Benthic invertebrate recolonization after stream restoration is a complex process. Repeatedly low habitat diversity and missing source populations are mentioned as factors hindering or delaying recolonization processes. Particularly in urban streams colonization sources are a big problem and additionally multiple stressors often impede ecological recovery.
The Boye system in Germany is a 78 km2 catchment area which flows through the Ruhr Metropolitan Area, a region which is inhabited by more than 5 million people. Most of the system was used as open sewers in the 20th century. In the beginning of the 21st century the wastewater was redirected to underground sewers and the streams morphologically restored.
Since 2012, benthic invertebrate samples were taken annually at 12 sites to monitor the recolonization. The data show clear changes in the communities and in the ecological quality. In the beginning good dispersing generalist taxa colonized the sites but with the years sensitive species became more abundant proving that recolonization sources are present and that recolonization takes time but has chances even in highly disturbed urban catchments. This talk will show details of community developments and improvements in ecological quality over more than a decade and highlight its drivers and pressures.