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A Region Under Stress-- Home
A Region Under Stress-- Introduction

Environmental Setting-- The Natural System
Watersheds and Coastal Waters
Kissimmee-Okeechobee-Everglades Watershed
Big Cypress Watershed
Charlotte Harbor Watershed
Estuaries and Bays
Florida Reef Tract
Coral Reefs and Sea Level

Environmental Setting-- The Altered System
Drainage and Development
Public Lands
Water Use
Water Budget

Water and Environmental Stress
Loss of Wetlands and Wetland Functions
Soil Subsidence
Degradation of Water Quality
Mercury Contamination
Effects on Estuaries, Bays, and Coral Reefs

Summary and Research Needs

Related Links

Download Circular 1134 PDF

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U.S. Department of the Interior
U.S. Geological Survey
Circular 1134

The South Florida Environment - A Region Under Stress

Environmental Setting--
The Natural System

Hydrologic features in south Florida
Figure 17. Hydrologic features and the natural direction of surface-water and coastal-water flows under predevelopment conditions in south Florida. Click on image to open larger picture (25.9k).

Watersheds and Coastal Waters

Kissimmee- Okeechobee- Everglades Watershed

The Kissimmee- Okeechobee- Everglades watershed, an area of about 9,000 mi2, once extended as a single hydrologic unit from present-day Orlando to Florida Bay, about 250 mi to the south (fig. 17). In the northern half of the watershed, the Kissimmee River and other tributaries drained slowly through large areas of wetlands into Lake Okeechobee, a shallow water body of about 730 mi2. The lake periodically spilled water south into the Everglades (Davis, 1943; Parker, 1974), a vast wetland of about 4,500 mi2. Under high water-level conditions, water in the Everglades moved slowly to the south by sheetflow, thus forming the area known as the River of Grass. Water discharged from the Everglades into Florida Bay and the Gulf of Mexico, and under high-flow conditions, also into the Atlantic Ocean through small rivers or transverse glades in the Atlantic Coastal Ridge or as seepage and spring flow into Biscayne Bay.
Photo of Everglades wetlands in the Shark River Slough
Figure 18. Aerial photograph of Everglades wetlands in the Shark River Slough (above), and a generalized section of the slough (below).
(McPherson, 1973a.) Click on images to open larger picture (above - 52.0k, below - 8.9k).
Generalized section of the slough

The Everglades was a complex mosaic of wetland plant communities and landscapes with a central core of peatland that extended from Lake Okeechobee to mangrove forest that border Florida Bay (Davis and others, 1994). The peatland was covered by a swamp forest of custard apple (Annona glabra) and willow (Salix caroliniana) along the southern shore of Lake Okeechobee and by a vast plain of monotypic sawgrass (Cladium jamaicense) to the south and east of the swamp forest. Farther southeast, the sawgrass was broken by sloughs and small islands of brush. Tree islands and sloughs became increasingly numerous to the south where the vegetation formed a mosaic of sawgrass strands interwoven with lily-pad-covered sloughs, wet prairies, and tree islands in Shark River Slough (fig. 18). A similar mosaic of sawgrass, slough, wet prairie, and tree islands was on peatland in the northeastern Everglades in the Hillsborough Lake Slough. The peatland was bounded by peripheral wet prairies, southern marl marsh, and, cypress (Taxodium distichum) forest. The peripheral wet prairies were sand-bottomed wetlands of mixed grasses, sedges, and other macrophytes that intermingled with higher altitude pine flatwoods and extended as transverse glades through parts of the Atlantic Coastal Ridge. To the south, the peatland and prairie vegetation blended into marl and rock- bottomed marshes of herbaceous plants, short sawgrass, and bay head tree islands and tropical hammocks.
Photo of fire

Water levels and flows in the Everglades fluctuated seasonally in response to rainfall and runoff. Much of the land was inundated during the year, and during heavy rains, all but the highest tree islands were flooded. During flood periods, water moved with enough force to cause tree islands to develop an alignment pattern that was parallel to the lines of surface-water flow (Parker, 1974). During the dry season, water levels generally were close to the land surface, but extreme droughts during some years lowered water levels substantially below the land surface, and severe fires swept over the land, burning vegetation and peat (Craighead, 1971).

Animal populations in the Everglades have adapted to and are dependent upon the seasonal hydrologic fluctuations (McPherson and others, 1976). Fishes and macroinvertebrates, which form the central link in the food chain, require flooded conditions for their growth and survival. As water levels decline during the dry season, fishes and other aquatic animals concentrate in deeper parts of the marsh and sloughs where they become prey for several groups of predators, especially wading birds (fig. 19) whose nesting season is especially timed to coincide with the high availability of food in the remaining pond water (Kushlan, 1991). The animal populations in the adjacent tidal waters also are dependent upon the seasonal flows of freshwater that create the salinity conditions that support productive estuarine and marine fish populations (Lindall, 1973).

Figure 19. Wading birds in south Florida (below).
Photos of wading birds
"When I first came to Florida, about 50 yrs ago, I found the country an almost untouched wilderness filled with beautiful wild life. Wild life fairly swarmed, especially the birds. Vast numbers of roseate spoonbills, snowy herons, American egrets, and the great white heron....winged their way far out over the pineland as they visited swamps in search of food. And food was abundant. In the Gulf of Mexico....there were schools of mullet, packed like sardines in a box and reaching away up and down the coast as far as the eye could carry."

Charles Torrey Simpson, 1920

Photo of storks

The Everglades has been dynamic during the approximately 5,500 years of its existence (Davis and others, 1994). Numerous shifts have occurred between marl- and peat-forming marshes and between sawgrass marshes and water-lily sloughs (Gleason and Stone, 1994). Fire, climate, sea level, topography, hydroperiods, alligator activity, and recently, man, have had long-term effects on the vegetation (Craighead, 1971; Parker, 1974; Gunderson and Snyder, 1994).

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