CS34 River Dynamics
Date: Wednesday, June 12, 2002
Time: 3:00:00 PM
Location: View Royal
 
WilczekS, Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, wilczek@igb-berlin.de
Fischer, H, , Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, fischer@igb-berlin.de
Brunke, M, , Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, brunke@igb-berlin.de
Pusch, M, , Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, pusch@igb-berlin.de
 
MICROBIAL DECOMPOSITION OF ORGANIC MATTER IN A SUBAQEOUS DUNE OF THE RIVER ELBE, GERMANY
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It is hypothesized that sediment structures on the river bottom play an important role in the retention and decomposition of particulate organic matter in rivers. Therefore we investigated the composition of organic matter settling on and flushed into a subaqueous dune in the River Elbe. Concomitantly, the heterotrophic microbial metabolism in the dune was assessed. We measured total community respiration as well as the activities of a set of extracellular enzymes (b-glucosidase, leucine aminopeptidase, b-xylosidase, and exocellulase). Particulate organic matter was characterized by its content of chlorophyll a, carbon, nitrogen, protein and polysaccharides. Furthermore sedimentological and hydrological variables were determined. Microbial activity correlated with all measured variables of organic matter and with the vertical hydraulic gradient. Infiltrating river water at the stoss (upstream) side of the dune transported mobile fine particles, organic matter and nutrients into the sediments. This continuous substrate supply probably caused high extracellular enzymatic activities and high rates of hyporheic community respiration. The results suggest that both the stoss and the lee sides of bedforms like subaqueous dunes are focal sites for microbial metabolism in a large river.