2019年长江口及其邻近海域溶解有机物的分布和季节变化特征

2019年3月和7月分别采集长江口及其邻近海域表层和底层的海水样品，测定了其中溶解有机碳（DOC）浓度和有色溶解有机物（CDOM）的吸收光谱。本文根据DOC浓度和CDOM吸收系数a₂₅₄、比紫外吸光度SUVA₂₅₄、光谱斜率S_275-295等参数对该区域溶解有机物（DOM）的分布情况和季节变化进行了研究。结果表明，DOC浓度和a₂₅₄指征的CDOM丰度总体表现出近岸高、外海低的特点；指征CDOM芳香性的SUVA₂₅₄和指征CDOM平均分子量的S_275-295分别随着离岸距离的增加逐渐降低和升高，表明CDOM的芳香性和平均分子量均逐渐降低；两个航次表层的DOC浓度、CDOM丰度、芳香性及平均分子量均显著高于底层；7月和3月相比，DOC浓度、CDOM丰度及芳香性较高，但未发现平均分子量存在显著的季节变化；DOC浓度、a₂₅₄、SUVA₂₅₄、S_275-295均与盐度呈现显著的相关关系，其中，DOC浓度、a₂₅₄、SUVA₂₅₄呈现负相关关系，而S_275-295呈现正相关关系。上述参数与盐度的相关系数（R2）表明，DOC和CDOM在3月较为保守，而在7月（尤其是在表层）不保守程度明显升高。

Distributions and seasonal variations of dissolved organic matter (DOM) in the Changjiang (Yangtze River) Estuary and its adjacent area in 2019

Surface and bottom seawater samples were collected in the Changjiang (Yangtze River) Estuary and the adjacent area in March and July 2019. Concentrations of dissolved organic carbon (DOC) and absorption spectra of chromophoric dissolved organic matter (CDOM) were measured in those samples. During both cruises, concentrations of DOC and abundances of CDOM (reflected by the decreasing a₂₅₄ values) generally decreased from land to sea. At the same time, the decreasing CDOM aromaticity (reflected by the decreasing SUVA₂₅₄ values) and the decreasing overall molecular weights of CDOM (reflected by the increasing S_275-295 values) were also found. DOC and CDOM generally showed significantly higher abundances, higher aromaticity, and higher molecular weights at the surface layer than those at the bottom of the same station. Moreover, the two components showed higher concentrations or abundances and aromaticity in July than in March, but molecular weights had no significant change. During each of the two cruises, DOC concentrations and CDOM parameters (a₂₅₄, SUVA₂₅₄, and S_275-295) all showed significant correlations with salinity, in which S_275-295 showed positive correlations while the others showed negative correlations. From the correlation coefficient values (R2), it can be concluded that DOC and CDOM were more conservative in March than in July, and they were more conservative at the bottom than at the surface in July.