Spatial variation of stable isotopes in different waters during melt season in the Laohugou Glacial Catchment, Shule River basin

Abstract

To evaluate isotopic tracers at natural abundances by providing basic isotope data of the hydrological investigations and assessing the impacts of different factors on the water cycle, a total of 197 water samples were collected from the Laohugou Glacial catchment in the Shule River basin northwestern China during the 2013 ablation seasons and analyzed their H- and O-isotope composition. The results showed that the isotopic composition of precipitation in the Qilianshan Station in the Laohugou Glacial catchment was remarkable variability. Correspondingly, a higher slope of δ18O-δD diagram, with an average of 8.74, is obtained based on the precipitation samples collected on the Glacier No.12, mainly attributed to the lower temperature on the glacier surface. Because of percolation and elution, the isotopic composition at the bottom of the firn is nearly steady. The δ18O /altitude gradients for precipitation and melt water were -0.37‰/100 m and -0.34‰/100 m, respectively. Exposed to the air and influenced by strong ablation and evaporation, the isotopic values and the δ18O vs δD diagram of the glacial surface ice show no altitudinal effect, indicating that glacier ice has the similar origins with the firn. The variation of isotopic composition in the melt water,varying from -10.7‰ to -16.9‰ (δ18O) and from -61.1‰ to -122.1‰ (δD) indicates the recharging of snowmelt and glacial ice melt water produced at different altitudes. With a mean value of -13.3‰ for δ18O and -89.7‰ for δD, the isotopic composition of the stream water is much closer to the melt water, indicating that stream water is mainly recharged by the ablation water. Our results of the stable isotopic compositions in natural water in the Laohugou Glacial catchment indicate the fractionations and the smoothing fluctuations of the stable isotopes during evaporation, infiltration and mixture.