Overview of the Everglades

Abstract

The Everglades is a freshwater wetland located in southern Florida. It originated 5500 years ago when rising waters of Lake Okeechobee and its vicinity fostered deposition of wetland soils through former uplands with widely exposed bedrock. Its development occurred in the presence of, and under the influence of Native Americans, their occupation having predated the Everglades by thousands of years. Prior to regional drainage, which began in the 1880s, the Everglades covered about 4000 square miles. It sloped southward at about 2.5 inches per mile from Lake Okeechobee to coastal tidal waters at the south end of Florida’s mainland. Just over half of the Everglades remains today, mostly broken into water-conservation impoundments controlled by levees and canals with only Everglades National Park at the south end still free-flowing. Pristine areas of the Everglades are oligotrophic, consisting mostly of marshes rich in periphyton. The marshes and periphyton are rapidly degraded by phosphorus enrichment over the maximum background of 10 ppb. Other enrichment of concern is sulfur and its association with elevated methylmercury, the latter biomagnified in Everglades fauna. Everglades marsh landscapes include long-hydroperiod sloughs (flooded 11+ months annually) and intermediate-hydroperiod sawgrass ridges (flooded 9–10 months), both underlain by peat soils, and smaller areas of short-hydroperiod, mixed-herb marshes (mostly flooded 3–7 months) underlain by marl. The latter occur around the edges of the southern Everglades. Unevenly distributed through these marshes are tree islands of several kinds based on their genesis and flora. One type was frequented through history by Native Americans, which influenced island development. Recent work has demonstrated the role of water flow in the evolution and maintenance of marsh and tree-island landscape features, all aligned with the pre-drainage direction of flow. Other Everglades features include small ponds called alligator holes that have various origins but are maintained by alligators and are ecologically important. Surrounding the Everglades are other plant communities, principally forests, and most outflows of water from the Everglades pass through extensive and highly productive tidal mangrove swamp forests before entering shallow marine waters at the south end of the system. Everglades wildlife responds to summer wet-season and winter-spring dry-season cycling, which characterizes southern Florida’s nearly tropical climate. Many introduced plants and animals have stressed the natural Everglades ecosystem, which supports 68 threatened and endangered species. Restoration efforts are in progress. Phosphorus reduction, initiated in the mid-1990s, has been successful but short of compliance targets. Overall ecosystem restoration is ongoing but slow. In combination with phosphorus reduction, it involves revision of South Florida’s water-control system to ensure the right quality, timing, and distribution of water.