Home >Introduction - Purpose - Hydrologic Setting - Site Information Hydrogeology of NC Everglades Quantifying Recharge and Discharge Use of Geochemical Tracers Effect of GW and SW Interactions Summary References PDF Version

Introduction

Surface-water resources in the Florida Everglades are managed to accommodate a rapidly growing urban area to the east and an agricultural industry operating in former wetlands to the northwest. Management of the north-central Everglades for flood control and water supply has changed the character of flow in the wetlands. Since the 1960s, the wetlands have been divided into large artificial basins called Water Conservation Areas (WCAs) that are fed by drainage from Lake Okeechobee, runoff from the Everglades Agricultural Area (EAA), rainfall, and ground-water discharge directly into wetlands or canals that overflow into the wetlands. Surface water flows from one conservation area to the next, moving southward through the wetlands, canals, culverts, and spillways, eventually into Florida Bay or the Gulf of Mexico (fig. 1). Along the way, surface flow may be depleted by evapotranspiration or by recharge to ground water. A portion of the surface water in the Everglades replenishes ground water that will be withdrawn later for domestic use from well fields to the east of the Everglades. In other areas, recharge contributes to high water tables and seepage problems for housing developments located just east of the Everglades. During wet periods in south Florida, a large amount of surface water moves eastward through canals and discharges directly to the Atlantic Ocean.

Concern has been growing for many years in south Florida over the long-term decreases in surface water flowing through the Everglades, and the effects of these decreased flows on wildlife within Everglades National Park (ENP). Simultaneous to the decreasing surface flow, there has been increasing awareness of the deteriorating surface-water quality in WCAs and accompanying changes in the ecology of the wetlands. Ecological changes include disappearance of tree islands, proliferation of cattails, and loss of wading bird populations. In the past 20 years, these concerns have fueled wide-ranging discussions on how to improve water management in the Everglades in a way that would restore proper ecosystem function. In 2000, Congress approved a plan for restoration of the Everglades, referred to as the Comprehensive Everglades Restoration Plan or CERP. The overall goal of CERP is to restore some of the pre-drainage conditions, including the overall volume of surface flow, and characteristics of the depth, duration, and flow patterns of surface water. Restoration objectives also include reducing excessive inputs of dissolved nutrients and other constituents that could have deleterious effects on biogeochemical processes and ecological characteristics in the Everglades (McPherson and Halley, 1996; South Florida Water Management District, 1995; Stober and others, 1996; Gerould and Higer, 1995).

Evaluating the success of ongoing management and restoration efforts depends on reliable hydrologic information, including a better understanding of interactions between surface and ground water. One of the major initiatives already underway is the extensive rerouting of surface-water inflows to WCAs so that water first passes through Stormwater Treatment Areas (STAs) to remove excess nutrients before water enters the WCAs. A concern regarding the function of STAs is their potential effect in mobilizing toxic forms of mercury. Addressing that concern required considerable effort on the part of the South Florida Water Management District and cooperating agencies (Florida Department of Environmental Protection, U.S. Geological Survey, and others). One difficulty in developing a reliable mercury mass balance for STAs is uncertainty about how mercury is affected by interactions between surface water and ground water.

In an effort to learn more about interactions between ground water and surface water in the Everglades, the U.S. Geological Survey (USGS) and the South Florida Water Management District (SFWMD) developed an agreement to undertake a detailed study of interactions between surface water and ground water in selected areas of the north-central Everglades. The study would provide insight about the effect of interactions between ground water and surface water and chemical balances of STAs and WCAs. Investigations of surface and ground-water interactions were focused in two principal areas. The first area was the 3,815-acre Everglades Nutrient Removal Project (ENR), a prototype STA. The second area was Water Conservation Area 2A (WCA-2A), a 105,000-acre basin with a long history of ecological research on the changing character of the Everglades.

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