极端天气陆地河流面源污染对珠江河口叶绿素分布的影响——评价方法构建与应用

近十年来，随着我国粤港澳大湾区的建设，珠江流域人口增长十分迅速，食品和能源需求急剧增加，导致流域上游省份农业用地面积增加，下游省份城市化进程加速，随之导致含农业化肥的农田灌溉用水和生活污水排放大幅度增加。流域的面源污染物进入珠江河口，导致河口海域赤潮发生频率明显增高。此外，全球变暖加剧了南海和西太台风等极端天气事件的发生频率，大量的台风在珠江口附近登陆，对人类活动产生的营养盐在海水中再分布产生较大影响。现场及卫星观测表明，台风等极端天气影响浮游植物时空分布的4个主要影响因子为：海水的垂直混合、流域的降水增加、河流淡水及营养盐的大量输入及风场变化。但是，尚未对这些因子如何影响叶绿素分布进行过清晰阐释。研究构建了粤港澳大湾区陆海气集成模拟系统，一方面通过控制实验来对模式敏感性进行测试，另一方面以台风“天鸽”过境珠江口为例，来对台风过境期间海表叶绿素时空变化机理进行探究。结果表明，陆地模式径流分辨率的提高对模拟结果有很大影响，台风“天鸽”过境时，向岸的风抑制了珠江冲淡水排出，促进外海水涌入，提高海表盐度，降低叶绿素浓度。而台风所致的陆地降水在过境后四天(8月27日)通过径流输出至河口，此次剧...

Impacts of non-point source pollutants from river on chlorophyll distribution in the Pearl River Estuary under the extreme weather conditions: the framework and application

Over the last 10 years, progressive development of the Guangdong-Hong Kong-Macau Greater Bay area in our country has caused rapid population growth within the Pearl River watershed. In the meantime, demand for food and energy has increased dramatically. These result an expansion of agriculture land in the upper reaches of the Pearl River catchment and an increase in the rate of urbanization in the downstream area. As a result, groundwater and surface runoff entering the Pearl River up-stream now contains higher levels of fertilizer than previous, whilst in urban areas sewage and effluent production has increased considerably. A side effect of these changes is that the amount of pollution entering the estuary in a non-point source manner has increased, leading to widespread eutrophication there. Besides, global warming increased typhoons from South China Sea and Western Pacific making landfall near the Pearl River estuary, resulting in the enhanced redistribution of anthropogenic nutrients into the oceanic water. Both in-situ and satellite have been used to investigate the impact these typhoons have on Pearl River phytoplankton dynamics. They identified four factors impacting the redistribution of phytoplankton include the vertical mixing of oceanic water, high precipitation in the watershed, the large freshwater discharge and nutrients loading, and the variation of wind fields. To date, there have been no studies address how these four factors work together to influence the distribution of chlorophyll in the Pearl River estuary. In this research, we built a land-ocean-atmosphere modeling system for the China Great Bay Area. We conducted numerous controlled experiments to examine the sensitivity of the system to multiple forcing conditions. We also investigated the effect of each controlling mechanism has on phytoplankton dynamics, using the incidence of Hurricane Hato''s arrival in the area as an opportunity to collect first-hand, real-time observations. Our results show that the temporal resolution of river runoff data used in the modeling system has a profound impact on the simulation results. Using daily river runoff data from land surface models produced very different results from those using monthly data. As Hato passed by, strong onshore winds inhibited the spread of freshwater from the Pearl River, increasing the influx of seawater which in turn increased sea surface salinity and reduced the concentration of surface chlorophyll. Four days (August 27th) after Hato had passed by, water that had fallen on land as precipitation during the typhoon entered the Estuary as runoff. The dramatic increase of river discharge coincident with this event enhanced the level of nutrient loading and caused dramatic phytoplankton growth. Chlorophyll levels were still increasing two weeks after the typhoon Hato passing by (September 1st). The land-ocean-atmosphere modeling system built for the Pearl River Estuary in our research could be adapt to other estuarine and coastal regions and would ultimately help predict algal blooms, hypoxia within the aquatic environment, and other ecological hazards in the future.