Browsing by Author "Rao, WB"

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    Identifying the source of atmospheric moisture over arid deserts using stable isotopes (2H and 18O) in precipitation
    (John Wiley & Sons, Inc, 2018-01-03) Rao, WB; Zhang, WB; Yong, B; Tan, HB; Meredith, KT; Jin, K; Zheng, FW; Wang, S
    Precipitation is a major component of the hydrologic cycle in arid desert areas. To date, however, few studies have been conducted on investigating the isotope characteristics and moisture sources of precipitation in arid desert environments. The Alxa Desert Plateau is a critical arid desert area in North China. This study is the first to analyse the stable isotopic composition of precipitation to identify the sources of atmospheric moisture over this plateau. Our results show that the δD and δ18O values of precipitation across the plateau change greatly at both daily and monthly timescales, and exhibit seasonal variations. Among the main meteorological parameters, atmospheric temperature is the most predominant factor controlling the isotopic composition and the δD–δ18O relationship of local precipitation. Analyses of the precipitation isotopes with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model reveal that (a) the westerly and polar moisture sources are the dominant controls on summer and winter precipitation and (b) the evaporation of local lake water significantly affects winter precipitation even though it only represents a small amount. Based on the isotope data of 2013–2016 precipitation, a local meteoric water line (LMWL) is derived: δD = (8.20 ± 0.22)·δ18O + (8.15 ± 2.16)‰ for the study site. Compared to the global meteoric water line, the LMWL has a greater slope and lower d-excess. This can be explained by admixing of atmospheric moisture resulting from the evaporation of local lake water. Based on this LMWL, we are able to trace that groundwater of the Badain Jaran Desert originates from the surrounding mountains with altitudes of <4,000 m. The newly derived LMWL shows that the recharge altitudes of desert groundwater are overestimated on the basis of the previous LMWLs. This study not only provides insights into the hydrological cycle but also offers guidance for water resource management in arid desert areas of China. Additionally, this study provides techniques that can be applied to the analyses of precipitation isotopes in similar arid regions of the world. © 2018 John Wiley & Sons, Ltd.
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    Study of groundwater recharge using combined unsaturated‐and saturated‐zone chloride mass balance methods
    (Wiley, 2023-06-19) Jiang, SY; Rao, WB; Han, LF; Meredith, Karina T
    Understanding groundwater recharge mechanisms is essential for reliable groundwater recharge estimation for sustainable groundwater resource assessment and management, especially in arid and semiarid areas. In this study, chloride, together with stable isotopes (18O and2H), in 1‐year rainfall, soil water from representative profiles, and groundwater samples, collected in the Ordos Plateau, northern China were analysed. Groundwater recharge was estimated using unsaturated‐ and saturated‐zone chloride mass balance (CMB). An equation that describes the relationship between chloride concentrations in saturated zone water (Csz) and soil water residence time (τ) was derived. With the help of the relationship, chloride concentrations in unsaturated zone water (Cuz) and in groundwater (Csz) can be used to uncover water flow and chloride transport in the unsaturated zone. The relationship betweenCszandCuzindicates that, the groundwater was recharged mainly by intense rainfall events. Small rainfall events did not lead to groundwater recharge but contributed to the flux of chloride to soil surface. Stable isotopic compositions of18O and2H provided corroborative evidence of the recharge processes. The relationship betweenCszandτindicates further that there is no source of chloride in the groundwater other than that from precipitation. Thus,Cszcan give more reliable recharge estimates.Cuzwas influenced by heavy rainfall‐induced runoff, run‐on and bypass flow events and cannot give reliable recharge estimates. However, if used jointly withCsz,Cuzcan help to gain insights into recharge processes and yield groundwater recharge estimates with higher certainty. The outcomes of this study can assist for groundwater recharge investigation and assessment in regions where the assumptions and boundary conditions necessary for the correct application of the CMB method may not be met. © 1999-2024 John Wiley & Sons
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    Water uptake of riparian plants in the lower Lhasa River Basin, South Tibetan Plateau using stable water isotopes
    (John Wiley & Sons, Inc, 2020-05-25) Rao, WB; Chen, X; Meredith, KT; Tan, HB; Gao, M; Liu, JT
    Riparian plants can adapt their water uptake strategies based on climatic and hydrological conditions within a river basin. The response of cold-alpine riparian trees to changes in water availability is poorly understood. The Lhasa River is a representative cold-alpine river in South Tibet and an under-studied environment. Therefore, a 96 km section of the lower Lhasa River was selected for a study on the water-use patterns of riparian plants. Plant water, soil water, groundwater and river water were measured at three sites for δ18O and δ2H values during the warm-wet and cold-dry periods in 2018. Soil profiles differed in isotope values between seasons and with the distance along the river. During the cold-dry period, the upper parts of the soil profiles were significantly affected by evaporation. During the warm-wet period, the soil profile was influenced by precipitation infiltration in the upper reaches of the study area and by various water sources in the lower reaches. Calculations using the IsoSource model indicated that the mature salix and birch trees (Salix cheilophila Schneid. and Betula platyphylla Suk.) accessed water from multiple sources during the cold-dry period, whereas they sourced more than 70% of their requirement from the upper 60–80 cm of the soil profile during the warm-wet period. The model indicated that the immature rose willow tree (Tamarix ramosissima Ledeb) accessed 66% of its water from the surface soil during the cold-dry period, but used the deeper layers during the warm-wet period. The plant type was not the dominant factor driving water uptake patterns in mature plants. Our findings can contribute to strategies for the sustainable development of cold-alpine riparian ecosystems. It is recommended that reducing plantation density and collocating plants with different rooting depths would be conducive to optimal plant growth in this environment. © 2020 John Wiley & Sons Ltd