Occurrence and Rates of Terminal Electron‐Accepting Processes and Recharge Processes in Petroleum Hydrocarbon‐Contaminated Subsurface

Abstract

The occurrence and rates of terminal electron acceptor processes, and recharge processes in the unsaturated zone of a boreal site contaminated with petroleum hydrocarbons in the range C(10) to C(40) were examined. Soil microcosms were used to determine the rates of denitrification, iron (Fe) reduction, sulfate (SO(4)) reduction, and methanogenesis in two vertical soil profiles contaminated with oil, and in a noncontaminated reference sample. Furthermore, the abundances of the 16S rRNA genes belonging to Geobacteracaea in the samples were determined by real-time quantitative polymerase chain reaction (PCR). Analyses of ground water chemistry and soil gas composition were also performed together with continuous in situ monitoring of soil water and ground water chemistry. Several lines of evidence were obtained to demonstrate that both Fe reduction and methanogenesis played significant roles in the vertical profiles: Fe reduction rates up to 3.7 nmol h(-1) g(-1) were recorded and they correlated with the abundances of the Geobacteracaea 16S rRNA genes (range: 2.3 x 10(5) to 4.9 x 10(7) copies g(-1)). In the ground water, ferrous iron (Fe(2+)) concentration up to 55 mg L(-1) was measured. Methane production rates up to 2.5 nmol h(-1) g(-1) were obtained together with methane content up to 15% (vol/vol) in the soil gas. The continuous monitoring of soil water and ground water chemistry, microcosm experiments, and soil gas monitoring together demonstrated that the high microbial activity in the unsaturated zone resulted in rapid removal of oxygen from the infiltrating recharge thus leaving the anaerobic microbial processes dominant below 1.5 m depth both in the unsaturated and the saturated zones of the subsurface.

Presence of Actinobacterial and Fungal Communities in Clean and Petroleum Hydrocarbon Contaminated Subsurface Soil

“…At soil depths below 2 m the microbial PLFA concentrations in the contaminated soil was more than 5 times higher than in the corresponding clean soil layers at the same depth, despite the fact that the availability of oxygen was very low in the contaminated soil profile. Bacterial numbers in the deepest soil layers estimated based on the PLFA data [18] were 1.2 x 10 7 bacterial cells (g dry weight) -1 or 3.1 x 10 9 bacterial cells (g organic matter) -1 in the contaminated soil layer at 7 m and 3.3 x 10 6 bacterial cells (g dry weight) -1 or 3.9 x 10 8 bacterial cells (g organic matter) -1 in the clean subsurface soil at 6 m. Information on bacterial numbers in deep subsurface is scarce but recent reports indicate that bacterial numbers of specific groups in deep subsurface soils may be considerable [2]. The impact of PHC as potential carbon source explains the larger bacterial numbers in the anaerobic contaminated soil compared to the clean soil [9].…”

“…Therefore, it is not clear if the subsurface microbial communities are closely linked to the surface soil microbes or if they represent a distinct microbial community [1]. The role of microbial communities and especially their activities in subsurface environments is receiving increased attention due to their importance to ecosystem function, agriculture and environmental management [2, 3]. The bioremediation processes, where microorganisms degrade hazardous compounds like petroleum hydrocarbons (PHCs) to non-hazardous inorganic compounds, is an example of environmental services provided by soils.…”

Assessment of Ecological Risks at Former Landfill Site Using TRIAD Procedure and Multicriteria Analysis

“…Other characteristics of the site, e.g., geology, hydrogeology, and physicochemical soil properties, are described in detail elsewhere. ( 42‐44 )…”

Acetate and ethanol as potential enhancers of low temperature denitrification in soil contaminated by fur farms: A pilot-scale study

“…The rate of denitrification in soil microcosms was determined by using the acetylene-inhibition method according to Salminen et al [12]. Twenty grams of soil was added into a 120-mL glass serum bottle that was then closed tightly with a butyl rubber septum and flushed with oxygen-free N 2 for 4 min.…”