Ecosystems face a combination of stressors that can interact in complex ways, leading to either synergistic (amplifying) or antagonistic (dampening) effects. It is necessary to understand how these interactions affect food web structure.

Freshwater lakes and ponds are among the most biodiverse habitats on Earth, and they are subjected to multiple environmental pressures including climate change, nutrient pollution, and pesticide contamination.

In a study published in Global Change Biology, Prof. XU Jun’s team from the Institute of Hydrobiology of the Chinese Academy of Sciences, along with collaborators from Germany, the UK, and Sweden, revealed that the combined effects of warming, nutrient enrichment, and the insecticide imidacloprid can simplify food web structures, shift energy flows, and potentially destabilize aquatic ecosystems, which sheds new light on how multiple stressors interact to affect freshwater food webs.

Researchers conducted a large-scale mesocosm experiment, simulating subtropical shallow lake ecosystems. They exposed 48 experimental systems to various combinations of stressors, i.e., warming, nutrient enrichment, and the insecticide imidacloprid over ten months. They monitored changes across the entire food web from primary producers to top predators. 

Researchers found that each stressor individually affected different components of the food web. Warming significantly reduced the biomass and diversity of higher trophic level consumers like fish and shrimp, while nutrient loading and insecticide pollution promoted phytoplankton blooms. 

However, the combined effects of these stressors were found to be more complex. Warming and insecticide pollution exhibited antagonistic interactions, where the presence of one stressor mitigated the effects of the other. In contrast, nutrient loading and insecticide pollution showed synergistic effects, exacerbating the negative impacts on the food web. 

As the number of stressors increased, the food web structure became simpler with fewer trophic links and a shift in energy flow from benthic to pelagic pathways. This shift increased the risk of ecosystem regime shifts, where clear-water states dominated by submerged plants transitioned to turbid states dominated by phytoplankton. Such changes can have profound implications for biodiversity and ecosystem services. 

This study highlights the importance of considering multiple stressors in environmental management and conservation efforts. Researchers advocate integrated, systemic strategies to mitigate the impacts of multiple stressors on freshwater ecosystems.