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Hydrodynamic Controls on Microplastic Transport in the Pearl River Estuary: Insights from Seasonal Field Observations and Modeling
Summary
Scientists tracked tiny plastic particles (microplastics) flowing through a major river system in China and found that heavy rain seasons wash far more plastic into coastal waters, with certain river outlets acting as "highways" for spreading it long distances out to sea. This matters because these waterways often connect to seafood harvesting areas and drinking water sources, meaning understanding when and where plastic pollution spreads worst can help communities time monitoring and cleanup efforts to reduce human exposure through the food and water we consume.
Understanding the environmental behavior of microplastics in estuarine systems was essential for mitigating their ecological risks and informing coastal management strategies. This study investigated the spatiotemporal distribution and transport mechanisms of microplastics in the Pearl River Estuary, a major freshwater outflow system in South China. Field surveys were conducted in both dry and wet seasons of 2022 at 18 representative stations, and a two-dimensional hydrodynamic model (MIKE21) was applied to simulate microplastic dispersion under varying tidal and runoff conditions. Results showed that microplastic abundance and composition exhibit significant seasonal variability, with markedly higher concentrations and broader dispersal during the wet season. Fibers and fragments dominated across both periods, with polyethylene and polypropylene being the primary polymer types. Numerical simulations revealed that high discharge outlets, especially Humen and Jiaomen, served as major pathways for long-distance microplastic transport, while high-density particles tended to accumulate near estuarine mouths due to limited mobility. Sensitivity experiments demonstrated that particle settling velocity played a critical role in controlling the horizontal spread of microplastics, with lower settling rates favoring offshore transport. This study highlighted the dual risk of widespread dispersal and localized accumulation, underscored the need for outlet-specific and seasonally adaptive management strategies to mitigate microplastic pollution in estuarine-coastal systems.