Dynamics of a marsh-bay boundary
Abstract
The boundary between intertidal marshes and coastal bays is one of the most commonly occurring types of terrestrial-marine boundaries. The boundary is inherently dynamic, tending to advance or retreat depending on sediment supply, sea-level rise and storm wave conditions. Here, field measurements and modeling are combined to examine the dynamics of a bay-marsh boundary fringing a large shallow bay on the Eastern Shore of Virginia. Field measurements include 60-yr lateral erosion rates, 6 years of high-resolution vertical erosion/deposition rates, and seasonal time series of waves, tides, suspended sediment concentrations and sediment flux at the bay-marsh boundary. The results indicate relatively rapid marsh-edge retreat of 1-2 m/yr that are similar on annual and decadal time scales. Sediment supply to the marsh platform, located about 0.5 m above mean sea level, is largely controlled by flooding frequency. At this site, wind conditions suitable for generating waves that elevate suspended sediment concentrations generally coincided with peak tidal elevations that are too low to flood the marsh. Sediment is accumulating 20 m interior to the marsh at rates exceeding relative sea-level rise (4 mm/yr) but the marsh surface near the edge is eroding vertically at rates of several cm/yr, which increase as the laterally migrating marsh edge moves closer the measurement site. This transition from marsh interior to edge as the marsh boundary migrates through the marsh, is also characterized by an increase in macroporosity, primary as a result of crab burrowing, a decrease in vegetation density and height, and an increase in bearing strength.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP21B0879W
- Keywords:
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- 1902 Community modeling frameworks;
- INFORMATICSDE: 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICSDE: 4217 Coastal processes;
- OCEANOGRAPHY: GENERALDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL