Spatial-temporal Variation Characteristics Of Water Chemistry And Its Controlling Factors In Mountainous Areas Of The Ili Kashi River Basin In Xinjiang,China

Rivers are a key component of the hydrological cycle,and their important characteristics of water chemistry can reflect the basic laws of migration and transformation of different water bodies of rivers to a certain extent,the regional environmental chemistry and the overall status of environmental quality.The composition of the water chemistry of the river water body records the lithology,vegetation cover status,climatic characteristics,human activities and main types of soil in the river basin,which is helpful for in-depth exploration of the overall environmental quality of the basin and the important characteristics of rock weathering and physical geochemistry.In recent years,the effects of global warming have exacerbated year-round snow cover and glacier melting,and altered river water chemistry.In the context of global warming,it is of great significance to further study the specific characteristics of water chemistry in dry areas.The Kashi River is the second largest tributary of the Ili River,a major river in the western section of the Tianshan Mountains in the Xinjiang Uygur Autonomous Region,and is an important source of supply for the upper reaches of the Ili River.In this paper,taking the water bodies in the Mountain Basin of the Kashi River as the main research objects,the water chemistry test data of surface water,groundwater samples and soil samples in the Kashi River Basin of Ili from January 2019 to November 2020 are used,combined with relevant information,to analyze the spatio-temporal variation characteristics and influencing factors of river water chemistry in the mountainous areas of the Kashi River Basin,and to discuss the sources of their substances.The main conclusions of this study are as follows:(1)The surface water and groundwater p H of the main stream in the mountainous areas of the Kashi River Basin are weakly alkaline,and the water chemistry characteristics of different water bodies are significantly different,the mineralization degree(TDS)of the water body is groundwater>surface water,the dominant anions of surface water and groundwater in the basin are HCO₃^-,Ca²⁺and HCO₃^-,Na⁺,respectively,and the chemical types of surface water and groundwater are HCO₃^--Ca²⁺-Mg²⁺,HCO₃^--SO₄^2--Na⁺-Ca²⁺,HCO₃^--SO₄^2--Na⁺-Ca²⁺,respectively The variation range of surface water is 29.4?558.1 mg·L^-1,the average value is 227.8 mg·L^-1,a low mineralization river;its mean(227.8 mg·L^-1),which is lower than the TDS mean of surface water in the semi-arid regions of the world(370 mg·L^-1),and below the mean TDS of surface water in arid regions(440 mg·L^-1),however,the mean TDS of surface water in the study area was higher than the world river mean(115 mg·L^-1)High.The mean EC is 174.9?S·cm^-1,EC and TDS are positively correlated,the more soluble salts dissolved in water,the higher the mineralization,the better the conductivity,and the greater the conductivity value of the water.Groundwater TDS varies from 440.1 to1045.3 mg·L^-1,average concentration 825.2 mg·L^-1?(2)The mass concentration of different main ions changes with the monthly trend,the concentration of each ion decreases in April and May,and the mass concentration in April is higher,the main reason is that the gradual rise of temperature makes the snowmelt water merge into the river,the ions enriched in the snow are replenished in the river water,and the time change of the mass concentration content of each water chemical ion is characterized by the increase or decrease of runoff,rain erosion,and groundwater recharge.The main reason for the high concentration of SO₄^2-ion mass is the interaction between strata and rivers in the study area.(3)The main stream of the Kashi River basin EC and TDS show seasonal changes:winter>spring>autumn>summer,and gradually decline with the increase of altitude.Moreover,the concentrations of Ca²⁺,HCO₃^-,Na⁺,K⁺ions were manifested as winter>spring>autumn>summer,SO₄^2-,Cl^-,Mg²⁺ion concentrations were manifested as winter>autumn>spring>summer,and the main ion concentration in space decreased with the increase of altitude,mainly because of the high proportion of ice and snow meltwater in high-altitude watersheds and the decrease in river ion concentration.(4)The average concentration of water chemical ions in the spring of the Ili Kashi River is higher than that in summer,which is due to the dilution of the main ions of the river water by rainfall,ice and snow meltwater and glacial meltwater dilution in the summer,diluting the main ion concentration of the river water,the dissolved ion content of the river water is generally low,the winter is affected by groundwater mixing,the solubility ion concentration of the river water is generally higher,and the spring is affected by the soil water melting effect,in addition,the spring precipitation is less,the flow rate is reduced,in the runoff process,the contact time between the river water and the surrounding environment is increased,and the number of ions dissolved is more,The solubilized ion content of the river water has increased again,and the main sources of replenishment of the river in autumn are groundwater and precipitation.The mass concentration of K⁺ions in the kashi water in spring and summer is less diluted.(5)The main ions of the Ili Kashi River water body are affected by rock weathering and cation exchange,and the main ions are derived from the weathering and dissolution of carbonate rocks and silicate rocks,which can be seen from the Pearson correlation coefficient that the mass concentration content of HCO₃^-and Ca²⁺in river water affects the size of TDS.HCO₃^-,Mg²⁺,Ca²⁺and SO4^2-mainly from the weathering and dissolution of carbonate salts such as dolomite,Cl-ions mainly include dissolution from evaporated salt minerals,Na⁺and K⁺derived from feldspars on the weathering and dissolution of silicate rocks.TDS at an altitude of 1792 m,Cl^-,Na⁺,SO₄^2-concentrations at an altitude of 1992 m and 2277 m above sea level showed an upward trend compared with 2460 m above sea level,but the concentration of ions varied little,and the influence of human activities on ion composition was weak.The water chemical composition carried by soil dissolution has a certain influence on the ionic composition of the Kashi River.