October 1992

Document Type


Degree Name



Dept. of Environmental Science and Engineering


Oregon Graduate Institute of Science & Technology


Leaking underground storage tanks contaminate soils and groundwater with petroleum hydrocarbons. The objective of this research was to better understand hydrocarbon biodegradation in soil by examining the effects of soil moisture content, temperature, hydrocarbon concentration, hydrocarbon chain length, and nutrient additions on hydrocarbon biodegradation rates. Hydrocarbon biodegradation was examined in serum-bottles containing an unsaturated sandy soil incubated aerobically with hydrocarbons and various added nutrients. A majority of the experiments used propane and butane as catabolic substrates. Temperature (15-20°C) and water contents (>75% of field capacity) had little effect on hydrocarbon biodegradation. Hydrocarbon concentrations greater than 0.5% of the serum-bottle headspace inhibited biodegradation unless the organisms were previously exposed to a lower concentration. Nutrient limitation studies showed that fixed nitrogen (N) was initially a limiting nutrient, but that N-limitation could be overcome by N2 fixation under some conditions. Propane and butane degradation proceeded similarly during the first 3 months of incubation. Bacteria in soil amended with N oxidized these hydrocarbons more rapidly than in controls without nutrient additions or in soil with added phosphate or trace minerals. Both propane- and butane-amended soil apparently became N-limited after the initial bioavailable N was utilized, as indicated by a decrease in degradation rates. After 3 months, propane and butane degradation proceeded differently. Propane-degrading soil apparently remained N-limited, because degradation rates stayed low unless more N was added. In contrast, butane-degrading soil appeared to overcome its N-limitation, because degradation rates continued to increase regardless of whether more N was added. Total-N analyses and acetylene-reduction assays supported this apparent surplus of N in butane amended soil. Total N was significantly (P<.01) higher in soil incubated with butane and no N amendments than in soil incubated with propane, even when the latter was amended with N. Acetylene reduction occurred only in butane-amended soil. These results indicate that N2 fixation occurred in butane-amended soil, but not in propane-amended soil.





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