The test of the ecohydrological separation hypothesis in a dry zone of the northeastern Tibetan Plateau

The ecohydrological separation hypothesis has generated considerable scientific interest and debate in ecohydrological studies, and it assumes there exist two water pools in subsurface water, one of which is soil water used by plants and the other is that supplied to groundwater. Although this hypothesis has been tested in several humid sites, a further test in arid and semiarid conditions is still needed. Based on the isotopic ratios in different water bodies collected during a 2-year field work, the hypothesis was tested in a drier zone located in the Qilian Mountains of the northeastern Tibetan Plateau in order to investigate whether this separation phenomenon existed in a drier climate, and whether this may be a common characteristic or an exception. The results suggested that the hydrological separation does not necessarily exist and may not even be determined by stable isotopes; there is a clear need to more precise experimental methods.