Background and Objective

In contrast to direct effects of atmospheric pollutants on forest ecosystems (Necrosis or dead needles and leafs) the indirect and longterm effects e.g. soil acidity, eutrophication or nutrient imbalance are less obvious. Critical Loads are an instrument to estimate this longterm impact of one or more pollutants on the ecosystem. It is assumed that below this load none significant harmful effects on ecosystem structure and function occur (Nilsson and Grennfelt 1988). Therefore the Critical Load concept is implemented in the “Convention on Long Range Transboundary Air Pollution” of the United Nations Economic Commission for Europe (UNECE) as an instrument to define and quantify the goals of emission policy.

Within the National Soil Survey (BZE) Critical Loads and their exceedance for acidifying sulphur and nitrogen and for eutrophying nitrogen in forest ecosystems are calculated.

Nilsson and Grennfelt 1988: Critical Loads for Sulphur and Nitrogen. The Nordic Council of Miniaters. Kopenhagen. Report 1988, 15.

Approach

The deposition rates are compared to the buffer and accumulation processes on each BZE-plot. Thus sites with an exceedance of Critical Loads are identified and mapped. Chemical criteria of soil solution (Critical Limits) which are applied in mapping Critical Loads are e.g. critical pH, ratio between base cations and aluminium or critical aluminium concentration in the rooting zone.