Estuaries and Coasts

, Volume 40, Issue 3, pp 626–639 | Cite as

The Declining Role of Organic Matter in New England Salt Marshes

  • J. C. Carey
  • S. B. Moran
  • R. P. Kelly
  • A. S. Kolker
  • R. W. Fulweiler


The Northeast USA is experiencing severe impacts of a changing climate, including increased winter temperatures and accelerated relative sea level rise (RSLR). The sediment-poor, organic-rich nature of many Southern New England salt marshes makes them particularly vulnerable to these changes. In order to assess how marsh accretion has changed over time, we returned to Narragansett Bay, RI where salt marsh vertical accretion rates were documented almost 30 years ago. Using radionuclide tracers (210Pb and 137Cs), we observe no significant change in overall accretion rates (0.27–0.69 cm year−1) compared to historical averages (0.24–0.60 cm year−1), but we document a shift in how these marshes maintain elevation. Organic matter now plays a smaller role in contributing to vertical accretion across all study sites, declining by 22 % on average. We attribute this reduction to potentially higher decomposition rates fueled by higher water temperature. Inorganic matter also contributes less to accretion (declining by 44 % on average at marshes located more internal to the estuary), likely due to diminishing sediment supply in this region. With organic and inorganic solids accounting for less of the total accretion, several of the marshes are experiencing symptoms of swelling, with water and porespace contributing more towards accretion compared to historical values. Accretion rates (0.27–0.45 cm year−1) at these organic-rich (>40 % sediment organic matter) marshes are predominantly lower than the current (30 years) rate of RSLR (0.41 ± 0.07 cm year−1). These results, combined with the increased rate of RSLR and the hardened shorelines inhibiting landward migration, call into question the long-term survivability of these marshes.


Salt marshes Accretion rates Sea level rise Organic matter Decomposition Climate change New England 



We thank the editors of Estuaries and Coasts for approving this focus issue for publication. We are grateful for field assistance by Courtney Zambory, Marc Zemel, Jules Opton-Himmel, and Kenneth Raposa. We thank Sarah Sargent for laboratory assistance. This research was conducted under an award from the Estuarine Reserves Division, Office of Ocean and Coastal Resource Management, National Ocean Service, National Oceanographic and Atmospheric Association Graduate Research Fellowship to J.C.C. We also thank the Department of Earth and Environment at Boston University for partial funding support of J.C.C. Finally, we thank Scott W. Nixon whose foresight and intellectual generosity started us on this research path.


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Copyright information

© Coastal and Estuarine Research Federation 2015

Authors and Affiliations

  • J. C. Carey
    • 1
  • S. B. Moran
    • 2
  • R. P. Kelly
    • 2
  • A. S. Kolker
    • 3
    • 5
  • R. W. Fulweiler
    • 1
    • 4
  1. 1.Department of Earth and the EnvironmentBoston UniversityBostonUSA
  2. 2.Graduate School of OceanographyUniversity of Rhode IslandNarragansettUSA
  3. 3.Louisiana Universities Marine ConsortiumChauvinUSA
  4. 4.Department of BiologyBoston UniversityBostonUSA
  5. 5.Department of Earth and Environmental SciencesTulane UniversityNew OrleansUSA

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