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