Transport of Solutes in Hyporheic Zones with Temperature-Dependent Reversible Sorption

Abstract:

One of the most important processes impacting the mobility of heavy metals in rivers and their hyporheic zones is reversible sorption to sediment. Reversible sorption has been shown to be a temperature dependent process, however the impact of this variability on heavy metal fate and transport, as well as environmental metal concentrations, has not received much attention. In this study we used zinc as an example heavy metal. Previous studies of the impact of temperature on the sorption of zinc on a goethite substrate show a change in partitioning coefficient and thus retardation factor of 10 to over 60 percent with a temperature change from 10 to 25*C, depending on concentration of dissolved zinc in the water. This relationship was extrapolated to estimate the change in reversible sorption of zinc on silicate sand. This change was then utilized within a finite-element model coupling hyporheic fluid flow in porous media with heat transfer and solute transport with reversible sorption to explore the ways in which variations in surface water temperature over varying timescales can drive changes in both zinc sorption and dissolved zinc fluxes at the bedform scale. These linked processes are of fundamental importance when considering the number of different ways in which surface water temperatures can be varied through both human and non-human activities.