Biological feedback of unprecedented hydromorphological side channel restoration along the Upper Rhine (France)

In Europe, large rivers have been greatly impacted by engineering and hydraulic works. The Upper Rhine channelization has notably led to a disconnection between the main channel and its floodplain and side channels. Between 1998 and 2006, unprecedented restoration projects led to the reconnection of nine Rhine side channels to the main channel or the Rhine Drainage Canal. The structures of recolonizing macroinvertebrate communities observed in the restored side channels, either in 2009 or 2010, were compared to the ones of three reference side channels. The aims of the study were (i) to analyze the recolonizing macroinvertebrate communities and (ii) to identify the drivers of the community structure. The restored side channels exhibited macroinvertebrate community structures similar to those of the reference side channels. These communities were characterized by a high abundance of nonnative and invasive taxa and a structure not linked to either the time since restoration or the water and sediment chemistry. Significant correlations existed between the macroinvertebrate community structures and the mosaics of habitats, driven by the variations in side channel morphometry and discharge. Therefore, the diversity of habitat characteristics of the side channels might help conserve and increase macroinvertebrate biodiversity at the floodplain scale.