Which limit of "good ecological status" for benthic invertebrates in rivers? Contribution of spatial extrapolation models linking the IBGN index to land cover

Abstract

For the implementation of the European Water Framework Directive, there is a need of pressures/impacts models allowing to set the priority actions for the restoration. We developed "large scale" pressures/impacts models, linking aquatic invertebrate index (IBGN) to watershed land cover. We used decision trees method to generate classifi cations allowing spatial extrapolation. Validated spatial extrapolation models were used to represent on a national scale the probable current ecological status of rivers
based on IBGN. Urban land cover appeared as the fi rst negative impact factor followed by agriculture (arable land); natural areas appeared as a positive factor on ecological status. We used this model to test two hypothesis for the "good status" boundary, and to simulate the results at the national scale. Many areas under high agricultural pressure (lowlands and Mediterranean region) are in borderline situation according to the "good status" hypothesis,