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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. [ABSTRACT FROM AUTHOR]

The hydraulic management of large rivers led to a disconnection of side-channels. Restoration works were to reconnect these side-channels to the main course in order to recover hydrological and ecological functions. The aim of the study was to analyze the vegetation dynamics after restoration and to link it to the change in chemical and hydro-geomorphological characteristics. Changes in species richness, cover and composition of the macrophytes communities were studied in nine side-channels of the Rhine river (France) after reconnection which occurred between 1998 and 2006. Vegetation dynamics was surveyed between 2007 and 2011 and compared to the ones of three target side-channels (never disconnected). Three vegetation communities were identified: one characterized by rheophilic species, a second one by mesotrophic species, and a third one by eutrophic species. Distribution of communities depended mainly on the flow velocity and the sediment texture of the side-channels. The floristic composition of communities evolved rapidly and remained stable a few years after restoration. Changes in species richness and cover remained relatively low in all side-channels over the study period. Time after restoration did not affect the dynamics of colonization. Reconnection allowed the restored side-channels to exhibit vegetation dynamics similar to those of the target side-channels. [ABSTRACT FROM AUTHOR]

Large wood is a key component of river channels that affects numerous hydrological, physical and geomorphological processes. It promotes a diversity of benthic habitats in-channel and has shown to support more abundant and diverse benthic macroinvertebrate assemblages in previous ecological studies. However, the effects of large wood on the structural and functional diversities of hyporheic invertebrates are less well studied, and simultaneous examination of these diversity metrics on hyporheic and benthic compartments of the stream bed has not been conducted previously. Therefore, this study investigates the taxonomic and functional diversities of hyporheic and benthic invertebrate assemblages around natural accumulations of large wood in a British lowland river. Taxonomic and functional diversities were partitioned (into alpha, beta, and gamma diversities) and examined in reaches with and without large wood (control). We found that functional diversity is often decoupled from taxonomic diversity, demonstrating a functional redundancy of the macroinvertebrate assemblage for both hyporheic and benthic zones. Moreover, the highest functional variability at alpha-scale was observed in large wood habitats, which suggests that taxonomic diversity is enhanced by the small-scale environmental heterogeneity around large wood. To this end, this study contributes empirical evidence of functional and structural responses of invertebrates to large wood accumulation. Such information could be used to better understand the ecological implications of restoration works in lowland rivers and guide more effective management strategies. [ABSTRACT FROM AUTHOR]