Distribution and Mixing Behavior of Chromophoric Dissolved Organic Matter in the Yangtze River Estuary and Adjacent Areas in Autumn
[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.
the Yangtze River estuary and adjacent areaschromophoric dissolved organic matter(CDOM)dissolved organic carbon(DOC)absorption spectrumfluorescence spectrum
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