Source Analyies Of Groundwater Nitrate In Mining Area Based On IsoSource Model

Mineral resources are abundant in Inner Mongolia,and the Shiguai mining area is an important coal supply in Inner Mongolia.The climate of the area is arid,and groundwater is the main source of drinking water in the area,and the groundwater quality is drastically affected by mining.In order to reasonably utilize water resources and ensure the drinking water safety of residents in the area,it is important to investigate the nitrate pollution distribution characteristics of groundwater in the mining area and trace the pollution sources.In this paper,we take Shiguai mining area as the research object,and investigate the spatial and temporal distribution of groundwater nitrate,statistical analysis of groundwater chemical components,sources of groundwater nitrate pollution and the contribution of pollution sources through conventional index detection,water chemistry,isotope detection,Iso Source model and other technical methods,combined with the type of land use and current geological disasters in the study area.The results showed the following.（1）Groundwater nitrite in the study area met the standard,ammonia nitrogen slightly exceeded the standard,and groundwater nitrate seriously exceeded the standard.The exceedance rate of nitrate in groundwater at the sampling sites was 40%,showing significant spatial and temporal characteristics.The nitrate content in the residential area has a significant increase from May to September,and there is no significant change in the mine area in all seasons.Along the groundwater flow direction,the nitrate content exceeded the standard in the downstream of the mine area and the upstream of the residential area.The values of p H,dissolved oxygen（DO）,conductivity,and redox potential reflect the occurrence of nitrification in groundwater in the study area.Through the above monitoring values combined with the analysis of geological conditions and different land use types,the preliminary judgment of groundwater nitrate pollution sources is mainly two aspects:agricultural production and the residual effects of mining.（2）The type of groundwater in the contaminated area is mainly bicarbonate-sulfate-calcium water,which is in line with the type of water chemistry in Inner Mongolia.The first principal factors are K⁺,Na⁺,and Mg²⁺,and the second principal factors are HCO₃^-,SO₄^2-,Ca²⁺,and Cl^-.The correlation between water chemistry ions and environmental factors indicates that the groundwater water chemistry components are influenced by mining and agricultural and domestic wastewater.（3）The variation of δ¹⁵N-NO₃^-in groundwater ranged from 0.07 to 2.69‰,and the variation ofδ¹⁸O-NO₃^-ranged from-5.09 to-2.85‰.Qualitative analysis of isotopic characteristic values and quantitative tracing by Iso Source showed that soil nitrogen and NH₄⁺nitrification from fertilizers were the main sources of groundwater nitrate,and the data indicated that the closer the distance to the mine site,the higher the contribution of soil organic nitrogen,proving that the groundwater quality in the shutdown mine is recovering.The mine has been closed for many years and the water quality has gradually recovered,but nitrate pollution still exists in the groundwater of resource-depleted mining areas.A series of targeted initiatives are proposed for the nitrate pollution characteristics and sources of groundwater in the study area,aiming to provide a basis for water pollution control planning in this type of resource-depleted urban groundwater,and also provide theoretical support for subsequent management of groundwater quality in this type of area.