Spatiotemporal Variations Of Hydrogen And Oxygen Stable Isotope Compositions For Soil Water And Soil Evaporation In Shaliu River Basin,Qinghai Lake

Soil water is an important part of water resources.It bears the primary task of material transmission and energy transfer in the soil-plant-atmosphere continuum(SPAC),and plays a key role in the normal operation of the entire ecosystem.Soil water is also an indispensable part of the regional water cycle,and soil evaporation is the main way for soil to participate in the regional water cycle.Applying the hydrogen and oxygen stable isotope technology to soil water research,by estimating the amount of soil evaporation loss,we can understand the soil evaporation at the watershed scale,which has a very important reference value for the quantitative study of the proportion of each link in the water cycle process on the watershed scale.This study is based on the determination results of stable hydrogen and oxygen isotopic compositions(?¹⁸O,?²H)of soil water and precipitation samples in the growing seasons between 2018 and2019 in the Shaliu river basin of Qinghai Lake,analyzing the temporal and spatial variation characteristics of the hydrogen and oxygen stable isotopic composition of soil water in the Shaliu river basin of Qinghai Lake.The Craig-Gordon model is used to calculate the ratios of soil evaporation loss in this watershed,revealing the spatiotemporal characteristics of soil evaporation intensity in the Shaliu river basin of Qinghai Lake during the growing season.The main results are as follows:(1)The?¹⁸O,?²H and d-excess values of soil water during the growth season in2018 in the Shaliu river basin of Qinghai Lake ranged from-13.58‰to-1.67‰,-93.59‰to-12.03‰and-15.30‰to 22.93‰,respectively.The average values were-6.73±1.59‰,-46.84±10.02‰and 6.11±5.12‰,respectively.The variations of the hydrogen and oxygen stable isotope compositions for soil water in the growing season in 2018 on the river scale were generally depletion?enrichment?depletion.The range of?¹⁸O,?²H and d-excess values of soil water in the growing season in2019 ranged from-16.48‰to-1.26‰,-126.53‰to-9.72‰,and-13.05‰to28.13‰,respectively.The average values were-6.36±1.74‰,-45.54±11.59‰and4.76±5.05‰,respectively The change trend of hydrogen and oxygen isotopic composition of soil water in the growing season in 2019 was depletion?enrichment?depletion?enrichment.(2)In terms of profile changes,the hydrogen and oxygen stable isotope composition of soil water in the growing season of 2018 and 2019 fluctuated greatly from 0?30 cm,and the overall trend was to gradually deplete with depth.The fluctuation of stable isotope composition of hydrogen and oxygen in soil water below30 cm decreased,and the overall change showed the characteristics of gradual depletion.(3)There was a significant correlation between the?¹⁸O and?²H of soil water(the linear regression equation was called the soil waterline).Except that the slope of soil water line is higher than that of local atmospheric precipitation line in some months,the slope of soil water line at different depths is lower than that of local atmospheric precipitation line;The results show that the intercept and slope of soil water line at different depths are related to the change of local atmospheric drawdown line,which indicates that the soil water in Shaliu river basin of Qinghai Lake is mainly supplied by atmospheric precipitation,and the soil water in individual months is affected by the mixed supply of previous precipitation.(4)In 2018,the monthly average ratio of soil evaporation loss during the growing season in the Shaliu river basin of Qinghai Lake increased and then decreased.Spatially,the average proportion of soil evaporation loss in growing season fluctuated greatly.The high-value areas were mainly distributed in the northeast of the watershed,and the low-value areas were mainly distributed in the southwest of the watershed.In terms of the depth of the soil profile,the proportion of annual average soil evaporation loss in the alpine steppe zone kept decreasing with the deepening of soil depth.In the growing season of 2018,the average ratio profile changes of soil evaporation loss in the alpine meadow zone and the alpine cold desert zone showed the characteristics of first increasing and then decreasing.The average ratios in growing season of soil evaporation loss in alpine grassland,alpine meadow,and alpine desert was 58%,55%,and 63%,respectively.In the growing season of 2019,the average ratio of soil evaporation loss in the growing season of the Shaliu river basin of Qinghai Lake increased first,then decreased,and then increased.Spatially,the growth season average ratio of soil evaporation loss in the Shaliu river basin was relatively large and fluctuated relatively little.The spatial distribution characteristics were high in the north and low in the south,and high in the west and low in the east.In the depth of soil profile,the average ratio of soil evaporation loss in growing season in alpine steppe and alpine meadow decreased with the depth.The annual average proportion of soil evaporation loss in the alpine cold desert zone first increased and then decreased.The average ratios in growing season of soil evaporation loss in alpine grassland,alpine meadow and alpine desert were 52%,77%,and 67%,respectively.Comparing the soil evaporation loss at different heights in the two growing seasons,the monthly average ratio in 2019 was greater than that in 2018.