Influence of substratum on the degradation processes in diesel polluted sub-Antarctic soils (Crozet Archipelago)

Biodegradation by naturally occurring populations of microorganisms is a major mechanism for the removal of oil hydrocarbons from the environment. Therefore, follow-up of bacterial populations and chemical indices of biodegradation are important components of contaminated site assessment studies. Over a 4-year period following an accidental diesel contamination of the sub-Antarctic Crozet Archipelago (51 degrees 51'E-46 degrees 25'S), a field study was carried out in the contaminated area that is located in a transition zone between an arid fell-field (upstream) and a wet vegetated area (downstream). This study included a monitoring of heterotrophic and hydrocarbon-degrading bacterial abundance and chemical analysis of the remaining hydrocarbons. Significant higher number of heterotrophic and hydrocarbon-degrading bacterial counts revealed a rapid acclimation of sub-Antarctic microbial soil communities to the diesel fuel contamination. A chemical survey conducted during the last 2 years (2002 and 2003) showed that the total extractable hydrocarbons (TPH) content in arid fell field was reduced to <= 50% of their value while it was reduced only to <= 65% in vegetated soil. In addition, the decrease of TPH was always higher in the presence of fertilizer in the arid contaminated area, while fertilizer addition was almost inefficient in the wet contaminated one. All these results demonstrate a serious influence of the soil properties on the degradation rate. However, all chemical indices showed a significant reduction of alkanes and light aromatics in both contaminated area confirming a regular oil degradation process.