Critical Limits
Critical limits of soil solution element concentrations are important input parameters for the calculation of Critical Loads. They mark a threshold concentration above which adverse effects on the vegetation may occur.
Critical Loads are defined as "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" (ICP Modelling and Mapping).
Soil solution assessments at Level II plots were used to calculate exceedances of critical limits for N concentrations and [Mg+Ca+K]/Al ratio (Further information on methods in Technical Report 2010.) In the case of N, nutrient imbalances, reduced root growth and enhanced sensitivity to frost and fungi are important effects of high N concentrations in the soil solution of the rooting zone (Figures 1-3). Increased leaching of N to ground and surface water bodies occurs if N concentrations below the rooting zone are higher than 1 mg per l. High Al concentrations in the soil solution may be toxic and are evaluated in relation to the sum of basic cations. The critical limit is tree species specific and ranges from 0.3 to 2 (Figure 5 and 6). Single exceedance of Critical Limits will not lead to instant dieback but will cause higher sensitivity to natural stressors. The maps below show how often critical limits were exceeded during soil solution monitoring. The more often critical limits were exceeded the higher the probability that described adverse effects occur and of reduced vitality and growth of forest vegetation.
Critical Limit Exceedances
