Influence of electron donor on the minimum sulfate concentration required for sulfate reduction in a petroleum hydrocarbon-contaminated aquifer

Fluctuations in the availability of electron donor (petroleum hydrocarbons) affected the competition between sulfate-reducing bacteria (SRB) and methanogenic bacteria (MB) for control of electron flow in a petroleum hydrocarbon-contaminated aquifer. The data suggest that abundant electron donor availability allowed MB to sequester a portion of the electron flow even when sulfate was present in sufficient concentrations to support sulfate reduction. For example, in an area of abundant electron-donor availability, SRB appeared to be unable to sequester the electron flow from MB in the presence of 1.4 mg/L sulfate. The data also suggest that when electron-donor availability was limited, SRB outcompeted MB for available substrate at a lower concentration of sulfate than when electron donor was plentiful. For example, in an area of limited electron-donor availability, SRB appeared to maintain dominance of electron flow at sulfate concentrations less than 1 mg/L. The presence of abundant electron donor and a limited amount of sulfate reduced competition for available substrate, allowing both SRB and MB to metabolize available substrates concurrently.