Investigation And Analysis Of Pollution Sources In Dongpu And Dafangying Reservoirs

Dongpu and Dafangying Reservoir are the drinking water sources of Hefei City,and their water quality affects the hearts of countless Hefei people.In recent years,under the strong leadership of the Party Central Committee and the vigorous rectification of the local government,the water quality of Dongda Reservoir has been improving year after year,but there is still a lack of specific understanding of the sources of pollution in the watershed.The precise control of pollution brings challenges.In order to study and analyze the pollution sources of Dongpu and Dafangying reservoirs,this study lasted for one year（July 2020 to June 2021）,and conducted field investigations on pollution sources within the watersheds of Dongpu and Dafangying reservoirs.Collect and organize surveys and other related data,calculate and analyze the amount of contamination in storage.The conventional water quality indicators of18 points in the reservoir area and 14 points of the rivers entering and leaving the reservoir are monitored by on-site measurement,sampling and laboratory analysis,and historical data are collected and sorted.Two points in the upstream and downstream of the two reservoirs were selected to carry out stable isotope tracing on the sources of nitrate nitrogen to understand the main sources of nitrate nitrogen pollution in the reservoir area.The results of the study are as follows:（1）Monitor COD,ammonia nitrogen,nitrate nitrogen,total nitrogen,total phosphorus,total dissolved phosphorus,chlorophyll a and other indicators at 18 points in the reservoir area and 14 points in the rivers entering and leaving the reservoir,and combined with historical data,The comprehensive nutritional status index method was used to evaluate the water quality.The results show that during the period from July2020 to June 2021,the water quality of the rivers entering the reservoir could not stably reach the surface class III water quality standard,and the water quality in the reservoir area was generally maintained at the class II-III level.From a spatial point of view,there are obvious upstream and downstream differences between the two reservoirs.In general,the total nitrogen content of the water quality indicators in the Dongpu and Dafangying reservoir areas was the highest,with the peak values reaching1.08 mg/L and 1.13 mg/L,respectively.The inflow water from the upstream（the inflow of the river）,the reservoir bay and the reservoir branch are higher in concentration than the downstream near the dam.Judging from the comprehensive nutritional index,the average comprehensive nutritional index of Dongpu Reservoir is47.7,and the comprehensive nutritional status index of Dafangying Reservoir is slightly lower than that of Dongpu Reservoir,with an average of 45.5.The two reservoirs are basically in the middle nutrient level and the water quality is good.（2）Using nitrogen stable isotope tracing technology,qualitatively analyze the sources of nitrate nitrogen pollution in Dongpu Reservoir and Dafangying Reservoir.Two points in the upstream and downstream of the two reservoirs were selected to trace the source of nitrate nitrogen pollution.Comparing theδ¹⁵N ranges of different nitrate nitrogen pollution sources,it can be seen that the nitrate pollution in Dongpu Reservoir and Dafangying Reservoir mainly comes from rainfall,soil organic matter and inorganic fertilizers.Verification by other means shows that surface runoff is the main source of pollution,so the nitrate pollution in the reservoir area may be caused by rainwater scouring the soil along the way into the reservoir river,and the inflow river flowing into the reservoir area.（3）Based on the PMF model,the pollution sources of Dongpu Reservoir and Dafangying Reservoir were quantitatively analyzed,and their comprehensive pollution contribution rates were obtained.The pollution contribution rate of Dongpu Reservoir in descending order is:urban surface runoff pollution（30.3%）>agricultural non-point source pollution（28.6%）>large-scale livestock and poultry breeding（25.0%）>rural domestic pollution（16.1%）;The pollution contribution rate of Fangying Reservoir in descending order is:urban surface runoff pollution（34.5%）>large-scale livestock and poultry breeding pollution（26.5%）>agricultural non-point source pollution（19.6%）>urban domestic sewage（19.4%）.（4）The Dongpu and Dafangying Reservoir watersheds are part of the Chaohu Lake watershed.Refer to the guidelines such as the five-phase pollution source accounting coefficient around Chaohu Lake,and combine the actual situation of the watershed to determine the storage coefficients of various pollutants and calculate the pollutants storage coefficients.According to calculations,within the watersheds of Dongpu and Dafangying reservoirs,the storage volume of COD is 1999.66t/a,the storage volume of ammonia nitrogen is 88.71t/a,the storage volume of total nitrogen is 249.71t/a,and the storage volume of total phosphorus is 1999.66t/a.It is15.97t/a.According to the analysis of administrative regions,the amount of pollutants entering the reservoir from high to low is Changfeng County>Shushan District>Luyang District.According to the analysis of pollution sources,the inflow COD of Dongpu and Dafangying Reservoir mainly comes from urban surface runoff（1224.04t/a）and farmland non-point source（370.69t/a）.