The aim of this study was to evaluate the impact of oil exploitation on soil nematode communities. Six oil wells (N46°39'30″-46°41'0″; E124°53'30″-124°58'30″) were selected in the Daqing Oilfield, away from villages and in a homogeneous environment. The main vegetation is reeds and low grass with coverage of 75%-90%. Soil samples were collected in triplicate at distances of 0, 3, 6, 10 and 30 m from the wellhead and in three directions of radiation. The nematodes in each soil sample were isolated and identified to genus level under an optical microscope.
Thirty genera from 18 families of soil nematodes were identified, which included 15 genera of bacterivores, 9 genera of herbivores, 4 genera of fungivores, and 2 genera of omnivore-predator nematodes. Dominant groups were Filenchus and Cephalobus which were 42.5% of the total. Common groups included 13 genera, representing 51.7% of the total. Rare groups included 15 genera, representing 6.34% of the total. The largest proportion of nematodes (71.8% of the total) belonged to the life history strategy c-p 2 guild with lesser proportions of c-p 3 and c-p 1 guilds. The smallest proportion of nematodes was of the c-p 4 guild, representing only about 4% of the total, and c-p 5 guild was not present. Nematodes around the oil well were mostly of the r-strategists, which indicate their relative resistance to environmental stress. Thus, nematodes adapted to the interference and stress of oil exploitation by increased reproduction.
Total numbers of nematodes in the soils around the different wells were not significantly different (P>0.05) but were significantly lower than the control (P<0.001). Numbers of herbivores and fungivores between the different wells were not significantly different (P>0.05). Significantly larger (P>0.05) numbers of bacterivores were found in oil well II. The enrichment and structure indexes of nematode communities in all oil wells were less than 50, showing that the degree of interference of each well was high and the soil food-web in the soil tended to be degraded. The community structure of nematodes between the different wells was not significantly different (P>0.05).
Total numbers of nematodes at increasing distance from the well were not significantly different, but were significantly lower than in the control (P<0.05). Numbers of bacterivore, herbivore and fungivore nematodes showed no significant differences (P>0.05) at different distances from the well. Numbers of omnivore-predator nematodes were significantly greater (p>0.05) at 30 m from the well than at other distances. However, with increasing distance from the oil well, abundance, the Simpson Index and the Shannon-Wiener diversity index of nematodes gradually increased. The results of this study establish a theoretical foundation for remediation of soils contaminated by oil exploitation.