Scientists who study the exchange of chemicals in rivers and streams examine activity taking place within the nutrient-rich portions of streambeds, floodplains, and riverbanks known as hyporheic zones – which provide habitat for various aquatic organisms. Berkeley Lab researchers investigating hyporheic exchange have now shown that meanders near the headwaters of the Colorado River absorb metals and excess nutrients during certain river conditions, thus helping sustain river water quality.
A recent paper published in the journal Water Resources Research, and of which EESA research scientist Dipankar Dwivedi is lead author, describes discoveries made by the Watershed Function Scientific Focus Area (SFA) program team at Berkeley Lab. The researchers conducted their study in an area along the East River catchment near the Upper Colorado River headwaters.
Hyporheic zones perform important ecological functions by linking terrestrial and aquatic systems within watersheds. Composed of nutrient-rich sediment, these water-filled spaces between grains of unconsolidated sediment can act as a source or sink for various metals and nutrients. Dwivedi and his team explored the influence of factors such as groundwater flow dynamics, river-stage fluctuations, and rainfall or snowfall on interactions between nutrient-rich groundwater and oxygen-rich river water in the hyporheic zone.
The study is the first of its kind to apply data from field observations to research into the influence of transient hydrological conditions on the hyporheic biogeochemistry. Using high-resolution hydrodynamic assessments of the hyporheic zone combined with detailed pore-water sampling, the researchers sought to quantify subsurface exports of carbon, iron, and other geochemical species from a single meander to the river under these changing conditions.
Simulation results demonstrated that intra-meander hyporheic zones display distinct anoxic and suboxic regions, the latter localized along sides of the meander bend. The work also showed that permeability has a more significant impact on biogeochemical zonation compared to the reaction pathways for transient hydrologic conditions, and that micro-topographic features such as gullies have outsized influence over chemical reactions that involve the transfer of electrons between two species, or redox processes.