Stable isotopic information for hydrological investigation in Hailuogou watershed on the eastern slope of Mount Gongga, China

Hydrological systems have been seriously affected by changes of glaciations and snow covers in Mount Gongga, Sichuan, China, but the relevance of ice-snow melt for alpine river basin hydrology is so far not well known. To better understand hydrological features of the Hailuogou River, changes of δ¹⁸O and δ²H were investigated by analyzing 117 water samples collected from May 2008 to November 2009. Our results show that the stream water contains a relatively intermediate magnitude of isotopic variations, with δ¹⁸O ranging from ?18.09 to ?13.08 ‰ and δ²H from ?126.5 to ?88.8 ‰. The average values are both higher than those of ice-snow meltwater, but lower than those of meteoric water. These data also show a gradually increasing trend from upstream to downstream, and these changes might document the fingerprint of ice-snow melt in the headwater region and indicate the increasing recharge of heavy isotope-enriched waters with flow distance. The similarity in slopes of δ²H and δ¹⁸O relationship for meteoric waters and stream waters suggests that the isotopic signature of precipitation is well preserved in stream flow, and during the rainfall and stream flow the evaporation is only minor. Based on δ¹⁸O model, the results suggested that the fraction of ice-snow meltwater input over the total stream flow ranged from 84.50 to 86.52 % in the headwater region, but the fraction of ice-snow meltwater input from upper basin downward was significantly decreased. The study demonstrates that ice-snow meltwater is a substantially important water source in alpine regions on the edge of Tibetan Plateau.