G. Lynn Wingard¹, T. M. Cronin¹, C. W. Holmes², S. E. Ishman³ and D. A. Willard^1
1U.S. Geological Survey, Reston, VA, USA
²U.S. Geological Survey, St. Petersburg, FL, USA
³Geology Department, Southern Illinois University, Carbondale, IL, USA

A compilation of data from twelve sediment cores collected in Biscayne Bay, Florida Bay, and the southwest coastal area, beginning in 1994, illustrates important natural patterns and trends in the estuaries of south Florida and suggests alteration of those patterns by anthropogenic activities. Understanding the sequence and patterns of change during the 20^th century and the longer term trends leading up to 1900 are essential for successful restoration. A major goal of the Comprehensive Everglades Restoration Plan (CERP) is to restore more natural flow of freshwater into south Florida's estuaries, and performance measures and target salinity values are one of the tools being used to achieve that goal. Determining what these target values should be, however, is not an easy task given the tremendous spatial and temporal variability that occurs within the estuaries. Paleoecologic data from sediment cores provides the long term temporal perspective necessary to set effective performance measures and targets.

In the nearshore transition zones, assemblage data from the sediment cores indicate that in some locations long-term gradual trends towards increasing salinity began prior to the 20^th century. During the 20^th century these gradual natural trends were offset, and an increase occurred in the rate of change toward higher average salinities. In isolated basins in central Florida Bay, a loss of low salinity and freshwater indicators occurs in the lower portion of the cores, and during the 20^th century, there was an increase in species tolerant of broad fluctuations in salinity. In the Biscayne Bay system, cores from Card Sound Bank indicate a shift around mid-20^th century from species tolerant of estuarine fluctuations to species more typical of stable, nearly marine salinities. In the more open central Biscayne Bay, assemblages have shifted toward slightly more marine species, but like the more open waters of central Florida Bay, these changes have not been dramatic.

Our core analyses show that the nearshore areas have undergone more significant changes over the last century than the open bay areas, but the central isolated basins of Florida Bay also have changed significantly. The spatial variation in the estuaries makes the development of performance measures and targets very complex. The temporal variation seen in the cores illustrate that in addition to anthropogenic changes, some long term natural trends and/or cycles have affected south Florida's estuaries. These changes may be outside the scope of restoration (e.g. climate change, sea-level rise). In order to be attainable and sustainable, the target salinity values need to consider the balance of forces at work – both anthropogenic and natural – because the existing ecosystem represents a combination of these factors.

Contact Information: G. Lynn Wingard, U.S. Geological Survey, MS926A National Center, Reston, VA 20192, USA, Phone: 703-648-5352, Fax: 703-648-6953, Email: lwingard@usgs.gov

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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