Role of Iron in the Biodegradation of Fuel Hydrocarbons

In aquifers contaminated by petroleum hydrocarbons, subsurface microorganisms may use ferric iron as an electron acceptor to oxidize dissolved contaminants after oxygen and nitrate are depleted. The available evidence suggests that iron reduction can have significant effects on contaminant fate and transport. However, the exact mechanism of microbial iron reduction is still poorly understood. In this project, we will test the hypothesis that the rate of petroleum hydrocarbon degradation via iron reduction is strongly influenced by the spatial distribution of bioavailable iron in the subsurface. Ongoing research in related areas supports this hypothesis. In this Phase I study, we will characterize a small portion of a hydrocarbon contaminated aquifer where active iron reduction is occurring. We will characterize spatial variations in aqueous and solid phase geochemistry, hydraulic properties, and microbial populations, and measure spatial variations in anaerobic hydrocarbon degradation rates. Results will be used in combination with geochemical models and advection-dispersion-decay models to evaluate the effects of heterogeneity on macroscale degradation and precipitation/dissolution reactions. In Phase II, we will develop: (1) a more fundamental understanding of the interactions of the microbes with the iron mineral surfaces; and (2) mechanistic models that can relate small-scale heterogeneity in aquifer characteristics and microbial populations to large-scale plume behavior.