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MONITORING OXIDATION-REDUCTION PROCESS DURING GROUND WATER-SURFACE WATER INTERACTIONS AT THE CHICKASAW NRA
Citation:
Wilkin*, R T. MONITORING OXIDATION-REDUCTION PROCESS DURING GROUND WATER-SURFACE WATER INTERACTIONS AT THE CHICKASAW NRA. 2001.
Description:
Mineralized ground waters at the Chickasaw National Recreational Area contain hydrogen sulfide, i.e., sulfur in the -2 valence state. As these mineralized ground waters discharge at the surface and mix with oxygen-rich waters a series of abiotic and biotic reactions occur that convert sulfur from the reduced form to elemental sulfur (0 valence state) and finally to sulfate (+6 valence state). The reaction pathway and rate of this redox transformation is being studying using field and laboratory geochemical techniques. Platinum electrode measurements of Eh do not correspond to the equilibrium Nernstian relationship predicted from the half-cell reaction: HS- = S + 2e- + H+. The greatest deviation from Nernstian behavior is observed at the Hillside Spring where hydrogen sulfide concentrations are <1 ppm; whereas, near-equilibrium conditions are present at Vendome where hydrogen sulfide concentrations are >5 ppm. Non-Nernstian behavior, apparently characteristic of ground water-surface water interactions, is likely a result of a mixed-potential electrode response to the sulfide-elemental sulfur half-cell reaction and the oxygen-water half-cell reaction. These findings better define the conditions for appropriate interpretations of Eh measurements within the context of equilibrium and non-equilibrium processes.