| In recent years,as the problem of agricultural non-point source pollution has received increasing attention,comprehensive agricultural development projects have been widely implemented nationwide,aiming at controlling non-point source pollution,reducing soil and water loss,and restoring agricultural ecosystems.However,in the process of project construction and implementation,it may lead to changes in the production and life of farmers in small watershed,and have an impact on their soil and water environment.In this study,by selecting Bailong River small watershed in Jiange County Project area of"Yangtze River Green Ecological Corridor Project for Comprehensive Agricultural Development with Asian Development Bank Loan",and combining the questionnaire survey,sampling and monitoring data of the small watershed in three periods before,during and after construction,the output coefficient method,discharge coefficient method and equal standard pollution load method were used to calculate the source intensity of agricultural non-point source pollution.Sand collecting tank method was used to analyze soil and water loss,single factor evaluation and comprehensive pollution index method were combined to analyze water quality and pesticide residues,and improved Nemero index method and other methods were used to analyze changes in soil texture,soil nutrients,soil heavy metals and pesticide residues.The impact of comprehensive agricultural development projects on agricultural non-point source pollution in small watershed was analyzed from the three aspects of non-point source pollution generation,migration and characterization,and the non-point source pollution assessment system of the study area was constructed based on the analytic hierarchy process,so as to comprehensively analyze the non-point source pollution before and after the implementation of Bailong River small watershed project.The main research conclusions are as follows:(1)In the Bailong River basin,planting pollutants account for the highest proportion,followed by rural domestic pollution.TN is the pollutant with the highest pollution load rate.The total isostandard pollution load of agricultural non-point source pollutants will decrease year by year from 2020 to 2022,reaching 37.61×10~6m~3/a in 2020 and 34.8×10~6m~3/a in 2021.In 2022,it was 31.83×10~6m~3/a.Among them,the contribution of planting industry pollutants decreased significantly,which decreased by 10.76%in 2021 and25.95%in 2022 compared with 2020.It may be that the implementation of measures such as the promotion of organic fertilizer,soil testing and formula fertilization in comprehensive agricultural development projects is conducive to reducing the application of chemical fertilizer by farmers,and the construction of slopes can also effectively reduce the amount of pollutants into the river and improve non-point source pollution from the source.(2)From 2021 to 2022,the soil and water loss in Bailong River Basin was 981.83 t and 180.38 t,respectively,which decreased by 81.63%.The main reason is the decrease of rainfall in the study area in 2022,but it may also be due to the fact that slope modification,planning channels,field roads,and mountain-flat pond renovation projects in ADB projects can reduce soil and water loss and improve non-point source pollution during migration and diffusion.(3)The monitoring of soil environmental quality shows that most areas in the study area are silty loam,while a few areas are loam.From 2020 to 20223,the comprehensive fertility index of the five soil sample monitoring sites showed a downward trend.In the past three years,pesticide residues and heavy metal content in soil decreased significantly.Comprehensive pollution in 2022 also decreased compared with that in 2020,which may be caused by the development of soil testing and formula fertilization,biopesticide and organic fertilizer promotion.The monitoring of water environment quality shows that the concentrations of TN and TP have decreased significantly after the implementation of the project,but because the livestock and poultry industry and rural living pollution are less affected by the project,and the rainfall in 2022 is about 50%lower than that in 2020,the river water volume has decreased,and the concentration of COD,BOD5 and other pollutants in the water body has increased.Through point analysis,it is found that reservoir,slope modification and river dike ecological bank protection works can effectively reduce soil and water loss,play a role in soil and fertilizer conservation,and prevent some pollutants from entering the water body.However,the implementation of planning channel,field road and other projects may cause topsoil disturbance,which will have a short impact on the surrounding water quality.(4)The non-point source pollution evaluation system based on analytic hierarchy process was used to comprehensively evaluate the non-point source pollution in the three periods before,during and after the implementation of the project in the study area.The final scores of the study area during 2020-2022 were 0.58,0.55 and 0.23,respectively,indicating that the environmental quality of the study area was improved year by year after the implementation of the comprehensive agricultural development project. |
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