Examining Coastal Marsh Sedimentation In Northeastern North Carolina

Abstract

Coastal marshes are critical environments that are ephemeral on geologic timescales. Understanding the dynamics that naturally maintain these systems is becoming increasingly important in the face of accelerated sea-level rise. Ceramic tiles, radioisotopes (²¹⁰Pb and ¹³⁷Cs), shoreline mapping, and stable isotope ([delta]¹³C and [delta]¹⁵N) analysis were used to evaluate short-term deposition relative to decadal-scale accumulation and assess whether two marshes in northeastern North Carolina were maintaining their systems relative to sea-level rise. It was determined that deposition is highly influenced by marsh geomorphology, with higher deposition rates along the shoreline, and lower deposition rates in the marsh interior. Continuous berms severely reduced interior marsh deposition, while discontinuous berms allowed for more direct inundation and sedimentation. Deposition was varied temporally, but was generally dependent on wind events. Hurricanes provide enhanced deposition to the marsh, which aids in vertical marsh accretion. While shoreline erosion provided some sediment for vertical accretion, a large amount of the eroded material is transported elsewhere. Accumulation rates suggested that these marshes have been keeping pace with sea-level during the last century.