Home Introduction Climate Variability Impacts on Ecosys. Degradation & Restoration in Chesapeake Bay Baseline Variability: Chesapeake Bay Chesapeake Bay WQ & Climate Variability >FL Everglades: Hydro. Changes & Degradation Everglades Climate Variability & Relevance Role of Time in Restoration Planning Acknowledgements References Figures

In the Florida Everglades and Florida and Biscayne Bays, land-use and water management practices dating as far back as the late 19^th century have changed the distribution and composition of plant and animal communities throughout the system. The "predrainage" (pre-1900) Everglades were influenced primarily by seasonal rainfall and underlying topography. Overflow of water from Lake Okeechobee during the wet season produced seasonal sheet flow across the Everglades, draining into Florida Bay and Biscayne Bay. Wetland hydroperiods and water depths and estuarine salinity were primarily a function of precipitation. Human alteration of the natural hydrologic patterns of the Everglades began in the early 20^th century with construction of canals and the Hoover Dike around Lake Okeechobee (Light and Dineen, 1994). A second wave of canal and levee construction in the 1950's and 1960's significantly changed the quantity and seasonality of freshwater flow through the wetland and fragmented the ecosystem. By the early 21^st century, the spatial extent of the Everglades wetland had been reduced by approximately one half (Fig. 5) (Lodge, 2005).

These land-use changes also affected water delivery from the Everglades to adjacent marine ecosystems in Florida and Biscayne Bays. Hypersalinity and resulting seagrass dieoffs in Florida Bay were of particular concern and were attributed to decreased runoff of freshwater from canal building and water management (Robblee et al., 1991). In addition, increased nutrient loading from agricultural land use may have changed estuarine ecosystems from a clear water system with abundant benthic primary production to one with high turbidity and common algal blooms (Rudnick et al., 2005).

The degradation of wetlands and associated wildlife resulted in passage of the Everglades Forever Act in 1994, which aimed to restore healthy ecosystem function to the Everglades. More recently, the recognition that the health of the greater Everglades ecosystem and the quality and availability of water affected the economy and culture of south Florida prompted the Comprehensive Everglades Restoration Plan (CERP) to restore natural hydroperiods, seasonality, and connectivity of the ecosystem through modification of existing water-control structures.

Figure 5. The Florida Everglades occupy ~10,000 km2 on the southern tip of Florida. Extensive land-cover changes since the early 20th century significantly changed wetland hydrology, plant community distribution, and substrate characteristics. The white line indicates the extent of the freshwater Everglades wetland. (modified from Lodge, 2005; Marshall et al., 2004). a) Reconstruction of pre-1900 AD vegetation is based on a combination of paleoecological proxies and historical references. b) 1992-93 land cover was derived from satellite images and modern vegetation maps. Modeling simulations indicate that land-cover changes alone were sufficient to increase diurnal temperature variability and decrease summer rainfall (Marshall et al., 2004). [larger image]