Lateral podzolization in a granite landscape

Analysis of soil pattern, especially the pattern of depletion and accumulation zones, is a powerful tool to decipher pedogenic processes at the landscape scale. To clarify the pedogenesis of a distinct pattern of podzolized soils in the cool, perhumid Black Forest (Germany) we performed a study in the forested upper part of a granitic catchment (Barhalde). From detailed soil mapping we selected a typical catena of four pedons, which were analyzed for physical (bulk densities and particle-size distribution), chemical (pH, organic C, pyrophosphate, oxalate, dithionite, and total Al, Mn, Fe), and mineralogical (clay minerals) properties. Standard mass balance calculations were modified to include a two-component system with regard to parent material. Results showed a shift from two-mica granite to granite-porphyry downslope. Soil pattern revealed podzolized soils with thick E horizons and thin spodic horizons developed in the upslope areas, whereas in downslope soils the reverse was found (thick spodic B and thin E horizons). Soil chemical and mineralogical properties were linked to soil morphology in that contents of organic C, pedogenic oxides, hydroxy-interlayered vermiculites (HIV), and pH increased from eluvial to illuvial horizons as well as from up- to downslope soils. Mass balances of Fe and Al showed negative fluxes in upslope soils and positive fluxes in downslope soils during pedogenesis. We concluded from these results that a catenary eluvial-illuvial sequence (lateral podzolization) develops as a result of upslope mobilization followed by a (partially) lateral transport and subsequent immobilization in downslope zones, probably because the base-richer parent material built up a geochemical barrier.