Post-sedimentary pedogenesis in colluvial soils in the context of the landscape sedimentary history (Czechia)

Colluvisols, representing a significant part of the erosional catena in undulating landscapes, often changed by long-term agricultural management, undergo a complex development with alternating phases of material deposition and slope stability, with subsequent initiation of soil formation processes. The presented study focuses on the detailed description of the post-depositional evolution of four up to 4m-deep colluvial profiles, formed in different colluvial positions in two environmentally and historically distinct areas of Czechia, situated in the loess region of South Moravia and Central Bohemian Upland, built on plutonic rocks. A multi-proxy approach consisting of analyses of clay mineralogy, micromorphology, humic acids 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, assessed using optically stimulated luminescence dating and 137Cs activity. Marked differences in the type and maturity of pedogenetic features were identified not only in individual plots but also in different colluvial positions within the same plot. While signs of bioturbation, mainly related to root activity and soil fauna, were observed even in recent colluvial layers after a short period of stabilization, more advanced processes of weathering, organic matter stabilisation and clay illuviation 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. 

Study was supported by grant nr. 21-11879S of the Czech Science Foundation.