Microbial activity in hydrocarbon-contaminated soil was characterized and quantified to determine the potential for natural attenuation at a former oil field in California. Plate counts, direct microscopic counts, and carbon dioxide and methane production rates were used to quantify the populations and activity of soil microorganisms. Terminal restriction fragment (TRF) analysis provided preliminary identification of dominant microorganisms and community shifts as depth and contaminant concentrations changed. Plate counts under aerobic conditions resulted in 1.5 to 22 × 106 colony-forming units (CFU) per gram of soil, and direct microscopic counts of total bacteria were 3 to 33 × 106 cells per gram. Carbon dioxide production rates of 1.3 to 5.5 μL CO2/g soil per day were measured in the aerobic samples. Methane production rates in sealed anaerobic microcosms were higher in samples with more highly contaminated soil, and ranged from 0 to 20.9 ppmv CH4/day. Terminal restriction fragment analysis revealed the presence of three distinct microbial communities at the site. The aerobic non-contaminated zone included Actinomyces, Pseudomonas, and other microorganisms. The transition zone included Streptomyces, and the zone with the highest TPH concentrations was characterized by microorganisms including Mycobacteria and Actinobacteria. Communities of both aerobic and anaerobic bacteria appear to be biodegrading hydrocarbons in situ.
Available at: http://works.bepress.com/ckitts/5/