A conceptual management framework for multiple stressor interactions in freshwater lakes and rivers.
Freshwater ecosystems are among the most threatened on Earth. The 5 key human-caused pressures are water extraction, habitat degradation (e.g., fragmentation or chemical pollution), overexploitation of fisheries resources, aquatic invasive species, and climate change. Understanding how multiple stressors associated with these pressures interact to affect rivers, lakes, and fishes is integral to successful management and conservation. We reviewed the scientific literature to examine interactions of multiple stressors on fishes in rivers and lakes. Additive interactions occur when stressors sum to negatively affect ecosystems; synergistic interactions are when stressors amplify each other's negative effects; and antagonistic interactions are when stressors mitigate each other but have an overall negative effect. Ecological surprises occur when stressors interact to positively affect ecosystems. Our results showed that habitat degradation was the most researched pressure, with studies linking warming associated with climate change to sedimentation, acidification, nutrification, or water diversions also being common. Thirty per cent of the summarized interactions were additive, 27% were synergistic, 34% were antagonistic, 6% were ecological surprises, and 2% showed no interactions. However, determining multiple stressor interactions and their effects in freshwater ecosystems is complex. The types of interactions can vary based on the fish species, life stage, indicator, stressor magnitude, and ecosystem studied. We developed a conceptual Driver-Pressure-State-Impact-Response framework to map and incorporate interactions among stressors into fish and freshwater ecosystem management.