Disentangling the effects of multiple stressors on freshwater macroinvertebrates: A quantitative analysis of experimental studies

Multiple stressors in freshwater ecosystems usually interact and produce synergistic, antagonistic, reversal or additive effects on organisms. However, the understanding of the interactive types of stressors on macroinvertebrate assemblages is still limited. We synthesized 1,087 experimental treatment–control observations extracted from 32 publications to quantify the individual and combined effects of 14 stressors on macroinvertebrates (abundance and richness) and to determine the effect types of paired-stressor interaction. We find that multiple stressors acted mostly through additive effects (84.85%) on freshwater macroinvertebrates. Among the non-additive interactions, antagonistic (7.18%) and reversal (6.41%) effects were more common, while synergistic effects were relatively rare (1.55%). Notably, these interactions often occurred in EPT taxa, with synergistic interactions between increases in fine sediment and temperature often occurring for EPT richness. Additionally, antagonistic and reversal effects were commonly observed between fine sediment increase and either flow decrease or nutrient increase. Our study provides a quantitative basis for accounting for the effect types of multiple stressors in freshwater macroinvertebrate-based biodiversity assessment and ecosystem management. Our study also highlights the consideration should be given to the variability in interactions resulting from different combinations of stressors and emphasizes how realized effects may differ among taxonomic groups.