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Microplastics and co-occurring nitrogen synergistically accelerate blue carbon loss
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Scientists found that "biodegradable" plastic (PLA) combined with nitrogen fertilizer runoff dramatically speeds up the breakdown of carbon stored in coastal ecosystems like seagrass meadows—nearly tripling CO₂ emissions compared to unpolluted soil. This matters because these coastal habitats are major carbon sinks that help fight climate change, and the study suggests that plastic waste and fertilizer pollution together—not just separately—could be quietly undermining nature's ability to lock away carbon, with ripple effects on the broader environment humans depend on.
Blue carbon ecosystems (BCEs)—including seagrass meadows, mangroves, and salt marshes—store vast amounts of organic carbon, yet their carbon sink function is increasingly threatened by hazardous microplastics and co-occurring nitrogen pollution. Here, we used a controlled microcosm experiment and multi-omics analysis (16S rRNA amplicon sequencing, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and Ultra-Performance Liquid Chromatography-Mass Spectrometry) to investigate how two common microplastics—polyethylene terephthalate (PET) and polylactic acid (PLA)—interact with nitrogen fertiliser (N-dominated fertiliser with co-delivered nutrients) to influence seagrass soil biogeochemistry. We showed that PLA combined with N-fertiliser increased CO₂ emissions from seagrass soil by 106% relative to nitrogen alone and by 195% compared to controls (p < 0.01), while PET addition had negligible effects. PLA degradation released carboxylic acid and derivatives, supporting putative sulphate-reducing and fermentative bacteria, and increasing the formation of organic-oxygen compounds (e.g., disaccharides, o-glycosyl compounds). N-fertiliser addition further enriched putative organic matter-degrading microbial taxa, particularly Clostridia and Bacteroidia, and elevated microbial metabolic potential across pathways. Combined PLA and nitrogen treatments resulted in the lowest (–37% vs control) residual dissolved organic carbon concentrations, indicating accelerated carbon loss. These findings suggest that microplastics, especially PLA biopolymer, and nitrogen act as hazardous co-contaminants that enhance microbial mineralisation of soil organic matter, potentially weakening blue carbon storage. Plastic waste and fertiliser inputs should therefore be considered together in future risk assessments of coastal carbon stocks and in the development of strategies to safeguard BCEs.
More Papers Like This
Microplastics and co-occurring nitrogen synergistically accelerate blue carbon loss
AI summary Read the abstract
Scientists found that "biodegradable" plastic (PLA), when combined with nitrogen fertilizer runoff, dramatically speeds up the breakdown of carbon stored in coastal ecosystems like seagrass meadows—nearly tripling CO2 release compared to untreated soil. This matters because these coastal habitats act as major carbon sinks that help buffer climate change, and the combo of plastic pollution and fertilizer runoff could be quietly undermining that protective function, meaning the "eco-friendly" label on some biodegradable plastics may be misleading when it comes to environmental impact.
Effects of Plastic Pollution on Blue Carbon Ecosystems
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Coastal wetlands like mangroves and seagrasses (called "blue carbon" ecosystems) are prized for trapping and storing carbon that would otherwise warm the planet—but this research found that plastic pollution collecting in these areas can actually backfire, breaking down and fueling bacteria that release extra CO2 and methane back into the atmosphere. So-called "biodegradable" plastics were often worse offenders than conventional plastic, especially when mixed with fertilizer runoff or "forever chemicals" (PFAS), suggesting that plastic waste doesn't just pollute these ecosystems—it
Biodegradable plastics can alter carbon and nitrogen cycles to a greater extent than conventional plastics in marine sediment
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Researchers showed in controlled sediment microcosms that biodegradable plastics stimulate decomposition of buried marine organic carbon more than conventional plastics, producing twice the CO2 release to the water column and suppressing nitrogen flux — effects that could undermine coastal ecosystems' capacity to sequester carbon.
Distinct impacts of microplastics on the carbon sequestration capacity of coastal blue carbon ecosystems: A case of seagrass beds
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Researchers examined how microplastic pollution affects the ability of seagrass beds to capture and store carbon, a process important for combating climate change. Evidence indicates that microplastics can alter sediment properties, disrupt microbial communities, and inhibit seagrass growth, all of which reduce carbon storage capacity. The study highlights that microplastic contamination may be undermining one of nature's key tools for removing carbon dioxide from the atmosphere.
Plastics in blue carbon ecosystems: a call for global cooperation on climate change goals
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Researchers warn that plastic pollution is increasingly accumulating in coastal blue carbon ecosystems — tidal marshes, mangroves, and seagrass meadows — which are critical carbon sinks, and argue that plastic-related carbon emissions must be factored into global climate goals before growing plastic stocks undermine these vital ecosystems.
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