Study On The Isotope Characteristics Of Different Water And Their Transformation Relationship In Subalpine Shrubland In The Eastern Of Qilian Mountains

Due to the response of stable isotopes to environmental changes,the difference in composition is caused.Therefore,stable isotopes have become natural tracers in water cycle research,and they play an important role in the research of the sources and transformation processes of different water bodies.As the main water supply area of the Hexi Corridor,Qilian Mountain is an important ecological security barrier in Northwest China.In order to understand fully the ecological hydrological process and water cycle mechanism in the subalpine shrubland of the Qilian Mountains,this paper uses the vegetation growth season from May to October in 2019 as the sampling period.At the same time,the precipitation,soil water,plant water,river water and spring water in the study area were collected to analyze qualitatively the characteristics of hydrogen and oxygen stable isotope of different water bodies and the differences of the isotope of similar water bodies on the different slopes.And the backward trajectory model,the MixSIAR model and the isotope mass balance model were used to calculate and analyze quantitatively the sources of precipitation water vapor,plant water sources,soil water,river water and spring water in the study area.On this basis,according to the isotope characteristics of different water bodies and their contribution rate of water sources,the relationship of water body transformation and the ecological hydrological process in the subalpine shrubland of Qilian Mountains is discussed,so as to provide a basis for ecological restoration and environmental construction in the region.The research results show the following:(1)Among the five types of water bodies in the study area,the isotope value of the shrub plant water is largest,and it is greater on the semi-shady slope than the sunny slope.The isotope value of precipitation fluctuates the most,and spring water fluctuates the least.The values of soil water and spring water are closest,and the seasonal changes show a relatively consistency.(2)The Local Meteoric Water Line(LMWL)in the study area was?D=7.63?¹⁸O+14.06(R²=0.95,n=57).Its slope is slightly smaller,and the intercept is larger,reflecting the characteristics of strong evaporation but relatively humid in the study area during sample collection.The distribution of hydrogen and oxygen stable isotopes in various water bodies is concentrated in the LMWL or its vicinity,reflecting that precipitation has a certain replenishment effect on other water bodies.(3)The water vapor of precipitation in the study area is mainly affected by the westerly circulation.The soil water in the study area comes mainly from precipitation and spring water,and their contribution rates reache 45.8%and 36.8%,respectively.For the soil water,the contribution rate of precipitation decreases with the deepening of the soil layer,while the contribution rate of spring water is opposite.The shrub plant water is most recharged by soil water of 0-20cm,reaching 38.1%.The river water is mainly supplied by precipitation and spring water,with contribution rates of 29.2%and 25.7%respectively.Spring water comes mainly from soil water,and the contribution rate of soil water to spring water reaches 32.4%.(4)The precipitation in summer in the study area contributes the highest rate of soil water,reaching 57.2%.The soil water in spring and autumn is mainly recharged by river water and spring water,respectively.The contribution rate of precipitation to the shrub plant water reaches the maximum in spring,and soil water from 0 to 20 cm in summer and autumn becomes the dominant source of the shrub plant water.Soil water contributes the most to river water in spring,and precipitation in summer becomes the dominant source of river water,and spring water is the main source of replenishment for river water in autumn.Spring water is closely related to soil water,and soil water has the largest replenishment ratio to spring water in summer.(5)In different slope directions,the change trend of the water source contribution of soil water and shrub plant water is the same basically.The difference in the contribution rate of soil water source of different slope directions is related to the physical and chemical properties of the soil,and the difference in water contribution rate between different plants is related to the root characteristics of the plants.The contribution rate of sunny slope soil water to spring water is greater than that of semi-shady slope soil water.