2020年夏季长江流域特大洪水期间长江口POC和DOC的分布特征

Distributions of POC and DOC in the Changjiang(Yangtze)River Estuary in response to the extreme flood occurring in the river basin in summer of 2020

为了追踪2020年夏季长江流域特大洪水对长江口及其邻近海域重要生源要素的影响,本研究于2020年7月和2020年8月在该区域连续进行了两个航次的系统观测,测定了表层海水样品中悬浮颗粒物(suspended particulate matter,SPM)、颗粒有机碳(particulate organic carbon,POC)和溶解有机碳(dissolved organic carbon,DOC)的浓度,并将上述两个航次的结果与长江普通洪季月份(2019年7月)的相关结果进行了对比。结果表明,极端洪水导致口门内长江输出较高浓度的SPM、POC和DOC;长江增加的径流量和增加的上述3种陆源物质的输出通量对邻近海域的影响具有滞后性。与其他两个航次相比,在极端洪水影响下的2020年8月,外海海域也具有更高的SPM、POC和DOC浓度。另外,SPM中有机物占比POC(%)、POC/DOC(mol/mol)和POC/PN(mol/mol)3个指标的分布变化结果显示,2020年8月,长江口及其邻近海域具有最为强烈的陆源物质分布信号。

In order to trace the influence of this extreme flood which occurred in 2020 on the river-dominated marine ecosystem,two cruises were carried out in the Changjiang(Yangtze)River Estuary and the adjacent area.During the cruises the concentrations of suspended particulate matter(SPM),particulate organic matter(POC),and dissolved organic matter(DOC)were measured in the surface samples collected at all stations.We compared the results of the above two cruises with those obtain in July 2019.Our results showed that,the flood event in July 2020 greatly elevated the concentrations of SPM,POC and DOC in the Changjiang that were ready to be transported out to the adjacent oceans.There existed a time lag for the influence of the flood on the adjacent area.In the pelagic oceans with higher salinities,concentrations of SPM,POC,and DOC generally showed highest values in July 2020,when compared with the other two cruises in July 2019 and July 2020.During the August 2020 cruise,the three parameters indicating the chemical properties of organic matter,i.e.,POC(%),POC/DOC(mol/mol)and POC/PN(mol/mol),also showed the strongest terrestrial signals among the three cruises conducted in the study area.