Study On Non-point Source Pollution Simulation And Best Management Measures In Harbin Section Of Songhua River

Nowadays,the severity of water pollution has been concerned by the whole world.Water pollution mainly includes point source pollution and non-point source pollution.The non-point source has already become the main cause of water environment deterioration.It has become the concern of countries all over the world to take relevant management measures to control the non-point source pollution and improve the water environment pollution.The best management practices(BMPs)can reduce the impact of agricultural non-point source load on watershed water body,which can be divided into engineering management measures and non-engineering management measures.The implementation of the best management measures is of great significance for watershed non-point source pollution control.In this paper,taking Harbin section of Songhua River as the research area,the spatial and temporal distribution characteristics of non-point source pollution in Harbin section of Songhua River are analyzed and studied by using SWAT model,and the management measures of different scenarios are set,and the simulation evaluation of BMPs in the basin is carried out by using SWAT model,and the reduction effect of each scenario is compared.The main conclusions are as follows.(1)Through the collection and analysis of spatial data and attribute data,the spatial database and attribute database of Harbin section of Songhua River are input into the model.Based on the actual situation of Songhua River in Harbin,27 sub basins and 107 hydrological response units were formed.Then,sensitivity analysis was carried out on the model parameters.The monthly runoff from 2012 to 2016 and TN and TP from2012 to 2016 in the study area were calibrated and verified.The results showed that SWAT model was suitable for the study area.(2)After adjusting the parameters,the SWAT model was run to obtain the temporal and spatial distribution characteristics of non-point source loads TN and TP in the study area in 2016.In terms of time,rainfall is directly proportional to non-point source load,and the non-point source load in rainy season is significantly higher than that in dryseason.The precipitation in 2016 is positively correlated with the load of TN and TP,and the correlation coefficients are 0.72 and 0.84 respectively.In addition,by analyzing the relationship between runoff and TN,TP non-point source load,it can be seen that TN and TP load are mainly distributed in flood season(from may to September).The non-point source TN load from May to September accounted for 67.40% of the total load in 2016,of which the non-point source TN load in August was the largest,1205.25 tons,accounting for 19.86% of the total load in 2016;the non-point source TP load from May to September accounted for 68.28% of the total load in 2016,and the TP load in August was the largest,reaching 140.21 tons,and the proportion of total load in the whole year is 21.17%.From the perspective of space,through the calculation and analysis of the area of each sub basin in the study area,rainfall and non-point source TN and TP load values,it can be seen that in 2016,TN output intensity was between0.89-25.86kg/ha,among which the largest TN loss was No.23 sub basin,with a loss of646.60 tons,followed by No.2 sub basin,with a loss of 530.2 tons.The output intensity of TP is between 0.04-5.76kg/ha.The area with the most TP loss is No.23 sub basin,with 144.02 tons of TP loss,followed by No.2 sub basin,with 94.65 tons of TP loss.(3)In the study of the best management measures,No.23,No.2,No.1,No.12 and No.16 sub basins are selected,and six scenarios are set up to simulate TN and TP non-point source loads,including three engineering facilities and three non-engineering facilities.Through the operation of SWAT model to simulate each scenario and carry out quantitative evaluation,the following conclusions are drawn.The reduction rate of engineering measures is higher than that of non-engineering measures,among which the10 meter vegetation buffer zone has the best reduction rate.By setting 10 meter vegetation buffer zone,the reduction rates of TN in No23,No2,No1,No12 and No16 sub basins are 54.23%,68.95%,72.41%,59.26% and 71.58% respectively;the reduction rates of TP are 69.85%,75.69%,83.02%,72.59% and 83.56% respectively.