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Gas Diffusivity in Undisturbed Volcanic Ash Soils

Test of Soil-Water-Characteristic-Based Prediction Models

^a Dep. of Environ. Engineering, Aalborg Univ., Sohngaardsholmsvej 57
^b City and Environment Section, Aalborg Municipality, Vesterbro 14, DK-9000 Aalborg, Denmark
^c Osozawa), Dep. of Regional Crops Science, Natl. Agric. Res. Center for Western Region, Senyu 1-3-1, Zentsuji, Kagawa, 765-8508 Japan
^d Yamaguchi), Graduate School of Science and Engineering, Saitama University, 255 Shimo-okub, Saitama, 338-8570 Japan
^e Soils and Biogeochemistry, Dep. of Land, Air, and Water Resources, Univ. of California, Davis, CA 95616

View larger version (33K): [in a new window]   Fig. 1. Water retention (open symbols) and gas diffusivity (solid symbols) for Miura 4 Andisol. Measurements on three closely sampled 100-cm3 undisturbed soil samples are shown. The solid line is the Campbell (1974) soil-water characteristic model fitted to data. = volumetric water content, m3 m-3; DP = gas diffusion coefficient in soil, m3 soil air m-1 soil s-1; D0 = gas diffusion coefficient in free air, m2 air s-1; pF = Log(- in cm H2O).

View larger version (22K): [in a new window]   Fig. 2. The Campbell soil-water characteristic model (solid lines) fitted to measured data for 11 Andisols and Gray-lowland soils. The solid lines are the Campbell (1974) soil-water characteristic model fitted to data. = volumetric water content, m3 m-3; pF = Log(- in cm H2O).

View larger version (45K): [in a new window]   Fig. 3. Test of the Buckingham-Burdine-Campbell (BBC), Eq. [5], and the macroporosity-dependent (100), Eq. [7], gas diffusivity models against measured data for 15 undisturbed Andisols. Values of Campbell b and total porosity (, m3 m-3) for each soil are given. Except for Kyushu 4, the measured value at the smallest and highest soil-air contents correspond to -10 cm H2O (pF 1) and -15000 cm H2O (pF 4.2) of matric potential, respectively, as illustrated in Fig. 3a,f,k. = soil air content; DP/D0 = relative soil-gas diffusion coefficient, with DP as the gas diffusion coefficient in soil, m3 soil air m-1 soil s-1; pF = Log(- in cm H2O).

View larger version (19K): [in a new window]   Fig. 4. Test of the Buckingham-Burdine-Campbell (BBC), Eq. [5], and the macroporosity-dependent (100) (Eq. [7]), gas diffusivity models against measured data for four undisturbed Gray-lowland soils (paddy field soils). Values of Campbell b and total porosity (, m3 m-3) for each soil are given. = soil air content; DP/D0 = relative soil-gas diffusion coefficient, with DP as the gas diffusion coefficient in soil, m3 soil air m-1 soil s-1.

View larger version (31K): [in a new window]   Fig. 5. Illustration of soil-type-dependent behavior of gas diffusivity in undisturbed soils. Data for two soils with different soil-water characteristic (SWC) behavior (different Campbell b values). Also shown are predictions by two SWC-independent gas diffusivity models (Eq. [2] and [4]), and the Troeh et al. (1982) model (Eq. [10]) fitted to the measured data. = soil air content; DP/D0 = relative soil-gas diffusion coefficient.

View larger version (38K): [in a new window]   Fig. 6. Scatterplot comparison of predicted and measured gas diffusivities (DP/D0) in 18 undisturbed Andisols and four undisturbed Gray-lowland soils. Test of the (a) Penman (1940) model, Eq. [2]; (b) Millington and Quirk (MQ; 1960) model, Eq. [3]; (c) Millington and Quirk (1961) model, Eq. [4]; (d) Buckingham-Burdine-Campbell (BBC) model, Eq. [5]; (e) macroporosity-dependent (100) model, Eq. [7], with DP,100 predicted from Eq. [6]; and (f) macroporosity-dependent model, Eq. [7], using the measured DP,100 value. Andi = Andisols; Gray = Gray-lowland soils; RMSE = root mean square error.

View larger version (28K): [in a new window]   Fig. 7. Test of Eq. [6] to predict gas diffusivity (DP,100/D0) at -100 cm H2O of matric potential, 100 = macroporosity. Data for 18 undisturbed Andisols and four undisturbed Gray-lowland soils. Solid line is Eq. [6]. Dotted lines are 95% prediction interval obtained when applying Eq. [6] to data for 144 undisturbed European soils (Moldrup et al., 2001).

View larger version (31K): [in a new window]   Fig. 8. Gas diffusion fingerprint for six Japanese soils, identifying three soils with high soil aeration potential (open symbols) and three soils with low soil aeration potential (closed symbols). = soil air content; DP/D0 = relative soil-gas diffusion coefficient; IRC = incremental relative change in gas diffusivity; pF = Log(- in cm H2O).