HR: 1340h
AN: B33A-0843    [Abstracts]
TI: Seasonal Changes in the Biogeochemistry of Bacteriogenic Iron Oxides in a Groundwater- Supplied Wetland
AU: * Gault, A G
EM: agault@uottawa.ca
AF: University of Ottawa, Department of Earth Sciences, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada
AU: Ibrahim, A
AF: University of Ottawa, Department of Earth Sciences, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada
AU: Langley, S
AF: University of Ottawa, Department of Earth Sciences, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada
AU: Renaud, R
AF: AECL, Chalk River Laboratories, Chalk River, ON K0J 1J0, Canada
AU: Clark, I D
AF: University of Ottawa, Department of Earth Sciences, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada
AU: Fortin, D
AF: University of Ottawa, Department of Earth Sciences, 140 Louis Pasteur, Ottawa, ON K1N 6N5, Canada
AU: Ferris, G
AF: University of Toronto, Department of Geology 22 Russell Street, Toronto, ON M5S 3B1, Canada
AB: Bacteriogenic iron oxides (BIOS), composed of a mixture of poorly ordered hydrous ferric oxides and intact and partially decomposed bacterial cells, are thought to play an important role in regulating aqueous trace element concentrations in groundwater-supplied wetland environments. We have initiated a study examining the seasonal variation in the biogeochemistry of BIOS and its role in contaminant sequestration in a wetland site at Chalk River, Ontario, Canada, an area that hosts an exceptional abundance of BIOS. Surficial BIOS and subsurface cores were collected in spring (April) and summer (July) for microbial and bulk geochemical characterization. In addition, dialysis `peepers` samplers were deployed to examine the changes in selected dissolved elements with depth. SEM inspection of representative BIOS samples found a predominance of sheaths similar to Leptothrix spp., Fe(II)-oxidizing microbes known to thrive in the circumnetural pH, high dissolved Fe(II) (up to 5 mg L^-1) and low dissolved oxygen (<5 mg L^-1) environment found at the groundwater springs of our study site. Helical stalks reminiscent of iron-oxidizing Gallionella spp. were also occasionally observed. The BIOS mineralogy was dominated by 2-line ferrihydrite, although interestingly samples collected further downstream from the groundwater discharge zone appear more closely related to 6-line ferrihydrite. Iron reduction was noted at depth in both the sedimentary and porewater profiles, with the dissolved Fe(II) peak in the latter occurring at shallower depths in summer compared to the spring. Strontium, a contaminant of concern at this site, showed little seasonal variation, but its concentration was broadly correlated with that of dissolved iron and manganese. In addition, porewater strontium concentrations were 2-3 fold higher at a nearby control site where BIOS was absent, indicating the likely importance of BIOS in attenuating migration of this contaminant.
DE: 4875 Trace elements (0489)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting