U.S. Department of the Interior
U.S. Geological Survey
FS-144-96
Project Goals | Clues in the Cores | Planned Products | Evidence of Past Changes | Continuing Research | Anticipated Schedule
In the past decade seagrass die-offs, algal blooms, and declining numbers of shellfish and sponges have occurred in Florida Bay. These changes have been attributed to human activities; however, neither the natural patterns of change, nor the pre-human baseline for the environment have been determined. Currently, efforts are underway to restore the Everglades ecosystem to a more natural state, but the restoration should be guided by a clear understanding of the natural range of variability that exists within the ecosystem.
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The U.S. Geological Survey�s " Ecosystem History: Florida Bay and the Southwest Coast " Project utilizes basic paleoecologic tools to determine the characteristics of the ecosystem prior to significant human alteration. These characteristics include the natural range of variation that exists within the ecosystem. By analyzing the animal and plant remains that exist within shallow cores taken in Florida Bay we can establish the extent, range and timing of hydrologic and corresponding ecologic changes to the ecosystem during the last 150-200 years. The ages for the cores are established using isotopic dating methods, primarily lead-210 (210Pb).
The numbers and types of animals and plants present at different depths within the cores provide important clues to the biological, physical and chemical parameters of the environment at different intervals in the past. Each core is examined for bottom-dwelling (benthic) animals, including ostracodes, foraminifera and mollusks; cysts from planktonic plants, the dinoflagellates; and pollen. The benthic animals record the salinity and substrate types present when the organisms were alive. Dinoflagellate cysts indicate nutrient supply, currents, or general salinity range. The wind- and water-borne pollen present in the marine cores indicate the contemporaneous terrestrial vegetation. By correlating the marine habitat with the terrestrial realm, we can determine regional changes that may have affected the entire Everglades ecosystem, such as climate, hydroperiod (the length of each wet and dry cycle), and nutrient supply.
Products that will be developed through this project include:
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EVIDENCE OF PAST CHANGES
Plot showing fluctuations in the salinity of Florida Bay from the Bob Allen Core.
Preliminary analysis of a core from the Bob Allen mud bank has indicated that significant changes have occurred in Florida Bay during the last 150-200 years. The late 1700�s and early 1800�s were characterized by a period of relatively stable salinities intermediate between freshwater and normal seawater (20-30 ppt), moderate amounts of sub-aquatic vegetation, and moderate numbers and types of bottom-dwelling animals.
The period from approximately 1810-1892 was characterized by continued stable salinities intermediate between freshwater and normal seawater (15-25 ppt), very little subaquatic vegetation, and limited numbers and types of bottom-dwelling animals. Pollen grains present in the lower half of the core, from the late 1700�s to approximately 1892, are indicative of an inland freshwater swamp or marsh. No substantial human alteration of the environment had occurred before 1892.
Beginning around 1892, the salinities indicated by the bottom-dwelling animals in the Bob Allen core began to fluctuate a great deal, ranging from intermediate salinities to salinities in excess of normal seawater (20->40 ppt). The salinities in excess of normal seawater (hypersaline; >40 ppt) were not recorded prior to the turn of the century. During this same time period the numbers and types of bottom-dwelling animals increased, and sub-aquatic vegetation was abundant. The pollen indicate increases in the hardwoods and mangroves; increase in mangrove pollen in the upper half of the core is indicative of coastal swamps and marshes. The early 1900's marked the beginning of increasing human activity in southern Florida. The early canal systems were constructed, and the Flagler Railroad was built during this period.
From approximately 1947 to 1981, there was a return to more stable salinities intermediate between fresh water and normal seawater (15-30 ppt). Sub-aquatic vegetation and the numbers and types of bottom-dwelling animals decreased at the same time; conditions appear to resemble those seen from 1810-1892. Beginning around 1981, Florida Bay entered a period of fluctuating salinities, including periods of hypersaline conditions. These trends continue to the present.
The results obtained so far raise a number of intriguing questions. What caused the dramatic decline in numbers and types of bottom-dwelling animals in the early 1800�s, prior to any significant human alteration of the environment? Was the decline a local or regional occurrence? What caused the fluctuation in salinities beginning around 1892? Is lower diversity the more "natural" condition for this portion of Florida Bay?
The next step is to determine if these patterns can be seen in other cores in Florida Bay and if they correspond to changes detected onshore as well. Preliminary analyses of cores from Little Madeira Bay and several terrestrial sites indicate that similar changes have occurred at other locations. Some of these changes appear to be part of natural variations within the ecosystem, and some appear to correspond to human activities in the region. Additional work is necessary to clarify these patterns.
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For more information contact:
G. Lynn Brewster-Wingard
U.S. Geological Survey
MS 926A
Reston, VA 20192
[email protected]
Related information:
SOFIA Project: Ecosystem History: Florida Bay and the Southwest Coast
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/publications/fs/144-96/print.html
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Last updated: 04 September, 2013 @ 02:03 PM(TJE)
