Monitoring changes in surface water geochemistry is critical for identifying and predicting ecological response to restoration in Florida Bay. Many basic estuarine processes directly impact water quality and vice versa. For example, calcification, photosynthesis, and respiration directly affect dissolved oxygen, pH, dissolved inorganic carbon, and a number of other chemical characteristics of the water column. Alternatively, changes in salinity, carbon speciation in the water column, and other water quality parameters affect rates of metabolism and growth of estuarine species and rates of carbonate sedimentation. These processes are sensitive to changes in water quality that result from flow modifications in the Everglades. Bay-wide geochemical surveys were conducted bimonthly throughout the year to establish baseline data from which to gauge restoration impacts.

Geochemical survey tracts target the perimeter of each of the smaller basins within Florida Bay, transect larger basins, and include sampling sites near canal and slough discharge areas. Salinity, conductivity, temperature, pH, and dissolved oxygen were measured using a flow-through analytical system towed at a speed of less than 15 knots. Data from each parameter was logged once every 4 to 8 seconds of travel resulting in collection of approximately 20,000 data points for each parameter through the entire bay within three to four days. Water samples were collected from each of 24 sites distributed throughout the Bay and analyzed for total alkalinity and total carbon via rapid scan linear array spectrophotometry and carbon coulometry, respectively. Air:sea CO₂ gas fluxes were directly measured at each of the 24 sampling sites using a floating bell and a LiCor 6252 infrared CO₂ gas analyzer. Each carbon dioxide exchange rate reflects the linear slope with a best Pearson product moment correlation coefficient (r²) calculated from a curve of approximately 900 data points.

Results from bimonthly geochemical surveys show the persistence of elevated salinity events in central Florida Bay during spring and early summer months. Air:sea CO₂ gas flux data show a persistent trend of CO₂ uptake into surface waters in the central region, and CO₂ out gassing in the eastern region throughout the year (fig. 1). Carbon dioxide gas flux data were superimposed over bottom-type data to identify potential correlations between benthic processes and gas exchange trends. No apparent correlation exists between bottom type and gas exchange rate. Other processes that may affect gas flux rates include plankton and macro-algal blooms, transport and degradation of dissolved and particulate organic carbon, and changes in other physicochemical parameters. Potential correlations among these parameters remain to be determined. Preliminary analysis of pH and dissolved oxygen data show no consistent spatial trends in variation. Total alkalinity and total carbon data are currently being analyzed. Statistical correlations will be made between surface water geochemical parameters to gain insight into the interdependencies of water quality parameters, the processes affecting them, and the potential impact of freshwater flow modifications resulting from restoration.

Figure 1. Example of Florida Bay air:sea carbon dioxide exchange data from April 2001. Boxes with and "x" indicate transfer of CO2 from the air to surface waters. Boxes with a "•" indicate transfer of CO2 from surface water to the air. Similar maps have been generated for salinity, temperature, pH, dissolved oxygen, total alkalinity, and total carbon. [larger image]

Contact: Kimberly Yates, U.S. Geological Survey, 600 Fourth Street South, St. Petersburg, FL, 33701, Phone: 727-803-8747, Fax: 727-803-2031, Email: kyates@usgs.gov, Poster, Question 4

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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