Preliminary paleontologic report on cores 19A and 19B, from Russell Bank, Everglades National Park, Florida Bay

The fauna and flora preserved in two cores, 19A and 19B, from the south side of Russell Bank (N 25 03.831’, W 80 37.486’) in north-central Florida Bay, Everglades National Park, Florida, record a history of environmental change over the last century. The benthic foraminifera and molluscs indicate fluctuating salinities with increasing average salinity upcore in core 19B. Shifts from low salinity (12-15 ppt) to higher average salinity (30 ppt) occurred at 70-66 cm and 24-18 cm in core 19B (approximately 1937-1940 and 1975-1980). The inverse, shifts from periods of higher average salinity to periods of lower salinity, occurred at 140 cm, 90 cm, and 42 cm (approximately 1880, 1921, and 1960). Significant changes in the molluscan fauna indicative of specific substrate types occur at 88 cm, 68 cm, and 22 cm. The lower portion of the core is dominated by a mixture of sediment and grass dwellers, the middle portion by sediment dwellers, and the upper portion of the core by grass and finally grass and algae dwellers. Changes occur in the floral assemblages in core 19A, but the significance of these changes is unclear. Three subtle shifts occur in the pollen assemblages indicating the onshore vegetation was responding to some environmental factor. Two peaks in dinocyst abundance occur in core 19A, but the composition of dinocyst assemblages remains relatively stable throughout the core. Correspondence between changes in salinity and onshore vegetation changes is consistent with results from previous cores. The pattern of increased salinity upcore is consistent with patterns seen in core T24 from the mouth of Taylor Creek and in core 6A from Bob Allen mudbank. INTRODUCTION The fragile and unique ecosystems of southern Florida, including Florida Bay, the terrestrial Everglades, and Biscayne Bay, have been the focus of a substantial scientific effort in response to environmental, economic and political concerns. These concerns are focused on returning the Everglades to its "natural state" as mandated by the Everglades Forever Act (passed in 1994), while at the same time addressing the conflicting interests of the ever-growing population of southern Florida, the environmentalists, the farmers, and the tourist industry, among others. Consequently, Federal, State, and local jurisdictions are faced with decisions related to the ecosystem restoration goals, mediation of conflicting interests, and monitoring of change. An essential part of the decision making process is to understand the history of the ecosystem prior to significant human alteration, and to separate natural variability in the ecosystem from human-induced change. The U.S. Geological Survey (USGS), in cooperation with National Oceanic and Atmospheric Administration (NOAA), South Florida Water Management District (SFWMD), the National Park Service (NPS), the Army Corps of Engineers (ACOE), and other Federal, State and local agencies, is conducting research to provide information on the history of the Everglades ecosystem over the last 150-200 years. The distribution of fauna and flora in a series of sediment cores taken throughout the Everglades ecosystem provides information on the biological, physical and chemical parameters of the system over time. Sediment cores were taken in February of 1995 by researchers from the U.S. Geological Survey (St. Petersburg, FL), in cooperation with South Florida Water Management District (SFWMD) and the Everglades National Park (ENP), for use by USGS investigators conducting research in Florida Bay. Three cores were taken from the south side of Russell Bank (N 25 03.831’, W 80 37.486’) in north-central Florida Bay (Figure 1). Cores 19A and 19B are replicate cores, taken side by side from a grass bed in 0.51 m of water. Core 19C was taken 54 m north of 19A and 19B from a mud flat, on top of the south side of Russell Bank. Core 19A penetrated 140 cm of sediment, spanning approximately 115 years, and has been sampled for Pb and palynologic analyses. Core 19B penetrated 144 cm of sediment, spanning approximately 118 years, and has been sampled for Pb and calcareous fossil analyses. Core 19C penetrated 158 cm of sediment and has been sampled for Pb analysis. This report is produced by the "Ecosystem History of Florida Bay and the Southwest Coast" component of the U.S. Geological Survey’s Ecosystem Program, and is one of a series of USGS Open-File Reports on the distribution of biogenic components in sediments sampled from the southern Florida region. The data presented in these reports can be used to estimate changes in salinity, substrate, and other critical components of the ecosystem over time. ACKNOWLEDGMENTS We would like to thank Robert Halley and Gene Shinn, U.S. Geological Survey, St. Petersburg, FL, for collecting the cores and making them available to us for analysis. We would like to thank our colleagues at South Florida Water Management District, National Oceanic and Atmospheric Administration, and Everglades National Park for their cooperation and assistance in this investigation. We have benefited from discussions with William Lyons, Florida Marine Research Institute, St. Petersburg, FL; and Thomas Scott, Florida Geological Survey, Tallahassee, FL. Our reviewers, Thomas Cronin and John Sutter, U.S. Geological Survey, Reston, VA, provided helpful comments and suggestions to improve this manuscript. Marci Marot, U.S. Geological Survey, St. Petersburg, FL, prepared the samples for isotopic and calcareous analysis. Assistance in sample processing was provided by Jill D’Ambrosio, Ian Graham, Lisa Weimer, Neil Waibel, Patrick Buchanan, Nancy Carlin, and Steve Wandrei of the U.S. Geological Survey, Reston, VA. Rob Stamm and Patrick Buchanan, U.S. Geological Survey, Reston, VA, assisted in the preparation of illustrations for this report and Jill D’Ambrosio assisted in compiling the final report. MODERN SAMPLING SITES Seasonal collecting starting February 1995 Seasonal collecting starting February 1996 Seasonal collecting starting February 1997 8 1 3