Modeling Solute Leaching in Soils by Diffusion‐Limited Aggregation: Basic Concepts and Application to Conservative Solutes

The diffusion‐limited aggregation (DLA) model introduced by Witten and Sander (1981) was modified to describe leaching of conservative solutes through soils. In the DLA concept, particles that move by random walk (diffusion) form aggregates. This model was adapted by modifying the walking probabilities and by introducing layers. The model does not describe the actual random walk of solutes in a heterogeneous flow field, but it can describe results of observed experimental outcomes with a minimal set of parameters. The modified model is versatile: homogeneous distributions of chemicals can be simulated, such as those produced with piston flow on the one hand, and complicated distributions arising from macropore flow and fingering on the other hand. The model was successfully applied to the results of a field experiment where preferential flow of bromide occurred.