The impact of dredging of a small lowland river on water beetle fauna (Coleoptera)

Using the example of a regulated stretch of the Krąpiel River (NW Poland), an analysis of the impact of dredging on the aquatic beetle (Coleoptera) fauna was made. After dredging the beetle fauna became markedly poorer quantitatively and had lower species diversity. Moreover, the qualitative composition and dominance structure were highly transformed. However, species number and diversity increased rapidly and were restored within just half a year. The structure of the restored fauna was most strongly influenced by vegetation, flow velocity and bottom sediment composition. The first to colonize the river were eurytopic beetles and species typical of small water bodies, which had significant refuges in the form of fish ponds bordering on the river; these species dominated the assemblage throughout the study period. Rheophiles with less dispersal power appeared later, and finally rheobionts, in low numbers but occupying an increasing number of sampling sites.