CAREER: Multiphysics research and education for understanding coupled mechanical-biogeochemical surface-subsurface processes

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CAREER: Multiphysics research and education for understandingcoupled mechanical-biogeochemical surface-subsurface processesRivers are connected to aquifers, to riparian zones, and to floodplains, and this coupling is an integral component of aquatic systems. The connection is mediated by fluid flow between the channel and its bed and bank; this exchange is also referred to as hyporheic flow. Processes occurring along the river-sediment interface or the hyporheic zone (HZ) significantly impact nutrient and metal chemistry, ecology, and thermal energy budgets. The study is integrating research and education to advance the application of coupled mechanical-biogeochemical modeling and emerging observational technology. The scientific hypotheses include: 1) riverbed topography exerts first order control on nutrient cycling within the sediment by affecting hyporheic-flow-inducing turbulent flow in a river; 2) heat transfer from the channel to the sediment due to hyporheic flow leads to variable riverbed temperatures which in turn leads to changes in biogeochemical reaction rates; 3) temporal thermal variability in the riverbed causes reversal in sorption of metals which causes transient surface water chemistry; and 4) heterogeneity in sediment hydraulic properties leads to broader fluid residence time distributions resulting in sharper and patchier biogeochemical gradients which may favor reaction hotspots. While the scientific hypotheses apply to a variety of nutrients and metals, this study will focus on denitrification, as an example of nutrient cycling, and zinc and copper mobility, as examples for temperature-dependent metal transport. The hypotheses are being tested using tandem flume and column experiments supported by numerical models that consider turbulent flow in the flume channel and non-isothermal flow and reactive transport in the flume hyporheic zone. Temperature and dissolved oxygen are being mapped in 2D within the HZ down to the millimeter scale. The educational effort is integrating inquiry-based multiphysics modeling exercises into teaching to enhance learning and student motivation. The impact of developing and disseminating biogeochemical coupled models for interactive inquiry-based learning exercises is being qualitatively and quantitatively assessed.