Hydrochemical And Isotope Evidence Of Surface Water And Groundwater Conversion In Manas River Basin

Manas River Basin is located in the southern margin of Junggar Basin,where evaporation is intense,precipitation is scarce and water resources are relatively scarce.Water resources are an important factor restricting local economic development and affecting the production and life of urban residents.The transformation relationship and amount of surface water and groundwater are important links in the water resources evaluation of the basin.It is of great value and significance to carry out the research on the transformation relationship and transformation mode of surface water and groundwater for further revealing the water cycle model of the basin,evaluating the water resources quantity of the basin,and formulating a reasonable water resources development and utilization plan.In this paper,the Manas River Basin is taken as the research area.On the basis of fully analyzing the geological and geomorphological conditions for controlling groundwater flow movement and collecting and utilizing the existing achievements,and guided by the theory of groundwater flow system,the basic pattern of surface water and groundwater transformation in the basin is discussed by comprehensive analysis method.Combined with groundwater flow numerical simulation,hydrogeochemistry,environmental isotope and other methods,the characteristics of water cycle in the basin are analyzed,and the transformation relationship between surface water and groundwater in different geomorphic units is further revealed.The main results of the study are as follows:(1)Starting from the geological and geomorphological conditions and tectonic movements of the basin,the research basis of the predecessors is fully analyzed,and the transformation relationship between surface water and groundwater in the basin under natural conditions and environmental changes is clarified.Geological and geomorphological conditions control the basic pattern of surface water-groundwater transformation in the basin.From the southern intermountain depression to the northern Tailu Lake,surface water and groundwater have been transformed many times.In the Intermountain depression,surface water and groundwater have undergone two transformations.From Kenswat to the Intermountain spillover zone,the river seeps to recharge groundwater,and from the Intermountain spillover zone to the outlet.Groundwater overflows to recharge river water due to the obstruction of the second row structure.When the alluvial fan river water is disconnected from groundwater,the river water seeps into the phreatic surface to recharge groundwater through a thick aeration zone,and the groundwater recharges the river water at the spillover zone.The relationship between river water and groundwater in fine soil plain is complex,but the general trend is groundwater recharge.Under the influence of climate change and human activities,the transformation range of surface water and groundwater in the basin is expanded,and the transformation relationship is more complex.(2)The dynamic process of surface water-groundwater transformation in the basin is analyzed by using the numerical simulation technology of groundwater flow.The results show that there are three local flow systems,one intermediate flow system and one regional flow system from the southern intermountain depression to the Tailu Lake.Groundwater runoff in local flow system is faster,runoff velocity is more than 1 m/d,groundwater age is less than 50 years;groundwater runoff condition in intermediate flow system is slower,runoff velocity is 0.1-1 m/d,groundwater age is between 50-2000 years;groundwater circulation in regional flow system is slower,runoff velocity is less than 0.1 m/d,groundwater age is older than 2000.(3)With the change of geomorphic units,the hydrochemical types and characteristics of surface water and groundwater in Manas River Basin have obvious spatial variability.From intermountain depression to Tailu Lake,TDS of river water and phreatic water increased along the river course.The overall evolution trend of river water chemical types was from HCO3·SO4-Catype in intermountain depression to SO4·Cl-Na type in fine soil plain,and finally to Manas Lake to Cl-Na type.The chemical types of diving evolved from SO4·HCO3-Ca to SO4·HCO3-Ca,then gradually to SO4·Cl-Na(Na·Ca)and Cl·SO4-Na.The evolution of groundwater chemical composition reveals the hydrogeochemical effect of groundwater in the process of flow,in which the groundwater in alluvial fan and spillway zone is mainly controlled by rock leaching,while the groundwater in fine soil plain is mainly controlled by evaporation and concentration,and the confined water is mainly controlled by rock leaching.(4)Isotopic characteristics show that the river water and groundwater in Manas River Basin originate from the precipitation and melting water of ice and snow in the southern alpine region,but the river water in the lower reaches of Manas River Basin deviates from the local precipitation line and is at an angle with the precipitation line.This indicates that the river water in Manas River Basin has experienced strong evaporation when it passes through the lower reaches of the fine soil plain.The proportion of evaporation in the lower reaches reaches 17.36%~30.43%.The spatial evolution characteristics of Hydrochemistry and isotopes show that the upstream of Intermountain depressions and Alluvial-diluvial fans in front of mountains are the recharge runoff areas of the whole region,the Intermountain depressions are near the mountain pass,the spillover zone begins to be the discharge area of groundwater from the fine soil plain,and the river water and phreatic water are closely related and constantly transformed,while the relationship between confined water and river water is weak.