Resuspension and Biogeochemistry in Coastal Environments: Results from a Coupled Model for Seabed-Water Column Fluxes
Julia Moriarty1, Courtney Kay Harris2, Christophe Rabouille3 and Marjorie A. M. Friedrichs2, (1)US Geological Survey, Woods Hole, MA, United States, (2)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (3)Lab Sci Climat & Environnement, Gif Sur Yvette Cedex, France
Abstract:
Seabed resuspension in coastal environments can entrain deposited organic material and porewater into the overlying water and alter sediment biogeochemistry and fluxes. The extent to which these sediment fluxes affect water-column biogeochemistry and carbon remineralization is debated and can be challenging to measure, yet a modeling approach promises a means of quantifying these fluxes for a range of conditions. Typically, however, water column biogeochemistry models have used simplifying assumptions to represent benthic boundary conditions, such as the instantaneous remineralization of organic matter deposited on the seabed. These assumptions can significantly affect model estimates of oxygen, carbon, and nutrient fluxes. Meanwhile, diagenetic models usually assume a steady accumulation of material on the seabed. Yet, observations from dynamic coastal environments indicate that oxygen fluxes may increase during resuspension events, indicating that biogeochemical fluxes may be sensitive to cycles of erosion and deposition.
To evaluate the role of sediment resuspension on biogeochemical fluxes, we developed a coupled model within the Regional Ocean Modeling System (ROMS) framework that includes hydrodynamic, sediment transport, and biogeochemical processes. To link the sediment transport and biogeochemical modules, a diagenetic model was added to the seabed. The coupled model accounts for processes including resuspension, diffusion within the seabed porewater and at the sediment-water interface, and organic matter remineralization. It was applied to the Rhone River delta and the riverine-influenced Gulf of Mexico. Consistent with observations from the Rhone delta, modeled oxygen fluxes from the water-column to the seabed increased during resuspension. Model results were sensitive to diffusion within the seabed. Ongoing work includes analysis of nitrogen fluxes, and implementing a three-dimensional version of the model for a river-influenced shelf.
