State Key Laboratory of Estuarine and Coastal Research, Institute of Eco-Chongming, East China Normal University, Dongchuan Rd. 500, 200241 Shanghai, China.
Water Res. 2022 Oct 15;225:119180. doi: 10.1016/j.watres.2022.119180. Epub 2022 Sep 28.
Hypoxia has become a serious threat to the sustainability of marine ecosystems globally. As one of the leading components of eutrophication, river-delivered organic matter (ROM) regulates estuarine/coastal dissolved oxygen condition and contributes to hypoxia formation both directly via remineralization and indirectly via the nutrients released during remineralization. However, the impacts of ROM on the coastal environment have long been underestimated because the indirect contribution has been overlooked and left largely unknown. This study used the Changjiang River, the second-largest ROM source in the world, as a prototype. A coupled physical-biogeochemical model was used to explore the indirect contribution of Changjiang ROM to marginal sea deoxygenation and hypoxia formation. Here I show that ROM remineralization contributed 5.4% directly and 7.3% indirectly to the total oxygen consumption in the off-estuary hypoxic zone. The indirect contribution persistently sustained in a large part of the northwest Pacific marginal seas. Strict mitigation is required to manage the ecosystem impacts of deoxygenation. The findings of this study also indicate that river discharge, freshwater turbidity, and interactions between freshwater and shelf circulation are fundamental factors that regulate the contributions of ROM to hypoxia formation and shelf deoxygenation.
缺氧已经成为全球海洋生态系统可持续性的一个严重威胁。作为富营养化的主要组成部分之一，河流输送的有机物质（ROM）通过再矿化直接调节河口/沿海溶解氧状况，并通过再矿化过程中释放的营养物质间接导致缺氧形成。然而，由于间接贡献被忽视，长期以来人们一直低估了 ROM 对沿海环境的影响。本研究以世界第二大 ROM 源——长江为例。使用耦合的物理-生物地球化学模型来探索长江 ROM 对边缘海脱氧和缺氧形成的间接贡献。结果表明，ROM 再矿化直接贡献了 5.4%，间接贡献了 7.3%，占河口缺氧区总耗氧量的比例。这种间接贡献在西北太平洋边缘海的大部分地区持续存在。为了管理脱氧对生态系统的影响，需要采取严格的缓解措施。本研究的结果还表明，河流流量、淡水浑浊度以及淡水与陆架环流之间的相互作用是调节 ROM 对缺氧形成和陆架脱氧贡献的基本因素。
