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A tale of two stressors: Nitrogen, microplastics, and their influence on estuarine organic matter degradation
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Researchers tested how microplastics and nitrogen addition — individually and together — alter organic matter degradation in estuarine sediments hosting different invertebrate communities, finding that single-stressor effects on key environmental drivers were decoupled when both stressors were applied together, indicating that standard single-stressor models underestimate the complexity of real-world estuarine carbon cycling under combined anthropogenic pressures.
Estuaries are highly dynamic systems with strong physicochemical and biological gradients that drive ecosystem functions. Increasing anthropogenic pressures have altered carbon cycling and degradation processes and reduced key ecosystem functions, leading to a marked decline in global estuarine health. This study investigates the individual and combined effects of two common anthropogenic stressors (microplastics and nitrogen) across a gradient of soft-sediment habitats with contrasting infaunal communities that reflect dominant functional traits: head-down deposit-feeding polychaetes, deep-dwelling facultative-feeding bivalves, and a mix of both. In situ rapid organic matter assays (ROMA) were used to assess whole-community organic matter degradation using media with different stressor combinations (nitrogen addition, microplastics, or both). Separate models were developed for each treatment, with predictors selected using the Akaike Information Criterion (AIC) to achieve model parsimony without compromising model fit. Our results clearly demonstrate that, in this system, single stressor models may not adequately capture organic matter cycling in sediments following exposure to multiple stressors. In single-stressor treatments, the role of sedimentary organic matter content on organic matter degradation increased significantly in plastic-treated media, and the density of a head-down deposit feeding polychaete was significantly related to the extinction rate of organic matter with sediment depth in nitrogen treated media. These relationships were decoupled when a secondary stressor was added in the multiple-stressor treatment. While direct effects of nitrogen and microplastic addition were not detected, the treatment-specific models indicate that environmental drivers of degradation vary across stressor contexts, highlighting nuanced estuarine responses to anthropogenic pressures.
More Papers Like This
[Article Dataset] A tale of two stressors: nitrogen, microplastics, and their influence on estuarine organic matter degradation
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This dataset accompanies an in-situ experiment examining how added microplastics and nitrogen — either alone or combined — affect the rate at which organic matter breaks down in estuarine sediments, across communities of different burrowing invertebrates. The data enables analysis of how two of the most widespread human-caused stressors interact at the base of coastal food webs, where organic matter recycling underpins the productivity of estuaries.
Combined effects of microplastics and nitrogen on bivalve‐mediated biogeochemical cycling
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Researchers investigated the combined effects of microplastic pollution and excess nitrogen on coastal sediment ecosystems mediated by bivalves. They found that when both stressors were present together, nitrogen processing responses changed in ways not seen with either stressor alone, and sediment health conditions worsened significantly. The study suggests that multiple environmental stressors can interact in unexpected ways that single-stressor studies would miss.
[Article Dataset] A tale of two stressors: nitrogen, microplastics, and their influence on estuarine organic matter degradation
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This dataset supports a study examining how microplastics and excess nitrogen interact to affect organic matter breakdown in estuarine sediments, using a 10-day field experiment across varied seafloor community types. The research matters because estuaries are critical carbon-cycling zones and understanding how combined pollution stressors alter that cycling helps predict broader ecosystem consequences.
Impacts of microplastics and nitrogen on invertebrate-mediated biogeochemical cycling in estuarine ecosystems
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Researchers used estuarine mesocosms and field assays to show that microplastics and nitrogen enrichment interact in non-additive ways, altering bivalve-driven nutrient fluxes, degrading sediment redox conditions, and decoupling organic matter breakdown from the environmental factors that normally predict it.
Warming Modulates Microplastic Impacts on Coastal Nitrogen Cycling by Synergistically Amplifying Sediment Hypoxia and Restructuring the Denitrifying Microbiome
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Climate warming and microplastic pollution are converging stressors in coastal environments, but their combined effects on ocean chemistry were poorly understood. This microcosm study found that warming and microplastics interacted in complex, non-additive ways to disrupt nitrogen cycling in coastal sediments—sometimes amplifying each other's harmful effects and sometimes canceling them out, depending on the plastic type and the specific biological process. Most concerning, warming combined with both polyethylene and PBAT microplastics created more intense oxygen-depleted zones in sediments, which can trigger dead zones that suffocate marine life. These findings suggest that the ecological risks of microplastic pollution will worsen as oceans warm, complicating predictions based on either stressor studied alone.
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