RESILIENCY OF SOUTH FLORIDA’S MANGROVE COAST: LINKING OBSERVATIONS AND SEDIMENT RECORDS

South Florida contains the most continuous mangrove ecosystem in the United States and these mangroves serve as natural buffers from coastal storms and flooding for both the urban and natural landscapes of south Florida. Based on sediment core records from four islands in Florida Bay (Everglades National Park (ENP)), the mangrove coast of south Florida was inundated between 3.4 to 2.8 ka (kiloannum) during a period of low relative rates of sea-level rise (RSLR; 0.67 mm yr^-1). This inundation occurred in less than 200 years at two sites with nearly complete sediment records during that interval. Comparison to other records from the Caribbean suggests this inundation may have been caused by high frequency and high amplitude shifts in the Inter-tropical Convergence Zone and El Niño Southern Oscillation. The impact of 20^th century storms on mangrove forests of southwest ENP has been investigated by other researchers, who identified complex feedback mechanisms that can lead to inland migration of the coast. If the coast can be inundated due to climate variability alone, this raises the question, what will happen over the next century with the current RSLR at 2.47-3.7 mm yr^-1 and the anticipated increases in storm frequency and intensity?

To gain additional insights into mangrove resiliency, we have established surface elevation tables (SETs) and mangrove monitoring plots on an island in Florida Bay (1 of 4 islands cored) that was heavily impacted by Hurricane Irma in 2017. Storm impacts included significant deposition on some parts of the island, erosion of the narrow eastern mangrove berm, and mangrove die-off. Observations since 2017 and preliminary mangrove plot data, indicate the island is being reshaped by the combined processes of RSLR, storms, and mangrove loss/recovery. Mangrove ecosystems have evolved in tropical regions and are resilient to the impacts of storms, but the critical question for resource management is whether sea-level rise is approaching the point at which the mangroves cannot recover fast enough before being inundated. If the rate and/or intensity of tropical storms increases, as the passage of two strong September hurricanes (Irma and Ian (2022)) within five years indicates, Floridians may be facing a future of increased storms and continued loss of the natural storm buffer provided by the mangroves.