Study On Simulation Of Rural Diffused Pollution Load And Best Management Practices In Jinxiuchuan River Basin

At present,the problem of regional water environmental pollution caused by diffused pollution has become one of the most important environmental hot spots in the world.Rural diffused pollution has certain difficulties in governance and prevention due to its own characteristics.Best management practices(BMPs),which combines non-engineering measures with engineering measures,has become the most effective way to control rural diffused pollution.Jinxiuchuan river basin is one of the important drinking water sources in Jinan.At present,the problem of rural diffused pollution caused by the application of farmland chemical fertilizers and the discharge of domestic sewage is becoming more and more prominent.Therefore,it is of great significance to systematically study the characteristics and prevention of rural diffused pollution in this basin for improving the water environment quality and realizing the sustainable development of the basin ecological environment.The Jinxiuchuan river basin was regarded as the study area,based on the evaluation of current situation of water environment,and HSPF hydrological model was constructed to simulate the flow,total nitrogen and total phosphorus,and temporal and spatial distribution characteristics of rural diffused pollution were analyzed,and the scenario analysis method was used to study the reduction effect and cost-benefit under the situation of measures to screen the best management measures in the basin.The main conclusions are as follows:(1)The water quality of sixteen sampling sections in the basin was tested and evaluated by using the fuzzy comprehensive evaluation model.The results showed that the concentration of total nitrogen and total phosphorus first increased and then decreased during the study period(from March to September),and reached the highest level in July,and then decreased significantly with the increase of river flow.The concentration of total nitrogen and phosphorus in each tributary increased along the flow direction.The water quality evaluation results of Jinxiuchuan river basin were all V-type water,and the water quality was poor.(2)The HSPF hydrological model of Jinxiuchuan river basin was constructed,and the parameters were calibrated,and the model was tested.The results showed that the total relative error of stream flow was 23.88%,and the Nash efficiency coefficient was 0.971;the relative error of total nitrogen was 16.92%,and the Nash efficiency coefficient was 0.722;the relative error of total phosphorus was 28.44%,and the Nash efficiency coefficient was 0.702,which indicated the HSPF model met the requirements of simulation accuracy and had good applicability for the study area.(3)The calculation results of rural diffused pollution load in Jinxiuchuan river basin show that the total nitrogen load is the main source of diffused pollution,and the production of diffused pollution is closely related to flow,and the diffused pollution load increases with the increase of flow during the simulation period,which is more in summer than in winter.The flow is proportional to the precipitation.The precipitation in flood season accounts for more than 1/2 of the whole year,and the flow accounts for about 40% of the whole year,and the diffused pollution load accounts for about 45% of the whole year.From the perspective of spatial variation,the spatial distribution of diffused pollution in the basin is obviously different,and the pollution load gradually accumulates from upstream to downstream.(4)In the evaluation of reduction effect and cost-benefit of scenario BMPs,it was concluded that filter strips with the best reduction effect of single BMP on diffused pollution was 36.25%,followed by constructed wetlands with the reduction rate of 25.53%,and the reduction effect of comprehensive engineering measures was better than that of land use change measures.The reduction rate of diffused pollution under combined BMPs scenarios was higher than the sum of the two BMPs in the combination.Under the scenarios of 2014-2016,the average diffused pollution reduction rate was more than 30%,and the best reduction effect was the combination of returning farmland to forest and filter strips,with a reduction rate of 46.73%.The highest cost-benefit value was constructed wetland,followed by filter strips.Overall,the cost-benefit value of interception measures is higher than that of source control measures,but the construction and maintenance costs of interception measures are higher.