publications > open file report > Ecosystem History of Southern and Central Biscayne Bay: Summary Report on Sediment Core Analyses - Year Two
Ecosystem History of Southern and Central Biscayne Bay: Summary Report on Sediment Core Analyses - Year Two
U.S. Geological Survey Open File Report 2004-1312
G. Lynn Wingard, Thomas M. Cronin, Charles W. Holmes, Debra A. Willard, Gary Dwyer, Scott E. Ishman, William Orem, Christopher P. Williams, Jessica Albietz, Christopher E. Bernhardt, Carlos A. Budet, Bryan Landacre, Terry Lerch, Marci Marot, Ruth E. Ortiz
The Comprehensive Everglades Restoration Plan (CERP) lists restoration of the timing, quantity, and quality of the natural flow of freshwater as one its primary goals. Before restoration can occur, however, the baseline conditions of the environment prior to significant human alteration must be established and the range of variation within the natural system must be determined. In addition, the response of the system to human alterations during the 20th century should be evaluated. Resource managers can use this information to establish targets and performance measures for restoration and to predict the system's response to changes invoked by restoration.
The objectives of the U.S. Geological Surveys Ecosystem History of Biscayne Bay research project are to examine historical changes in the Biscayne Bay ecosystem at selected sites on a decadal-centennial scale and to correlate these changes with natural events and anthropogenic alterations in the South Florida region. Specific emphasis is being placed on historical changes to (1) amount, timing, and sources of freshwater influx and the resulting effects on salinity and water quality; (2) shoreline and sub-aquatic vegetation; and (3) the relationship between sea-level change, onshore vegetation, and salinity.
This report compiles and summarizes results on analyses of cores from eleven sites in the Biscayne Bay ecosystem collected from 1996 to 2003. The following are the significant findings discussed:
A general trend emerges from the multiproxy analyses of all the cores examined - increasing salinity during the 20th century. Although the timing and onset of increased salinity varies at the different core sites, there are no exceptions to this trend. In the nearshore sites, the increase in average salinity has been accompanied by an increase in variability of salinity. In contrast, the central Biscayne Bay sites have shown increasingly stable salinity over the last century, indicated in part by the influx of increasing numbers of marine species. These trends could be a result of a number of factors, including (1) rising sea level; (2) changes in the natural flow of freshwater into the bay either through surficial or groundwater processes; (3) changes in average rainfall or rates of evaporation; (4) changes in sedimentation rates; or (5) a combination of factors. The timing of changes at some of the near-shore sites suggests both anthropogenic and natural factors are involved.
In addition to the general salinity trend for Biscayne Bay, the near-shore sites at Middle Key and north of Black Point have illustrated distinct, but site specific, changes in freshwater influx over time. Our data suggest that sites we assumed had historic point-source inflow of freshwater may not have. The wetlands cores (near Military Canal) also illustrate that sites in very close proximity to each other have historically been affected by very localized hydrologic regimes.
These results have significant implications for restoration planning. First, the recognition that Biscayne Bay appears to be evolving toward a more marine environment due to both natural and anthropogenic factors must be factored into the planning process. Second, generalized performance measures and targets for the near-shore and wetlands areas may not reflect the natural variability seen at these sites. Third, the nearshore environments are dramatically different from the mid-bay mudbanks, and have been for hundreds of years. Influx of freshwater into the bay appears to have a subtle or indirect effect on the benthic fauna of the mudbanks. Changes in flow during restoration may have little effect on the central bay mudbanks.
Examining decadal-centennial trends in a variety of habitats within the Biscayne Bay ecosystem provides a realistic means to set performance measures, predict system response to changes invoked by restoration, and to enlighten the public on what the natural system of the bay looked like.
For more information, please visit:
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 15 January, 2013 @ 12:43 PM(HSH)