A reactive transport model for integrated surface-subsurface hydrology

Abstract:

The investigation of carbon and nutrient cycling in terrestrial systems is driving the need to model the interactions between climate drivers, hydrological processes, vegetation dynamics, and biogeochemical reactions. Models applicable at different scales, from the hyporheic zone scale to the watershed scale, also require careful consideration of the mass fluxes within the surface and subsurface compartments and across their interface. This makes it possible to capture the relevant processes in key subsystems such as hyporheic zones, hillslopes, meanders, wetlands and lagoons. Integrated hydrology models have been increasingly used in applications at the river-corridor and watershed scales and beyond for their ability to simulate coupled surface-subsurface flow processes in 3-dimensional, highly-resolved domains. However, they still lack consideration of the fate of the chemical constituents and biogeochemical processes. Development of such models is often complex as it involves a large number of software components, each representing a process model, that must be combined in a single code. Here we use the principles of interoperable code development and software sustainability to develop a biogeochemical reactive transport model for integrated hydrology problems. The code can simulate flow, transport and reactions in surface-subsurface environments. We build on an existing integrated hydrology model and expand it by adding a solute transport solver and by using a well-defined interoperable interface to access existing biogeochemical codes. We demonstrate the use of the resulting code in the simulation of hyporheic exchange in a section of a river channel, and in the simulation of mineral dissolution in a hillslope subject to wet-dry cycles.