Study On Management Plan Of Non-Point Source Pollution For Water Quality Based On SWAT Model In An Agricultural Watershed In Huai River Basin

The contribution of agricultural non-point source(NPS)pollution to surface water body has been a serious problem with the urban and industrial point source pollution control effectively in China.NPS,which from China’s wide rural areas,has seriously threatened the water environment health.However,such pollution has not been effectively controlled in our country because of its characters of wide range,strong time randomness,and difficulty to quantify the amount of reduction.Therefore,in order to contain the situation of water pollution and protect the ecological water environment,it is necessary to study the migration law of agricultural NPS pollution,and put forward a set of agricultural NPS pollution control scheme suitable for China’s national conditions.Previous studies have focused on the calculation of regional pollution reduction,less consideration of planning from watershed scale,or lack of practical feasibility of the proposed reduction targets.The Bali river Basin was selected for this study because it is a typical agricultural polluted watershed near the estuary of Shaying river into the Huai river.Although the area of this basin is only 425km2,the agriculture activities are highly intensive.A large amount of NPS pollution not noly results in deteriorate of local environment,but also threatens the water quality of downstream.To prevent pollution situation,we have done series of researches.A agricultural NPS pollution simulation of Bali river has been constructed and run,then we find critical pollution source areas of this basin.On the basis of this,we set several schemes to cut local pollution and provide forecast results and some suggestions.The researches and results are follows:First of all,water environment investigation and water quality monitoring were carried out,and the pollution sources were investigated.The results show that,the surface water and groundwater have exceeded the standard in different degrees.The temporal and spatial distribution of nitrogen,phosphorus and CODcr in surface water varied greatly,and the highest concentration of pollutants appeared in November to December.At the same time,high concentration of nitrogen pollutants exists in groundwater under Shibalipu town,Sanshilipu town and Gengpeng town.Secondly,the foundation database of Bali river region agricultural NPS pollution simulation research is established.Based on GIS technology,we build spatial database including Digital Elevation Model,land use type map and soil type map.Also we built attribute database.Then we collected weather,rainfall and pollution information,to simulated ammonia nitrogen,total nitrogen and CODCr NPS pollution process in Bali river region.Through SWAT model adjusting,simulating and verifyng,the service ability and reliability of SWAT model are analyzed and evaluated in Bali river basin.The simulation results of period of 1996～2016 show that,average annual ammonia nitrogen,total nitrogen and CODCr load out of the basin are 1.5,476 and 719.6 tons.Organic nitrogen load is more than 60%of total nitrogen load.The maximum monthly load out of basin appeared in November.By analyzing critical pollution source,we found Liu Gou were the main source of NPS pollution in Bali river basin.On the basis of NPS pollution simulation,the load source structure of ammonia nitrogen,total nitrogen and CODCr was analyzed.It is found that the largest pollution source in the Bali river Basin is starch wastewater,followed by livestock and poultry breeding,while the impact of chemical fertilizer input and domestic sewage is relatively small.Thirdly,the water quality objectives of the Bali river Basin were determined,and the water environmental capacity was calculated and analyzed.The results show that the order of annual environmental capacity is water year>flat water year>dry year,and monthly environmental capacity of June～August are higher than rest of months.In order to ensure the implementation of the water quality target scheme,flow rate in the low water year is set as hydrological design condition.The annual capacity of ammonia nitrogen,total nitrogen and CODCr is 239.7 tons/year,319.6 tons/year and 7259 tons/year respectively.Based on the simulation of non-point source pollution and the calculation of water environmental capacity,the load reduction of each township was determined.The results show that polluted areas undertake tough reduction task,such a s:Geng Peng town,Shencheng town,Shibalipu town and Sanshilipu Town.In These reduction task,the ammonia nitrogen ones are the lightest,however,the total nitrogen reduction between 128～186 tons/year,and the CODCr ones need to achieve reduction between 137～563 tons/year.Finally,based on the above conclusions,different scenarios of pollution sources reduction were selected to simulate and the results were analyzed.It was found that the remediation of starch wastewater and livestock pollution was the most effective pollution control measure for the Bali river basin.Considering the actual factors,we provide three kinds of NPS pollution reduction schemes,then simulated by SWAT.The results show that the all schemes exceeded ammonia nitrogen reduction targets and completed CODCr reduction target basically,however,it is hard to get the goal of total nitrogen reduction targets.Plan 1 completed total nitrogen reduction target,while plan 2 and Plan 3 achieved 60%of reduction targets.These three schemes can be used for different actual demands.Finally,proposals for cuts in the Bali river Basin are proposed.