A new exponential model for predicting soil gas diffusivity with varying degree of saturation

Lakshani, MMT and Chamindu Deepagoda, TKK and Hamamoto, S and Elberling, B and Fu, W and Yang, T and Fan, J and Ma, X and Clough, T and Smits, KM and Parameswaran, TG and Sivakumar Babu, GL and Chanakya, H (2022) A new exponential model for predicting soil gas diffusivity with varying degree of saturation. In: Vadose Zone Journal .

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Abstract

Soil gas diffusivity (Dp/Do, gas diffusion coefficients in soil and in free air, respectively) and its relation to soil moisture is of great importance for describing and quantifying essential provisional and regulatory functions associated with terrestrial ecosystems such as soil aeration and greenhouse gas (GHG) emissions. Because gas migration in terrestrial soil systems is predominantly diffusion controlled, soil gas diffusivity becomes a fundamental prerequisite to quantify diffusive gas fluxes. Descriptive–predictive models are often used to estimate Dp/Do from easily measurable soil physical properties. Most of the available models take the form of power-law functions and often tend to mischaracterize soil moisture effects at high moisture regimes. Based on a wide range Dp/Do data available in literature representing both intact and repacked soils, this study developed a novel air-saturation-dependent exponential (ASEX) gas diffusivity model to model Dp/Do in relation to soil air saturation. The model variable α, which represents the diffusivity at half air saturation normalized by the same in complete soil air saturation, could potentially differentiate moisture effects on different soil structural states. For specific applications in intact soils, we propose corresponding α values for upper-limit (α =.6) and lower-limit (α =.05) estimates of diffusivity, while an average value (α =.3) for general applications in both intact and repacked soils. As expected, our model based on a few a priori measured supportive data showed a better performance over the classical predictive models that do not use such measurements. The new model was further used to derive useful implications to showcase soil density effects on Dp/Do.

Item Type:	Journal Article
Publication:	Vadose Zone Journal
Publisher:	John Wiley and Sons Inc
Additional Information:	The copyright for this article belongs to John Wiley and Sons Inc.
Keywords:	Gas emissions; Greenhouse gases, Air saturation; Degree of saturations; Exponential models; Gas diffusion; Gas diffusivity; Predictive models; Regulatory functions; Repacked soils; Soil gas; Terrestrial ecosystems, Soil moisture
Department/Centre:	Division of Mechanical Sciences > Civil Engineering
Date Deposited:	09 Jan 2023 07:20
Last Modified:	09 Jan 2023 07:20
URI:	https://eprints.iisc.ac.in/id/eprint/78918

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