Multistressor effects on river biofilms under global change conditions

Highlights: • River ecosystems are often affected by a combination of chemical and physical stressors. • A full factorial design revealed the short-term effects of four stressors on river biofilms. • Responses to stressors combination were 85.5% additive and 14.5% non-additive. • Non-additive responses were classified as antagonisms (75%) and synergisms (25%). Freshwater ecosystems are confronted with multiple chemical, biological and physical stressors. Co-occurring stressors commonly result in additive responses, but non-additive interactions may also occur, hindering our predicting capacity. Despite growing interest in multiple stressor research, the response of freshwater communities to co-occurring chemical and climate change-related physical stressors remains largely unexplored. Here, we used a microcosm approach to evaluate the effect of the combined action of chemical and physical stressors on river biofilms. Results showed that additive responses dominated, whereas 14.5% of all responses were non-additive (75% antagonisms and 25% synergisms). Among these non-additive interactions, physical stressors dominated over chemicals and drove the overall responses. Overall, the occurrence of these non-additive interactions, together with the dominance of the climate-change related physical stressors, might lead to unexpected responses as a result of climate change.