HR: 08:30h
AN: B11A-02    [PDF]
TI: Characterization of Newly-Formed Manganese (Hydr)oxides in Biofilms in Pinal Creek, Arizona
AU: Gilbert, H
EM: hanna@hwr.arizona.edu
AF: University of Arizona, Department of Hydrology PO Box 21001, Tucson, AZ 85721 United States
AU: * Conklin, M
EM: mconklin@ucmerced.edu
AF: University of California, Merced, School of Engineering PO Box 2039, Atwater, CA 95344 United States
AU: O'Day, P
EM: poday@ucmerced.edu
AF: University of California, Merced, School of Natural Sciences PO Box 2039, Atwater, CA 95344 United States
AB: Active, biologically mediated precipitation of manganese (hydr)oxides (Mn-oxides) in Pinal Creek, Arizona, a stream with a history of high manganese levels due to historic mining practices, was studied to determine the identity of newly formed phases and their ability to sequester other metals. Packages of crushed grains of eight clean mineral substrates, quartz, ilmenite, microcline, rutile, magnetite, hematite and labradorite, were placed in Pinal Creek for one to three months. Glass slides were set out as well in order to characterize biofilm formation. After retrieval and drying, the coating distributions were characterized using scanning electron microscopy (SEM), energy dispersive analysis, and X-ray absorption spectroscopy. Morphologically, coating material developed on the different substrates after one month appeared similar to those developed after two and three months. Overall, the SEM images indicate poorly crystalline, aggregated particles that are small (less than a few microns in general) and lack geometric regularity, although size estimates are somewhat hindered by particle aggregation. The coatings that formed on the microscope slides are characterized as biofilms, as numerous microorganisms were observed using microscopy, both confocal and SEM. Samples were further characterized using extended x-ray absorption fine structure spectroscopy (EXAFS) on coatings that had been separated from mineral substrates. EXAFS spectra of material from rutile and quartz substrates and the biofilm were analyzed and fit, using a natural and synthetic birnessite compounds as reference spectra. This analysis suggests that the rutile, quartz, and biofilm samples are composed of a disordered Mn-oxide that is similar in local structure to a natural birnessite of low symmetry. The formation of disordered, poorly crystalline birnessite is important, as it is an extremely efficient metal scavenger and the interlayer vacancies in the birnessite structure aids in metal sequestration.
DE: 0400 Biogeosciences
DE: 1030 Geochemical cycles (0330)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting