Estimates of Accretion Rates of Salt Marsh Islands in Southern New Jersey

Abstract

Salt marshes are an essential ecosystem for connecting nutrients between coastal and land environments, protecting shorelines from erosion, and providing habitat for various species. Anthropogenic climate change causing sea level rise poses threats to salt marshes and the coastal communities nearby. In southern New Jersey, the relative rate of sea level rise (4.21 ± 0.15 mm/yr from 1911-2022; SLR; NOAA, 2023) is greater than the global average (3.4 ± 0.04 mm/yr). In this study, I measure chronologies, bulk density and organic content (loss on ignition, LOI) from cores collected in 2021-22 at four locations in the Seven Mile Island Innovation Lab (SMIIL) in Stone Harbor, New Jersey to determine multidecadal accretion rates. Chronologies are developed from a radionuclide dating analysis (using concentrations of 210Pb, 241Am, 137Cs and 7Be) following procedures similar to Boyd et al. (2017) and Landis et al. (2016). The accretion rates from 1911-2022 of the four cores analyzed are 4.3 ± 0.2 mm/year, 4.1 ± 0.1 mm/year, 5.2 ± 0.1 mm/yr, and 6.0 ± 0.2 mm/yr, respectively, which are similar to the local SLR rate and are within error of RSLR in Atlantic City. The mean LOI for the 4 four cores is 27.2 ± 19.0%, 21.3 ± 8.9%, 20.2 ± 7.5% and 14.2 ± 13.0%. The mean dry bulk density for the 4 cores is 437 ± 127 kg/m3, 380 ± 103 kg/m3, 415 ± 88 kg/m3, 657 ± 353 kg/m3. The higher accretion rates of the salt marshes in SMIIL compared to relative sea level rise and consistency with the Sadler Effect indicates that the salt marsh vertical accretion rate is keeping up with increases in sea level rise. Thus, the salt marshes are not in immediate risk for inundation from sea level rise and supports the adaptability and resiliency of the salt marsh ecosystem.