Microbial dynamics in oil-impacted prairie soil

A remote site in the Tallgrass Prairie Preserve (Osage County, OK) was cont aminated with crude oil by a pipeline break in 1992. In 1996, the contamina ted soil was bioremediated by blending with uncontaminated soil, prairie ha y, buffalo manure, and commercial fertilizers, and spreading in a shallow l ayer over uncontaminated soil to create a landfarm. The landfarm was monito red for two years for aerobic and anaerobic bacteria, soil gases indicative of microbial activity, and for changes in the concentration of total petro leum hydrocarbons (TPH). Levels of hydrocarbon degraders and soil gas indic ators of aerobic degradation were stimulated in the landfarm during the fir st warm season relative to uncontaminated prairie soil. However, these same indicators were less conclusive during the second warm season, indicating depletion of the more easily degradable hydrocarbons, although the landfarm still contained 6,800 mg/kg TPH on the average at the beginning of the sec ond warm season. Methane formation and methanogen counts were clearly stimu lated in the first warm season relative to uncontaminated prairie soil, ind icating that methanogenesis plays an important role in the mineralization o f hydrocarbons even in these shallow soils.