The melting of alpine snow and glaciers is an important hydrologic process on Mount Gongga, China. The relevance of ice-snow melt to the groundwater recharge in the glacierized Hailuogou watershed is so far not well known. To better understand the origin of groundwater and the hydrological interactions between groundwater, meltwater, and precipitation in this region, 148 environmental isotopic data of water samples were analyzed for changes in isotopic composition. The results indicate that the groundwater contains a uniform isotopic signature, with δ¹⁸O values between −13.5‰ and −11.1‰ and δ²H values between −90‰ and −75‰. The mean stable isotopic composition of groundwater is heavier than that of ice-snow meltwater but lighter than that of precipitation. The effect of evaporation on the isotopic variation of groundwater is very limited and the seasonal isotope variations in precipitation are attenuated in groundwater. A model based on the δ¹⁸O results suggests that approximately 35% of the groundwater is derived from ice-snow meltwater sources. The study demonstrates that ice-snow meltwater is a substantial source of shallow groundwater in the alpine regions on the edge of the Tibetan Plateau.

The Hailuogou River, on the south-eastern edge of the Tibetan Plateau, receives a substantial portion of its flow from meltwater. The stable isotopic composition and water temperature were observed for waters collected from the main stream and selected tributaries. The results indicate that the river water is generally more depleted in ¹⁸O and ²H than groundwater, but more enriched than meltwater. The river water in the upper reaches is characterised by more negative isotopic values, the isotopic fingerprint of meltwaters, and lower temperatures. Both δ¹⁸O and δ²H increase significantly during passage from the upper basin downward, at least partly due to enrichment from tributary-inputs. There are also an altitude δ¹⁸O-effect of −0.1‰ per 100-m rise, and an altitude δ²H-effect of −0.8‰ per 100-m rise, along the main stream. The positive correlation between isotopic composition and water temperature further highlights the role of meltwater in regulating the river9s isotope hydrology. The fraction of meltwater inputs over the total river flow ranges from 67% at Section 11 to 89% at Section 7, in the proglacial headwater region. The tributary-input enrichments and ice-snow melting are the main mechanisms controlling the isotopic composition of river runoff, but depending strongly on altitude.