Research On Transport Law Of Agricultural Non-point Source Pollution In Yanghe Basin

Yanghe basin is an important water conservation functional area,ecological environment supporting area and agricultural product supply base in Beijing-Tianjin-Hebei region.With the development of economy and society,the problems of natural water pollution and groundwater overexploitation in the basin are becoming increasingly serious.It is of great scientific significance to identify the main pollution sources and their migration modes in Yanghe Basin for water pollution control.According to the current water pollution situation in Yanghe basin,this paper comprehensively uses the output coefficient model and the basic flow segmentation method to identify whether the pollution load in Yanghe basin comes from non-point source pollution or point source pollution;On the basis of determining that the pollution load in the basin mainly comes from planting pollution in non-point source pollution,the characteristics of pollution migration path of farmland pollution sources in Yanghe basin are explored by means of in-situ simulated rainfall,dynamic monitoring of water and salt and laboratory tests According to the dynamic characteristics of water and salt in the main migration routes of farmland pollution,the Hydrus-1D model is used to quantitatively analyze the migration law and influencing factors of pollutants,which provides theoretical support for the prevention and control of environmental pollution in Yanghe Basin.The results show that:(1)From 2006 to 2015,the loads of total nitrogen,total phosphorus,ammonia nitrogen and COD of agricultural non-point sources in Yanghe Basin were higher than those of point source pollution,especially in 2015,the total phosphorus load of agricultural non-point sources accounted for 86.94%of the total load.Among the three major agricultural non-point source industries,the pollution load of agricultural planting industry is relatively high,with total nitrogen accounting for 51.11%～62.22%,total phosphorus accounting for 32.62%～40.74%and ammonia nitrogen accounting for 45.47%～58.92%.The amount of point sources entering the river accounts for a relatively high proportion of its output,of which total nitrogen is close to 45%,while the amount of non-point sources pollution entering the river is relatively small,with total nitrogen and total phosphorus both within 5%.Therefore,more than 90%of agricultural non-point source pollutants in the basin have not entered the mainstream of Yanghe River with rainfall runoff.(2)According to the field observation,monitoring data and indoor analysis,there is a significant positive correlation between water quality and water quantity during the migration of agricultural non-point source pollution in Yanghe Basin,especially the P value of the correlation analysis of water quality and water quantity in Zuowei,Jiangjiatun and Zhangjiabao is 0.01,and the rest points are also less than 0.5.Based on the relationship between water quality and quantity and field monitoring data,leaching solution accounts for 92.03%～98.32%of the total runoff.It can be judged that the main migration mode of agricultural non-point source pollution in Yanghe Basin is one-dimensional vertical along the direction of vadose zone,and the main driving force(carrier)is soil leaching solution,while the surface migration and lateral migration with surface runoff and soil flow seldom occur.(3)According to the simulation results of Hydrus-1D model,it can be seen that the rainfall intensity has little effect on the vertical migration of pollutants.Soil types have influence on pollutants.From the range analysis,it can be seen that with the increase of soil residual moisture content(0.05→0.06→0.07→0.08),the migration speed of pollutants slows down significantly,while the migration amount of pollutants increases gradually;With the increase of pollution source intensity(0.1g/m~2→0.2g/m~2→0.3g/m~2→0.4g/m~2),the migration speed of pollutants has little change,but the migration amount of pollutants has increased significantly;With the decrease of rainfall intensity(40mm/h→30mm/h→20mm/h→10mm/h),the migration speed of pollutants gradually slows down,and the migration amount of pollutants also decreases gradually.The analysis of variance shows that the main factor affecting the migration speed of pollutants is soil properties in vadose zone,followed by rainfall intensity and pollution source intensity,and the main factor affecting the migration quantity of pollutants is pollution source intensity,followed by rainfall intensity and soil properties in vadose zone.