Relationships of multiple stressors and biological responses in freshwaters: Impact, scales and mechanisms
European freshwater ecosystems are commonly exposed to multiple stressors, with diffuse pollution and hydromorphological degradation being most frequent. The interaction of stressors in affecting lake and river biota is poorly understood, and it is currently not possible to predict under which circumstances stressors will interact. This knowledge gap needs to be filled to underpin future land management decisions or climate mitigation interventions, for protecting and restoring freshwater ecosystems. We analysed original data from European lakes and rivers, resulting from the MARS and GLOBAQUA projects, combining data across scales from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies producing 180 combinations of paired-stressor effects on a biological response variable. Generalised linear models showed that only one of the two stressors had a significant effect in 40% of the analysed cases, while 27% of the paired-stressor combinations resulted in additive and 33% in interactive (antagonistic, synergistic, opposing or reversal) effects. While for lakes the frequency of additive and interactive effects did not differ significantly between scales, for rivers this frequency increased with scale. Nutrient enrichment was the overriding stressor for lakes, generally exceeding those of secondary stressors. For rivers, the effect sizes of nutrient enrichment were dependent on the specific stressor combination and biological response variable. These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting that river management requires more bespoke management solutions.
Based on the results, I will present a concept on the mechanisms of how multiple stressors affect freshwater biota and will discuss the suitability of management measures applicable to multiply stressed waterbodies.
Host: Jens Kiesel