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Vast amounts of methane (CH4) stored in submarine sediments are susceptible to release in a warming Arctic, further exacerbating climate change in a positive feedback. It is therefore critical to monitor CH4 over pan-regional scales to detect early signs of CH4 release. However, our ability to monitor CH4 is hampered in remote northern regions by sampling and logistical constraints, and few good baseline data exist in many areas. From high-resolution atmospheric CH4 measurements and discrete surface water samples, we estimated instantaneous sea–air CH4 fluxes at various locations. We also created a baseline study of current background levels of CH4 in North Atlantic waters based on the atmospheric CH4 data over 22 d in summer 2021 on a roughly 5100 km voyage in the northern Labrador Sea and Baffin Bay between 55 and 72∘ N. In addition, we measured CH4 concentrations across the water column at various stations. Measured atmospheric mixing ratios of CH4 ranged from 1944 to 2012 ppbv, with a mean of 1966 ± 8 ppbv and a baseline of 1954–1981 ppbv. Dissolved CH4 concentrations in the near-surface water peaked at 5.3 nmol L−1 within 1 km down-current of a known cold seep at Scott Inlet and were consistently oversaturated throughout the water column in Southwind Fjord, which is an area that has been recently affected by submarine landslides. Local sea–air CH4 fluxes ranged from 0.003–0.119 µmol m−2 d−1, indicating that the ocean released only small amounts of CH4 to the atmosphere at all stations. Atmospheric CH4 levels were also driven by meteorological, spatial, and temporal variations, and both onshore and ocean-based contributions to atmospheric CH4 mixing ratios are likely. Coupled high-resolution measurements of marine and atmospheric CH4 data have the potential to provide ongoing monitoring in a region susceptible to CH4 releases, as well as critical validation data for global-scale measurements and modelling.

Canada was an early adopter of methane regulation in the oil and gas sector, and recently announced a more ambitious goal to reduce 75% of methane emissions by 2030. New stricter methane regulations should also help reduce loading of air pollutants typically associated with methane emissions (H2S, VOCs, ozone). To examine regional emission trends and to derive an inventory estimate for Canada’s upstream oil and gas sector, we measured methane emissions at 6650 sites across six major oil and gas producing regions in Canada. Our research suggests that methane emissions from the oil and gas industry are underestimated in Canada by ~1.5. For Canada’s largest producing province, Alberta, we found a greater than 1000-fold variation in methane intensity per unit of fossil energy production within the cohort of oil and gas producers. Producer self-published methane emission intensities in ESG materials showed a low bias and tended to mirror regulatory submissions that require reporting only on specific source types. Our measurements suggest that methane-associated pollutants produced by oil and gas activities are also underestimated and communities near these activities may face higher loading of methane-accessory contaminants than might be predicted by Canada’s National Pollutant Release Inventory (NPRI). Using accepted pollutant emission factors, reported flaring and other combustion activity, the federal methane inventory, and our methane measurements, we generated air quality exposure maps reflecting air pollutant loads on Canadian communities. Stricter methane regulation has the potential to significantly decrease methane, but also pollutant loads in several heavy oil communities including the Lloydminster - Bonnyville area.

Canada is a signatory to the Global Methane Pledge and is aiming to achieve a 75% cut in methane from 2030 levels from oil and gas production through regulatory updates and a 50% cut in waste sector emissions using new regulations. Despite numerous large-scale studies that have measured and identified emission sources from Canada's oil and gas sector, there are virtually no measurements of emissions from landfills in Canada. As such, inventory values for landfill emissions are based on a combination of industry-submitted data and emission factors. Canada could design better policies and regulations if policymakers had access to actual emission rates and source types. Therefore, we designed and carried out a large-scale measurement campaign targeting minimally 125 landfills across Canada, using aircraft mass balance measurements and truck-based measurements (i.e., downwind and onsite transects) coupled with Gaussian inversions to determine emission rate. This study focuses on methodologies used to determine source locations, or methane hotspots, on the landfill surface. In Particular, source attribution methods included a Lagrangian back trajectory footprint analysis of mobile surveys, onsite mixing ratios and winds measured with the truck, as well as Landsat thermal retrievals that have been shown in prior studies to correlate with methane hotspots. Measurements were carried out between June and December 2022 using one or more measurement methodologies for a total of 143 sites. We performed truck-based measurements of mixing ratios across navigable portions of 59 landfills. All indicators showed some correlation to mixing ratios collected onsite, although Lagrangian analysis products from downwind measurements were somewhat more reliable in flagging hotspots than the satellite thermal indices. The indicators often highlighted the active disposal face, leachate impoundment ponds, or compost areas, as the active source area. This study will help contribute much-needed source information for solid waste sector regulatory design in Canada and has the potential to help improve models of landfill methane generation.

Methane (CH4) measurements are needed to better understand emissions from oil and gas sources. While many CH4 measurement studies have been done in Canada, they have not yet targeted offshore production from which low emission intensities are reported by industry. For this study, a Twin Otter aircraft was equipped with a Picarro 2210-i gas analyzer and an Aventech wind measurement system (AIMMs_30) to measure CH4 emissions from three oil production facilities in offshore Newfoundland and Labrador. Each facility was visited three times to account for daily variability. Measured concentrations were used to estimate emission rates and production-weighted intensities using two different methods, Top-down Emission Rate Retrieval Algorithm (TERRA), a mass conservation technique developed by Environment and Climate Change Canada, and a Gaussian Dispersion method (GD). Overall, TERRA mass balance-derived emission rates from our measurements were 2,890 ± 3,027 m3 CH4 day− 1(GD = 7,721 m3 CH4 day− 1), 3,738 ± 7,199 m3 CH4 day− 1 (GD = 13,131 m3 CH4 day− 1) and 7,975 ± 4,453 m3 CH4 day− 1 (GD = 7,242 m3 CH4 day− 1), respectively for SeaRose, Hibernia and Hebron. Based on results from both TERRA and Gaussian dispersion the weighted average was (considering number of samples in each method) 5,000 m3 CH4 day− 1 (3.35 tonnes CH4 day− 1), which is comparable to the federally reported estimate of 8,037 m3 CH4 day− 1 of federal estimates, reported in 2019. Production-weighted methane intensities calculated using measured emission rates and reported oil production show that Canadian offshore production ranges from 0.4–2.2 MJ emitted/MJ produced, making it among the least methane-intensive oil produced in Canada.

Canada’s academic science funding system requires substantial collaboration and partnership with stakeholders in government and industry. Meaningful and robust science, whether it is applied or fundamental, often depends on the ability to clearly communicate the nature and benefits of research. But the vocabulary of academic scientists and researchers usually differs from those in government and industry. Visual art and media, including artistic documentaries, creative writing, and animation, has potential to illustrate commonalities among stakeholder groups, and reach new audiences. Our research group, FluxLab, has generated effective visual media using a variety of strategies, including an informal artist-in-residence program, photography training for graduate students, and by using a graphic designer for print and web materials. In this presentation we share films, drawings, animations, newsletter layouts, and other materials used in stakeholder communication, along with context, aims, and success of each initiative.

The Mackenzie River Delta is the second largest Arctic river delta in the world. Thin and destabilizing permafrost coupled with vast natural gas reserves at depth, high organic content soils, and a high proportion of wetlands create a unique ecosystem conducive to high rates of methane production from biogenic and thermogenic sources. Hotspots are known to have a significant contribution to summertime CH4 emissions in the region, but little research has been done to determine how often geologic or biogenic methane contributes to CH4 hotspots in the Mackenzie River Delta. In the present study, stable carbon isotope analysis was used to identify the source of CH4 at several aquatic and terrestrial sites thought to be hotspots of CH4 flux to the atmosphere. Source stable carbon isotope (δ13C-CH4) signatures were derived from keeling plots of point samples and ranged from -42 to -88 ‰ δ13C-CH4, identifying both biogenic and thermogenic and mixed biogenic/thermogenic sources. A CH4 source was determined for eight hotspots, two were thermogenic in origin, four were biogenic in origin, and two were from mixed biogenic/thermogenic sources, as evidenced by δ13C-CH4 signatures. This indicates that the largest hotspots of CH4 production in the Mackenzie River Delta are caused by a variety of sources. In addition to biogenic production at the surface we have identified CH4 migration to the surface from the Taglu gas field over an area of approximately 20 km from north to south and two different sites of mixed biogenic/thermogenic CH4 that were approximately 30 km apart.

Vast amounts of methane (CH4) stored in permafrost and submarine sediments are susceptible to release in a warming Arctic, further exacerbating climate change in a positive feedback. It is therefore critical to monitor CH4 over pan-regional scales to detect early signs of CH4 release. However, our ability to monitor CH4 is hampered in remote northern regions by sampling and logistical constraints and few good baseline data exist in many areas. To create a baseline study of current background levels of CH4 in North Atlantic waters, we collected continuous real-time atmospheric CH4 data, along with ambient air temperature and wind parameters over 22 days in summer 2021 on a roughly 5100 km voyage in the northern Labrador Sea and Baffin Bay up to 71° N. In addition, we measured CH4 concentrations in the water column using discrete water samples at selected stations. Measured atmospheric mixing ratios of CH4 ranged from 1944.7 ppb to 2012.0 ppb, with a mean of 1966.0±7.4 ppb and a baseline of 1954.2−1980.6 ppb. Dissolved CH4 concentrations in the near-surface water peaked at 56.58±0.05 nM within 1 km down-current of a known cold seep at Scott Inlet but were consistently super-saturated throughout the water column in Southwind Fjord, which is an area recently affected by submarine landslides. Local sea-air CH4 fluxes ranged from 0.1−14.1 µmol m-2 d-1 indicating that the ocean acted as a CH4 source to the atmosphere. Atmospheric CH4 levels were also driven by meteorological, spatial, and temporal variations. Highest atmospheric CH4 mixing ratios were detected in the Cumberland Sound in Nunavut, suggesting onshore sources from nearby waterbodies and wetlands, whereas ocean-based contributions at this location could not be ruled out. Coupled real-time measurements of marine and atmospheric CH4 data have the potential to provide ongoing monitoring in a region susceptible to CH4 releases, as well as critical validation data for global-scale measurements and modelling.

Vehicle-based measurements of wind speed and direction are presently used for a range of applications, including gas plume detection. Many applications use mobile wind measurements without knowledge of the limitations and accuracy of the mobile measurement system. Our research objective for this field-simulation study was to understand how anemometer placement and the vehicle's external air flow field affect measurement accuracy of vehicle-mounted anemometers. Computational Fluid Dynamic (CFD) simulations were generated in Ansys FLUENT to model the external flow field of a research truck under varying vehicle speed and wind yaw angle. The CFD simulations provided a quantitative description of fluid flow surrounding the vehicle, and demonstrated that the change in windspeed magnitude from the inlet increased as the wind yaw angle between the inlet and the vehicle's longitudinal axis increased. The CFD results were used to develop empirical speed correction factors at specified yaw angles, and to derive an aerodynamics-based correction function calibrated for wind yaw angle and anemometer placement. For comparison with CFD, we designed field tests on a square, 12.8 km route in flat, treeless terrain with stationary sonic anemometers positioned at each corner. The route was driven in replicate under varying wind conditions and vehicle speeds. The vehicle-based anemometer measurements were corrected to remove the vehicle speed and course vector. From the field trials, we observed that vehicle-based windspeed measurements differed in average magnitude in each of the upwind, downwind, and crosswind directions. The difference from stationary anemometers increased as the yaw angle between the wind direction and the truck's longitudinal axis increased, confirming the vehicle's impact on the surrounding flow field and validating the trends in CFD. To further explore the accuracy of CFD, we applied the function derived from the simulations to the field data, and again compared these with stationary measurements. From this study, we were able to make recommendations for anemometer placement, demonstrate the importance of applying aerodynamics-based correction factors to vehicle-based wind measurements, and identify ways to improve the empirical aerodynamic-based correction factors.

Methane emissions were measured at ~7000 sites across major oil and gas producing regions in Canada to examine regional emission trends, and to derive an inventory estimate for Canada’s upstream oil and gas sector. Emissions varied by fluid type and geographic region, with the heavy oil region of Lloydminster ranking highest on both absolute and intensity-based scales. Emission intensities varied widely for natural gas production, where older, low-producing developments showed high emission intensities, and where emissions intensity in newer developments was amongst the lowest in North America. Emissions from offshore production were in-line with reported estimates. When allocated to individual producers, we found that methane emissions intensity varied more than 1000-fold as determined by geographical factors and infrastructure portfolio. Reporting and disclosure frameworks in Canada are improving but we found that producers could easily under-report emissions and emissions intensity if relying only on regulatory requirements. Overall, we estimate that the Canadian upstream oil and gas methane inventory is underestimated by a factor of 1.5, which is consistent with previous studies of individual regions.

In Canada, offshore oil production facilities are exempt from new methane mitigation requirements that apply to onshore producers. Since onshore oil and gas operations have been shown in Canada to emit more methane than is reported in the federal inventory, it is reasonable to question methane emission levels, and intensity, of Canada’s offshore oil production. In this study, we measured methane emissions from an aircraft equipped with Picarro 2210-i gas analyzer and Aventech wind measurement system (AIMMs_30). The top-down emission rate retrieval algorithm (TERRA) was used to calculate the emission rate using a mass balance technique. The algorithm was developed by Environment and Climate Change Canada and has been used previously for airborne emissions measurement campaigns around oil and gas facilities. In addition to mass balance estimates, we also derived estimates from downwind transects using a Gaussian Dispersion model. We flew around each of the 3 offshore facilities 3 times to ensure accurate measurements considering the unpredictable offshore weather conditions. Our emissions estimates were overall comparable with inventory estimates, which demonstrate a much lower methane emissions intensity than onshore oil production in western Canada. We compared our results against reported values for other aircraft-based measurement studies including those in the North Sea and the Gulf of Mexico. Although average measured emission rates in Eastern Canada are higher in absolute terms than similar platforms in the Gulf of Mexico or the North Sea, methane emission intensity is lower because production levels are very high.Keyword: Methane emission rate, Inventories, Mass balance, Top-down, Airborne measurement

Abrupt permafrost thawing is expected to release large amounts of greenhouse gasses to the atmosphere, creating a positive feedback to climate warming. There is, however, still large uncertainty in the timing, duration, magnitude, and mechanisms controlling this process, which hampers accurate quantification of permafrost carbon climate feedback cycles. The current understanding supports that abrupt permafrost thaw will lead to surface inundation and create anaerobic landscapes, which dominantly produce methane during the decomposition process. Over time, natural succession and vegetation growth may decrease methane release and increase net carbon uptake. We investigated how rapid permafrost thawing and subsequent natural succession over time affect CO2, CH4, and N2O release at a field site in northern Norway (69ᵒN), where recent abrupt degradation of permafrost created thaw ponds in palsa peat plateau-mire ecosystems. The site exhibits a natural gradient of permafrost thaw, which also corresponds to a strong hydrological gradient (i.e. dry peat plateau underlain by intact permafrost, seasonally inundated thaw slumps, thaw ponds, and natural succession ponds covered by sphagnum and sedges). Since 2017, we used a range of manual and automated techniques to measure changes in vegetation, soil and water microclimate, biogeochemistry, and soil CO2, CH4, and N2O concentrations and fluxes across the permafrost thaw gradient. In the three-year observations, we show that abrupt permafrost thaw and land surface subsidence – both intermediate slumping and pond formation – increase net annual carbon loss. Permafrost thaw accelerated CO2 release greatly in thaw slumps (177.5 gCO2 m-2) compared to intact permafrost peat plateau (59.0 gCO2 m-2). During the growing season, peat plateau was a small sink of atmospheric CH4 (-2.5 gCH4 m-2), whereas permafrost thaw slumping and pond formation increased CH4 release dramatically (ranging from 9.7 to 36.1 gCH4 m-2). Furthermore, CH4 release continues to increase even in natural succession pond likely due to aerenchyma transport of CH4 from deeper soil. The overall N2O release was negligeable except in the bare soil peat plateau. The net radiative forcing of ecosystem carbon balance will depend on the carbon uptake from the natural succession of vegetation, but we show that greenhouse gas emissions continue to increase beyond abrupt permafrost thaw event towards natural succession.

As oil and gas wells age and the number of wells drilled increases to meet demand, we may see more instances of fugitive soil gas migration (GM) and associated methane (CH4) emissions. Due to the immense spatiotemporal variability of soils and uncertainty in measurement practice, the detection and quantification of GM emissions is a challenge. Two common measurement techniques include the shallow in-soil gas concentration approach and soil surface flux measurements using flux chambers. In this numerical modeling study, both methods were compared to determine how soil texture, environmental conditions (water content, temperature), and CH4 leak rates into the soil profile influenced in-soil CH4 concentration and surface CH4 flux rates. We observed that in-soil CH4 concentration was strongly controlled by soil texture and environmental conditions, whereas surface CH4 flux rates were far less sensitive to those same parameters. Flux measurements were more useful for determining severity of the CH4 leak into the soil and allowed us to differentiate between leak and nonleak scenarios in soils with biological CH4 production which could complicate a GM assessment. We also evaluated field measurements of carbon dioxide from an enhanced oil recovery site to demonstrate how seasonal conditions can influence concentrations of trace gases in shallow soil. Based on our model results and supplemental field measurements, we propose that flux chamber measurements present a more reliable tool to assess the incidence and severity of fugitive GM.

The oil and gas industry is Canada’s largest contributor to national methane (CH4) emissions. To quantify the input of active and inactive (suspended and abandoned) oil and gas infrastructure to regional CH4 budgets, we conducted truck-based measurements (transect-based and OTM 33A) with a greenhouse gas analyzer, complimented with optical gas imaging at oil-producing sites of Saskatchewan, including understudied regions. We found that inactive sites regionally accounted for roughly 43% of total measured CH4 emissions in Lloydminster, 9% in Kindersley, and 0% in Swift Current. Thus, CH4 emissions from oil production in southwestern Saskatchewan are underestimated by almost 25% if emissions from inactive sites are ignored. Measured mean CH4 emissions of actively producing oil and gas infrastructure in Lloydminster were at least 50% lower (36 ± 7 m3/day) than found in previous studies potentially due to declines in production schemes, effective implementation of emission reduction approaches, or spatial differences between sampled sites. Unlike previous studies, measured emissions in Lloydminster were lower than reported values (147 ± 10 m3/day). In contrast, measured emissions in Kindersley (64 ± 17 m3/day) and Swift Current (23 ± 16 m3/day) were close to reported emissions despite observed tank vents and unlit flares. Unlit flares emitted at least 3 times more CH4 than other infrastructure types and were the “super-emitters” in this study. Currently, provincial and federal regulations target only active infrastructure, but regulators may consider extending regulations to inactive sites where data suggest significant emission reduction potential.

Despite oil and gas related methane (CH4) emissions being the largest anthropogenic source of CH4 in Canada, there are few measurement studies on such emissions to date. That being said, understanding the emissions footprint of different development types is becoming increasingly important in Canada, as the oil and gas sector faces new aggressive regulations to reduce CH4 emissions to 45% below 2014 levels by 2025. In this study, a vehicle-based measurement technique was used to quantify fugitive and vented CH4 emissions from the Weyburn CO2 Enhanced Oil Recovery (EOR) field in southeastern Saskatchewan, Canada. In total, 162 infrastructure sites consisting of 211 active wells and 13 facilities were sampled two or more times. Emission occurrences were substantially low in comparison to other recent emission studies in Canada and the United States, with only 1.85% of sampled sites emitting CH4. We estimated the average emission rate of CH4 at these sites to be ∼0.5 m3/day, which is small compared to the proposed 2020 federal venting cap of ∼110 m3/day. As expected, the low levels of emissions are likely a result of the field's unitized (closed-loop) design, coupled with the operators ongoing commitment to best practice, and the in-depth understanding of the field's characteristics from historical research.

Earth system scientists working with radiocarbon in organic samples use a stable carbon isotope (δ13C) correction to account for mass-dependent fractionation, but it has not been evaluated for the soil gas environment, wherein both diffusive gas transport and diffusive mixing are important. Using theory and an analytical soil gas transport model, we demonstrate that the conventional correction is inappropriate for interpreting the radioisotopic composition of CO2 from biological production because it does not account for important gas transport mechanisms. Based on theory used to interpret δ13C of soil production from soil CO2, we propose a new solution for radiocarbon applications in the soil gas environment that fully accounts for both mass-dependent diffusion and mass-independent diffusive mixing.

The polar deserts of the McMurdo Dry Valleys, Victoria Land, Antarctica, are among the most hostile places on Earth, where terrestrial biota is limited to small patches of hospitable land. Carbon dioxide (CO2) soil surface flux has been used to estimate the rates of biological activity in hospitable areas, but researchers have also observed CO2 fluctuations at sites with low biological activity, including strong negative fluxes suggestive of an abiotic sink for CO2. To better characterize the biotic and abiotic controls on soil surface CO2 flux, and their relative contributions to variability, we designed and executed a long-term monitoring experiment in four of the McMurdo Dry Valleys. This experiment used automated temporal monitoring of both CO2 efflux, and soil concentrations, at sub-diel timescales. In general, the fluxes we observed were well under

Cold heavy oil production with or without sand (CHOPS, or CHOP) are prevalent methods of oil extraction in western Canada. CHOP(S) sites account for over 40% of all reported vented methane (CH4) from oil production in Alberta, and high rates of CH4 emissions have been confirmed in independent measurement studies. In this study, we used truck-based surveys coupled with qualitative optical gas imaging (OGI) to quantify and characterize methane emission rates and sources at nearly 1350 and 940 well sites in two major CHOP(S) developments respectively in 2016 and 2018. The studies were conducted in Lloydminster, Alberta, where produced gases are sweet (i.e., 0.5% sulfur) odorous emissions (hydrogen sulfide, BTEX, etc.). Based on results from all surveys, in Peace River, 43% of measured sites were emitting CH4, compared to 37% in Lloydminster. The measured CH4 emission rates in Peace River were, however, significantly lower than in Lloydminster for both years, and had fallen from 2016 to 2018. In 2018, emissions in Lloydminster were fairly unchanged relative to previous measurements taken in 2016. OGI showed that tanks in Peace River continue to emit CH4 despite regulatory interventions and a reported venting rate of zero. The continued emissions were thus classified as “unintended venting”, which can be a consequence of the non-routine malfunction (e.g., inappropriate operator action or poor equipment design/sizing) of vapor recovery equipment. Mitigation strategies implemented in Peace River targeting olfactory compounds were beneficial in reducing and keeping CH4 emissions lower, since these gases are co-emitted, and could even be co-regulated provincially. Reciprocal to that, we might expect future air quality improvements as a consequence of the new provincial requirements to reduce CH4 emissions under amended Directives 060 and 017.

Global scale warming has led to permafrost thaw, which may release large amounts of carbon to the atmosphere as CO2 and CH4, potentially accelerating global warming (i.e. a positive feedback). However, uncertainty in the mechanisms controlling carbon mineralization is compounded by concurrent changes in soil hydrology associated with permafrost thaw. Thawing permafrost can lead to surface water accumulation in some areas and seasonal or permanent soil drying in areas where permafrost thaw opens up new channels of water to penetrate into the groundwater system. The complexity of the hydrologic response to permafrost thaw increases the challenge in generating reliable estimates of the permafrost carbon climate feedback. Furthermore, limited observational data exist to i) quantify the effects of permafrost thaw on net tundra carbon budgets, particularly on an annual basis, and ii) as well as constrain the underlying processes governing carbon release under aerobic and anaerobic conditions.Here, we investigated how changes in local hydrology affects CO2 and CH4 release from permafrost soils by establishing a field gradient study in northern Norway (69ᵒ N), where recent abrupt degradation of permafrost created thaw ponds in palsa-mire ecosystems. The site exhibits a natural gradient of permafrost thaw, which also corresponds to a strong hydrological gradient (i.e. dry palsas with intact permafrost, seasonally inundated thaw slumps, and thaw ponds). Since 2017, we have used a range of manual and automated techniques to measure changes in vegetation, soil and water microclimate, biogeochemistry, and soil CO2 and CH4 concentrations and efflux across the permafrost thaw gradient.Our preliminary results show that abrupt permafrost thaw and landscape subsidence – both intermediate slumping and thaw pond formation – increase net annual carbon loss from this type of subarctic wetland. Permafrost thaw approximately doubles CO2 emissions from thaw slumps compared to vegetated or soil palsas. Furthermore, CH4 release greatly increased across the permafrost thaw gradient. While vegetated palsas were small sinks of atmospheric CH4 during the growing season, permafrost thaw slumping and pond formation led to a dramatic increase in CH4 efflux compared to bare palsas. In contrast, bare soil palsas on were the most important source of N2O. Soil profile CO2 and CH4 concentrations in thawed permafrost plots were overall highly enriched relative to palsa profiles, reflecting soil conditions with inundated pore space and low oxygen availability along the permafrost thaw gradient. We therefore conclude that abrupt thaw will increase annual carbon loss in subarctic palsa wetlands.

Chamber measurements form a fundamental approach in quantifying the exchange of trace gases between soils and the atmosphere. A range of chamber approaches has been used, reflecting the progress in our understanding of soil gas flux dynamics and technical capabilities. Minimizing measuring artefacts that are associated with soil chamber measurements have mainly driven these advances, along with a need to obtain soil flux data of appropriate spatial replication and temporal resolution. We here present an overview of the main classic CO2 flux chamber approaches, noting that general principles apply also to chamber measurements of other trace gases. The chapter introduces measuring principles, data evaluation, and key parameters, and covers recent advances in autonomous measurements in the field. We explicitly address the respective strengths and weaknesses of some automated measuring approaches, as these are likely to be critical for long-term assessments of gas flux across many biomes and linked to other atmospheric gas exchange approaches.

Methane emissions were measured at 6650 sites across six major oil and gas producing regions in Canada to examine regional emission trends, and to derive an inventory estimate for Canada’s upstream oil and gas sector. Emissions varied by fluid type and geographic region, with the heavy oil region of Lloydminster ranking highest on both absolute and intensity-based scales. Emission intensities varied widely for natural gas production, where older, low-producing developments such as Medicine Hat, Alberta showed high emission intensities, and newer developments in Montney, British Columbia showed emission intensities that are amongst the lowest in North America. Overall, we estimate that the Canadian upstream oil and gas methane inventory is underestimated by a factor of 1.5, which is consistent with previous studies of individual regions.

Groundwater methane (CH4) in areas of fossil fuel development has been a recent focus of study as high CH4 concentrations pose water quality concerns and potential explosive hazards. In 2013, a provincial study in Nova Scotia identified areas with elevated groundwater CH4. However, due to limited data, the specific sources and local distribution of CH4 in those areas remain unknown. In this study, we examined the Stellarton Basin in central Nova Scotia, Canada, a region with an abundance of coal formations, numerous abandoned coal mines, and an active open pit coal mine. Methane was detected in 94% of water samples that were sampled from 45 private water wells. Six water wells exceeded the 28 mg/L hazard mitigation threshold with CH4 levels of up to 72.7 mg/L. The δ13CCH4 (−85.5 to −48.5‰) and the δ2HCH4 (−280 to −88‰) indicated that >95% of samples had CH4 of microbial origin. However, the detection of ethane (C2H6) up to 2.97 mg/L and propane (C3H8) up to 0.008 mg/L, as well as the δ13CC2H6 values (−30.1 to −15.6‰) suggested a mixture of microbial CH4 with trace thermogenic gas, likely migrated from Stellarton coals (δ13CC2H6 of −27.6 to −15.35‰). A mobile greenhouse gas analyzer survey was conducted within the perimeter of residences and off-gassing from taps had atmospheric CH4 measurements as high as 66 ppmv. This study integrates multiple sampling and monitoring methods to investigate groundwater CH4 in a coal-bearing region. The findings advance the understanding of the origin and occurrence of CH4 in complex groundwater systems. The data acquired in this study may be used as a pre-drill baseline for groundwater CH4 concentrations and origins should coal-bed methane operations in Nova Scotia proceed in the future.

The Marcellus Shale Energy and Environment Laboratory (MSEEL) in West Virginia provides a unique opportunity in the field of unconventional energy research. By studying near-surface atmospheric chemistry over several phases of a hydraulic fracturing event, the project will help evaluate the impact of current practices, as well as new techniques and mitigation technologies. A total of 10 mobile surveys covering a distance of approximately 1500 km were conducted through Morgantown. Our surveying technique involved using a vehicle-mounted Los Gatos Research gas analyzer to provide geo-located measurements of methane (CH4) and carbon dioxide (CO2). The ratios of super-ambient concentrations of CO2 and CH4 were used to separate well-pad emissions from the natural background concentrations over the various stages of well-pad development, as well as for comparisons to other urban sources of CH4. We found that regional background methane concentrations were elevated in all surveys, with a mean concentration of 2.699 ± 0.006 ppmv, which simply reflected the complexity of this riverine urban location. Emissions at the site were the greatest during the flow-back phase, with an estimated CH4 volume output of 20.62 ± 7.07 g/s, which was significantly higher than other identified urban emitters. Our study was able to successfully identify and quantify MSEEL emissions within this complex urban environment.

Carbon Capture and Storage (CCS) is playing a greater role in reducing CO2 emissions. The Aquistore project at Estevan, Saskatchewan, Canada is an operational CCS demonstration and research site. Surface soil gas geochemistry is one method of Measurement, Monitoring, and Verification (MMV) techniques used for detection of leakage at CO2 injection sites. We have been operating the surface soil gas MMV program for several years, which has involved measuring gas concentrations of CO2, O2, N2, CH4, the stable isotope of CO2 (δ13C), and radiocarbon isotope Δ14CO2 as tracers for storage containment analysis. Soil CO2 surface flux measurements were also conducted during the baseline monitoring program. At Aquistore, CO2 concentration is typically elevated relative to the mean for the location, but such values are characteristic in this area. Ratio-based tracer analyses, such as O2 vs. CO2, CO2 vs. N2, and CO2 vs. N2/O2, all indicated that storage is secure. The Δ14CO2 values observed in soil gas were interesting in the parts of the site which had a more depleted baseline than expected. To date, there have been no changes in the soil gas indicators since the injections started. These observations will help to inform new research aimed at improving the effectiveness and efficiency of soil gas MMV at Aquistore and similar projects worldwide.

Methylmercury (MeHg) bioaccumulation is a growing concern in ecosystems worldwide. The absorption of solar radiation by dissolved organic matter (DOM) and other photoreactive ligands can convert MeHg into less toxic forms of mercury through photodemethylation. In this study, spectral changes and photoreactivity of DOM were measured to assess the potential to control photoreactions and predict in situ MeHg concentration. Water samples collected from a series of lakes in southwestern Nova Scotia in June, August, and September were exposed to controlled ultraviolet-A (UV-A) radiation for up to 24 hr. Dissolved organic matter photoreactivity, measured as the loss of absorbance at 350 nm at constant UV-A irradiation, was positively dependent on the initial DOM concentration in lake waters (r2 = 0.94). This relationship was consistent over time with both DOM concentration and photoreactivity increasing from summer into fall across lakes. Lake in situ MeHg concentration was positively correlated with DOM concentration and likely catchment transport in June (r = 0.77) but not the other sampling months. Despite a consistent seasonal variation in both DOM and Fe, and their respective correlations with MeHg, no discernable seasonal trend in MeHg was observed. However, a 3-year dataset from the 6 study lakes revealed a positive correlation between DOM concentration and both Fe (r = 0.91) and MeHg concentrations (r = 0.51) suggesting a more dominant landscape mobility control on MeHg. The DOM-MeHg relationships observed in these lakes highlights the need to examine DOM photoreactivity controls on MeHg transport and availability in natural waters particularly given future climate perturbations.

Lakes may function as either sinks or sources of CO2. Their response to climate change is uncertain, as we lack continuous data of lake CO2 efflux and its drivers. This is especially true in the littoral zone of lakes, which can be very dynamic from the continuous injection and remobilization of terrestrial nutrients. This study used high-frequency measurements of CO2 exchange during the ice-free season by prototype low-power floating Forced Diffusion (FD) autochambers. We quantified the net surface flux of CO2 across a transect of the littoral zone of a small deep oligotrophic lake in eastern Nova Scotia, Canada, and examined potential drivers. The littoral zone was a net source for CO2, on average emitting 0.171 ± 0.023 µmol CO2 m-2 s-1, but we did observe significant temporal variation across diel and seasonal periods, as well as with distance from shore. While no pelagic environmental driver appeared to explain this variability in CO2 exchange, our study suggests that factors which vary on a fine spatial scale within the littoral zone may effectively regulate CO2 exchange. If environmental drivers of pelagic CO2 exchange are unrelated to CO2 exchange in the littoral zone, this may have large implications for current mechanistic understandings of lake carbon dynamics, and for upscalings of fluxes. This work shows the spatial and temporal variability of littoral CO2 efflux, as well as the utility of low-power FD automated chambers for observing lake-atmosphere net CO2 exchange.

Winter soil carbon dioxide (CO2) respiration is a significant and understudied component of the global carbon (C) cycle. Datasets have shown that winter soil CO2 fluxes can be surprisingly variable, owing to physical factors such as snowpack properties and wind. This study aimed to: quantify the effects of advective transport of CO2 in soil-snow systems on the sub-diurnal to diurnal (hours to days) timescale, use an enhanced diffusion model to replicate the effects of CO2 concentration depletions from persistent winds, and use a model-measure pairing to effectively explore what is happening in the field. We took continuous measurements of CO2 concentration gradients and meteorological data at a site in the Cape Breton Highlands of Nova Scotia, Canada to determine the relationship between wind speeds and CO2 levels in snowpacks. We adapted a soil CO2 diffusion model for the soil-snow system, and simulated stepwise changes in transport rate over a broad range of plausible synthetic cases. The goal was to mimic the changes we observed in CO2 snowpack concentration to help elucidate the mechanisms (diffusion, advection) responsible for observed variations. On sub-diurnal to diurnal timescales with varying winds and constant snow levels, a strong negative relationship between wind speed and CO2 concentration within the snowpack was often identified. Modelling clearly demonstrated that diffusion alone was unable to replicate the high frequency CO2 fluctuations, but simulations using above-atmospheric snowpack diffusivities (simulating advective transport within the snowpack) reproduced snow CO2 changes of the observed magnitude and speed. This confirmed that wind-induced ventilation contributed to episodic pulsed emissions from the snow surface and to suppressed snowpack concentrations. This study improves our understanding of winter CO2 dynamics to aid in continued quantification of the annual global C cycle, and demonstrates a preference for continuous wintertime CO2 flux measurement systems.

North American leaders recently committed to reducing methane emissions from the oil and gas sector, but information on current emissions from Canadian unconventional developments is lacking. This study examined the incidence of methane in an area of unconventional natural gas development in northwestern Canada. In August to September 2015 we completed almost 8000 km of vehicle-based survey campaigns on public roads dissecting developments that mainly access the Montney formation in northeastern British Columbia. Six survey routes were repeated 3–6 times and brought us past over 1600 unique well pads and facilities developed by more than 50 different operators. To attribute on-road plumes to infrastructural sources we used gas signatures of residual excess concentrations (anomalies above background) less than 500 m downwind from infrastructural sources. All results represent emissions greater than our minimum detection limit of 0.59 g/s at our average detection distance (319 m). Unlike many other developments in the US for which methane measurements have been reported recently, the methane concentrations we measured at surface were close to normal atmospheric levels, except inside natural gas plumes. Roughly 47 % of active wells emitted methane-rich plumes above our minimum detection limit. Abandoned and under-development well sites also emitted methane-rich plumes, but the incidence rate was below that of producing wells. Multiple sites that pre-date the recent unconventional Montney development were found to be emitting, and in general we observed that older infrastructure tended to emit more often (per unit) with comparable severity in terms of measured excess concentrations on-road. We also observed emissions from facilities of various types that were highly repeatable. Emission patterns in this area were best explained by infrastructure age and type. Extrapolating our results across the Montney development, we estimate that the emission sources we located (emitting at a rate > 0.59 g/s) contribute more than 111,800 tonnes of methane annually to the atmosphere. This value exceeds reported bottom-up estimates of 78,000 tonnes for all oil and gas sector sources in British Columbia, of which the Montney represents about 55 % of production. The results also demonstrate that mobile surveys could be used to exhaustively screen developments for super-emitters, because without our intensive 6-fold replication we could have used single-pass sampling to screen 80 % of Montney-related infrastructure. This is the first bottom-up study of fugitive emissions in the Canadian energy sector, and these results can be used to inform policy development in an era of methane emission reduction efforts.

Aquistore is an independent research project managed by the PTRC demonstrating the storage of carbon dioxide (CO2) deep underground in a brine sandstone formation. Results from the baseline MMV program are compared with measurements after the injection of 36,000 tonnes of CO2. Surface seismic results indicated excellent repeatability with baseline surveys; the data achieved a global NRMS of 10%, allowing for the detection of small amounts of CO2 at significant depths. Passive seismic monitoring detected no injection-induced seismicity. Post-injection groundwater and soil gas sampling was relatively unchanged, and indicate there are no signs of seepage of CO2 at the site.

Salt marshes are ecologically sensitive ecosystems where mercury (Hg) methylation and biomagnification can occur. Understanding the mechanisms controlling gaseous Hg flux from salt marshes is important to predict the retention of Hg in coastal wetlands and project the impact of environmental change on the global Hg cycle. We monitored Hg flux from a remote salt marsh over 9 days which included three cloudless days and a 4 mm rainfall event. We observed a cyclical diel relationship between Hg flux and solar radiation. When measurements at the same irradiance intensity are considered, Hg flux was greater in the evening when the sediment was warm than in the morning when the sediment was cool. This is evidence to suggest that both solar radiation and sediment temperature directly influence the rate of Hg(II) photoreduction in salt marshes. Hg flux could be predicted from solar radiation and sediment temperature in sub-datasets collected during cloudless days (R2 = 0.99), and before (R2 = 0.97) and after (R2 = 0.95) the rainfall event, but the combined dataset could not account for the lower Hg flux after the rainfall event that is in contrast to greater Hg flux observed from soils after rainfall events.

Recent warming in the Arctic, which has been amplified during the winter1–3, greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)4. However, the amount of CO2 released in winter is not known and has not been well represented by ecosystem models or empirically based estimates5,6. Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October–April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (−1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario—Representative Concentration Pathway 4.5—and 41% under business-as-usual emissions scenario—Representative Concentration Pathway 8.5. Our results provide a baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions. Winter warming in the Arctic will increase the CO2 flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.

Energy reserves have been exploited in the Atlantic Canadian provinces since the early 1600s, and many fossil fuel extraction sites have been abandoned over this long history of energy development. Oil, natural gas, and coal extraction sites are a source of greenhouse gas emissions, particularly for methane (CH4). In this study, we used multiple sampling methods to measure CH4 from abandoned coal mine openings in Nova Scotia and a legacy oilfield in New Brunswick. Atmospheric and shallow soil gases were sampled around legacy sites using flux rate chamber measurements (spatial and temporal) and plot-scale atmospheric gas surveys, in addition to regional gas screening surveys over larger populations of sites to confirm whether small-scale observations were reflected regionally. Only one oil and gas site (2.4 ± 3.1⋅ 102 mg m− 2 day− 1) and one abandoned coal mine opening (1.0 ± 1.1⋅ 102 mg m− 2 day− 1) were affected by soil CH4 migration, though rates of leakage were minimal and would rank as low severity on industrial scales. Plot-scale atmospheric gas screening showed super-ambient CH4 concentrations at 5 sites in total (n = 16), 2 coal adits and 3 abandoned oil and gas wells. Regional gas screening surveys suggest that 11% of legacy oil and gas sites have some emission impacts, compared with 1–2% of legacy coal sites. These frequencies are close, albeit lower than the 15% of legacy oil and gas sites and 10% of abandoned coal mine openings flagged from our aggregated small-scale observations. These sites may emit less than other developments studied to date either because more time has elapsed since extraction, or because differences in regional geology reduce the likelihood of sustained emissions. This study provides valuable information to help understand the methane emission risks associated with legacy energy sites.

Aggressive reductions of oil and gas sector methane, a potent greenhouse gas, have been proposed in Canada. Few large-scale measurement studies have been conducted to confirm a baseline. This study used a vehicle-based gas monitoring system to measure fugitive and vented gas emissions across Lloydminster (heavy oil), Peace River (heavy oil/bitumen), and Medicine Hat (conventional gas) developments in Alberta, Canada. Four gases (CO2, CH4, H2S, C2H6), and isotopic δ13CCH4 were recorded in real-time at 1 Hz over a six-week field campaign. We sampled 1,299 well pads, containing 2,670 unique wells and facilities, in triplicate. Geochemical emission signatures of fossil fuel-sourced plumes were identified and attributed to nearby, upwind oil and gas well pads, and a point-source gaussian plume dispersion model was used to quantify emissions rates. Our analysis focused exclusively on well pads where emissions were detected >50% of the time when sampled downwind. Emission occurrences and rates were highest in Lloydminster, where 40.8% of sampled well pads were estimated to be emitting methane-rich gas above our minimum detection limits (m = 9.73 m3d–1). Of the well pads we found to be persistently emitting in Lloydminster, an estimated 40.2% (95% CI: 32.2%–49.4%) emitted above the venting threshold in which emissions mitigation under federal regulations would be required. As a result of measured emissions being larger than those reported in government inventories, this study suggests government estimates of infrastructure affected by incoming regulations may be conservative. Comparing emission intensities with available Canadian-based research suggests good general agreement between studies, regardless of the measurement methodology used for detection and quantification. This study also demonstrates the effectiveness in applying a gaussian dispersion model to continuous mobile-sourced emissions data as a first-order leak detection and repair screening methodology for meeting regulatory compliance.

The present study examined potential effects of seasonal variations in photoreactive dissolved organic matter (DOM) on methylmercury (MeHg) photodemethylation rates in freshwaters. A series of controlled experiments were carried out using natural and photochemically preconditioned DOM in water collected from one lake in June, August, and October. Natural DOM concentrations doubled between June and August (DOC = 10.2–21.2 mg C L−1) and then remained stable into October (DOC = 19.4 mg C L−1). Correspondingly, MeHg concentrations peaked in August (0.42 ng L−1) along with absorbances at 350 nm (A350) and 254 nm (SUVA254). Up to 70% of the MeHg was photodemethylated in the short 48-hour irradiation experiments with June having significantly higher rates than the other sampling months (p 0.10). However, MeHg photodemethylation efficiencies (quantified in mole MeHg lost/mole photon absorbed) were higher in treatments with less photoreactive DOM. Congruently, MeHg photodemethylation efficiencies also decreased over summer by up to 10× across treatments in association with increased photoreactive DOM, and were negatively correlated with DOM concentration. These results suggest that an important driver of MeHg photodemethylation is the interplay between MeHg and DOM with greater potential for photodemethylation in freshwaters with more photobleached DOM and lower DOM content. This article is protected by copyright. All rights reserved

Soil is a significant source of CO2 emission to the atmosphere, and this process is accelerating at high latitudes due to rapidly changing climates. To investigate the sensitivity of soil CO2 emissions to high temporal frequency variations in climate, we performed continuous monitoring of soil CO2 efflux using Forced Diffusion (FD) chambers at half-hour intervals, across three representative Alaskan soil cover types with underlying permafrost. These sites were established during the growing season of 2015, on the Seward Peninsula of western Alaska. Our chamber system is conceptually similar to a dynamic chamber, though FD is more durable and water-resistant and consumes less power, lending itself to remote deployments. We first conducted methodological tests, testing different frequencies of measurement, and did not observe a significant difference between collecting data at 30-min and 10-min measurement intervals (averaged half-hourly) (p

Biogeochemical processes driving the spatial variability of soil CO2 production and flux are well studied, but little is known about the variability in the spatial distribution of the stable carbon isotopes that make up soil CO2, particularly in complex terrain. Spatial differences in stable isotopes of soil CO2 could indicate fundamental differences in isotopic fractionation at the landscape level and may be useful to inform modeling of carbon cycling over large areas. We measured the spatial and seasonal variabilities of the δ13C of soil CO2 (δS) and the δ13C of soil CO2 flux (δP) in a subalpine forest ecosystem located in the Rocky Mountains of Montana. We found consistently more isotopically depleted values of δS and δP in low and wet areas of the landscape relative to steep and dry areas. Our results suggest that the spatial patterns of δS and δP are strongly mediated by soil water and soil respiration rate. More interestingly, our analysis revealed different temporal trends in δP across the landscape; in high landscape positions δP became more positive, whereas in low landscape positions δP became more negative with time. These trends might be the result of differential dynamics in the seasonality of soil moisture and its effects on soil CO2 production and flux. Our results suggest concomitant yet independent effects of water on physical (soil gas diffusivity) and biological (photosynthetic discrimination) processes that mediate δS and δP and are important when evaluating the δ13C of CO2 exchanged between soils and the atmosphere in complex terrain.

Physical soil properties create lags between temperature change and corresponding soil responses, which obscure true Q10 (temperature sensitivity) values and other biophysical parameters such as depth of production. This study examines an inversion approach for estimating Q10 and e-folding depth of CO2 production (Zp) using physically based soil models, constrained by observed high-frequency surface fluxes and/or concentrations. Our inversion strategy uses a one-dimensional (1-D) multi-layered soil model that simulates realistic temperature and gas diffusion. We tested inversion scenarios on synthetic data using a range of constraining parameters, time-averaging techniques, mechanisms to improve computational efficiency, and various methods of incorporating real data into the model. Overall, we have found that with carefully constrained data, inversion was possible. While inversions using exclusively surface-flux measurements could succeed, constraining the inversion using multiple shallow subsurface CO2 measurements proved to be most successful. Inversions constrained by these shallow measurements returned Q10 and Zp values with average errors of 1.85 and 0.16 % respectively. This work is a first step toward building a reliable framework for removing physical effects from high-frequency soil CO2 data. Ultimately, we hope that this process will lead to better estimates of biophysical soil parameters and their variability on short timescales.

In Weyburn, Saskatchewan, carbon dioxide (CO2) is injected into the Weyburn oilfield for Enhanced Oil Recovery (EOR). Cenovus Energy Inc. operates more than 1000 active wells, processing plants, and hundreds of kilometres of pipeline infrastructure over a >100 km2 area. While vehicle-based atmospheric detection of gas leakage would be convenient for a distributed operation such as Weyburn, implementing atmospheric detection schemes, particularly those that target CO2, are challenging in that natural ecosystems and other human activities both emit CO2 and will contribute to regular false positives. Here we present field test results of a multi-gas atmospheric detection technique that uses observed trace gas ratios (CO2, CH4, and H2S) to discriminate plumes of gas originating from different sources. This work is part of a larger project focused on multi-scale fugitive emissions detection and plume discrimination. During 2013 and 2014, we undertook vehicle-based mobile surveys of CO2, CH4, H2S, and δ 13CH4, in the Weyburn oilfield, using customized Cavity Ring Down Spectroscopy (CRDS) instruments that also alternated as stationary receptors. Mobile surveys provided georeferenced observations of atmospheric gas concentrations every 20–30 m, along a route driven at roughly 70 km h−1. Data were uploaded to remote servers and processed using visualization tools that allowed us to constrain the location and timing of potential emission events. Results from one day of mobile surveying, September 24, 2013, are presented here to illustrate how industrial activities, combustion engine and flare stack source emissions can be discriminated on the basis of excess mixing gas ratios, at distances from a few hundreds metres, to kilometres, in the Weyburn oilfield.

Permafrost soils currently store approximately 1672 Pg of carbon (C), but as high latitudes warm, this temperature-protected C reservoir will become vulnerable to higher rates of decomposition. In recent decades, air temperatures in the high latitudes have warmed more than any other region globally, particularly during the winter. Over the coming century, the arctic winter is also expected to experience the most warming of any region or season, yet it is notably understudied. Here we present nonsummer season (NSS) CO2 flux data from the Carbon in Permafrost Experimental Heating Research project, an ecosystem warming experiment of moist acidic tussock tundra in interior Alaska. Our goals were to quantify the relationship between environmental variables and winter CO2 production, account for subnivean photosynthesis and late fall plant C uptake in our estimate of NSS CO2 exchange, constrain NSS CO2 loss estimates using multiple methods of measuring winter CO2 flux, and quantify the effect of winter soil warming on total NSS CO2 balance. We measured CO2 flux using four methods: two chamber techniques (the snow pit method and one where a chamber is left under the snow for the entire season), eddy covariance, and soda lime adsorption, and found that NSS CO2 loss varied up to fourfold, depending on the method used. CO2 production was dependent on soil temperature and day of season but atmospheric pressure and air temperature were also important in explaining CO2 diffusion out of the soil. Warming stimulated both ecosystem respiration and productivity during the NSS and increased overall CO2 loss during this period by 14% (this effect varied by year, ranging from 7 to 24%). When combined with the summertime CO2 fluxes from the same site, our results suggest that this subarctic tundra ecosystem is shifting away from its historical function as a C sink to a C source.

Earth system scientists working with radiocarbon in organic samples use a stable carbon isotope (δ13C) correction to account for mass-dependent fractionation caused primarily by photosynthesis. Although researchers apply this correction routinely, it has not been evaluated for the soil gas environment, where both diffusive gas transport and diffusive mixing are important. Towards this end we applied an analytical soil gas transport model across a range of soil diffusivities and biological CO2 production rates, allowing us to control the radiocarbon (Δ14C) and stable isotope (δ13C) compositions of modeled soil CO2 production and atmospheric CO2. This approach allowed us to assess the bias that results from using the conventional correction method for estimating Δ14C of soil production. We found that the conventional correction is inappropriate for interpreting the radio-isotopic composition of CO2 from biological production, because it does not account for diffusion and diffusive mixing. The resultant Δ14C bias associated with the traditional correction is highest (up to 150 ‰) in soils with low biological production and/or high soil diffusion rates. We propose a new solution for radiocarbon applications in the soil gas environment that fully accounts for diffusion and diffusive mixing.

Recent studies have examined temporal fluctuations in the amount and carbon isotope content (δ13C) of CO2 produced by the respiration of roots and soil organisms. These changes have been correlated with diel cycles of environmental forcing (e.g., sunlight and soil temperature) and with synoptic-scale atmospheric motion (e.g., rain events and pressure-induced ventilation). We used an extensive suite of measurements to examine soil respiration over 2 months in a subalpine forest in Colorado, USA (the Niwot Ridge AmeriFlux forest). Observations included automated measurements of CO2 and δ13C of CO2 in the soil efflux, the soil gas profile, and forest air. There was strong diel variability in soil efflux but no diel change in the δ13C of the soil efflux (δR) or the CO2 produced by biological activity in the soil (δJ). Following rain, soil efflux increased significantly, but δR and δJ did not change. Temporal variation in the δ13C of the soil efflux was unrelated to measured environmental variables, and we failed to find an explanation for this unexpected result. Measurements of the δ13C of the soil efflux with chambers agreed closely with independent observations of the isotopic composition of soil CO2 production derived from soil gas well measurements. Deeper in the soil profile and at the soil surface, results confirmed established theory regarding diffusive soil gas transport and isotopic fractionation. Deviation from best-fit diffusion model results at the shallower depths illuminated a pump-induced ventilation artifact that should be anticipated and avoided in future studies. There was no evidence of natural pressure-induced ventilation of the deep soil. However, higher variability in δ13C of the soil efflux relative to δ13C of production derived from soil profile measurements was likely caused by transient pressure-induced transport with small horizontal length scales.

Monitoring is cited as a mechanism by which operators can drive public acceptance in CO2 geosequestration and energy projects. In this synthesis study we inter-compared a broad suite of geochemical monitoring indicators, to identify which could contribute best to an affordable, yet effective, monitoring system. We examined two very comprehensive datasets, collected during a leak investigation, from a CO2 enhanced oil recovery (EOR) project in Weyburn, Canada, and applied an existing signal to noise ratio (SNR) approach to build a quantitative benchmark for each indicator. Despite the fact that a leak would be composed mostly of CO2, the analysis shows that a leak would be difficult to identify at this site based on CO2 or 13C-CO2, owing to the high variability of natural sources. Affordable alternatives such as N2, Ar, He, and CO2/O2 ratio would be less impacted by background variability. The most definitive indicators were 4He/20Ne (a proxy), and radiocarbon-CO2 (a direct indicator), though cost limits their everyday applicability. We conclude that a narrowed suite of indicators could achieve effectiveness at reduced cost, but that definitive indicators should be favoured in cases where leakage is suspected.

This paper examines the sources of uncertainty for the Forced Diffusion (FD) chamber soil respiration (Rs) measurement technique and demonstrates a protocol for uncertainty quantification that could be appropriate with any soil flux technique. Here we sought to quantify and compare the three primary sources of uncertainty in Rs: (1) instrumentation error; (2) scaling error, which stems from the spatial variability of Rs; and (3) random error, which arises from stochastic or unpredictable variation in environmental drivers and was quantified from repeated observations under a narrow temperature, moisture, and time range. In laboratory studies, we found that FD instrumentation error remained constant as Rs increased. In field studies from five North American ecosystems, we found that as Rs increased from winter to peak growing season, random error increased linearly with average flux by about 40% of average Rs. Random error not only scales with soil flux but scales in a consistent way (same slope) across ecosystems. Scaling error, measured at one site, similarly increased linearly with average Rs, by about 50% of average Rs. Our findings are consistent with previous findings for both soil fluxes and eddy covariance fluxes across other northern temperate ecosystems that showed random error scales linearly with flux magnitude with a slope of ~0.2. Although the mechanistic basis for this scaling of random error is unknown, it is suggestive of a broadly applicable rule for predicting flux random error. Also consistent with previous studies, we found the random error of FD follows a Laplace (double-exponential) rather than a normal (Gaussian) distribution.

A gas concentration sensor comprising a long period grating with a high refractive index coating is reported. The deposition of a high refractive index coating on the optical fiber allows a reorganization of the cladding modes which leads to a substantial increase in the sensitivity to the surrounding refractive index. To maximize the grating sensitivity in the vicinity of the refractive index of CO 2 , the grating was coated with a 365 nm layer of polystyrene. The results show that the sensor is able to distinguish between the CO 2 and N 2 gases with high reproducibility and reversibility. The sensitivity of the sensor is 1.23 pm/%CO 2 .

Measurements of the stable isotope composition of soil flux have many uses, from separating autotrophic and heterotrophic components of respiration to teasing apart information about gas transport physics. While soil flux chambers are typically used for these measurements, subsurface approaches are becoming more accessible with the introduction of field-deployable isotope analyzers. These subsurface measurements have the unique benefit of offering depth-resolved isotopologue flux data, which can help to disentangle the many soil respiration processes that occur throughout the soil profile. These methods are likely to grow in popularity in the coming years and a solid methodological basis needs to be formed in order for data collected in these subsurface studies to be interpreted properly. Here we explore the range of possible techniques that could be used for subsurface isotopologue gas interpretation and rigorously test the assumptions and application of each approach using a combination of numerical modeling, laboratory experiments, and field studies. Our results suggest that methodological uncertainties arise due to poor assumptions and mathematical instabilities but certain methods, particularly those based on diffusion physics, are able to cope with these uncertainties well and produce excellent depth-resolved isotopologue flux data.

Fiber-optic sensors for dissolved CO 2 are an emergent technology for monitoring marine geologic CO 2 sequestration sites. Fiber- optic sensing technology has been used successfully in the oil and gas sector and is advantageous because it is capable of cost- effective, instantaneous, distributed sensing. This is an improvement over current practice, which normally requires samples to be pumped to the surface for analysis. Biofouling of fiber-based sensors is a concern for the marine environment, as the biofouling can cause signal drift and also adversely impact the sensor's ability to detect dissolved CO 2 . Single mode optical fibers with long period gratings etched onto the core of the fiber were used for this study. Pseudoalteromonas sp. NCIMB 2021 was cultured and grown on sensing elements using nutrient-dense synthetic seawater. Biofouling was shown to cause shifts in the baseline signal. Post-fouling sensitivity of the sensor was also reduced relative to pre-fouling levels. Mechanical cleaning of the sensors restored sensor sensitivity to that seen prior to bacterial colonization.