Abstract
Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity.
Highlights
IntroductionI.e. the spatial arrangement of mineral, organic, air and water, and other phases at the sub-Darcian scale, defines all local (i.e. at the scale of measurement) and effective (i.e. describing flow processes in an upscaled homogeneous medium, referred-to as Darcy scale) soil properties
Soil microstructure, i.e. the spatial arrangement of mineral, organic, air and water, and other phases at the sub-Darcian scale, defines all local and effective soil properties
In this article we focused on soil structure in 2D, as both the thin-section measurements and the reconstruction of soil structure using correlation functions provided 2D information only
Summary
I.e. the spatial arrangement of mineral, organic, air and water, and other phases at the sub-Darcian scale, defines all local (i.e. at the scale of measurement) and effective (i.e. describing flow processes in an upscaled homogeneous medium, referred-to as Darcy scale) soil properties. In addition to filtration properties, structure defines such soil properties as molecular diffusion [8,9,10], mechanical properties [11,12], electrical resistivity [13,14], heat transfer and evaporation [15,16,17], and hydrodynamic dispersion [18,19,20] These physical properties combined govern geochemical reactions and weathering [21,22], transport of solutes, nutrients, viruses or colloids [23,24,25,26], and affect living conditions of microorganisms [27,28]. Throughout this paper, all references to the term ‘structure’ refer to microstructure
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