SOFIA - Poster - Changes in the Mangrove/Marsh Ecotone of the Florida Everglades

Changes in the Mangrove/Marsh Ecotones of the Florida Everglades

Ann M. Foster¹ and Thomas J. Smith III²

¹USGS Florida Caribbean Science Center 412 NE 16th Ave., Gainesville, FL 32653
²USGS Center for Coastal & Regional Marine Studies 600 4th St. South, St. Petersburg, FL 33701

ABSTRACT:

The influence of climate change on the extent and structure of the mangrove / marsh ecotone of the Florida Everglades has been a subject of discussion over the past several years. 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. Select areas along the western coast of Everglades National Park are examined using a time series of aerial photographs from the park archives. The changes in the position of the ecotone are determined and potential causal factors identified.

INTRODUCTION:

Figure 1: The western coast of Everglades National Park. Area of interest is noted by the yellow arrow in the northwest corner of the park. [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. Beginning in the 1940's efforts began to develop the Everglades from a 'wasteland' to more productive uses. As a result of this beginning and the development projects that followed, the Everglades of today is a tremendously altered system from what it once was. Efforts are presently underway to restore the functional aspects of the Everglades and to preserve what remains. The area we are currently examining is located in the northwestern area of Everglades National Park. Due to its remote location, this area has seen minimal direct human impact over the last 70 years.

METHODS:

Images from the Everglades National Park photo archives were used to examine an area for change over the last 70 years. These sites are located the vicinity of the Lopez River (yellow arrow; Fig 1). Images of these areas were scanned and then georeferenced using ArcGIS 8.1 software. Marsh areas were delineated from the mangroves for each of the sites and years examined. Comparisons were made regarding the changes in the proportions of marsh and mangrove found in these areas.

Table 1: Sources of imagery for comparisons

Coverage Sources: (counterclockwise, from left) 1927 - T-sheets derived from 1927 aerial photography; 1940 - SCS flight, black and white, 1:40,000; 1990 - NASA flight, color infrared, 1:32,500. Click on images for larger versions.

DISCUSSION:

The Florida Everglades provides 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 has been converted to the Everglades Agricultural Area for production of sugarcane, sod and winter vegetables. Additionally the flow of freshwater to the estuaries has been decreased, reducing the freshwater head in the system, thereby emulating a 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. In the area we examined, the greatest decrease in freshwater marsh occur closest to the coastline. The marsh has persisted further inland and has even shown signs of returning along the edges of some rivers and bays. 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. 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.

Figure 2: Time series of change in the area occupied by marsh in the vicinity of the Lopez River, from 1927 to 1990.

(From left to right:) 1927, 1940, 1990, composite of all years. Click on image for larger version.

Table 2: Percent change in marsh from 1927 to 1999

Year

From To % Change % left

1927 1940 -49.40 loss from 1927 50.60

1940 1990 +27.45 gain from 1940 level 78.05

1927 1998 -21.95 overall loss from 1927 78.05

ACKNOWLEDGEMENTS:

Financial support for this research was received from both the USGS' Place-Based Studies and Global Climate Change Programs. Additional support came from the Dept. of Interior's "Critical Ecosystems Studies Initiative" administered by Everglades National Park. Base funds were provided by the USGS Florida Caribbean Science Center. This poster was presented at the 16th Biennial Conference of the Estuarine Research Federation, in St. Petersburg Beach, Florida, November 2001.

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