Original paper

The sedimentfauna in the uppermost parts of the impoundment "Altenwörth" (Danube, stream km 2005 and 2007)

Bretschko, Gernot


Sediment fauna and sediments were studied at two bank sites and two transects at the upstream end of the impoundment "Altenwörth" (km 2005 and 2007). In this part of the impoundment, water velocities are still high, only water level changes are decreased. An artificial gravel bar (km 2005) was dumped in midstream at km 2005 about one year before sampling started. Typical successional processes last over a period of about two years. To a certain degree, the observed succession was comparable with successions initiated by dynamic processes in a natural river. A large gravel bar near the left bank at km 2007 forms a deep bay. In the bay, gravel sediments change gradually towards mud, from downstream to upstream. A similar sediment development was observed in the impoundment proper, from upstream to downstream. Because of hydrological differences, the faunal biocoenoses of the muddy bay areas are not comparable with those of the muddy areas in the impoundment. They are more similar to the gravel biocoenoses but greatly depauperate. According to the literature, mid-channel gravel areas are supposed to contain only very small faunal biocoenoses, because of the fast flowing water and bedload movements. On the basis of appropriate sampling techniques, midstream faunal densities were of the same order of magnitude as in areas near the bank. The same is reported from the river Rhein.


sedimentfaunaAltenwörthbiocoenoseflowing water