Sun Xiangyu, Zhang Jingjing, Li Hongliang, Zhu Yong, He Xingju, Liao Yibo, Jiang Zhibing, Shou Lu, Wang Zhiwen, Jennerjahn Tim C, Chen Jianfang
Ocean College, Zhejiang University, Zhoushan 316021, China; Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China.
Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082, China; Observation and Research Station of Yangtze River Delta Marine Ecosystems, Ministry of Natural Resources, Zhoushan 316021, China.
Sci Total Environ. 2024 Feb 20;912:168875. doi: 10.1016/j.scitotenv.2023.168875. Epub 2023 Nov 25.
With accelerating anthropogenic activities, the overloading of land-derived nutrients and the resultant eutrophication are threatening coastal aquatic habitats worldwide. In semi-enclosed coastal bays, eutrophication is always considered a local problem that can be mitigated by nutrient reduction at a regional scale. However, as the main nutrient drains major global river discharges can have far-reaching effects over hundreds of kilometers alongshore, which are usually not precisely recognized in local coastal zone management. Here, we first quantified the contributions from both local and remote nutrient sources in Xiangshan Bay (XSB), a eutrophic semi-enclosed bay in China 200 km south of the mouth of the Changjiang River (CJR, the world's third largest river), employing a salinity-based conservative mixing model. We found that the nutrients in Xiangshan Bay were mainly supplied by intruded coastal water fed by CJR discharge, contributing 63 % of dissolved inorganic nitrogen (DIN), 65 % of dissolved silicon (DSi), and 49 % of dissolved inorganic phosphorus (DIP) during the summer of 2017, and 75 % of DIN, 75 % of DSi and 60 % of DIP during the winter of 2019. Additionally, long-term interannual trends in the nutrient concentrations of XSB were generally synchronous with those of the downstream portion of the CJR, indicating that CJR discharge seems to be a strong driver of the eutrophication observed in XSB. In contrast, the impact of local nutrient inputs, such as riverine sewage drainage, aquaculture, biogenic activities, and elemental recycling, was much lower and was regionally limited to the inner bay. Interestingly, the DIP contributions of the local and remote sources were similar, indicating the greater relevance of the internal process. Overall, to mitigate eutrophication in large river-adjacent coastal bays, the inter-regional united practices for nutrient source regulation and ecosystem restoration should be permanently applied along the entire river basin-estuary-coastal continuum.
随着人为活动的加速，陆源养分的过度负荷及其导致的富营养化正威胁着全球沿海的水生栖息地。在半封闭的沿海海湾，富营养化一直被视为一个局部问题，可以通过区域尺度上的养分减少来缓解。然而，作为主要的养分排放源，全球主要河流的排放可以在沿岸数百公里范围内产生深远影响，而这在当地沿海地区管理中通常未得到准确认识。在此，我们首先利用基于盐度的保守混合模型，量化了象山港（XSB）（中国长江口以南200公里处的一个富营养化半封闭海湾）本地和远程养分源的贡献。我们发现，象山港的养分主要由长江径流补给的入侵沿岸水提供，在2017年夏季贡献了63%的溶解无机氮（DIN）、65%的溶解硅（DSi）和49%的溶解无机磷（DIP），在2019年冬季贡献了75%的DIN、75%的DSi和60%的DIP。此外，象山港养分浓度的长期年际趋势总体上与长江下游部分的趋势同步，这表明长江径流似乎是象山港富营养化的一个重要驱动因素。相比之下，当地养分输入（如河流污水排放、水产养殖、生物活动和元素循环）的影响要小得多，且在区域上仅限于内湾。有趣的是，本地和远程源的DIP贡献相似，这表明内部过程的相关性更大。总体而言，为缓解大河相邻沿海海湾的富营养化，应在整个流域 - 河口 - 沿海连续体上长期实施跨区域联合的养分源调控和生态系统恢复措施。
