Analysis Of Water Pollution Characteristics And Load Of Non-Point Source Pollution In Yazhou Section Of Ningyuan River

With the rapid growth of economy in our country,the water ecological environment has been seriously damaged and the problem of water environmental pollution has become more and more serious,which has a serious impact on the sustainable development of the economy and society,the production and life safety of the people.Ningyuan River is the fourth longest river in Hainan Province,the upper reaches is the largest water supply source in Sanya City,and the middle and lower reaches are the main water source for agricultural water in Yazhou District.Maintaining and keeping the water quality of Ningyuan River is very important for the sustainable development of social economy in Yazhou.In order to promote the environmental protection and rational development of Ningyuan River,this paper investigates the pollution sources,coastal living and production of the Yazhou section of Ningyuan River by means of investigation and typical section monitoring methods,carries out the sampling detection for 13 sections and 3 sewage outlets of the river basin,analyzes the pollution characteristics and non-point source pollution load of the river basin,clears the causes of water pollution in this basin,and then puts forward the pollution control and management measures,so as to provide scientific basis for non-point source pollution control and water environment protection in Ningyuan River.The main conclusions are as follows:1.The detection and evaluation of water quality in Yazhou section of Ningyuan River shows that the water body in this section has been slightly polluted and tends to deteriorate.The main pollution factors in Ningyuan River Cliff are total nitrogen and total phosphorus,the total nitrogen content of which increased year by year in 2018 and 2019,and reached 1.22mg/L in 2019,which has surpassed the Grade-III standard of surface water?GB 3838-2002?;Total phosphorus increased year by year from 2016 to 2019,reaching 0.093 mg/L in 2019 and approaching the Grade-III standard of surface water.From 2016 to 2019,the comprehensive pollution index of Yazhou section of Ningyuan River is between 0.65 and 1.17,the water quality is slightly polluted and tends to worsen.2.The research clarifies the pollution distribution characteristics and causes of the upper,middle and lower reaches of Yazhou section of Ningyuan River.?1?Dalong Reservoir to the Longtan River estuary is the upper reaches,which belongs to the hilly land,the main stream of Ningyuan river bank is the natural coastline,and the mountains around the basin are mainly secondary forest;The tributary of Longtan River flows through Bijialing and Langdiantianyang.Four main monitoring sections are arranged in the upper section,representing the water quality of secondary forest-farmland ecosystem.The monitoring results show that the water quality in the upper reaches of Yazhou section of Ningyuan River is good,which meets Grade-II standard of surface water environmental quality?GB 3838-2002?,the water quality of the main stream is hardly affected.?2?Longtan River estuary is the middle section of the Bandai bridge,the riverbank is mainly natural coastline,the area of the sloping fields in the north-west coast is about 12700 mu,the area of the Baichao fields in the southeast coast is about 3800 mu,anti-season vegetables are mainly planted.The middle section is set up 3 main monitoring sections,representing the water quality of the river of farmland ecosystem.The monitoring analysis shows that the water quality in the middle section is Grade-III of surface water environment.The cultivated land in this section is more and the water quality is mainly affected by agricultural non-point source pollution.The main pollution factors are TN,CODCr,TP and BOD_5,among which the total nitrogen concentration is as high as 2.94 mg/L,which exceeds the Grade-V water.?3?Bandai Bridge to the Ningyuan River estuary is the lower section,spur dike revetment project is constructed on the river bank,which flows through Yazhou city,and there are many drainage outlets for rainwater or domestic sewage in the river reaches.In the lower part,6 main monitoring sections and 3 main sampling points are set up,which represents the water quality of the river of urban ecosystem.The monitoring results show that the water quality in the lower section is poor as a whole,which belongs to Grade-?water quality of surface water environment.The primary pollutants are fecal coliform and total nitrogen.The fecal coliform mainly comes from domestic sewage discharge,and the amount of fecal coliform in the outlet of the health centre is up to 700000,exceeding 16.5 times of the Grade-V standard of water.The main source of total nitrogen is agricultural non-point source pollution and domestic sewage discharge,the total nitrogen concentration of market domestic sewage outlet is up to 14.84 mg/L,exceeding 6.4 times of Grade-V standard of water.At the same time,total phosphorus,five days'biochemical oxygen demand,chemical oxygen demand,ammonia nitrogen and other secondary pollutants have also caused local pollution,the main reason is because of the more intensive production activities,there are a large number of domestic sewage and agricultural irrigation tail water flowing in and affecting water quality.3.Non-point source pollution is the main cause of water quality deterioration in the middle and lower reaches of Ningyuan River,a quantitative analysis of non-point source pollution load is carried out in Yazhou section of Ningyuan River..According to the field survey and analysis of pollution characteristics,the main cause of water quality in Yazhou section of Ningyuan River is non-point source pollution.By investigating the living conditions,sewage discharge,agricultural cultivation and aquaculture production of residents along the Ningyuan River,on the basis of the data collection,sorting,calculation and analysis,the non-point source pollution load of the Yazhou section of Yongyuan River is obtained as follows:the intakes of COD,TN,TP and NH3-N in Yazhou section of Ningyuan River coast are 4006.14 t/a,236.87 t/a,14.21 t/a and 175.46 t/a respectively.Only agricultural non-point source accounts for 93.13%in COD intake,followed by domestic sewage,which accounts for 4.63%;The agricultural non-point source accounts for 76.19%,domestic sewage accounts for 13.7%,and livestock and poultry breeding accounts for 9.53%in TN intake.The domestic sewage in TP intake is the first,which accounts for 52.23%,followed by agricultural non-point source accounting for 44.42%;The agricultural non-point source accounts for 77.13%,domestic sewage accounts for 13.22%and livestock breeding accounts for 9.65%in NH3-N intake.Overall,the highest proportion of pollution load in Yazhou section of Ningyuan River is agricultural non-point source pollution,followed by domestic sewage,which is in consistent with field survey results and analysis of pollution characteristics..4.The countermeasures and suggestions for environmental protection of Ningyuan River are put forward.Combined with the pollution characteristics and non-point source pollution load of the river basin,this paper makes a comprehensive analysis on the pollution causes in Yazhou section of Ningyuan River,and clarifies the main pollution sources and causes of pollution in this basin.On this basis,the paper puts forward five measures of water environment management and pollution control,such as strengthening water environment management,systematically promoting ecological restoration,strengthening the control of domestic pollution source,controlling agricultural pollution and strengthening biodiversity,so as to provide scientific decision-making basis for water environment protection management and pollution control in Ningyuan River.