Wenbo Rao

Isotope fractionation of sandy-soil water during evaporation – an experimental study

ABSTRACT Soil samples containing water with known stable isotopic compositions were prepared. The soil water was recovered by using vacuum/heat distillation. The experiments were held under different conditions to control rates of water evaporation and water recovery. Recoveries, δ18O and δ2H values of the soil water were determined. Analyses of the data using a Rayleigh distillation model indicate that under the experimental conditions only loosely bound water is extractable in cases where the recovery is smaller than 100 %. Due to isotopic exchange between vapour and remaining water in the micro channels or capillaries of the soil matrix, isotopic fractionation may take place under near-equilibrium conditions. This causes the observed relationship between δ2H and δ18O of the extracted water samples to have a slope close to 8. The results of this study may indicate that, in arid zones when soil that initially contains water dries out, the slope of the relationship between δ2H and δ18O values should be close to 8. Thus, a smaller slope, as observed by some groundwater and soil water samples in arid zones, may be caused by evaporation of water before the water has entered the unsaturated zone.

Identifying the source of atmospheric moisture over arid deserts using stable isotopes (2H and 18O) in precipitation

State Key Laboratory of Hydrology‐Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China 2 Institute of Isotope Hydrology, College of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China Australian Nuclear Science and Technology Organisation, Kirrawee DC, New South Wales 2232, Australia Correspondence Wenbo Rao and Bin Yong, State Key Laboratory of Hydrology‐Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China. Email: raowenbo@163.com; yongbin@hhu. edu.cn Funding information Fundamental Research Funds for the Central Universities, Grant/Award Number: 2017B19614; National Natural Science Foundation of China, Grant/Award Numbers: 40973001, 41271041 and 41273015

Geochemical constraints on seasonal recharge of water and major dissolved solutes in the Huangshui River, China

The Huangshui River, an important tributary in the upper reaches of the Yellow River, has been regarded as a mother river which gestates Qinghai civilization in China. This paper presents the results of hydrogen and oxygen isotopic and water chemical analyses for the summer and winter Huangshui River water to study its seasonal recharge and major dissolved solutes. Characteristics of hydrogen and oxygen isotopes suggest that precipitation in the Qilian Mountains is the original recharge of the Huangshui River. However, in winter, the basic flow of the Huangshui River only depends on spring recharge and spring water originates from melt and infiltration of bottom layer glaciers. In summer, besides spring water, much rainfall directly recharges the Huangshui River, thus making its flux increase greatly. Water chemistry shows that the processes affecting dissolved solutes in the Huangshui River are also different between summer and winter. In summer, major ions in the river water are dominantly derived from carbonate and evaporate dissolution and anthropogenic inputs. In winter, carbonate dissolution decreases greatly while anthropogenic inputs play a much more important role for dissolved solutes in the river. Hence, further measures should be taken to lay stress on the winter Huangshui River water in order to protect the environment of the Huangshui River and reduce effects of dissolved solutes on, or prevent their pollution toward the upper Yellow River. Moreover, some measures also need to be introduced to prevent the possibility of water eutrophication caused by agricultural activities or stock raising in summer.

Understanding recharge of soil water in a sand dune at the Nuoertu of Badain Jaran Desert using isotopes of H and O

A typical megadune in the hinterland of Badain Jaran Desert has been monitored from 2013 to 2014. Six soil profiles have been analyzed for the recharge source and movement mechanism combined with Cl− concentration and stable isotopes. The analysis results show that local precipitation is the main recharge source of the soil water while shallow groundwater only influences the soil water which interfaces groundwater table. The recharge rates are calculated by chloride mass balance method for one hydrological year. The high recharge rates also reflect the significance of local precipitation for recharging soil water at the Nuoertu area in this desert. The variation characteristics of oxygen and hydrogen isotopes of soil profiles suggest that the piston-type flow should be the primary mode in the Nuoertu area. This approach is applicable to analyzing soil water characteristics of unsaturated zone in similar arid desert areas around the world.