The Research On Non-point Source Pollution In JiubuJiang Irrigation Area Based On SWAT Model

Zhuzhou JiubuJiang Irrigation District is an important grain production base in Hunan Province,grain production accounts for one-third of Zhuzhou,However,in recent years,under the premise of gradually controlling point source pollution in irrigation areas,the large use of chemical fertilizers has prompted the unabsorbed part of fertilizer to enter groundwater or flow into surface rivers with rainwater runoff,resulting in eutrophication of water bodies,increasingly prominent water environment problems,and agricultural non-point source pollution has gradually become the main reason for affecting water quality.In this paper,taking the Tiehe River,the main retreating river in the Jiubu River Irrigation Area,as the research object,the land use type maps of 2010 and 2020 were produced by ENVI software,the land use type change of the river basin was analyzed,the SWAT model database was constructed,the runoff and nutrients of the watershed were simulated and studied by the model,the applicability of the model was evaluated in the study area,and the non-point source pollution contribution rate,load spatial distribution characteristics and non-point source pollution load of different land use types were obtained by simulation,and finally the nitrogen fertilizer was reduced by simulation.The scenario of phosphate fertilizer,the impact of agricultural management measures on the non-point source pollution load in the river basin.The main conclusions drawn are as follows:(1)The main land types in the Tiehe River Basin are forest land and cultivated land,accounting for 65.67%and 25.13%respectively,from 2010 to 2020 land use transfer matrix,it can be seen that the area of cultivated land,water and construction land has increased,the area of forest land and grassland has decreased,and the main conversion method of land use in the basin is the conversion of forest land to cultivated land,the conversion of woodland to grassland and the conversion of cultivated land to forest land.(2)To simulate the runoff and nutrients of the Tiehe River Basin,and to construct a SWAT model database based on hydrometeorological data and water quality data,and divide the Tiehe River Basin into 19 sub-basins and 256 hydrological response units.Finally,the regular R2 and Ens in the runoff simulation were 0.95 and 0.91,the R2 and Ens in the verification period were 0.96 and 0.93,respectively,and the total nitrogen and total phosphorus in the nutrient simulation R2 and Ens exceeded 0.7,and the above simulation results achieved the accuracy of the model.(3)The calibrated SWAT model was used to simulate the non-point source pollution in the basin,and the spatial distribution of pollutant contribution rate and load was analyzed,and the results showed that:① the sub-basin with the largest total phosphorus and nitrogen load and contribution rate was the No.1 sub-basin located in the Tiehe estuary,and there was no obvious linear relationship between the contribution rate and the size of the sub-basin area,which were mainly related to the runoff and land use types in the basin;② the impact of different land use types on the pollution load was analyzed,and the highest was cultivated land,followed by woodland and grassland;③ In the model,the facilities reduced the use of 50%nitrogen fertilizer and 50%phosphate fertilizer respectively,and the output results of total nitrogen and total phosphorus were obtained by running the model,and compared with the initial scenario,it was found that reducing 50%nitrogen fertilizer could reduce the total nitrogen load by 12.1%,and the reduction of 50%phosphorus fertilizer use could reduce the total phosphorus load by 8.2%.