Hydrogen And Oxygen Stable Isotopic Composition Characteristics And Transformation Relationships In The Water Bodies On The Southern Slope Of Qilian Mountains

In recent years,the trend of global warming has become increasingly severe,and study of the terrestrial ecosystem water transport process has become a scientific hotspot.In this paper,taking the southern slope of Qilian Mountains as the research area,Hydrogen and oxygen stable isotopes value of precipitation,river water,glacial meltwater,groundwater and soil water samples are measured,which has been collected in August 2018 and August 2019.This study analyzed the hydrogen and oxygen stable isotope data of different water bodies,clarified the composition and spatial variation characteristics of hydrogen and oxygen stable isotopes in different water bodies on the southern slope of Qilian Mountains.With the help of backward trajectory and trajectory clustering methods,we simulate the main water vapor sources and corresponding proportions in the study area.Combining end-element mixing model,GIS spatial analysis technology and?¹⁸O-?D relationship diagram of water body,we discuss the migration and transformation relationship between different water bodies,determines the river water supply end-elements and the corresponding recharge ratio,and explore the interrelationships between water bodies,determined the river water recharge end element and the corresponding recharge ratio,and the source of soil moisture.The article main research conclusions are as follows:?1?Hydrogen and oxygen stable isotope values of precipitation are mainly affected by altitude and latitude on the southern slope of the Qilian Mountains,and the environmental effects are very significant.In terms of spatial distribution,the stable hydrogen and oxygen isotope values in precipitation gradually depleted from Southeast to Northwest,and the deuterium surplus value gradually enriched on the whole.In terms of water vapor sources,westerly wind,continental air mass and southeast monsoon are the main water vapor sources during the sampling period,and there is also the contribution of local recirculation of water vapor.From northwest to southeast of the study area,the influence of westerly wind gradually weakens and the southeast monsoon strengthens.?2?The of?¹⁸O and?D values of the river are relatively big,and the equation of evaporation line is?D=4.87?¹⁸O-9.08?R²=0.87,n=158?.The evaporation intensity of the four major river water in the region is successively:Tuole River<Yeniugou River<Babao River<Datong River.In terms of the variation of?¹⁸O value along the river,Datong River was enriched first and then depleted,Yeniugou River and Babao River showed a trend of gradual enrichment,and Tuole River showed a phenomenon of depletion first and enrichment later,and most river sections shows an anti-elevation effect.In terms of stable hydrogen and oxygen isotope composition of groundwater,well water>spring>hot spring,and the equation of evaporation line is?D=4.39?¹⁸O-12.64?R²=0.73,n=31?.In terms of spatial variation,the groundwater isotope values show a trend of increasing?decreasing?increasing from southeast to northwest.Among them,the low-value areas are mainly located in the lower reaches of the sea,while the high-value areas are located in the higher mountains.?3?The equation of soil water evaporation line is?D=6.18?¹⁸O-6.24?n=593,R²=0.92?.In terms of vertical variation,?¹⁸O and?D values on the surface of soil water fluctuate greatly.In addition to arbor,with the increase of soil depth,?¹⁸O and?D values of different landscape types gradually decrease and tend to be stable at30-50cm.In terms of the spatial distribution,?¹⁸O values of different soil depth roughly shows a trend of decreasing?increasing?decreasing from southeast to northwest,among them,the western and middle south area has a?¹⁸O high value,and the northwest and middle east areas are low value areas,hydrogen and oxygen stable isotopes of the main landscape vegetation types in the qilian mountains from large to small is:cultivated land>arbor>meadow>grassland>shrub.?4?The main types of water recharge are precipitation,river water,groundwater,soil water and glaciers on the southern slope of Qilian Mountains,and the water bodies are closely related to each other.Among them,After water bodies are replenished by precipitation,which are affected by varying degrees of evaporation,supplement and discharge relationship between river water and groundwater is obvious,and soil water may recharge river water and groundwater.The inflow of different recharge sources has a great impact on the stable hydrogen and oxygen isotope values of river water in the basin.The upper and middle areas of Datong River are mainly recharged by rainfall,and the proportion is 80.8%;the middle and lower reaches were mainly replenished by groundwater,and the replenishment ratio was67.4%.The recharge sources of Yeniugou River are mainly precipitation and groundwater,accounting for 40.9%and 53.9%respectively;The upper reaches of Babao River are mainly affected by precipitation and groundwater,and the downstream is mostly affected by groundwater.while Tuole River is mainly recharged by rainfall and groundwater,with the proportions are 46.9% and 53.1%,respectively.