Multifractal Analysis of Pore Size Distributions as Affected by Simulated Rainfall

Characterization of the soil pore system provides a realistic base to understand the retention and movement of water in soil. The objective of this work was to estimate multifractal parameters from Hg injection porosimetry data on the uppermost soil surface layer as affected by simulated rainfall. Soil aggregates were sampled at the 0- to 2-cm depth in a loamy soil, both on a recently tilled soil surface and on its disturbed counterpart after 260-mm cumulative rainfall. Pore size distributions (PSDs) were determined by Hg intrusion porosimetry from 0.005- to about 100-μm pore diameters on 10 samples per surface stage. The rainfall reduced aggregate pore volume, showing significant differences between the pore space of the reference and the disturbed soil surfaces. A multifractal analysis was performed by means of scaling of the moments ranging from -10 < q < 10 for all PSDs. Mean values of the entropy dimension, D1, and correlation dimension, D2, in the aggregate set sampled after rain disturbance were lower than those of the reference stage; however, mean values of the difference delta (D1 - D2), the Hölder exponent of order zero, α(0), and widths of the left (α(0) - α(q+)) and right (α(q-) - α(0)) hand sides of the singularity spectra f(α) after rainfall action were higher than those of the initial soil surface. Entropy dimension, D1, and the width of the left (α(0) - α(q+)) hand side of the f(α) spectra best discriminated between PSDs of the reference initial soil surface vs. soil surface disturbed by rain.