Hydrochemical And Stable Isotopic Characteristics And Analysis Of Water Supply Sources In The Kashi River Mountain Area Of Ili

Water resource is one of the important basic resources for human survival.At present,a serious problem of social development is to protect water resource and water environment.Using hydrochemistry and stable hydrogen and oxygen isotope technology can reveal the hydrologic environment and hydrologic cycle,which is beneficial to protect the balance of water resources and water quality,and rationally develop and utilize water resources in the basin.Kashi River basin of Ili is the second largest tributary of Ili River,which is an important water source in this region and an important guarantee for the economic development and ecological civilization construction in Ili.At present,the problems of water resources and water environment are affecting the local economic development.In this study,Kashi River basin of Ili was selected as the research area to study the hydrochemistry and stable hydrogen and oxygen isotopes in different water bodies,which is to provide scientific guidance for the rational development and utilization of water resources in inland river basin in arid area of northwest China,and enrich the hydrological cycle research of inland river basin.It is of great significance to protect the balance of local water resources and water environment.Based on precipitation,spring water,groundwater,snowmelt water and ice melt water samples were collected in Kashi River Basin from 2018 to2020,through the hydrochemical and stable isotopic data of samples,combined with the regional climate and geological data,the temporal and spatial variation characteristics of hydrochemistry and stable hydrogen and oxygen isotopes of samples were analyzed,and the following conclusions were drawn:(1)The hydrochemical characteristics of different water bodies were significant differences in the basin.The TDS of groundwater is the highest which is 831.74mg/L,followed by that of spring water which is 413.03mg/L,and TDS of river water is the lowest which is 255.92mg/L.The p H of river,groundwater and spring in the basin was 8.06,8.18,7.84,respectively,which is weakly alkaline.The dominant ions of water in the basin are mainly Ca²⁺and HCO₃^-,the differences of hydrochemical control factors led to the dominant ions were different in different water bodies.According to shukalev's classification,the river water was Ca²⁺-HCO₃^-type,the groundwater was Na⁺-Ca²⁺-HCO₃^--SO₄^2-type,the spring water changed from Ca²⁺-Mg²⁺-Na⁺-HCO₃^--SO₄^2-type and Ca²⁺-HCO₃^-type to Ca²⁺-HCO₃^--SO₄^2-type with altitude increasing.The seasonal variation of hydrochemical indexes in river water of the basin were high in winter and low in summer.The physical and chemical properties of groundwater were relatively stable,and the temporal variation characteristics of hydrochemical indexes were not obvious.The hydrochemical indexes of river water and spring water decreased with elevation.The hydrochemical indexes of river water is prone to abnormal spatial variation due to the influence of water conservancy facilities.The main controlling factors of river and spring water chemical composition were rock weathering hydrolysis,and the groundwater chemical composition was controlled by evaporation concentration and rock weathering.The main weathering process was the hydrolysis of carbonate minerals in the basin.In addition,pyrite(Fe S₂)oxidation was found in the rock weathering process of river water,while hydrochemistry of groundwater was affected by weathering of sulfide minerals and evaporative salt minerals,hydrochemistry of spring water was affected by weathering of sulfide minerals.(2)The seasonal variation of stable isotope in precipitation was depleted in winter and spring,and enriched in summer and autumn in the basin.The d-excess of precipitation was high in the cold season and low in the warm season.At the seasonal scale,the effect of temperature was significant in precipitation,while the effect of precipitation was weakened.The local meteoric water line(LMWL)was?D=7.24?¹⁸O+8.23(R~2=0.94),indicating that the precipitation process has experienced different degrees of evaporative fractionation.The stable isotopes of river were enriched in autumn and winter,depleted in spring and summer.The d-excess of river was high in spring and summer and low in autumn and winter.The stable isotopes of river water gradually becomes depleted with the increase of altitude,and its variation of altitude is abnormal due to the influence of water conservancy facilities.The decreasing rate of?¹⁸O with altitude were0.5‰/100m and 2.6‰/100m in 2018 and 2019,respectively.The stable isotopic variation of groundwater was relatively stable,and its variation range was smaller than that in river and precipitation.The stable isotope of spring water was obviously depleted at low altitude and enriched at high altitude under the influence of different recharge source components.The river line of the basin was?D=3.06?¹⁸O-46.07(R~2=0.39),The evaporation line of groundwater was?D=1.84?¹⁸O-70.48(R~2=0.57),The evaporation line of spring water was?D=8.80?¹⁸O+27.50(R~2=0.99),the slope of above three water bodies indicated the degree of evaporative fractionation in the process of precipitation replenishment.The degree of evaporative fractionation was stronger in the process of recharging river water and groundwater by precipitation,but weaker in the process of recharging spring water.(3)The variations of hydrochemistry and stable isotope of river,groundwater and spring water were mainly affected by supply source components.Precipitation was the main supply source in the basin.Based on the analysis of hydrochemistry and stable isotopes in the river,The recharge source of the river is mainly fissure bedrock water in winter.Precipitation and snowmelt water are main supply source in spring.Snowmelt water,ice melting water,and precipitation are main supply source in summer.The main recharge sources of river water are groundwater and precipitation in September and October,while the main supply source is fractured bedrock in November.Using the binary segmentation model based on?¹⁸O,which calculated the proportion of river water supply sources of headstream region in July and the recharge proportion of precipitation and groundwater in river water in different seasons.The recharge proportion of ice melt water was higher than that of snowmelt water in the river source region,and their proportion of supply were 55.52%and 44.48%,respectively.Groundwater is the vital component of the supply sources in Kashi River of Ili.The recharge proportion of groundwater in spring,summer and September was 93.70%,83.39%and 91.11%,respectively.Due to the influence of permafrost,the recharge proportion of groundwater was reduced to 79.5%in October.