USGS identifier

Highlight 12--Protecting the Everglades Ecosystem

Everglades National Park, the magnificent "River of Grass" in South Florida, is threatened by enormous water demands for rapid urban development and water diversions for intensive agriculture and flood control. The flow of freshwater through the Everglades into Florida Bay at the southern coastal tip of Florida is critical to the well-being of this fragile ecosystem. The USGS is participating in a multibillion dollar restoration program, in partnership with other Federal agencies, to mitigate the impact of current water management policies in South Florida. A major concern is the degree of saltwater intrusion into the aquifer underlying the Everglades, causing changes in plant communities that adversely affect fish and wildlife habitats.

USGS scientists use a helicopter-borne electromagnetic device to conduct rapid and economical surveys of aquifer quality where ground access is difficult; these surveys determine ground-water salinity by mapping changes in electrical resistivity of shallow subsurface rocks. The surveys have demonstrated an abrupt increase in resistivity 5-10 km (3-6 miles) inland from Florida Bay, corresponding to the infiltration of seawater beneath the Everglades (fig. 12). In addition to mapping saltwater intrusion, these surveys monitor changes in subsurface conditions and help constrain regional flow models. The imprint of human activity is dramatically apparent at several locations within the park, particularly along old roads and canals. This information is contributing to strategies that the NPS is using to protect living resources in the endangered Everglades ecosystem.

Figure 12. Satellite image showing mapped area and map showing saltwater intrusion beneath the Everglades. Ground-water salinity can be determined by mapping changes in electrical resistivity of subsurface rocks. Increases in resistivity (measured in ohm-meters) correspond to the incursion of seawater beneath the Everglades. From Fitterman (1996).

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