U.S. Department of the Interior
U.S. Geological Survey
OFR 2010-1125

Analyses of core GLBW601 RL1 collected in Rankin Basin (see fig. 1), Florida Bay, Everglades National Park, in June 2001 indicate that significant environmental changes occurred at the site over the last two centuries. The core was collected at a site of documented seagrass die-off in 1987-1988. The purpose of this study was to document the long-term sequences of events leading up to the die-off event. Analyses have been conducted to examine (1) faunal changes in the ostracodes and mollusks, (2) biochemistry of the ostracode shells, (3) floral changes in the pollen assemblages, and (4) geochemical and elemental changes in the sediment. The faunal assemblage analyses provide information on the salinity and benthic habitat at the site. The biochemical and geochemical data provide information about the water chemistry and sedimentation rates. The floral assemblage provides data about the nearby terrestrial environment and the first occurrence of pollen of the Australian pine, Casuarina equisetifolia, serves as a biostratigraphic marker for the beginning of the 20th century. These data provide clues to the cause and effect of the seagrass die-off and changes in salinity patterns and also illustrate decadal-scale patterns of change.

The analyses of GLBW601 RL1 show two important results. First, prior to 1900, Rankin Basin tended to be oligohaline to mesohaline on the basis of faunal data showing the assemblage to be similar to that of the lowest portions of a core from Taylor Creek. Second, prior to the documented seagrass die-off, the faunal assemblages indicate an increase in the amplitude of salinity fluctuations; a significant increase occurs in the mollusks Brachidontes exustus and Anomalocardia auberiana, two species that tolerate fluctuations in salinity.

Figure 1. Location of the Rankin Basin Core (GLBW601 RL1) collected in June 2001 from a site of documented seagrass die-off. [larger image]

Acknowledgments

We thank our colleagues at a number of other agencies, including South Florida Water Management District and Everglades National Park, who have collaborated and cooperated on this research. This work was conducted under NPS Permit # EVER-2001-SCI-0048 (Study # EVER-00048). We would especially like to thank the staff of Keys Marine Laboratory, who provided field support and facilities. The collection and initial research of the Rankin Basin core (GLBW601 RL1) was funded by the U.S. Geological Survey, Eastern Region Venture Capital Fund (2001). Subsequent analyses and the writing of this report have been generously supported by the Greater Everglades Priority Ecosystem program, coordinated by G. Ronnie Best (USGS).

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Related Information:

SOFIA project: Determining Target Salinity Values for Restoration of the Estuaries of the Greater Everglades