Characteristics of water isotopes and hydrograph separation during the wet season in the Heishui River, China

Runoff generation and dynamics is an important issue in watershed and water resource management, but the mechanism in large scale is unclear and site-dependent. For this reason, spatial variations of δD and δ¹⁸O of river water and their sources within large-area of the Heishui Valley of the upper Yangtze River in western China were investigated during the wet season. A total 117 river water samples were collected at 13 sampling sites located at the junction of the principal river course and its tributaries. The results showed no spatial variations of either δD or δ¹⁸O values existed among tributary sampling sites A, B, E, F, H and I during the wet season, and significantly spatial variation occurred between tributary sampling sites A, B, E, F, H, I and site K; which indicated different proportions of rain entering river water should lead to spatial variation of water isotopes. The hydrograph separation analysis, based on the isotope data of river water, meltwater and rain water samples, showed the contribution of snow and glacier meltwater varied from 63.8% to 92.6%, and that of rain varied from 7.4% to 36.2%; which meant that snow and glacier meltwater was the main supplying water source of baseflow in the Heishui Valley. And the roles of glacier and snow meltwater should be significantly noticed in water resource management in this alpine valley at the rim of the Tibetan Plateau.