Influence of Water Flow on In Situ Rates of Bacterial Fe(II) Oxidation

A survey of a low-flow wetland drainage channel rich in flocculent bacteriogenic iron oxide (BIOS) deposits was conducted to investigate the in situ kinetic behaviors of bacterial Fe(II) oxidation and its dependence on water flow. On the basis of analytical solutions to the advection-dispersion-reaction (ADR) equation and the channel's Fe(II) concentration profile, the pseudo-first order rate constant for Fe(II) oxidation () was 0.78 +/- 0.20 min(-1). The difference in this estimate from that obtained in a previous study on a lotic groundwater discharge channel with an intact BIOS mat (1.70 +/- 0.20 min(-1)) demonstrates the effects of water flow on Fe(II) oxidation kinetics in circumneutral pH, Fe(II)-rich settings. Importantly, these results also re-emphasize the discrepancies between rates obtained from in situ geochemical data and those of conventional ex situ batch studies in assessing the dependencies of in situ reaction rates on water flow and reactive transport across a range of hydraulic regimes characterizing natural systems.