Abstract:Pollution generated during the processes of oil drilling and extraction is caused primarily by crude oil leaks, drilling mud, wastewater from washing equipment, and flushing of wells. After contamination by petroleum, the physical and chemical properties of soil may change and the community structure and species diversity of soil animals may be altered. This study aimed to evaluate whether oil exploitation affects soil nematode communities and the range of such effects. Six oil wells(38°00' 35.2" to 38°01' 29.9" N and 118°37' 21.4" to 118°39' 43.8" E)in the Loess Plateau of East Gansu Province, with different exploitation periods (1,10, and 20 a), were selected for study. Triplicate soil samples were collected at distances of 3, 6, 10, 20, and 50m from wellheads and in three directions from the well bases. Soil nematodes were identified to the genus level.There were a total of 43 genera in 22 families, including 26 genera of bacterivores, nine genera of herbivores, two genera of fungivores, and six genera of omnivore-predator nematodes. Dominant groups belonged to Rhabditis and Aporcelaimus, with 15.2% and 10.0% of total nematodes, respectively. Common groups (17 genera), accounted for 68.7% of all nematodes, whereas rare groups (15 genera), accounted for only 6.1% of the total.The largest colonizer-persister (c-p) proportion of nematodes belonged to the c-p 2 guild with 48.2% of total nematodes.The smallest c-p proportion was c-p 4, with 2.2% of the total.The proportion of c-p 2 and c-p 5 nematodes changed significantly with sample distance from the wellheads(P < 0.01).The minimum nematode abundance occurred at 3 m ((23.5±7.1)ind/100 cm3) from a wellhead.The minimum nematode abundance was greatest ((122.7±15.5) ind/100 cm3)outside of the work area (50m).Nematode abundance was significantly higher at 50m than within the oilfield operations area (3 m,6 m,10m,20m). The most abundant feeding type was bacterivores, followed by herbivores.The number of herbivores,fungivores, and omnivores-predators increased significantly with increase in the distance from the wellheads (3m, 6m, 10m, 20m and 50m).The Shannon-Wiener index (H') of soil nematodes was also significantly higher at 50m than within the operation areas (P < 0.05).However, the differences in Simpson index (λ), Evenness index (J), and Wasilewska index(WI)of soil nematodes between distances was not significant in operation and non-operation areas.The H',Maturity index(MI)and WI indices were significantly different between 1, 10, and 20 a oil wells (P <0.05).The wells with 10 a of exploitation showed the lowest H', MI, and WI for the soil nematode community, compared to oil wells used for 1 or 20 years. Oil exploitation reduced soil moisture and increased total petroleum hydrocarbon (TPH) content. However, no significant correlation was found between the distribution of soil nematodes and soil moisture or TPH. The results showed that oil exploration did affect the composition and community structure of soil nematodes, but the effect range was limited to wellsite operationsin the range of about 20m around the well bases.The Shannon-Wiener index and MI was useful for evaluating the effect of oil exploration on the soil nematode community.
