Abstract
Sea level rise and the associated inland shift of the marsh-mangrove ecotone in south Florida have raised many scientific and management concerns in recent years. Holocene paleoecological records can provide an important baseline to shed light on the long-term dynamics of vegetation changes across this ecotone in the past, which is needed to predict the future. In this study, we present palynological, X-ray fluorescence, and loss-on ignition data from four sedimentary cores recovered from a 20-km marine-to-freshwater transect along the Shark River Estuary, southwest Everglades, to document the patterns and processes of coastal vegetation changes in response to sea level rise since the mid-Holocene. Our record indicates that freshwater marsh progressively replaced marl prairies at the Shark River Estuary between 5700 and 4400 cal yr BP. As marine transgression continued, marine influence reached the threshold necessary for mangroves to establish at the current mouth of the Shark River Slough at 3800 cal yr BP. During the next 3000 years, although sea level rise in the Western North Atlantic slowed down to 0.4 mm/yr, a spatial and temporal gradient was evident as the marsh-mangrove ecotone shifted inland by 20 km from 3800 to 800 cal yr BP, accompanied by a gradual landward replacement of freshwater marsh by mangrove forest. If sea level continues to rise at 2.33 mm/yr in the 21st century in south Florida, it is possible that marine influence will reach the threshold for mangroves to establish in the central Everglades, and we could expect a much more aggressive mangrove encroachment toward the northern and interior parts of south Florida in the next few centuries.
Highlights
Contemporary global climate changes are expected to cause many unprecedented ecological impacts on coastal ecosystems around the globe [1]
In SRM, the longest core retrieved from the mouth of the River, the peat started to accumulate from ~5700 cal yr BP but it did not start until ~4800 cal yr BP at site SRS-6
Our record indicates that marl prairies were the dominant vegetation type before they were progressively replaced by freshwater marshes after *5700 cal yr BP
Summary
Contemporary global climate changes are expected to cause many unprecedented ecological impacts on coastal ecosystems around the globe [1]. In North America, one of the most extensive brackish marshes and the largest mangrove swamp is located in the coastal areas of the Everglades in south Florida [2]. More than 200,000 ha of mangrove forests, sawgrass marshes, PLOS ONE | DOI:10.1371/journal.pone.0173670. More than 200,000 ha of mangrove forests, sawgrass marshes, PLOS ONE | DOI:10.1371/journal.pone.0173670 March 10, 2017
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