Research On Spatiotemporal Changes Of N And P From Farmland Non-Point Sources Pollution In The Haihe River Basin Based On InVEST Model

The Haihe River Basin is located in North China.In recent years,non-point source pollution of farmland has become the main reason for the deterioration of the water environment in the basin.Therefore,the research on the nitrogen(N)and phosphorus(P)load of non-point source pollution in the river basin is of great significance to the treatment of non-point source pollution of farmland and the improvement of water quality in the Haihe River Basin.Non-point source pollution has the characteristics of extensiveness,randomness and uncertainty,which makes it difficult to control.At present,applying models to quantitatively estimate non-point source pollution load is one of the main research methods.To analyze the temporal and spatial variation characteristics of non-point source pollution of N and P in farmland in the Haihe River Basin,this article is based on land use types,DEM,meteorological data,statistical data,etc.in 2005,2010 and 2015.First,based on the transfer matrix and other methods,the temporal and spatial changes of land use in the Haihe River Basin are analyzed.Then based on statistical data and the "Manual of National Farmland Non-point Source Pollution Emission Coefficients" to regionalize the parameters of N and P.Then apply the InVEST model to estimate the farmland N and P non-point source pollution in the Haihe River Basin in 2005,2010 and 2015.Analyze the temporal and spatial distribution characteristics of pollutants in combination with GIS and Origin software,and analyze the influence of different influencing factors on the output load of N and P.Finally,use the best management measures for scenario simulation.The main research results of this paper were as follows:(1)Analysis of land use change in Haihe River Basin.During the three phases of land use changes in the Haihe River Basin in 2005,2010,and 2015,the areas of dry land and paddy fields all showed a downward trend;dry land in the basin is the land use type with the largest transfer area,and most of the land is converted to construction land and grassland;The main sources of transfer are grassland and dry land.(2)Pattern matching of non-point source pollution of farmland N and P and regionalization of N and P parameters in the Haihe River Basin.Based on the "National Farmland Non-point Source Pollution Discharge Coefficient Manual",following the principle of element pattern matching of "agricultural area-slope-dry land/paddy field-planting pattern",the matching results of farmland non-point source pollution patterns in the Haihe River Basin were obtained.Analyze the temporal and spatial changes of agricultural non-point source pollution patterns.The amount of N and P fertilizers required for different planting patterns in the Haihe River Basin is different,and the area of planting patterns changes,and the amount of N and P applied in farmland also changes accordingly.From the spatial distribution of N and P application intensity,it can be seen that the intensity of N and P fertilizer application is higher in the middle east and south of the watershed,and the distribution of N and P fertilizer application intensity is spatially similar.The spatial distribution of N and P application intensity is closely related to the topography and planting structure of the watershed.contact.(3)Estimation of farmland non-point source pollution load and analysis of influencing factors in the Haihe River Basin.Based on the modified In VEST model,the output load of N and P from farmland in the Haihe River Basin in 2005,2010 and 2015 was estimated.The results show that the total output of N and P in different farmland non-point source pollution modes were 41,100 tons and 16,400 tons respectively,the output load of N and P per unit area is 2.89kg/hm2 and 1.03kg/hm2 respectively in 2005.The total output of N and P in 2010 were 37,900 tons and 13,700 tons,the output load of N and P per unit area is 2.41kg/hm2 and 1.04kg/hm2 respectively.The total output of N and P was 37,900 tons and 13,700 tons,the output load of N and P per unit area is 2.31kg/hm2 and 0.67kg/hm2 respectively in 2015.The total P output was 32,500 tons and 9,100 tons respectively.The analysis is carried out with the sub-basin and prefecture-level cities as the unit.The results show that the more severely polluted areas in the river basin are mainly distributed in the central and southern parts of the river basin,such as the Zhangwei River system,Heilonggang Yundong River,and Tuhaima The pollution of N and P in the southern part of the Jiahe River and Ziya River system is more serious.The high-value areas of N and P fertilizer output load are mainly concentrated in Tangshan City,Qinhuangdao City,Shijiazhuang City,and Anyang City,Hebi City,Xinxiang City,Jiaozuo City and Jincheng City in the south.Based on the Origin software analysis of the influence of different influencing factors on the output load of N and P in the Haihe River Basin,the output of N and P in the plain area is relatively large,accounting for more than 70%of the total;dry land contributes more than 90%of the total output of N and P;N per unit area The models with higher P output load are basically double cropping in the field or dryland vegetables and garden plots.These planting models require large amounts of chemical fertilizers.The application intensity of N and P fertilizers showed the same changing trend as the output load of N and P;the output load of N and P increased with the increase of rainfall.Under the same rainfall conditions,the output load of nitrogen and phosphorus decreased year by year,indicating that the non-point source pollution of farmland in the Haihe River Basin has been reduced.(4)Key source area identification and scenario simulation.GIS hotspot analysis identifies key source areas.Based on non-engineering measures and engineering measures,5 different scenarios are set up to evaluate the reduction rate of N and P fertilizers under different measures.The results show that N and P hotspots are mainly concentrated in the watershed.The southern part of the country,namely Jiaozuo City,Xinxiang City,Hebi City,Puyang City,Anyang City,Handan City,Liaocheng City and Jincheng City,etc;With a certain reduction effect,N and P fertilizers are reduced by 10%,20%,and 30%respectively,and the reduction rate increases in turn;the reduction rate of establishing a 10m vegetation buffer zone is higher than that of a 5m vegetation buffer zone,and the reduction of chemical fertilizers is better than that of establishing a vegetation buffer zone.