Lateral podzolization in a sandstone catchment

A sandstone catchment of the cool, perhumid Black Forest, Germany, was studied with respect to podzolization processes on a landscape scale. Soil mapping along a steep slope (25%) revealed Spodosols with thick E-horizons combined with thin spodic horizons in the upper catchment area. Lowermost parts of the landscape showed thinnest E- and thickest Bhs-horizons. This catenary trend was quantified by a non-linear increase of the “illuviation–eluviation ratio of podzolization” (IERpodzol). Soil texture, pedogenic oxides (Feo, Fed, Alo, Mnd), pH (CaCl2), Corg, and mineralogical composition of the clay and medium sand fraction were determined in six representative pedons. Chemical analysis matched morphology in that very low contents and mass densities of Feo, Fed, Alo, and Mnd were found in upslope soils. The distal pedons were 2–5-fold higher in these elements. The catenary trends corresponded to a downslope increase in pH as well as organic carbon in mineral soils. Mineralogical analysis showed a decrease in feldspar weathering and an increase in hydroxy-interlayered vermiculites towards the downslope soils. The morphological, chemical, and mineralogical results led to the conclusion of a process sequence of (i) an upslope mobilization and depletion of iron, manganese and aluminum (“E-Spodosols”), (ii) a lateral translocation (≈30% of catchment discharge occurred as interflow), and (iii) a downslope immobilization resulting in a (relative or absolute) accumulation of the translocated soil compounds (“Bs-Spodosols”). The immobilization probably was controlled by an admixture of Fe- and base-richer rocks into the parent material downslope. The concept of lateral podzolization developed in a granite landscape was confirmed in the sandstone area studied.