Three-Porosity Model for Predicting the Gas Diffusion Coefficient in Undisturbed Soil
- Per Moldrup *a,
- Torben Olesenb,
- Seiko Yoshikawac,
- Toshiko Komatsud and
- Dennis E. Rolstone
- a Environmental Engineering Section, Dep. of Life Sciences, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
b City and Environment Section, Aalborg Municipality, Vesterbro 14, DK-9000 Aalborg, Denmark
c Dep. of Hilly Land Agriculture, National Agricultural Research Center for Western Region, Ikano 2575, Zentsuji, Kagawa, 765-0053 Japan
d Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Saitama, 338-8570 Japan
e Soils and Biogeochemistry, Dep. of Land, Air and Water Resources, University of California, Davis, CA 95616
The soil gas diffusion coefficient (D P) and its dependency on air-filled porosity (ε) govern most gas diffusion-reaction processes in soil. Accurate D P(ε) prediction models for undisturbed soils are needed in vadose zone transport and fate models. The objective of this paper was to develop a D P(ε) model with lower input parameter requirement and similar prediction accuracy as recent soil-type dependent models. Combining three gas diffusivity models: (i) a general power-law D P(ε) model, (ii) the classical Buckingham (1904) model for D P at air saturation, and (iii) a recent macroporosity dependent model for D P at −100 cm H2O of soil–water matric potential (ψ), yielded a single equation to predict D P as a function of the actual ε, the total porosity (Φ), and the macroporosity (ε100; defined as the air-filled porosity at ψ = −100 cm H2O). The new model, termed the three-porosity model (TPM), requires only one point (at −100 cm H2O) on the soil–water characteristic curve (SWC), compared with recent D P(ε) models that require knowledge of the entire SWC. The D P(ε) was measured at different ψ on undisturbed soil samples from dark-red Latosols (Brazil) and Yellow soils (Japan), representing different tillage intensities. The TPM and five other D P(ε) models were tested against the new data (17 soils) and data from the literature for additional 43 undisturbed soils. The new TPM performed equally well (root mean square error [RMSE] in relative gas diffusivity <0.027) as recent SWC-dependent D P(ε) models and better than typically used soil type independent models.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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