Bioremediation is being used or proposed as a treatment option at many hydrocarbon-contaminated sites, including sites in the Arctic. One such site is a former bulk-fuel storage facility near Barrow, Alaska, where contamination persists after approximately 380 m3 of JP-5 were spilled in 1970. The soil at the site is primarily fine gravel with low organic carbon (< 1%) and low moisture (1-3%) contents. We examined the effects of nutrient additions on microorganisms in contaminated soil from this site in laboratory microcosms and in mesocosms incubated for 6 weeks in the field. Nitrogen was the major limiting nutrient in this system, but microbial populations and activity were maximally enhanced by additions of both nitrogen and phosphorus. When nutrients were added to soil in the field at three levels of N:P (100:45, 200:90 and 300:135 mg/kg), the greatest stimulation in microbial activity occurred at the lowest, rather than the highest, level of nutrient addition. After six weeks of field incubation, semi-volatile hydrocarbon concentrations were higher in soils that received the highest fertilizer concentration than in unfertilized reference plots. We hypothesize that the decline in microbial activity with increasing levels of fertilizer is related to the low soil-moisture at the site. The total soil water potentials ranged from -2 to -15 bars with increasing levels of fertilizer. The low soil-moisture conditions that prevail at this and many arctic sites are exacerbated by low annual precipitation and the presence of shallow permafrost. These results indicate that an understanding of nutrient effects at a specific site is essential for successful bioremediation.
JOAN F. BRADDOCK Institute of Arctic Biology University of Alaska Fairbanks Fairbanks, Alaska 99775-7000 phone: (907) 474-7991 fax: (907) 474-6967 e-mail: ffjfb@aurora.alaska.edu JAMES L. WALWORTH Palmer Research Center University of Alaska Fairbanks Fairbanks, Alaska 99645 KATHLEEN A. McCARTHY U.S. Geological Survey - Water Resources Division 10615 SE Cherry Blossom Drive Portland, Oregon 97216