Increased soil methane emissions and methanogenesis in oil contaminated areas

Abstract

AbstractCrude oil exploration and related activities cause severe soil contamination and land degradation. However, how soil CH4 and CO2 fluxes respond to oil contamination is poorly understood. To address this question, we conducted in situ investigation of CH4 and CO2 emissions in the Shengli Oilfield, China. CH4 emissions from contaminated soils were 60–1,800 μg·m−2·hr−1, much higher than those from uncontaminated soils (29–33 μg·m−2·hr−1). CO2 fluxes of 2–78 mg·m−2·hr−1 were lower from contaminated soils compared with uncontaminated controls (78–104 mg·m−2·hr−1). The variance of CH4 and CO2 fluxes could be explained to 78.0% by soil properties and oil well age (p < .001) as suggested by the redundancy analysis and the variance partitioning analysis. On the basis of the Illumina MiSeq sequencing of the archaeal 16S rRNA gene, the relative abundance of methanogens over archaea increased by 8 times in contaminated soils compared with that in the uncontaminated soils, suggesting enhanced methanogenesis processes. The proportion of hydrogenotrophic methanogens over the total methanogens increased from 35% in the uncontaminated soil to 43% in the contaminated soils, consistent with the higher apparent fractionation factor (αC) in the stable isotope analysis. Both microbial and isotopic results suggested that the hydrogenotrophic methanogenesis relatively enhanced with the oil contamination, with less dominance of the acetoclastic methanogenesis. The dramatically increased CH4 emissions under oil contamination call for great attention as a potentially important anthropogenic source of CH4 in the atmosphere.