Analytical Study Of Groundwater Nitrate Sources Based On Isotope And Numerical Simulation

The source of groundwater nitrate pollution is complex,and it is difficult to find the discharge source,so once the groundwater is polluted by nitrate,it will be difficult to control.In order to effectively prevent and control nitrate pollution in groundwater,it is very important to identify the sources of nitrate pollution in groundwater.This study to zhangjiakou xuanhua area as the research area,the shallow groundwater sampling inspection,on the basis of analysis of time and space distribution characteristics of groundwater chemical characteristics and nitrate,using nitrogen oxygen stable isotope technology to the qualitative analysis of groundwater nitrate pollution source category,using the quantitative calculation of various kinds of SIAR model don’t pollution contribution ratio,Modflow model of groundwater in the study area was established to identify the spatial location of nitrate pollution sources.he main results of this study are as follows:1.By sampling and analyzing 15 chemical indexes of 23 groundwater monitoring Wells in the study area,the status quo and spatial and temporal distribution of nitrate pollution in groundwater in the study area were obtained.The results showed that nitrate nitrogen was the main pollutant in groundwater in the study area,and the annual average concentration was 27.23mg/L,which was 1.36 times higher than the groundwater quality standard of Ⅲ(20mg/L)(GB/T 14848-2017).The distribution of nitrate concentration in the dry season was larger than that in the rainy season.Using Arc GIS software,the spatial interpolation analysis of nitrate concentration showed that the nitrate concentration in the study area was higher in construction land than in cultivated land.2.Nitrogen and oxygen isotope technology was used to qualitatively identify the groundwater nitrate pollution in the study area,and the source categories of groundwater nitrate pollution were obtained.The distribution of δ15N in soil and feces and sewage ranged from 1.46‰ to 7.71‰,and the distribution of δ15N in feces and sewage ranged from 9.49‰ to 17.57‰.The results can be used to enrich the distribution database of nitrogen and oxygen isotopes.The variation range of δ15N-NO3-and δ18O-NO3-of groundwater monitoring Wells in the study area are-2.57‰～4.20‰ and10.80‰～49.20‰,respectively.The characteristic values fall within the range of soil nitrogen,feces and sewage,and nitrogen and oxygen isotopes of inorganic fertilizers.It can be determined that the main sources of groundwater nitrate pollution in the study area are: Soil nitrogen,feces and sewage,inorganic fertilizer.3.The SAIR model was used to quantitatively calculate the nitrate pollution of groundwater in the study area,and the contribution rates of each pollution source category were obtained.Suggestions on prevention and control of nitrate pollution in groundwater were put forward.Nitrification is the main process of nitrogen migration and transformation in the study area,which has little effect on the fractionation of nitrogen,and the effect of fractionation is not considered when the SIAR model parameters are assigned.The SIAR model was run based on the qualitative identification results of nitrate pollution sources.The results showed that the average contribution rates of feces and sewage,soil nitrogen,inorganic fertilizer and industrial wastewater were 46.46%,44.5%and 9.03%,respectively.The contribution rates of soil nitrogen,feces and sewage to nitrate pollution were higher than that of inorganic fertilizer.In the process of groundwater pollution prevention and control,agricultural irrigation efficiency should be improved,fecal discharge management of livestock breeding should be standardized,sewage collection and treatment should be strengthened in rural and urban areas,and the use of agricultural fertilizer should be controlled.4.Modflow groundwater flow model was established with GMS software to find out the spatial location of nitrate pollution sources in groundwater in the study area.GMS software was used to build the Modflow groundwater model,and based on the reliable Modflow groundwater model,the Modpath module was run to trace the groundwater recharge area under the conditions of 1 year,3 year,5 year and 10 year,and the spatial location of nitrate pollution sources was identified through the groundwater recharge area.