A COMPARISON OF MODERN SEDIMENTOLOGY FOR SEVERAL HYPERSALINE LAKES OF SAN SALVADOR ISLAND, BAHAMAS: FRENCH POND, TRIANGLE POND, NO NAME POND, AND STORR'S LAKE

The island of San Salvador, Bahamas is formed of calcium carbonate, accreted from marine sediments dating back to the Jurassic period. There are many inland lakes of various sizes across the island. Most of these are hypersaline with salinity levels widely varying over time and have been reported as high as 300 ppt. These conditions lead to somewhat unique saline-carbonate lacustrine environments that provide support for limited biological activities. Among the organisms thriving in these lakes are microbial mats composed of cyanobacteria along with other microorganisms all working as a synergetic community. At present, little is known about the relationships that exist with the mats, involving a pond’s salinity and carbonate environment. The goal of this project is to compare and contrast the activities occurring in several of the hypersaline lakes of San Salvador from a recent sedimentological perspective. The lakes selected for this purpose are: French Pond, Triangle Pond, No Name Pond, and Storr’s Lake.

In June, 2009, surface sediment samples were collected from each of the four lakes along a transect from shoreline to depocenter. Measurements of the lake waters, including temperature, salinity, conductivity, dissolved ion content, dissolved oxygen, pH, alkalinity, and depth also were taken. After noting physical properties, the sediments were later analyzed for grain size, density, water content, and composition, using various additional techniques. Loss on ignition was used to determine bulk organic, carbonate, and residual content. X-ray diffraction was used to determine mineral content, while ESEM was used for elemental analysis.

The results from the sediment and water analyses indicate that the four lakes studied were generally similar: sediments were dominated by calcium carbonate, but also contained substantial amounts of organic matter and varying amounts of residual mineral matter. No evidence was found indicating detrimental effects from salinity, but rather salinity appears to serve a critical role in protecting the established ecosystems. A key factor to sustaining the microbial mats appears to be allochthonous mineral matter entering the lakes. Conversely, the biological communities of the lakes appear to have at least some influence over the form and composition of lake sediments.