Impacts of sediment recharges into the Upper Rhine river downstream of the Kembs diversion dam : Ecological monitoring of plants and macroinvertebrates
Résumé
Over the last two centuries, the Upper Rhine River was subjected to important hydraulic engineering works which have severely damaged its functioning. The Old Rhine is a 50-km long by-passed single bed paved channel, which is located downstream of the Kembs dam. In 2010, a restoration program was initiated to diversify aquatic and riparian habitats: minimum flow increase and artificial sediment feeding into the channel. A first experimental sedimentary recharge was conducted during the program "INTERREG IV A 2009-2012" in the Rhine by-passed section between Kembs dam and Breisach. In February 2015, ‘Electricité de France’ (EDF, the French hydroelectric power plant manager) implemented a similar artificial sediment recharge in the Old Rhine. In both sediment recharge experiments, the ecological consequences are evaluated with a monitoring program of riparian/aquatic vegetation, benthic macro-invertebrates and fish. A confounding effect with the sediment feeding is the minimum flow increase and an important flood. An analysis of the dynamics of these biological communities is underway to identify the links between physical changes and ecological functioning. The minimum flow increase induced the development of new habitats on banks. Floods induced bedload transport which makes benthic habitats less stable for invertebrates and plants. The new gravel bars tends to favor the settlement of pioneer plant species and in border, it is characterized by a lower abundance of invasive species compared with the spatio-temporal reference stations. The higher density of invertebrates species which are adapted to sedimentation areas but relatively polluo-tolerant, contributes to a gain in diversity.