Geochemistry of Loess Derived Soils in Two Southern Illinois Landscapes.

Distribution of elements across the landscape is governed by parent material composition and soil forming processes.  This study investigated the redistribution of trace and major elements within pedons across two similar landscapes with the objective of documenting dominant pedogenic drivers in loess-derived soils of southern Illinois.  Seventeen pedons (representing different hillslope profile positions) in two landscapes (cultivated Morgan Pond (MP) and forested Bean Ridge (BR)) were sampled by horizon.  The Ap horizons of MP had significantly greater concentration of As, Cr, Cu, and V compared to A horizons of BR, while BR had significantly greater Ba, Cd and Hg.  Elements significantly greater in subsoils versus topsoils at both locations included Al, Fe, K, Mg, As, Co, Cr, Cu, Ni, P, V, Zn.  Principal component analysis showed these elements were most closely associated with clay and citrate dithionite extractable Fe, suggesting that this elemental increase was related to mineral weathering and clay translocation or neoformation in subsoils.  Greater Ca in A horizons at both sites may be tied to biocycling, but correlation of Ca to pH (r=0.55) suggested that this trend may be due to past lime applications.  Erosion was also a major soil forming factor in these landscapes based on depth functions of trace elements (e.g., Zn) in different hillslope positions.  The backslope positions appear to have eroded sufficiently in the past to have A horizons that were developed in former subsoil materials.