Boundary layer fluxes over restored oyster reefs

Lawrence P Sanford, University of Maryland Center for Environmental Science, Horn Point Laboratory, Cambridge, MD, United States, Melanie Leigh Jackson, University of Maryland Center for Environmental Science Horn Point Laboratory, Cambridge, MD, United States, Kevin Kahover, University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, United States, Ella Kaplan, University of Minnesota Twin Cities, Minneapolis, MN, United States, Kiera Givens, Meridian Institute, Washington, DC, United States, Jeffrey C Cornwell, University of Maryland Center for Environmental Science Horn Point Laboratory, Horn Point Laboratory, Cambridge, United States, Lora Harris, University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, United States and Allison Colden, Chesapeake Bay Foundation, Annapolis, MD, United States
Abstract:
Oyster reef restoration activities are underway world-wide, with multiple goals including restoring depleted historical oyster populations and restoring associated ecosystem functions. Oyster reefs filter fine seston from the water column, provide a food source for other aquatic organisms, provide valuable habitat for complex benthic communities, and promote nutrient sequestration, burial, or denitrification. Restored oyster reefs also significantly increase bottom roughness, which increases mixing with the overlying water column while promoting deposition and retention of fast settling biodeposits. This paper synthesizes recent observations and models of boundary layer exchanges over three experimental oyster reef restoration sites in Chesapeake Bay, USA: two natural reef mimics in the Harris Creek Oyster Sanctuary and one reef ball deployment in the Severn River. Water depths ranged from 1.5 m to 8 m, with oyster densities of 20-60 m-2 in Harris Creek and 240 reef balls in a 100 m2 patch in the Severn River. Data collected at different sites included ADCP velocity profiles, near-bottom dissolved gas and nutrient profiles, water column profiles of particle characteristics and water quality, and benthic flux chamber incubations. Various models of boundary layer flow, drag partitioning, turbulence, and material fluxes were compared to the data. In general, the velocity observations were consistent with expectation for turbulent flow over a rough bottom, with roughness and drag coefficient estimates comparing reasonably to formulations for enhanced biogenic roughness. Particle, dissolved gas, and nutrient profiles also were mostly consistent with expectation for turbulent benthic fluxes. However, observable oyster reef influences were confined to the bottom boundary layer. Advection and local water column processes appeared to dominate mid-depth and surface waters at all sites.
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