Critical Loads Calculations

Sammanfattning.

Projected emissions of sulfur and nitrogen are expected to have continuing negative impacts on forests, in spite of reductions in sulfur emissions as a result of SO2 control programs. Sulfur and nitrogen emissions present serious long-term threats to forest health and productivity in the United States. This report is intended to explain the differences in approaches for calculating critical loads for forest ecosystems in Europe, Canada, and the United States; it is directed to air quality regulators and Federal Land Managers (FLMs) in the United States, and addresses concerns particular to U.S. Federal lands. The paper describes the basic mass balance approach for calculating critical loads, presents the various critical thresholds, and explains the assumptions inherent in the calculation and data selection procedure. The input necessary from FLMs in the process of estimating the critical load is described.

This paper identifies sources of numerical instability within the critical loads for acidity calculation developed by Sverdrup and de Vries and examines the effects of these instabilities on critical load calculations for sitka spruce forests in Wales. It is shown that the instabilities can introduce large changes in the calculated critical load for small changes in the calculation parameters and that it is essential for researchers to be aware of such unstable parameter regions before applying the equations to experimental situations or to regional mapping.

This book provides a unique overview of research methods over the past 25 years assessing critical loads and temporal effects of the deposition of air pollutants. It includes critical load methods and applications addressing acidification, eutrophication and heavy metal pollution of terrestrial and aquatic ecosystems. Applications include examples for each air pollution threat, both at local and regional scale, including Europe, Asia, Canada and the US. The book starts with background information on the effects of the deposition of sulphur, nitrogen and heavy metals and geochemical and biological indicators for risk assessments. The use of those indicators is then illustrated in the assessment of critical loads and their exceedances and in the temporal assessment of air pollution risks. It also includes the most recent developments of assessing critical loads and current and future risks of soil and water chemistry and biodiversity under climate change, with a special focus on nitrogen. The book thus provides a complete overview of the knowledge that is currently used for the scientific support of policies in the field of air pollution control to protect ecosystem services.

Sammanfattning.

The concept of critical loads is of great ecological, economic and political importance. Although a simple concept - the threshold at which a pollutant load causes harm to the environment - turning this basic idea into scientifically-acceptable criteria is an ambitious undertaking. Nevertheless, governments are pressing ahead with European legislation on air pollution based on acceptable critical loads. However, there has been little opportunity for the ecological community as a whole to participate in these vital discussions on European policy, or for those who have been involved to present the results of their deliberations to their scientific peers.