Tracing anthropogenic fingerprints: Sedimentological and geochemical insights into Vienna's floodplain archives

The Danube River floodplain downstream of Vienna (Austria), contains anthropogenic signals, which are exposed in erosional cuts. Sedimentological, geochronological, and chemo-stratigraphic techniques were applied to reconstruct past floods and understand anthropogenic signals at regional to supra-regional scales. Key facies associations were identified, aiding depositional analysis and palaeoenvironmental reconstruction. Deposition began with channel infilling (FA1) behind a mid-channel island. By 1916, the island has docked onto the riverbank, leading to lateral point bar deposition (FA2), throughout which floods occur with increasing intensity (FA3 and FA4). Using field sedimentological techniques and 137 Cs, seven major flood events from 1954 to 2013 were identified, overall exhibiting a coarsening-upward sequence, which contrasts typical “natural” overbank fining sequences and reflects changes potentially linked to upstream hydro-power infrastructure. Geochemical signals indicate: i) singular events resulting from local human agency e.g., Sn contamination peak in 1991 due to local pollution; ii) shifts in provenance signals indicating catchment-scale changes of sediment transport and connectivity, e.g., decrease in CaO as upstream hydro-power stations act as sediment sinks; and iii) supra-national signatures connected to atmospheric emission trends, e.g., Zn, Cd, Pb increase since the Great Acceleration and decline during the phase-out of leaded fuels. This multi-proxy archive provides a baseline for future cross-site correlation, and for understanding the impacts of river management and restoration measures. • Event-based dating of modern floodplain deposits by using field sedimentology, radiogenic nuclides, and historical records. • Coarsening- and thickening-upward trend in recent flood deposits potentially linked to remobilisation from hydropower dams. • Both local and global trends in environmental pollution over more than 100 years can be pinpointed. • Element composition and sedimentary structures reflect the impact of human activities on sediment composition and balance.