By
G.L. Brewster-Wingard, S.E. Ishman, D.A. Willard, L.E. Edwards, and C.W. Holmes
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Abstract
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.
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Last Updated 05.17.99