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Tortuosity, Diffusivity, and Permeability in the Soil Liquid and Gaseous Phases

^a Dep. of Environmental Engineering, Aalborg Univ., Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^b Dep. of Civil and Environmental Engineering, Faculty of Engineering, Hiroshima Univ., 1-4-1 Kagamiyama, Higashi-Hiroshima, 739, Japan
^c Dep. of Crop Physiology and Soil Science, Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
^d Soils and Biogeochemistry, Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616

View larger version (20K): [in a new window]   Fig. 1. Liquid-phase impedance factor, fl, as a function of soil water content, , for a sandy (L1), a loamy (L3), and a clayey (L5) soil. The intercept with the -axis defines the threshold water content, th, where solute diffusion ceases. Data from Olesen et al. (1999)

View larger version (16K): [in a new window]   Fig. 2. Threshold soil water content for solute diffusion, th, as a function of volumetric soil surface area, SAvol. Data from Olesen et al. (1996)(1999) and present study

View larger version (22K): [in a new window]   Fig. 3. Predicted, Eq. [6], and measured gas diffusivity in undisturbed soil at -100 cm H2O of soil water matric head (DP,100/D0). Data for 144 soils. Fine broken lines represent 95% prediction interval. Coarse broken lines represent different values of content of large pores, 100, in Eq. [6]

View larger version (29K): [in a new window]   Fig. 4. Influence of fluid-phase (water or air) content, soil volumetric surface area (SAvol), and content of large pores (100) on tortuosities in (a) the soil liquid phase and (b) the soil gaseous phase. Solid lines are calculated from Eq. [10] combined with Eq. [3] through [7], assuming = 0.5. Open triangles are data from literature for gas diffusion in completely dry soil

View larger version (24K): [in a new window]   Fig. 5. Measured tortuosities as a function of fluid-phase content in the soil liquid phase (from solute diffusion data, = ) and soil gaseous phase (from gas diffusion data, = ) for (a) four sieved, repacked soils and (b) undisturbed compared with sieved, repacked L1 soil. Data from Olesen et al. (1996)(1999), Schjønning et al. (1999), and Moldrup et al. (2000b)

View larger version (22K): [in a new window]   Fig. 6. Relative soil water content where the soil liquid- and gaseous-phase tortuosities become the same. Solute and gas diffusion data from Olesen et al. (1999) and Moldrup et al. (2000b) used to obtain the observed values (symbols) for L1, L3, and L5 soils. Model prediction (solid line) from Eq. [10] combined with Eq. [3] and [5]

View larger version (28K): [in a new window]   Fig. 7. Equivalent pore diameter at -100 cm H2O of soil water matric head (d100) for six soils (L1–L6) sampled along a soil texture gradient. Pore diameter was calculated from measured gas diffusivities and air permeabilities, Eq. [11]. The structurally disturbed soil is repacked soil that has been allowed to develop soil structure for 17 mo. Data from Schjønning et al. (1999) and present study

View larger version (28K): [in a new window]   Fig. 8. Measured air permeabilities and gas diffusivities in two soils where the packing procedure has resulted in the formation of soil aggregates at higher soil water contents (lower air contents). Solid line is model prediction for gas diffusivity in repacked soil, Eq. [5]. Data from present study and Moldrup et al. (2000b)

View larger version (29K): [in a new window]   Fig. 9. Measured gas diffusivities and air permeabilities in L3 sandy clay loam and L5 sandy clay. (a), (c) Sieved, repacked soil. Model predictions (solid lines) by Eq. [5] and [12]. (b), (d) Undisturbed soil (closed symbols) and structurally disturbed soil (open symbols). Note the different ka axes on (c) and (d). Data from present study and Schjønning et al. (1999)

View larger version (24K): [in a new window]   Fig. 10. Parameter analysis based on the Campbell-type model, Eq. [13]. (a) Model fit of air permeability and gas diffusivity relations for soil L1. (b) Slope of Campbell-type model, , as a function of Campbell pore-size distribution index, b. The interval for water permeability is calculated by the Alexander and Skaggs (1986) and Campbell (1974) expressions ( = b + 3 and 2b + 3). The values for the remaining parameters are based on data from Olesen et al. (1999) and Schjønning et al. (1999) for soils L1 through L6

View larger version (23K): [in a new window]   Fig. 11. Parameters, links, and differences to be considered towards a unifying concept of diffusive and convective transport parameters in the soil liquid and gaseous phases