Beyond these few studies cited here, there is relatively little comprehensive information available about the hydrogeology beneath the central Everglades in western Palm Beach and Broward counties. Miller (1988) illustrated some of the effects that water management has had on ground water levels in that part of the central Everglades. Recent work characterized the geology and hydraulic properties of the surficial aquifer beneath the northern WCAs in greater detail than previously available (Harvey et al. 2002). The present study extended that work through collection of additional hydraulic conductivity data from shallow layers (1a and 1b, Table 1). Table 1 combines and summarizes basic hydrogeologic information collected beneath WCA-2A, which is representative of much of the central Everglades.

Everglades Nutrient Removal Project

The ENR Project was constructed and operated in the 1990s as a prototype to test the capacity of larger constructed wetlands, called storm water treatment areas, to remove nutrients from agricultural drainage waters (Figures 1 and 3a). ENR is comprised of a 1545 ha area that was formerly part of the Everglades, but was drained and farmed beginning in the mid-1900s, and then recently returned to management as a constructed wetland. The source of surface water to ENR is pumpage from agricultural land to the west and from surface water from Lake Okeechobee. ENR's location in the Everglades landscape affects interactions between surface water and ground water. To the east of ENR is WCA-1, where water surface elevations are maintained at relatively high elevations compared with the rest of the Everglades. To the west of the ENR is the Everglades Agricultural Area (EAA ), where subsidence and canal drainage have substantially decreased the ground elevation and water table relative to WCA-1 and ENR. Proximity to the agricultural area has a significant effect on the ENR water budget, with recharge in ENR accounting for flow equal to 30% of the pumped inflow of surface water (Choi and Harvey 2000).

Water Conservation Area 2A

Located 10 km to the south of ENR, WCA-2A is 25 times larger in area (42,525 ha) than ENR (Figure 3b). Studying WCA-2A is a logical complement to investigations in ENR, because of the much larger area and much longer history of nutrient pollution (Urban et al. 1993; Jensen et al. 1995). WCA-2A shares boundaries with WCA-1 and the EAA , lands developed for light industrial and residential areas to the east, and WCA-3A to the southwest. In the 1950s, construction began on a new system of levees and borrow canals to connect the canal and levee systems that bordered WCA-2A to the north and south (Light and Dineen 1994). By about 1963, WCA-2A was completely surrounded by levees and canals (Figure 3B).

Researchers started investigating the ecology of WCA-2A beginning about 1975, documenting, for example, the loss of tree islands and a transition from a sawgrassdominated wetland to one affected by extensive cattail growth in some areas (Jensen et al. 1995). Possible causes for those ecological changes are excess nutrients from agricultural runoff, and excessive periods of drying and wetting due to water-management practices.

Figure 3. Research sites, instrumentation, and natural and manmade features in (a) ENR Project and (b) WCA-2, central Everglades, south Florida. [larger version]