TEMPORAL AND SPATIAL CHANGES OF TERMINAL ELECTRON-ACCEPTING PROCESSESIN A PETROLEUM HYDROCARBON-CONTAMINATED AQUIFER AND THE SIGNIFICANCE FOR CONTAMINANT BIODEGRADATION

Measurements of dissolved hydrogen and other biologically active solut es in groundwater from a shallow petroleum hydrocarbon-contaminated aq uifer indicate that the distribution of microbial terminal electron-ac cepting processes (TEAPs), such as methanogenesis, sulfate reduction, and ferric iron (Fe (III)) reduction, is highly dynamic in both time a nd space. Delivery of sulfate to methanogenic zones by infiltrating re charge or lateral transport can result in a TEAP shift from methanogen esis to sulfate reduction. Conversely, lack of recharge and consumptio n of available sulfate can result in a shift from sulfate reduction to methanogenesis. Temporal shifts between sulfate and Fe (III) reductio n were also observed. Time lags associated with TEAP shifts ranged fro m less than 10 days to about 3 1/2 months. The relation between TEAP a nd biodegradation rates of a variety of organic compounds indicate tha t biodegradation rates of petroleum hydrocarbons probably vary tempora lly and spatially in a contaminated aquifer.