Discharge And Evaluation Of Nitrogen And Phosphorus Pollution Load In Small Watershed Of Irrigation District

Irrigation district is the foundation of agricultural development and a significant pillar of promoting the development of economy,and it is also an important ecological preservation area.With the development of economy,irrigation district is facing the risk of deterioration of ecological environment.Thus it is necessary to carry out the nitrogen and phosphorus discharge load research and water pollution assessment in irrigation area.Huixian Wetland is called "the kidney of Lijiang River",it has the function of purifying water quality,protecting water source,maintaining the diversity of ecosystem and so forth.In recent years,non-point source pollution has become the main pollution of Huixian wetland.The water area of Huixian Wetland is decreasing and the water quality is deteriorating day by day,which has seriously affected the water environment safety.This paper takes the Huixian watershed of Qingshitan Irrigation area in the middle and upper reaches of Lijiang River as the research area and conducts a study on the migration,transformation and the discharge of pollution load of nitrogen and phosphorus at different scales in the Huixian Watershed,which plays a significant role in controlling the water pollution and promoting ecological harmony.In this paper,based on Arc GIS,Huixian experimental area is divided into several basins.Combined with the actual situation,some typical rivers like Mudong River,Huixian River,western section of the Ancient Guiliu Canal and Xiangsi River in Huixian Watershed are selected,and a dozen of chosen sampling points are distributed within the typical rivers.After continuous monitoring the water quality of the sampling points,analyzed the characteristics of nitrogen and phosphorus discharge load in different scale,finally the comprehensive evaluation of surface water quality of Huixian experimental area came to conclusion.The main the results are as follows:(1)The concentration of nitrogen and phosphorus in different water systems varies greatly in time distribution..For the spatial distribution of nitrogen and phosphorus concentration in Ancient Guiliu Canal varies less while in Huixian River shows a great variety;The nitrogen and phosphorus mass concentration of Mudong River increases from upstream to downstream,while in Xiangsi River,the concentration decreases along the channel.(2)Pearson correlation analysis is used to analyze the correlation of nitrogen and phosphorus concentration in different water systems.The result indicated the high correation between nitrogen and phosphorus concentration in Huixian River,Mudong River's and Xiangsi River's are moderate and that of Ancient Guiliu Canal is relatively weaker.(3)Measured the nitrogen and phosphorus concentration in the river basin outlets of four different scales in a hierarchical relationship,result shows that as the scale increases(from scale 1(1.36 km2)to scale 4(328.34 km2)),the concentration of nitrogen and phosphorus first increases then decreases and gradually trends gently.(4)Under similar conditions of land use type,as the scale increases from 1(1.36km2)to 2(7.48km2),3(226.42km2)to 4(328.34 km2),the nitrogen and phosphorus emission loads show a downward trend.However,when scale grows from 2 to 3,as the proportion of paddy fields and residential areas increase dramatically,the nitrogen and phosphorus emission load also increases.(5)Used the single factor evaluation method and the comprehensive pollution index evaluation method to evaluate the water quality of each water systems in Huixian pliot area,the results show that the water quality along the Xiangsi River was the worst,and the overall water quality was grade ? or worse than grade ?,followed by Huixian River and Ancient Guiliu Canal(western section);The water quality along the Mudong River is relatively good,and the comprehensive evaluation of water quality is between slight pollution to heavy pollution.