Inhaltszusammenfassung

River ecosystems are threatened by multiple stressors, including habitat degradation, pollution and invasive species. However, freshwater ecologists have largely disregarded the contribution of toxicants to stress in rivers, whereas ecotoxicologists have primarily examined toxicant effects in artificial systems. As a result, there is a paucity of information on the co-occurrence of organic toxicants with other stressors and on the relative importance of toxicants for overall ecological risk i...River ecosystems are threatened by multiple stressors, including habitat degradation, pollution and invasive species. However, freshwater ecologists have largely disregarded the contribution of toxicants to stress in rivers, whereas ecotoxicologists have primarily examined toxicant effects in artificial systems. As a result, there is a paucity of information on the co-occurrence of organic toxicants with other stressors and on the relative importance of toxicants for overall ecological risk in rivers. We used monitoring data for German rivers to analyse the individual and joint occurrence of four stressors: habitat degradation, invasive species, nutrient pollution and organic toxicants. All stressors were examined for ecological risks in terms of whether they exceeded low- and high-risk thresholds derived from published studies and regulatory thresholds. Nutrients and habitat degradation exceeded low and high risk thresholds at c. 85% of the sites and invasive species and organic toxicants at c. 50% of the sites. At least one stressor exceeded thresholds at all sites for which data on all four stressors were available. Toxicity showed weak positive correlations with nutrients and habitat degradation (0.2<Spearman's <0.34, 0.009<P<0.08). The risks of ecological effects arising from habitat degradation and invasive species were higher in lowland rivers, particularly for invasive species. Our assessment shows that organic toxicants contribute notably to risks of ecological effects in rivers, to a similar extent as invasive species, although habitat degradation and nutrients are the dominant stressors. Exposure to multiple stressors is the typical situation prevailing in rivers. Consequently, mitigation measures focusing on individual stressors may not be effective at reducing ecological risks. This suggests that integrating concepts and data from freshwater ecology and ecotoxicology is essential to meet the challenge of managing multiple stressors in river ecosystems. » weiterlesen» einklappen

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