title: Vertical gradients in carbon flow and methane production in a sulfate-rich oil sands tailings pond.
abstract: Oil sands tailings ponds are primary storage basins for tailings produced during oil sands processing in Alberta (Canada). Due to microbial metabolism, methane production contributes to greenhouse gas emissions, but positively affects tailings densification, which is relevant for operational water re-use. Depending on the age and depth of tailings, the activity of sulfate-reducing bacteria (SRB) may control methanogenesis due to the competition for substrates. To assess the depth-related impact of sulfate reduction on CH4emissions, original tailings of two vicinal pond profiles were incubated in anoxic microcosms with/without molybdate as selective inhibitor of microbial sulfate reduction. Integrating methane production rates, considerable volumes of CH4emissions (∼5.37 million L d-1) may be effectively prevented by the activity of SRB in sulfidic tailings between 3.5 and 7.5 m. To infer metabolic potentials controlling methanogenic pathways, a set of relevant organic acids (acetate, formate, propionate, butyrate, lactate) was added to part of the microcosms. Generally, organic acid transformation shifted with depth, with highest rates (305-446 μmol L-1d-1) measured in fresh tailings at 5.5-7.5 m. In all depths, a transient accumulation of acetate revealed its importance as key intermediate during organic matter decomposition. SRB dominated the transformation of acetate, butyrate and propionate, but were not essential for lactate and formate turnover. Acetate as methanogenic substrate was important only at 13.5 m. At 1-7.5 m, methanogenesis significantly increased in presence of organic acids, most likely due to the syntrophic oxidation of acetate to CO2by SRB and subsequent conversion to CH4.
authors.affiliation: Department of Lake Research, UFZ - Helmholtz Centre for Environmental Research, Brückstraße 3a, 39114 Magdeburg, Germany. Electronic address: sebastian.stasik@uniklinikum-dresden.de.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Stasik
authors.affiliation: Department of Lake Research, UFZ - Helmholtz Centre for Environmental Research, Brückstraße 3a, 39114 Magdeburg, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Wendt-Potthoff
mesh_terms: D002244:Carbon; D008697:Methane / Q000378:metabolism; D061329:Oil and Gas Fields; D061005:Ponds; D013431:Sulfates / Q000378:metabolism
chemical_list: D013431:Sulfates; D002244:Carbon; D008697:Methane
keywords: Carbon transformation; Inhibitors; Methanogenesis; Oil sands tailings ponds; Sulfate reduction