Lao Qibin, Lu Xuan, Chen Fajin, Chen Chunqing, Jin Guangzhe, Zhu Qingmei
College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China; Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China; Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang 524088, China.
College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China; Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China; Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang 524088, China.
Sci Total Environ. 2023 Dec 10;903:166853. doi: 10.1016/j.scitotenv.2023.166853. Epub 2023 Sep 8.
Typhoons and rainstorms (rainfall >250 mm day) are extreme weather events that seriously impact coastal oceanography and biogeochemical cycles. However, changes in the mixing of water masses and nutrient supply induced by typhoons and rainstorms can hardly be identified and quantified by traditional methods owing to the complex hydrological conditions in coastal waters. In this study, we analysed a comparative data set of dual water isotopes (δD and δO), hydrological parameters, nutrients, and chlorophyll-a from three periods (normal summer, rainstorm, and typhoon periods) in Zhanjiang Bay, a typical semi-enclosed mariculture bay in South China, to address this issue. The results revealed a significant increase in contributions from freshwater during rainstorms and typhoons. Correspondingly, nutrient supplies from freshwater during these periods remarkably increased compared to the normal summer, indicating that heavy rainfall can transport substantial amounts of terrestrial nutrients into the bay. Furthermore, disparities in hydrodynamic processes between typhoon and rainstorm periods were notable due to inconsistencies in freshwater diffusion paths. During rainstorms, freshwater primarily diffuses towards the outer bay in the upper layer due to strong stratification and cannot form an ocean front. However, under intense external forces caused by the typhoon, high-salinity water intruded into the bay, and enhancement of vertical mixing disrupted stratification. The massive influx of freshwater column during the typhoon mixed with higher salinity seawater column in the bay led to the formation of an ocean front, which could retain contaminants. This study suggests that although both rainstorms and typhoons can discharge large quantities of terrestrial nutrients into Zhanjiang Bay, the front formed during the typhoon period impedes the contaminant transportation to open sea thereby deteriorating water quality and affecting mariculture activities within the bay.
台风和暴雨（日降雨量>250毫米）是严重影响沿海海洋学和生物地球化学循环的极端天气事件。然而，由于沿海水域复杂的水文条件，传统方法很难识别和量化台风和暴雨引起的水体混合和营养供应变化。在本研究中，我们分析了中国南方典型的半封闭海水养殖湾——湛江湾三个时期（正常夏季、暴雨期和台风期）的双水同位素（δD和δO）、水文参数、营养物质和叶绿素-a的对比数据集，以解决这一问题。结果显示，暴雨和台风期间淡水的贡献显著增加。相应地，与正常夏季相比，这些时期淡水的营养供应显著增加，表明强降雨可将大量陆地营养物质输送到海湾。此外，由于淡水扩散路径不一致，台风期和暴雨期的水动力过程存在显著差异。暴雨期间，由于强烈的分层作用，淡水主要在上层向外湾扩散，无法形成海洋锋面。然而，在台风引起的强烈外力作用下，高盐度海水侵入海湾，垂直混合增强破坏了分层。台风期间大量淡水柱与海湾中盐度较高的海水柱混合，导致形成海洋锋面，该锋面可截留污染物。本研究表明，尽管暴雨和台风都可将大量陆地营养物质排入湛江湾，但台风期间形成的锋面阻碍了污染物向公海的输送，从而恶化了水质并影响了海湾内的海水养殖活动。
