Rates of Sediment Accumulation in a Tidal Freshwater Marsh

Abstract

ABSTRACT Rates of sediment accumulation were determined for a Delaware River tidal freshwater marsh utilizing radiometric, palynological and sediment flux estimating techniques plus historical reviews. All techniques showed good agreement, indicating that tidal freshwater marshes are capable of preserving evidence of processes and events that have shaped the estuary through time. Prior to 1940, the marsh was a slowly accreting swamp accumulating material at the rate of 0.04 cm yr-1 prior to colonization of the region in the late 1600s and a somewhat more accelerated rate of 0.12 cm yr-1 prior to the introduction of regular tides in 1940. Between 1940 and 1988 average rates of accumulation ranged between 1.04 and 1.38 cm yr-1, being highest near the tidal channe . During the period 1954-65, rates averaged 1.67 cm yr-1 due to increased storm activity. Since 1966, storm activity has decreased and sediment accumulation rates have averaged 0.97 cm yr-1, reflecting these changes. The current average rate of accumulation is four times the rate of sea-level rise for this region of the estuary. It is hypothesized that sediment accumulation will continue to exceed sea level rise until the marsh surface approximates mean high water.