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TitleMicrobially-mediated iron mobility in lake sediments: Evidence from 57Fe tracer experiments
AuthorAlpay, S; Gould, W D; Smith, C W; Skaff, M; Lortie, L; Pawlak, M
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts vol. 33, 2008 p. 6-7
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20090253
MeetingJoint Meeting of the Geological Association of Canada, Mineralogical Association of Canada, Society of Economic Geologists and the Society for Geology Applied to Mineral Deposits; Quebec City; CA; May 26-28, 2008
Mediapaper; on-line; digital
Subjectshydrogeology; iron; lake sediments; metals
ProgramPeople Support
AbstractLaboratory simulation experiments were designed to test the hypothesis that lake sediment profiles do not necessarily provide an accurate chronological record of metals in their original order of deposition. The stable isotope, 57Fe, and bacterial enumerations were used to trace microbially-mediated iron transport in experiment columns packed with natural aquatic sediments from an acidic kettle lake within geographic reach of smelter emissions from Rouyn-Noranda, Quebec. Since Fe and Mn oxyhydroxides serve as carrier phases where metals/metalloids frequently co-precipitate or adsorb, post-depositional processes that immobilize Fe likely also affect metal(loid) mobility.
Triplicate sets of column experiments were established with 5 cm of lake sediments overlain by 4 cm of bottom lake water. A 1-cm thick bottom sediment layer included 200 mg of 57Fe-labelled synthetic ferrihydrite incorporated into the homogenized natural sediments. An abiotic control set was identical and was sterilized with gamma radiation. The columns were incubated and destructively sampled at 1-cm depth intervals in a time series.
As the experiments proceeded, iron concentrations in both the bulk sediment and pore water increased in the upper sediment layers and decreased in the lower 57Fe-enriched layer. Over 50% of the total mass of 57Fe was released from the bottom amended sediment layer to pore water, overlying sediments, and the water column over a period of 355 days. In contrast, the parallel series of abiotic control experiments did not show appreciable 57Fe mobility over 161 days of incubation, indicating that the changes in iron distribution in the biotic columns were caused by neither physical disturbance during sampling nor chemical iron reduction and remobilization. The process that initiated Fe transport was microbially-mediated reductive dissolution followed by vertical transport through pore water pathways and re-precipitation/adsorption higher in the sediment profile or release to the overlying water column.
The study demonstrates that lake sediments are not necessarily accurate historical archives of metal deposition and that metal fluxes can occur, not only within the sediments, but also from the sediments to the overlying water. Kinetic control on metal remobilization is enhanced by microbially-mediated processes during early diagenesis.