Multiphase Reactive Transport modeling of Stable Isotope Fractionation of Infiltrating Unsaturated Zone Pore Water and Vapor Using TOUGHREACT
Numerical simulations of transport and isotope fractionation provide a method to quantitatively interpret vadose zone pore water stable isotope depth profiles based on soil properties, climatic conditions, and infiltration. We incorporate the temperature-dependent equilibration of stable isotopic species between water and water vapor, and their differing diffusive transport properties into the thermodynamic database of the reactive transport code TOUGHREACT. These simulations are used to illustrate the evolution of stable isotope profiles in semiarid regions where recharge during wet seasons disturbs the drying profile traditionally associated with vadose zone pore waters. Alternating wet and dry seasons lead to annual fluctuations in moisture content, capillary pressure, and stable isotope compositions in the vadose zone. Periodic infiltration models capture the effects of seasonal increases in precipitation and predict stable isotope profiles that are distinct from those observed under drying (zero infiltration) conditions. After infiltration, evaporation causes a shift to higher 18O and D values, which are preserved in the deeper pore waters. The magnitude of the isotopic composition shift preserved in deep vadose zone pore waters varies inversely with the rate of infiltration.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE. Assistant Secretary for Environmental Management. Office of Science and Technology, Hanford Science and Technology Program Contract DE-AC06-76RL01830 (US)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 837736
- Report Number(s):
- LBNL-54052; R&D Project: 465103; TRN: US200506%%366
- Journal Information:
- Vadose Zone Journal, Vol. 3, Issue 3; Other Information: Submitted to Vadose Zone Journal: Volume 3, No.3; Journal Publication Date: August 2004; PBD: 28 Aug 2003
- Country of Publication:
- United States
- Language:
- English
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Numerical modeling of stable isotope fractionation and multiphase reactive transport of water and water vapor using TOUGHREACT