2023年7月长江特枯水情下长江口营养盐的分布特点  

Distribution characteristics of nutrients in the Changjiang River Estuary under the watershed extreme drought in July 2023

作　　者：力清影 姚爱林 蒋昕桐 明玥 王梦宇 朱礼鑫 王宪业 高磊[1] Li Qingying;Yao Ailin;Jiang Xintong;Ming Yue;Wang Mengyu;Zhu Lixin;Wang Xianye;Gao Lei(State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai 200241,China;State Environmental Protection Key Laboratory of Marine Ecosystem Restoration,National Marine Environmental Monitoring Center,Dalian 116023,China)

机构地区：[1]华东师范大学河口海岸学国家重点实验室,上海200241 [2]国家海洋环境监测中心国家环境保护海洋生态环境整治修复重点实验室,辽宁大连116023

出　　处：《海洋学报》2025年第1期36-50,共15页

基　　金：上海市教育委员会科研创新计划重大项目(2021-01-07-00-08-E00102);国家自然科学基金(42276217,U2243207,42249903);基金委共享航次(NORC2023-03)。

摘　　要：长江入海径流量极大地控制着长江冲淡水在长江口的扩散范围,以及河口生源要素的生物地球化学行为。2023年7月,长江流域发生了历史罕见的洪季干旱事件。为了研究洪季长江特枯水情下长江口营养盐的分布特点,于当月在长江口海域进行了32个典型站位的样品采集,并将其结果与2016年和2020年洪季长江洪水到达长江口前后的采样结果进行对比。在2023年7月流域干旱条件下,河口盐淡水混合区域收缩,N O_(3)~--N和SiO_(3)^(2-)-Si产生不保守过程的时间和空间均受限,导致这两种营养盐与2016年和2020年洪季相比更加保守。同时,由于在长江特枯水情下河口表层低、中盐度(<25)的海水被局限在水深较浅的区域,使得底部通过沉积物再悬浮释放的PO_(4)^(3-)-P较易被输送至海水表层,从而促进了表层PO_(4)^(3-)-P浓度的升高以及“源”效应的产生。而随着盐度的继续升高,表层浮游植物吸收施加的“汇”效应的影响逐步显现;并且随着深度增加,沉积物再悬浮释放的PO_(4)^(3-)也越来越难以贯穿至海水表层,两者共同作用导致PO_(4)^(3-)-P浓度在高盐度(>25)海水表层迅速下降。由此,2023年7月表层PO_(4)^(3-)-P浓度随盐度的变化表现出了特殊的“上凸”趋势。在目前长江径流量年际间较大变幅的情景下,本研究丰富和深化了对长江口生源要素生物地球化学过程的认识,也有助于进一步回答长江口等磷限制型河口中赤潮的触发机理等关键科学问题。The freshwater discharges of the Changjiang(Yangtze)River into the sea largely control the extension range of the Changjiang Diluted Water in the estuary and the inherent biogeochemical behaviors of biogenic elements.In July 2023,a summer drought event occurred in the Changjiang River basin,with extremely lower river discharge.In order to study the distribution characteristics of nutrients in the Changjiang River Estuary in response to this drought,samples were collected from 32 stations in the Changjiang River Estuary that month,and the results were further compared with those obtained before and after the arrivals of the Changjiang River watershed floods occurring in the summers of 2016 and 2020.Under the drought condition in July 2023,the estuarine mixing area of freshwater and seawater greatly shrank,and the time and space for the occurrences of non-conservative processes of NO_(3)^(-)-N andSiO_(3)^(2-)-Si were largely restricted,resulting in that these two nutrients being more conservative compared to those in the flood seasons of 2016 and 2020.At the same time,since the surface seawaters with low-to-medium salinity values(<25)under the drought condition were confined to areas with shallower water depths,PO_(4)^(3-)-P released through sediment resuspension from the bottom was more easily transported to the surface,and thePO_(4)^(3-)-P concentrations at surface increased and displayed a“source”mode.As the salinity continued to increase,the impact of the“sink”mode owing to surface phytoplankton assimilation gradually became dominant.In addition,with the increasing water depths,the PO_(4)^(3-)-P released via bottom sediment resuspension could not penetrate into the surface layer anymore.The combined effect of the above two processes led to a rapid decrease inPO_(4)^(3-)-P concentrations at surface when salinity was higher than 25.Thus in July 2023,the surfacePO_(4)^(3-)-P concentrations showed a special“concave”trend.This study enriches and deepens our understanding on the response and feedback mech

关 键 词：营养盐 洪季 干旱 生物地球化学 不保守行为 长江口 

分 类 号：P734.44[天文地球—海洋化学]