Coherent structures are ubiquitous in environmental and geophysical flows. Recent advances in the identification of fi nite-time transport barriers have enabled the extraction of organizing templates for passive scalars in the limit of infinitesimal diffusion. In this presentation, we show, by using examples of reaction processes, that they can also be tied to finite-time Lagrangian measures. Specifically, the reaction rate and even the final fate of scalar concentrations may be dependent on the initial flow topology they were in. Some most recent efforts on more complicated reaction processes will also be discussed.