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Predicting the Gas Diffusion Coefficient in Undisturbed Soil from Soil Water Characteristics

^a Environ. Engineering Lab., Dep. of Civil Engineering, Aalborg Univ., Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^b Dep. of Crop Physiology and Soil Sci., Danish Inst. of Agric. Sci., Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
^c Dep. of Civil and Environ. Engineering, Faculty of Engineering, Hiroshima Univ., 1-4-1 Kagamiyama, Higashi-Hiroshima, 739, Japan
^d Soils and Biogeochemistry, Dep. of Land, Air, and Water Resour., Univ. of California, Davis, CA 95616 USA

View larger version (22K): [in a new window]   Fig. 1 Gas diffusivity as a function of air-filled porosity at -100 cm H2O of soil water potential. Data for 126 different soils and soil layers (752 measurements)

View larger version (24K): [in a new window]   Fig. 2 Illustration of the model parameters in the new gas diffusivity model (Eq. [7]). (a) dotted line is fitted soil water characteristic curve in a log(-)–log() plot. Straight line is predicted gas diffusivity in a log(DP/D0)–log() plot. (b) predicted gas diffusivity function in a normal scale plot. The air-filled porosity at -100 cm H2O (100) is marked. Standard deviations of both and DP/D0 (six closely spaced measurements) are shown. Data from Schjønning et al. (1999)

View larger version (29K): [in a new window]   Fig. 3 Test of the new soil water characteristic–dependent DP/D0 model (Eq. [7]) against independent gas diffusivity data for six undisturbed soils. Data from Freijer (1994)

View larger version (23K): [in a new window]   Fig. 4 Scatterplot comparison of predicted (Eq. [7]) and measured gas diffusivities for 21 undisturbed soils. Note logarithmic scale

View larger version (24K): [in a new window]   Fig. 5 Scatterplot comparison of predicted soil water characteristic–dependent (SWC-dependent), Penman (1940) and Millington and Quirk (1961)(MQ), and measured gas diffusivities at high air-filled porosities (/ > 0.9)

View larger version (22K): [in a new window]   Fig. 6 Scatterplot comparison of predicted soil water characteristic–dependent (SWC-dependent), Penman (1940) and Millington and Quirk (1961)(MQ), and measured gas diffusivities for the three Hjørring subsoil horizons. See Table 2 for data. Note logarithmic scale