Long-Term Effects of Crude Oil Contamination and Bioremediation in a Soil Ecosystem

Abstract

Analysis of samples taken from three experimental soil lysimeters demonstrated marked effects on the soil chemistry and on bacterial, fungal, nematode, and plant communities 3 years after the application of crude oil. The lysimeters are located at the Amoco Production Research Environmental Test Facility in Rogers County, Oklahoma, where they had been installed to evaluate the effectiveness of managed (application of fertilizer and water, one lysimeter) vs. unmanaged bioremediation (one lysimeter) of Michigan Silurian crude oil compared to one uncontaminated control lysimeter. Five 2-foot-long soil cores were extracted from each lysimeter, each divided into three sections, and the like sections were mixed together to form composited soil samples. All subsequent chemical and microbiological analyses were performed on these nine composited samples. Substantial variation was found among the lysimeters for certain soil chemical characteristics [% moisture. pH, total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH4-N), phosphate phosphorus (PO4-P), and sulfate (SO4 −2)]. The managed lysimeter had 10% the level of total petroleum hydrocarbons (TPH) of the unmanaged lysimeter. Assessment of the microbial community was performed for heterotrophic bacteria, fungi, and aromatic hydrocarbon-degrading bacteria (toluene, naphthalene, and phenan-threne) by dilution onto solid media. There was little difference in the number of heterotrophic bacteria, in contrast to counts of fungi, which were markedly higher in the contaminated lysimeters. Hydrocarbon-degrading bacteria were elevated in both oil-contaminated lysimeters. In terms of particular hydrocarbons as substrates, phenanthrene degraders were greater in number than naphthalene degraders, which in turn outnumbered toluene degraders. Levels of sulfate-reducing bacteria seem to have been stimulated by hydrocarbon degradation. Nematodes were extracted from soil samples, identified as to genus, and classified according to their mode of nutrition. All vegetation and roots were removed from each lysimeter after the soil samples were taken, representative plants were pressed for identification, and the dry weight of all plants (total biomass) for each lysimeter was determined. The plant species were predominantly those typically found in disturbed habitats. The greatest number of species was found in the control lysimeter, but the total biomass was highest in the managed lysimeter.