From Floodplains to Fallout: Anthropocene stratigraphic signals in Danube floodplain archives downstream Vienna

Human impact has become an external forcing control on Earth’s environmental and geological processes, reshaping entire landscapes and leaving traces in geological archives. Even though this anthropogenic influence can be seen on a global scale, regional studies characterizing the scope and growth of anthropogenic influence is scarce, especially for urban or peri-urban environments.

In this study, we investigate the anthropogenic impact of the metropolis Vienna on its peri-urban environment, and correlate and evaluate the main geological signals for a potential Holocene-Anthropocene transformation in the 1950s during the so-called “Great Acceleration” of Earth System Sciences by applying sedimentological and geochemical methods.  The study area is located downstream of Vienna, in the National Park Donau-Auen, where direct human intervention into the archived Danube river sediments is currently nil and floodplain archives allow to trace and quantify the human stratigraphic fingerprint and test dating techniques using (artificial) radionuclides in an alluvial setting. Sedimentological, geochronological, and chemostratigraphic markers are applied to characterize date anthropogenic strata in the proximal floodplain sediments, i.e. erosional profiles, of the Danube. The age of flood deposits was evaluated by field sedimentological method and cross-validated by the radiogenic nuclides ¹³⁷Cs and ^239/240Pu, which give evidence of the atmospheric ‘bomb spike’ from nuclear weapon testing. First observations indicate three periods of distinct sedimentation patterns reflecting the river system’s response to human interventions in the upstream area. The first phase marks the first extensive river channelization between 1870 and 1900 resulting in rapid erosion of mid-channel bars and aggradation of dammed backwater areas. The second phase is characterized by laterally extensive and thick flood deposits indicating the fast and undamped sediment transport through the straightened river bed during extreme events. The last phase is marked by the onset of very thick, uniform, and seemingly structureless flood deposits. These silt-sized beds are interpreted remobilized sediment that has accumulated in barrier lakes since the construction of hydro-power stations between 1956 -1998.

The archive of natural Danube deposits is analysed for artificial radiogenic isotopes, trace metals, and (micro-)plastics with the aim (i) characterise the interplay between upstream human interventions and local river dynamics, (ii) to identify and evaluate the geological signal of the Great Acceleration of Earth System Sciences since the 1950s, and (iii) to evaluate global markers for a potential Holocene-Anthropocene transformation downstream of Vienna.