Small scale distribution of Al, heavy metals, and PAHs in an aggregated Alpine Podzol

Abstract

Aggregates of the EA horizon, the Bhs and the Bs horizons of an Alpine Podzol were separated into core and surface fractions. In the air-dried aggregate fractions CEC, C org, 7 fractions of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn using a sequential extraction procedure, and PAHs were determined. Cation exchange capacity, C org and PAHs were determined in homogenized bulk soil samples, too. Both cation exchange capacity and C org were higher in the aggregate surface than in the core fractions. Total concentrations of Al, Mn, Fe, Cr, Ni, and Zn were lower in the aggregate surface fraction of the EA horizon and generally higher in the B horizons. Total Cu, Cd, and Pb, however, were enriched in the aggregate surface compared to the core fractions, at least in the upper two horizons. All metals were more available in the aggregate surface than in the core fractions. The total concentration of PAHs was higher in the aggregate surface than in the core fractions. The enrichment in the aggregate surface fraction was highest for the more soluble compounds with low molecular weight and decreased with depth. These results suggest that the small scale heterogeneity of metals and PAHs is the result of both atmospheric input with preferential sorption at aggregate surfaces, and soil internal redistribution due to eluvial and illuvial processes. Implications may arise for interpreting plant availability of heavy metals and PAHs as well as for modeling transport in aggregated soils.