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Isotopic composition of bare soil evaporated water vapor. Part II: Modeling of RUBIC IV experimental results.

Abstract : Stable water isotopes such as oxygen 18, are tracers of water movement within the soil–vegetation–atmosphere system. They provide useful information for a better understanding of evaporation and water vapor transport within soils. In part I of this paper, we presented a novel control experimental set-up under non steady conditions, dedicated to the measurement of the evaporation flux and corresponding isotopic composition from six bare soil columns. Data analysis raised several questions about the soil depth controlling the isotopic composition of the evaporated water vapor, suggesting different behavior before and after the appearance of back diffusion. Experimental data also suggested a time variable value of the kinetic fractionation factor. The present paper presents the modeling of the experimental results using the coupled heat, water and stable isotope transfer model SiSPAT_Isotope. Model results were used for investigating the above questions more in details. For this purpose, model parameters were calibrated for each soil column in order to reproduce the data. Then model results were inverted to estimate the kinetic fractionation factor. The results show that the hypothesis that the kinetic fractionation factor varies in time is plausible but the uncertainty is too large to derive firm conclusions. The largest uncertainty is found when the soil relative humidity is lower than one but water vapor is still negligible. When back diffusion has occurred, model results are the most robust and confirm that the isotopic composition of the evaporated water vapor is controlled by the soil isotopic composition of the liquid water at the peak. In this case, the retrieved kinetic fractionation factor is close to 18.9‰, corresponding to laminar flow.
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https://hal-insu.archives-ouvertes.fr/insu-00411962
Contributor : Pascale Talour <>
Submitted on : Monday, August 31, 2009 - 11:45:21 AM
Last modification on : Friday, September 25, 2020 - 11:02:44 AM

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I. Braud, T. Bariac, P. Biron, Michel Vauclin. Isotopic composition of bare soil evaporated water vapor. Part II: Modeling of RUBIC IV experimental results.. Journal of Hydrology, Elsevier, 2009, 369 (1-2), pp.17-29. ⟨10.1016/j.jhydrol.2009.01.038⟩. ⟨insu-00411962⟩

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