Research On The Relationship Between Agricultural Non-point Source Pollution And Water Quality Response And Risk Zoning In Hunan

Agricultural non-point source pollution has become an important factor restricting the construction of rural ecological civilization and the comprehensive improvement of rural living environment,and has a serious impact on ecological security and ecological economic construction.The occurrence of agricultural non-point source pollution is random and uncertain,accurate monitoring is difficult,and the degree of impact on water environment is uncertain.The response relationship between agricultural non-point source pollution and water environment quality is unclear,and the water environmental quality is rarely considered in the current research on agricultural non-point source pollution zoning.Based on this,this paper takes Hunan as an example,and uses the pollutant discharge coefficient method to calculate the COD,TN,TP and NH₄⁺-N pollutants from agricultural non-point sources（planting,livestock and poultry breeding,rural domestic sewage and aquaculture）at the district and county scale.Emission load and contribution rate;analyze the load degree and spatial distribution characteristics of agricultural non-point source pollution;identify the main pollutants and pollution sources of agricultural sources in various districts and counties in Hunan.Using the monitoring data of rural water environment quality in Hunan,to explore the response relationship between agricultural non-point source pollution load and rural water environment quality,and to determine the load index of agricultural non-point source pollution risk zoning.The first-level risk level division and the second-level pollution control division are carried out to realize hierarchical management and classified control,and provide technical support for agricultural non-point source pollution control in Hunan.The main conclusions are as follows:（1）The pollution load of agricultural non-point source in Hunan was calculated using the pollutant discharge coefficient method and the equal standard pollution load method.The results show that:the total emissions of COD,TN,TP,NH₄⁺-N,the main pollutants of agricultural non-point source in Hunan in 2019,The equivalent pollution loads are 4.69,15.00,9.05,and 54,900 t,respectively;the equivalent pollution loads per unit of land area are 30.18,95.63,57.88,34.12 t/km²,and the unit surface runoff,etc.The standard pollution loads are 3.47,10.92,6.62 and 3.88 mg/L respectively.（2）The equal standard pollution load method was used to identify the main pollution sources and pollutants of agricultural non-point source pollution in Hunan.The results showed that the main pollution sources in Hunan were livestock and poultry breeding and rural domestic sewage,and the equal standard pollution load ratios were35.2%,34.83%;the main pollutants are TN and TP,and their equivalent pollution load ratios are 43.85%and 26.43%,respectively.（3）The monitoring data on the environmental quality of rural surface water in Hunan was analyzed,and the results showed that in 2019,the number of districts and counties in Hunan’s rural water quality category II,III,IV,V,and inferior to V was 3,16,and 15,respectively.The average concentrations of COD,TP and NH₄⁺-N in 46districts and counties have all reached the water quality standard of Class III,and the counties with water above Class IV are all TN exceeding the standard,and TN is the main source of water quality in rural Hunan.categorization factor.（4）The correlation analysis method was used to analyze the response relationship between agricultural non-point source pollution load and rural surface water environmental quality in Hunan.The results showed that the standard pollution load per unit of land area and the standard pollution load per unit surface runoff were significantly related to the water quality category.Positive correlation,the correlation coefficients are 0.9423,0.9083,respectively,and there is no correlation between the standard pollution load and the water quality category;among the four pollutants,TN,TP,NH₄⁺-N and other standard pollution loads per unit of land area and surface runoff are related to water quality.The coefficients are all above 0.9,of which TN is the decisive factor for the water quality category.（5）The group analysis of ArcGIS was used to cluster the pollution load of unit land area and unit surface runoff in Hunan,and the method of equal standard pollution load was used to identify the main pollution sources of each district and county.The results showed that agricultural non-point source pollution in Hunan was divided into There are three risk levels:high-risk area,medium-risk area,and low-risk area.The pollution types are divided into five types:livestock and poultry breeding pollution,rural domestic pollution,aquaculture pollution,livestock and poultry breeding and rural domestic sewage pollution,and compound pollution.Comprehensive risk levels and pollution types,Hunan is divided into 3 first-level areas（pollution risk levels）and 11second-level areas（pollution types）.（6）A zoning method for agricultural non-point source pollution based on standard pollution loads such as unit land area and unit surface runoff was constructed.Through application and verification in Hunan Province,the results show that this method is more in line with the needs of water environment quality management than zoning based on the total amount.