Photochemical Characteristics and Source Analysis of Dissolved Organic Matter in Tidal Creek System of Chongming Dongtan
The concentration of dissolved organic carbon(DOC),UV-visible light absorption characteristics and three-dimensional fluorescence spectrum characteristics of chromophoric dissolved organic matter(CDOM)were measured in surface water collected from typical tidal creeks of Chongming Dongtan during the spring tide in July 2018.Combined with parallel factor analysis and statistical analysis,the sources,composition and influencing factors of dissolved organic matter in salt marsh wetland during the flood and ebb tides were discussed.The results showed that the UV absorption coefficient at 355 nm,a(355),during the tidal process was significantly correlated with DOC concentration,which characterized DOC concentration and behavior to a certain extent.The spectral slope Sg and specific ultraviolet absorbance SUVA254 indicated that the aromaticity of salt marsh water was stronger than that of estuarine water,suggesting the important role of terrestrial input.The three-dimensional fluorescence spectrum of CDOM revealed that it contained terrestrial humic-like substances,protein-like substances and marine humic-like substances,which were significantly correlated with tidal changes,in which C2 components from terrestrial higher vegetation were consistent with tidal height changes.The fluorescence index(FI)and humification index(HIX)of the sampling water were 1.19～1.40 and 1.71～2.75,respectively,and biological index(BIX)＜1.The dissolved organic matter in the water was mostly terrestrial input,but the humification degree was relatively low.Based on the results of principal component analysis and fluorescence characteristics analysis,the terrestrial organic matter from higher plants or soil organic matter dominated the source of CDOM.The composition of dissolved organic matter in salt marshes was complex and changeable due to the combined effects of local resuspension,pore water release and tidal lateral transport.In the future,it is necessary to expand the time and space comparison to explore the generation,demise and trajectory of CDOM.
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