Hydrochemical Characteristics And Formation Mechanism Of Basalt Groundwater In Zhangbei County

Zhangbei County is located in Bashang area at the south foot of Inner Mongolia Plateau.It is an important vegetable planting base and an important ecological barrier protection area in the capital.The basalt groundwater with good quality is an important pillar of economic development in this area.However,with the continuous expansion of agricultural water demand,many years of dynamic monitoring data of water quality show that the increase of mineral degree and deterioration of water quality in basalt aquifer seriously threaten the sustainable development of the region.Based on the systematic analysis of the geological and hydrogeological background of Zhangbei County,this paper studies and analyzes the chemical characteristics and evolution law of basalt groundwater by means of mathematical statistics,ion proportion coefficient,isotope analysis and hydrogeochemical simulation,so as to provide scientific basis for the sustainable development and utilization of groundwater resources in the region.The results show that the chemical types of shallow groundwater in the exposed area of basalt in the study area are mainly HCO3-Ca and HCO3-Ca-Mg,while the hydrochemical types of deep groundwater in the concealed area are relatively complex,including HCO3-Ca,HCO3-Ca·Mg,Cl·SO4-Na·Mg and Cl·SO4-Na·Mg.The spatial distribution of the main ions and TDS in the groundwater is as follows:the TDS and other anions in the shallow water of basalt do not appear high value area,while the deep water of basalt appears high value area from the lower reaches of Angulinao to Gonghui Town,and the TDS near ergegu and glassy river in baotouying Township appears high value area,and along the direction of groundwater flow,the TDS value gradually increases from supply runoff area to discharge area,and the water quality also gradually increases In Gibbs diagram,the ion proportion relationship shows that basalt groundwater is obviously affected by water rock interaction,and the cation in groundwater is mainly affccted by the dissolution of aluminosilicate minerals,and the cation is affected by the alternate adsorption,and the anion is mainly controlled by the dissolution of rock salt and gypsum.At the same time,basalt groundwater is greatly affected by human activities;hydrogen and oxygen isotopes further indicate that the main source of groundwater recharge is atmospheric precipitation,and it is affected by evaporation in the process of receiving recharge;reverse simulation results show that basalt groundwater in the study area is mainly affected by weathering and dissolution of silicate,rock salt,sulfate and other minerals,cation exchange adsorption,calcite sedimentation In addition,human activities have different effects on the evolution of groundwater.