Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/2004
Publication Date: 12/15/2004
Citation: Ryu, J., Dahlgren, R.A., Gao, S., Tanji, K. 2004. Characterization of Redox Processes in Shallow Groundwater of Owens Dry Lake, California. Environmental Science and Technology, Vol 38, pp 5950-5957. Interpretive Summary: Redox conditions regulate aqueous biogeochemistry thus the fate of toxic elements because the oxidation state of elements affects their solubility, adsorption behavior, toxicity, and distribution between solid, aqueous and gas phases. This information is particularly important in assessing vegetation recovery effort in reducing dust generation at Owens Dry Lakebed area. Redox conditions of the shallow groundwaters were characterized using Eh measurement, oxidative capacity (OXC) and terminal electron accepting processes (TEAPs), as well as examining the energetics of TEAPs. Sulfate reduction was the major process regulating redox conditions in most shallow groundwaters of Owens Dry Lake. Thermodynamic calculations showed that available energy yield for sulfate reduction in the shallow groundwater was higher than other systems due to the high sulfate concentration. This is one of the few studies thoroughly examining redox status in a natural saline and alkaline system. This study provides an important view of the chemical and physical processes controlling the redox of a saline groundwater and may serve as a template to others working in redox chemistry of saline systems.
Technical Abstract: 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 (oxygen, hydrogen gas, methane), aqueous redox species (nitrate, Mn(II), Fe(II)/Fe(III), sulfate/hydrogen sulfide, dissolved organic carbon), 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 '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 hydrogen gas 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.