Abstract: In recent 20 years,with the rapid development of key town economy in the river basin,affected by human activities and global climate change,the basin water cycle factors changed. It is necessary to carry out the research on groundwater circulation and water quality evolution rule. Buha river water,the main source of Qinghai Lake,a main place for breeding Gymnocypris przewalskii of Qinghai Lake,is significant to the stability of water resources and quality according to the surface water circulation and water chemistry. We investigated the regional hydrogeology background to outline the relationships of river water and groundwater as well as using water geochemistry and isotopes. The results suggested that the origin of river water came from precipitation and snow melt water in the river source area with elevation of 4 600 m,river water recharged groundwater in the river valley area,and main flow path of groundwater was from the basement rock mountainous area to piedmont alluvial plain. With respect to groundwater circulation,the first and second terrace was recharged by river water leakage,and the third terrace was recharged by river water leakage and lateral runoff from piedmont alluvial plain. The study result reveals the different types of groundwater recharge source and circulation change rule,and provides a scientific reference for studying the groundwater environmental evolution of the river basin and the influence of human activities on the groundwater environment in further.

Key words: environmental isotope, hydrogeochemistry, water circulation, Buha River basin, Qinghai Lake