Diatoms (Figure 1) are particularly well preserved in the sediments of lakes Stadt- and Schlosssee of Bad Waldsee and were chosen as lead bioindicators for this study. These microscopic algae are found in almost all types of aquatic systems, form the basis of the food chain and are sensitive to changes in chemical water parameters such as salinity, pH, and nutrients. Moreover, physical variables such as water depth, length of ice cover and stratification or mixing of the water column have a great influence on the occurrence and abundance of the various types of diatoms. Accordingly, these organisms are already established proxies for determining both qualitatively and quantitatively eutrophication and acidification of water bodies as well as climate changes. As part of the project, the potential of other organism groups (e.g. ostracods and cladocerans) for paleo- reconstructions will be determined as well.

In addition, stratigraphic variations in the stable isotopic composition of carbonates and organic matter of sediments will be used to reconstruct temporal changes in productivity, hydrology, and surface water temperatures of the water body. Stable isotopes will be analyzed in cooperation with Dr. Birgit Plessen from the GFZ German Research Centre for Geosciences in Potsdam.

This project part aims to trace environmental developments in the catchment area of the city of Bad Waldsee and associated changes in the two lakes as well as human impact on the aquatic ecosystem from the Middle Ages to the early modern period. We expect detailed information about the response of surface waters to changing urban emissions and the resilience of aquatic ecosystems. Climatic phases such as the "Little Ice Age" (approx. 1550 to 1850) and historical developments such as settlement intensification, plague waves and the Thirty Years' War are of particular interest.