Research On Best Management Practices For Non-point Source Pollution In The Qinshui River Watershed Based On SWAT Model

Non-point source pollution,especially agricultural non-point source pollution caused by human agricultural activities,has become a major factor in the deterioration of water environment quality.Numerous studies at home and abroad have shown that the control of non-point source pollution is already at an imminent stage.The adoption of non-point source pollution control and treatment measures is of great significance to the improvement of water environment in the Watershed.Best Management Practices?BMPs?are a series of measures to avoid pollution caused by agricultural production in the water environment of the river Watershed.It is divided into engineering measures and management measures.The assessment of best management measures has guidance for water environment management in the river Watershed.significance.Taking the Lushui River Watershed in Beijing as an example,this paper analyzes the non-point source pollution characteristics of the Guishuihe Watershed by using the SWAT model assessment tool,and identifies the key source areas according to the loss intensity of the pollutants.Then,different scenarios were set up,and the SWAT model was used to evaluate the efficiency of single-scenario measures and the efficiency of combined scenario measures,and analyzed the reduction effects of each scenario to provide quantitative analysis for non-point source pollution load identification and regulation in the Guishuihe Watershed.The main findings are as follows:?1?Through the field investigation and data collection,the spatial database and attribute database are constructed.The spatial database includes digital elevation map,land use map and soil type map.The attribute database includes meteorological database,soil attribute database and pollution source database.The base and the research area DEM divide the sub-basin,and use the Burn In function in the model to modify the water system,and finally obtain 25 sub-basins and 275 hydrological response units.Using SWAT-CUP to analyze the sensitivity of the model parameters,the runoff,TN and TP were determined and verified respectively at the monthly scale.The verification results were all satisfied with E_NS?0.50 and R²?0.60,indicating that the model has good applicability.?2?By analyzing the model results,the load changes of TN and TP in the study area have obvious period changes,and the load in the rainy season is significantly higher than the annual dry season,which is positively correlated with rainfall.The difference of nitrogen and phosphorus loss intensity in different sub-basins is very obvious.The main distribution trend of TN loss intensity is that the southern part of the basin is larger than the northern part of the basin,and the main distribution trend of TP loss intensity is gradually increasing from upstream to downstream.There is a certain difference in the spatial distribution of nitrogen and phosphorus loss,and there is also a big difference with the distribution of rainfall,indicating that rainfall is only a factor affecting the intensity of nitrogen and phosphorus loss.Land use types,soil properties and other factors also affect nitrogen and phosphorus.Loss strength.In the TN and TP loss pollution contribution load,the forest status ranked first,accounting for 49.44%and 46.23%of the total contribution of TN and TP pollution in the basin respectively;followed by cultivated land,accounting for 30.1%and 29.53%respectively.In terms of TN and TP loss load intensity,they are sorted into residential land?0.39kg/ha,0.18kg/ha?,cultivated land?0.35kg/ha,0.12kg/ha?,and grassland?0.34kg/ha,0.11kg/ha?and woodland?0.24kg/ha,0.07kg/ha?.?3?Using the loss intensity index method to identify the key source areas of non-point source pollution in the study area,according to the natural crack classification method,the nitrogen and phosphorus loss intensity is divided into five grades,namely high,high,medium and low.Low these five grades,the final source of non-point source pollution is the sub-basin of 6,11,17,19,22,and 23 sub-basins,which account for 24.6%of the entire study area,TN load It accounted for 54.3%of the entire study area,TP load accounted for 56.2%,and nitrogen and phosphorus pollution load accounted for more than half of the pollution load of the entire study area.?4?Eight scenarios were set up,including engineering measures and management measures.The efficiency of each scenario was evaluated by converting the various scenarios into parameters and variables of the SWAT non-point source pollution model,of which scenario 2?grassed channel?Scenarios 3 and 4?vegetation buffer?have the best reduction efficiency.The average reduction efficiency for TN is 34.3%,59.5%,and 71.4%,respectively.The average reduction efficiency for TP is 31.0%,60.7%,and 76.7%,respectively.Scenarios5 and 6 Fertilizer Reduction Measures and Scenario 7 No-tillage measures The nitrogen and phosphorus reduction efficiency is less than 10%.The scenario 8 wreckage and tillage cultivation has a good reduction efficiency of TP,which is 12.9%.The spatial variation in the intensity of nitrogen and phosphorus losses in the study area after the adoption of each scenario has also changed.The reduction efficiency of the combined scenario scenario of scenario 2 and scenario 6 and scenario 8 is evaluated.The average reduction efficiency for TN is 38.5%,and the average reduction efficiency for TP is 50.1%.Except for the sub-Watershed of No.11 and No.23,the intensity of nitrogen and phosphorus loss in sub-Watershed in other key source areas has improved.When selecting measures,it is necessary to combine agricultural production activities and water quality management objectives in the local area.