科研之友
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摘要
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 (D-s/D-o) are usually evaluated at the core scale. The objectives of this study were to (i) define a quantitative %26apos;pseudo-macroporosity(gas)%26apos; 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-macropores(gas) 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 Renyi spectra show that the multifractal behaviour of the pseudo-macroporosity(gas) distribution for a given CT image thresholding varied among soil columns. Correlations found between D-s/D-o and some parameter estimates of the singularity spectrum suggest that the distribution of pseudo-macropores(gas), depending on the CT image thresholding, influenced D-s/D-o. In particular, a strong correlation between D-s/D-o and the entropy dimension (D-q = 1) indicates that D-s/D-o was influenced by the degree of spatial heterogeneity of the pseudo- macroporosity(gas) distribution. The correlation dimension (D-q = 2) was also linked to D-s/D-o, suggesting that a second-order power law might describe the scaling relationship between pseudo- macroporosity(gas) distribution and D-s/D-o. 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.
- 出版日期2012-12
