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projects > ecosystem history of biscayne bay and the southeast coast > abstract
Temporal Salinity and Seagrass Changes in Biscayne BayScott E. Ishman, G. Lynn Brewster Wingard, Thomas M. Cronin, and Debra A. Willard The objectives of the Ecosystem History of Biscayne Bay and Southeast Coast project are to:
(1) assess the spatial variability in the distribution of modern biota (foraminifera, ostracodes, molluscs,
diatoms, and palynomorphs) in Biscayne Bay; (2) determine how these distributions relate to the
present environmental conditions (fresh water input, salinity, nutrient supply, seagrass, and
contaminants) in the Bay; (3) interpret the temporal variability in the measured environmental
conditions by applying modern biotic and environmental associations and geochemical data to biotic
and geochemical data from downcore sediments; and (4) analyze the timing of environmental changes
as determined by 210Pb dated samples and relate the changes to historical events in South Florida.
This project is using faunal (foraminifera, ostracodes, and mollusks), floral (palynology and
diatoms), and geochemical (stable isotopes and trace element geochemistry) data to examine the
ecosystem history of Biscayne Bay and adjacent regions. Surface sediments collected from sites
within Biscayne Bay and adjacent regions are being analyzed for their faunal and floral compositions.
These data are correlated to water column data (temperature, salinity, pH, dissolved oxygen, nutrients,
and redox potential) from each collection site and ground-water data (salinity, nutrient, stable isotope
and trace element) collected at specific sites. Calcareous shells of living organisms are analyzed at
Duke University for their trace element composition. In addition, the National Oceanic and Atmospheric Administration is currently gathering surficial sediment geochemistry data on samples
collected near or at many of the ecosystem sites. Quantitative analyses of these data are used to
determine controls on the modern faunal and floral distributions in the Bay. The data are also used to
identify organisms that are useful environmental indicators, derive trace element (Mg/Ca ratio)
calibration equations for modern bay salinities and temperatures, and determine the source areas for
specific submarine ground-water flows into the Bay.
Distinct faunal distributions are identified within Biscayne Bay that are strongly associated with
salinity, nutrient, and seagrass distributions. Trace element geochemical analyses of water and shells
indicate a strong correlation between salinity and shell trace element geochemistry. Faunal
distributions and shell geochemistry from sediment core samples, dated using An understanding of pre-existing ecosystem conditions in Biscayne Bay and the evolution of the
Bay is necessary to establish the range of natural variability and the impact of human influences in the
region. The faunal and floral events detailed in Biscayne Bay show natural variability in salinity with
a progressive increase in salinity throughout the last 150 years. This trend is punctuated by discrete
events attributed to construction of the Flagler Railway, implementation of water management
practices, and channelization of freshwater flow in South Florida. These results suggest that conditions
within Biscayne Bay and adjacent regions during the past several decades may not represent the norm,
and that significantly different salinity and seagrass conditions existed before intense water
management practices and land development in southern Florida began. Restoration efforts need to
reflect this possibility and incorporate this information into the present hydrologic and circulation
models for Biscayne Bay and adjacent regions. This record reflects the importance of volume and rate
of freshwater flow into Biscayne Bay and adjacent regions for the stability of the ecosystem and
suggests an increase in freshwater inflow to maintain and improve the natural health of the Bay.
Results to date for this project have been provided to the Central and South Florida Restudy
Project describing the impact of reduced freshwater flow to Biscayne Bay and surrounding regions.
This project will establish methodologies for application to restoration of other Fragile Environments
within our Nation. Spatial reconstructions of environmental conditions for the last 150 to 200 years
will be used to produce synoptic maps of salinity, nutrient, and substrate conditions for Biscayne Bay.
The data are compiled and can be accessed at http://geology.er.usgs.gov/gmapeast/fla/home.html (note: this site has moved to http://sofia.usgs.gov/flaecohist/),
and a summary publication is being prepared on the ecosystem history of Biscayne Bay. These data
are necessary for setting restoration objectives, supplying circulation modelers with control points to
test their circulation models and modeling future outcomes of land and water management decisions,
and locating sites at which restoration objectives can be monitored.
This project has benefited from collaboration with Biscayne National Park, Metro-Dade Department of Environmental Resources Management (Metro-Dade DERM), South Florida Water
Management District (SFWMD), National Oceanic and Atmospheric Administration (NOAA), and Duke University.
(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)
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U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology This page is: http://sofia.usgs.gov /projects/eh_bbsec/ehbbsecabsfrsf.html Comments and suggestions? Contact: Heather Henkel - Webmaster Last updated: 11 October, 2002 @ 09:29 PM (KP) |