长江口及其邻近海域表层水中溶解Mn浓度的季节变化特征

Seasonal variations of dissolved Mn concentration in the surface water of the Changjiang River Estuary and its adjacent area

锰(Mn)是海洋中的生命必需痕量元素。河口位于河流和海洋的交界区域,其对Mn的改造作用会影响陆源Mn向海输送的生物地球化学过程。本研究使用自动固相萃取−电感耦合等离子体联用技术对2019年9月(秋季)、2021年3月(春季)和2021年7月(夏季)长江口及其邻近水域的表层溶解Mn浓度进行了测定和分析。结果显示,溶解Mn的平均浓度和河口行为表现出了季节性差异:夏季的溶解Mn浓度最高,表现为先移除后添加的分布特征;秋季的溶解Mn浓度次之,表现为添加型分布;春季的溶解Mn浓度最低,表现为保守型分布。显著性分析结果表明,长江携带的溶解Mn仅在淡水端元浓度值较高的季节会显著影响长江口及其邻近水域溶解Mn的分布;当长江淡水端元浓度值较低时,长江口溶解Mn则受多种生物地球化学过程的共同主导。长江口的中低盐度海水中高悬浮颗粒物浓度是造成该区域溶解Mn移除的重要因素,而高盐度海水中溶解Mn的添加机制则有待进一步研究。

Manganese(Mn)is an essential trace element for the marine ecosystem.As the transitional zone between rivers and oceans,estuaries have a significant effect on dissolved Mn and its terrigenous input.In this study,the distribution of dissolved Mn,investigated in the surface water of Changjiang River Estuary and its adjacent area during September 2019(autumn),March 2021(spring)and July 2021(summer),was analyzed by automatic solid phase extraction and inductively coupled plasma mass spectrometry.The results indicated that the average concentration and estuarine behaviors of dissolved Mn showed seasonal variations between the three cruises:the maximum average concentration occurred in summer and dissolved Mn was removed firstly and then added with the increase of salinity;the medium average concentration occurred in autumn and dissolved Mn was mainly removed with the increase of salinity;the minimum average concentration occurred in spring and dissloved Mn was mainly conservative with the increase of salinity.The results of significance test indicated that only in the season when the fresh water had high concentrations,dissloved Mn carried by the Changjiang River had significant influence on the distribution of dissolved Mn in the Changjiang River Estuary and its adjacent area;the distribution of dissolved Mn was co-dominated by a variety of biogeochemical processes in the season when the concentrations were low in the fresh water.The high suspended particulate matter concentrations were the important factor of the removal of dissolved Mn in the Changjiang Estuary’s water with medium-low salinity.And the addition mechanism of dissolved Mn in water with high salinity needs further vestigation.