Silts with a human touch: the shift from natural to anthropogenically controlled fluvial dynamics in the Kinzig River floodplains, southwestern Germany

Abstract. Central European fluvial systems shifted from naturally to anthropogenically controlled during the middle to late Holocene, responding uniquely to non-synchronous and interdependent natural and anthropogenic forcings. Previous research mainly focused on either large river systems or small catchments, yet meso-scale systems linking these have received little attention so far. Floodplains constitute an ideal setting to address this issue as their sediments recorded past river dynamics and human activity. This study investigates the transition from natural to anthropogenic control in the meso-scale Kinzig River in southwestern Germany using a combination of sedimentology, geochemical analysis, luminescence dating, and geophysical surveys. In the Kinzig catchment, three phases of floodplain accumulation are identified with characteristic sedimentation rates: late Pleistocene–early Holocene until 9.0 ka (0.1 mm a−1), middle–late Holocene from 9.0 until 0.82 ka (0.3 mm a−1), and the modern era from 0.82 ka until current times (1.1 mm a−1). Characterising these phases are decreasing grain sizes and increasing heavy metal concentrations (barium, lead, copper) in overbank fines, correlating with historical mining activity (peaking in the 16th and 18th centuries). This indicates the impact of mining on sediment delivery via deforestation that caused hillslope instability and sediment contamination. A cross-reference of floodplain stratigraphy with the catchment land use history reveals a gradual shift to an anthropogenically altered system, with intensified human impacts over the last 1000 years, approximately. This aligns with high floodplain sedimentation rates related to human presence. These findings depict the timing and dynamics of anthropogenic impacts on meso-scale fluvial systems in previously natural landscapes.