Formation of Colluvisols in different soil regions and slope positions (Czechia): Post-sedimentary pedogenesis in colluvial material

Colluvisols, representing an important soil unit in erosion-affected landscapes, undergo a complex development with alternating phases of material deposition and slope stability, with subsequent initiation of pedogenetic processes. The present study focuses on the detailed description of the post-depositional evolution of four up to 4 m-deep colluvial profiles, formed in different colluvial positions in two environmentally and historically distinct areas of Czechia. A multi-proxy approach consisting of analyses of clay mineralogy, micromorphology, humus quality and geochemical parameters was applied to distinguish the inherited and in-situ developed pedogenetic features and link them with the sedimentary history of the studied soils. Marked differences in the type and maturity of pedogenetic features were identified not only in individual plots but also in different colluvial po-sitions within the same plot. While signs of bioturbation, mainly related to root activity and soil fauna, were observed even in very young colluvial layers after a short period of stabilization, more advanced processes of weathering, clay illuviation and organic matter stabilisation are typical only for early-sedimented layers with long post-depositional development. Redoximorphic features were more pronounced in the side valleys compared to the toe-slope colluvial positions; similarly marked differences between colluvial positions were observed for humus quality, with significantly more stable organic matter concentrated within side valleys. In both sites, distinct and largely contradictory trends in the transformation of clay minerals, reflected in the proportions of different phyllosilicate layers, were observed, corresponding to the specific conditions of soil development.