Three‐Dimensional Quantification of Intra‐Aggregate Pore‐Space Features using Synchrotron‐Radiation‐Based Microtomography

Abstract

Pore network geometries of intra‐aggregate pore spaces are of great importance for water and ion flux rates controlling C sequestration and bioremediation. Advances in non‐invasive three‐dimensional imaging techniques such as synchrotron‐radiation‐based x‐ray microtomography (SR‐μCT), offer excellent opportunities to study the interrelationships between pore network geometry and physical processes at spatial resolutions of a few micrometers. In this paper we present quantitative three‐dimensional pore‐space geometry analyses of small scale (∼5 mm across) soil aggregates from different soil management systems (conventionally tilled vs. grassland). Reconstructed three‐dimensional microtomography images at approximate isotropic voxel resolutions between 3.2 and 5.4 μm were analyzed for pore‐space morphologies using a suite of image processing algorithms associated with the software published by Lindquist et al. Among the features quantified were pore‐size distributions (PSDs), throat‐area distributions, effective throat/pore radii ratios as well as frequency distributions of pore channel lengths, widths, and flow path tortuosities. We observed differences in storage and transport relevant pore‐space morphological features between the two aggregates. Nodal pore volumes and throat surface areas were significantly smaller for the conventionally tilled ( Conv.T. ) aggregate (mode ≈ 7.9 × 10 −7 mm 3 /≈ 63 μm 2 ) than for the grassland aggregate (mode ≈ 5.0 × 10 −6 mm 3 /≈ 400 μm 2 ), respectively. Path lengths were shorter for the Conv.T. aggregate (maximum lengths < 200 μm) compared with the grassland aggregate (maximum lengths > 600 μm). In summary, the soil aggregate from the Conv.T site showed more gas and water transport limiting micromorphological features compared with the aggregate from the grassland management system.