CASE STUDY: THE EVERGLADES AND BIG CYPRESS SWAMP

6.5 CASE STUDY: THE EVERGLADES AND BIG CYPRESS SWAMP

Southern Florida, from Lake Okeechobee southward to Florida Bay, contains several unique natural wetlands. Within a 34,000-km 2 area are three major types of wetlands: the Everglades, the Big Cypress Swamp, and the coastal mangroves of Florida Bay. The rela- tive locations of these wetland systems are shown in Figure 6.9.

Florida

National Big Cypress

Preserve

20 miles

Fort Myers

Lake Okeechobee

visitor center Gulf Coast Shark Valley visitor center

Miami

Fort Myers

Gulf of er Slough Mexico

k Riv Shar

Big Cypress

Florida City

Swamp

Gulf of Mexico

Florida Bay

Mangroves of Florida Bay

(a) (b) FIGURE 6.9 Wetland systems in south Florida: (a) map of south Florida; (b) satellite view. (From

NASA, 2005a.)

WETLANDS

Water flowing through the Everglades from Lake Okeechobee to Florida Bay is typi- cally only a few centimeters deep and about 80 km wide. For this reason, the Everglades has been a ffectionately called the “river of grass” (Douglas, 1947). The Everglades is dom- inated by sawgrass (Cladium jamaicense), which is actually a sedge, not a grass. In addi- tion to sheet flow, the Everglades contains deeper water sloughs and tree islands, or hammocks , that support a vast diversity of plants, including hardwood trees, palms, orchids, and other air plants. Surface water in the Everglades flows in a generally southerly or southwesterly direction through the grasses and other macrophytes at relatively low velocities that generally range from 0.5 to 2 cm/s (Ricassi and Scha ffranek, 2003). Under most conditions, flow conditions are in the laminar regime (Lee et al., 2004). Tracer exper- iments in the Everglades have indicated longitudinal dispersion coe fficients on the order of 5

⫻ 10 2 ⫺5 m /s in regions where the average velocity is on the order of 0.3 cm/s (Harvey et al., 2005).

About half of the original Everglades has been lost to agriculture and urban develop- ment, and the health of the Everglades has been a ffected significantly by changes in the quantity, quality, timing, and distribution of water entering the Everglades. For example, natural phosphorus levels in the Everglades are on the order of 10 µg/L, and where the phosphorus levels rise from 10 µg/L to 50 µg/L an invasion of cattails and other foreign species signi ficantly changes the local wetland ecology and affects the habitat for many endangered species. To address these and other impacts, the Everglades is currently the site of the largest wetland-restoration e ffort in the United States. The comprehensive restora- tion blueprint includes plans for improving the water quality as it enters the Everglades from agricultural areas to the north and for modifying the hydrology to conserve and restore habitat for declining populations of wading birds such as the wood stork and the white ibis.

The Big Cypress Swamp is dominated by cypress trees interspersed with pine flatwoods and wet prairie. The Big Cypress Swamp receives about 125 cm of rainfall per year but does not receive major inputs of overland flow as the Everglades does. The third major wetland type, mangroves, forms impenetrable thickets where the sawgrass and cypress swamps meet the saline waters of the Florida coastline.