HR: 0830h
AN: B51C-0968    [PDF]
TI: Microbial Diversity Associated With Geochemical Changes in a Deep Subsurface Aquifer
AU: * Davidson, M M
EM: markd@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08540 United States
AU: Onstott, T C
EM: tullis@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08540 United States
AU: Pratt, L M
EM: prattl@indiana.edu
AF: Department of Geological Sciences, Indiana University, Bloomington, IN 47405-1405 United States
AU: Boice, E
EM: aboice@indiana.edu
AF: Department of Geological Sciences, Indiana University, Bloomington, IN 47405-1405 United States
AU: Southam, G
EM: gsoutham@uwo.ca
AF: Department of Eart Sciences, University of Western Ontario, London, ON N6A 5B7 Canada
AU: Wanger, G
EM: gwanger@uwo.ca
AF: Department of Eart Sciences, University of Western Ontario, London, ON N6A 5B7 Canada
AU: Sherwood-Lollar, B
EM: bsl@quartz.geology.utoronto.ca
AF: Department of Geology, University of Toronto, Toronro, ON M5S 3D1 Canada
AU: Lippmann, J
EM: Lippmann@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegraphenberg, Haus B, 320, Potsdam, 14473 Germany
AU: Seymoor, W
EM: WalterS@harmony.co.za
AF: Geology Department, Evander Gold Mine, Harmony Gold Mining Company Ltd., Evander, 2000 South Africa
AB: The microbial diversity of a 1.83km deep, thermophilic, fluid-filled subterranean fracture was monitored over a three and a half month period and correlated to observed changes in the geochemistry of the system. Three water samples were analyzed using 16S rDNA molecular techniques for microbial diversity, isotopic and geochemical composition. Gibbs' free energy of microbial redox reactions predicted that at in situ conditions sulfate reduction, methanogenesis and acetogenesis should be dominant metabolic pathways utilized by microbes, whereas Fe(III)-reduction should only have been favorable in the last sample. Noble gas isotopic data yielded a subsurface residence time of $\sim$10-100 Myr. and the non-meteoric $\delta$D vs. $\delta^{18}$O values were indicative of water-rock alteration at $<$100$\deg$C. $\delta^{34}$S of sulfide and sulfate differed by 15$\permil$, consistent with fractionation by sulfate reducing bacteria. H$_{2}$ concentrations declined with time, which in conjunction with the $\delta^{34}$S data, suggested that hydrogenotrophic sulfate reducing bacteria dominate the community. This was compatible with 16S rDNA analysis, which yielded clones similar to {\it Desulfotomaculum} and {\it Desulfofustis} species appearing in the three 16S libraries. $\delta^{13}$C and $\delta$D values of CH$_{4}$ and light hydrocarbons indicated methanogenic CH$_{4}$ was mixing with abiogenically formed CH$_{4}$. This is consistent with the presence of Archaeal 16S sequences similar to {\it Methanosaeta} and {\it Methanosarcina} species. The temporal increase in acetate concentration could be attributed to clone types similar to known acetogenic bacteria such as {\it Moorella glycerini}, which were present in the last sample. Clones similar to known Fe(III)-reducing bacteria such as {\it Geovibrio} species were observed in the first and last samples.
DE: 0400 Biogeosciences
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
SC: Biogeosciences [B]
MN: 2003 Fall Meeting