Wetlands created by the divagation of rivers are characterized by contrasting environmental characteristics, in terms of stress induced by nutrient supplies, disturbances linked to river overflows, and hydrology, related to groundwater origin, discharge and quality. Consequently, such wetlands have very contrasting functioning at a small spatial scale, depending on the magnitude of these different environmental pressures. The questions adressed are : how flood disturbances (either erosion or deposition processes) rule 1) the nutrient content of cut-off channels, 2) the hydrology of such channels –in terms of water origin and discharge-, and how aquatic plants inform about these processes.
Results/Conclusions
Biotic communities and among them, aquatic macrophytes, are strongly influenced by these environmental pressures. Aquatic macrophytes are a particularly good model for assessing the functioning of such abandoned channels. Indeed, most aquatic species are rooted, and directly submitted to disturbances without any possibility to escape. Furthermore, they are strongly organized by the nutrient content of the water, itself determined by the water inputs to the channel (surface water, seepage or groundwater). A method of diagnosis of the functioning of abandoned channels based on aquatic plant communities (species richness, composition and simple plant traits) has been built, illustrated for some European rivers and for the Sacramento river. This method allows to determine the successsion pattern in the channels, and thus the need for managements and/or restoration of such channels, and the outcomes of these restoration projects.
