School of Marine Sciences/Guangdong Key Laboratory of Marine Resources and Coastal Engineering, Sun Yat-Sen University, Guangzhou 510275, China; South China Sea Environmental Monitoring Center, State Oceanic Administration, Guangzhou 510300, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China.
South China Sea Environmental Monitoring Center, State Oceanic Administration, Guangzhou 510300, China.
Mar Pollut Bull. 2020 Feb;151:110814. doi: 10.1016/j.marpolbul.2019.110814. Epub 2020 Jan 29.
Several large semi-enclosed seas and coastal bodies have formed seasonal hypoxic water masses over large areas. The dominant cause for such formations is believed to be the increasing inflow of nutrients from watersheds and urban areas into estuaries and coastal waters. Several studies have reported hypoxic events in the Pearl River estuary (PRE). However, hypoxia events appear to be episodic, which are neither seasonal nor estuary-wide. The reasons for such occurrences are not understood fully. The objectives of this study are to use 24-year time series data obtained during 1988-2011 to analyze the long-term variability in dissolved oxygen (DO) in summer over the entire estuary from urban areas to estuarine coastal waters and examine regulating factors for the occurrences of hypoxia. The results showed that various regulating factors were responsible for the variability of DO in different regions of the PRE. DO decreased in the urban reach, upstream and main estuarine zones of the PRE from about 2000. It was hypoxic (DO <2.0 mg L) in the urban reach zone and periodic low DO (DO <3.5 mg L) and episodic hypoxic in the upstream zone after 2000, mainly influenced by the increasing sewage discharge. The main estuarine zone experienced episodic low DO and sporadic hypoxia after 2000. The ecosystem buffering capacity was characterized by turbidity, well vertical mixing and short residence time which diluted the pressure for the formation of hypoxia. The eastern shelf appeared to be more vulnerable to hypoxia because of its deeper topography, plume front position, and stratification of the water column compared with the western shelf. Its bottom waters experienced seasonal low DO but seldom hypoxia. In comparison, low DO rarely occurred in the western shelf because of its shallow topography and short residence time. In brief, 24-year series data captured from 1988 to 2011 showed a lack of seasonal and estuary-wide hypoxia in the PRE.
几个大型的半封闭海域和沿海水体已经在大面积范围内形成了季节性缺氧水体。这种情况的主要成因被认为是流域和城市地区的营养物质不断流入河口和沿海水域。有几项研究报告了珠江河口（PRE）的缺氧事件。然而，缺氧事件似乎是间歇性的，既不是季节性的，也不是全河口范围的。这些事件发生的原因还没有完全理解。本研究的目的是利用 1988-2011 年 24 年的时间序列数据，分析整个河口从城市地区到河口沿海地区夏季溶解氧（DO）的长期变化，并研究缺氧发生的调节因素。结果表明，各种调节因素是造成 PRE 不同区域 DO 变化的原因。自 2000 年以来，PRE 的城市河段、上游和主要河口区的 DO 下降。城市河段缺氧（DO <2.0mg/L），上游区周期性低 DO（DO <3.5mg/L），2000 年后偶发性缺氧，主要受污水排放量增加的影响。主要河口区 2000 年后也出现了间歇性低 DO 和偶发性缺氧。浊度、良好的垂向混合和短停留时间的生态系统缓冲能力，减轻了缺氧形成的压力。与西部陆架相比，东部陆架由于地形较深、锋面位置和水柱分层，更容易受到缺氧的影响。其底层水季节性缺氧，但很少发生缺氧。相比之下，由于地形较浅和停留时间较短，西部陆架很少发生低 DO 现象。简而言之，1988 年至 2011 年 24 年的连续数据表明，PRE 缺乏季节性和全河口范围的缺氧现象。
