title: 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.
authors.affiliation: a Institute of Isotope Hydrology, College of Earth Sciences and Engineering, Hohai University , Nanjing , People's Republic of China.
authors.forename: Wen-Bo
authors.initials: WB
authors.lastname: Rao
authors.affiliation: b Isotope Hydrology Section, Division of Physical and Chemical Sciences, Department of Nuclear Sciences and Applications , International Atomic Energy Agency , Vienna , Austria.
authors.forename: Liang-Feng
authors.initials: LF
authors.lastname: Han
authors.affiliation: a Institute of Isotope Hydrology, College of Earth Sciences and Engineering, Hohai University , Nanjing , People's Republic of China.
authors.forename: Hong-Bing
authors.initials: HB
authors.lastname: Tan
authors.affiliation: a Institute of Isotope Hydrology, College of Earth Sciences and Engineering, Hohai University , Nanjing , People's Republic of China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Wang
mesh_terms: D005591:Chemical Fractionation; D003903:Deuterium / Q000032:analysis; D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis*; D010103:Oxygen Isotopes / Q000032:analysis; D012987:Soil / Q000737:chemistry*
chemical_list: D010103:Oxygen Isotopes; D012987:Soil; D003903:Deuterium
keywords: Evaporation; hydrogen-2; incomplete extraction; isotope fractionation; isotope hydrology; oxygen-18; sandy soil; soil water