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QUANTIFYING ECOSYSTEM SERVICES PROVIDED BY HYPORHEIC EXCHANGE

Stanley B. Grant and Morvarid Azizian Civil and Environmental Engineering, University of California Irvine & Infrastructure Engineering, University of Melbourne. Objectives. Present an analytical model of benthic exchange and reaction Pumping of solute across bedforms

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QUANTIFYING ECOSYSTEM SERVICES PROVIDED BY HYPORHEIC EXCHANGE

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  1. Stanley B. Grant and MorvaridAzizian Civil and Environmental Engineering, University of California Irvine & Infrastructure Engineering, University of Melbourne Objectives • Present an analytical model of benthic exchange and reaction • Pumping of solute across bedforms • Advection-dominated mass transport • First-order reaction in sediment • Evaluate model • Compare to numerical solution • Derive solution for soluteflux into the sediment • Application • Correlations for mass transfer coefficient • Trade-off between volume of water processed in the sediment and extent of reaction Solution approach (neglect dispersion & diffusion) Numerical simulation results predicted concentration field (analytical) predicted concentration field (numerical) streamline geometry QUANTIFYING ECOSYSTEM SERVICES PROVIDED BY HYPORHEICEXCHANGE predicted concentration field Elliot and Brooks Velocity Model • Numerical and analytical solutions near-identical • Numerical simulation carried out with COMSOL • Mechanical dispersion & molecular diff. negligible • Dirichletb.c. at surface causes gradient artifact mass-transfer-limited flux Applications variable definitions Analytical model supports use of mass transfer coefficient flux into sediment bed • Flux ~ conc. diff. in upwelling & downwelling zones • Mass transfer coefficient = downwelling velocity Ecosystem services Numerical approach (governing equations) • Flux into sediment = mass removal in sediment • Mass removal in sediment = ecosystem service (N, P, C processing; CEC removal) • Model identifies trade-off between volume of water processed by hyporheic zone and extent of reaction in sediment (hard to optimize both) normalize by wave number variable definitions advection/dispersion equation variable definitions pressure head dispersion tensor velocity field Acknowledgements Funding by the National Science Foundation Partnerships for International Research and Education (PIRE) Award No. OISE-1243543. A huge THANK YOU to Keith Stolzenbach (UCLA), Megan Rippy (UCI), Mike Stewardson (UoM), and Perran Cook (MonashUniv).

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