Multifractal properties of porosity as calculated from computed tomography (CT) images of a sandy soil, in relation to soil gas diffusion and linked soil physical properties

• Published in: European journal of soil science Vol. 63; no. 6; pp. 861 - 873
• Main Authors: Lafond, J. A., Han, L., Allaire, S. E., Dutilleul, P.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2012; Blackwell
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Correlation; Earth sciences; Earth, ocean, space; Entropy; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Gas diffusion; Heterogeneity; Porosity; Soil (material); Soil science; Soils; Spectra; Surficial geology; physical properties; Gaseous diffusion; textures; porosity; Property of soil; sandy soils; Earth science; Multifractal system; Axial tomography; Image; Soil science; Computerized axial tomography; soils; Link
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/j.1365-2389.2012.01496.x

Relationships between soil porosity and diffusive gas flux are poorly understood, partly because of a difference in measurement scales between the two. The complexity of soil pore systems can be described by multifractal analysis at the microscopic scale, whereas relative soil gas diffusion coefficients (Ds/Do) are usually evaluated at the core scale. The objectives of this study were to (i) define a quantitative ‘pseudo‐macroporositygas’ from high‐resolution X‐ray computed tomography (CT) scanning images and characterize it for 10 intact soil cores, (ii) analyse the frequency distribution of pseudo‐macroporesgas in the columns with a multifractal approach and (iii) assess relationships between Ds/Do measured at the core scale and multifractal parameters describing the pore system heterogeneity within a core. The shape and symmetry of the singularity spectra and the degree of curvilinearity of the Rényi spectra show that the multifractal behaviour of the pseudo‐macroporositygas distribution for a given CT image thresholding varied among soil columns. Correlations found between Ds/Do and some parameter estimates of the singularity spectrum suggest that the distribution of pseudo‐macroporesgas, depending on the CT image thresholding, influenced Ds/Do. In particular, a strong correlation between Ds/Do and the entropy dimension (Dq = 1) indicates that Ds/Do was influenced by the degree of spatial heterogeneity of the pseudo‐macroporositygas distribution. The correlation dimension (Dq = 2) was also linked to Ds/Do, suggesting that a second‐order power law might describe the scaling relationship between pseudo‐macroporositygas distribution and Ds/Do. In conclusion, the multifractal description of soil porosity as calculated from CT images may be regarded as a way to improve our understanding of gas movement in soils at the core scale.