Assessing Biological Orders of river sites and biological structures of watercourses using ecological traits of aquatic insects

International audienceA new method is proposed to assess Biological Orders (BO) of river sites and to compare biological structures of watercourses using two general ecological traits (typological preferendum and typological amplitude) of 187 species of aquatic insects (Plecoptera, Trichoptera, Ephemeroptera) specified in a previous database (Verneaux et al., 2003). A community is defined as an arrangement of species which have various abundances, typological preferenda (tp) and typological amplitudes (ta). In the field, any species assemblage was considered possible, and a river site community was analyzed using two descriptors: its relative species richness and its Biological Order, calculated using the abundance and the ecological traits ( tp, ta) of the recorded species. The BO of a river site, with a range from 0 to 10, constitutes a mean community point which plots the site on a theoretical upstream-downstream gradient defined by a species continuum ( Verneaux et al., 2003). The grounds and the BO assessment are presented, followed by the method applied to a site of the upper course of the Loue River ( French Jura). Community changes which occurred between 1975 and 2000 are specified. The Loue pattern was then plotted with other watercourses in a typological graph where biological structures of rivers are compared using a biological templet. This method, showing differences to the templet, allows to estimate biological changes referable to different levels of disturbance. Biological Orders and the significance of the biological templet are then discussed. The proposed typological analysis, giving both the Biological Order of a river site and its distance from the biological templet, constitutes a useful tool for running waters diagnosis and biological integrity assessment