ACCRETION RATES AND SEDIMENT ACCUMULATION OF THE DELAWARE ESTUARINE MARSHES

Estuarine salt marshes are important components of the coastal system. In recent decades dramatic losses of marshes related to sea level rise, wave erosion and anthropogenic changes to sediment supply have been reported. Future acceleration in the rate of sea level rise and human activities affecting marsh hydrology and sedimentation may severely impact estuarine marshes. In order to predict the impact of future environmental changes on the Delaware estuarine marshes, vertical accretion rates and sediment chronologies for Sea Breeze (NJ) marsh were calculated using Pb-210 and Cs-137 activities. Results indicate that currently studied marsh is accreting at an average rate of 9.1 mm/yr, which is three times faster than the sea level is rising. Lithology of subsurface marsh sediments and stratigraphy indicate significant changes in marsh sedimentation during the last century. Prior to 1954 A.D. estuarine marsh in the study area was dominated by dense high marsh vegetation. An abrupt change in sedimentation from organic rich to mineralogenic sediments had occurred around 1954 A.D. Sharp contacts between high marsh peat and mud units documented in the cores indicate that mud deposition followed marsh erosion or was caused by a dramatic increase in concentration of suspended sediments delivered on the marsh platform. While mechanism(s) responsible for mid-20^th century change in sediment supply remains debatable, stratigraphy and geochronology indicate that marsh recovery began around 1975 A.D. and was completed around 1998 A.D. Similar changes in sediment supply were documented through the late-Holocene sedimentary record in Sea Breeze. Repeated sequences characterized by a sharp boundary, high percentage of mineralogenic sediment towards the bottom and upward increase in organic matter demonstrate that sedimentation pattern of mid-estuarine marshes had changed number of times during the last 2,000 years.