6. For slow growing moorland vegetation a t low ambient NO2 concentrations, very small rates of NO2 deposition have been observed (1-2 mm s-1). Similarly in cuvette measurements on Scots pine (Pinus syluestris) shoots, Johannson, 1987 has shown the presence of a large surface resistance to NO2 uptake at low ambient NO2 concentrations (< 10 ppb). An important complication in the measurement of NO2 exchange by gradient micrometeorological techniques is that of air chemistry in the lower layers of the atmosphere between NO, NO2

562

v)

u

C m c

.-

v)

v,

d

301

I

i

20

O

0

LI 300 600 900 1200 1500 1800 2100 2400

Time (GMT)

Figure 6

Canopy resistances for NO2 and 0 3 over a wheat crop showing the close link between these gases

and 03. In practice the analysis of vertical profiles in the concentrations of these three species to provide fluxes between the atmosphere and the ground requires more information than the gradients in concentration and windspeed. In particular, the photolysis rate coefficient JN02 is required. The analysis of NO2, NO and 0 3 flwdgradient data by Duyzer (1991) and by Kramm et al. (1991) has shown the magnitude of these effects in field conditions. Grassland on the Halvergate marshes was shown to be a significant sink for NO2 and stomata were the primary sink. The field data for NO2 are at last therefore beginning to show a more consistent pattern of uptake for agricultural vegetation,in which stomatal uptake dominates, and which can therefore be simulated using the big-leaf resistance analogy, Hicks and Matt, 1988. The regional concentrations of NO2 may therefore be used together with a stomatal resistance model and land use data to compute NO2 deposition. For hill land and forests the inputs are less certain,as a consequence of poor understanding of the factors which control the magnitude of the internal or surface resistance, but it is at least possible now to compute regional estimates of NO2 dry deposition fluxes.

HNoa

The presence of gaseous nitrous acid at concentrations in the range 0.1 to 5 ppbV has been detected at night in measurements in Germany (Lammel et ul. 1989 and in the UK Kitto and Harrison, 1992). This gas is rapidly photolysed during the day to form the OH radical and nitric oxide and is therefore an important nocturnal reservoir for the OH radical. Measurements by Kitto and Harrison (1992) indicate that the HNO2 present close to the ground at night may be the product of heterogeneous reaction of

563

NO2 on moist vegetation and may therefore be closely linked with NO2 deposition processes. Production rates of HNO2 at the ground or on aerosol surfaces, have also been estimated by Lammel et al. 1989. Such hypotheses require further testing but are an indication of the growing tendency t o incorporate atmospheric chemistry field studies with those of trace gas flux measurements.

soa This gas is absorbed readily by stomata and in many laboratory and field studies the primary sink has been shown to be stomata (Fowler 1978,Black & Unsworth 1979, Garland et al. 1978). In the absence of any mesophyll resistance to SO2 uptake by stomata, and using a constant and small rate of uptake on external plant surfaces, it has been possible to model SO2 deposition to the landscape using land use, meteorological and monitored SO2 concentration data (Fig. 7). These modelling approaches have been applied in North America and in parts of Europe and it is now time to extend the application of these models to permit comparisons between the large scale, long range transport model estimates of dry deposition fluxes and the process based resistance analogy models working largely from monitoring data. The most pressing current limitation to our understanding of SO2 uptake by vegetation is the leaf surface uptake, its variability and the chemical processes taking place on surfaces. In particular, it is known that leaf surface uptake is not constant; the presence of liquid water on leaf surfaces has been shown to change the surface resistance. Fowler and Unsworth (1979)showed that initially dew reduced surface resistances to zero but with time, as dewfall rates decreased, a surface resistance reappeared. These changes were interpreted as effects of the equilibrium chemistry of SO2 but have not been confirmed by detailed measurements of the reactants and products in the field.

0

500

1000

1500

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2500

Time

Figure 7

The seasonal dependence of SO2 deposition velocity onto a spruce forest simulated using a big leaf model

564

More recently it has been suggested that the presence of gaseous ammonia may influence SO2 deposition rates on leaf surfaces (Adema 1986, van Hove et al. 1989) and some field data have been obtained which are consistent with these suggestions (Fowler et al. 1991). The laboratory work at large NH3 and SO2 concentrations is certainly indicative of the co-deposition hypotheses but do not show that the process occurs at the concentrations experienced in field conditions. The field observations of small canopy resistances in the presence of concentrations of NH3 and SO2 adequate for their reaction at the surface to produce (NH412SO4 are also consistent with the co-deposition hypothesis and the data (Figure 8) provide an example of this phenomenon. The detailed behaviour of surface resistance for SO2 and the apparent surface concentration for NH3 (at zo) show the presence of a significant surface resistance to SO2 deposition with concentrations of NH3 still adequate for the complete reaction of S02. The determination of rate coefficients from data of this nature will continue to be problematical because of the difficulty in controlling or measuring the wide range of variables which all influence the chemistry. It is clear however that there is an effect of rates of NH3 on SO2 exchange. Also consistent with these data are the earlier field data for SO2 deposition in the UK and the USA which found large and fairlyconstant canopy resistances for non-stomata1uptake, typically of 400 s m1 or greater. These measurements were generally made at ambient SO2 concentrations in the range 10 to 30 ppb, between 1and 2 orders of magnitude greater than the likely NH3 concentrations! Simulation of the surface Chemistry of these gases within the models of net exchange is a relatively straightforward matter when the mechanisms of reaction are understood and shown to be consistent with field data. m

S

The subject of ammonia exchange over natural surfaces has become central to the current debate on acidification. First, the microbial nitrification of deposited NH4+ leads to acidification; second, over substantial areas of the Netherlands, Germany, Denmark and the UK, deposited NH4+and NH3 (wet and dry) dominate the deposition budget for deposited nitrogen, and third, the presence of atmospheric NH3 has been shown to influence rates of deposition of SO2 as described above. "he processes of surface-atmosphere NH3 exchange are similar to those for NO2 or SO2 but the strongly bidirection nature of the fluxes of this gas lead to some agricultural fields representing net sources while adjacent fields act as sinks for the gas and the spatial heterogeneity in fluxes, at least in agricultural districts, is a major feature of the behaviour of NH3. Over heathland, moorland and forests the rates of NH3 deposition have been shown to be large, and most studies show that the gas is deposited at rates close to the upper limit set by rates of turbulent transfer (Duyzer et al. 1987, Sutton, 1990). These data led to a rather simplified approach t o estimating the likely annual inputs of NH3 for natural vegetation (Sutton, 1990). These generalizations appear to be valid for measurements made at sites in N. Britain with small ambient NH3 concentrations (0.1 to 5 ppb) and

565

Ammonia and sulphur dioxide exchange at Halvergate 100

- 90 -80

- 70

RH(G)

("w

60

Air conc.(1 m) (Pel m-3,

5-

N"3

-

so2 A Trace gas - ................................ flux (ng m - W -50 . soz 400 0 loo NH3 50

0600

-i

59-

1200

1800

emission

. ....

, ,

deposition

10

2400

0600

Time (GMT)

Figure 8

Fluxes and resistances in the exchange of NH3 and SO2 over the Halvergate grassland (U.K.)

during periods of high humidity. However, during periods of low humidity and especially at sites with large ambient NH3 concentrations (as during the Dutch Heathland experiment at Leende) in warm dry conditions, large surface resistances to NH3 deposition have been observed. At this site even upward fluxes were recorded. Figure 9 shows an example of the bidirectional exchange of NH3 over the Dutch heathland during this study, during which the change from emission to deposition occurs at the transition from dry to wet surfaces of the vegetation late in the day as radiative cooling at the ground led to dew formation on the vegetation. "he flux is bi-directional on both seasonal and daily scales. A pulse of ammonia emission occurs following fertilizer application, which may result from fertilizer residues in the soil as well as an increase in the equilibrium NH3 concentration, or 'compensation point', in plant tissues. A second peak in emission may occur following hay cutting or during senescence of annual crops (Dabney and Bouldin 1990). On a daily scale, emission is favoured during warm dry conditions, whereas deposition generally occurs when the surface is wet of frozen (Sutton et al. 1992). At present, the integration of these fluxes over annual scales for crop vegetation must be regarded as very approximate.

566

Ammonia exchange at Leende Heide '-

I

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Emission -30

. ,

.

1200

I

.

, 2400

6 May 1991

very dry

Figure 9

. ,

.

I

. ,

1200

,

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.

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7 May 1991

humid

very dry

humid

Fluxes of N H 3 over Dutch heathland at Leende showing the bidirection nature of N H 3 exchange at this site

k u g b f a l land stamfbw measurements

Many research groups throughout the last three decades of acid rain research have made measurements of the change in precipitation chemistry as the water and solutes pass through plant canopies. The work has mainly (though not exclusively) been applied to forest vegetation (e.g. Miller et al. 1984, Cape et al. 1987a). The measurements have provided a valuable contribution to the general field of bio-geochemical cycling of a range of elements and the objectives of the measurement have been varied. One objective of such measurements has been to estimate the input of a range of elements from the atmosphere. Many reviews of the different techniques applied and their success have been published (Lindberg et al. 1991). It is not the purpose of this review to repeat the conclusions of the earlier reviews of the throughfall and stemflow measurements. Rather it is to identify scientific issues which have not been solved by the work so far and which require a solution before any such techniques are applied as a monitoring instrument to obtain areal estimates of inputs for critical loads or other mapping purposes. Although in some studies, notably the Integrated Forest Study

567

(Lindberg et al., 1991) there has been apparent agreement for sulphur between modelled deposition from the atmosphere using actual concentration and meteorological data, and measured deposition in throughfall and stemflow, the errors involved are potentially large. Quoted error estimates for deposition modelling to forests are f 50%, or more where occult deposition is important. Error estimates for deposition in throughfall and stemflow are typically 1530%. The apparent agreement between modelled deposition and throughfall and stemflow data only holds for long-term averaging (one or more full years) and does not apply on weekly or monthly time scales, despite the use of hourly averaged data for modelling, and event sampling for deposition. There are large uncertainties in the short-term processes which control storage and release of sulphate in forest canopies. Moreover at some sites (e.g. Cape et al. 1987b) measured annual deposition below canopy was shown to be so far in excess of modelled deposition from the atmosphere that significant additional sources of sulphate were required to make up the deficit, suggesting a role for the internal cycling of sulphur. If internal cycling of sulphate is a major contributor to sulphate measured below canopy then throughfall and stemflow measurements cannot easily be used to quantify net deposition. Attempts to quantify sulphur cycling have been made using radioisotopes. Garten (1988,1990) injected trees with 35so4 and followed the partitioning of the isotope in foliage and throughfall, and deduced that leaching (internal cycling) contributed only a few percent to below-canopy deposition. His studies, on isolated or edge trees, probably underestimated the contribution in a closed forest stand, because below-canopy deposition a t the forest edge would have been much greater than in a uniform block of forest, as described above. Cape et al. (1992) applied 36so4 to the forest floor and followed the appearance of the isotope in foliage and throughfall. Apparent leaching was initially almost loo%, falling to c.5% of below-canopy deposition after 6 weeks. These data illustrate the uncertainties in using isotopes, where assumptions about equilibrium within the canopy do not in general apply. The role of internal cycling remains unclear, but given the relative uncertainties involved, throughfall and stemflow measurements may provide an adequate upper estimate of sulphur deposition for critical load assessment if appropriate measures are taken to avoid the sampling bias introduced by the large spatial heterogeneity below forest canopies. For nitrogen compounds (ammonium or nitrate) existing methods of sampling throughfall and stemflow are generally inadequate, given the rapid microbial degradation of water samples. Interpretation of the results is even more difficult than for sulphur, as nitrogen may be taken up by foliage, by stems, by epiphytic lichen or other microflora, or may be leached (as amino acids) from the canopy. Once measurement techniques have improved, deposition to the forest floor may be quantifiable, but canopy interactions will still dominate the pathway between atmospheric deposition and the ground. CONCLUSIONS Two important conclusions may be drawn from the above review for science and application in the policy field: firstly, that current uncertainties in estimates of S and N inputs by dry deposition are likely to lead to continual changes in estimated regional inputs of S or N of typically 50%, as current

568

understanding is refined, and that this uncertainty must be incorporated in the critical load calculations to avoid failure to protect given ecosystems when emission controls are fully implemented. Secondly, and this applies to the regions dominated by wet deposition, that the spatial resolution of total inputs in complex terrain must be improved to match the current scales of information on landscape sensitivity to acidic inputs . The initial conclusion follows from the inability of the research community to unravel the scientific understanding at the pace and timetable agreed by policy makers. It follows from these two statements and the high cost of emission controls that a cost-benefit analysis would show that a much larger investment in research would be entirely justified on financial grounds simply to reduce the uncertainty in inputs and therefore the magnitude of emission controls necessary. An alternative and more practical appeal would be to encourage more widespread application of current understanding by modellers. Modellers have become a n effective channel of communication between the process orientated scientists and policy makers. This would therefore assist in using the best available information to direct policy.

ACKNOWLEDGEMENTS The authors gratefully acknowledge financial support for this work from the Air Quality Division of the U.K. Department of the Environment and the Commission of the European Communities.

REFERENCm Adema, E.H. (1986). On the dry deposition of NO2, SO2 and NH3 on wet surfaces in a small scale wind tunnel. Proceedings of the 7th World clean air congress, Sydney, p. 1.18. Apsimon, H.M., Kruse, M. and Bell, J.N.B. (1987). Ammonia emissions and their role in acid deposition. Atmos. Enuiron. 21, 1939-1946. Black, V.J. and Unsworth, M.H. (1979). Resistance analysis of SO2 fluxes to Vicia faba. Nature,282,68-69. Cape, J.N., Fowler, D., Kinnaird, J.W., Nicholson, I.A. and Paterson, I.S. (1987a). Modification of rainfall chemistry by a forest canopy. In Pollutant Transport and Fate in Ecosystems. eds, P.J. Coughtrey, M.H. Martin and M.H. Unsworth. Blackwell, Oxford. pp. 155-169. Cape, J.N., Fowler, D., Leith, I.D. and Paterson, I.S. (198713). Measurements of sulphate in throughfall, and dry deposition of SO2 to a forest. In Direct Effects of Dry and Wet Deposition on Forest Ecosystems - in Particular Canopy Interactions. ed. P. Mathy. Air Pollution Research Report 4(EUR 112641, CEC, Brussels, pp. 86-91.

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Cape, J.N., Sheppard, L.J., Fowler, D., Harrison, A.F., Parkinson, J.A., Dao, P. and Paterson, I S . (1992).Contribution of canopy leaching to sulphate deposition in a Scots pine forest. Environ. Pollut. 75,229-236. Chamberlain, A.C. (1975).The movement of particles in plant communities. In Vegetation and the Atmosphere, Vol. 1, pp. 115-201,ed, J.L. Monteith. London: Academic Press. Duyzer, J.H., Boumann, A.M.H., Diederen, H.S.M.A and Van Aalst, R.M. (1987).Measurement of dry deposition velocities of N H 3 and NH4+ over natural terrains. Report R 87/273 Netherlands Organisation for Applied Scientific Research (TNO). Dabney, S.M. and Bouldin, D.R. (1985).Fluxes of ammonia over a n alfalfa field. Agron. J. 77,572-578. Dollard, G.J., Unsworth, M.H. and Harvey, M.J. (1983).Pollutant transfer in upland regions by occult deposition. Nature, 302,241-247. Dore, A.J., Choularton, T.W., Fowler, D. and Storeton-West, R.L. (1992).Field measurements of wet deposition in a n extended region of complex topography. Q. J. Roy. Met. Soc.(in press). Dore, A.J., Choularton, T.W. Fowler, D. and Crossley, A. (1992).Orographic enhancement of snowfall. Environ. Pollut. 75, 175-180. Fowler, D. (1978).Dry deposition of SO2 on agricultural crops. Atmos. Environ. 12,369-373. Fowler, D. and Unsworth, M.H. (1979). Turbulent transport of sulphur dioxide to a wheat crop. Quart. J. Roy. Met. SOC.105,767-783. Fowler, D., Cape, J.N., Leith, I.D., Choularton, T.W., Gay, M.J. and Jones, A. (1988).The influence of altitude on rainfall composition a t Great Dun Fell. Atmos. Environ. 22, 1355-1362. Fowler, D., Cape, J.N., Deans, J.D., Leith, I.D., Murray, M.B., Smith, R.I., Sheppard, L.J. and Unsworth, M.H. (1989).Effects of acid mist on the frost hardiness of red spruce seedlings. New Phytol. 113, 321-335. Fowler, D., Duyzer, J.H. and Baldocchi, D.D. (1991).Inputs of trace gases, particles and cloud droplets to terrestrial surfaces. Proc. Roy. SOC. Edinburgh m,35-59. Fuzzi, S. (1988).Fog chemistry and deposition in the Po Valley. In Acid Deposition at High Elevation Sites, ed. M.H. Unsworth and D. Fowler. Kluwer, Dordrecht, pp. 443-452.

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LIST OF PARTICIPANTS

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575 Adema, E.H. Agricultural University 6700 EV WAGENINGEN The Netherlands tel.: 8370-82100 fax: 8370-84457

Al, G.J.A. Ministry of Housing, Physical Planning and Environment P.O.Box 450 2260MB LEIDSCHENDAM The Netherlands tel.: 70-3 174155 fax: 70-3174448

Amann, M. USA Schlossplatz 1 A-2361 LAXENBURG Austria tel.: 2236-71521 fax: 2236-71 3 13

Bakema, A.H. National Institute of Public Health and Environmental Protection P.O.Box 1 3720 BA BILTHOVEN The Netherlands tel.: 30-743704 fax: 30-250740

Barth, H. European Economic Commission, DG XII 200, Rue de la Loi B-1049 BRUSSELS Belgium tel.: 32-2-2358160 fax: 32-2-2363024

Bekker, M. Ministry of Agriculture, Nature and Fisheries P.O.Box 20401 2500 EK DEN HAAG The Netherlands tel.: 70-3792250 fax: 70-3825752

Bertills, U. Swedish Environmental Protection Agency S-17185 SOLNA Sweden tel.: 46-8-7991000 fax: 46-8-283008

Bleuten. W. Dept.of Physical Geography, Univ. of Utrecht P.O.Box 801 15 3508TC UTRECHT The Netherlands tel.: 30-540604 fax: 30-532780

Bouma, W.J. CSIRO, Division of Atmospheric Research Private Bag no. 1 3195 ASPENDALE, Victoria Australia tel.: 61-3-5867666 fax: 61-3-5867600

Bresser, A.H.M. National Institute of Public Health and Environmental Protection P.O.Box 1 3720 BA BILTHOVEN The Netherlands tel.: 30-743043 fax: 30-250740

Briill, N.J.H.C. The Netherlands America Institute P.O.Box 2225 6202HA MAASTRICHT The Netherlands tel.: 43-897602 fax:

Buijsman, E. National Institute of Public Health and Environmental Protection P.O.Box 1 3720 BA BILTHOVEN The Netherlands tel.: 30-7423 18 fax: 30-28753 1

Cowling, E.B. College of Forest Resources, North Carolina State University RALEIGH, NC USA tel.: 919-515-7564 fax: 919-515-7231

Cuypers, C.M. Catholic University Leuven E.van Evenstraat 2b 3000 LEUVEN Belgium tel.: 32-16-2831 14 fax: 32-16-283253

576 Dalziel, R.T.K. Powergen, Ratcliffe Technology Centre RATCLIFFE-ON-SOAR, Nottingham NG11 OEE United Kingdom tel.: 602-832257 fax: 602-83271 1

Denvent, R.G. Department of the Environment B 358 Romney House 43 Marsham Street LONDON SWlP 3PY United Kingdom tel.: 71-2768881 fax: 7 1-2768299

Downing, R.J. National Institute of Public Health and Environmental Protection P.O.Box 1 3720 BA BILTHOVEN The Netherlands tel.: 30-743532 fax: 30-250740

Draaijers, G. University of Utrecht P.O.Box 80115 3508TC UTRECHT The Netherlands tel.: 30-534014 fax: 30-540604

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Farmer, A.M. English Nature NGhminster House PE11UA PETERBOROUGH United Kingdom tel.: 733-340345 fax: 733-68834

Forsberg, E. Ministry of Environment S-10333 STOCKHOLM Sweden tel.: 46-8-7632041 fax: 46-8-7231 160

Fowler, D. Institute of Terrestrial Ecology Bush Estate PENICUICK MIDDLOTHIAN EG25 OQB United Kingdom tel.: 44-31-4454343 fax: 44-31-4453943

Gaasbeek, P. Shell Nederland B.V. P.O.Box 1222 3000BE ROTTERDAM The Netherlands tel.: 10-4696035 fax:

Giilli, Mrs.B. Feded Office of Environment CH-3003 BERN Switzerland tel.: 44-31616857 fax: 44-31618057

Gregor, H.D. Umweltbundesamt Bismarckplatz 1 D-1000 BERLIN 33 Germany tel.: 49-30-89032130 fax: 49-30-89032285

511 Grennfelt, P. Swedish Environmental Research Institute P.O.Box 47086 402 58 GOTEBORG Sweden tel.: 3 1-460080 fax: 31-482180

Grinsven, J.J.M.van National Institute of Public Health and EnvironmentalProtection P.O.Box 1 3720 BA BILTHOVEN TheNetherlands tel.: 30-743397 fax:

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Hannessen, H. Ministry of Housing, Physical Planning and Environment P.O.Box 450 2260 MB LEIDSCHENDAM The Netherlands tel.: 70-3174427 fax: 70-3174448

Heammerli, F. Institut de Recherches sur la Foret, la Neige - et le Paysage CH-8903 BIRMENSDORF ZH Switzerland tel.: 41-17-392111 fax: 41-17-392215

Heij, G.J. National Institute of Public Health and EnvironmentalProtection P.O.Box 1 3720 BA BILTHOVEN The Netherlands tel.: 30-743108 fax: 30-250740

Hertz, J. Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) Ziircher&rasse 111 BIRMENSDORF 8903 Switzerland tel.: 1-7392464 fax: 1-7392488

Hettelingh, J.P. National Institute of Public Health and EnvironmentalProtection P.O.Box 1 3720 BA BTLTHOVEN The Netherlands tel.: 30-743048 fax: 30-250740

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Hordijk, L. Centre for Environment Studies AgriculturalUniversity P.O.Box 9101 6700 HB WAGEMNGEN The Netherlands tel.: 31-8370-84919 fax: 31-8370-84919

Hultberg, H. Swedish Environmental Research Institute P.O.Box 47086 402 58 GOTEBORG Sweden tel.: 3 1-460080 fax: 31-482180

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Jattke, A. Institut for Industrial Production Hertzstrasse 16 D-7500 KARLSRUHE 21 Germany tel.: 49-721-6084551 fax: 49-721-758909

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Koster, L. Shell Nederland B.V. P.O.Box 1222 3000BE RO'ITERDAM The Netherlands el.: 10-4696035 fax:

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Landmann, G. Programme DEFORPA, Centre de Recherches Forestiers - INRA 54280 CHAMPENOUX France tel.: 33-83394072 fax: 33-83317160

Leaf. D.A. US EPA 401 M Street S.W.(ANR-445) WASHINGDON DC 20460 USA tel.: 202-2609306 fax: 202-2600892

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Lubbers, F. N.V. SEP Utrechtseweg 310 6812 AR ARNHEM The Netherlands tel.: 85-721 111 fax: 85-430858

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Marseille, Mrs.H. Ministry of Housing, Physical Planning and Environment P.O.Box 450 2260 MB LEIDSCHENDAM The Netherlands tel.: 70-3174402 fax: 70-3174449

Matzner, E. Lehrstuhl fur Bodenkunde, BITOK, Univ.Bayreuth Postfach 101251 8580 BAYREUTH FRG tel.: 921-553508 fax:

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Mohren, G.M.J. De Dorschkamp, Institute for Forestry and Urban Ecology P.O.Box 23 6700 AA WAGENINGEN The Netherlands tel.: 8370-95322 fax: 8370-24988

Nagel, H. Institut fiir Oekosystemforschung Magdalenstr. 17-19 0- 1 130 BERLIN Germany tel.: fax: 37-2-23722034

Nilsson, J. Vattenfall 16287 VALLINGBY Sweden tel.: 8-7395000 fax:

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Salm, C.van der Winand Staring Centre P.O.Box 125 6700 AC WAGENINGEN The Netherlands tel.: 8370-74326 fax: 8370-24812

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