Effective kinetics driven by dynamic concentration gradients under coupled transport and reaction

Biogeochemical reaction kinetics are generally established from batch reactors where concentrations uniform. In natural systems, many biogeochemical processes characterized by spatially and temporally variable concentration gradients that often occur at scales which not resolved field measurements or reactive transport models. Yet, it is clear how these sub-scale chemical affect compared to kinetics. Here we investigate this question studying the paradigmatic case of localized pulses solute reacting with a solid dissolved species in excess. We consider non-linear reactions, representative mineral dissolution, adsorption redox quantify using simplified power-law The combined effect diffusion leads effective differ quantitatively qualitatively Depending on nonlinearity (reaction order) local kinetics, effects lead either enhancement decrease overall rate, result rich variety dynamics. derive analytical results for validated comparison direct numerical simulations broad range Damköhler numbers order. Our findings provide new insights into interpretation imperfectly mixed lab experiments, systems intermittent reactant release integration