Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/4515
AuthorsRogers, K. L.* 
Amend, J. P.* 
Gurrieri, S.* 
TitleTemporal Changes in Fluid Chemistry and Energy Profiles in the Vulcano Island Hydrothermal System
Issue Date2007
Series/Report no.6/7(2007)
DOI10.1089/ast.2007.0128
URIhttp://hdl.handle.net/2122/4515
KeywordsHydrothermal systems
Vulcano
Energetics
Geochemistry
Subject Classification03. Hydrosphere::03.04. Chemical and biological::03.04.01. Biogeochemical cycles 
03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters 
03. Hydrosphere::03.04. Chemical and biological::03.04.04. Ecosystems 
03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases 
03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems 
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry 
AbstractIn June 2003, the geochemical composition of geothermal fluids was determined at 9 sites in the Vulcano hydrothermal system, including sediment seeps, geothermal wells, and submarine vents. Compositional data were combined with standard state reaction properties to determine the overall Gibbs free energy (deltaGr) for 120 potential lithotrophic and heterotrophic reactions. Lithotrophic reactions in the H-O-N-S-C-Fe system were considered, and exergonic reactions yielded up to 120 kJ per mole of electrons transferred. The potential for heterotrophy was characterized by energy yields from the complete oxidation of 6 carboxylic acids—formic, acetic, propanoic, lactic, pyruvic, and succinic—with the following redox pairs:O2/H2O, SO4 2-/H2S, NO3 -/NH4+, S0/H2S, and Fe3O4/Fe2+. Heterotrophic reactions yielded 6–111 kJ/mol e-. Energy yields from both lithotrophic and heterotrophic reactions were highly dependent on the terminal electron acceptor (TEA); reactions with O2 yielded the most energy, followed by those with NO3-, Fe(III), SO4 2-, and S0. When only reactions with complete TEA reduction were included, the exergonic lithotrophic reactions followed a similar electron tower. Spatial variability in deltaGr was significant for iron redox reactions, owing largely to the wide range in Fe2+ and H+ concentrations. Energy yields were compared to those obtained for samples collected in June 2001. The temporal variations in geochemical composition and energy yields observed in the Vulcano hydrothermal system between 2001 and 2003 were moderate. The largest differences in deltaGr over the 2 years were from iron redox reactions, due to temporal changes in the Fe2+ and H+ concentrations. The observed variations in fluid composition across the Vulcano hydrothermal system have the potential to influence not only microbial diversity but also the metabolic strategies of the resident microbial communities.
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