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loss of wetlands and wetland functions
As stated throughout this report, drainage and development have had severe environmental effects on the natural system of south Florida. The landscape has been greatly altered, and its natural functions eliminated or changed over large areas. Water quality has deteriorated. The native plant and animal communities have been reduced and stressed by the altered hydrologic system and by competing exotic species. Changes in the natural system also are adversely affecting the growing human population of the region.
Loss of Wetlands and Wetland Functions
Drainage and development have eliminated or severely stressed wetlands in south Florida. About half the original Everglades has been eliminated (Davis and others, 1994). All the custard apple and willow swamps south of Lake Okeechobee (148,260 acres), and most of the peripheral wet prairie (289,110 acres) and the cypress forest (30,000 acres) in the eastern Everglades have disappeared. About 50 percent, or 897, 000 acres, of the sawgrass-slough communities and 24 percent, or 146,000 acres, of the southern marl marshes have been eliminated. Many of the remaining wetlands have been adversely affected by a reduced hydroperiod that has been caused by accelerated runoff in drainage canals. The increased frequency and spatial extent of wetland drying has reduced aquatic production at all levels of the food chain. Compared with the predrainage system, surface-water refugia that support populations of aquatic fauna and their predators during droughts are smaller and fewer and are relocated and subdivided in the currently managed system. In addition, these hydrologic changes have disrupted wading bird nesting, which depends on concentrated food supplies that occur under normal dry-season conditions (Kushlan, 1991).
Loss of wetlands in south Florida has significantly reduced landscape heterogeneity, habitat options, and long-term population survival for animals with large spatial requirements. Wading birds, snail kites, and panthers, for instance, have become increasingly stressed by the fragmentation and loss of habitat (Robertson and Frederick, 1994). Wildlife populations generally have declined. At present, 18 species have been designated as threatened or endangered by the U.S. Fish and Wildlife Service and 12 more are under review to determine their status (South Florida Water Management District, 1992). The number of wading birds has decreased from about 2.5 million in 1870 to about 70,000 in 1973 (Crowder, 1974). The large decreases in wading birds is a direct result of hydrologic alterations (Kushlan and others, 1975).
Drainage and development in south Florida have increased the opportunities for exotic species to become established. Exotic species often compete with and replace native species. Perhaps the most dramatic invasion into the region is the rapid spread of melaleuca tree into the Everglades (Kushlan, 1991). Melaleuca was introduced to Florida in the early 1900's and now grows as dense strands that have replaced native vegetation in parts of the eastern Everglades.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 15 January, 2013 @ 12:43 PM(KP)