Estimation of evaporation losses based on stable isotopes of stream water in a mountain watershed

Water stable isotopes (δ2H and δ18O) can record surface water evaporation, which is an important hydrological process for understanding watershed structure and function evolution. However, the isotopic estimation of water evaporation losses in the mountain watersheds remains poorly explored, which hinders understanding spatial variations of hydrological processes and their relationships with the temperature and vegetation. Here we investigated δ2H, δ18O, and d-excess values of stream water along an altitude gradient of 2130 to 3380 m in Guan’egou mountain watershed at the east edge of the Qinghai-Tibet Plateau in China. The mean δ2H (− 69.6 ‰ ± 2.6 ‰), δ18O (− 10.7 ‰ ± 0.3 ‰), and d-excess values (16.0 ‰ ± 1.4 ‰) of stream water indicate the inland moisture as the major source of precipitation in study area. Water stable isotopes increase linearly with decreasing altitudes, based on which we estimated the fractions of water evaporation losses along with the altitude and their variations in different vegetations. This study provides an isotopic evaluation method of water evaporation status in mountain watersheds, the results are useful for further understanding the relationship between hydrological processes and ecosystem function under the changing climate surrounding the Qinghai-Tibet Plateau.