Analysis Of DOM Composition Characteristics,spectral Characteristics And Source Analysis Of Water Bodies In Xi’an During The Typical Period

Water body DOM is closely related to the cycle of carbon dioxide in its environment,the photosynthesis of plants in the water,the metabolism of total microorganisms in the water,and the redox of pollutants.Therefore,the composition,spectral characteristics and sources of DOM in the water environment are one of the key areas of concern and research in the environmental pollution control community.Using three-dimensional fluorescence spectrophotometry and ultraviolet spectroscopy and other measurement methods,parallel factor analysis and correlation analysis,to explore the fluorescent components,ultraviolet fluorescence spectral characteristics and sources of DOM in water bodies in Xi’an during typical periods,and to explore DOM ultraviolet fluorescence spectral parameters correlation with water quality parameters in order to discover spectral parameters used to characterize and enable rapid detection of DOM content or properties.In order to reveal the migration law of water body DOM and its environmental indication significance,it can provide a basis for water quality improvement and ecological environment restoration.The p H,DO and EC of water bodies in Xi’an are 6.91-8.91,4.2-16.7 mg/L and 144-2050μS/cm,respectively.The p H of the water body is the lowest in the dry season,and the DO and EC are the highest;The DOC content in the water bodies are 1.69-9.74 mg/L,and the average concentration of DOC in the three periods is from high to low:normal water period,dry period and wet period.The DOM of the water bodies in the dry,flat and wet periods of Xi’an all contain ultraviolet light-like humus and visible light-like humus,the DOM also contain protein-like humus in the dry and flat water periods,and the marine humus and phytoplankton produced humus in the wet period.The sum of the two types of humus in the DOM in the dry season is 74.12%,the proportion of protein-like and two types of humus（C1+C2）in the DOM in the flat water period is 47.67%and 52.33%,respectively.In the wet season,the proportion of fulvic acid-like C1 in DOM was 52.73%,and the proportion of humic acid-like C2 was 26.55%.The DOM in the water body in the dry season is dominated by humus-like substances,and the main fluorescent components of DOM in the wet season are humic-like substances（fulvic-like and humic acid-like）.The UV₂₅₄,UV₂₅₃/UV₂₀₃,SUVA₂₅₄,SUVA₂₆₀,E₂/E₃,E₃/E₄,S_350-400 and S_R of water DOM are 0.024-0.234 cm^-1,0.009-0.124,1.30-9.01 L·（mg·m）^-1,1.20-8.47 L·（mg·m）^-1,3.6-29.0,2.5-31.0,0.001-0.050 nm^-1 and 0.30-3.17,respectively.The relative order of UV₂₅₄,α₃₀₀,α₃₅₀,α₃₅₅,hydrophobic components and humus content of DOM in water bodies is:wet season>dry season>flat water period,and the degree of substitution of benzene rings is in the following order:high water period>flat water period>dry season.The molecular weight of DOM in the water in the flat water period is relatively low,and the degree of aromatization of the DOM in the water in the wet period is relatively strong.In the three periods,the degree of benzene ring substitution of DOM in the river water bodies are higher in the downstream than in the upstream,while the substitution degree of benzene in the DOM in the Feng River and the relative content of hydrophobic components are lower in the downstream than in the upstream.The content of hydrophobic components in DOM in Ba River,Wei River and Yu River in dry and flat water periods are higher in the downstream than in the upstream.The FI,HIX,BIX andβ:αof water bodies DOM are 1.50-2.54,0.58-78.26,0.56-3.98 and 0.53-3.11,respectively.In dry season,the sources of DOM in water bodies are mainly endogenous sources,and some water bodies have the characteristics of mixing endogenous and exogenous sources,with strong or moderate intensity of autogenic characteristics,and the degree of humification is weak.During the flat water period,most of the water bodies had obvious autogenic characteristics of DOM,the proportion of newly generated DOM in the DOM is relatively large,and the degree of humification is weak.During the wet season,most of the DOM sources in the water bodies are mainly mixed with endogenous and exogenous sources,and had strong humus characteristics,while autogenic characteristics are relatively weak.The UV₂₅₄,α₃₀₀,α₃₅₀,α₃₅₅ and fluorescence intensity of fluorescence peak D in Xi’an water bodies can indirectly indicate the content of COD,I_Mn and DOC in the water body of the three phases,and the UV-type humic substances.The autogenic characteristics and aquatic biological activity of water DOM are positively correlated with the protein-like content of DOM.E₂/E₃ and E₃/E₄ and S_350-400 of water body DOM in dry season and wet season are positively correlated with each other（P<0.01）.