SWAT Model-based Nitrogen And Phosphorous Pollution In Qingyi River Basin,China

Water pollution is one of the top 10 environmental issues in the world.In recent years,the phenomenon of water pollution has become increasingly serious in major drainage basins.Basin is the best natural division unit for studying nitrogen and phosphorus pollution in the water environment and the SWAT model can simulate the quantity and sediments of the basin,and the circulation process of watershed,sediment,nutrients such as nitrogen and phosphorus,and chemical substances.Qingyi River Watershed is an important source of water source in the Tianfu new area of Chengdu and the urban agglomeration of the Yangtze River economic belt.The natural ecological hydrological system is very fragile and sensitive,and its water quality is related to the sustainable development of the national regional social,economic and ecological environment.The author discusses the temporal and spatial distribution characteristics and the transformation regulations of the nitrogen and phosphorus pollution and other pollutants in different morphology in the basin based on the SWAT model to identify the influencing factors,the production conditions and the formation mechanism of the nitrogen and phosphorus pollution in the watershed;the paper analyzes the features of evolution and the change rules of the nitrogen and phosphorus pollution in the basin under different scenarios,such as rainfall,temperature,land utilization,and other complex patterns;the author studies the regulation and control of the nitrogen and phosphorus pollution by different regulatory measures.The folloming conclusions can be drawn:1.A SWAT model database for the QRW has been established and the watershed was discretized so that the study area was divided into 29 sub-basins and 1384 hydrological response units.2.By using runoff,sediment,and water quality and monitoring datum from multiple hydrological stations over the years,the calibration and verification can be done.The decisive coefficients(R~2)of runoff,sediment and water quality were all greater than 0.6,and the effective coefficient of Nash-sutclific(NSE)is greater than 0.5,which has been proven that the simulation results are more reliable.3.The well-proven and validated model simulates the production,change,and spatial distribution of the pollution loads of nitrogen and phosphorus from 1985 to 2014.The results shows that the degree of the nitrogen and phosphorus pollution in the QRW generally followed the pattern that pollution has increased from the upstream to the downstream,in which the pollution of the nitrogen and phosphorus was most serious in Yucheng District,Hongya County and Jiajiang County.The average contribution rates of pollution loads from different sources for many years could be ranked as follows:the loss of soil nutrients>livestock and poultry breeding>crop planting>domestic pollution and industrial pollution.The average contribution rate of pollution loads in different forms of nitrogen and phosphorus over many years could be ranked as follows:organic nitrogen>nitrate nitrogen>ammonia nitrogen>nitrite nitrogen;organic phosphorus>inorganic phosphorus.4.Scenario analysis method is used to explore the impact of climate change on nitrogen and phosphorus pollution in basins.The results shows that the increase in temperature leads to the decrease in the total phosphorus load,and the decrease rate increases with the increase of temperature;the increase in rainfall leads to the decrease in the total phosphorus load,the reduce in rainfall leads to the increase in the total phosphorus load.While it is not clear to find the regulation that the total nitrogen will be changed with different climate,the decline in rainfall leads to the decline in the total nitrogen load.5.The multi-attribute decision-making method based on scenario analysis and information entropy proposes and analyzes the best management measures for the river basin.The results show that conversion of cropland to forestland is suitable for the regulation of nitrogen and phosphorus pollution in a small area;banded cultivation is suitable for the regulation of large-scale nitrogen and phosphorus pollution.