Stable Hydrogen And Oxygen Isotopes Of Precipitation In The Eastern Tarim River Basin And Their Controlling Factors

Among the common environmental isotopes,stable isotopes of hydrogen and oxygen,as a component of water,are the important media of material and energy transfer in the surface environment.The monitoring of stable hydrogen and oxygen isotopes(?²H and?¹⁸O)in precipitation is the basis of the application of isotope tracer technology in environmental science.It helps to understand the process of phase change,mixing and transportation of water bodies in different environments,and provides a reference for the engineering application of water resource allocation,disaster prevention,weather modification and other aspects.Due to the arid climate in the eastern Tarim River Basin of southern Xinjiang,water resources are the key factor affecting the sustainable development.However,the knowledge of factors controlling stable hydrogen and oxygen isotopes in precipitation is still limited.Taking the eastern Tarim River Basin as the research region,this paper analyzes the temporal and spatial distribution of stable hydrogen and oxygen isotopes in precipitation through the in–situ monitoring,and discusses the environmental factors impacting the stable hydrogen and oxygen isotopes.This paper aims to provide a reference for the application of environmental isotope tracer technology in arid areas,and provide necessary data for the rational use of local water resources.The main conclusions are as follows:(1)The observations at four sampling sites(Bayanbulak,Korla,Tikanlik and Qiemo from north to south)in the eastern Tarim River Basin show that the stable hydrogen and oxygen isotope values in precipitation are higher in the south and lower in the north;on a seasonal basis,the isotope values are higher in summer months and lower in winter months.The average d–excess in the study region is smaller than the national average.The slope of the local meteoric water line in the study region shows a significant arid characteristics,and the slopes and intercepts at all sampling sites are relatively small.(2)The stable isotopes of hydrogen and oxygen in the precipitation of the eastern Tarim River Basin present a positive correlation with air temperature,while the d–excess values show a weak negative correlation.The relationship between isotope values and precipitation amounts is not significant,but there is a strong negative(and positive)correlation between stable isotope values(and d–excess)and relative humidity.Based on an improved Stewart model of raindrop evaporation,the below–cloud secondary evaporation influencing the stable hydrogen and oxygen isotopes in precipitation were quantitatively evaluated across the eastern Tarim River Basin.Spatially,Bayanbulak in the northern mountainous area has the largest remaining ratio of evaporated raindrop and the smallest difference of stable isotopes in raindrops between the surface and the cloud base.On the contrary,Tikanlik has the smallest remaining ratio and the largest difference of isotopes in raindrops below the cloud base.(3)The Lagrangian backward trajectory shows that the eastern Tarim River Basin is mainly controlled by the mid–latitude westerlies,instead of marine moisture.The air mass usually comes from the middle and short distance,and the water vapor in the Mediterranean Sea,Caspian Sea,Black Sea and inland surface is more likely to be the main sources.The results of concentration weighted trajectory show that the farther away from the sampling site,the more stable the d–excess in air mass.The closer to the sampling site,the more frequent the concentration changes,indicating that the d–excess value is greatly affected by the local water vapor cycle.