The Redox and Iron-Sulfide Geochemistry of Salt Pond and the Thermodynamic Constraints on Native Magnetotactic Bacteria

Peter Canovas III, S.M., 2006
Katrina Edwards, Wolfgang Bach, Advisors

Salt pond is a meromictic system with a density contrast allowing for the formation of a chemocline that is the habitat for magnetotactic bacteria (MB). The spatial and temporal distribution of MB in the system along with geochemical (Fe2+, H2S, pH, O2 (aq), etc.) profiles have been analyzed from 2002 – 2005. Magnetite-producing cocci occupy the top of the chemocline and greigite-producing MB occur at the base of the chemocline and in the sulfidic hypolimnion. This distribution may be attributed to analyte profiles within the pond; depth profiles show a sudden drop of dissolved oxygen at the chemocline associated with an increase in dissolved Fe (II) where both O2 and H2S are low. In the sulfidic hypolimnion, Fe (II) concentrations decrease, suggesting buffering of Fe(II) by sulfide phases. Stability diagrams within EH/pH space and measured voltammetric data verify fields of incomplete oxidation resulting in the production of elemental sulfur, thiosulfate and polysulfides. Calculations of the Gibbs free energy indicate abundent potential energy available for metabolic growth. Iron can be permenantly sequestered by MB into the sediments after death because the organelles containing the iron phases are resistant to degredation. Geochemical and microbial processes relating to the cycling of iron heavily impact this system and others that contain a chemocline.