Non-point Source Pollution In The Small Watershed Of Jinguihe River In The Upper Reaches Of Lijiang River

Lijiang River basin is the main water source for industrial and agricultural water,living water and ecological landscape,as well as the polluted Guilin of the area,because of the rapid development of economy and society,the water environmental condition of Lijiang River is not optimistic.Because of the tradition of agricultural production mode and the complexity of agricultural activity management,the agricultural non-point source pollution in Lijiang River basin is more outstanding.In addition,the spatial distribution of agricultural non-point source pollution is more dispersed,and the pollution condition is affected by topography,meteorology,hydrology,irrigation and drainage,and its migration and transformation laws are complex and changeable,and the monitoring is difficult,which arouses extensive attention of the society.In this paper,we carry out field in situ test in the Qingshitan irrigated area of Lijiang River,and the sewers is a tributary of the Western Main canal of Qingshitan Irrigation area upstream of Lijiang River.Based on DEM analysis and drainage system analysis,considering the water movement path,the Jingui River test area is divided into multiple sub basins with hydraulic connections,and then the sampling points can be set up in the Sub basin,and the field Monitoring and laboratory analysis of runoff drainage and nitrogen and phosphorus emission are carried out.Results of nitrogen and phosphorus pollution output concentration in small watershed of the Jingui River show that the amount of rainfall has an effect on the output concentration of nitrogen and phosphorus in the small watershed,the decrease of rainfall in the rainy season,the decrease of runoff in the watershed,the decrease of pollutant output concentration,the increase of rainfall in the rainy season,the increase of surface runoff,the runoff erosion and the migration of pollutant,In addition to the frequent farming activities,resulting in a higher concentration of nitrogen and phosphorus in the watershed,although the nitrogen and phosphorus output concentration increased with the increase in rainfall,but to a certain period after the fall,overall is proportional to rainfall.The variation of seasonal temperature has great influence on the concentration of nitrogen and phosphorus in the basin.When the water temperature rises,the output of total nitrogen in the basin is mainly ammonia nitrogen,and when the temperature is reduced,the output of total nitrogen in the basin is mainly nitrate nitrogen,which is due to the temperature affecting the microbial content in the water body,further affecting the dissolved oxygen content in the water body,The dissolved oxygen content in water directly restricts the conversion of ammonia nitrogen to nitrate nitrogen,and the increase of water temperature can promote the release of phosphorus in river sediments,and increase the concentration of total phosphorus.The output concentration of nitrogen and phosphorus was also affected by the different mat,and the culture of the surface nitrogen,phosphorus output is the largest,followed by fish ponds under the surface,which is due to the free discharge of aquaculture waste water,farmland on the surface of nitrogen and phosphorus output mainly concentrated in the growth stage of rice,during the period of the soil,fertilization and other agricultural activities on nitrogen,phosphorus output content,The lower surface of fruit trees is the least of nitrogen and phosphorus.The distribution of nitrogen and phosphorus output shows that the annual output distribution of nitrate,total nitrogen and total phosphorus in the small watershed of the Jingui river is basically consistent,and there are some differences in the distribution of ammonia and nitrogen,and the distribution of ammonia nitrogen is affected by the human activities and the amount of runoff.The statistical analysis of nitrogen and phosphorus emission load in the hydrological period of the Jingui River basin shows that the variation of ammonia nitrogen and total nitrogen in the basin during the whole hydrological years is relatively stable.The influence of nitrogen and phosphorus output load on downstream water quality in the Jingui Creek Basin shows that the total nitrogen output of the beetle is high year-round,aggravating the burden of the water environment capacity of downstream water,and the total phosphorus has a relatively small impact on the downstream water.Based on data of DEM,soil type,land use type and hydrological data,SWAT model was used to simulate runoff and nitrogen and phosphorus emission in the small watershed of the Jingui River.The SWAT model was validated by using the monthly runoff data of the 1995-2017-year beetle and the measured data of nitrogen and phosphorus in October 2016-November 2017.The correlation coefficient R₂?0.6,E_NS?0.5 model is applied to the basin.Regular correlation coefficient of runoff rate R₂=0.85;E_NS=0.71,the R₂=0.88,E_NS=0.65 of the total nitrogen rate was R₂=0.73,E_NS=0.71,the correlation coefficient was R₂=0.69,E_NS=0.54,the correlation coefficient of the total phosphorus rate was R₂=0.64,E_NS=0.60,The correlation coefficient of verification period R₂=0.60;ens=0.51.