Holocene river activity: analysing 14C-dated fluvial and colluvial sediments from Germany

Records of fluvial dynamics in response to long-term changes of climate and land use impacts are rare. Therefore cumulative probability functions (CPFs) of 401 14C ages originating from German rivers and hillslopes were compiled to reconstruct phases of increased geomorphic activity and stability during the Holocene. An improved analytical method is suggested to normalise CPFs and eliminated the effects of wiggles of the calibration curve and the young age bias. Nine periods of activity are identified (peaking at 7050, 6250, 5525, 3690, 2250, 1350, 820, 325 BC and since 875 AD) and are compared with climatic, palaeohydrological and human impact proxy data. Until 2250 BC, events of geomorphic activity are mainly coupled to wetter and/or cooler climatic phases. Due to growing population and intensive agricultural activities during the Bronze Age the increased geomorphologic activity between 1300 and 820 BC cannot unequivocally be related to climate. Since 875 AD the growing population density is considered as the major external forcing. Differential geomorphic activity of hillslopes and floodplains suggest that the hillslope-channel coupling during the Holocene is mainly controlled by human impact with a strong increased coupling after 1500 BC.