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Since implementation of the Central and Southern Florida Project for Flood Control and Other Purposes, passed by the United States Congress in l948, the historic Everglades has been divided by canals and levees into three major areas: the Everglades Agricultural Area, the Water Conservation Areas, and Everglades National Park (Fig. 1). Water in the northern Everglades (the EAA and WCAs) is fresh and derived from rainfall and outflow from Lake Okeechobee. Water from Lake Okeechobee irrigates the EAA and then flows into the WCAs via a network of canals and pumping stations where it is impounded in wetlands and eventually released for flood control and water supply needs. Recent studies (Craft and Richardson, 1993; Koch and Reddy, 1992; DeBusk et al., 1994) indicate that agricultural runoff has increased the input of nutrients in parts of the WCAs adjacent to canals draining the EAA. Increased nutrient loading has resulted in changes in the type and amount of vegetation growing in the impacted areas.

The surficial and ground waters of the freshwater Everglades are components of a continuous, non-confined aquifer system, the uppermost unit of which is the Biscayne Aquifer (Sonntag, 1987). Limestone bedrock underlies the Everglades peat (Gleason and Stone, 1994). Recharge to the aquifer is mostly from rainwater, with lesser amounts supplied by drainage from Lake Okeechobee and other areas to the west and north (Fish, 1988; Waller and Earle, 1975). Groundwater flow patterns in the WCAs vary seasonally and are not well known, although the WCAs and the canals are known to be hydrostatic high points on a regional scale (Fish, 1988). The surface waters are circum-neutral with pH values generally near 7 (unpublished data, Orem).

Taylor Slough in the southern Everglades (Fig. 2) has freshwaters in its northern region. The head of the Slough is adjacent to agricultural fields and is nutrient impacted (Orem et al., 1999). The dominant plants in the northern part of the Slough are sawgrass, waterlily and periphyton algae. Marine water influence is felt in the mangrove swamps in the near-coastal areas of the Slough. Freshwater flows from the Slough into the marine waters of Florida Bay (Fig. 2).