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Influence of flow disturbances on a macrobenthic community in a lowland river

The main aim of study was to describe the response of a benthic community to medium and high flow disturbance in the lowland Drzewiczka River. The investigated site of the 4th order river was located downstream of a dam reservoir and of a wild–water slalom canoeing track. This site may be described as a mosaic of bed patches with different stabilities and contributions to the patchy distribution of benthos; five habitats dominated at this site. In order to test which of them show the highest stability during high discharges “semi-experiments” were conducted. After two-three weeks of natural discharge we released through the dam amounts of water that exceeded three times (in September), four times (in March) and sixteen times (in February) that produces the natural water level; this last event took place during the complete emptying of the reservoir, before its dredging. In each habitat morphometric, hydraulic and biotic parameters were measured before and immediately after water releases. Chironomidae, in terms of density, dominated at each habitat, reaching the highest abundance at the riffle habitat; other groups that played a key role in lotic assemblages included Oligochaeta, and other insects: Trichoptera and Ephemeroptera. Three to five-fold increase in discharge did not caused no substantial changes in macrobenthic density, but the sixteen-fold increase in discharge had a great influence on sediment and the river biota. However, even a spate did not cause the depletion of the entire riverbed – community stability was highest at the submersed macrophyte habitat, dominated by macrobenthic taxa with different modes of life (epiphytic and pelophilous fauna). Thus the macrophyte habitat in the Drzewiczka River was only partly damaged by disturbance and thus may be classified as a refugium, from which organisms may potentially colonize the depleted sections.

Influence of flow disturbances on a macrobenthic community in A lowland river Influence of flow disturbances on a macrobenthic community in a lowland river

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