Water Stable Isotopes in an Alpine Setting of the Northeastern Tibetan Plateau

Abstract

Hydrological processes produce effects on water resources in inland mountainous regions. To perform a comprehensive investigation of the important segments of the water cycle, using the Qilian Mountains as a case study, precipitation, soil, plant, river, and groundwater were collected during the plant growing season of 2016. All samples were collected on a monthly basis, except precipitation, which was collected on a per event basis. The results showed that: the “temperature effect” was apparent, which suggested a drier climate background; there were differences in the slope and intercept of the local meteoric water line, using different regression methods; and the δ18O of soil water varied greatly in the topsoil, tended to be similar in the deep soil, and became increasingly depleted as the soil depth increased. The responses of the soil water isotopes to precipitation pulses had different boundaries. The major water source for Caragana Fabr. in no-precipitation month was located in the 0–30 cm soil layer, but was different in months when precipitation occurred. Overall, the findings from the stable isotopes provide insights into hydrological processes and offer a platform to understand mountainous water cycle in arid areas.

The Stable Isotopic Composition of Different Water Bodies at the Soil–Plant–Atmosphere Continuum (SPAC) of the Western Loess Plateau, China

“…The local meteoric water line (LMWL) is described by the equation δ 2 H = (7.08 ± 0.34) δ 18 O + (5.12 ± 1.90) (R 2 = 0.93, p < 0.0001, n = 35). The slope is smaller than the global meteoric water line (GMWL), indicating relatively low humidity and strong kinetic fractionation, due to evaporation in Lanzhou City [25,27,29]. The variation of hydrogen and oxygen isotopes in the river water ranged from −71.90% to −60.31% and from −10.51% to −9.20% , respectively, with very little variation.…”

“…The selected plant samples were in good growth condition, thus, eliminating any external "noise signal", due to plant growth conditions [15]. In order to avoid leaf transpiration and any residual dew on the leaves that could affect the isotopic composition of the plants, all samples were strictly taken between 08:00 and 11:00 a.m. [25]. A total of 186 plant xylem samples and 270 plant leaf samples were collected.…”

“…(2) Soil samples: A 1 m soil profile was excavated, and we collected samples at 10 cm intervals in four sites in order to determine the vertical profile variation of soil water isotopes. The samples were collected from 2 cm below the surface, to avoid the soil samples being influenced by the free atmosphere [25]. The soil samples were divided into two categories: (1) Samples collected into self-contained aluminum boxes and used for measuring the soil water content (SWC); three replicate samples were taken from each layer.…”

“…All water samples were analyzed using a DLT-100 liquid water isotope analyzer developed by Los Gatos Research, USA. We used LWIA-Spectral Contamination Identifier (LWIA-SCI) software to review spectral contamination for the measured plant water data [25,26]. The measurement precision of the instrument was ±0.6% for the δ 2 H and ±0.2% for the δ 18 O, respectively [25][26][27][28].…”

“…The isotope standards were provided by Los Gatos Research. According to the isotope ratio range of our samples, three standards were selected from the LGR standards (expressed relative to the V-SMOW), and the precision of δ 2 H and δ 18 O were 3c: −97.3 ± 0.5% and −13.39 ± 0.15% , 4c: −51.6 ± 0.5% and −7.94 ± 0.15% and 5c: −9.2 ± 0.5% and −2.69 ± 0.15% , respectively [25,27].…”