Study On The Runoff Sources Based On Stable Isotope Tracing In The Source Region Of The Yangtze River

Under the background of global warming,the drastic melting of cryosphere on the one hand causes the sharp decrease of solid water resources,on the other hand,the increasing melting water volume is gradually changing the hydrological process and water cycle characteristics.In particular,the changes of runoff components and hydrological effects caused by the increase of liquid precipitation and the severe melting of glacier,snow and frozen soil,which have resulted in the evolution of runoff and the generation of water cycle mechanism in the cold watershed.It has a profound impact on the spatial and temporal allocation of water resources and the development and utilization of hydropower resources.Then how to quantify the change of runoff composition in cold region under climate warming and severe melting of the cryosphere? Therefore,this paper takes the source region of the Yangtze River as the study area,a total of 1770 samples of precipitation,glacial snow meltwater,supra-permafrost water and river water were collected during sampling period.This paper studied the characteristics of stable isotopes and the indication of hydrological process of runoff by using the methods of stable isotope tracing and end element mixed runoff segmentation model in the source region of the Yangtze River.Then,the hydraulic relationship between runoff and precipitation,glacial snow meltwater,supra-permafrost water was analyzed based on stable isotope tracing.Finally,the components of runoff were determined.Meanwhile,the contributions of possible resources to the runoff,different types of tributaries and supra-permafrost water were quantified.In this paper,supra-permafrost water and its influence on the runoff in the cold region are taken as the research content for the first time,and it is confirmed that the supra-permafrost water is the main part of the runoff.In addition,the isotopic hydrology research is carried out from the perspective of water cycle process in the cold region,which takes the lead in quantifying the water supply sources of differenttypes of tributaries and supra-permafrost water and the temporal and spatial variation characteristics of the water supply sources,thus expanding the isotopic hydrology in the cold region.The results provide parameter support and theoretical basis for simulation and prediction of runoff change in cold region,then provide a scientific basis for a more systematic understanding of the hydrological effects caused by the change of underlying surface in cold region,and finally provide the decision-making basis for the rational development and utilization of water resources in the basin.The main conclusions are as follows:(1)Due to the local environment and the difference in the proportion of different water supply,the spatiotemporal variation of stable isotopes for the mainstream and the tributary river was significant.The spatial variation of stable isotopes of river water mainly reflected the the difference of recharge source and proportion of river water at different altitudes,the difference of precipitation conflux and dilution effect at different altitudes and the difference of evaporation at different altitudes.(2)The stable isotopic characteristics of glacial snow meltwater and supra-permafrost water were mainly affected by the ablation process,evaporation and change of supply sources in the source region of the Yangtze River.The altitude effect of oxygen isotopes of supra-permafrost water was bounded by 4400-4600 m.When the altitude was lower than the boundary altitude,the oxygen isotope of supra-permafrost water had an anti-altitude effect,while when the altitude was higher than the boundary altitude,the oxygen isotope of supra-permafrost water had an altitude effect.This phenomenon is mainly due to the increase of the recharge proportion of the ground ice meltwater to the supra-permafrost water with the increasing of elevation in study area.(3)Supra-permafrost water was the main source of the runoff in the source region of the Yangtze River.Compared with precipitation,glacial snow meltwater and supra-permafrost water,the stable isotopes in river water were more stable and less volatile from year to year,which suggested that the water bodies were firstly mixed into groundwater and then recharged into runoff.More importantly,the isotopic composition of the intersection between the local evaporation line of river water and the Local meteoric water line is very close to that of the supra-permafrost water.The clustering distribution and hydraulic relationship of stable isotopes in various water bodies indicated that the runoff were composed of three end elements,including supra-permafrost water,the precipitation and glacial snow meltwater in the sourceregion of the Yangtze river.(4)For the TTH station,supra-permafrost water,precipitation,and glacial snow meltwater accounted for 51%,26%,and 23% of river water,respectively.For the ZMD station,calculations indicated that 49% of the recharge was contributed by supra-permafrost water,with precipitation and glacial snow meltwater contributing by34% and 17%,respectively.The contribution from glacial snow meltwater to runoff displayed a decreasing trend from the source region to the river outlet in the study area,while the contribution of precipitation showed an increasing trend,and that of supra-permafrost water was nearly stable.Supra-permafrost water dominated the runoff in May,June and October,but the contribution rate of precipitation in July and August was about 50%.(5)Supra-permafrost water was the main source of the tributary river water in the glacier permafrost region,the permafrost region and mainstream at different altitudes.The supply proportion of the supra-permafrost water was not much different from that of the atmospheric precipitation and glacial snow meltwater during the strong ablation period.For the tributary river water in the glacier permafrost region,the supply proportion of atmospheric precipitation and glacial snow meltwater to the tributary river water was relatively low.However,atmospheric precipitation was the main source of the mainstream at different altitudes during the strong ablation.(6)Atmospheric precipitation was the main source of the supra-permafrost water in the source region of the Yangtze River.And then was ground ice meltwater,but the supply proportion of ground ice meltwater was far lower than that of atmospheric precipitation.However,the supply of glacial snow meltwater to the permafrost was only at the initial and end ablation period.Moreover,the supply of glacial snow meltwater to the supra-permafrost water was only limited to the area with higher altitude and supply proportion was also small.