Sea-level changes and paleoenvironmental responses in a coastal Florida salt marsh over the last three centuries

Abstract

Florida’s coastal salt marshes are vulnerable to both direct and indirect human impacts, including climate change and consequent sea-level rise. For a salt marsh to survive in the face of ongoing sea-level rise, organic and/or mineral sediment must accumulate at a rate equal to or faster than that of sea-level increase. We explored the effects of Late Holocene sea-level variations in the Suwannee River Estuary within the Big Bend region of Florida (USA). We conducted a paleoenvironmental study of a sediment core collected from a salt marsh near Cedar Key, on Florida’s Gulf of Mexico coast. The core spans the last ~ 320 years of sediment accumulation. Carbon isotope (δ13C) data and diatom assemblages indicate the salt marsh was relatively stable during that time frame and was dominated by C3 vegetation, likely Juncus roemerianus, but experienced moderate variations in salinity that likely reflect changes in sea-level, with an increase in salinity and marine incursions between ~ 1850 and 1930 CE. Whereas small vertical changes in sea-level have the potential to inundate large areas of the low-gradient salt marsh, as observed during the interval ~ 1850–1930 CE, the salt-marsh vegetation recovered quickly after 1930 CE, indicating that the rate of aggradation and vegetation growth kept pace with the rate of sea-level rise. Despite the apparent resiliency of Big Bend salt marshes and likelihood that they will persist through accretion and migration, we expect to see major changes in salt-marsh ecology if rates of sea-level rise continue to accelerate.