Vadose Zone Journal, 2012, Vol.11(1), p.0
Gas diffusion is a dominant transport mechanism for climate and regulated gases in the vadose zone. Soil-gas diffusion is governed by the gas diffusion coefficient (D (sub p) , m (super 2) s (super -1) ) which is highly dependent on soil texture, such as sand, silt, clay, and organic matter contents, as well as soil physical properties such as soil-air content (epsilon , m (super 3) m (super -3) ) or total porosity (Phi , m (super 3) m (super -3) ). Soil organic matter is a key contributor to the formation of the soil pore structure (i.e., total porosity and air-filled pore tortuosity), and it highly affects D (sub p) behavior under variably saturated conditions. In this study, based on numerous D (sub p) data sets across soil types including sands, loamy clay soils, volcanic ash soils, and organic soils, predictive D (sub p) models incorporating a percolation threshold (epsilon (sub th) , m (super 3) m (super -3) ) and pore tortuosity factor (X') are proposed. The observed relations between either epsilon (sub th) or X' and either Phi or volumetric organic matter fraction (OMF, m (super 3) m (super -3) ) were embedded in the proposed D (sub p) model. The proposed D (sub p) models, coupled with predictive epsilon (sub th) and OMF models, performed well against the measured D (sub p) data across soil types. Finally, a sensitivity analysis of the OMF in relation to the D (sub p) and pore-network tortuosity (T) showed a reduction in D (sub p) and increase in T with increasing OMF under the same epsilon conditions.
Soils ; Asia ; Diffusion ; Far East ; Gases ; Grain Size ; Hokkaido ; Honshu ; Hydrology ; Japan ; Loam ; Memuro Japan ; Moisture ; Nishi-Tokyo Japan ; Organic Compounds ; Percolation ; Permeability ; Physical Properties ; Porosity ; Power Law ; Saitama Japan ; Saturation ; Size Distribution ; Soil Gases ; Soils ; Statistical Analysis ; Tortuosity ; Transport ; Unsaturated Zone ; Volcanic Soils ; Water;
Vadose Zone Journal