Modeling oxygen diffusion in aggregated soils. I. Anaerobiosis inside the aggregates

• Published in: Soil Science Society of America journal Vol. 58
• Main Authors: Renault P, Stengel P
• Format: Journal Article
• Language: English
• Published: 01.07.1994
• Subjects: agua; aislamiento; anaerobiose; anaerobiosis; biologia del suelo; biologie du sol; caract morfologicas del suelo; denitrificacion; denitrification; diffusion; difusion; eau; insulation; isolation; mathematical models; modele mathematique; modelos matematicos; oxigeno; oxygen; oxygene; soil biology; soil morphological features; soil structural units; trait morphologique du sol; unidades estructurales de suelos; unite structurale du sol; water
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1994.03615995005800040004x

Denitrification may appear in anaerobic regions of soil aggregates. In order to evaluate the dependence of anaerobiosis on aggregate shape, on contact with other aggregates, and on surface occlusion by water, a numerical method was used to simulate O2 diffusion and consumption in three-dimensional models of water-saturated aggregates. The aggregates were assumed to be homogeneous in regard to porosity, gas diffusion, and microbial respiration. After equilibration, the calculated anaerobic fractions of simulated aggregates were compared with those obtained for homogeneous spherical ones having the same unblocked external surface area/total aggregate volume ratio. Anaerobiosis of unoccluded aggregates may be predicted by the spherical model with an uncertainty less than approximately 5%. When there are occlusions, anaerobiosis may still be predicted by the spherical model for aggregates with a radius greater than some critical radius, but the uncertainty may be as high as 100%. The critical radius corresponds to the radius of the smallest homogeneous spherical aggregate that has an anaerobic center when there is no occlusion of its external surface. For smaller aggregates, we proposed an empirical reduction of the anaerobic fraction predicted by the spherical model in order to predict their actual anaerobic fraction.