This book contains the results and conclusions of extensive research on the causes and effects of acidification of forests/forest soils and heathland in the Netherlands. In 1985 the Dutch Priority Programme on Acidification was started in order to give a more concrete form to the increasing interest of policy-makers in the effects of air pollution on ecosystems in particular.In the last three years, the research has focused on obtaining a more accurate estimate of the emission of ammonia on the deposition of SOx, NOy and NHx, and also on quantifying effects on forest and heathland ecosystems. This quantification of effects included experimental work model analyses, and derivation of critical loads and levels for forest and heathland ecosystems. Furthermore, scenario analyses were made with the Dutch Acidification Systems Model (DAS) in order to evaluate the effectiveness of policy measures.The research itself, which formed the basis for this book, has been described in the reports on individual projects. A summary of the scientific results and conclusions is given in thematic reports (added as annex). An independent Review Team has provided a critical assessment of the research carried out since 1988. The Review Report has been incorporated as annex.

Providing a wealth of reference material for research scientists and policy makers, these proceedings address the extremely complex problem of acidification - a phenomenon which is causing serious deterioration of natural environments in Europe and North America. Papers review the effects of acidification on the aquatic environment, flora, fauna and vegetation, and materials, and also review cultural properties, the ecology as a whole and the economic impact of acidification. The papers on forest-dieback cover potential stress factors and the effects on materials and cultural properties. Scientific research results are presented which deal with models as tools for abatement strategies, and underline the application of models in policy-making. The review papers of scientific research on acidification are followed by the official report of the conference, and presentations by representatives of the EEC member countries giving an overview of national research programmes and policies regarding acidification.

A large number of nationwide research programmes in the field of acidification have been carried out in the last decade. Especially in Western Europe, extensive programmes have resulted in a good overview of all the effects - mostly negative - caused by acidifying substances. There is now consensus that types of acidification damage relate to the unique geography of an area: air pollution affects vegetation; acid aerosol the ozone layer. New in this volume, is the relation between scientific results of integrated research programmes and policy actions to prevent, reduce and limit the widespread damage caused by acidification. The results of many different national research programmes are evaluated and compared to present a unique compilation for the research scientist and policy maker. In this volume thematic reviews on specific topics of acidification research are presented, followed by overviews of acidification policy plans and actual abatement plans. The result is the best review of acidification research carried out worldwide during the last decade and presentation of the critical relation between research results and policy actions.

The book begins with an overview of the research topics which were addressed in the three different phases of the Dutch Priority Program on Acidification (DPPA), executed between 1985 and 1994. This chapter is followed by a chapter which deals with the emissions of acidifying substances, the concentrations and the deposition to forest and nature conservation areas. Prognoses are given for the acid deposition in 2000 and 2010; the deposition in the countries surrounding the Netherlands is also mentioned. The differences in the results of the DPPA-II are analysed.The third chapter deals with the effects of exposure and load on forests. The chapter moves from small-scale to large-scale: first the effects in laboratory-scale studies are described, then the effects in the field, both at stand level and on a regional scale. In addition, the critical thresholds (critical level of concentration and critical load of deposition) are discussed.The fourth chapter covers terrestrial ecosystems (or parts thereof) as well as weakly buffered surface waters, springs and other streams. Critical levels and loads are also discussed. The most important results are given in chapter 5.In the appendices of the book, so-called umbrella theme reports on deposition, stand modelling and effects on forests are presented which describe in more detail the scientific work performed in the third phase of the DPPA.This book will be of interest to anyone involved in research related to acidification and eutrophication; i.e., not only those who perform the research in the causal chain from emissions to effects, but also policy-makers and students.

Proceedings of a Symposium held in Arnhem, the Netherlands, December 1989