Research On The Characteristics Of Groundwater Recharge And Evolution Along The Middle And Upper Reaches Of The Jinghe River Basin

Groundwater is an extremely important strategic resource in the world and plays an important role in production,life and economic development.Affected by climate change and human activities,groundwater resources in arid and semi-arid regions have undergone great changes in recent years,and even serious overexploitation and pollution problems have occurred,threatening regional water security and ecological security.The middle and upper reaches of the Jing River are located in the Loess Plateau of Longdong,the central part of the Yellow River Basin.Groundwater is one of the important local water resources.Due to the lack of understanding of the properties of groundwater resources,the problem of groundwater overexploitation is very serious.Therefore,it is necessary to further carry out research on the evolution of regional groundwater cycle,fully understand the status of groundwater resources,accurately and effectively distinguish the groundwater recharge environment and migration characteristics,estimate groundwater recharge amount,for the management and protection of regional groundwater resources,ensure water safety and ecological safety,and promote the Yellow River.The construction of ecological civilization and high-quality development in the basin is of great significance.Through the application of hydrochemistry and isotopic techniques,combined with the calculation of water balance,the paper analyzes the recharge source and runoff characteristics of groundwater along the middle and upper reaches of the Jinghe River Basin,studies the mutual transformation relationship between groundwater and surface water,and reveals the recharge and discharge of groundwater in the Jinghe River Valley.characteristics,the following conclusions are drawn:（1）The change of water chemical composition in the study area has a certain trend and regularity,and the sources of groundwater recharge in the valley are diverse.According to the analysis of the hydrochemical characteristics of surface water and groundwater samples,the hydrochemical types of the main stream of the Jing River are mainly HCO₃-Ca and SO₄·HCO₃-Ca,and the hydrochemical types of each tributary are mainly HCO₃-Ca·Na.The types of groundwater are mainly HCO₃·SO₄-Ca·Na and HCO₃-Ca,and the TDS distribution of groundwater in the Jinghe River Valley and on both sides of the river shows an increasing-decreasing-increasing trend from west to east in space.In the Kongtong section,the distribution regularity of TDS is not strong.It can be roughly seen that the TDS of groundwater in the main stream of the Jing River is relatively large,and the TDS in the plateau areas and mountainous areas on both sides of the river is relatively small.The Gibbs distribution model shows that the chemical components of groundwater and surface water are controlled by rock weathering,groundwater and surface water are closely related,and some water bodies are also affected by human activities.The saturation index index shows that the main minerals that contribute to groundwater ions are anhydrite（Ca SO₄）,rock salt（Na Cl）,gypsum（Ca SO₄:2H₂O）,potassium salt（KCl）and so on.Under the indication of hydrochemical characteristics,it is judged that the groundwater recharge in the valley mainly comes from the infiltration recharge of the river,while the upstream groundwater underflow recharge,the lateral recharge of groundwater on both sides,the infiltration recharge of agricultural irrigation and the recharge of atmospheric precipitation also have a certain recharge to the groundwater..（2）The isotopic characteristics show that the main source of the water body in the study area is atmospheric precipitation,and the isotopic characteristics are quite different.According to the stable isotope characteristics of the collected water samples,combined with the International Atomic Energy Agency’s Global Atmospheric Precipitation Isotope Observation Network（GNIP）,the local atmospheric precipitation line（LMWL）in the study area was obtained as:δD=7.33δ¹⁸O-0.65.The deuterium surplus value shows that the main sources of water vapor in the study area are the dry and cold air of the westerly wind and the warm and humid air mass of the southeast monsoon.The slope of the fitting curve of surface waterδD-δ¹⁸O is 1.0,which is quite different from the slope of the atmospheric precipitation line,and it is obviously enriched by evaporation.The variation range of hydrogen and oxygen isotopes of groundwater in the study area is larger than that of surface water,and the enrichment degree is slightly larger.The variation range of ¹⁸O is-8.96‰～-10.92‰,the average is-9.84‰,and the slope is 7.30.The two slopes are similar,The slopes of the two are similar,indicating that the main source of groundwater recharge is also precipitation,and compared with surface water,the evaporation effect has less impact on groundwater,but evaporation is still the main reason for the enrichment of hydrogen and oxygen isotopes in groundwater.The hydrogen and oxygen isotope characteristics of surface water and groundwater show that the mixed area of surface water and groundwater is mainly distributed betweenδ¹⁸O=-10‰～-8‰,and the hydraulic connection between surface water and groundwater is quite close.Using the correlation between isotopeδ¹⁸O and Cl^-concentration,the sources of individual water samples and different environments are shown.According to the isoline map ofδ¹⁸O andδD spatial distribution,the characteristics of groundwater hydrogen and oxygen isotopes in the study area are depleted in the north and enriched in the south.Especially in the southwest of the study area,the isotope enrichment is the largest.（3）The Jinghe Valley has a wide range of diving sources,and the supply and discharge are relatively balanced.The Jinghe valley phreatic water belongs to loose rock pore water,and its main feature is rapid alternation.The groundwater level fluctuates for many years,the groundwater level has gradually recovered since 2017.The total recharge of groundwater in the Jinghe River Valley is 112.1159 million m³/a,the groundwater reserves are 368 million m³,and the exploitable groundwater volume is 89.6927 million m³.The total discharge volume is 115.301 million m³/a,the equilibrium difference is-3.1852 million m³/a,and the relative equilibrium difference is-2.84%.The groundwater in the Jinghe Valley is basically in equilibrium during the equilibrium period.