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 (Fe-o, Fe-d, Al-o, Mn-d), pH (CaCl2), C-org, and mineralogical composition of the lay and medium sand fraction were determined in six representative pedons. Chemical analysis matched morphology in that very low contents and mass densities of Fe-o, Fe-d, Al-o, and Mn-d 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 (approximate to 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. (C) 2001 Elsevier Science BN. Ail rights reserved.