The Greater Everglades Ecosystem

The Natural System

The southern Florida peninsula encompasses a mosaic of subtropical habitats connected and sustained by water. Before European settlement, this region of about 18,000 square miles was dominated by wetlands, which originated in the Kissimmee River drainage basin and flowed southward, through Lake Okeechobee and the Everglades, into highly productive estuaries and nearshore coastal waters, including Biscayne and Florida Bays.

South Florida receives between 40 and 65 inches of rainfall annually, most occurring during the wet season (June through October). The area is characterized by very low topographic relief. The nearly flat topography, proximity of thousands of miles of coastline, and high annual rainfall make much of the area susceptible to flooding.

Historically, water levels and flows in the wetland areas of the Everglades fluctuated seasonally in response to rainfall and runoff. During heavy rains, all but the tree islands were flooded. During the dry season, water levels generally were close to the land surface, but during droughts they often fell substantially below it. Major fires were a natural occurrence during droughts, and they swept over the land, burning vegetation and peat.

The freshwater marshes were characterized by extremely low levels of nutrients, creating the conditions conducive to extensive wetland sawgrass prairies—known as "the river of grass." These wetlands were punctuated with relatively low "uplands," which provided forested refuges for migratory species during times of flooding, as well as habitat for a diversity of year-round communities. In and around the estuaries, freshwater mingled with salt to create habitats supporting mangroves and nurseries for wading birds and fish. Beyond, nearshore islands and coral reefs provided shelter for an array of terrestrial and marine life.

The habitat in South Florida originally supported far-ranging animals, like the Florida panther, and super-colonies of wading birds, such as herons, egrets, roseate spoonbills, ibis, and wood storks.

Human Alterations to the Natural System

Some early land developers saw the potential for "improving" the Everglades wetlands through development and agriculture. However, efforts to reclaim the area for development and human habitation evolved slowly, as the marsh and sloughs were largely impenetrable and uninhabitable.

The conflict of human versus natural elements in South Florida began in earnest in the early 1900s, when the control of water and the drainage of wetlands were first considered essential for commerce and human safety. Loss of life due to hurricane-related flooding in the 1920s accelerated flood protection projects, culminating in the congressional authorization in 1948 of the Central and Southern Florida (C&SF) Flood Control Project. Over the course of the next 50 years, population growth, urbanization, and agricultural practices significantly altered the natural system.

Today South Florida encompasses significant remnants of the Everglades, including four national parks, thirteen national wildlife refuges, and numerous state parks and conservation areas, along with important urban centers, including Miami, and agricultural areas, including the Everglades Agricultural Area (EAA). The C&SF Project, which provides for the diverse water-related needs of the region, consists of more than 1,400 miles of primary canals and more than a hundred water-control structures.

Providing for the diverse water-related needs of this area over many decades has resulted in unintended consequences for the Greater Everglades. Less than half the original wetland acreage of South Florida remains. Surface water flow within the Greater Everglades is fragmented and disrupted, changing the quantity and natural timing of water deliveries and negatively affecting the water quality and natural areas . Water flows from the Kissimmee River into Lake Okeechobee, and outflows from the lake, are through manmade canals. In the EAA, water is drained during wet periods and augmented during dry periods. Many wetlands that historically functioned as natural filters and water-retention areas are either severely impacted or entirely lost due to drainage changes or development. Compared to historic flows, canal discharges into Biscayne and Florida Bays are heavier during wet periods and lighter during dry periods, creating greater salinity fluctuations in the bays and affecting habitats along the gulf coast and within the reef tract from Key Biscayne to the Dry Tortugas. Additionally, the two bodies of water between Florida Bay and Biscayne Bay, Card and Barnes Sounds, have been essentially cut off from natural water deliveries.

The drainage system imposed by canals and other drainage features has impacted groundwater storage capacity. Aquifers provide municipal water supplies in the region. By 1990 about 872 million gallons of water per day (94% of it ground water) was being consumed by the nearly 6 million people living in or visiting the South Florida area. Another 2.7 million gallons per day (divided nearly evenly between ground water and surface water) was being used for agriculture.

Water quality is degraded in some areas by high levels of nutrients (such as phosphorus and nitrogen), pesticides, and other contaminants in agricultural and urban runoff. Nutrients and sulfur in major rivers (such as the Kissimmee and Caloosahatchee) and in canals draining the EAA affect Lake Okeechobee, the Everglades wetlands, and estuaries. These changes in water quality affect wetland vegetation. Replacement of the normal diversity of Everglades plants with cattails creates unsuitable habitat for Everglades animals, including fish and wading birds. Scientists have observed that the wetland area dominated by cattail is expanding, and if unchecked, could soon affect major portions of the remaining Everglades.

The evidence that the changes in surface and groundwater flows and water quality have had negative effects on habitats and organisms includes a 90% reduction in wading bird populations, 69 species on the federal endangered or threatened list, widespread invasion by exotic species, declines in commercial and recreational fisheries in Biscayne and Florida Bays, a significant decrease in the number of Everglades tree islands, the invasion of coastal sawgrass prairies by mangroves and compositional and structural changes in habitats throughout the region.