Responses of hydrochemical parameters, community structures, and microbial activities to the natural biodegradation of petroleum hydrocarbons in a groundwater–soil environment

Responses of hydrochemical parameters, bacterial community structures, and microbial activities during the natural biodegradation of hydrocarbons leaking from a crude oil pipeline at a site in northeastern China were studied using the hydrochemical method, the polymerase chain reaction amplification of 16S rDNA genes, and denaturing gradient gel electrophoresis (DGGE).The concentrations of PHs and the main physicochemical characteristics (Eh and pH) were increased gradually at longitudinal ZK1–ZK3–ZK6 section in June 2010, suggesting that the degree of biodegradation decreased gradually from the pollutant source to downstream. The electron acceptor (SO4²⁻) participated in biodegradation process responds identical trend to the degree of biodegradation at the same section while the biodegradation reduction products (Fe²⁺, Mn²⁺, and HCO₃ ⁻) respond to it in opposite trend. The concentrations of Fe²⁺, Mn²⁺, and SO₄ ²⁻ at wells ZK1 and ZK3 indicate that sulfate-reducing biodegradation was the dominant process experienced at contaminated sites rather than iron–manganese reduction processes. The dynamic changes of hydrochemical parameters suggest that the degree of biodegradation would be intensified at the center of pollutant plume and iron–manganese reduction processes experienced earlier than sulfate-reducing biodegradation. The community diversities and microbial activities in different soil depths were responded to PHs, but the relationship is not simply linear. The community diversities and microbial activities increased significantly with rise in PH concentration of soil until about 20 mg/kg and then peaked off sharply, suggesting that community succession would be occurred in microhabitat when the PH concentration in soil exceeds 20 mg/kg. The major DGGE bands found in the soil samples were sequenced. One sequence affiliated with γ-Proteobacteria showed high similarities to uncultured bacteria which had been found in offshore oil pollution environment. These bacterial species were found to have similar petroleum degradation functions to the bacteria at the sites studied here.