Additive effects prevail: The response of biota to multiple stressors in an intensively monitored watershed

• Published in: The Science of the total environment 2017-09, Vol.593-594, p.27-35
• Main Authors: Gieswein, Alexander, Hering, Daniel, Feld, Christian K.
• Format: Article
• Language: English
• Subjects: Animals; Biota; Boosted Regression Trees; Conservation of Natural Resources; Ecosystem; Environmental Monitoring; Fishes; Generalised Linear Modelling; Germany; Interactions; Invertebrates; Monitoring data; Multiple stressors; Plants; Riverine ecosystems; Rivers; Stress, Physiological
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2017.03.116

Freshwater ecosystems are impacted by a range of stressors arising from diverse human-caused land and water uses. Identifying the relative importance of single stressors and understanding how multiple stressors interact and jointly affect biology is crucial for River Basin Management. This study addressed multiple human-induced stressors and their effects on the aquatic flora and fauna based on data from standard WFD monitoring schemes. For altogether 1095 sites within a mountainous catchment, we used 12 stressor variables covering three different stressor groups: riparian land use, physical habitat quality and nutrient enrichment. Twenty-one biological metrics calculated from taxa lists of three organism groups (fish, benthic invertebrates and aquatic macrophytes) served as response variables. Stressor and response variables were subjected to Boosted Regression Tree (BRT) analysis to identify stressor hierarchy and stressor interactions and subsequently to Generalised Linear Regression Modelling (GLM) to quantify the stressors standardised effect size. Our results show that riverine habitat degradation was the dominant stressor group for the river fauna, notably the bed physical habitat structure. Overall, the explained variation in benthic invertebrate metrics was higher than it was in fish and macrophyte metrics. In particular, general integrative (aggregate) metrics such as % Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa performed better than ecological traits (e.g. % feeding types). Overall, additive stressor effects dominated, while significant and meaningful stressor interactions were generally rare and weak. We concluded that given the type of stressor and ecological response variables addressed in this study, river basin managers do not need to bother much about complex stressor interactions, but can focus on the prevailing stressors according to the hierarchy identified. [Display omitted] •Multiple stressors have serious negative effects on river biota, particularly if stressors interact.•Quantified stressor effects and interactions can help river basin managers to derive suitable management actions.•Biological and abiotic data resulting from monitoring schemes provide a solid basis to disentangle multiple-stressor effects.•We investigated the hierarchy and interactions of anthropogenic stressors using standard WFD monitoring data.•Stressor interactions were rare and weak, thus implying independently-acting stressors.