Surface Water Geochemical Surveys in Florida Bay
Kimberly Yates, Iuri Herzfeld, Nathan Smiley, and Chris Dufore
U.S. Geological Survey, Center for Coastal and Watershed Studies, St.
Petersburg, FL
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 (Figure 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.
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