Estuarine mangroves are crucial for trapping microplastics and contributing to coastal protection; however, their effectiveness during extreme weather events remains unclear. This study investigated the effects of typhoons on microplastic dynamics within the watershed-estuary-offshore system and the changes in the role of estuarine mangroves. Surface water from the Shenzhen River and sediments from estuarine mangroves were sampled after typhoons (Saola and Haikui) and during periods of stable hydrodynamic conditions. Our findings indicated that after typhoons, the microplastic content in estuarine water was the lowest at 363 n/m³ compared to upstream and downstream locations, while it was the highest at 812 n/m³ during the dry season. Additionally, microplastic abundance in sediments was higher during low-flow conditions (11,153 n/kg) than after typhoons (1134 n/kg), with only about 10 % retained. Considering river flow, the microplastic flux in the estuary during the typhoon season reached its highest value of 21,816 n/s, indicating that riverine microplastics could be washed downstream and diluted due to increased flow. Polypropylene was the dominant type of microplastic (29.9 %), while synthetic rubber also accounted for a significant proportion, especially after typhoons, likely due to traffic from vehicles and boats around the watershed. Correlation analyses revealed that strong hydrodynamic forces led to a more uniform distribution of microplastics along the river, re-releasing those deposited in estuarine mangroves during the dry season and contributing to marine microplastic pollution. This study highlights how extreme weather shifts urban estuarine mangroves from microplastic sinks to sources, providing new insights into pollution dynamics under climate change.

中文翻译：

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打破沿海屏障：台风将河口红树林转化为海洋微塑料的来源


河口红树林对于捕获微塑料和促进海岸保护至关重要;然而，它们在极端天气事件中的有效性仍不清楚。本研究调查了台风对流域-河口-近海系统内微塑料动力学的影响以及河口红树林作用的变化。在台风（Saola 和 Haikui）之后和稳定的水动力条件下，对深圳河的地表水和河口红树林的沉积物进行了采样。我们的研究结果表明，台风过后，河口水域中的微塑料含量最低，为363 n/m³，而旱季最高，为812 n/m³。此外，在低流量条件下 （11,153 n/kg） 低于台风后 （1134 n/kg），沉积物中的微塑料丰度更高，仅保留了约 10%。考虑到河流流量，台风季节河口的微塑料通量达到最高值 21,816 n/s，表明河流微塑料可以被冲到下游并因流量增加而被稀释。聚丙烯是微塑料的主要类型 （29.9%），而合成橡胶也占很大比例，尤其是在台风之后，这可能是由于流域周围的车辆和船只的交通。相关性分析表明，强大的流体动力导致微塑料沿河分布更加均匀，在旱季重新释放沉积在河口红树林中的微塑料，并导致海洋微塑料污染。本研究强调了极端天气如何将城市河口红树林从微塑料汇转变为源头，为气候变化下的污染动态提供了新的见解。