Identification Of The Source Contribution Of Groundwater Nitrogen Pollution In The Typical River-side Areas Of Weihe River

This paper selects the typical river section of Weihe--the county of Qixian County(the section of Xizhangzhuang Village to WangSizhuang Village of Xiaohe Town,Weihe River)as the research area,and analyzes the groundwater nitrogen through field investigation,laboratory test,numerical simulation and other techniques and methods.The source of pollution,the contribution rate of different pollution sources is calculated,and the research results can provide scientific support for the prevention and protection of groundwater pollution in the study area.Firstly,the paper investigates the pollution situation in the study area,analyzes the water chemistry characteristics and typical pollutant characteristics of the study area,and analyzes the lithology,surface permeability coefficient and characteristic pollution of the study area through field survey,data collection,field sampling analysis and literature review.The parameters such as concentration,nitrification and denitrification were divided into sections,and the spatial superposition of each zone was carried out to complete the vertical infiltration zone of surface pollutants in the study area.The numerical simulation of nitrogen migration and transformation in the aeration zone was established by using Hydrus-1D software.The model analyzes the level and distribution characteristics of pollutants;the calculation results of moisture and nitrogen in the model of the aeration zone are used as the input values of the aquifer model,and the nitrogen migration and transformation model of the aquifer is constructed by Visual Modflow to simulate the nitrogen in the groundwater.The migration and transformation,so as to construct a joint model of nitrogen in the surface,aeration zone and aquifer system;according to the calculation results of the model,the input of nitrogen from different sources of groundwater in the study area is obtained,and the source of nitrogen pollution of groundwater is calculated by the equilibrium method.Contribution rate.The main conclusions of the paper are:(1)According to the river surface water and surrounding shallow groundwater samples in the study area,Piper three-line diagram,Gibbs diagram,ion component proportional coefficient and factor analysis were used to study the chemical evolution characteristics of surface water and groundwater in Weihe River.And analysis of typical pollutants.The results show that there are three types of surface water in the study area,and the type,and the groundwater is quite different,which can be divided into 16 types.The chemical composition of surface water in the study area is mainly controlled by evaporation-precipitation;the chemical causes of groundwater are controlled by evaporation and sedimentation and water and rock interaction.At present,Weihe River water belongs to inferior V water.Among the groundwater samples tested from 2015 to 2018,Class V water accounted for 15.8%of the total number of tests,Class IV water accounted for 31.6%of the total number of tests,Class III water accounted for 52.6%of the total number of tests,and groundwater quality was better than river water.The changes of NH4-N and NO2-N content in the soil profile of the study area were not obvious with the depth,and the NO3-N content decreased with depth.The deeper the depth,the more obvious the denitrification.(2)According to the numerical simulation model of nitrogen migration and transformation in the aeration zone,the vertical infiltration simulation results of surface pollutants in the study area show that the concentration of ammonia nitrogen in the bottom of the aeration zone of the study area is higher in the southwest region,and the concentration range is 0.006mg/L~0.046mg/L;nitrite nitrogen concentration did not change much in the whole study area,the concentration range was 0.00013mg/L~0.00045mg/L;and the nitrate concentration in the northeast of the study area is higher,the concentration range It is from057 mg/L to 8.12 mg/L.(3)According to the numerical simulation model of groundwater in the study area,the groundwater flow field and nitrogen concentration field in the study area are well fitted to the actual field.The model meets the accuracy requirements and can truly reflect the actual groundwater flow field and nitrogen concentration in the study area.Field characteristics,model calculation results are reliable.The simulation results show that the main recharge source of the aquifer in the study area is the vertical infiltration replenishment of the vadose zone.The recharge amount during the simulation period is 377.12×10~4m~3,accounting for36.31%of the total recharge;the recharge of the river is second,the recharge is 158.06×10~4m~3,accounting for 15.22%of the total recharge;excretion is mainly downstream discharge,the excretion during the simulation period is 423.21×10~4m~3,accounting for 40.76%of the total replenishment.(4)The calculation results of the contribution rate of groundwater nitrogen source in the study area indicate that the nitrogen in the groundwater of the balanced area of the study area mainly comes from vertical infiltration,river recharge and nitrogen exchange in the two regions,and the contribution rate of ammonia nitrogen source is 59.99%.5.86%,4.15%;the contribution rates of nitrite nitrogen sources were 62.02%,33.36%,and 4.62%,respectively;the contribution rates of nitrate nitrogen sources were 64.41%,30.36%,and 5.23%,respectively.The groundwater nitrogen in the balanced 2 area is mainly derived from two aspects.The contribution rates of vertical nitrogen infiltration and river recharge are 95.79%and 4.20%,respectively.The contribution rates of nitrite nitrogen vertical infiltration and river recharge are 92.81%and 7.19 respectively.%;the contribution rates of nitrate nitrogen vertical infiltration and river recharge were 93.97%,and 6.04%,respectively.