Degradation and recovery: comparing the response of freshwater inhabiting organism groups to stressors and restoration measures.

Abstract:

About 200 European rivers were sampled for environmental variables, benthic diatoms, macrophytes, invertebrates and fish as part of the European STAR project. Using multivariate methods complex environmental gradients were identified in the dataset to which biological metrics were correlated. While all four organism groups respond strongly to a combined pollution/eutrophication gradient, the response to land use and hydromorphological gradients is more complex and differs greatly between organism groups. Hydromorphological degradation is nowadays the most widespread stressor type affecting central European rivers. To obtain legally binding quality goals (such as the "good ecological status" demanded for by the European Water Framework Directive") river hydromorphology is frequently being restored. However, surprisingly little is known about the effects of such measures on the biota and thus on the ecological status. Based on a conceptual model on the linkages between restoration measures, hydromorphology and the biota we have investigated the effects of seven restoration measures targeting medium-sized mountain rivers on floodplain vegetation, riparian arthropods and benthic invertebrates. While there are strong effects on the first two organism groups, there has been no effect on the latter. Reasons for the differences between organism groups and suggestions for alternative restoration strategies are discussed.

D. Hering (http://www.uni-duisburg-essen.de/hydrobiologie/hering/) has been strongly involved in the following European River projects:

• AQEM: The Development and Testing of an Integrated Assessment System for the Ecological Quality of Streams and Rivers throughout Europe using Benthic Macroinvertebrates.
  
  
• Euro-limpacs: Integrated project to evaluate impacts of global change on European freshwater ecosystems.
  
  
• STAR