Characteristics of hydrogen and oxygen isotopes and their differences of different water bodies in the subalpine shrubland of the eastern Qilian Mountains in China

Abstract

As the main bodies of water transformation, precipitation, soil water, plant water, river water and ground water play important roles in water cycle. Based on stable isotope values of five types of water bodies collected in the subalpine shrubland of the eastern Qilian Mountains from May to October in 2019, the characteristics of hydrogen and oxygen isotopes and their differences of different water bodies were studied. The results showed that the slope of the local meteorological water line (LMWL) was lower (7.63 < 8) and the intercept was higher (14.06 > 10) than those of the global meteorological water line (GMWL), indicating that the precipitation isotopes were enriched by evaporative fractionation. Stable isotope values of soil water mainly recharged by precipitation vary significantly and seasonally (summer > autumn > spring) and decreased with increasing of soil depth, where there were some differences in different aspects. Plant transpiration was more intense than evaporations of other water bodies, thus stable isotope values of plant water were the highest among five water bodies. There were differences in stable isotope values among plant species at different stages in growing season (germination and leaf development stage > flowering and fruiting stage > leaf drop decline stage), and those of plant water were higher on semi-shady slopes than on semi-sunny slopes. Stable isotope values of tributary streams were higher than those of main streams, and there were seasonal differences between them (main streams: autumn > spring > summer, tributaries: autumn > summer > spring). Among five types of water bodies, the fluctuation variation of stable isotope values was the greatest in precipitation and the smallest in ground water. This study can help to improve the understanding of ecohydrological processes in subalpine shrubland and provide a reference basis for the ecological management in the Qilian Mountains and the rational utilization of water resources in the Shiyang River Basin.