Biodiversity of macroinvertebrate communities as describer of hydraulic variabiliy: the example of two by-passed sections of the Middle Rhône River
The aquatic communities of a hydrosystem are constantly subject to the space-time variability of the environment. As a result, the dominant species are those presenting the biological characteristics and the ecological preferences best adapted with the various types of habitats of the river mosaic. A multiparametric description of physical structure from macroinvertebrate communities, taking into account both indicators of structure and functioning of these communities, was tested on the Middle Rhône River (France). The study of four physically dissimilar stations located in two by-passed sections showed that the arrangement due to the current velocity (functional units) corresponded to trophic and ecological differences, whereas the arrangement due to physical conditions (reach of river) corresponded to taxonomic differences. The availability in habitats for the invertebrates was correlated with the configuration of the channel of the section considered. The patches of species answered thus, through their occurrence and their abundance, to a physical gradient. This approach, predictive and applied, with parallel between the biological report and the physical structure of the stations and the environments, makes it possible to establish a functional typology of the aquatic ecosystems considered and to propose an integrated management adapted to the problems arising (management of the habitats and of their biodiversity, hydraulic and ecological restoration of the environments, etc).