Land Use Structure Of Typical Small Watershed Of Mayi River Effect On Non-point Source Nitrogen Output

With the development of human society,ecological and environmental issues have gradually become the focus of attention.Among them,non-point source pollution caused by improper land use has become a hot issue in current research.Based on the influence of land use structure on non-point source pollution,this paper selects the typical small watershed of Ant River in the Songhua River tributary as the study area to study the correlation and influence of land use structure and non-point source pollutant nitrogen.The multi-objective optimization model is proposed to propose a land use structure optimization plan,which will provide a basis for future research on land use structure and non-point source pollution.The following are the main conclusions of this paper:（1）The land use types in the study area are mainly cultivated land,followed by forest land and residential areas.The types of land use in the basin are mainly based on the“source”type.Cultivated land and settlements are 74.6%of the total area,while forest land and grassland are 15%of the total area.Through hydrological analysis,the watershed is divided into 8 sub-basins.Through the analysis of sub-basin land use structure,the area of dryland from the upstream to the downstream of the basin has gradually increased.（2）By monitoring the water sample data in the field,it is concluded that the nitrogen output of the ant river small watershed is dominated by nitrate nitrogen（NO₃^--N）.NO₃^--N/TN showed that the concentration was in the flat water period>dry season>high water period in each water quantity period.The concentration of NH₄⁺-N/TN is in the period of high water>flat water>dry season.In residential areas,cultivated land promotes the output of nitrogen,and the role of residential areas is higher than that of cultivated land.In forest land,pasture has a retention effect on nitrogen,and it is concluded that the interception of nitrogen by forest land is higher than that of pasture.In the whole year scale,among the different land use structures,the most relevant to the NO₃^--N/TN in the wet season is the dry land,and the most relevant to the NH₄⁺-N/TN is the residential area.In the flat water period,it is related to NO₃^--N/TN,which is related to NH₄⁺-N/TN,which is related to nitrogen,and is related to nitrogen in the dry season.（3）Based on the previous research,an optimization model aiming at maximizing the economy and minimizing the non-point source pollution was established,and the optimization plan of the land use structure was obtained.As a result,the area of cultivated land decreased by 5.36%,the area of forest land increased by 2.68%,the area of pasture increased by3.76%,and the land for construction decreased by 1.08%.By using the non-point source pollution accounting method,it is verified that the contaminant target annual source pollution has a tendency to reduce compared with the base period annual source pollution load,and effective suggestions are put forward.（4）The land use structure has certain restrictive effects on the formation of non-point source pollution.This paper combines the field monitoring of non-point source pollutant output and land type to provide an innovative discussion on land use structure optimization and land in similar areas.Resource allocation research and ecological environment protection provide a theoretical basis.