HR: 14:10h
AN: B42C-03    [PDF]
TI: Impact of Iron Oxide Structure on Fe(II)-Catalyzed Reductive Biomineralization
AU: * Hansel, C M
EM: hansel@pangea.stanford.edu
AF: GES Stanford University, Stanford University, Stanford, CA 94305 United States
AU: Benner, S G
EM: sbenner@dri.edu
AF: Hydrologic Sciences, DRI, Las Vegas, NV 89119 United States
AU: Fendorf, S
EM: fendorf@stanford.edu
AF: GES Stanford University, Stanford University, Stanford, CA 94305 United States
AB: Due to the reactivity of ferrous Fe, the fate of Fe(II) following dissimilatory iron reduction will have a profound bearing on biogeochemical cycles. Ferric (hydr)oxides vary from well-ordered phases in mature environments to short-range order minerals such as ferrihydrite in those subject to varying redox conditions. Structural order may have appreciable impacts on the extent and rate of Fe(III) reduction and subsequent Fe(II) generation. Here we compare the reducing capacity, biomineralization, and microbial colonization of goethite and hematite to 2-line ferrihydrite under advective flow. Introduction of organic carbon results in the onset of reduction of all three Fe phases. Although overall surface area normalized reduction rates are equivalent, the extent of Fe(III) reduction and fate of Fe(II) differs among the three systems. The amount of Fe(III) reduced within the ferrihydrite, goethite, and hematite columns is 25, 5, and 1%, respectively. While 83% of Fe(II) produced in the ferrihydrite system is retained within the solid-phase, merely 17% is retained by goethite and hematite. The fate of Fe(II) within all three systems involves sequestration of Fe(II) within magnetite yet the degree of conversion varies as a function of Fe(II) production. Goethite and hematite illustrate a similar control on Fe(II) dynamics, where Fe(II) primarily remains in the aqueous phase and is eluted from the system. Despite differences in initial reduction and sequestration, subsequent Fe(II) generation and accumulation within the three Fe oxides reaches an equivalent steady-state (300 h), where similar aqueous Fe(II) concentrations, cell colonization, and Fe(III) reduction rates are supported. The decline in microbial reduction is, most likely, due to preferential consumption of higher energy surface sites via reductive dissolution and magnetite nucleation, regardless of oxide structural order and surface area. Due to the transient nature of reactive sites on ferrihydrite, prolonged microbial reduction and colonization of ferrihydrite may not differ substantially from that of goethite and hematite. Given the greater abundance of crystalline iron oxides in the environment, reduction of phases such as goethite and hematite may impart an equivalent or potentially greater impact on sustained Fe(II) generation and sequestration.
DE: 4805 Biogeochemical cycles (1615)
DE: 4840 Microbiology
DE: 4851 Oxidation/reduction reactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting