秋季长江口及邻近海域有色溶解有机物的分布及河口混合行为

Distribution and Mixing Behavior of Chromophoric Dissolved Organic Matter in the Yangtze River Estuary and Adjacent Areas in Autumn

【目的】探究秋季长江口及邻近海域有色溶解有机物(chromophoric dissolved organic matter,CDOM)的分布特征与河口混合行为及影响CDOM分布的因素,以深入了解本研究区域CDOM动态变化机制。【方法】测定研究海域溶解有机碳(dissolved organic carbon,DOC)质量浓度、吸收系数a(350)等参数,分析CDOM含量水平;使用三维荧光光谱-平行因子分析(EEMs-PARAFAC)技术鉴别研究海域CDOM荧光组分。运用物理稀释模型分析CDOM河口混合行为。【结果】研究海域b-a4断面DOC质量浓度的变化范围为0.92~2.36 mg·L^(-1),c-a6断面DOC质量浓度的变化范围为1.00~2.40 mg·L^(-1)。b-a4断面a(350)的变化范围为0.22~1.60 m^(-1),c-a6断面a(350)的变化范围为0.15~1.42 m^(-1)。b-a4断面光谱斜率S275-295的变化范围为0.014~0.022 nm^(-1),c-a6断面S275-295的变化范围为0.016~0.024 nm^(-1)。鉴定出4个荧光组分:类腐殖质组分C1(激发波长265 nm、发射波长445 nm)、类蛋白质组分C2(275、325 nm)、类腐殖质组分C3(245、390 nm)和类蛋白质组分C4(235、340 nm)。【结论】长江口及邻近海域DOC质量浓度和a(350)均呈现出由长江口内向口外逐渐减小的趋势,陆源输入是影响CDOM分布的主要因素;远岸S275-295值高于近岸,主要受浮游生物生产活动的影响,陆源输入影响小;4个荧光组分的高值都出现在河口处,且随离岸距离增加而降低,这是受到陆源输入的影响;两个断面的4个荧光组分均符合理论稀释线,CDOM整体呈现保守混合行为。

【Objective】To investigate the distribution characteristics and estuarine mixing behaviour of chromophoric dissolved organic matter(CDOM)in the Yangtze River estuary and adjacent waters in autumn and the factors affecting the distribution of CDOM,to gain insight into the mechanisms of CDOM dynamics in this study area.【Method】The level of CDOM was analysed by determining the mass concentration of dissolved organic carbon(DOC),absorption coefficient a(350)and other parameters in the study area.Excitation-Emission-Matrix spectra and parallel factor analysis(EEMs-PARAFAC)were used to identify the fluorescence components of CDOM in the study area.A physical dilution model was applied to investigate the mixing behaviour of CDOM in the estuary.【Result】The DOC mass concentration in the b-a4 section of the study sea area varied from 0.92 to 2.36 mg·L^(-1),and the DOC mass concentration in the c-a6 section varied from 1.00 to 2.40 mg·L^(-1).a(350)in the b-a4 section varied from 0.22 to 1.60 m^(-1),and a(350)in the c-a6 section varied from 0.15 to 1.42 m^(-1).S275-295 varied from 0.014 to 0.022 nm^(-1)in section b-a4 and from 0.016 to 0.024 nm^(-1)in section c-a6.Four fluorescence fractions were identified:humic-like fraction C1(265,445 nm),protein-like fraction C2(275,325 nm),humic-like fraction C3(245,390 nm)and protein-like fraction C4(235,340 nm).【Conclusion】The DOC mass concentration and a(350)in the Yangtze River estuary and adjacent areas showed a trend of decreasing from inside the Yangtze River estuary to the outside of the estuary,and the input from land-based sources was the main factor affecting the distribution of CDOM;the S275-295 values were higher in the far shore than in the near shore,which was mainly affected by the plankton production activities,and the input from land-based sources had little effect;the high values of the four fluorescence fractions appeared at the estuary,and decreased with the increase of the distance away from the shore,which was influenced by the input from the land-based sources.The four fluorescence components in both sections conform to the theoretical dilution line,and the CDOM as a whole shows a conservative mixing behaviour.