The degradation of coastal seawater quality off the Changjiang Estuary and adjacent waters is typically associated with monsoon wind, ocean currents and inputs of terrestrial pollutants. In addition to these factors, the passage of typhoons can be also important in driving short-term fluctuations in coastal water quality. Using a coupled Regional Ocean Modeling Systems (ROMS) and carbon, silicate, and nitrogen ecosystem (CoSiNE) model with Eulerian tracers, we investigated the transport processes of pollutants discharged from the Changjiang during the passage of Typhoons Lingling and Tapah (2019). The model results show that Typhoons Lingling and Tapah significantly enhanced the southward transport of these pollutants, leading to a sudden and noteworthy degradation of water quality in the Zhejiang coastal region during early autumn, despite no considerable change in monsoon pattern or river discharge compared to normal years. As Lingling and Tapah successively passed through the East China Sea in September, the average nitrate concentration in the Zhejiang coastal waters rose by 77%, and the percentage of heavily polluted water increased by 28%. Our numerical experiments showed that the impacts caused by Lingling and Tapah on nitrate levels in these waters lasted for approximately 34 and 23 days, respectively. These results indicate that typhoons play a crucial role in regulating the transport of pollutants in coastal waters, with significant sub-seasonal effects on the marine biogeochemical environment.

中文翻译：

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台风过境导致水质恶化——以2019年浙江近岸海域为例


长江口及邻近水域沿岸海水质量的恶化通常与季风、洋流和陆地污染物的输入有关。除了这些因素之外，台风的通过对于推动沿海水质的短期波动也很重要。利用耦合区域海洋模拟系统（ROMS）和带有欧拉示踪剂的碳、硅酸盐和氮生态系统（CoSiNE）模型，我们研究了台风“玲玲”和“塔帕”（2019）通过期间长江排放污染物的迁移过程。模型结果显示，台风“玲玲”和“塔帕”显着增强了这些污染物的南移，导致初秋时浙江沿海地区水质突然显着恶化，尽管季风格局或河流流量与正常情况相比没有明显变化年。 9月，随着零陵、打巴先后通过东海，浙江近海硝酸盐平均浓度上升77%，重度污染水体比例上升28%。我们的数值实验表明，零陵和塔巴对这些水域硝酸盐水平造成的影响分别持续了大约 34 和 23 天。这些结果表明，台风对近岸海域污染物输送起着至关重要的调节作用，对海洋生物地球化学环境具有显着的次季节影响。