KINETIC ISOTOPIC EFFECT: STATIC RAYLEIGH EQUATION AND BASIC DYNAMIC ISOTOPE EQUATION FOR THE SUBSTRATE IN THE DESCRIPTION OF NITRITE-DEPENDENT ANAEROBIC OXIDATION OF METHANE

The article analyzes the results of modeling the dynamics of nitrite-dependent methane oxidation (N-DAMO) by Methylomirabilis oxyfera microorganisms using the standard isotope dynamic equations. Without specifying a specific function of the rate of the process, the traditional static Rayleigh equation is derived from the basic dynamic isotope equation. Thus, the equation of the 1st order in terms of the substrate is only a special case in the derivation of the Rayleigh equation. It was shown that the dominant fractionation of carbon isotopes occurs in the process of the microbiological reaction of anaerobic oxidation of methane by nitrite, and not in the physical process of mass transfer of dissolved methane into the gas phase. In contrast to the static Rayleigh equation, the dynamic description of the process of fractionation of stable isotopes is important when describing the parallel transformations of the substrate.

Isotopic and Chemical Assessment of the Dynamics of Methane Sources and Microbial Cycling during Early Development of an Oil Sands Pit Lake

Water-capped tailings technology (WCTT) is a key component of the reclamation strategies in the Athabasca oil sands region (AOSR) of northeastern Alberta, Canada. The release of microbial methane from tailings emplaced within oil sands pit lakes, and its subsequent microbial oxidation, could inhibit the development of persistent oxygen concentrations within the water column, which are critical to the success of this reclamation approach. Here, we describe the results of a four-year (2015–2018) chemical and isotopic (δ13C) investigation into the dynamics of microbial methane cycling within Base Mine Lake (BML), the first full-scale pit lake commissioned in the AOSR. Overall, the water-column methane concentrations decreased over the course of the study, though this was dynamic both seasonally and annually. Phospholipid fatty acid (PLFA) distributions and δ13C demonstrated that dissolved methane, primarily input via fluid fine tailings (FFT) porewater advection, was oxidized by the water column microbial community at all sampling times. Modeling and under-ice observations indicated that the dissolution of methane from bubbles during ebullition, or when trapped beneath ice, was also an important source of dissolved methane. The addition of alum to BML in the fall of 2016 impacted the microbial cycling in BML, leading to decreased methane oxidation rates, the short-term dominance of a phototrophic community, and longer-term shifts in the microbial community metabolism. Overall, our results highlight a need to understand the dynamic nature of these microbial communities and the impact of perturbations on the associated biogeochemical cycling within oil sands pit lakes.

Baseline surface- and groundwater monitoring prior to an onshore shale gas operation in the Vale of Pickering, UK

A comprehensive programme of baseline groundwater hydrochemical monitoring has been carried out in connection with the proposed hydraulic fracturing of a 2 to 3 km deep Bowland Shale gas reservoir in borehole KM8 at Kirby Misperton, North Yorkshire, UK. The monitoring infrastructure encompassed: five on-site boreholes with hydraulically open intervals ranging from shallow weathered cover to a c. 200 m deep Corallian limestone aquifer, six off-site wells (hydraulically open in superficial materials and/or Kimmeridge Clay) and four surface water monitoring stations. Groundwater chemistry was high stratified with depth, ranging from slightly acidic, fresh, very hard Ca-HCO3-SO4 waters in shallow weathered cover, to brackish, calcium-depleted, highly alkaline waters in the Corallian aquifer. Dissolved methane was detected in most boreholes, with 10 µg/L being typical of shallow boreholes and around 50 mg/L in the Corallian. Low ethane concentrations and isotopic evidence suggest that the methane was predominantly microbial in origin (carboxylate fermentation at shallow depth, natural methanogenic CO2 reduction at greater depth). Elevated dissolved ethane (20-30 µg/L) was found in one well of intermediate depth, suggesting admixture of a possible thermogenic component, although this could be derived directly from the Kimmeridge Clay penetrated by the well.