Oscillating redox environment of the hyporheic zone of tidally forced rivers

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The groundwater in the Lower Fraser River Delta surface aquifer contains high concentrations of iron and other species that are not compatible with dissolved oxygen. Much of this groundwater discharges from the aquifer into the base of Fraser River through the so-called hyporheic zone, the zone of the subsurface where river water and groundwater mix. This mixing is driven in part by the tidal action of the Fraser River. In the hyporheic zone, the oxygen in the Fraser River water is expected to cause the iron in the groundwater to oxidize and form low-solubility iron-oxide (rust-like) precipitates, which are known to adsorb trace metals from the water. The objective of this research is to study the physical and geochemical processes that occur in the hyporheic zone, and to study the processes that by which the groundwater in the Fraser River Delta aquifers acquire their dissolved loads. The research is important because the geochemical processes in the hyporheic zone and the Fraser River Delta surface aquifer can have a strong effect on contaminants in groundwater and nutrient loading to surface waters.