Seasonal dynamics of methanotrophic bacteria in a boreal oil sands end-pit lake

Biodegradation in oil sands process-affected water: A comprehensive laboratory analysis of the in situ biodegradation of dissolved organic acids

Oil sands process-affected water (OSPW) is a by-product of the extraction of bitumen, and volumes of OSPW have accumulated across the Alberta oil sands region due to the governments zero-discharge policy. Some dissolved organics in OSPW, including toxic naphthenic acids (NAs), can be biodegraded in oxic conditions, thereby reducing the toxicity of OSPW. While there has been much focus on degradation of NAs, the biodegradation of other dissolved organic chemicals by endogenous organisms remains understudied. Here, using the HPLC-ultrahigh resolution Orbitrap mass spectrometry, we examined the microbial biodegradation of dissolved organic acids in OSPW. Non-targeted analysis enabled the estimation of biodegradation rates for unique heteroatomic chemical classes detected in negative ion mode. The microcosm experiments were conducted with and without nutrient supplementation, and the changes in the microbial community over time were investigated. Without added nutrients, internal standard-adjusted intensities of all organics, including NAs, were largely unchanged. The addition of nutrients increased the biodegradation rate of O2- and SO2- chemical classes. While anoxic biodegradation can occur in tailings ponds and end pit lakes, microbial community analyses confirmed that the presence of oxygen stimulated biodegradation of the OSPW samples studied. We detected several aerobic hydrocarbon-degrading microbes (e.g., Pseudomonas and Brevundimonas), and microbes capable of degrading sulfur-containing hydrocarbons (e.g., Microbacterium). Microbial community diversity decreased over time with nutrient addition. Overall, the results from this study indicate that toxic dissolved organics beyond NAs can be biodegraded by endogenous organisms in OSPW, but reaffirms that biological treatment strategies require careful consideration of how nutrients and dissolved oxygen may impact efficacy.

Phytoplankton ecology in the early years of a boreal oil sands end pit lake

BACKGROUND

Base Mine Lake (BML) is the first full-scale end pit lake for the oil sands mining industry in Canada. BML sequesters oil sands tailings under a freshwater cap and is intended to develop into a functional ecosystem that can be integrated into the local watershed. The first stage of successful reclamation requires the development of a phytoplankton community supporting a typical boreal lake food web. To assess the diversity and dynamics of the phytoplankton community in BML at this reclamation stage and to set a baseline for future monitoring, we examined the phytoplankton community in BML from 2016 through 2021 using molecular methods (targeting the 23S, 18S, and 16S rRNA genes) and microscopic methods. Nearby water bodies were used as controls for a freshwater environment and an active tailings pond.

RESULTS

The phytoplankton community was made up of diverse bacteria and eukaryotes typical of a boreal lake. Microscopy and molecular data both identified a phytoplankton community comparable at the phylum level to that of natural boreal lakes, dominated by Chlorophyta, Cryptophyta, and Cyanophyta, with some Bacillariophyta, Ochrophyta, and Euglenophyta. Although many of the same genera were prominent in both BML and the control freshwater reservoir, there were differences at the species or ASV level. Total diversity in BML was also consistently lower than the control freshwater site, but consistently higher than the control tailings pond. The phytoplankton community composition in BML changed over the 5-year study period. Some taxa present in 2016-2019 (e.g., Choricystis) were no longer detected in 2021, while some dinophytes and haptophytes became detectable in small quantities starting in 2019-2021. Different quantification methods (qPCR analysis of 23S rRNA genes, and microscopic estimates of populations and total biomass) did not show a consistent directional trend in total phytoplankton over the 5-year study, nor was there any consistent increase in phytoplankton species diversity. The 5-year period was likely an insufficient time frame for detecting community trends, as phytoplankton communities are highly variable at the genus and species level.

CONCLUSIONS

BML supports a phytoplankton community composition somewhat unique from control sites (active tailings and freshwater lake) and is still changing over time. However, the most abundant genera are typical of natural boreal lakes and have the potential to support a complex aquatic food web, with many of its identified major phytoplankton constituents known to be primary producers in boreal lake environments.

Untapped talents: insight into the ecological significance of methanotrophs and its prospects

The deep ocean is a rich reservoir of unique organisms with great potential for bioprospecting, ecosystem services, and the discovery of novel materials. These organisms thrive in harsh environments characterized by high hydrostatic pressure, low temperature, and limited nutrients. Hydrothermal vents and cold seeps, prominent features of the deep ocean, provide a habitat for microorganisms involved in the production and filtration of methane, a potent greenhouse gas. Methanotrophs, comprising archaea and bacteria, play a crucial role in these processes. This review examines the intricate relationship between the roles, responses, and niche specialization of methanotrophs in the deep ocean ecosystem. Our findings reveal that different types of methanotrophs dominate specific zones depending on prevailing conditions. Type I methanotrophs thrive in oxygen-rich zones, while Type II methanotrophs display adaptability to diverse conditions. Verrumicrobiota and NC10 flourish in hypoxic and extreme environments. In addition to their essential role in methane regulation, methanotrophs contribute to various ecosystem functions. They participate in the degradation of foreign compounds and play a crucial role in cycling biogeochemical elements like metals, sulfur, and nitrogen. Methanotrophs also serve as a significant energy source for the oceanic food chain and drive chemosynthesis in the deep ocean. Moreover, their presence offers promising prospects for biotechnological applications, including the production of valuable compounds such as polyhydroxyalkanoates, methanobactin, exopolysaccharides, ecotines, methanol, putrescine, and biofuels. In conclusion, this review highlights the multifaceted roles of methanotrophs in the deep ocean ecosystem, underscoring their ecological significance and their potential for advancements in biotechnology. A comprehensive understanding of their niche specialization and responses will contribute to harnessing their full potential in various domains.

Abiotic and biotic constituents of oil sands process-affected waters

The oil sands in Northern Alberta are the largest oil sands in the world, providing an important economic resource for the Canadian energy industry. The extraction of petroleum in the oil sands begins with the addition of hot water to the bituminous sediment, generating oil sands process-affected water (OSPW), which is acutely toxic to organisms. Trillions of litres of OSPW are stored on oil sands mining leased sites in man-made reservoirs called tailings ponds. As the volume of OSPW increases, concerns arise regarding the reclamation and eventual release of this water back into the environment. OSPW is composed of a complex and heterogeneous mix of components that vary based on factors such as company extraction techniques, age of the water, location, and bitumen ore quality. Therefore, the effective remediation of OSPW requires the consideration of abiotic and biotic constituents within it to understand short and long term effects of treatments used. This review summarizes selected chemicals and organisms in these waters and their interactions to provide a holistic perspective on the physiochemical and microbial dynamics underpinning OSPW .

Ebullition enhances chemical mass transport across the tailings-water interface of oil sands pit lakes

Base Mine Lake (BML) was the first commercial-scale demonstration oil sands pit lake established in northern Alberta, Canada. Recent studies indicate that ebullition enhances internal mass loading of dissolved constituents during settlement and dewatering of methanogenic fluid fine tailings (FFT) below the overlying water cap. Here, we describe results of integrated field measurements and numerical modelling to (i) determine potential for ebullition and enhanced mixing within BML, and (ii) assess impacts on chemical mass transport across the tailings-water interface. We observed sharp increases in [CH_4(aq)] with depth from <0.1 mg L^-1 immediately above the interface to >60 mg L^-1 over the upper 1.5 to 3.0 m of FTT. Thermodynamic modelling revealed that maximum [CH_4(aq)] values represent 60 to 80% of theoretical saturation, and corresponding total dissolved gas pressures approach or exceed fluid pressures. These findings supported integration of enhanced mixing into one-dimensional (1-D) advective-dispersive transport models, which substantially improved upon previous simulations of conservative tracer (i.e., Cl^-) profiles and chemical mass fluxes. The models revealed a positive relationship between CH_4(aq) saturation and enhanced mixing, showing that ebullition enhances internal mass loading. This information has potential to inform ongoing assessments of pit lake performance and support improved closure and reclamation planning at oil sands mines.