Hydrologic Flow Controls on Biologic Iron(III) Reduction in Natural Sediments

Abstract

Bacterial reduction of a hematite-rich natural coastal sand was studied in flow-through column reactors at flow rates which varied from 0.62 to 11 pore volumes d(-1). Sand columns were wet-packed with the dissimilatory metal-reducing bacterium (DMRB) Shewanella putrefaciens CN32, and a PIPES-buffered, lactate-containing growth medium was pumped through the columns for over 20 days. Soluble Fe(II), acetate and lactate concentrations measured in the column effluents showed that steady-state conditions were established after a few days with every flow rate. The steady-state effluent Fe(II) concentration was directly controlled by the flow rate where [Fe(II)]ss decreased as the flow rate increased. Increased flow rate increased biologic activity based on the steady-state flux of soluble Fe(II) and total Fe(II) production (included Fe(II) extracted from sand at the conclusion of the experiment), decreased the fraction of lactate oxidized for energy that likely increased cell synthesis, and decreased the concentration of sorbed Fe(II) that, in turn, decreased the relative percentage of Fe(II) retained by the column materials. Increased biologic activity was likely promoted by greater reactant delivery (i.e., lactate, N, P) and greater advective removal of Fe(II). These results demonstrate that biologic Fe(II) reduction, cell growth, and abiotic Fe(II) sorption are all coupled to the hydrologic flow rate.

Solute transport in low‐heterogeneity sandboxes: The role of correlation length and permeability variance

“…A wet packing procedure [ Minyard and Burgos , ] was used to prevent the trapping of air bubbles in the porous media that can lead to pore clogging and change of permeability. The packing was done layer by layer to remove air and to establish different zones.…”

Microbial Reducibility of Fe(III) Phases Associated with the Genesis of Iron Ore Caves in the Iron Quadrangle, Minas Gerais, Brazil

“…As a result, BIF/iron ore experience extensive water circulation and associated weathering, especially in the Iron Quadrangle, which receives approximately 1.5 m/year of rain [6][7][8]. This hydrologic flow may enhance Fe(III) bioreduction by delivering organic electron donor and nutrients to support FeRB activities [48], while exporting biogenic Fe(II), and consequently alleviating Fe(II)-induced inhibition of Fe(III) reduction [48][49][50]. Indeed, while complete bioreductive dissolution of crystalline Fe(III) phases is rarely observed in batch incubations, nearly complete reduction of goethite (α-FeOOH) was achieved in continuous-flow columns inoculated with the FeRB S. putrefaciens CN32 [51].…”

Aggregate-scale spatial heterogeneity in reductive transformation of ferrihydrite resulting from coupled biogeochemical and physical processes

“…The physical and chemical environments in which bacterial Fe(III) reduction takes place determine the rate and extent of reduction and the mineralogy of the secondary mineral phases (Fredrickson et al, 1998;Zachara et al, 2002;Minyard and Burgos, 2007). The reductive transformation of ferrihydrite depends on a number of geochemical variables (e.g., pH, presence of Fe complexing ligand, etc.)…”