A Reactive Transport Modeling Approach for Understanding Concentration-Discharge in East River, Colorado

Concentration-discharge (C-Q) relationships have been used in previous studies to understand the geochemical processes controlled by hydrolog. Field observational data indicate that some aquatic geochemical components, such as sulfate and calcium, exhibit distinct characteristics under snowmelt and baseflow conditions. Subsurface geologic structure and mineral composition may have a strong influence on C-Q relationships and geochemical responses with different water infiltration and groundwater level scenarios. This study seeks to test this conceptual model in a quantitative manner with an integrated-hydrology reactive transport model (RTM). For this purpose, a high-resolution (50-meter) RTM is developed and applied using the Advanced Terrestrial Simulator (ATS) coupled with PFLOTRAN via the Alquimia interface. The RTM quantitatively simulates the integrated hydrology, solute transport and chemical reactive processes with the interaction between surface and subsurface Copper Creek, one of the largest catchments in the watershed of East River, Colorado. The simulations are performed on NERSC supercomputers owing to the large computational requirements of the model. Two key minerals and geochemical processes, including calcium dissolution and pyrite oxidation, are examined with river discharge under the scenarios of precipitation, snowmelt and groundwater level fluctuations. This study aims to understand the interactions of hydrology and major subsurface geochemistry processes, provide insights to the variability of water quality in a watershed scale under a changing climate environment.