Open AccessMultiphase Reactive Transport Modeling of Seasonal Infiltration Events and Stable Isotope Fractionation in Unsaturated Zone Pore Water and Vapor at the Hanford Site
Author(s) -
Singleton Michael J.,
Sonnenthal Eric L.,
Conrad Mark E.,
DePaolo Donald J.,
Gee Glendon W.
Publication year - 2004
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2004.0775
Subject(s) - vadose zone , infiltration (hvac) , isotope fractionation , groundwater recharge , pore water pressure , water content , moisture , isotope , groundwater , hydrology (agriculture) , capillary fringe , loess , soil science , soil water , geology , environmental chemistry , chemistry , fractionation , aquifer , geomorphology , materials science , geotechnical engineering , physics , organic chemistry , quantum mechanics , composite material
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 δ 18 O and δD 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.