Study On The Characteristics Of Non-point Source Pollution In A River Basin

In recent years,with the control of point source pollution,non-point source pollution has been recognized as the primary source of water pollution,causing serious ecological environmental problems.Therefore,it is of great theoretical and practical significance to carry out the research on the characteristics of non-point source pollution in river basin for the comprehensive management and protection of river water environment.In this paper,the Mouwen River Basin is selected as the research object.The Mouwen River Basin is a typical area of water erosion in Tai-yi Mountains,Central South of Shandong Province.In recent years,the water pollution in this area is serious,the ecological environment is deteriorating,and the problem of non-point source pollution is prominent.Based on meteorological data,DEM digital elevation,soil,land use,runoff,and nutrient(total nitrogen and total phosphorus)data from2010 to 2017,a SWAT non-point source pollution model was established,through the model simulation,this paper studied the watershed non-point source under different hydrological conditions of total nitrogen,total phosphorus pollution load time and space distribution characteristics,this paper quantitatively analyzed the main sources of non-point source pollution and the contribution of different land use types to the nitrogen and phosphorus pollution load in the river basin,and it put forward the corresponding non-point source pollution control measures according to the actual situation of the river basin.It is expected to provide a theoretical basis for the comprehensive management of water environment in Mouwen River Basin.The main research conclusions are as follows:(1)This paper established a SWAT non-point source pollution model in the Mowen River Basin,and it used SWAT-CUP software to conduct sensitivity analysis on runoff,sediment,nutrients and other related parameters,and it carried out calibration verification on runoff,total nitrogen and total phosphorus in the Mowen River Basin from 2010 to 2017.The comprehensive evaluation of ENS and R2 showed that both of them met the requirements of model accuracy,suggesting that SWAT model was suitable for the simulation of non-point source total nitrogen and total phosphorus pollution load in the Mowen River Basin.(2)From the perspective of time variation,the annual variation trend of TN and TP pollution loads from non-point sources in the basin is consistent with that of precipitation and runoff in wet years,normal years and dry years.The TN and TP pollution loads from non-point sources in the basin increase with the increase of precipitation and runoff.In interannual variation,the annual load of total nitrogen and total phosphorus from non-point sources in the basin is wet year > normal year >dry year.From the perspective of the spatial distribution,in typical hydrological years,the pollution load and loss intensity of total nitrogen and total phosphorus from non-point sources are mainly distributed in the regions with more precipitation and more cultivated land and rural residential land.The spatial differences of pollution load and loss intensity of total nitrogen and total phosphorus from non-point sources are great in wet years,but small in normal years and dry years,which is related to rainfall runoff.(3)From the perspective of pollution sources,the contribution of soil nutrient loss to the pollution load of non-point source TN and TP was the largest,which was 51% and 61%,respectively.The second was agricultural chemical fertilizer,whose contribution rates were 30%and 26% respectively.The contribution rate of livestock and poultry breeding was 13% and8%.The contribution rate of rural domestic sewage is 6% and 5% respectively.From the perspective of land use types,the total nitrogen and total phosphorus pollution loads from nonpoint sources on cultivated land were the largest,accounting for 70.52% and 47.4% of the total,respectively,followed by residential land,accounting for 24.18% and 41.98% of the total,respectively,followed by grassland and woodland.However,the discharge intensity of total nitrogen and total phosphorus from different land use types in the basin is as follows: residential land > cultivated land > Woodland.The results showed that the total nitrogen and total phosphorus of non-point source pollution were mainly from soil erosion and agricultural fertilizer,and the pollution load was mainly concentrated in cultivated land and rural residential areas.(4)According to the characteristics of non-point source pollution in muwen river basin and the actual situation of muwen river basin in laiwu,shandong province,this paper puts forward the corresponding non-point source pollution prevention and control measures from three aspects of soil erosion prevention and control,scientific and rational fertilization and pollution prevention and control in rural residential areas,so as to provide theoretical basis for the water pollution prevention and control in the river basin.