Study On The Relationship Between DOM Spectral Fingerprint Characteristics And Water Quality Response In Wuliangsuhai Watershed

Wuliangsuhai is located in Bayannaoer City,Inner Mongolia Autonomous Region.It is one of the eight freshwater lakes in China,and it is a typical farmland lake.In recent years,the concentration of pollutants in lake water has increased,and the water quality of lakes has gradually deteriorated.Therefore,this paper focuses on the spectral characteristics of dissolved organic matter（DOM）in Wuliangsuhai from 2018 to 2019and the response relationship between DOM and water quality.The DOM in Wuliangsuhai water body was characterized by UV Vis,EEMs and FTIR.The composition,structure,source and humification degree of DOM in different seasons were identified.By using the structural equation model and water quality parameters,the relationship between main influencing factors and DOM components is constructed,and the direct and indirect factors that cause DOM component changes are explored.The results show that:（1）the water quality indexes of Wuliangsuhai show a certain spatial and temporal difference.The COD basically exceeds the standard of Class IV water bodies throughout the year.The concentration of TN and TP is higher in autumn and winter.The pollution level throughout the year is winter>spring>autumn>summer.（2）According to the characteristics of the ultraviolet spectral index,it can be seen that the DOM concentration in the northern waters is higher than that in the central and southern waters.Water from the near-drainage area is mainly input by external sources,and water from the far-drainage area is released internally.The degree of humification is highest in the northern waters,followed by the southern waters,and the lowest in the central waters.The proportion of fulvic acid in the water near the outlet is high,and the proportion of humic acid in the water near the outlet is high.（3）The infrared transmission peaks of the samples from the Lake entrance and the lake area show some differences.It is mainly reflected in the changes of polysaccharides,proteins and aromatic unsaturated substances with seasonal changes.The content of DOM in the lake area and the water at the entrance of the lake changed with the change of seasons to the material with a high degree of humification.DOM in the water body of the lake changes with the water flow,except that in winter it changes to the material with a lower degree of humification,and in other seasons it changes to the material with a higher degree of humification.（4）DOM in Lake area and drainage area mainly contains protein-like and fulvic acid-like components.The content of DOM in the drainage area is larger than that in the Lake area with seasonal changes,but the trend of DOM changes is similar to that in the Lake area.The protein like components reached the highest in spring,then decreased gradually,reached the lowest in autumn,and then began to rise in winter;fulvic acid was the opposite.Due to the photodegradation effect,DOM in ice is mainly composed of protein-like components.According to the spectral indexes（FI,BIX,HIX）,DOM mainly comes from the endogenous input in spring,mixed partial endogenous input in summer,mixed partial exogenous input in autumn and winter.（5）The correlation analysis shows that fulvic acid and total phosphorus have similar migration rules,and their sources are likely to come from the discharge of domestic sewage.The content of nitrogen and phosphorus is closely related to the water quality of Wuliangsuhai.The increase of COD content in the lake area is closely related to the input of fulvic acid-like components.The quality of water quality shows the same change rule with the content of TN and TP.Protein like components,fulvic acids like components and water quality parameters can directly or indirectly affect the degree of humification in water.In the indirect influence,the humification degree of the water body is mainly affected by the source of organic matter.DOC,HIX and A₂/A₁are the main indirect factors.