Microbial diversity and biogeochemical processes in the Deilmann tailings management facility, Key Lake, Saskatchewan

The Deilmann Tailings Management Facility (DTMF) at Key Lake in northern Saskatchewan, Canada, is an active deposition site for uranium tailings and it has been in operation since 1996. In terms of geochemical stability of the tailings, a ferrihydrite secondary phase is utilized for the sequestration of contaminants, such as As, Ni, Mo, and Se, under alkaline and highly oxic conditions. Arsenic is highly abundant in the DTMF tailings and the principal environmental concern is the possibility for leaching of ferrihydrite-attached As into the surrounding environment. Microorganisms can proliferate in a broad range of habitats and their activities are key factors in determining fate and transport of contaminants in various environments. This thesis attempts to obtain insights into the biogeochemical processes that may occur during the early phase of the DTMF’s history that could potentially become significant over extended periods of time that run from 100’s to 1000’s of years. Hence, a primary focus was to characterize microbial diversity and extrapolate their potential functional roles as well as their potential to chemically alter the Eh and ferrihydrite, which are the primary controlling conditions within the DTMF tailings and in the mineral secondary phase, respectively. To achieve these goals, two molecular techniques (clone library construction and Ion Torrent sequencing), a range of conventional culture-based techniques, metabolic assays addressing metabolic transformation and resistance to metals/metalloids, microscopic technique (Confocal Laser Scanning Microscope), spectroscopic analyses (Scanning Transmission X-ray Microscope) and bench-scale microcosm assays were carried out. Culture-dependent and -independent methods revealed that the most prevalent microbial groups in the water column, tailings mass and at the tailings-water interface affiliated into phyla (e.g., Proteobacteria, Actinobacteria, Firmicutes and Bacteriodetes) that have previously been detected at uranium-, heavy metal- and complex hydrocarbon-contaminated sites. Phylotypes closely related to well-characterized sulfate-, thiosulfate- and iron-reducing bacteria (e.g., Desulfosporosinus, Dethiobacter, Geoalkalibacter, Ralstonia, Georgfuchsia) were also detected at low frequency, with the exception of the tailings-water interface where sequences closely related to Desulfosporosinus were abundant. The readily culturable heterotrophs (e.g., Pseudomonas, Arthrobacter, Massilia, Hydrogenophaga, Polaromonas, Bacillus) retrieved from the tailings exhibited reducing/oxidizing capabilities as well as high tolerance to metal/metalloids. Bench scale microcosm assays showed that heterotrophs native to the DTMF site could not only reduce ferrihydrite but could also create highly reducing (< -300 mV) conditions within the tailings amenable to strict anaerobic bacteria such as Desulfosporosinus. STXM image analyses confirmed the presence of reduced iron in close proximity to bacterial cells in biofilm grown in situ and in microcosm tailings, strongly suggesting that ferrihydrite served as electron acceptor during microbial processes. Reduced iron detected in situ also indicated that microscale iron reduction could occur even though macroscale DTMF chemistry remained oxidizing. Overall, the nature of microbial community present in the DMTF system strongly indicated that complex hydrocarbons (e.g., kerosene) discharged into the tailings during processing could potentially support microbial processes that involve Fe and S cycling and that this process could become significant over extended period of times, contributing to arsenic escape into the environment

On the lack of semimartingale property

We prove that the median process defined in Prokaj et al (2011) is not a semimartingale. The same process appears also in Hu and Warren (2000) where the question of the semimartingale property is raised but not settled. In the proof we use that if a function of a semimartingale remains a semimartingale, then under certain conditions the function must have intervals where it is a difference of two convex function. This extends the characterization of semimartingale functions in Cinlar et al (1980) to the non-Markovian setting.Comment: 25 page

SOM and microbes - what is left from microbial life in soils

Soil organic matter (SOM) is the basis for many soil functions and plays an important role for soil fertility and mitigation of global change. Recently, novel analytical tools have been adopted and significant progress has been made in the field of SOM characterisation and elucidation of SOM processes. The results obtained led to the perception of SOM as a continuum of plant and microbial residues at different stages of decay rather than newly synthesised macromolecules. There is increasing evidence that microbial residues make a large contribution to SOM. Here, we review processes involved in SOM formation and turnover. Plant-derived material is processed by microorganisms and transformed into microbial biomass and finally necromass. The latter is persistent in soil, mainly by its spatial organisation and by interactions with soil minerals. SOM formation therefore is embedded in the triangular relationship between soil, plants and microorganisms. Critical flux controlling factors in this process chain are the energy content and the availability of plant-derived carbon to the microorganisms, their carbon use efficiency, which determines the yield of biomass produced per substrate consumed, and the effectivity of stabilisation of the necromass. These factors depend on microbial abundance and metabolism as well as on environmental factors. Microbes and microbial communities are thus both drivers and substantial contributors to SOM dynamics in soil. This improved understanding offers various options to assign properties and processes in soils to processes of living organisms, which was previously not possible. Mechanistic insight into the carbon flow from plant material input through the microbial foodweb to microbial necromass stabilisation and finally to SOM will be the basis for future improvements of SOM models. These improved models will be the basis of knowledge-based land management options for sustainable soil use

Geochemical Controls on Uranium Release from Neutral-pH Rock Drainage Produced by Weathering of Granite, Gneiss, and Schist

We investigated geochemical processes controlling uranium release in neutral-pH (pH ≥ 6) rock drainage (NRD) at a prospective gold deposit hosted in granite, schist, and gneiss. Although uranium is not an economic target at this deposit, it is present in the host rock at a median abundance of 3.7 µg/g, i.e., above the average uranium content of the Earth’s crust. Field bin and column waste-rock weathering experiments using gneiss and schist mine waste rock produced circumneutral-pH (7.6 to 8.4) and high-alkalinity (41 to 499 mg/L as CaCO₃) drainage, while granite produced drainage with lower pH (pH 4.7 to >8) and lower alkalinity (<10 to 210 mg/L as CaCO₃). In all instances, U release was associated with calcium release and formation of weakly sorbing calcium-carbonato-uranyl aqueous complexes. This process accounted for the higher release of uranium from carbonate-bearing gneiss and schist than from granite despite the latter’s higher solid-phase uranium content. In addition, unweathered carbonate-bearing rocks having a higher sulfide-mineral content released more uranium than their oxidized counterparts because sulfuric acid produced during sulfide-mineral oxidation promoted dissolution of carbonate minerals, release of calcium, and formation of calcium-carbonato-uranyl aqueous complexes. Substantial uranium attenuation occurred during a sequencing experiment involving application of uranium-rich gneiss drainage into columns containing Fe-oxide rich schist. Geochemical modeling indicated that uranium attenuation in the sequencing experiment could be explained through surface complexation and that this process is highly sensitive to dissolved calcium concentrations and pCO₂ under NRD conditions.Science, Faculty ofNon UBCEarth, Ocean and Atmospheric Sciences, Department ofReviewedFacult

Biogeochemical Importance of the Bacterial Community in Uranium Waste Deposited at Key Lake, Northern Saskatchewan

<p>The long-term stability of immobilized elements of concern in uranium tailings deposited in the Deilmann Tailings Management Facility (DTMF), northern Saskatchewan, is dependent upon maintenance of highly oxic conditions within the tailings mass. The main objective of this study was to investigate the effect of stimulating microbial activity on the redox potential and state of ferrihydrite, which are considered to be the primary controlling condition and mineral phase, respectively, within the tailings. To determine the potential for biologically mediated decreases in redox potential and ferrihydrite reduction, a series of microcosm assays were performed. Non-sterile material from the tailings–water interface of the DTMF site was inoculated with indigenous flora previously isolated from the tailings material and enriched with a carbon source (50 ppm trypticase soy broth) and incubated under continuous-flow or intermittent-flow conditions, and compared with an uninoculated, no-carbon control that received continuous flow. Highly reducing conditions with redox potentials of less than −300 mV were detected after 2 days of incubation within the carbon-enriched tailings of microcosms receiving continuous flow, and less than −280 mV after 11 days of incubation within carbon-enriched tailings in microcosms receiving intermittent flow. The lowest recorded Eh value (−545 mV) was recorded after 14 days in a carbon-enriched microcosm receiving intermittent flow. In contrast, the redox conditions in the control microcosm never dropped below −93 mV; thus, it was clear that microbial activity and available carbon drove the Eh conditions to become highly reducing. The occurrence of low redox conditions was concomitant with the bulk chemical detection of Fe (II) in the effluent of treated microcosms. Sites of microbial ferrihydrite reduction were also detected using scanning transmission X-ray microscopy where Fe (II) species were observed in close proximity with bacterial cells. Analysis of the microbial diversity present within the microcosms confirmed that microbes indigenous to the DTMF system have the potential to generate conditions suitable for the proliferation of sulfate and iron reducing bacteria, such as <i>Desulfosporosinus</i>, which was detected by high-throughput 16S rRNA gene sequencing.</p