Simulation of reactive solute transport in the critical zone: a Lagrangian model for transient flow and preferential transport

Abstract. We present a method to simulate fluid flow with reactive solute transport in structured, partially saturated soils using Lagrangian perspective. In this context, we extend the scope of Soil Water and Solute Transport Model (LAST) (Sternagel et al., 2019) by implementing vertically variable, non-linear sorption first-order degradation processes during substances through soil matrix macropores. For sorption, develop an explicit mass transfer approach based on Freundlich isotherms because common retardation factor is not applicable particle-based LAST. The tested against data plot- field-scale irrigation experiments herbicides isoproturon flufenacet at different conditions over various periods. Simulations HYDRUS 1-D serve as additional benchmark. At plot scale, both models show equal performance matrix-flow-dominated site, but LAST better matches indicators preferential macropore-flow-dominated site. Furthermore, successfully simulates effects adsorption breakthrough behaviour leaching remobilization. results demonstrate feasibility framework highlight advantage structural macropore domain well cope bypassing topsoil subsequent re-infiltration into subsoil matrix.