Restoration of Skjern River and its valley—Short-term effects on river habitats, macrophytes and macroinvertebrates

The lower 19 km of the Skjern River was restored and transformed into a 26 km long meandering river. Three survey reaches and one control reach upstream of the restoration area were surveyed to assess the short-term effects of the restoration on river habitats, macrophytes and macroinvertebrates. The reaches were surveyed before the restoration in 2000 and again after the restoration in 2003. Morphological adjustments were evident in the re-meandered river and the habitat structure (depth, current velocity and substratum) became more diverse. The macrophyte coverage was 34% before the restoration. Restoration included removal of dense near bank vegetation stands of Glyceria maxima, and in 2003 re-colonization of the restored reaches had resulted in 24% macrophyte coverage. Species composition and growth patterns changed significantly in the edge habitat and the dominant macrophyte G. maxima was replaced by Elodea canadensis and Sparganium sp. Macroinvertebrates rapidly colonized the restored reaches and increased the community diversity. Only one taxon, Heptageniidae, significantly increased in abundance after the restoration and a more even distribution of taxa developed on the restored reaches. Biological communities will continue to develop over the coming years as the river becomes more physically stable. Hence the macroinvertebrate and macrophyte communities will adjust and colonization from upstream sources and other systems will probably increase biodiversity.