Accumulation patterns of heavy metals in soil profiles as affected by forest clear-cutting

Abstract

Vertical distribution of Zn, Pb, Cu and Cd was studied in podzol soil profiles of adjacent forested and clear-cut areas in a region contaminated with Zn, Pb and Cd from long-range atmospheric transport. This was in order to investigate possible effects of deforestation on accumulation and distribution patterns of these metals in surface soil profiles. Lower Zn and Cd contents were observed in the H horizon of clear-cut area soils than in forest area soils. However, this was not sufficient to entail a significantly lower total Zn and Cd pool in the humus layer of clear-cut area soils compared to forest area soils. The total content of Pb in the L + F + H horizons was significantly lower in clear-cut than in forested areas, attributable to distinctly lower Pb contents in the H horizon of clear-cut area soils. This fact combined with significantly thinner humus layers in clear-cut areas compared to forested areas, presents evidence for increased losses of Pb from the humus layer after clear-cutting. Higher Pb contents in the Ae and B horizons of clear-cut area soils than in forest area soils, show that at least parts of the Pb lost from the H horizon in clear-cut areas were re-adsorbed or re-precipitated in the Ae and B horizon. As in the case of Pb, Cu concentrations were higher in the Ae and B horizons of clear-cut area soils compared to forest area soils. In the case of Cu, however, this cannot be explained by increased inputs from the humus layer following forest clear-cutting, but rather by increased weathering in the Ae and B horizons. The high retention of Zn, Cu and Cd in the humus layer of clear-cut areas, compared to that of Pb, is most probably due to a stronger accumulation of these metals in ectomycorrhizal biomass.