Restoration of the rivers Brede, Cole and Skerne: a joint Danish and British EU-LIFE demonstration project, V—short-term impacts on the conservation value of aquatic macroinvertebrate and macrophyte assemblages

Abstract

1. This paper describes the short-term effects of river restoration on the wetland macrophyte and aquatic macroinvertebrate assemblages of two rivers, the R. Brede (Denmark) and the R. Cole (UK). The effects of the restoration work were assessed in terms of changes in species richness, rarity and abundance on (i) the restored sections and (ii) potentially impacted sections downstream of the restoration works. 2. In the restored areas of both rivers the species richness of wetland macrophyte assemblages recovered to at least pre-restoration levels 1–2 years after restoration. Macroinvertebrate species richness recovery was more variable. The abundance of macroinvertebrates and wetland macrophytes generally recovered less rapidly than species richness. For wetland macrophytes, the recovery process was enhanced by the presence of refugia. 3. Uncommon invertebrates were slower to recolonize the restored sections in the year after restoration (monitored on the R. Cole only). The number of uncommon wetland macrophyte species recorded was similar throughout the restoration and recovery period. 4. Potentially impacted sections of the river up to 1.2 km downstream of the restored area showed a relative decline in invertebrate species richness 1–2 months after the physical works were completed, but little difference from pre-restoration levels after 1 year. Plant surveys downstream of the restored area showed no evidence of a significant change in species richness, neither was there evidence that uncommon plant or invertebrate species were affected by downstream impacts (sediment or nutrient release) due to restoration. © 1998 John Wiley & Sons, Ltd.