Rates of biodegradation and volatilization were documented twice 12 yr apart at a crude-oil spill site near Bemidji. Minnesota. Model results indicated that the coupled pathway has resulted in significant hydrocarbon mass loss at the site, and it was estimated that ??? 10.52 kg/day were lost in 1985 and 1.99 kg/day in 1997. In 1985, 3% of total volatile hydrocarbons diffusing from the floating oil were biodegraded in the lower 1 m of the unsaturated zone and increased to 52% by 1997. Rates of hydrocarbon biodegradation above the center of the floating oil were relatively stable from 1985 to 1997, as the primary metabolic pathway shifted from aerobic to methanogenic biodegradation. Model results indicate that in 1997 biodegradation under methanogenic conditions represented ??? 50% of total hydrocarbon biodegradation in the lower 1 m of the unsaturated zone. Further downgradient, where substrate concentrations have greatly increased, total biodegradation rates increased by greater than an order of magnitude from 0.04 to 0.43 g/sq m-day.
Additional publication details
Long-term evolution of biodegradation and volatilization rates in a crude oil-contaminated aquifer