SPB Academic Publishing bv, Amsterdam Inorganic Sediment Budget for the North Inlet Salt Marsh, South Carolina, U.S.A.

Most salt marshes along the east coast of North America appear to accumulate sediment at a rate sufficient to keep pace with the rise in eustatic sea level and local subsidence. Thus, these marshes must be importing sediment from the coastal ocean andlor the adjacent estuaries. The sediment accumulating in the North Inlet salt marsh, South Carolina, is 80 % inorganic, and, based on 2 1 0 ~ b dating, is accreting at a rate of 0.098 g cmp2 yr-l, equal to a 2.7 mm yr- ' vertical sedimentation rate. Tide gauge records show a relative sea level rise of 2.2 to 3.4 mm yr-l, indicating this marsh is maintaining its elevation relative to mean sea level rise. The North Inlet salt marsh has two avenues of sediment exchange: (1) through the tidal inlet to the ocean and (2) through Winyah Bay, the adjoining estuary. Long-term inorganic suspended sediment flux through the inlet is calculated to be a net import of.1.35 kg s-', based on application of a tidal hypsometric flow mod-el to seven years of daily suspended sediment concentrations. However, the import required to balance rela-tive sea level rise is only 0.80 kg s-', implying an excess net import of 0.55 kg s-'. The difference between import and accumulation is explained by the progradation of the marsh toward Winyah Bay, a conclusion which is supported by the geomorphology and stratigraphy of the marsh-estuary border. Thus, the North Inlet marsh imports sediment on the average through the tidal inlet, at a rate which allows for both vertical accu-mulation at a rate approximately equal to the relative sea level rise and also lateral expansion of the marsh