Effects of Oxbow Reconnection Based on the Distribution and Structure of Benthic Macroinvertebrates

This study focuses on the assessment of relationships between flow and macrozoobenthos structure that was performed in a reconnected oxbow lake located in the S?upia River floodplain (northern Poland). The lake was created during river straightening at the beginning of 20th century by cutting off the right‐bank meander. The oxbow restoration was performed to enhance the ecological viability of this water body and restore riverine wetland. In July 2000 the oxbow was connected with the river channel through PVC pipes which enabled free water movement. Macrozoobenthos sampling, as well as chemical analyses of water and hydrological measurements, took place both before and after the oxbow reconnection. Before the oxbow reconnection, the dominant species was Asellus aquaticus, whereas after the reconnection the structure of benthic species changed significantly. During the first year it was replaced by bivalves and Chironomidae larvae and then A. aquaticus. After the reconnection, macrozoobenthos mean density was 5‐fold higher and the mean wet biomass was 77‐fold higher than before the reconnection. The number of taxa increased from 4 before the oxbow reconnection to 17 during the first year after the performed works and 20 in the next year. We stated that the revitalization process of the reconnected oxbow lake has long‐term consequences for the benthic communities. The most significant feature of the oxbow reconnection is the qualitative and quantitative recolonization by riverine macrozoobenthos species. The performed restoration significantly improved ecological status of the oxbow lake by the increase in biodiversity and water quality.