Aggregate formation dynamics driven by 3D fluid flow in natural porous media

Fluid flow and reactive transport in natural porous media take place in a three-dimensional, hierarchically organized network of voids and pores in the size range of sub-micrometers inside small aggregates to several millimeters in, e.g., earthworm burrows or cracks. Thus, fluid flow regimes are manifold with consequences not only for the transport of solutes, but also for the displacement of colloidal particles and organic matter and thus, for their inclusion into soil aggregates. Therefore, we incorporated the simulation of three-dimensional fluid flow in pore networks typical for natural porous media into our recent approach to model soil aggregate formation using DLVO theory and diffusion-limited aggregation to overcome its previous limitation to suspensions at rest. To visualize the model capabilities, we simulated aggregation in pore networks that were either synthetically designed to represent certain structural features such as pore junctions and dead-end pores, or taken directly from X-ray µ-CT measurements of undisturbed soil cores. We explored the development of structural aggregated features that evolve in response to flow, transport and the topology of the soil pore space. The resulting three-dimensional arrangement of compounds and the entire aggregates were classified according to their morphological metrics, e.g. the pore space distribution, and functional properties, e.g. the water retention capacity, that are provided by these structures. By this fusion of complementary modeling approaches, we significantly contribute to the fundamental mechanistic understanding of the complex interplay and feedback of structure, interactions and functions on the scale of (micro-)aggregates.