Characteristics Of Groundwater Stable Isotopic Compositions In Eastern Qaidam Basin:Implications For Moisture Sources And Climate Change

Groundwater is an important water source for human survival and economic development in the arid area of northwest China.Under the condition of global warming,the moisture source and transport pattern controlling the generation of precipitation will affect the groundwater recharge and distribution of water resources and play an important role in the hydrological cycle,which is of great significance to the rational utilization of water resources.In this paper,the eastern Qaidam Basin is the main study area.The stable isotopes(?D,?¹⁸O)of atmospheric precipitation,river water and groundwater,groundwater ¹⁴C and HYSPLIT backward trajectory modeling were combined to determine the recharge source of river water and groundwater,illuminate the spatiotemporal distribution of groundwater stable isotopes and the main controlling factors,and to reveal the evolution of moisture source and climate change during the last 30 ka.In addition,the stable isotopic spatial distribution of groundwater collected from 12 basins and plains in China was also discussed as well as their relationship with moisture source and transport pattern,and the climate changes in different basins and plains and their relationship were analyzed.The main conclusions can be drawn as follows:(1)The climate characteristics obtained from the relationship between?D and?¹⁸O of atmospheric precipitation in the northern and southern study area were similar.River water was mainly recharged by the precipitation and snowmelt water from the mountainous area.The river stable isotopic compositions showed a depleted tendency in space(from west to east)in the southern study area,whereas were similar in different regions of the northern study area.The stable isotopic compositions and high d-excess of precipitation and river water indicated that the Qaidam Basin was mainly controlled by Westerlies,and the water vapor mainly came from the region with dry climate.(2)The main recharge source of groundwater was precipitation and snowmelt water in the mountainous areas.Groundwater stable isotopes showed different spatial distribution characteristics in the northern and the southern study areas,which has not changed obviously since the late stage of the Late Pleistocene.In the northern study area,the groundwater with the most depleted stable isotopes was from Yuka area located in the west,and the groundwater stable isotopes in Daxiao Qaidam and Delingha are similar and more enriched than those of Yuka.However,the stable isotopes of groundwater in the southern study area showed a trend of gradual depletion in space from west to east.A combination of groundwater d-excess and HYSPLIT backward trajectory modeling indicated that the Qaidam Basin was mainly dominated by the water vapor controlled by the Westerlies,which may not have changed since the late stage of the Late Pleistocene.The Westerlies and local geographical factors(elevation effect)are respectively the main factors controlling the spatial distribution of groundwater stable isotopes in the southern and northern study areas,and the moisture recycling also affected Delingha.(3)In the continental-scale area,the spatial distribution of stable isotopes in groundwater is influenced by moisture sources and transport pattern,local geographical factors and climate conditions.Along the water vapor transport trajectory,the groundwater stable isotopes in the monsoon region were gradually depleted,and those in the non-monsoon region did not show a spatial distribution characteristic due to the local geographical factors and climate conditions.However,the groundwater stable isotopes showed a depleted trend for a small-scale region such as Hexi Corridor and southeastern Qaidam Basin in the non-monsoon region.During the period of15-3 ka,the climate of different basins and plains showed similar changing trends,which contribute to understand the distribution of regional groundwater resources.