Molluscs and Ostracods as Bioindicators in Holocene Floodplain Sediments of the Rivers Echaz and Eger (Southern Germany)

The floodplains of the rivers Echaz (3^rd order tributary of the Rhine) and Eger (3^rd order tributary of the Danube) in southern Germany were both heavily anthropogenically modified from the Middle Ages to early Modern times. Water pollution from the larger cities and the usage of water meadows are two important examples of human activities that are visible in the sediment, which ostracods and molluscs can provide more information about.

Actualistic studies of ostracods in central European rivers have confirmed that they are good indicators for documenting water turbulence and phytal zones as well as non-permanent water covers. With fossil assemblages thereby also the spatial extent of water bodies can be assessed. Water pollution by organic substances or heavy metals may be indicated and assessed by oxygen or heavy metal sensitive species. The frequency of aquatic and terrestrial gastropods, bivalves, and macrobotanical remains provide further information about the floodplain development, the palaeoenvironment, and the past land use.

In both colluvial and overbank deposits, taphonomic effects play an important role in the distribution of micro- and macrofossils. Transport can be detected by, e.g. disarticulation, fragmentation or abrasion of ostracod carapaces and mollusc shells. Although the springs of both Echaz and Eger derive from the Swabian Jura and are characterized by calcareous water, the overbank sediments often show dissolution, especially the thinner ostracod valves. Local changes in dissolution patterns can, however, also be used to indicate groundwater levels or the spatial location or proximity of a water body.