The Lobau floodplain section of the Danube is one of the last relatively ‘natural’ sections of the Upper Danube. Although heavily impacted by regulation structures upstream and by levee systems, the section of river between Vienna and Bratislava is considered, in European terms, to be ‘free flowing’. The river is controlled along this section by lateral levees constructed in the late 19th century that limit exchange with floodplain habitats. Although some floodplain areas remain somewhat connected, progressive river incision over the last 100+ years is thought to have resulted in further reductions in connectivity since the construction of the lateral levees.
This study uses sediment records from several floodplain side arms of the river to explore the question of whether this incision has led to declining connectivity and what the ecological consequences of a detected decline might be. Sediment cores were taken from four side arm habitats in the lower Lobau. These locations were selected to cover a range in connectivity from 0 days per year up to 250-365 days per year.
Cores ranged in depth from 0.25m to 0.65m. Radiometric dating suggests that mixing and perhaps hiatuses were a problem in some cores, but that basic chronology could be established at two sites based on Pb210 activity and Cs-137 peaks (denoting the Chernobyl accident; Chernobyl ~ 1000km ENE of the study area). These chronologies suggest that the cores cover the last 60 to 150 years. Preliminary analysis of diatom stratigraphy from the two dated cores suggest increased stability, or reduced frequency of disturbance over the past 50 years. Future studies will examine stratigraphic changes in preserved plant and animal remains to provide a more complete picture of the ecological changes. Further chronostratigraphic analyses will also be carried out to refine the chronology of change.