Investigation Of Water Environment In Xiangxi River Basin And Study Of Non-point Source Pollution

With the rapid development of the local economy and the improvement of people’s living standards,the water environment issues in the Xiangxi River Basin have become increasingly prominent.The water quality has shown a deteriorating trend,which has threatened the sustainable use of local water resources and brought the unfavorable effect to the local economy.In order to take advantages of local water resources,this paper takes the Xiangxi River Basin as the research object.After evaluating on the status of the water environment,we calculated the water environment capacity and put forward the amount of the pollution allocation for each unit.By means of Numerical Simulation,We set up the SWAT model to explore the characteristics of non-point source pollution in river basins.The main results are as follows:(1)After the investigation of the water environment of the river basin,the single-factor assessment method and the Nemerow index method were used to evaluate the current situation of the water environment.The total-nitrogen was always beyond the standard while the total-phosphorus was occasionally.The pollution level was moderate mainly.(2)We analyzed the sources of nitrogen and phosphorus production in the basin based on the discharge coefficient method.In 2014,the problem of non-point source pollution in the river basin was prominent.Total non-point nitrogen emissions werel 3,569.13 tons while total non-point phosphorus were 1,274.49 tons.Among them,animal production was the main source of total nitrogen,which accounted for 57.7%and agricultural productionr sources was the main source of total phosphorus,which accounted for 50.4%of the totaL(3)In order to further explbre the characteristics of non-point source pollution in Xiangxi River Basin,SWAT model was constructed.The results showed that both the R2(>0.6)and Ens(>0.5)met accuracy requirement for both calibration and modeling,which means the model was appropriate for this area.(4)According to the simulation results of the SWAT model,total non-point nitrogen and non-point phosphorus output in flood season accounted for 75%and 73%of the total annual output respectively.We can concluded that this period was the key for non-point source pollution control in the basin.In space,the losd intensity was higher in Gufu river and Nanyang river.(5)The calculation results for the dynamic water environment capacity of the river basin indicate that the ideal water environment capacity for total-nitro gen in the river basin is 1480.94 tons/year,and the ideal water environment capacity for total phosphorus is 231.19 tons/year.According to the SWAT model output,the annual average total nitrogen input into the river basin during the period from 2007 to 2015 was 1,610.79 tons/year,exceeding the load of 129.85 tons/year..The average total phosphorus input river toad was 208.57 tons/year,remaining 22.62 tons/year.(6)In order to control the continuous deterioration of the water environment in Xiangxi River Basin,afiir and reasonable allocation of the water environment capacity and a rationality test of the distribution were carried out using the Gini coefficient method.The total-initrogen pollutant discharge control should focus onNo.1-No.5units.While the total phosphorus governance should be concertrated on No.1,No.3 and No.4 units.(7)After setting up three management measures including nutrient management,returning farmland to forests,and setting up filter belts,this paper dicussed the reduction rate of the non-point pollution based on the SWAT simulation and gave different meatures to different units.For units with large reduction rates,such as TN in No.1,No.3,No.4 and TP in No.land No.3,we recommend setting up filter belts to control the non-point pollution;For units with nomal reduction rates,such as TN in No.2,No.5 and TP in No.4,we recommend returning farmland to forests;For units with ower reduction rates,such asTN in No.6,reducing the amount of chemical fertilizers may be considered.