title: Groundwater ecosystem resilience to organic contaminations: microbial and geochemical dynamics throughout the 5-year life cycle of a surrogate ethanol blend fuel plume.
abstract: The capacity of groundwater ecosystem to recover from contamination by organic chemicals is a vital concern for environmental scientists. A pilot-scale aquifer system was used to investigate the long-term dynamics of contaminants, groundwater geochemistry, and microbial community structure (by 16S rRNA gene pyrosequencing and quantitative real-time PCR) throughout the 5-year life cycle of a surrogate ethanol blend fuel plume (10% ethanol + 50 mg/L benzene + 50 mg/L toluene). Two-year continuous ethanol-blended release significantly changed the groundwater geochemistry (resulted in anaerobic, low pH, and organotrophic conditions) and increased bacterial and archaeal populations by 82- and 314-fold respectively. Various anaerobic heterotrophs (fermenters, acetogens, methanogens, and hydrocarbon degraders) were enriched. Two years after the release was shut off, all contaminants and their degradation byproducts disappeared and groundwater geochemistry completely restored to the pre-release states (aerobic, neutral pH, and oligotrophic). Bacterial and archaeal populations declined by 18- and 45-fold respectively (relative to the time of shut off). Microbial community structure reverted towards the pre-release states and alpha diversity indices rebounded, suggesting the resilience of microbial community to ethanol blend releases. We also found shifts from O2-sensitive methanogens (e.g., Methanobacterium) to methanogens that are not so sensitive to O2 (e.g., Methanosarcina and Methanocella), which is likely to contribute to the persistence of methanogens and methane generation following the source removal. Overall, the rapid disappearance of contaminants and their metabolites, rebound of geochemical footprints, and resilience of microbial community unequivocally document the natural capacity of groundwater ecosystem to attenuate and recover from a large volume of catastrophic spill of ethanol-based biofuel.
authors.affiliation: State Key Laboratory of Heavy Oil Processing, Beijing Key Lab of Oil & Gas Pollution Control, China University of Petroleum-Beijing, Beijing 102249, China; Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005, USA. Electronic address: rubpmj@sina.com.
authors.forename: Jie
authors.initials: J
authors.lastname: Ma
authors.affiliation: Gene by Gene, Ltd, Houston, TX 77008, USA.
authors.forename: Carlos W
authors.initials: CW
authors.lastname: Nossa
authors.affiliation: Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005, USA.
authors.forename: Pedro J J
authors.initials: PJ
authors.lastname: Alvarez
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism; D001554:Benzene / Q000032:analysis / Q000737:chemistry; D001673:Biodegradation, Environmental; D017753:Ecosystem; D000431:Ethanol / Q000032:analysis* / Q000737:chemistry; D014644:Genetic Variation; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry / Q000382:microbiology; D006863:Hydrogen-Ion Concentration; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013997:Time Factors; D014050:Toluene / Q000032:analysis / Q000737:chemistry; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D012336:RNA, Ribosomal, 16S; D014874:Water Pollutants, Chemical; D014050:Toluene; D000431:Ethanol; D001554:Benzene
keywords: Biofuel; Diversity; Metagenomic; Phylogenetic; Resilience; Taxonomic