Source Analysis And Contribution Rate Of Groundwater Nitrogen Pollution In The Plain Area Of Northeast Beijing

With the acceleration of the urbanization process,the human impact on the groundwater environment is increasing.The problem of groundwater pollution has received widespread attention from the society.Nitrogen pollution,as a common groundwater pollutant,has become the focus of groundwater pollution research.The plain area in the northeastern part of Beijing belongs to the piedmont plain with good groundwater storage conditions and is an important water source in Beijing.However,due to the hydrogeological characteristics of the piedmont plain,groundwater is more susceptible to pollution,so the shallow groundwater nitrogen in this area Pollution research is very necessary.The research systematically studied the topography and geomorphology and hydrogeological conditions of the plains in the northeast of Beijing;using traditional hydrochemical analysis methods,the groundwater chemistry laws in the study area were analyzed,combined with Arc GIS 10.5 software to draw the main pollution distribution map in the area,revealing the area The distribution characteristics of groundwater chemistry,nitrogen pollution and other elements under human influence;on this basis,statistical analysis methods are used to identify nitrogen pollution influencing factors and pollution sources,and the source identification results,the distribution of potential pollution sources and land use are used to determine the nitrogen in the study area.Source analysis of pollution sources.The main conclusions are shown in the following 4 points:（1）The study area has a strong leaching effect.The groundwater chemical type is mainly HCO₃·SO₄-Ca·Mg type,and the Cl^-concentration distribution is abnormal,indicating that the hydrogeological characteristics of the study area are affected by humans in addition to hydrogeological conditions.The impact of activities.NO₃^-,As,NO₂^-,COD,Zn,Fe,Mn,TDS,and p H in the groundwater in the study area all exceed the standard.Among them,the NO₃^-is the most serious,with the highest exceeding 8.9 times（calculated by 20mg/L）,the exceeding rate as high as 69.01%,the rate of exceeding the standard of other indicators is not high.In terms of the spatial distribution of groundwater pollution,there are two high concentration areas of NO₃^-,and the polluted areas are quite extensive.It can be seen that NO₃^--N is the main pollutant of groundwater pollution in the study area.（2）Using multivariate statistical analysis methods to identify groundwater pollution sources into 5 categories,namely,the leaching-migration action factor（F1）,the geological background action factor（F2）,and the natural condition impact factor（F3）,industrial pollution factor（F4）and domestic pollution factor（F5）.Among them,the leaching-migration factor,the geological background factor and the natural condition factor reflect the influence of hydrogeology and natural action on groundwater quality,and the industrial pollution factor and domestic pollution factor reflect the influence of human activities on groundwater quality.According to the results of correlation analysis,NO₃^-has a good correlation with SO₄^2-,Cl^-,TDS,Zn and other indicators,indicating that NO₃^-is affected by greater human activities;NO2^-and NO3^-are negatively correlated with Fe and Mn Etc.showed a positive correlation,indicating that NO₂^-may be derived from denitrification.（3）The absolute principal component score-multiple linear regression model（APCS-MLR）is used to quantitatively calculate the contribution rate of pollution sources.NO₃^-is mainly affected by leaching-migration,natural conditions and industrial pollution,and the contribution rates are 27.79%,17.13%and 19.80%;NO₂^-is mainly affected by natural conditions,with a contribution rate of 19.81%,in addition to 49.02%of unidentified sources;NH₄⁺is mainly affected by domestic pollution,with a contribution rate of as high as 42.71%.（4）According to the investigation results of potential pollution sources in the study area and the estimation method of characteristic pollutants,the nitrogen pollution emissions of each potential pollution source in the study area were calculated by towns.The towns in the study area that contributed significantly to nitrogen pollution emissions were mainly Beixiaoying Town,Gulou Street,Mulin Town,Shilipu Town,Xitian Gezhuang Town,Zhaoquanying Town and Yang Town,with a contribution rate of 7.77%.,7.98%,17.98%,10.29%,11.92%,7.14%,6.80%.The remaining 16 towns and villages emit less nitrogen pollution,and the nitrogen pollution caused by the application of agricultural chemical fertilizers is mainly used,and the contribution rate to the nitrogen pollution in the study area is only 20.12%.