Synergistic Effects of Multiple Stressors on Aquatic Ecosystems in Coastal and Inland Waters

Abstract

Coastal and inland aquatic ecosystems globally are under mounting stress from simultaneous anthropogenic and environmental threats. These critical biodiversity cradles are fast approaching tipping points beyond which system resilience can no longer withstand combined thermal anomaly (climate-driven) and chemical contamination (land-use-driven) stresses. The current literature is dominated by reductionist approaches, wherein the combined effects of pollutants are assessed based on a comparison with single-stressor impacts, while ignoring nonlinear, synergistic interactions that promote higher levels of ecosystem collapse. In this study, it addresses this knowledge gap by developing an Integrated Stressor-Response Framework (ISRF), whereby a multi-level interaction matrix is used to quantitatively assess how coupled stresses transform biological response patterns as opposed to their individual actions. Specifically, synergistic amplification, the combined impact of thermal stress and nutrient enrichment, results in considerably faster metabolic rates and greater hypoxic episodes than summed alone. Moreover, alteration in hydrology coupled with chemical contamination elevates contamination bioavailability and residence times, leading to system-level regime-shifting collapses of benthic communities. Ultimately, controlling pollutants one at a time is inadequate to promote long-term persistence of aquatic ecosystems, calling for a future of "Synergy-Aware Adaptive Management" (SAAM) leveraging high-frequency IoT sensors, climate-adaptive permits, and land-use-based spatial planning to avoid tipping points by preventing the condition from being established, which will enhance ecosystem redundancy and maintain water security in the Anthropocene.