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Shifts in the Position of the Marsh/Mangrove Ecotone in the Western Florida Everglades

By Ann M. Foster1 and Thomas J. Smith III2

1U.S. Geological Survey, Center for Aquatic Studies, Gainesville, FL., USA
2U.S. Geological Survey, Center for Water and Restoration Studies, St. Petersburg, FL., USA

map showing western coast of Everglades National Park
Figure 1. Western coast of Everglades National Park. The area in the vicinity of the Lopez River is enclosed in a box in the upper left corner. [larger image]
The Everglades of southern and central Florida are a unique system that has been recognized as a valuable global resource. Up until the 1940's it had remained relatively undisturbed, with only minor incursions along the coastal fringe. This results in a situation in which to study the impacts of both global climate change and land use change on coastal ecosystems. In 1900, a broad freshwater system stretched from Lake Okeechobee southward for more than 160 km before draining into the estuaries along the southern tip of the Florida mainland. Today, over 600,000 ha of marsh have been converted to the Everglades Agricultural Area for production of sugarcane, sod and winter vegetables.

It has been hypothesized that shifts in the position of the mangrove/marsh ecotone are pulsed events, possibly initiated by large-scale disturbance and (or) influenced by sea level rise. As the flow of freshwater to the estuaries decreases, this results in an emulation in the rise in sea level. This reduction in freshwater flow, in conjunction with events such as hurricanes, fire, sea-level rise, and decreased precipitation may be influential in the migration of the mangrove forest into the freshwater marsh.

Select areas along the western coast of Everglades National Park (fig. 1) are examined using a time series of aerial photographs from the park archives (Briere et al, this volume; Coffin et al, this volume).

In some of the areas we examined, the decreases in the freshwater marsh occur closest to the coastline. In these areas the marsh has persisted further inland and has even shown signs of returning along the edges of some rivers and bays (fig. 2). Historical aerial photos have shown in some areas that the migration of the mangrove forest into the freshwater marsh is evident. In other regions no change is apparent.

images showing the location of the marsh in the vicinity of the Lopez River in 1927, 1940, and 1990
Figure 2. Location of the marsh in the vicinity of the Lopez River in 1927, 1940, and 1990. The shaded areas indicate the extent of the marsh for a specific year. [larger image]

Determining which factor or combination of factors contributes to this migration remains to be answered. However, it would appear given the diversity of patterns we see along the marsh/mangrove ecotone, it is a complex process.

Contact: Ann M. Foster, U.S. Geological Survey, 412 NE 16th Ave. Rm 250, Gainesville, FL 32601, 352-372-2571 x25, ann_foster@usgs.gov


(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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