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| Home > Publications database > Investigation of Kinetic Isotopic Fractionation of Water During Bare Soil Evaporation |
| Journal Article | FZJ-2018-05543 |
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2018
Wiley
[New York]
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Please use a persistent id in citations: http://hdl.handle.net/2128/19834 doi:10.1029/2018WR023159
Abstract: The kinetic fractionation factor (αK) controls to a large extent the isotopic enrichment of surface waters during evaporation (E). In contrast to the well-known vapor-to-liquid isotopic equilibrium fractionation factor, αK has still not yet been properly characterized for soil water evaporation. In this study, we investigated the αK daily dynamics during a series of three laboratory experiments differing in soil water availability and aerodynamic conditions. For this, we applied a commonly-used isotopic evaporation model and tested it in two different approaches. First, a two-end member mixing model (“Keeling plot”) was fitted to the measured isotopic composition of the laboratory air water vapor to obtain αK. In a second approach, αK was obtained from the slope of the “evaporation line” in a dual isotopic coordinate system. For both methods, the isotopic composition of the soil water was determined non-destructively and online by sampling the soil water vapor with gas-permeable microporous tubing. Results highlighted the limitation of the first approach, as the determination of the isotopic composition of E with the Keeling plot was challenging with the laboratory setup. The second approach provided αK values within the range (α_K^(2_H ) = 1.0132 ±0.0013; α_K^(〖18〗_O ) = 1.0149 ±0.0012) reported in the literature and pointed to the prevalence of turbulent water vapor transport under water-saturated soil conditions, but also at soil water content significantly lower than the saturated value. In a third experiment, temporal dynamics of the atmospheric water vapor intrusion in the topmost soil layer could be observed during an isotopic labeling pulse.
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