About This Item
Share This Item
Studies along the South Atlantic coastline show that the geomorphology of tidal flats and salt marshes is commonly altered or controlled by the development of Crassostrea virginica oyster mounds. Two major mechanisms for geomorphic control have been recognized. (1) The oyster mound is a long sinuous bar encompassing large parts of the tidal-flat fringe. This bar acts as a barrier, slowing and in some areas completely impeding drainage of the flat during the receding tide. The impoundment of sediment-laden water increases the rate of deposition over the flat, eventually raising the surface topography and accelerating the progradation of the fringing salt marsh. (2) An oyster mound grows perpendicular across a small tidal channel, effectively damming the channel, causing in reased rates of sedimentation. Sometimes the tidal prism of the channel has been sufficiently altered so that an initiation of lateral tidal-creek migration occurs. Migration rates up to 1 m/year have been measured. In other cases, the channel fills with a fine-grained plug.
Coring of two marsh systems in South Carolina shows that oyster mounds can play an important role in the depositional history of the marsh. In areas where lateral tidal creek migration occurs, much of the stratigraphic record is dominated by channel-fill point-bar sequences. Combining modern process data with subsurface cross sections derived from over 20 cores, a three-dimensional model showing the effects of oyster mounds on the back barrier environment has been developed.
End_of_Article - Last_Page 1661------------