156A—Florida Everglades and Associated Areas

This MLRA (shown in blue in the figure above) is entirely in Florida. It makes up about 6,915 square miles (17,920 square kilometers). Miami and other cities are on the Atlantic coast, the eastern edge of the area. Interstate 75 bisects the northern half of the largest part of this MLRA, and Interstate 95 parallels the Atlantic coast. A small part of this MLRA is north of Florida’s Turnpike and west of Interstate 95, in Brevard County. Everglades National Park, Big Cypress National Preserve, the Big Cypress Seminole Indian Reservation, and the southeast half of Lake Okeechobee occur in this area.

Physiography

This area is in the Floridian Section of the Coastal Plain Province of the Atlantic Plain. It is on a level, low coastal plain that has large areas of swamps and marshes. Poorly defined and broad streams, canals, and ditches drain the area to the ocean. Most of the area is flat, but in the interior, hummocks rise 3 to 6 feet (1 to 2 meters) above the general level of the landscape and low beach ridges and dunes, mainly in the eastern part of the area, rise 10 to 15 feet (3 to 5 meters) above the adjoining swamps and marshes. Elevation ranges from sea level to less than 80 feet (25 meters).

The only major Hydrologic Unit Area (identified by a four-digit number) that makes up this MLRA is Southern Florida (0309). The area has no major rivers, but a number of canals cross the northern half of the area.

Geology

This area is a young marine plain underlain by Tertiary-age rocks, including very fine grained shale, mudstone, limestone, and dolomite beds. Limestone rock is the dominant subsurface material in this MLRA. A sandy marine deposit of Pleistocene age occurs at the surface in the northern part of the area and in the part in Brevard County.

Climate

The average annual precipitation in this area is 40 to 62 inches (1,015 to 1,575 millimeters). About 60 percent of the precipitation occurs from June through September. The center of the area is the driest part. Most of the rainfall occurs as moderate-intensity, tropical storms that produce large amounts of rain from late spring through early autumn. Late autumn and winter are relatively dry. The average annual temperature is 73 to 78 degrees F (23 to 25 degrees C). The freeze-free period averages 355 days and ranges from 345 to 365 days.

Water

Following are the estimated withdrawals of freshwater by use in this MLRA:

Public supply—surface water, 2.7%; ground water, 22.9%
Livestock—surface water, 0.1%; ground water, 0.3%
Irrigation—surface water, 38.9%; ground water, 10.8%
Other—surface water, 11.4%; ground water, 12.8%

The total withdrawals average 1,850 million gallons per day (7,000 million liters per day). About 47 percent is from ground water sources, and 53 percent is from surface water sources. Rainfall and surface and ground water sources provide an abundance of water. Unless the water level in naturally wet areas is controlled, shallow water covers the surface during much of the rainy season. Canals and ditches control the ground water level for crops and pasture. Excess water is pumped out during the rainy season, and irrigation water is applied during the growing season. The surface water is generally of good quality.

Domestic water is obtained mainly from wells in a shallow, nonartesian aquifer of sand, shells, and limestone or from the Biscayne aquifer in the eastern half of this MLRA. The shallow aquifer provides limited quantities of good-quality water. The Biscayne aquifer is a “sole source” drinking water supply for much of Dade and Broward Counties and parts of Monroe and Palm Beach Counties. The aquifer consists of very permeable limestone that has good-quality water. Some high-capacity irrigation wells tap the Biscayne aquifer. All of the ground water is a calcium bicarbonate type and is hard or very hard. Some saline water problems occur in the Biscayne aquifer near the coast. These aquifers are susceptible to contamination from surface activities.

The northern part of this MLRA has abundant surface and ground water of good quality. The Floridan aquifer is the primary source of ground water in Brevard County. This aquifer consists of deep limestone and dolomite beds. The water in this aquifer is a calcium bicarbonate type and is hard.

Soils

The dominant soil orders in this MLRA are Entisols and Histosols. The soils in the area dominantly have a hyperthermic soil temperature regime, an aquic or udic soil moisture regime, and carbonatic mineralogy. They are very shallow to very deep, generally moderately well drained to very poorly drained, and loamy or sandy. Udorthents (Krome series) formed in residuum on flats. Fluvaquents (Biscayne and Perrine series) and Psammaquents (Hallandale series) formed in marine sediments on flats and in depressions and sloughs. Haplosaprists (Pahokee and Terra Ceia series) formed in organic deposits in marshes.

Biological Resources

This area supports freshwater marsh and swamp vegetation. Sawgrass, pickleweed, willow, buttonbush, and maidencane are the dominant marsh species. Bald cypress is the dominant swamp species. Mangrove trees grow in saltwater swamps along the eastern, southern, and southwestern coasts.

Some of the major wildlife species in this area are white-tailed deer, feral hog, snipe, bobcat, raccoon, skunk, otter, squirrel, bobwhite quail, and woodpecker. Alligators, turtles, and wading birds, including wood storks, white ibis, glossy ibis, egrets, and herons, are abundant in the swamps and marshes. The species of fish in the area include black drum, red drum, sea trout, sheepshead, snook, tarpon, and largemouth bass.

Land Use

Following are the various kinds of land use in this MLRA:

Cropland—private, 11%
Grassland—private, 8%; Federal, 24%
Forest—private, 3%; Federal, 7%
Urban development—private, 12%
Water—private, 5%; Federal, 4%
Other—private, 26%

About one-third of this area is in Indian reservations, national parks, game refuges, or other large holdings. Cypress forests are extensive in the area, but mangrove forests are widespread along the eastern and southern coasts. A large part of the area is open marsh. Much of the area is used for hunting, fishing, and other recreational activities. The cropland in the area is used mainly for winter vegetables, but citrus fruits, avocado, and papaya are grown on the better drained soils. Sugarcane is an important crop on the organic soils south of Lake Okeechobee. The acreage of improved pasture is increasing. Beef cattle are the principal kind of livestock, but dairying is an important enterprise locally. Urbanization is extensive along the eastern coast.

The major soil resource concerns are wind erosion, maintenance of the content of organic matter and productivity of the soils, and management of soil moisture and soil subsidence. Conservation practices on cropland generally include conservation crop rotations, cover crops, nutrient management, pest management, water-control structures, surface drainage systems (field ditches, mains, and laterals), pumping plants, and irrigation water management (including microirrigation systems and surface and subsurface irrigation systems). Conservation practices on pasture and rangeland generally include prescribed grazing, brush management, pest management, prescribed burning, and watering facilities. Conservation practices on forestland generally include forest stand improvement, firebreaks, pest management, prescribed burning, and management of upland and wetland wildlife habitat.

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