Abstract
Understanding the isotopic composition and interrelations of different water bodies at the soil–plant–atmosphere continuum (SPAC) is crucial to reveal the processes and mechanisms of regional water cycles. Rainfall, river water, plant, and soil samples from Lanzhou City, China, were collected from April to October 2016. The hydrogen (δ2H) and oxygen (δ18O) of the local precipitation, river water, soil water, plant xylem water, and leaf water were determined. We found that trees mainly uptake the middle (30–60 cm) and deep (60–100 cm) layer soil water during the growing season, and the shrubs mainly uptake the middle soil water. All herbs uptake the shallow soil water (0–30 cm) during the growing season. The δ18O of shallow soil water was found to be isotopic-enriched because of evaporation and exhibited a decline from the shallow soil layer towards the deeper layer. The variation of δ18O and soil water content (SWC) was remarkable in shallow soil, which was mainly due to evaporation and precipitation infiltration, while water in the middle and deep layer was less affected by these phenomena.
Highlights
The hydrogen and oxygen stable isotopes of water have been widely used as “fingerprints” of different reservoirs in ecological and hydrological field studies [1,2,3]
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 slope of the local meteoric water line (LMWL) is smaller than the GMWL, indicating low relative humidity and a kinetic fractionation process, due to evaporation
Summary
The hydrogen and oxygen stable isotopes of water have been widely used as “fingerprints” of different reservoirs in ecological and hydrological field studies [1,2,3]. Comparisons with the isotopic composition of different water bodies, like soil water, river water, and plant water, can help us to understand the recharge relationship between them, as well as the precipitation infiltration mechanism at the regional and local scale [7,8]. Some studies have demonstrated that the mechanism of soil water migration includes piston-type flow and preferential flow in unsaturated soil [8,9], and the contribution rate of soil water at different depths to plants can be investigated by comparing the isotopic composition of plant xylem water and soil water [10,11]
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