Characterization of redox processes in shallow groundwater of Owens Dry Lake, California.

Redox status of shallow groundwaters (1-3 m depths) at Owens Dry Lake was studied to help guide mitigation efforts for attenuating dust generation from the dry lakebed. Redox conditions were characterized by Eh, oxidative capacity (OXC), and terminal electron accepting processes (TEAPs) as well as examining the energetics of TEAPs. Groundwater chemistry related to redox status was determined by major solute concentrations, dissolved gases (O2, H2, CH4), aqueous redox species (NO3, Mn2+, Fe2+/ Fe3+, SO4(2-)/HS-, DOC), and major redox sensitive components in the solid phase (extractable Fe/Mn). All of these measures of redox status indicate that sulfate reduction is the major process regulating redox conditions in most shallow groundwaters of Owens Dry Lake. Dissolved sulfate concentrations were regulated primarily by evaporation resulting in increasing concentrations as water migrates from the shoreline (<1 mM) to the center (up to 417 mM) of the dry lakebed. Eh values were generally in the range of -240 to -170 mV. The oxidative capacity demonstrates the dominant contribution of sulfate to OXC. The dominance of sulfate restricts further redox development, such as methanogenesis. Dissolved H2 concentrations ranged from 0.5 to 7.8 nM. According to the empirically defined H2 ranges, sulfate reduction was the most predominant TEAP. Moreover, thermodynamic calculations of TEAPs for H2 utilization support favorable energetics for both sulfate reduction and methanogenesis. The calculated available energy yield for sulfate reduction in the shallow groundwater of Owens Dry Lake was higher than other systems due to the high sulfate concentration.