春季长江口颗粒有机碳年际分布变化及其影响因素分析

根据2013—2016年春季(5月)长江口及其邻近海域4个航次环境综合调查数据,探讨春季长江口水体颗粒有机碳(POC)时空分布特征及其环境影响因素。结果显示:2013—2016年春季长江口POC浓度范围为0.22~16.99 mg/L,均值为1.80 mg/L,总水域POC年际间变化显著,底层浓度高于表层。从口门区、近岸区和近海区三个子水域来看,除近岸底层POC浓度处于高值,年际差异不显著之外,其余水域的表、底层均存在空间变异和年际差异。POC浓度在口门附近偏南部水域达到高值,后沿长江冲淡水(CDW)方向降低,低值区位于近海底层,但表层POC在近海水域123°E附近出现次高值。POC浓度与盐度之间具有显著负相关关系,且相关性逐年递减;POC浓度与总悬浮物浓度(TSM)呈显著正相关,底层相关性高于表层;近海区表层POC与叶绿素a正相关关系极显著,二者高值区均分布在123°E附近。入海径流量与长江口春季POC浓度呈现出截然相反的年际变化趋势,径流对有机碳的稀释作用高于其输入作用。长江口春季POC主要以碎屑源为主,其分布与有机碳源、海水的稀释作用、悬浮物运动等多种因素有关,高浊水体中悬浮物影响显著,陆源有机碳对POC的影响在长江口近海水域有所弱化,而浮游植物对POC的贡献凸显。

Interannual distribution of particulate organic carbon and its influencing factors in the Yangtze River Estuary in spring

Based on a comprehensive survey of the four voyages from 2013 to 2016 during spring, the temporal and spatial distribution characteristics of particulate organic carbon (POC) in the Yangtze River Estuary and its adjacent waters were discussed and its environmental impact factors were analyzed. The results show that: (1) From 2013 to 2016 spring, the POC concentration ranged from 0.22 to 16.99 mg/L, with an average of 1.80 mg/L in the Yangtze River Estuary, where the overall annual variation was significant and the bottom layer concentration was higher than the surface layer. There are spatial variability and interannual differences between different waters (entrance area, nearshore area, and offshore area) except the bottom layer of the nearshore area with high-concentration POC; (2) The POC concentration reached a high value in the southern waters near the entrance area, and then decreased in the direction of the Changjiang Diluted Water (CDW) but the surface POC showed a second highest value in the offshore waters near 123°E; (3) There is a negative correlation between POC and salinity, which shows a non-conservative change with salinity. The total suspended matter (TSM) is significantly positively correlated with POC but negatively with POC%, as well as, there is a very significant positive correlation between the surface POC and chlorophyll a in the offshore area where their high-value areas coincide around 123°E; (4) Different from autumn, the interannual variation between the runoff and POC concentration into the Yangtze River Estuary presents a diametrically opposite trend, which indicates that the dilution effect of runoff on organic carbon is higher than its input. (5) The distribution of POC in spring was mainly affected by various factors such as organic carbon sources, seawater dilution, suspended matter movement. Especially, the high-concentration suspended matter has a significant influence on the POC concentration. As the impact of terrestrial input on POC gradually weakened from mouth to the adjacent waters, biological production became the main contribution in the offshore area.