Monitoring Soil Ecosystem Recovery Following Bioremediation of a Terrestrial Crude Oil Spill With and Without a Fertilizer Amendment

The effect of fertilizer as an amendment in the bioremediation of a terrestrial crude oil spill has been investigated in terms of the subsequent recovery of the soil ecosystem following bioremediation. Two different spills in the same area with different initial hydrocarbon concentrations (33,500 mg kg^-1 and 4,800 mg kg^-1) were compared. At the higher initial hydrocarbon concentration fertilizer addition increased the rate of bioremediation (first-order rate constant of 0.0033 days-1 with fertilizer amendment vs. 0.0020 days-1 without) and resulted in more rapid recovery of soil bacteria (numbers, community structure, diversity) and nematodes (trophic diversity and community structure). The effect of the fertilizer amendment was more significant at the higher initial concentration of crude oil hydrocarbons, presumably due to greater depletion of soil nutrient pools in the absence of the amendment. A second objective of this work was to identify sensitive and cost-effective ecological indicators useful for monitoring the recovery of soil ecosystems impacted by crude oil. Ecological indicators used included: microbial numbers, community structure, and activity as revealed by biomarker analysis (phospholipid fatty acids); nitrogen availability; nematode numbers and community structure (trophic groups and colonizer-persister classes); and ultimately, plant cover and diversity. All ecological indicators investigated were sensitive to disturbances in the soil food web in a hydrocarbon-impacted site. However, nematode community structure analysis offered the greatest sensitivity coupled with low cost and readily available sources for the analysis.