缺氧和酸化是沿海海域普遍存在的环境问题,尤其是在大型河流主导的架子上,东海陆架就是其中的典型。然而,沿海海洋缺氧和酸化状况对河流排放极端的反应仍有待揭示。这项研究调查了夏季干旱对长江口东海陆架缺氧和酸化状况的影响。2023年8月,夏季干旱期间,在长江口东海陆架上测量了碳酸盐系统参数和溶解氧(DO)。不出所料,在地表水中观察到溶解的无机碳(DIC)去除(最高>40μmolkg-1)和DO过饱和(最高>110%)以及高pH(最高>8.15)。然而,低DO(32-172μmolkg-1),在底部水中观察到低pH(7.63-8.04)和低饱和状态指数(ΩAr)(1.34-3.06)。过量DIC与DO消耗的关系,pH值和ΩAr与过量DIC表明,底水的缺氧和酸化主要是由于海洋来源的有机物的再矿化。然而,缺氧和酸化都得到了缓解,即缺氧区域较小,最小DO浓度,2023年8月文石的pH和饱和状态指数高于一般夏季条件下的pH和饱和状态指数。较低的长江排放量(长期月平均值的〜60%)减轻了东海陆架的富营养化,并减少了地表水中的浮游植物生物量,随后减少了底水的缺氧和酸化。然而,即使在夏季干旱期间,东海陆架底部水的酸化仍然很严重。仍然迫切需要调节人为对沿海边缘海的影响,以减轻酸化状况。
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-1) 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-1), low pH (7.63-8.04) and low saturation state index of aragonite (ΩAr) (1.34-3.06) in the bottom water were observed. Relationships of Excess DIC with DO consumption, and pH and ΩAr 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.