Offset Between Surface Elevation Table and Sediment Core Derived Accretion Rates: Case Study from Piermont Marsh, New York

Surface elevation tables (SETs) are a standard metric for measuring precise sediment accretion in wetlands. They are used to evaluate whether marshes are keeping pace with sea level rise and to determine whether management interventions are needed to prevent marsh inundation. The SET method combined with sediment core studies provides constraints on short-term (annual) and long-term (decadal) accretion rates. Sediment core records provide necessary constraints on slow occurring processes not adequately captured by SET methods such as subsurface decomposition and compaction. This long timescale view is relevant for land management in the context of sea level rise and carbon accumulation. New data are reported from Piermont Marsh, a brackish tidal wetland on the Hudson River. SET measurements reveal accretion rates from 3.1 to 6.5 mm/year from 2019 to 2024, while data from sediment cores collected 2 m from SETs provide rates of 2.4 mm/year and 3.9 mm/year since 1975. The contrast between methods is important for marsh managers interpreting accretion data and understanding the urgency presented by sea level rise for coastal marsh erosion. The relatively high accretion rates measured by SETs imply resilient marshes, but lower long-term rates indicate marshes are in need of assistance to survive. Future research on the North American Atlantic coast tidal wetlands should consider coupling SETs with lead (Pb) abundance measurements on sediment cores using X-Ray Fluorescence Spectroscopy; this is a relatively fast, nondestructive way, (in comparison to radionuclide measurements) to assess accretion rates on decadal timescales, which are needed to accurately estimate marsh resilience to inundation from sea level rise.