Characterising Central European fluvial (palaeo-)environments & anthropogenic impacts with ostracods

Ostracods, microscopic crustaceans living in all kind of aquatic habitats, are good bioindicators. They were widely applied for lacustrine palaeoenvironments so far, but only rarely for river sediments possibly due to generally lower densities and often occurring chemical dissolution processes in fluvial environments.
However, especially in river sediments from carbonate-rich waters, their combination with mollusk data seems promising for paleoecological analyses what deserves further research. For this, recent ostracod associations in several modern German river systems were analysed: The Saale and its tributaries around Jena, streams in the Thuringian Forest, and the Echaz and Eger rivers in southern Germany. Often high ostracod numbers in the samples allowed detailed statistical analyses. These showed that water quality assessment based on recent or fossil associations, similar to the saprobic system, may be possible and can be improved when combined with mollusc data. Further, ostracods are indicative of water turbulence, phytal zones and non-permanent water cover.
The applicability of these results is demonstrated in Holocene floodplain sediments of the rivers Echaz and Eger in southern Germany, which were both strongly modified by humans since the Middle Ages. The ostracod abundances in these sediments were generally very low, possibly due to small-scale environmental variations. Combined with mollusc data and macrobotanical remains, it was however possible to reconstruct the palaeoenvironmental history of most studied sites.
The case studies highlight that knowledge of ostracod ecology, combined with taphonomical knowledge (e.g. transport, disarticulation, fragmentation abrasion, dissolution) and co-occurrences of other faunal remains, are especially important for palaeoenvironmental reconstructions of floodplain sediments.