Numerical Simulation And Regulation Mechanism Of Agricultural Non-point Source Pollution In Accompanying River-marsh System

Agricultural non-point source pollution is one of the important causes of water environment pollution,Due to its wide spatial and temporal distribution and difficulty in monitoring,long-term distributed physical models such as SWAT have become important methods for estimating non-point source pollution loads,identifying critical periods and areas of pollution,and studying BMPs.The impact of agricultural non-point source pollution on the Sanjiang Plain caused by agricultural reclamation has become increasingly serious,directly affecting Qixinghe Wetland and other national-level nature reserves and seriously endangering the safety of the ecological environment.This study takes the typical associated river-marsh system in the Sanjiang Plain-Qixing River Basin as the research object,the SWAT model and agricultural non-point source pollution load estimation model were used to simulate the agricultural non-point source pollution load in the Qixing River Basin,analyze the spatial and temporal distribution characteristics of agricultural non-point source pollution load,and identify agricultural areas Key areas and periods of source pollution;establishing the best management measures combining engineering measures with non-engineering measures.This study provides theoretical basis and scientific basis for realizing agricultural non-point source pollution control in Qixing River Basin.Not only can it guarantee the safety of the ecological environment of the national nature reserve,but also has important theoretical and practical significance for the sustainable development of the ecological environment of the associated river marsh system and the entire Sanjiang Plain.The main results are as follows:?1?Based on the principle of mass balance,an agricultural non-point source pollution load estimation method was proposed,and the nitrogen and phosphorus load of agricultural non-point source pollution in Qixing River Basin was successfully estimated.Compared with the measured data,within the same order of magnitude,it proves that the estimation results are credible.Sex.The estimation result is used as the SWAT model water quality input data to calibrate and verify the water quality parameters.?2?The SWAT model was successfully constructed by combining DEM data,land use data,soil data,and meteorological data,etc.,using the measured data of the security station to determine the model water parameters,and using the estimation results to evaluate the water quality parameters.Both the water volume R² and the Nash coefficient E_NS are greater than 0.7,and the total nitrogen load rate is regularly compared with the verification period R²>0.6 and E_NS>0.5.It shows that the SWAT model in Qixing River Basin meets the requirements of simulation accuracy of monthly scale runoff and total nitrogen load,and can be well applied to the study of Total Nitrogen Load in Qixing River Basin.It is further verified that the estimation results in Chapter 3 are applicable.?3?Based on the simulation results of the total nitrogen load of the SWAT model from 2005 to2010,the temporal and spatial distribution of total nitrogen load in the Qixing River Basin was analyzed.The results show that the agricultural non-point source pollution discharge period in the Qixing River basin is basically consistent with the crop growth period.This is the critical period of agricultural non-point source pollution in the Qixing River Basin.The No.13 sub-basin is the key area of agricultural non-point source pollution in the Qixing River basin.The cultivated land is the key land use type of agricultural non-point source pollution in the Qixing River basin,which contributes 73%to the total nitrogen load.?4?Scenario simulation results show that the reduction effect of total phosphorus load is better than total nitrogen load.Reducing the amount of fertilization,adjusting the planting structure,protective tillage,and establishing a vegetation filter belt can effectively reduce the agricultural non-point source pollution load by more than 20%.The best measure for reducing the non-point source pollution load in the critical period is to adjust the planting structure,that is,to cover the crops in the study area into corn,which can reduce the total nitrogen load and total phosphorus load by 96.45%and 98.88%,respectively.The best measure for reducing the non-point source pollution load in key areas is the less tillage measure,which can reduce the total nitrogen load and total phosphorus load by 78.65%and 97%,respectively.Individual BMPs can effectively control agricultural non-point source pollution in the watershed,but combined BMPs have a better control effect on non-point source pollution,and can reduce total nitrogen load and total phosphorus load by 77.18%and 99.61%respectively.Combined BMPs have a better effect on reducing agricultural non-point source pollution load in key periods and key areas,and can reduce total nitrogen load and The total phosphorus load is 98.21%and 99.87%,which can reduce the total nitrogen load and the total phosphorus load in critical areas by 90.46%and 100%,respectively.?5?According to the scenario simulation results,the best management measures for the combination of non-engineering measures such as the establishment of vegetation filter belts,the use of wetland buffer zones,and farming management,nutrient management,etc.should be taken to prevent and control agricultural non-point source pollution in the Qixing River Basin.The actual situation further optimizes BMPs,At the same time,strengthen the supervision of land use,especially cultivated land;strengthen the control of key areas and periods of agricultural non-point source pollution in the Qixing River Basin;Strengthen publicity and education,enhance farmers'awareness of environmental protection,establish a protection system for farmers'participation system,and realize comprehensive regulation of agricultural non-point source pollution in associated river and marsh systems.