The potential of the spreading effect concept for the implementation of the European Water Framework Directive

Currently only few European surface waters meet the target of a good ecological status required by the Water Framework Directive of the European Union. The spreading effect concept could be of particular Importance, since it potentially improves the ecological status and connectivity of rivers without expensive structural measures. The spreading effect describes processes where organisms migrate from structurally intact and ecologically important, near-natural reaches (spreading source) into adjacent reaches that are hydro-morphologically degraded (spreading corridors). It is assumed that the spreading effect decreases with increasing distance from the spreading source, thus other reaches with good structural conditions are necessary within a certain distance to the source, to maintain this effect. By studying communities of benthic in-vertebrates in spreading sources and spreading corridors in highland rivers, and using a high-resolution sampling approach, the most important parameters for maintaining the spreading effect could be identified. These included the occurrence of a typical species pool in the catchment area and bed substrates in the canalized waterbody sections that can be colonized by the invertebrates. To significant extent, this can be obtained by relatively low-cost management activities, like actively integrating small-scale deadwood and/or substrate structures ("stepping stones") or not (completely) removing developed macrophytes or sediments brought in from the SDreadina source. © 2018 Friedr. Vieweg und Sohn Verlags GmbH. All rights reserved.