Study On The Evaluation And Analysis Of Rural Non-Point Source Pollution Load In Guangyuan City And The Corresponding Control Measurements

Guangyuan city is an extremely important water conservation area to protect the water safety of tens of millions of people in the cities along the downstream of the Jialing River upon its entrance to Sichuan province.However,the non-point source pollution in rural areas of Guangyuan city have become increasingly serious with the economic development,which is bound to have a negative impact on the water quality in the city.It is of great practical significance to identify the main pollution areas,main pollution sources and their response relationship with water quality for the control of non-point source pollution in the rural areas of Guangyuan city.This study makes a comprehensive evaluation of pollutants and pollution sources using isostandard discharge and isostandard discharge intensity based on the field monitoring and statistical data to explore the driving forces of rural pollution load in Guangyuan City.SPSS cluster analysis function was then adopted to classify pollution types and to distinguish the spatial distribution characteristics of rural non-point source pollution load.In addition,Arc GIS was used to perform pollution regionalization to explore the relationship between rural non-point source pollution and water environment quality in typical pollution areas.Finally,models were established by Origin software to predict the water environment quality in the next five years.Last but not the least,cost effective control measuments towards the agricultural non-point source pollution were proposed,for various polluted areas.The main conclusions are as follows:（1）In Guangyuan City,all pollution loads of COD,ammonia nitrogen,TP and TN increased from 2014 to 2020 reaching the respecive peak values in 2018.The contribution rates of 5pollution types towards COD emission from agricultural non-point sources all counties and districts were in the order of:farmland runoff>livestock and poultry breeding>domestic sewage>domestic waste>farmland solid waste.The pollutant discharge in Guangyuan City showed a significant"inverted U-shaped"relationship with economic development,and the inflection point was 10644 yuan（2018）.According to the pollution discharge of each county and district in 2018,the intensity of isostandard pollution load was calculated and analyzed.It was found that Lizhou District had the highest isostandard pollution load intensity of 20.68t·km^-2·a^-1with the main pollutants of TP and TN from the farmland runoff.（2）Based on the data from automatic monitoring system and statistics,the non-point sources pollution emission was dominated in Lizhou District.The highest pollution loads of COD and TP were mainly located in Baolan Town and Longtan Township;the highest NH₃-N load was mainly located in Baolan Town,and the lowest pollution loads were located in Xiaxi Street and Dongba Street.The water quality monitoring data were also evaluated according to the single factor evaluation method.It was found that TP was the worst water quality index in the district.Baolin Town,Dongba Subdistrict and Longtan Township were classified as poor Class V water.According to the comprehensive pollution index evaluation method,the overall water quality was good but the water quality was worse in wet season than the dry season.It was also found that there was a significant positive correlation between isostandard discharge intensity with water quality classification to establish a first order index model.The prediction effect of model was good with the fit degree of 0.944 and RMSE value of 0.4508-1.08.The water quality classification of each region in Lizhou District was predicted during the 14th Five-Year Plan period based on the first-order exponential function growth model.（3）It is predicted that 5 towns（subdistricts）in Lizhou District will not be unable to reach the water environment quality target by 2025.In order to improve the situation,various cost effective control measurements of rural non-point source are proposed from three aspects:source control,process reduction and end treatment for the respective town（subdistrict）.