The distribution of sequentially extracted Cu, Pb, and Zn fractions in Podzol profiles under dwarf pine of different stages of degradation in subalpine zone of Karkonosze Mts (central Europe)

Purpose Here, we aimed to assess the contamination of Podzol soils in a subalpine zone of the Karkonosze Mountains. Cu, Pb, and Zn concentrations in the soil and the patterns of their speciation are discussed in relation to the possible influence of airborne industrial emissions and the stage of degradation of dwarf mountain pine stands. Materials and methods The study was conducted in the Karkonosze, a mountain range in the Sudetes, on the boundary between Poland and the Czech Republic. We examined Podzols derived from granites under dwarf mountain pine stands at two stages of degradation (without visible degradation vs. dead). These two sites were 100 m apart, at an altitude of 1400 m above sea level (upper mountain forest zone). Soil samples were collected from all distinguished soil horizons and their basic soil properties and heavy metal (Cu, Pb, and Zn) concentrations (and their speciation) determined by sequential extraction according to the method of Zeien and Brümmer. Results and discussion The Cu concentrations in these soils were relatively low, typical for soils derived from granite and did not differ considerably within soil profiles. The residual Cu fraction was a predominant one in all mineral horizons. The Pb concentrations in the surface organic horizons were clearly higher than those in similar horizons of European lowland forest soils. This distribution of Pb in the mineral horizons was apparently associated with soil colloid distribution that developed in the process of podzolization, indicating the minimum concentrations in eluvial E horizons and enhanced concentrations in illuvial Bh horizons. The organically bound fraction made up about 40% of total Pb in the Bh horizons. Zn concentrations were highest in the deepest parts of the soil, where the predominant fraction was residual, while relatively high amounts of easily mobilizable Zn were present in ectohumus. Conclusions Very high concentrations of Pb in ectohumus have most likely been caused by a long-distance transport of anthropogenic emissions. The concentrations of Pb or other metals found in soils cannot be considered to have been the principal causes of the ecological disaster observed in the Karkonosze Mountains. The highest concentrations of Pb in ectohumus, as well as its high contributions in the organically bound fraction, confirm a crucial role of organic matter in Pb accumulation in soils.