Multiscale Framework for Modeling Multicomponent Reactive Transport in Stream Corriders

Travel time-based representations of transport, a highly successful strategy for modeling conservative tracer transport in stream corridors, are extended to accommodate multicomponent reactive transport. Specifically, convolution representations used to model exchange of solute with the hyporheic zone are shown to be equivalent to solving one-dimensional subgrid models in Lagrangian form coupled to the advection dispersion equation for the stream channel. Unlike the convolution-based representations of previous travel time-based stream transport models, the subgrid model generalizes to include multicomponent reactive transport with general nonlinear reactions. An example involving biomass growth, the establishment of redox zonation, and the resulting impact on denitrification rates demonstrate reach-scale application of the new approach. Although simplified, those example simulations show some of the key phenomena associated with hyporheic zone denitrification that are not represented with conventional first-order estimates.