Trends in soil water composition at a heavily polluted site - effects of decreased S-deposition and variations in precipitation

Precipitation, soils and soil water in a forested catchment in western Poland have been studied during the period 1992 - 96 (see also Vogt et al., this conf.). The S-deposition in the area during the study period was 2 - 3g S m-2 yr-1. In spite of decreasing anthropogenic emissions the S-deposition in the area did not change much during the study period mainly because the first years were exceptionally dry. However, the S-deposition was considerably higher during the previous decade. Based on soil water sulphate concentration, pH, acid neutralising capacity and the ratio of Al3+/(Ca2+ + Mg2+), there is apparently an amelioration in the conditions. A study using inter alia principal component analysis, indicates that this improvement is mainly due to more precipitation in the later part of the study period. Variations in precipitation amount have a pronounced effect on the soil-water chemistry, which makes it difficult to establish trends caused by changes in anthropogenic deposition. Long time series are therefore necessary to establish recovery due to reduced S-emissions.