Effect of iron bioavailability on dissolved hydrogen concentrations during microbial iron reduction

Area of Science:

• Environmental microbiology
• Geochemistry
• Biogeochemical cycling

Background:

• Dissolved hydrogen (H2) concentrations correlate with terminal electron accepting processes (TEAPs) in aquifers.
• Iron reduction is a significant TEAP in many subsurface environments.
• Understanding factors influencing H2 concentrations during iron reduction is crucial for environmental monitoring.

Purpose of the Study:

• To investigate the effect of iron bioavailability on dissolved hydrogen (H2) concentrations during microbial iron reduction.
• To assess the utility of H2 as an indicator for monitoring iron reduction rates and bioavailability.
• To examine the role of 9,10-anthraquinone-2,6-disulfonic acid (AQDS) in influencing iron reduction and H2 production.

Main Methods:

• Flow-through column experiments using soil from the Field Research Center (FRC), Oak Ridge, TN.
• Amending soil with acetate as an electron donor and inoculating with Geobacter sulfurreducens.
• Measuring dissolved H2 concentrations over extended periods (500 days and 100 days).
• Utilizing AQDS to manipulate iron bioavailability and assess its impact on iron reduction and H2 levels.

Main Results:

• Iron reduction was identified as the dominant TEAP in the FRC soil columns.
• The addition of AQDS significantly increased the rate of iron reduction.
• Steady-state H2 concentrations decreased from an average of 4.0 nM (without AQDS) to 2.0 nM (with AQDS).
• H2 concentrations fluctuated but averaged around 3.9 nM in the initial 500-day experiment.

Conclusions:

• Dissolved hydrogen (H2) concentrations are sensitive to changes in iron bioavailability and reduction rates.
• H2 can serve as a valuable real-time indicator for monitoring the dynamics of microbial iron reduction in aquifers.
• Bioavailability, influenced by compounds like AQDS, plays a critical role in controlling iron reduction and associated H2 production.