USE OF DISSOLVED H(2) CONCENTRATIONS TO DETERMINE DISTRIBUTION OF MICROBIALLY CATALYZED REDOX REACTIONS IN ANOXIC GROUNDWATER

The potential for using concentrations of dissolved H-2 to determine the distribution of redox processes in anoxic groundwaters was evaluated. In pristine aquifers in which standard geochemical measurements indicated that Fe(III) reduction, sulfate reduction, or methanogenesis was the terminal electron accepting process (TEAP), the H-2 concentrations were similar to the H-2 concentrations that have previously been reported for aquatic sediments with the same TEAPs. In two aquifers contaminated with petroleum products, it was impossible with standard geochemical analyses to determine which TEAPs predominated in specific locations. However, the TEAPs predicted from measurements of dissolved H-2 were the same as those determined directly through measurements of microbial processes in incubated aquifer material. These results suggest that H-2 concentrations may be a useful tool for analyzing the redox chemistry of nonequilibrium groundwaters.