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THE NEAR-EQUILIBRIUM OF MICROBIALLY MEDIATED REDOX COUPLES IN REDUCING GROUNDWATER ENVIRONMENTS
Citation:
Washington, J W. THE NEAR-EQUILIBRIUM OF MICROBIALLY MEDIATED REDOX COUPLES IN REDUCING GROUNDWATER ENVIRONMENTS. Presented at 220th American Chemical Society National Meeting, Washington, DC, August 20-24, 2000.
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
Redox couples are commonly held to be in disequilibrium among each other in most natural waters. To evaluate this view for microbially mediated, reducing, groundwater environments, monitoring data were examined for several couples under conditions ranging from nitrate-detectable to sulfide-precipitating. For these data, iron and sulfur redox couples show close consistency. Several samples were in approximate equilibrium with goethite, siderite and mackinawite, a condition that is promoted by oxidation of organic material via a negative feedback in the reaction stoichiometry. The ammonia/nitrate redox couple generally equated to redox values inconsistent with those of iron and sulfur. The Mn2+/Mn-oxide couple gave redox values that are inconsistent with the iron, sulfur and nitrogen couples. Analysis of previously published literature shows approximate consistency for redox couples involving Fe, S, H2 and CH4 for microbially mediated groundwater environments in many areas. Hence, it appears that reducing groundwater environments often reach near-equilibrium with a common effective redox state for several redox couples.