The Role of Seabed Resuspension on Oxygen and Nutrient Dynamics in Coastal Systems: A Numerical Modeling Study
Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Courtney K. Harris
Carl T. Friedrichs
Seabed resuspension can impact organic matter fate and water column biogeochemistry in coastal environments. Cycles of erosion and deposition can, for example, affect remineralization rates, seabed-water column fluxes of dissolved oxygen and nutrients, and light attenuation. Yet, models that incorporate both sediment transport and biogeochemical processes are rare, and nearly all neglect the effect of resuspension on oxygen and nutrient dynamics. Development of a novel tool, i.e. a coupled hydrodynamic-sediment transport-biogeochemical model, allowed for an investigation of the role of resuspension on oxygen and nitrogen dynamics within three distinct coastal environments. Called HydroBioSed, the coupled model was built within the Regional Ocean Modeling System and accounted for physical processes including the deposition and erosion of inorganic sediment and particulate organic matter from the seabed, as well as the flux of dissolved inorganic chemical species at the seabed-water column interface. The model also considered biogeochemical reactions including the remineralization of organic matter and oxidation of reduced chemical species, in both the seabed and the water column. HydroBioSed was first implemented as a one-dimensional vertical model for the Rhône River subaqueous delta. Results indicated that cycles of erosion and deposition altered rates of diffusion between the seabed and water column. This process increased fluxes of oxygen into the seabed during erosional periods, and the effect remained significant when results were averaged over time scales longer than individual events. The coupled model was next implemented in three-dimensions for the riverine-influenced northern Gulf of Mexico shelf. In this environment, resuspension-induced effects on bottom water biogeochemistry were dominated by increases in remineralization. Specifically, remineralization of resuspended organic matter increased oxygen consumption and ammonium production, especially in shallow areas where bed stresses were typically high. Finally, HydroBioSed was implemented for the Chesapeake Bay estuary and adapted to account for light attenuation by sediment and resuspended particulate organic matter. Here, resuspension-induced turbidity caused a down-stream shift in primary production. This shift, combined with remineralization of resuspended seabed organic matter, caused oxygen concentrations to decrease and ammonium concentrations to increase throughout the estuary. Overall, use of a novel coupled hydrodynamic-sediment transport-biogeochemical model, showed that cycles of erosion and deposition impact water column biogeochemistry, but the specific effects of resuspension varied across the three distinct environments studied.
© The Author
Moriarty, Julia Miege, "The Role of Seabed Resuspension on Oxygen and Nutrient Dynamics in Coastal Systems: A Numerical Modeling Study" (2017). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1516639567.