Nitrate Source Analysis Of Karst Groundwater In Southern Taihang Mountain Based On Hydrochemistry And Isotopes

Karst groundwater is an important source of drinking water for residents in South Taihang Mountain.It is of great ecological and environmental significance to protect this precious water resource.In this paper,the karst groundwater is taken as the main research object in the northern mountainous area of Jiaozuo,which mainly includes the source water of the Jiaozuo Waterworks and the spring water of Qingtian River,Qinglong Gorge and Yuntai Mountain scenic spots in the mountainous area.At the same time,the surface water of scenic spots is selected as the potential pollution source for the study.The mixing proportion of potential sources of nitrate in karst groundwater was quantitatively analyzed by means of hydrochemistry,hydrogen and oxygen isotopes(δD andδ¹⁸O-H₂O),nitrate nitrogen and oxygen isotopes(δ¹⁵N-NO₃^-andδ¹⁸O-NO₃^-)and Bayesian isotopic mixing model.This paper expounds the extent and extent of the influence of artificial input on karst groundwater in South Taihang Mountain,and provides an important scientific basis for the protection of karst groundwater.The main research conclusions of this paper are as follows:（1）The hydrochemical types of karst water are mainly HCO₃-Ca-Mg in the study area,and the hydrochemical types of karst water in some piedmont have changed to HCO₃-SO₄-Ca-Mg and HCO₃-Cl-Ca-Mg;HCO₃-Ca-Mg is the main hydrochemical type of surface water in the scenic spot,while the surface water of Qingtian River accepted the upstream sewage,and the hydrochemical type changed to HCO₃-SO₄-Ca-Mg.（2）There is no obvious seasonal variation of hydrogen and oxygen isotopes in the piedmont karst groundwater,while the hydrogen and oxygen isotopes of the spring water in the scenic spot have seasonal variation.Local precipitation is an important source of supply,and the surface water of the scenic spot experiences evaporation process after receiving spring water supply and slightly enriches hydrogen and oxygen isotopes.（3）The mean nitrate content in the piedmont karst water is 0.34 mmol/L,and the mean nitrate nitrogen and oxygen isotopes are 6.6‰and 2.8‰,respectively.The mean nitrate content of spring water in the scenic spot was 0.38 mmol/L,and the mean nitrate nitrogen and oxygen isotopes were 4.8‰and 12.8‰,respectively.The mean nitrate content of surface water in the scenic spot was 0.25 mmol/L,and the mean nitrate nitrogen and oxygen isotopes were 9.0‰and 11.8‰.Isotope results show that the surface water of Qingtian River is related to the input of human activities from upstream,and the surface water of Yuntai Mountain and Qinglong Gorge scenic area is affected by agricultural activities,and the karst groundwater in front of the mountain may receive the surface man-made pollutants through the broken zone of Fenghuangling fault,whlie the spring water in the scenic area is affected by agricultural activities to a certain extent.（4）The results of Bayesian isotope mixing model showed that the sources of nitrate in the karst water of piedmont include soil N（81.1%）and feces and domestic sewage（12.7%）.The nitrate sources of spring water in scenic spots included soil N（31.5%）,chemical fertilizer（30.6%）and atmospheric precipitation（23.2%）.The sources of nitrate pollution in the surface water of the scenic spots varied greatly.The sources of nitrate in the surface water of Qingtian River were feces and sewage（50.8%）and soil N（25.3%）,while the main sources of nitrate in the surface water of Yuntai Mountain and Qinglong Gorge were soil N（29.8%）,chemical fertilizer（27.4%）and atmospheric precipitation（24.5%）.