HR: 0830h
AN: B41D-0930    [PDF]
TI: What explains the sulfur isotope fractionation observed in the aquifer system of Puebla Valley, Mexico?
AU: * Velazquez-Oliman, G
EM: gvo@geol.niu.edu
AF: Northern Illinois University, Geology and Environmental Geosciences, DeKalb, IL 60115 United States
AU: Perry, E C
EM: T60ecp1@wpo.cso.niu.edu
AF: Northern Illinois University, Geology and Environmental Geosciences, DeKalb, IL 60115 United States
AU: Leal-Bautista, R M
EM: rlb@geol.niu.edu
AF: Northern Illinois University, Geology and Environmental Geosciences, DeKalb, IL 60115 United States
AU: Lenczewski, M E
EM: melissa@geol.niu.edu
AF: Northern Illinois University, Geology and Environmental Geosciences, DeKalb, IL 60115 United States
AB: Puebla Valley, Mexico is located in the central part of the Trans Mexican Volcanic Belt and is surrounded by 3 large volcanoes: Popocatepetl (active since 1994), Iztaccihuatl (extinct), and Malinche (dormant). The aquifer system of the Valley contains at least two productive units: an unconfined aquifer formed mainly of alluvial and volcanic deposits and a second, confined aquifer, which has chemically distinct water that is sulfur-rich, high in CO$_{2}$, and high in alkalinity. There is a current debate about the origin of the sulfur-rich water, which is being used, after treatment, to lessen the deficit of water supply to the city of Puebla (with a population of approximately 1.5 million). Sulfate and sulfide species in water from the confined aquifer have an average sulfur isotope fractionation difference of 24.6 %. This fractionation is, at least in part, the result of bacterial sulfate reduction as evidenced by testing for bacteria with BART kits. Molecular analysis to identify the specific bacteria is underway. However, analysis of carbon isotopes of dissolved CO$_{2}$ (with average delta $^{13}$C of 4.4%) and $^{3}$He/$^{4}$He with average ratios of 2.1 for specific wells, located in the upper aquifer and characterized by having low sulfate but also rich in CO$_{2}$ and alkalinity, suggest a possible magmatic component. The carbon and helium isotope analysis of water from the confined aquifer is currently underway.
DE: 1030 Geochemical cycles (0330)
DE: 1045 Low-temperature geochemistry
DE: 4803 Bacteria
SC: Biogeosciences [B]
MN: 2003 Fall Meeting