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Multiple stressors may pose greater risks to macrophyte community dynamics by driving complex and unanticipated higher-order interactions
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Researchers ran a full-factorial mesocosm experiment exposing two free-floating macrophyte species to microplastics, antibiotics, and antiviral drugs alone and in combination, finding that multi-stressor interactions were predominantly antagonistic at moderate levels but context-dependent — capable of reversing to enhanced toxicity under different conditions — highlighting the unpredictability of higher-order contaminant interactions for freshwater plant communities.
Freshwater ecosystems play a pivotal global role in water security and ecosystem services, but are increasingly threatened by multiple stressors, particularly emerging contaminants. These contaminants are in proximity to human activities and tend to accumulate in sediments, which further amplifies their ecological impacts on freshwater ecosystems. Nevertheless, most studies have focused on the effects of single or pairwise stressors, leaving the effects of complex higher-order interactions on macrophyte communities scant. Here, we conducted a full-factorial experiment using 96 glasshouse mesocosms in 10 L systems containing two macrophyte species (Lemna minor and Spirodela polyrhiza) maintained in a controlled glasshouse environment to investigate the single and higher-order interactive effects of the three emerging contaminants, including microplastics, antibiotics, and antiviral drugs, on two common free-floating macrophytes and their interactions. Our results show that individual and combined stressors cause species-specific responses in free-floating macrophytes, thereby directly or indirectly altering community dominance patterns. Multiple stressors mainly showed antagonistic interactions, triggering negative feedback regulation that alleviated macrophyte growth inhibition. And the feedback is context-dependent, as changes in environmental conditions and stressor combinations may reverse these feedback patterns, potentially enhancing ecological toxicity. Our findings highlight that the inherent complexity and unpredictability of higher-order interactions among multiple stressors can heighten risks to macrophyte communities. We advocate that evaluations of multiple stressors in freshwater ecosystems should integrate context-dependent responses, stressor interactions, and feedback due to redundancy and compensatory dynamics. Future studies should incorporate both biotic and abiotic stressors across multiple gradients and higher ecosystem levels, accounting for non-linear and context-dependent responses.
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Researchers set up outdoor experimental ponds to study how microplastics of different sizes combined with the antibiotic tetracycline affect communities of underwater aquatic plants. Smaller microplastics caused more harm to plant diversity and growth, and the combined exposure with antibiotics created worse effects than either pollutant alone. The study suggests that microplastic pollution could amplify the damage antibiotics cause to freshwater plant ecosystems.
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A meta-analysis of 124 experiments on submerged freshwater macrophytes found that combined stressors—including microplastics, PFAS, nutrients, and metals—predominantly produce additive rather than synergistic harm, though synergisms were most common when metals enhanced contaminant bioavailability. The findings underscore that real-world multi-stressor effects may be underestimated by simplified two-factor laboratory designs.
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Researchers developed a new analytical approach to evaluate the combined toxic effects of nanoplastics, copper, and phenanthrene on freshwater microalgae under varying environmental conditions. They found that the interactions between these pollutants were highly dependent on factors like pH, temperature, and dissolved organic matter. The study reveals that environmental context significantly changes how nanoplastic mixtures affect aquatic life in Canadian prairie ecosystems.
Press perturbations of microplastics and antibiotics on freshwater micro-ecosystem: Case study for the ecological restoration of submerged plants
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Researchers studied the combined effects of polyethylene microplastics and the antibiotic sulfanilamide on freshwater micro-ecosystems involving submerged plants, water, and sediment. The study found synergistic negative effects on ecosystem structure and function, including reduced plant diversity and disrupted nutrient cycling, highlighting concerns about the combined pollution impact on freshwater ecological restoration efforts.
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