Analysis Of Water Pollution Sources In Small Watershed Around Dongting Lake And Application Of QUAL2K Water Quality Model

Human development is inseparable from water resources,The current research on watershed governance mainly focuses on large and medium-sized watersheds.while there are few research cases based on small watershed.Insufficient facilities and lack of relevant data have made small watershed environmental governance difficult.The study of the temporal and spatial variation characteristics of water quality and the analysis of pollution sources in small watersheds are of great significance to the subsequent management of small watersheds.In this study,the small watershed of Baiyang Lake in Yunxi District of Yueyang City was selected as the study area.The pollutant data of the Baiyang Lake watershed was collected through field water quality monitoring.Using methods and technologies such as multivariate statistical analysis,geographic information technology,and water quality models to carry out pollution source analysis and construction of water quality models,the following research results have been mainly achieved:1.The main sources of pollution in the Baiyang Lake are industrial pollution sources,agricultural non-point sources and urban domestic pollution sources.Industrial pollution sources are mainly the enterprise park located in the southwest of the Baiyang Lake;agricultural non-point source pollution sources are scattered in the main stream and tributaries of the Baiyang Lake;and the urban life pollution sources are mainly the Lingang Yatai Garden and the capital of Chuangxin Port.In 2 residential areas,the domestic sewage is directly discharged into Baiyang Lake.2.The concentration of pollutants in Baiyang Lake is mainly affected by temperature and rainfall.The main pollutants in the Baiyang Lake are total nitrogen and total phosphorus.According to the parsons correlation analysis results,TN and ammonia nitrogen have a strong positive correlation with rainfall,and TP has a strong negative correlation with monthly average temperature and monthly maximum temperature.The average concentration of total nitrogen in Baiyang Lake in summer is 2.0 mg/L,the average concentration of total phosphorus is 0.085 mg/L,the average concentration of chemical oxygen demand is 41 mg/L,and the average concentration of ammonia nitrogen is 0.527 mg/L.In autumn,Baiyang LakeThe average concentration of total nitrogen is 1.788 mg/L,the average concentration of total phosphorus is 0.142 mg/L,the average concentration of chemical oxygen demand is 29 mg/L,the average concentration of ammonia nitrogen is 0.433 mg/L,the total nitrogen concentration of Baiyang Lake in winterThe average value is 1.936 mg/L,the average concentration of total phosphorus is 0.074 mg/L,the average concentration of chemical oxygen demand is 36 mg/L,and the average concentration of ammonia nitrogen is 0.213 mg/L.3.The concentration of pollutants in the Baiyang Lake has significant temporal and spatial distribution characteristics.From a spatial perspective,the average concentration of TN at the junction of the main stream and tributaries of Baiyang Lake is generally high,which shows that the nitrogen pollutants in Baiyang Lake mainly come from the tributaries.The monitoring sections with high average concentrations of TP are mostly located near farmland,residential areas and industrial area.In terms of time,the maximum average concentration of pollutants mostly occurs in summer and the concentration values are higher than the standard of surface water class Ⅳ.The minimum value mostly occurs in autumn,but the average concentration of most pollutants also exceeds that of surface water class Ⅳ Standards.4.The water quality of the Baiyang Lake was evaluated using the Nemeiro index modified model.The evaluation results showed that most of the water samples in the Baiyang Lake in summer,autumn and winter belong to the "extremely poor" interval,which indicates the water quality of Baiyang LakeNot optimistic.5.The analysis results of pollution sources in the Baiyang Lake Basin showed that the main pollution sources of Baiyang Lake can be divided into two types.One is a mixed pollution source based on nitrogen and phosphorus pollutants,which mainly include agricultural non-point source pollution,Urban sewage pollution source,and industrial pollution sources.The pollution contribution rate of this type of pollution source is 55.691%.It is another pollution source of livestock and poultry farming that is mainly organic pollutants.It mainly comes from the manure produced by free-range livestock and poultry and aquaculture farms.The contribution rate of this type of pollution source is 19.246%.6.The QUAL2K water quality model was used to simulate the future water quality of the Baiyang Lake,and the output results and the measured value fit well.This shows that the QUAL2K simulation effect in the Baiyang Lake watershed is good and its application is reasonable.the simulation effect of ammonia nitrogen and dissolved oxygen is better than that of total nitrogen and total phosphorus.