Modeling the formation of soil microaggregates

Abstract

The functions of soils are intimately linked to its aggregated structure. Microaggregates formed during pedogenesis from a vast variety of mineral, organic, and biotic materials are the smallest conceivable compounds at the basis of soil structural hierarchy. Qualitative hypotheses and concepts on how aggregates form are quite elaborate, but the consistent quantitative application within a mechanistic and physically rigorous framework is still missing. This is partly caused by the fact that such an endeavor requires the combination of synergistic concepts on the transport of particles and their interactions affected by shape, size, and surface properties in aqueous suspension. Here we present a novel quantitative approach for the formation of soil microaggregates in silico that integrates diffusion-limited cluster-cluster aggregation with a probabilistic attachment following the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of particle interactions. To represent universal mineral shapes found in soils, we implemented spherical, plate-like as well as rod-like particle morphologies inspired by weathered silicates, secondary clay minerals and pedogenic iron oxides. In this way, we developed a model that produces an explicit three-dimensional structure of aggregates emerging from hetero- as well as homo-aggregation in response to the chemical milieu. We then exploited the 3D morphology to assess functional properties of aggregates exemplified with the water retention curve and pore size distribution.