External groundwater recharge of Tianchi Lake in Changbai Mountain

Water sources in volcanic regions have long been a focal point in hydrogeology. Tianchi Lake of the Changbai Mountain in Northeast China, the world's highest volcanic lake, has historically faced water imbalance issues. This study offered a comprehensive analysis of the water sources of Tianchi Lake, examining water volume, hydrodynamics, hydrochemistry, and isotopic evidence. Flow simulations of the Changbai Mountain waterfall during the glacial period indicated that besides local precipitation stored within the mountain during the non-freezing period, other groundwater sources were involved. Additionally, the volume of spring water and the geological structures in the Tianchi Lake area suggested that even expanding the watershed boundary cannot fully account for water balance within the region. Comparative analysis of hydrogen and oxygen isotopes in groundwater and local precipitation within the Changbai Mountain region revealed that external water recharged Tianchi Lake via deep circulation, sustaining the stable flow of Tianchi Lake and its surrounding springs. This study provides valuable insights into the mechanisms and recharge processes of groundwater circulation in volcanic regions.