First Institute of Oceanography, Ministry of Natural Resources, 6 Xianxialing Road, Qingdao 266061, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, 1 Wenhai Road, Qingdao 266237, China.
First Institute of Oceanography, Ministry of Natural Resources, 6 Xianxialing Road, Qingdao 266061, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, 1 Wenhai Road, Qingdao 266237, China.
Sci Total Environ. 2021 Apr 10;764:142838. doi: 10.1016/j.scitotenv.2020.142838. Epub 2020 Oct 8.
The Changjiang (Yangtze River) Diluted Water (CDW) plume substantially impacts the biogeochemical processes off the estuary and its adjacent area, resulting in considerable environmental and ecological effects. Based on survey data in the northeastern area off the Changjiang Estuary (CE) obtained in the summers of 2008 and 2013, the hypoxia induced by the offshore detached CDW plume and the associated controlling mechanisms were investigated. The results show that the offshore transport of the CDW plume caused a dispersed low-salinity area in the northeastern area off the CE during summer, in sharp contrast with the surrounding high-salinity and high-density waters. There was a hypoxic area with low-pH (i.e., acidification) near the 40-m isobath in bottom waters in the northeastern area off the CE, and its position generally corresponded to the surface offshore CDW plume. In the area affected by the offshore low-salinity water, the surface patch-like phytoplankton bloom and the organic debris produced in situ were the material drivers of the bottom oxygen consumption and led to the corresponding relationship between the bottom hypoxic zone and the high chlorophyll-a (Chl-a) area at the surface. We consider that the local stratification caused by the offshore low-salinity water and the stable environment within the detached CDW plume constituted the external dynamic conditions for maintaining the bottom hypoxia. Our results demonstrate that the offshore detached CDW plume in the northeastern area off the CE may contribute to the formation of a local hypoxic center with low pH. This study would provide basis for understanding of the physical-biogeochemical processes and environmental responses in the offshore areas of the CDW plume.
长江淡水锋显著影响着河口及其毗邻海域的生物地球化学过程，产生了重要的环境和生态效应。本研究基于 2008 年和 2013 年夏季长江口东北海域的调查数据，探讨了离岸长江淡水锋锋舌所诱发的缺氧现象及其控制机制。结果表明，夏季长江淡水锋锋舌向岸传输，在长江口东北海域形成离散的低盐区，与周围高盐高密度水体形成鲜明对比。在长江口东北海域底层，近 40m 等深线处存在低氧低 pH（酸化）区，其位置与锋面离岸长江淡水锋锋舌的位置基本对应。在低盐度水体影响的海域，表层斑块状浮游植物水华和原地产生的有机碎屑是底层耗氧的物质驱动因子，导致底层缺氧区与表层高叶绿素 a（Chl-a）区之间存在对应关系。我们认为，离岸低盐度水引起的局地层化和离岸长江淡水锋锋舌内部稳定的环境为底层缺氧的维持提供了外部动力条件。本研究结果表明，长江口东北海域离岸长江淡水锋锋舌可能是形成局部低 pH 缺氧中心的原因之一。该研究为了解长江淡水锋锋舌外海域的物理-生物地球化学过程和环境响应提供了依据。
