Tidal and Hurricane Impacts on Saltmarshes in the Northeastern Coastal and Barrier Network: Theory and Empirical Results
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Tidal and Hurricane Impacts on Saltmarshes in the Northeastern Coastal and Barrier Network: Theory and Empirical Results

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    Estuaries and Coasts, 43, 1-14
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    The responses of marsh elevation in four National Parks affected by Hurricane Sandy were examined using empirical data from surface elevation tables (SET) and modeling. The parks examined were Fire Island National Seashore and Gateway National Recreational Area in New York; Cape Cod National Seashore, Massachusetts; and Assateague Island National Seashore, Maryland. Observed vertical accretion rates were compared with calculations made with the Marsh Equilibrium Model (MEM). MEM predicts vertical accretion resulting from the accumulation of organic material in soil and the capture of suspended inorganic material at the marsh surface. MEM simulations of a decade or more of marsh elevation change at 52 SET stations were generally consistent with observations. Park-specific averages of observed vertical accretion ranged from 0.16 ± 0.33 (± 1 SD) to 0.51 ± 0.21 cm/year, while the range of calculated rates was 0.15 ± 0.03 to 0.22 ± 0.05 cm/year, depending on the park. Grand means of observed and calculated rates were 0.36 ± 0.34 and 0.19 ± 0.06 cm/year, respectively. We defined a novel metric termed normalized elevation capital (NEC) that incorporates information about tide range and elevation capital. All but 2.3% of biomass collections from all the parks fell within 0 < NEC < 1. Consistent with marsh equilibrium theory, long-term vertical accretion rate tended to be greatest, 0.4 ± 0.2 cm/year, in the range 0.4 < NEC < 0.6 where vertical accretion is dominated by organic production. Average episodic accretion during the storm from mineral deposition also was greatest and positive, 0.6 ± 0.9 cm in the range 0.4 < NEC < 0.6. Finally, one marsh in Gateway NRA, restored by an application of sediment to NEC = 0.55–0.68, had post-treatment vertical accretion rates of 0.36 ± 0.31 cm/year, not statistically different from SET stations elsewhere in Gateway, 0.57 ± 0.54 cm/year. The sediment amendment placed restored sites in the range of NEC where theory predicts that biogenic accretion should dominate vertical accretion. Model simulations suggest that current rates of vertical accretion in the parks are close to their theoretical limits, and in the absence of new sediment, extant marsh communities in these parks are unlikely to survive continued acceleration of sea-level rise in the absence of periodic sediment renourishment.
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