Submerged Vegetation Modulates Sediment Connectivity between Subtidal Flats and Intertidal Marsh in Shallow Coastal Bays
Abstract
Back-barrier intertidal salt marshes are a favorable sediment sink for sediment transported from adjacent subtidal flats. Sustained sediment accumulation in these back-barrier marsh environments can reduce barrier island vulnerability to sea level rise. Fine sediment accumulation on back-barrier marshes relies on a supply of suspended sediment from nearby tidal flats. The presence of submerged seagrass meadows on the flats, however, can significantly attenuate tidal currents and wave heights, thereby reducing sediment suspension in the bay and sediment flux to the adjacent salt marsh platform. To assess the importance of subtidal seagrass meadows on sediment exchange between the coastal bay and fringing intertidal marshes, we apply the spatially resolved hydrodynamic and sediment transport model Delft3D in a shallow coastal bay in Virginia with seagrass meadows proximal to a back-barrier marsh (South Bay, Wreck Island). Our model includes both intertidal (salt marshes) and submerged (seagrass) vegetation effects on flow and wave attenuation, and is well calibrated using seasonal field hydrodynamic and suspended sediment data from the site. We use the model to explore the combined effect of seasonal wind patterns and submerged vegetation density variation on sediment connectivity between subtidal flats and intertidal marsh. We quantify sediment fluxes into and out of submerged seagrass meadows and adjacent marshes, and corresponding deposition/erosion rates, with and without submerged vegetation under: (1) typical summer southwesterly winds when seagrass density reaches a maximum, and (2) more frequent and stronger northeasterly winds during winter coinciding with minimum seagrass density. Our results underscore the tight coupling between marsh deposition rates and the controls on sediment resuspension in shallow coastal bays.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP51C2097Z
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 1804 Catchment;
- HYDROLOGY;
- 1815 Erosion;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY