Sediment Delivery and Vertical Accretion in Salt Marsh Wetlands of Jamaica Bay, Gateway National Recreation Area, New York, USA.

Over the last century, ~60% of the saltmarsh wetlands in Jamaica Bay (in the Gateway National Recreation Area of the Greater New York City region) have been converted to intertidal or subtidal unvegetated mudflats, and projections suggest that all of Jamaica Bay’s saltmarsh wetlands may disappear within the next two decades. After landfall of Super Storm Sandy in 2012, to better understand environmental controls on the maintenance of remaining Jamaica Bay wetlands, cores were collected from twelve saltmarsh locations in the bay to study the chronology of wetland vertical accretion and mineral sediment accumulation. In association with the USGS National Wetlands Research Center, cores were analyzed for Cs-137/Pb-210 geochronology, percent organics, and total water content. Preliminary results show that Cs-137 sediment accumulation rates for the wetlands are 0.5-0.8 cm/y. Analysis of sediment core mineral content indicates the uneven presence of a mineral-rich surface layer that is likely the result of sediment delivery from Super Storm Sandy. Results also document the presence of numerous subsurface layers of mineral-rich sediment interbedded between zones of organic-rich sediment. Based on Cs-137 chronologies, estimated deposition time windows for many, but not all of these mineral-rich layers correspond to the known landfalls of major hurricanes near Jamaica Bay over the last seven decades. Collectively, these preliminary results suggest that sediments are delivered unevenly by landfalling hurricanes to coastal wetlands, and other phenomena that flood coastal wetlands with suspended sediments, such as winter storms, are important sediment sources as well.