State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China.
State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China; Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Xiamen University, Xiamen 361102, China.
Mar Pollut Bull. 2024 Oct;207:116830. doi: 10.1016/j.marpolbul.2024.116830. Epub 2024 Aug 13.
Hypoxia and acidification are universal environmental issues in coastal seas, especially in large river dominated shelves, and the East China Sea shelf is a typical case among them. However, the responses of status of hypoxia and acidification in coastal seas to the extremes of river discharges are still to be revealed. This study surveyed the influences of a summer drought on the status of hypoxia and acidification on the inner East China Sea shelf off the Changjiang estuary. In August of 2023 during a summer drought, carbonate system parameters and dissolved oxygen (DO) were surveyed on the East China Sea shelf off the Changjiang estuary. As expected, dissolved inorganic carbon (DIC) removal (up to >40 μmol kg) and DO over-saturation (up to >110 %) accompanied by high pH (up to >8.15) in the surface water were observed. However, low DO (32-172 μmol kg), low pH (7.63-8.04) and low saturation state index of aragonite (Ω) (1.34-3.06) in the bottom water were observed. Relationships of Excess DIC with DO consumption, and pH and Ω with Excess DIC indicated that the hypoxia and acidification in the bottom water was due mainly to the remineralization of the marine-sourced organic matter. Nevertheless, both hypoxia and acidification were mitigated, i.e. the hypoxic area was smaller, the minimum DO concentration, pH and saturation state index of aragonite were higher in August of 2023 than under the general summer condition. The lower Changjiang discharge (∼60 % of the long-term monthly average) mitigated eutrophication of the East China Sea shelf and decreased the phytoplankton biomass in the surface water and subsequently the hypoxia and acidification in the bottom water. However, acidification of the bottom water on the East China Sea shelf was still severe even during the summer drought. Regulating the anthropogenic impact on the coastal marginal seas is still urgently needed to mitigate the acidification status.
缺氧和酸化是沿海海域普遍存在的环境问题，特别是在大河主导的陆架海域，而东海陆架就是其中的一个典型案例。然而，沿海海域缺氧和酸化状况对河川径流量极值的响应仍有待揭示。本研究调查了夏季干旱对长江口外东海陆架内部缺氧和酸化状况的影响。2023 年 8 月夏季干旱期间，对东海陆架长江口外海域的碳酸体系参数和溶解氧（DO）进行了调查。正如预期的那样，表层水中观察到溶解无机碳（DIC）去除（高达>40 μmol kg）和 DO 过饱和（高达>110%），同时伴有高 pH 值（高达>8.15）。然而，底层水中 DO 含量低（32-172 μmol kg）、pH 值低（7.63-8.04）和方解石饱和度指数低（Ω）（1.34-3.06）。过剩 DIC 与 DO 消耗之间的关系，以及 pH 值和 Ω 值与过剩 DIC 之间的关系表明，底层水中的缺氧和酸化主要是由于海洋源有机物质的再矿化所致。尽管如此，缺氧和酸化都有所缓解，即在 2023 年 8 月，缺氧区域较小，最低 DO 浓度、pH 值和方解石饱和度指数均高于夏季一般条件下的水平。长江径流量较低（约为长期月平均流量的 60%）减轻了东海陆架的富营养化，降低了表层水中的浮游植物生物量，进而减轻了底层水中的缺氧和酸化。然而，即使在夏季干旱期间，东海陆架底层水的酸化状况仍然很严重。仍然迫切需要对沿海边缘海域的人为影响进行调控，以减轻酸化状况。
