Investigations On Distribution Of Water Quality And Sources Tracing Of Nitrogen Pollution In Wujin District Surface Water

Wujin District,Changzhou City is located in the southern part of Jiangsu Province,various human activities in the region lead to eutrophication of water bodies.As one of the important factors for eutrophication of water bodies,nitrogen pollution could cause the deterioration of water quality,affect the growth of aquatic organisms and trigger a series of ecological problems.Therefore,it is of great significance to study water quality distribution characteristics and nitrogen pollution sources characteristics of surface water for the comprehensive treatment of regional water environment.Based on the collection and monitoring of water samples from the surface water bodies and various pollution sources in the study area for four consecutive quarters,surface water quality was analyzed and evaluated to obtain regional water quality distribution characteristics.Meanwhile,according to nitrogen concentration characteristics and nitrogen and oxygen isotope characteristics of pollution sources,the regional isotope value ranges of typical pollution sources were summarized.On this basis,mass balance model and Bayesian model were used to analyze the sources of nitrogen pollution in the main rivers and lakes.The distribution of water quality parameters in the study area had temporal and spatial characteristics,the concentrations of each index in winter were significantly higher than other seasons,the concentrations of TN,TP,NH3-N,NO3--N,COD and Cl-in the northern part on the canal and Yong'an River were higher in each season.According to Environmental Quality Standard for Surface Water(GB3838-2002),NH3-N,COD,TP were used to evaluate the regional surface water pollution with single-factor water quality assessment.The standard-reaching rates of the Class ? standard for water bodies were 73.7%.while NH3-N was a decisive index that affected the evaluation results.In view of the predominant nitrogen pollution of surface water,the nitrogen indexes of pollution source samples and the characteristics of nitrate nitrogen and oxygen isotopes were analyzed.Results showed that domestic and manure source,chemical fertilizers and industrial source,atmospheric deposition source,soil source and aquaculture source were the main nitrogen sources in regional water bodies.According to the measured isotope values of pollution sources and the research results of earlier studies,value ranges of various nitrogen pollution sources were determined,and that was used as the basis for the analysis of nitrogen pollution sources in regional water bodies.Based on isotope value ranges of nitrogen pollution sources,mass balance model and Bayesian model were used to analyze nitrogen sources of rivers and lakes in the area.The results showed that anthropogenic sources were the main factors influencing regional water nitrogen,the contribution rates of fertilizers and industrial source in spring and summer were higher than that in winter and autumn.The northern part on the canal and Yong'an River with more serious nitrogen pollution,were mainly contributed by domestic and manure source,as well as chemical fertilizer and industrial source.According to the usage conditions and contribution rate allocation of the models,mass balance model could reflect the change trend of the contribution of the main anthropogenic sources between the upstream and downstream sites of the rivers in each season,while Bayesian model could analyze the contribution rates of all nitrogen sources in rivers or lakes as a whole.Therefore,the combination of the two models could effectively improve the efficiency of source resolution.The results could provide a useful reference for the water environment management in Wujin District.