HR: 1330h
AN: B33C-04    [Abstracts]
TI: Geomicrobiology of Phreatic Caves Associated With Central Florida Springs
AU: * Giannotti, A L
EM: Amy.Giannotti@dep.state.fl.us
AF: Florida Department of Environmental Protection, Wekiva River Basin State Parks, 1800 Wekiwa Circle, Apopka, FL 32712 United States
AU: * Giannotti, A L
EM: Amy.Giannotti@dep.state.fl.us
AF: The Cambrian Foundation, 1234 East Concord Street, Suite A, Orlando, FL 32803 United States
AU: Tysall, T N
EM: Terrence@cambrianfoundation.org
AF: The Cambrian Foundation, 1234 East Concord Street, Suite A, Orlando, FL 32803 United States
AU: Franklin, R B
EM: Rima.Franklin-1@ksc.nasa.gov
AF: NASA Space Life Sciences Lab, Mail Code YA-E4-B, Kennedy Space Center, FL 32899 United States
AU: Mills, A L
EM: Aaron.L.Mills@nasa.gov
AF: NASA Space Life Sciences Lab, Mail Code YA-E4-B, Kennedy Space Center, FL 32899 United States
AB: Phreatic (underwater) limestone caves are common in Florida in association with the numerous springs that issue from the karst landscape. Extensive microbial mats and diverse communities of invertebrates have been observed by cave divers, but, as ecosystems, the caves are not well studied. Four aphotic aquatic caves were identified in which to investigate relationships between microbial communities and their geochemical surroundings, and to evaluate the potential for chemolithoautotrophic microbial activity to support higher-order consumers. The caves were associated with the discharge sites of four different second-magnitude springs (flow: 0.3 to 3 m³ s^-1) in central Florida in which communities containing microbial mats, isopods, amphiphods, and cave crayfish have been observed. Samples of bulk water and microbial mat were collected along the flow path in each cave; depths ranged from 0.5 to 15 m below the ground surface, and penetration distance extended up to 250 m from each cave entrance. Microscopic examination of the mats revealed the presence of sulfur-granule-containing, filamentous morphologies consistent with Thiothrix and Beggiatoa and an unidentified filamentous iron bacteria. The bacteria were found in all four springs, but H₂S was detected in water samples from only one of the caves. In many cases, the morphology of the organisms changed along the flow path within an individual spring, although there was little change in the associated water chemistry (pH, dissolved oxygen, conductivity, total Fe, NH₄⁺, NO₃^-, HS^-, SO₄^2-, PO₄^-, Cl^-, Fl^-, Ca²⁺, Na⁺, and Mg²⁺). The overall water chemistry of the four caves/springs was distinct (principal components analysis), and the major differences were due to Ca²⁺, K⁺, and Cl^- concentrations, pH (range: 7.3 to 8.4), and sulfur and iron availability. Efforts to culture the dominant organisms in each set of mats (using media prepared with cave or spring water) and community-level genetic analyses (T-RFLP) demonstrated that the communities are composed of a diverse mixture of both chemoautotrophic and heterotrophic bacteria. Elemental analysis (C, N, and S) of the mats revealed a high sulfur content (> 10 %), and low C:N ratios. The latter suggests the material would be a high quality food source for other members of the ecosystem. The results suggest that bacterial production from reduced inorganic compounds in these springs may provide a plentiful source of energy and nutrition to support the higher forms endemic there. Additionally, the microbes likely play an active role in speleogenesis in these phreatic caves, given that sulfuric acid is produced as a metabolic by-product of microbial sulfur oxidation. Additional work is needed to determine the influence of these bacterial communities on the rate and extent of cave formation.
DE: 0400 Biogeosciences
DE: 1010 Chemical evolution
SC: Biogeosciences [B]
MN: 2005 Joint Assembly