Large-scale relationships between basin and riparian land cover and the ecological status of European rivers

P>1. The main objectives of our study were (i) to establish the relative impact of pressures that degrade ecological status, especially those caused by agriculture and urbanisation, (ii) to identify regional patterns in these pressure-impact relationships and (iii) to evaluate the relative weight of the pressures acting at the basin and riparian corridor scales, and the possible buffering effect of riparian areas. 2. We developed large-scale models linking invertebrate indices of ecological quality to river basin and riparian land cover in France, Slovakia, Estonia and U.K. Invertebrate indices, transformed to ecological quality ratios (EQR), were taken from national monitoring networks. We based the models on partial least squares (PLS) regressions at national and a hydro-ecoregion (HER) scales. The HERs provided a framework for grouping data in terms of natural river features and human activities. 3. The different national methods provided consistent results that indicated the hierarchy of pressures impacting river invertebrates at the European scale. Artificial land cover (e.g. urban and industrial sites) in the river basin represented the pressure with the most negative impact on invertebrate indices, in all countries and regions. 4. The impact of agricultural land cover was more variable. Arable land had a smaller impact than urban areas and was insignificant in some models. The proportion of arable land in the river basin appeared to be a weak predictor of agricultural impacts by itself; the type of cultivation and intensity as well as the proximity to the river must be taken into account. 5. At the riparian corridor scale, the negative impact of artificial areas or arable land and the positive effects of forests and pastures were demonstrated in many regions. The protective effect of riparian forests against mixed agricultural and urban pressures was demonstrated in three regions in France. Riparian corridors appear to be manageable areas, and these results strongly support the idea of including their restoration in priority actions for achieving good ecological status.