Research On The Temporal And Spatial Characteristics Of Organic Pollution And Its Source In Lake Changdang

Water pollution in river basins,especially organic water pollution,is the key and difficult point of comprehensive management of river basins.As the third largest lake in the Lake Taihu Basin,Lake Changdang has shown moderate eutrophication in the overall water quality of the lake in recent years,especially the chlorophyl a content is much higher than that of many other lakes in the Lake Taihu Basin,and the eutrophication of the water body continues to deteriorate.Therefore,the overall traceability study of organic pollution in the Lake Changdang Basin is of great scientific and practical significance for improving the water quality of the lake and the comprehensive remediation of the river basin in the later stage.This study takes the Lake Changdang Basin as the research object.First of all,it comprehensively evaluates the water quality of the Lake Changdang Basin based on the single-factor index and the comprehensive nutritional state index method,and comprehensively analyses the spatial and temporal changes characteristics of key water body chemical indicators in the Lake Changdang Basin.Secondly,through the three-dimensional fluorescence region integration method and parallel the method identifies the pollution sources in the Lake Changdang Basin.On this basis,the inventory method is used to calculate the pollution load and the contribution rate of the pollution sources in the Lake Changdang Basin.The main conclusions are as follows:(1)The water pollution and eutrophication of Lake Changdang are more serious,and it is more prominent in summer.The environmental quality of surface water of Lake Changdang into the lake,lake area and out of the lake cannot meet the Class III standard.The main pollutants of Lake Changdang into and out of the lake are TN and COD.The main pollutants in the lake area are TN,TP and COD.TP,COD,NH3-N and Chl-a are more serious in summer.TN has a high content in winter and spring.Lake Changdang District is in a state of eutrophication throughout the year,and summer is more serious.Among them,the COD of the river entering the lake,the lake area and the river out of the lake has a linear relationship with NH3-N;while the COD of the lake area and the river out of the lake also has a strong correlation with TP.(2)The three-dimensional fluorescence spectroscopy parallel factor method shows that the main polluted organic matter in the Lake Changdang Basin has three components:land-sourced humic acid,tryptophan-like and microbial humic acid(denoted as C1,C2 and C3 respectively).C1 mainly comes from soil leaching,surface runoff,and decomposition of higher plants;C2 mainly comes from the main components of organic matter in printing and dyeing wastewater;C3 mainly comes from domestic sewage,such as excrement,kitchen waste liquid,washing wastewater,etc.and microbial activities.Through the correlation analysis of each component,the component C1 of the Lake Changdang Basin has a strong correlation with C3,indicating the homology of humus organic matter and microbial metabolites during this period.The enhancement of the correlation between the components C2 and C3 in summer and autumn indicates that protein substances are homologous with microbial metabolites,during which proteins may be produced by microbial metabolism.In the analysis of characteristic values,it is concluded that Lake Changdang is mainly polluted by internal sources,and microbial activities are obvious,but it is also affected by certain land sources.(3)The list method analyses the pollution sources in the Lake Changdang basin and finds that the four parts of sewage treatment plants,farmland runoff,aquaculture and Lake Changdang internal sources have a high contribution to COD,TN and TP.Among them,COD is mainly the contribution of aquaculture,sewage treatment plant and farmland runoff;TN is mainly the contribution of farmland runoff,other land runoff and aquaculture;TP is mainly a contribution of sewage treatment plant,livestock and poultry breeding and farmland runoff.In the vicinity of Lake Changdang and Hutou Bridge,most of the pollution is caused by the internal source of Lake Changdang.The accounting of internal and external pollution sources in the Lake Changdang Basin shows that COD external pollution sources account for 74%,and internal pollution sources account for 26%.TN exogenous pollution sources account for 88%,and endogenous pollution sources accounted for 12%.TP exogenous pollution sources account for 66%,and endogenous pollution sources account for 34%.COD external pollution sources in the control area account for 19%,and internal pollution sources account for 82%.TN external pollution sources account for 31%,and internal pollution sources account for 69%.TP external pollution sources account for 6%,and internal pollution sources account for 94%.The endogenous pollution source has become the main pollution source of Lake Changdang.