Contribution of organic toxicants to multiple stress in river ecosystems

• Published in: Freshwater biology 2016-12, Vol.61 (12), p.2116-2128
• Main Authors: Schäfer, Ralf B., Kühn, Bernhard, Malaj, Egina, König, Anne, Gergs, René
• Format: Article
• Language: English
• Subjects: Ecosystems; Freshwater; global change; Land degradation; land use; multiple stressors; Nonnative species; pesticides; River ecology; rivers
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1111/fwb.12811

Summary 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