Abstract Introduction Study Area Coring & Pore Water Extraction Analytical Methods Results & Discussion Summary Acknowledgments References PDF Version

The south Florida wetlands ecosystem is an environment of great size and diversity, covering an area of over 28,000 km² or about 450 km north to south and 100 km east to west at its maximum extent (Light and Dineen, 1994). The ecosystem encompasses a variety of wetland habitats, including the Kissimmee River system, Lake Okeechobee, freshwater marshes south of Lake Okeechobee (the Everglades), Big Cypress Swamp, mangrove swamps along the coast, and Florida Bay (Davis and Ogden, 1994). These diverse habitats are interconnected by the flow of fresh water from one part of the ecosystem to another, and provide a unique home for an abundance of wildlife, some of which are found nowhere else.

South Florida wetlands are currently in crisis due to the combined effects of urbanization, agriculture, and nearly 100 years of water management. Critical problems include: (1) contamination of freshwater marshes and Florida Bay with phosphorus (P) and other elements, resulting in changes in the native flora and possible secondary effects on native fauna (Koch and Reddy, 1992; Craft and Richardson, 1993; Davis 1994), (2) changes in the natural hydrologic flow of the region, resulting in the subsidence of organic soils, fires in the freshwater marshes, and diminished freshwater flow to Florida Bay (Light and Dineen, 1994; McIvor et al. 1994), (3) contamination of fish and other wildlife with mercury (Hg) at levels high enough to pose a potential threat to human health (Lambou et al., 1991; and Delfino et al., 1993), (4) large decreases in wildlife populations, especially those of wading birds (Robertson and Frederick, 1994), and (5) extensive algal blooms, hypersaline conditions, seagrass dieoff, and diminishing productivity of fisheries in Florida Bay (Boesch et al., 1993).

In response to these problems, the U.S. Geological Survey has established a Critical Ecosystems Program for south Florida to examine geologic, hydrologic, geochemical, and biological framework of this ecosystem, establish the important processes contributing to its degradation, and assist land and water managers in efforts to "restore" the ecosystem. Restoration within the context of south Florida implies finding solutions to allow the equitable coexistance of agriculture, urban areas, fisheries, and wildlife habitat. In this report we present initial chemical analyses of surface and pore waters that are part of a study designed to describe the biogeochemical cycling of elements in sediments from south Florida wetlands.

Biogeochemical processes in sediments play an important but little understood role in many of the problems facing south Florida wetlands. For example, biogeochemical processes in sediments are central to nutrient recycling and the ultimate fate of excess nutrients entering the Everglades from agricultural runoff. Sediments likely also play an important role in the geochemistry of mercury, as sulfate reduction in sediments is thought to be the principal mechanism in the conversion of dissolved mercury to methyl mercury, a neurotoxin and bioaccumulated form of mercury. Sediments also contain a record of past environmental conditions in the south Florida ecosystem. An understanding of past conditions is essential for any effort to restore this wetlands ecosystem to a pristine state.

For many decades geochemists have studied the chemistry of pore water (the water present in the pore spaces of sediments) to attempt to understand biogeochemical processes occurring in sediments (Berner, 1971 and 1980). The enrichment or depletion of various chemical species in pore water can indicate the nature of ongoing biogeochemical processes in the sediments; processes that are not readily apparent from studies of the solid phase geochemistry. Pore water chemical data also provides the basis for quantitative estimates of the rates of biogeochemical processes occurring in the sediments (Berner, 1980).

In this report we present surface water and pore water data from a number of sites in south Florida wetlands, including sites in the Water Conservation Areas (WCA), Everglades National Park (ENP), and Big Cypress National Preserve (BC). We present herein a brief overview of spatial trends in the data, and a description of the probable biogeochemical processes producing the observed trends. Future reports will emphasize a more quantitative approach, including modelling of the data and estimation of the rates of biogeochemical reactions. In addition to analyses of surface and pore waters, geochemical analyses of solid phase sediments were also conducted at each of the study sites detailed here. Results of these solid phase studies will be presented in future reports.