Tracing the major source area of the mountainous runoff generation of the Heihe River in northwest China using stable isotope technique

Based on the data of delta O-18 in precipitation during the period of April 2006 through May 2007 in the upper catchment of the main stream of the Heihe River in the Qilian Mountains, we found that there existed an evident altitude effect on delta O-18 in precipitation, and the delta O-18-altitude gradient was -0.18%/100 m. When delta O-18 in river water at the outlet of the mountainous drainage area of the main stream of the Heihe River was combined with the delta O-18-altitude relation, it was realized that the mountainous runoff was generated mostly at high altitudes. Using two component models, we revealed that 80.2% of the annual total mountainous runoff amount was generated at the alpine permafrost-snow-ice zone with an altitude of above 3600 m a.s.l.