Redox-zoning in high-energy subterranean estuaries as a function of storm floods, temperatures, seasonal groundwater recharge and morphodynamics

Abstract

Redox conditions are a major control for the concentrations and mass fluxes of water constituents, e.g., nutrients, metals and organic molecules within subterranean estuaries (STE). Due to the transient flow and transport processes in STEs as well as the variable temperatures and input of redox reactants, redox zoning in the STE is believed to be highly dynamic. In the present study we analyzed the individual and combined effects of storm floods, seasonal changes of temperatures and groundwater recharge rates, as well as beach morphodynamics on the redox zoning in the STE. For this purpose, a 2D cross-shore density-dependent flow and reactive transport model was set up representing a beach aquifer exposed to high-mesotidal and medium-to high-energy wave conditions, as well as to storm floods. The simulation results show that under the given conditions, redox dynamics may occur down to a depth of 20 m. Morphodynamics appear to be the most important factor for the transience of redox zones compared to the other factors. Seasonal changes in meteoric groundwater recharge rates appear to be least relevant for the redox dynamics in STEs.