Natural Attenuation of Oil-Polluted Peat Bog Soil in a Long-Term Field Experiment

The damaging effects of oil pollution on oligotrophic peat bog soil (Rheic Fibric Histosol), as well as the patterns of its natural attenuation processes, were studied in a long-term field experiment with varying oil concentrations (oil product content from 11 to 45% of the air-dry soil mass) in the Luga district of Leningrad region. It was found that at the minimum level of oil pollution tested in the experiment, vegetation condition, assessed by species composition and projective cover, and soil biological activity, determined by basal respiration and the environment-regulating capacity of soil microorganism complex, did not differ from the control. However, at the maximum pollution level of 45% oil products, severe disturbance of both vegetation and soil biological activity was observed—up to 70% of the control. Under fresh contamination, the total projective cover of vegetation and biological activity of soil were inversely related to the oil product content, with approximation reliability of 0.91 ± 0.21 and 0.92 ± 0.19, respectively. Within 20 years of the oil spill, vegetation in the experimental plots had completely recovered, with a new moss layer 10–15 cm thick forming (growing) on the surface of the experimental sites. The oil-contaminated peat layer was buried at a depth of 15–20 cm. Biological activity in the buried layer was significantly suppressed under all levels of contamination, and the oil product content in it remained virtually unchanged over the 20-year experiment. Thus, oil contamination was preserved within the peat bog soil while vegetation on its surface has fully recovered.