HOLOCENE INSIGHTS ON THE RESILIENCE OF SOUTH FLORIDA’S MANGROVE COAST, USA

South Florida is undergoing a large-scale ecological restoration effort and is challenged by conflicting demands of water availability and the need to control distribution of water during storms and droughts. Water management is further complicated by sea level rise and storms. Everglades National Park (ENP) in south Florida contains part of the most continuous mangrove ecosystem in the United States. These mangroves serve as natural buffers from coastal storms. Recent paleoecologic and geologic investigations are providing information on the role of sea level, storms, freshwater flow, and environmental alteration in shaping the Holocene coastal environment.

Sediment cores collected from four islands in Florida Bay (ENP) indicate that between 3.4 to 2.8 ka (kiloannum) the mangrove coast of south Florida was inundated during a period of low relative rates of sea level rise (RSLR; 0.67 mm yr^-1) in less than 200 years. Comparison to other records from the Caribbean suggest this inundation may have been caused by increased storm frequency and higher incidence of droughts. Other researchers have studied the impact of 20^th century storms on the mangrove forests of southwest ENP and their work has shown that storms cause a complex set of processes 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?

Additional research on cores from ENP wetlands and Florida Bay highlights the impact of reduced freshwater flow on the coastal zone. Paleoecologic data using different proxies from two regions of ENP (mollusks as proxy for salinity in Florida Bay; pollen as proxy for water level in wetlands) were coupled with statistical models to hindcast flow at the beginning of the 20^th century. The results indicate flow was reduced by >50% in the main flow path of ENP and by >65% into northern Florida Bay during the 20^th century as a result of water management. Although mangroves are considered resilient ecosystems, our analyses suggest the combined impacts of RSLR, storms, and water management will have a negative effect on the south Florida mangrove ecosystem, and without intervention, the system may not be sustainable.