Stoichiometric characteristics of microbial biomass in oil-contaminated soil in the loess hilly region

PURPOSE: The present study envisaged the stoichiometry of microbial biomass in petroleum-contaminated soil, in order to study the influence of the petroleum-contaminated soil on the ecosystem stability. METHODS: A typical oil well area in the Northern Shaanxi was considered the research object and the oil pollution status was assessed by studying the physical, chemical, and microbiological characteristics of the soil in the area. RESULTS: From the measurement and analysis of the petroleum pollutants in the soil samples, it was observed that the concentration of the petroleum pollutants around all the oil well areas was higher than the critical value of 500 mg/kg. Furthermore, the C to N ratio of 8 soil samples around the oil wells (0.8:1~13.3:1) was lower than that of the control soil samples in most cases and could not reach the nutrient proportion level required by soil microorganisms. It was observed that the oil organic carbon content at 0~10 m from the wellhead was obviously higher than that in other areas, and decreased with an increase in the distance from the well. Based on the determination of soil organic carbon, total nitrogen, total phosphorus, and the soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and phosphorus content analysis, it was observed that only the soil organic carbon was significantly positively correlated to the oil pollutants in soil. CONCLUSIONS: Imbalance in the C to N, SMBC, and SMBN ratio can lead to an acute shortage of the required nutrients than microorganisms, limit the soil microbial reproduction and growth, and thereby slow down the rate of indigenous microbial degradation of petroleum hydrocarbons, so as to reduce the impact of oil pollution on the stability of the entire ecosystem. Therefore, during the remediation of petroleum-contaminated soil in this study area, adequate nutrients need to be reasonably added to the soil.