Stable Isotope Characteristics Of Different Water Bodies And Water Sources Of Permafrost Active Layer In Hulugou Catchment Of The Heihe River

Heihe River is a typical arid inland river in northwestern China.Seasonal active layer in the upper reaches is a key zone between surface water and groundwater,and plays an important role in the ecosystem.Therefore,the study of characteristics of different water isotope and water sources of active layer has important scientific significance and value for revealing hydrological processes.In this paper,Hulugou catchment in the upper reaches of the Heihe River in the Qilian Mountains is used as a study area.On the one hand,stable isotope study data of the predecessors in the Hulugou catchment are collected.On the other hand,river water,marsh water,ice and snow melt water,active layer water,frozen soil and spring water are collected,and on-site determination of basic water quality parameters and brought back to laboratory to measure stable isotope values,and summarize data and analyze the stable isotope characteristics of each water body in the basin and hydraulic connection between the water bodies.On this basis,combined with the previous studies,qualitative analysis of water source of frozen soil active layer and river water was carried out by using end-member mixed analysis chart.According to the qualitative analysis results,appropriate End-Member Mixing Analysis?EMMA?is selected.The tracer value of potential water sources is introduced into the End-Member Mixed Analysis model,and average contribution rate and contribution range of water sources of frozen soil active layer and average contribution rate and contribution range of active layer water to the river water are obtained.The results show that rainfall has obvious isotope elevation effect:For every 100m increase,the loss of?¹⁸O value is 1.31‰,and the loss of?D value is 4.56‰.The slope and intercept of river water local evaporation line equation?LEL?are smaller than the global meteoric water line?GMWL?and the local meteoric water line?LMWL?,indicating that the river has experienced strong evaporation and the?18O and?D values of river water gradually decrease from the downstream channel to the upstream source region,showing an obvious isotope altitude effect(?¹⁸O:-0.46‰/100 m,R²=0.66;?D:-4.15‰/100 m,R²=0.44).The equation evaporation line?LEL-S?of the shallow groundwater is:?D=7.69?¹⁸O+8.24?R²=0.91?,main source of recharge is precipitation,and is discharged into river.The equation evaporation line?LEL-D?of deep groundwater is:?D=6.09?¹⁸O+3.24?R²=0.63?,mainly originating from ancient water supplement,this ancient water will also be partially replenished by modern water.Ground ice at different soil depths has distinctly different characteristics and different sources of recharge.The d-excess value of the 5-20 m ground ice is the largest,while d-excess value of the seasonal ice?0-5 m?of the active layer near the surface is the smallest.The stable isotope value of the overall ground ice is close to the stable isotope values of rainfall and frozen soil meltwater,indicating that the source of subsurface ice recharge is rainfall and ground frozen soil meltwater.Water sources of permafrost active layer mainly come from rainfall,accounting for 74.49%;secondly,it is derived from seasonal ice of active layer,and the contribution rate is 25.51%.The infiltration of glacier and snowmelt is limited by the pores filled by the active layer ice and vegetation coverage,so the contribution of glacier and snowmelt to the active layer is minimal.The average contribution rate of rainfall to river water is 34.34%.The contribution of ice and snow meltwater to river water is the largest,accounting for 42.71%,while the contribution of active layer water to river water is only a small part,which is 22.94%.This study will provide a theoretical basis for fully understanding hydrological processes in permafrost regions and predicting changes in the hydrological cycle,and provide data support for establishing better regional hydrological models.