Background and Rationale for Sampling Waters in Florida Bay



Sampling of waters in Florida Bay for stable isotopes was initiated in October 1993 and continues to the present day. Our present collection includes 106 stations in the Everglades and surrounding waters including Biscayne Bay and the west coast of Florida. Information on the hydrogen, oxygen, and carbon isotopic composition of the waters in South Florida provides information on the sources and history of water. Maps of analyses which have been completed to date are available on the Stable Isotope Laboratory Web Site.  As the samples were analyzed principally without any financial support the data base remains the property of the Stable Isotope Laboratory and is available upon request.


Maps and Movies: The maps and movies are generated using Matlab code.  The map of the oxygen isotopic intercept at zero salinity is made using 5 years of monthly data (n=60).  Each successive map represents a 60 month time slice starting one month later.  As data have now been analyzed for about 137 months, there are 77 images in this movie.  The map of the regression coefficient shows the degree of correlation between the salinity and oxygen isotopic composition.  The movies of the salinity and oxygen and carbon isotopic compositions of the waters are simply contour maps of the actual values measured.  The data set has been smoothed using a five month running average to help to eliminate data gaps.  During certain periods (November 1994 and August 1996) samples were only collected from 21 stations (rather than 28) in Florida Bay.  This results in the contouring artifact seen in the movies.

 

Trouble Viewing Movies: There are two versions an AVI version created directly from Matlab and a converted product (MPG).  The mpg files are much larger but generally tend to play on most computers.

Carbon: The carbon isotopic composition of the dissolved inorganic carbon (DIC) responds mainly to the amount of the oxidation of organic material. More negative values result from the oxidation of greater amounts of organic material and the overall carbon isotopic composition reflects mixing between marine waters which contain isotopically positive values (+2 to +3 ‰) and terrestrially derived waters (-15 to -18‰). Oxidation of marine organic material can also produce isotopically depleted signatures although not to the same degree as terrestrial waters.

Oxygen: The oxygen isotopic composition of the water responds to evaporation which tends to produce more positive values, dilution by rainwater (more negative values), and mixing with marine fluids. As a result of the complicated hydrological situation in South Florida many different scenarios can arise producing different correlations between salinity and the oxygen isotopic composition. For example, mixing between saline water and rainfall will produce a positive correlation between the oxygen isotopic value and the salinity (March, 1997). In contrast freshwater which has experienced significant evaporation, which is the case of much of the water in the Everglades, will produce an inverse correlation when mixed with saline water (December 1996). In the case of Florida Bay these relationship can be used to ascertain whether there is significant contribution of Everglades derived water to Florida Bay, or whether changes in salinity result from local precipitation. The periods during which the correlation coefficients are significantly greater than zero indicate that the main causes in the variation in precipitation are a result of local changes in precipitation. In contrast, negative correlation coefficients indicate a greater contribution of water which has experienced significant amount of evaporation.

 

 

 


Return to Projects

Last Updated July 23rd, 2005  by Peter Swart