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Microplastics as pathway-selective modulators rewire nitrogen cycling in coastal wetlands: Polymer identity outweighs concentration
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Coastal wetlands act like natural water filters, using bacteria to remove excess nitrogen pollution before it causes harmful algae blooms in our oceans. This study found that certain plastics—especially polystyrene (like foam cups) and polypropylene (common in packaging)—can disrupt this filtering process, causing wetlands to trap nitrogen as ammonium instead of safely releasing it as gas. This matters because it means plastic pollution isn't just about visible litter or ingestion risks—it could be quietly weakening one of nature's key defenses against water pollution that affects seafood safety and coastal ecos
Coastal wetlands are globally important nitrogen sinks that mitigate eutrophication via microbial denitrification and anammox. However, the impact of microplastic (MP) pollution on nitrogen transformation pathways remains poorly understood. Here, we conducted a field-based mesocosm experiment across high, middle, and low tidal marshes, exposing sediments to environmentally relevant concentrations (0.1-1.0% w/w) of four common polymers (PE, PP, PS, and PET). We revealed highly significant three-way interactions among tidal elevation, polymer type, and concentration, demonstrating strong context-dependency. Rather than acting as generic stressors, MPs functioned as pathway-selective modulators, fundamentally shifting nitrate fate from gaseous removal (N via denitrification/anammox) toward ammonium retention (NH via DNRA). Random Forest modeling indicated that polymer type exhibited higher predictive importance than concentration. Notably, in the low marsh, intermediate MP concentrations (0.5%) triggered a non-linear threshold response, elevating DNRA contributions from ∼10% to 65-70% of total nitrate reduction. Concurrently, nitrogen removal multifunctionality declined significantly under PS and PP treatments at concentrations of 0.5-1.0%, particularly in the middle marsh. These findings identify PS and PP as priority polymers for mitigation and underscore the necessity of incorporating polymer-specific characteristics into environmental policies to safeguard the nitrogen buffering capacity of coastal wetlands.
More Papers Like This
Mechanistic insights into microplastic-mediated shifts in nitrogen metabolism and sensory quality across emergent and submerged-plant wetlands: Evidence from metagenomics and physiological indicators
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Researchers exposed surface-flow constructed wetlands planted with emergent and submerged macrophytes to polystyrene microplastics and found a 12.64% reduction in total nitrogen removal in the emergent plant system, driven by shifts in nitrogen-cycling microbial communities. PS-MPs also altered sensory water quality indicators, with effects varying by plant type.
Environmentally aged microplastics alter archaeal and bacterial roles in ammonia oxidation of intertidal soils
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Scientists found that plastic pollution which has been broken down by sun, waves, and time (like the microplastics washing up on beaches and marshes) disrupts the natural process soil microbes use to cycle nitrogen, an essential nutrient for coastal ecosystems. Specifically, aged plastic bits threw off the balance between two types of nitrogen-processing microbes, slowing down the overall process by nearly a third. This matters because these coastal wetlands act as natural filters and buffers for our environment, and if microplastics are quietly disrupting the microbes that keep them healthy, it could have ripple effects on water qu
Effects of microplastics on carbon and nitrogen cycling in coastal wetlands: A critical meta-analysis
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This meta-analysis of over 1,000 data points from 34 studies found that microplastics significantly altered certain carbon and nitrogen cycling indicators in coastal wetlands under laboratory conditions, but tidal simulation experiments more representative of real environments showed no significant effects. The findings caution against over-interpreting lab results and highlight that tidal dynamics and vegetation factors are often missing from experimental designs.
Microplastics can Alter the Nitrogen Cycle in Surface Flow Constructed Wetlands
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Both conventional PVC and biodegradable PLA microplastics disrupted nitrogen cycling in constructed wetlands, with PVC causing ammonium accumulation and PLA acting as a carbon source, while both enhanced biofilm formation and enzyme activities at higher concentrations. These polymer-specific effects on nitrogen dynamics reveal that microplastic contamination poses distinct and complex threats to the water treatment functions of natural and engineered wetlands.
Unveiling the microplastic perturbation on surface flow constructed wetlands with macrophytes of different life forms: Responses of nitrogen removal and sensory quality
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Polystyrene microplastics initially boosted nitrogen removal in constructed wetlands used for water treatment, but over time they reduced removal efficiency by 25-34% and harmed the beneficial bacteria responsible for cleaning the water. This means microplastic contamination could undermine natural water treatment systems that communities rely on for clean water.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.