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Wetlands are the predominant landscape feature of south Florida (fig. 14). The prevalence of wetlands is a result of abundant rainfall and a low, flat terrain. Rainfall becomes ponded in wetlands where it is evapotranspired, infiltrates shallow aquifers, or moves slowly by sheetflow toward tidal waters. Peat develops in wetlands that are flooded for extensive periods during the year, and calcitic muds develop in wetlands where hydroperiods (time land is flooded) are shorter and limestone is near the surface (fig. 15). During the wet season, and for several weeks afterwards, much of the land surface in south Florida is inundated.
Before development, wetlands were more extensive, and water levels fluctuated over a wider range; water management has tended to reduce peaks and minimums in water levels and to lessen flooding and drought (fig. 16). Hydrologic models developed by the South Florida Water Management District for south Florida indicate that, in predevelopment times, surface water covered larger areas for longer periods of time than it does today. The models also indicate that the quantity and timing of surface and ground-water flow were significantly different than they are today (Fennema and others, 1994).
The type of wetland drainage varies from north to south in the region. In the northern part of the region, wetlands are drained by several large rivers, which include the Kissimmee, the Caloosahatchee, the Myakka, and the Peace Rivers. The Kissimmee River meanders through a broad floodplain and discharges into Lake Okeechobee. The Caloosahatchee, the Myakka, and the Peace Rivers discharge into Charlotte Harbor and into the Gulf of Mexico. In the southern part of the region, streams are smaller, and freshwater discharge to coastal waters is more dispersed.
With the exception of the Peace River, which drains a phosphate-rich area in central Florida and discharges large amounts of phosphorus to coastal waters, nutrient concentrations of water that drains south Florida's wetlands are typically low, and loading of nutrients to coastal waters is dispersed over broad areas by sheetflow. The freshwater typically flows through extensive mangrove forests into numerous tidal creeks, estuaries, and bays where it mixes with saltwater and becomes brackish. Mangrove trees contribute detrital materials that enrich the brackish water with nutrients that support a highly productive estuarine system.
Along the southwestern Gulf Coast, the gentle slope of the West Florida Shelf provides a broad, shallow zone where brackish water mixes with marine water of the open Gulf of Mexico. This shallow zone extends south to the Florida Keys. Several miles south and east of the Keys, the Florida Current flows north in the deep Straits of Florida. Water of the Florida Current is warm, clear, and salinity is constant.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:03 PM(KP)