Geological storage of CO2 is anticipated to play a significant role in the management and reduction of greenhouse gas emissions. Monitoring of CO2 injection facilities is essential to provide reassurance of the containment of the injected CO2. Here, we report results over six years (2018-2023) for a hydrogeological and geochemical (gas compositions, delta C-13(CH4,) delta C-13(CO2,) delta H-2(CH4) and noble gas concentration and isotopes) monitoring program at a small-scale CO2 injection facility located near Brooks, Alberta, Canada with injection similar to 300 m below ground. The results provide a comprehensive record of the subsurface hydrological and geochemical conditions over the six-year period. Injected CO2 was not detected in samples from the injection zone. There was also no indication of injected CO2 in samples collected from surface casing vents of the three similar to 300 m deep wells, nor was injected CO2 observed in samples from the six shallow groundwater wells (<105 m deep). Various compositional and isotopic changes have been observed over time which are interpreted to either be indirectly related to CO2 injection or completely unrelated indicating non-CO2 injection related variability in the baseline conditions of the site. Additionally, a progressive reduction in hydraulic head has been observed in some shallow aquifers consistent with drought conditions in the region. Our study implies that complex subsurface changes may occur at CO2 storage sites which may be unrelated to human activity, complicating the monitoring of CO2 injection.

The Milk River Aquifer (MRA) is a regional transboundary aquifer covering over 26,000 km2 across northern Montana (USA) and southern Alberta (Canada). Extensive groundwater extraction since 1960s has led to a decline in groundwater levels, thereby emphasizing the need for informed water management strategies. The objective of this study was to improve the understanding of spatial variations in major ion concentrations with respect to groundwater age and flow paths, and to identify key geochemical processes that influence groundwater quality within the aquifer. A comprehensive digital database was developed using hydrogeological and geochemical data from 1,429 water samples collected from 549 wells. Additionally, 20 new groundwater samples and associated gases were collected during a 2022 field campaign, and these samples were analyzed for concentrations of major and minor ions, gas composition, stable isotope ratios (2H/1H and 18O/16O of water, 13C/12C of DIC and 34S/32S of sulfate, 13C/12C and 2H/1H of methane), and radioactive isotopes (⁸¹Kr, ³⁶Cl and ¹⁴CDIC).Utilizing a newly updated groundwater numerical flow model (FEFLOW software) in combination with recent 14C and 81Kr-based groundwater age dates, distinct patterns in chloride (Cl) concentrations dependent on groundwater age and flow path were identified. Groundwater less than 34,000 years old exhibited Cl concentrations < 25 mg/L near the recharge zone, while groundwater exceeding 200,000 years in age had Cl concentrations > 100mg/L at distances of 125 km from the recharge zone. Increasing δ²H and δ¹⁸O values in older groundwater with elevated Cl concentrations indicate possible mixing of fresh recharge water with formation water from northern regions of the aquifer (Taber and Bow Island formations) or associated aquitards (Pakowki and Colorado formations). Ongoing analysis explores variations in other major ions with a specific interest in redox-sensitive species as a function of flow distance and groundwater age. Preliminary results reveal that elevated sulfate concentrations (> 1200 mg/L) in recharging groundwater are due to pyrite oxidation, but at groundwater flow distances between 50 and 75 km bacterial sulphate reduction becomes dominant resulting in sulfate concentrations < 1 mg/L. At flow distances >80 km, redox conditions become favourable for methanogenesis resulting in occurrence of biogenic methane in groundwater. A particle tracking algorithm within the updated numerical flow model was employed to compare residence times with groundwater ages determined from 81Kr measurements. The tracer ages (14C and 81Kr) were confirmed using a numerical particle tracking model based on an existing numerical steady-state groundwater flow model (FEFLOW). The outcomes of this study that utilizes innovative groundwater age dating tools (81Kr) are new insights into how geochemical processes evolve with respect to flow distance and groundwater age thereby modifying spatial variability of key water quality parameters within the Milk River Aquifer.

Nitrate pollution frequently impacts groundwater quality, particularly in agricultural regions across the world, but identifying the sources of nitrate (NO3−) pollution remains challenging. The extensive use of nitrogen-containing fertilizers, surpassing crop requirements, and livestock management practices associated with the spreading of manure can lead to the accumulation and transport of NO3− into groundwater, potentially affecting drinking water sources. We investigated the occurrence and distribution of NO3− in groundwater in Southern Alberta, Canada, a region characterized by intensive crop cultivation and livestock industry. Over 3500 samples from a provincial-scale groundwater quality database, collated from multiple projects and sources, involving domestic wells, monitoring wells, and springs, coupled with newly obtained samples from monitoring wells provided comprehensive geochemical insights into groundwater quality. While stable isotope compositions of NO3− (δ15N and δ18O) were exclusively available for groundwater samples obtained from monitoring wells, the stable isotope data were instrumental in constraining NO3− sources and transformation processes within the aquifers of the study region. Among all samples, 49

As the products of chemical sedimentation in the Archean oceans, Banded Iron Formations (BIFs) have been interpreted to record (bio)geochemical transitions in Earth's ancient biosphere. Nonetheless, the effects of diagenesis and metamorphism over the long history of these rocks make it difficult to identify the minerals involved in the earliest stages of BIF formation. A series of recent studies has suggested that greenalite (Fe32+Si2O5(OH)(4)), formed through hydrothermal fluid-seawater interactions, was among the primary mineral components of BIFs. However, the reactivity of greenalite as a function of relevant environmental parameters has not yet been mechanistically studied. The plausibility of its role in forming BIF deposits therefore remains speculative. Here, we fill this knowledge gap by conducting a series of kinetic experiments using a novel Si isotope doping method with hydrated, amorphous Fe(II)-silicate (a precursor to crystalline greenalite). The advantage of this technique is that it permits simultaneous determination of near-equilibrium forward and reverse reaction rates of Fe(II)-silicate-fluid interaction in plausible Archean ocean compositions. Reaction rate calculations indicate that the system's behavior is governed by Fe(II)-silicate saturation state, with SiO2 sorption becoming dominant once a saturation threshold is exceeded. Combining kinetic data and thermodynamic calculations for the Fe-silicate-seawater system permits determination of a new solubility product for amorphous Fe (II)-silicate as log(K) = 24.9 +/- 0.25. This value indicates maximum Fe2+ concentrations in Archean ocean waters at 25 degrees C would range from similar to 1 mmol/kg at pH 7 to similar to 10 mu mol/kg at pH 8. Combining these observations with calculations of Stokes' settling velocity implies that long-distance transport of greenalite nanoparticles - e. g., from deep-ocean hydrothermal vent sources to loci of BIF deposition - would have been feasible. Coupled with SiO2 sorption behavior on greenalite surfaces and the background SiO2 flux associated with the unique styles of Archean chert deposition, these results suggest that periodic waxing and waning of greenalite nanoparticle transport to BIF depositional environments can help to explain the Fe- and Si-enriched layers preserved in BIFs. Our results also provide a mechanistic underpinning for the exceptional preservation of greenalite in Archean sediments and its frequent association with chert. Ultimately, the readiness with which greenalite would have precipitated from Archean seawater and its apparent ability to be preserved despite transport across ocean basins suggests that it is time to reassess the traces of Earth's early oceans recorded in BIFs and the ways in which these may be interpreted in light of new depositional models.

Alkaline lakes are thought to have facilitated prebiotic synthesis reactions on the early Earth because their modern analogs accumulate vital chemical feedstocks such as phosphate through the evaporation of dilute groundwaters. Yet, the conditions required for some building block synthesis reactions are distinct from others, and these conditions are generally incompatible with those permissible for nascent cellular function. However, because current scenarios for prebiotic synthesis have not taken account of the physical processes that drive the chemical evolution of alkaline lakes, the potential for the co-occurrence of both prebiotic synthesis and the origins and early evolution of life in prebiotic alkaline lake environments remains poorly constrained. Here, we investigate the dynamics of active, prebiotically relevant alkaline lakes using near-surface geophysics, aqueous geochemistry, and hydrogeologic modeling. Due to their small size, representative range of chemistry, and contrasting evaporation behavior, the investigated, neighboring Last Chance and Goodenough Lakes in British Columbia, Canada offer a uniquely tractable environment for investigating the dynamics of alkaline lake behavior. The results show that the required, extreme phosphate enrichments in alkaline lake waters demand geomorphologically-driven vulnerability to evaporation, while the resultant contrast between evaporated brines and inflowing groundwaters yields Rayleigh–Taylor instabilities and vigorous surface–subsurface cycling and mixing of lake and groundwaters. These results provide a quantitative basis to reconcile conflicting prebiotic requirements of UV light, salinity, metal concentration, and pH in alkaline lake environments. The complex physical and chemical processing inherent to prebiotic alkaline lake environments thus may have not only facilitated prebiotic reaction networks, but also provided habitable environments for the earliest evolution of life.

Abstract Thermophilic microorganisms play critical roles in sulfur cycling within the deep biosphere, but knowledge of these biogeochemical reactions at temperatures >80 °C is generally restricted to marine hydrothermal systems1,2. Hydrocarbon extraction activities routinely interact with the deep subsurface, providing access to thermophilic environments where the thermal limits of life within sedimentary basins can be explored. Paramount to this, is understanding of how microbial communities in deep, hot biospheres are activated by and respond to disturbances such as the introduction of fluids from the surface. Here we show through chemical, stable isotope and microbiological analyses that microbial populations can actively catalyze sulfur cycling in subsurface hotter than 90 °C generating H2S via microbial sulfate reduction. These temperatures exceed previously reported thermal limits of sulfate reducing microorganisms3 thus narrowing the gap between temperatures permissive for biogenic and thermochemical sulfate reduction4. Our analyses demonstrate that the introduction of surface-derived fluids into nutrient-limited deep environments stimulates microbial sulfate reduction at temperatures >90 °C previously considered too high for this process with implications for underground storage activities such as CO2 and hydrogen storage.

Over the last two decades, all scenarios projected to achieve the goals of the Paris climate agreements have required negative emissions of greenhouse gases. Mineral carbonation of basalt is a promising negative emission technology for long-term storage of carbon dioxide (CO2). During mineral carbonation, dissolved CO2 is con-verted into solid carbonate minerals through reaction with silicate minerals. Plagioclase feldspars are the most abundant primary silicate minerals in basalts readily available for water-rock interactions. Despite numerous recent laboratory studies, the rate at which plagioclase dissolution occurs under the required conditions for large-scale carbon storage remain poorly constrained. In this study, we present new flow-through experiments quantifying the apparent dissolution rates of plagioclase in sodium chloride solutions with elevated concentra-tions of dissolved CO2 at temperatures between 25 degrees C and 125 degrees C and pressure of 200 bars. The mildly acidic conditions produced by carbonic acid yield apparent rates that are slower than those previously reported for plagioclase under more acidic conditions and alkaline conditions. We used these apparent rates to develop new temperature-dependent rate equations for plagioclase dissolution in solutions buffered by carbonic acid: [(-22.27 f 2.08) (1 ) ] kCa = 10- (9.811f0.664) exp center dot T -1 R Tr [(-33.99 f 1.40) (1 ) ] kSi = 10- (10.334f0.445) exp center dot T -1 R Tr where k is the rate constant (mol m- 2 s- 1) at any temperature (Tin K), R is the universal gas constant (8.3145 KJ/mol/K)and Tr is the reference temperature (298.15 K). Utilizing the new Ca rate equation into a geochemical model, we estimated that the reaction time to achieve carbonate saturation in a closed system with high CO2 ranges from a few days to a few years depending on water-to-mineral ratios. These results could have significant implications for required monitoring on projects or achieving gigaton-scale of carbon storage and mineralization annually, where planned injection rates of million(s) of tons of CO2 per well per year could overwhelm aquifer alkalinity, lower pH, and reduce the efficiency of carbon mineralization.

Groundwater ecosystems are globally wide-spread yet still poorly understood. We investigated the age, aqueous geochemistry, and microbiology of 138 groundwater samples from 87 monitoring wells (<250m depth) located in 14 aquifers in the Canadian Prairie. Geochemistry and microbial ecology were tightly linked revealing large-scale aerobic and anaerobic hydrogen, methane, nitrogen, and sulfur cycling carried out by diverse microbial communities. Older groundwaters contained on average more cells (up to 1.4×107/mL) than younger ground-waters. Organic carbon-rich strata featured some of the highest abundances, challenging current estimates of global groundwater population sizes. Substantial concentrations of dissolved oxygen (n=57; 0.52±0.12 mg/L [mean±SE]; 0.39 mg/L [median]) in older groundwaters could support aerobic lifestyles in subsurface ecosystems at an unprecedented scale. Metagenomics, oxygen isotope analyses and mixing models indicated that microbial “dark oxygen” contributed to the dissolved oxygen pool in subsurface ecosystems commonly assumed to be anoxic.

Analyses of the sulfur (S) and oxygen (O) stable isotope ratios (δ34SSO4 and δ18OSO4) of dissolved sulfate in streams and groundwater in Yukon Territory (YT, Canada) indicates that the dominant source of this major ion is oxidation of sulfide minerals. In these streams, sulfate has a large range in δ34SSO4 values (−19 to +10‰), which is consistent with the lower portion of the documented range for δ34S of sulfides in bedrock in YT (∼ −35 to +55‰). Furthermore, the large majority of the δ18OSO4 data plot within the expected field for sulfide oxidation in cross-plots of δ18OSO4 versus the O isotope ratios of ambient water (δ18OH2O). δ18OSO4 values plotting above that field were likely affected by microbial sulfate reduction, a process that enriches residual sulfate in both 34S and 18O. The stable isotope data indicate that dissolution of marine-evaporite gypsum, which has higher δ34SSO4 and δ18OSO4 values compared to all stream and groundwater samples, is a minor to negligible source of sulfate in the YT streams. Association of sulfate with other solutes indicates release of various metals from sulfide minerals, and suggests dominance of silicate weathering in response to oxidation of the sulfides. Variations in sulfate concentrations in YT streams are largely related to geology, while terrain and climate, including extent of permafrost, are also important factors. Long-term monitoring of sulfate concentrations in YT streams indicates increasing concentrations over time, in both streams impacted by mining, and in streams that have not been affected much by historical in-catchment industrial activities. Increases were largest in streams in northern and central-south YT in the presence of thawing continuous to discontinuous permafrost.

Hydraulic fracturing is a reservoir stimulation technique that involves the injection of high-pressure fluids to enhance recovery from unconventional hydrocarbon reservoirs. Often this involves the injection of surface waters (along with additives such as biocides) into formational fluids significantly different isotopic and geochemical compositions facilitating geochemical fingerprinting of these fluid sources. In some instances, the produced fluids experience an increase in hydrogen sulfide (H2S) concentration over the course of production resulting in an increased risk to health and safety, the environment, and infrastructure due to the toxic and corrosive nature of H2S. However, questions remain as to the origin and processes leading to H2S formation following hydraulic fracturing. In this study, we analyzed a series of produced waters following hydraulic fracturing of a horizontal well completed in the Montney Formation, Western Canada to evaluate variations in geochemical and microbiological composition over time and characterize potential sulfur species involved in the production of H2S. Initially, sulfur isotope ratios (d34S, VCDT) of dissolved sulfate in produced water had a baseline value of 27per mil similar to the d34S value of 25per mil for solid anhydrite derived from core material. Subsequently, d34S values of sulfate in produced fluids sequentially increased to 35per mil coincident with the appearance of sulfides in produced waters with a d34SH2S value of 18per mil. Oxygen isotope values of dissolved sulfate exhibited a synchronous increase from 13.2per mil to 15.8per mil VSMOW suggesting sulfate reduction commenced in the subsurface following hydraulic fracturing. Formation temperatures are &lt;100°C precluding thermochemical sulfate reduction as a potential mechanism for H2S production. We suggest that microbial reduction of anhydrite-derived sulfate within the formation is likely responsible for the increase in H2S within produced waters despite the use of biocides within the hydraulic fracturing fluids. Initial assessments of microbial communities indicate a shift in community diversity over time and interactions between in situ communities and those introduced during the hydraulic fracturing process. This study indicates that biocides may not be fully effective in inhibiting microbial sulfate reduction and highlights the role anthropogenic influences such as hydraulic fracturing can have on the generation of H2S in the subsurface.

Electrocoagulation (EC) in water treatment encounters several challenges, such as electrode fouling and passivation, especially when the effluent has a complex composition, such as produced water in the oil and gas industry. In this study, the effectiveness of applying an external magnetic field during EC with aluminum anodes (Al-EC) or mild steel anodes (Fe-EC) was investigated for the first time for the removal of inorganic contaminants (including silica, calcium, magnesium, and sulfide) from synthetic and field samples of produced waters. For Al-EC, the presence of a magnetic field perpendicular to the electric field was found to enhance the treatment performance and mitigate the fouling formation on the electrode surface. Chronoamperometric investigations indicated that the application of MF in Al-EC enhances the current density and reduces the time to form a fouling layer on the electrode. In contrast, with Fe-EC, the presence of the magnetic field increased the rate of fouling on the electrodes. Potentiodynamic and kinetic investigations indicate that the magnetic field improves mass transfer via Kelvin force and magnetohydrodynamic (MHD) effects with no impact on the type of kinetic model, while the change in the spin states of the accumulated species has a negligible impact on reducing the fouling. The resistivity of the accumulated fouling layer (δRF) was found to reduce by around 23% due to a magnetic field of 0.158 T. Although increasing the strength of the applied MF increases the mass transfer, the effect is not linear. The results indicate that applying a magnetic field in Al-EC can be an effective method to mitigate fouling during water treatment.

Mud-gas isotope logging (MGIL) of hydrocarbons (methane, ethane, propane) has become a widely used approach to fingerprint gas-bearing formations during the drilling of vertical and horizontal oil and gas wells often with the goal to assess potential cross-formational gas migration. In this study, we have used mud-gas molecular and isotope data to assess the usefulness of MGIL for the geochemical assessment of a single lowpermeability reservoir formation, the Montney Formation in Western Canada. An example from a well completed in British Columbia shows that hydrocarbon samples collected in IsoJars (R) tend towards more positive carbon isotope ratios compared to data for samples obtained using IsoTubes (R), potentially attributed to 13C enriched residual gas retained in the cuttings. Additionally, in publically available mud-gas data from 45 other wells, it was found that the carbon isotope ratios of mud-gas from the Montney Formation are overall consistent with the thermal maturity of this stratigraphic unit, but the data display a relatively scattered trend on a thermal maturity plot based on Delta 13CC1-C2 and Delta 13CC1-C3. Molecular parameters such as [C1/(C2 + C3)] can be modified via processes such as desorption and diffusion after sampling gases in IsoJars (R), while the i-C4/n-C4 ratio was found to be the most consistent molecular parameter between sampling techniques. We conclude that mud-gas molecular and isotope data derived from samples collected in IsoTubes (R) are suitable for geochemical assessment (e.g. thermal maturity, fluid-fluid correlations) of low permeability hydrocarbon reservoirs such as the Montney Formation.

Because it is an abundant, divalent cation-bearing mineral in sedimentary rocks and hydrocarbon reservoirs worldwide, glauconite has likely played a role in Earth's carbon cycle over geologic time and may be important for ongoing efforts to geologically store anthropogenic CO2. Yet, due to its complex chemistry and redox sensitivity, glauconite dissolution kinetics have so far been difficult to constrain. To fill this significant knowledge gap, we have undertaken a study to quantify the far-from-equilibrium rates of glauconite dissolution using a novel experimental apparatus specifically designed to explore mineral dissolution kinetics under strictly anoxic conditions. Steady-state glauconite dissolution rates were measured at varying pH from 1.7 to 11.2 and temperature from 24 to 80 degrees C. Temporal evolution of the differences between cation concentrations in the inlet and outlet solutions exhibits stoichiometric or close-to-stoichiometric glauconite dissolution for Fe, Mg, and Si. Fitting the rates calculated from Si release during the experiments to a standard Transition State Theory-derived, far-from-equilibrium rate law yields: k = 2.18 x 10(-12) . exp [(32.2/R). (1/T- 1T(r))]. a(H+)(0.37)+2.95 x 10(-14) .exp [(-37.5/R).(1/T-1/T-r)], where k is the rate constant (mol m(-2) s(-1)) at the temperature (T, Kelvin) and H+ activity (a(H+)) of interest, T-r is the reference temperature (298.15 K), and R is the ideal gas constant (8.314 x 10(-3) kJ mol(-1) K-1). Our experimental results show that the mechanism of glauconite dissolution is highly dependent on temperature and on pH in acidic solutions. Geochemical calculations based on the fitted rate equation predict that complete carbonation of glauconite in a system with a 10:1 water-rock ratio and 50 bar of CO2 fugacity can be expected after 17.5, 11.9, 7.1, and 3.8 kyr at 35 degrees C, 45 degrees C, 60 degrees C and 80 degrees C, respectively. While the lower-temperature simulations generally agree with previously published modelling efforts, the higher temperature reactions are significantly faster than previously predicted. These results high-light the importance of reservoir temperature for glauconite diagenesis and suggest that, when appropriate attention is paid to reservoir temperature during site selection, glauconite carbonation may present significant opportunities for CO(2 )mineralization. (C) 2022 Elsevier Ltd. All rights reserved.

One of the main challenges for the implementation of electrocoagulation (EC) in water treatment are fouling and passivation of the electrodes, especially for applications with high contaminant concentrations. For the first time, we investigated in this study the process of fouling mitigation by polarity reversal during the EC treatment of boiler blowdown water from oil-sands produced water, characterized by high silica concentrations (0.5-4 g L-1). This effluent is typically obtained from an evaporative desalination process in oil production industries. Potentiodynamic characterisation was used to study the impact of passivation on the anode dissolution. Although a charge loading of 4,800 C L-1 was found to remove about 98% of silica from a 1 L batch of 4 g L-1 Si solution, fouling reduced the performance significantly to about 40% in consecutive cycles of direct current EC (DC-EC) treatment. Periodic polarity reversal (PR) was found to reduce the amount of electrode fouling. Decreasing the polarity period from 60 to 10 s led to the formation of a soft powdery fouling layer that was easily removed from the electrodes. In contrast, with DC operation, a hard scale deposit was observed. The presence of organics in the field samples did not significantly affect the Si removal, and organics with high levels of oxygen and sulfate groups were preferentially removed. Detailed electrochemical and economic investigations suggest that the process operating at 85 °C achieves 95% silica removal (from an initial concentration of 481 mg L-1) with an electrical energy requirement of 0.52 kWh m-3, based on a charge loading of 1,200 C L-1, an inter-electrode gap of 1.8 cm and a current density of 16 mA cm-2.