Study On Water Quality And DOM Characteristics In Source Water Reservoir Of The Yellow River Diversion Project

In recent years,with the increasing rate of urbanization,people have over-exploited groundwater resources and reservoirs have become more and more important in urban water supply systems,and reservoirs have become the main water supply source for most cities.Surface water bodies such as reservoirs colored dissolved organic matter（CDOM）resulting in odor problems and disinfection by-products cause greater difficulties for drinking water treatment.Therefore,the study on the characteristics of reservoir CDOM has gradually become a hot spot for reservoir research in recent years.In this study,a storage reservoir of the Jiaodong Yellow River Diversion Project-Menlou Reservoir was selected as the main research object.Based on the eutrophication status index（TLI）,the eutrophication status of the reservoir was evaluated,and the vertical variation of water quality in a year cycle was analyzed;secondly,the water quality of the upstream river was analyzed,and the main causes of eutrophication in the reservoir were identified by combining the results of laboratory simulation of pollutant release experiments;finally,based on three-dimensional fluorescence spectroscopy and UV-Vis absorption spectroscopy,the characteristics of colored dissolved organic matter Finally,based on EEMs and UV-Vis absorption spectroscopy,we identified the components,sources and distribution characteristics of colored dissolved organic matter,explored the differences in the characteristics of colored dissolved organic matter in different seasons,and analyzed the water quality factors and the correlation between the spectral parameters in the reservoirs of the complete Yellow River Diversion Project（Jihongtan Reservoir）and the common type of reservoirs（Zhoucun Reservoir）.The results of the study provide basic information for further investigation of the environmental behavior of CDOM in the water source reservoirs of the Yellow River Diversion Project and the influence of other pollutants on the environmental behavior.The main conclusions of this paper include:（1）The mean value of TLI index of the surface waters of Menlou Reservoir is 63.12,which is in a moderate eutrophic state,and the water quality varies greatly with time.The COD_Mn index contributes the most to the eutrophication of Menlou Reservoir,and the TP index contributes the least to the eutrophication of Menlou Reservoir.The reservoir did not show thermal stratification of water bodies,but there was seasonal DO stratification.For other conventional water quality parameters,there was little difference in the vertical direction,and the water bodies in the reservoir area were well mixed and the water quality was more homogeneous.The reservoir faces a serious nitrate-nitrogen pollution problem,and nitrate-nitrogen from upstream rivers is the main cause of nitrate-nitrogen pollution in the reservoir.（2）The CDOM of the surface water of Menlou Reservoir contains a total of two components,including a humic-like component（C1）and a protein-like component（C2）.Component C1（E_x=355nm,E_m=476nm）is a long-wave humic substance with an excitation peak and emission peak,corresponding to the fluorescence peak C peak（320-360nm/420-460nm）region.Component C2（E_x=225nm,E_m=320nm）has an excitation and emission peak,located in the traditional T-peak region（220-230/320-350nm）,and this fluorescent component is similar to the spectral peaks produced by tryptophan-like substances.The CDOM in Menlou Reservoir has dual sources in different seasons,mainly authigenic sources with weak humification.The CDOM characteristics showed significant differences between water seasons,with the relative concentration levels of humic-like substances in the dry season being higher than those in the normal and wet season,and the CDOM concentration and aromaticity of the water column being higher than those in the normal and wet season,while the molecular masses of water-soluble organic matter were smaller than those in the normal and wet season.The differences in CDOM sources between sample sites in the dry period were small,while the sources of CDOM in the wet and normal season had large differences between different sites.（3）In the comparison of the CDOM characteristics of the three different types of reservoirs,the degree of water humification in Menlou Reservoir was the highest among the three reservoirs,and the concentration and molecular weight of water CDOM were also the highest among the three reservoirs.The proportion of exogenous CDOM input in Zhoucun Reservoir was the highest among the three reservoirs,and Zhoucun Reservoir and Jihongtan Reservoir had strong authigenic characteristics,and the ratio of waterbody de novo CDOM to degraded CDOM was higher than that of Menlou Reservoir.The terrestrial CDOM component in the water column of Jihongtan Reservoir is very low,CDOM is mainly generated from autogenous sources,and the aromaticity of the water column is also relatively low.The results of correlations between water quality indicators and spectral parameters indicated that TN,TP,NO₃-N and NO₂-N were homologous with terrestrial CDOM,while elevated NH₃-N concentrations might inhibit the production of protein-like substances in dissolved organic matter.