Biogenic CH4 Research Articles

Unlocking glycerol Potential: Novel pathway for hydrogen production and Value-Added chemicals

In the global fight against climate change, the bio-based supply chain represents an interesting solution as it offers the potential to produce high-value-added products and bioenergy through the utilization of waste and by-products. In this work, a new route is proposed for the conversion of bio-based glycerol to H2/CO2 and high value-added liquid and solid products. The innovative process used pure or crude glycerol or ethanol-glycerol mixture along with water and sodium metaborate as reagents at 300 °C under discontinuous conditions. The gas stream consists mainly of hydrogen, followed by biogenic CO2 (31–54 %), CO (4–13 %) and CH4 in traces. The presence of water in the tested crude glycerol improved the hydrogen selectivity to 55 %. Characterization of the liquid reaction products revealed the synthesis of products such as 1,2-propanediol, propanoic acid, acetic acid, cyclopentenones and cyclic diglycerol. In the solid phase, an aliphatic hydrocarbon resin with oxygenated carbon along the saturated chain and an aromatic cluster were also characterized by NMR, FTIR and TG analyses. Based on these findings, the global reaction route to the general reaction products was proposed.

Cyanobacteria decay alters CH4 and CO2 produced hotspots along vertical sediment profiles in eutrophic lakes

Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH4 and CO2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH4 and CO2, this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH4 and CO2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m2·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH4 and CO2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH4 and CO2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH4 and CO2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH4 and CO2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH4 and CO2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions.

Exploring the role of high-value crops to reduce agricultural greenhouse gas emissions in New Zealand

This study explores the potential benefits of transitioning from livestock farming to high-value alternative crops as a strategy for mitigating agricultural greenhouse gas (GHG) emissions in New Zealand. The government has set ambitious targets for reducing methane (CH4) emissions. However, since animal product exports play a crucial role in New Zealand’s economy, any shift in land use will have significant impacts on both the regional and national economy. We developed a GIS framework that integrated (i) growing requirements, (ii) GHG emissions and (iii) profitability for crops. Analysis of export market opportunities identified twelve high-value “alternative crops”. Availability of suitable land for crop expansion was not a limiting factor. Working with the Ministry for Primary Industries, we explored how land use change scenarios contributed to Government 2050 biogenic CH4 emission reduction targets. Doubling the area of alternative crops (a 195,000-ha increase) by reallocating land from livestock farming resulted in reducing biogenic CH4 emissions by 1.2 to 5.4% (0.35 to 1.57 Mt CO2-e) compared to 2017 baseline values, contributing to between 2.6 and 22.5% of the 2050 CH4 reduction targets, simultaneously increasing profitability by $NZ1.25 to 1.32 billion annually. While this approach demonstrates potential benefits of land use change, a deeper understanding of the complexity of land use decision-making is required to enable successful transitions. Addressing barriers to change requires collaborative efforts from land users, researchers and policy makers.

Controls of Atmospheric Methane on Early Earth and Inhabited Earth-like Terrestrial Exoplanets

Methane (CH4) is a primarily biogenic greenhouse gas. As such, it represents an essential biosignature to search for life on exoplanets. Atmospheric CH4 abundance on Earth-like inhabited exoplanets is likely controlled by marine biogenic production and atmospheric photochemical consumption. Such interactions have been previously examined for the case of the early Earth where primitive marine ecosystems supplied CH4 to the atmosphere, showing that the atmospheric CH4 response to biogenic CH4 flux variations is nonlinear, a critical property when assessing CH4 reliability as a biosignature. However, the contributions of atmospheric photochemistry, metabolic reactions, or solar irradiance to this nonlinear response are not well understood. Using an atmospheric photochemical model and a marine microbial ecosystem model, we show that the production of hydroxyl radicals from water vapor photodissociation is a critical factor controlling the atmospheric CH4 abundance. Consequently, atmospheric CH4 partial pressure (pCH4) on inhabited Earth-like exoplanets orbiting Sun-like stars (F-, G-, and K-type stars) would be controlled primarily by stellar irradiance. Specifically, irradiance at wavelengths of approximately 200–210 nm is a major controlling factor for atmospheric pCH4 when the carbon dioxide partial pressure is sufficiently high to absorb most stellar irradiance at 170–200 nm. Finally, we also demonstrated that inhabited exoplanets orbiting near the outer edge of K-type stars’ habitable zones are better suited for atmospheric pCH4 buildup. Such properties will provide valuable support for future detection of life signatures.

Integrated geochemical and microbiological assessments of Astroni lakes reveals Campi Flegrei unrest signatures

Astroni volcano in the Campi Flegrei caldera (southern Italy) is a 2 km wide, densely vegetated tuff ring and hosting several volcanic structures, including tuff cones, scoriae cones, lava domes, and three small lakes. Geochemical data of waters and dissolved gases from the lakes, coupled with microbiological analyses on lake water and sediments, were used to shed light on the possible relationship between the lakes and the hydrothermal fluid circulation system as suggested by previous geophysical surveys. Water chemistry was dominated by solutes, mainly Na+ and HCO3−, deriving from fluids and CO2-rich gases typically found in discharges located at the periphery of hydrothermal-volcanic systems. Lago Grande (LG) lake showed an anoxic hypolimnion with abundant non-atmospheric dissolved gases, consisting of biogenic CH4 and CO2, the latter having a twofold origin, biogenic and hydrothermal. The occurrence of anaerobic methanotrophs coupled with the lack of hydrogenotrophic methanogenic archaea along the whole vertical profile of LG suggested that CH4 was mostly produced from degradation of abundant terrestrial organic matter within the deep lake sediments, and then consumed during its diffusion through the lake. Notwithstanding, the output rate of CH4 from LG surface was anomalously high relative to those commonly measured in lakes. Carbon dioxide from the hydrothermal source and produced by CH4 oxidation was partially fixed in the lake via the acetyl-CoA pathway. Accordingly, the CO2 fluxes from the LG surface were relatively low, in the range of those measured in volcanic lakes dominated by biogenic CO2. The dependence of the chemistry of the Astroni lakes on inputs from the Campi Flegrei hydrothermal system, besides on biogeochemical processes, offers a possible explanation for the anomalous increase of the LG water level occurred in the last years, which was not consistent with the recorded local rainfall but likely caused by an increasing hydraulic pressure related to the enhanced hydrothermal activity recorded at Campi Flegrei in the last decades. According to this hypothesis, the future evolution of the current volcanic unrest may govern the fate of the lake water level with important implications for the functioning of the precious Astroni ecosystem.

Performance of wastewater treatment plants in emission of greenhouse gases

The present work has estimated greenhouse gas emissions in aerobic and anaerobic Wastewater Treatment Plants in Southern Italy. Greenhouse gases emissions from each treatment unit were calculated based on emission factors related to Chemical Oxygen Demand removal for biogenic CO2 and CH4 assessment and on Nitrogen removal for N2O. N2O, biogenic CO2, and CH4 emissions vary for aerobic and anaerobic-based WWTPs respectively from 73 kgCO2eq/PE*y for anaerobic plants to 91 kgCO2eq/PE*y for aerobic plants. In aerobic and anaerobic digestion systems WWTPs the contributions to CO2eq total emissions from N2O, CH4, biogenic CO2, and fossil CO2 are 30 %–33 %, 20 %–29 %, 22 %–25 %, and 26 %–16 %, respectively. N2O emissions from biological processes were found the most contributing sources of greenhouse gases while in the physical processes higher contribution is indirect carbon dioxide related to energy consumption. Compensatory measures are reported to reduce greenhouse gases emissions.

Six years of continuous carbon isotope composition measurements of methane in Heidelberg (Germany) – a study of source contributions and comparison to emission inventories

Abstract. Mitigation of greenhouse gases requires a precise knowledge of their sources at both global and regional scales. With improving measurement techniques, in situ δ(13C,CH4) records are analysed in a growing number of studies to characterise methane emissions and to evaluate inventories at regional and local scales. However, most of these studies cover short time periods of a few months, and the results show a large regional variability. In this study, a 6-year time record of in situ δ(13C,CH4), measured with a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg, Germany, is analysed to obtain information about seasonal variations and trends of CH4 emissions. The Keeling plot method is applied to atmospheric measurements on different timescales, and the resulting source contributions are used to evaluate the CH4 emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGAR v6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW). The mean isotopic carbon source signature for the Heidelberg catchment area derived from atmospheric measurements is (-52.3±0.4) ‰ and shows an annual cycle with 5.8 ‰ more depleted values in summer than in winter. This annual cycle can only be partly explained by seasonal variations in the 13C-enriched emissions from heating and reveals strong seasonal variations in biogenic CH4 emissions in the Heidelberg catchment area, which are not included in EDGAR v6.0. The comparison with emission inventories also shows that EDGAR v6.0 overestimates the CH4 emissions from less depleted sources. In situ CH4 isotope analysers at continental and urban monitoring stations can make an important contribution to the verification and improvement of emission inventories.

Thermogenic methane and hydrogen generation in subducted sediments of the Nankai Trough

Active and widespread CH4 accumulations and emissions in the Nankai Trough subduction zone are attested by numerous mud volcanoes, gas plumes, and gas hydrates containing biogenic and thermogenic CH4. However, the source rocks of the thermogenic CH4 and the geological source of H2 for microbial CH4 production by methanogens remain uncertain. Here, we reveal the timing and rate of thermogenic CH4 and H2 generation from shales and metapelites associated with oceanic plate subduction in the Nankai Trough by gas and geochemical analyses. The results show that the thermogenic CH4 and H2 are generated mainly in the underthrust sediments below the décollement. The sustainable H2 supply from the underthrust sediments can potentially contribute to microbial CH4 production. The findings enhance our understanding of the active CH4 emission, large-scale gas hydrate formation, and subseafloor biosphere in the oceanic plate subduction zone.

The Greenhouse Gas Budget of Terrestrial Ecosystems in East Asia Since 2000

AbstractEast Asia (China, Japan, Koreas, and Mongolia) has been the world's economic engine over at least the past two decades, exhibiting a rapid increase in fossil fuel emissions of greenhouse gases (GHGs) and has expressed the recent ambition to achieve climate neutrality by mid‐century. However, the GHG balance of its terrestrial ecosystems remains poorly constrained. Here, we present a synthesis of the three most important long‐lived greenhouse gases (CO2, CH4, and N2O) budgets over East Asia during the decades of 2000s and 2010s, following a dual constraint approach. We estimate that terrestrial ecosystems in East Asia is close to neutrality of GHGs, with a magnitude of between −46.3 ± 505.9 Tg CO2eq yr−1 (the top‐down approach) and −36.1 ± 207.1 Tg CO2eq yr−1 (the bottom‐up approach) during 2000–2019. This net GHG sink includes a large land CO2 sink (−1229.3 ± 430.9 Tg CO2 yr−1 based on the top‐down approach and −1353.8 ± 158.5 Tg CO2 yr−1 based on the bottom‐up approach) being offset by biogenic CH4 and N2O emissions, predominantly coming from the agricultural sectors. Emerging data sources and modeling capacities have helped achieve agreement between the top‐down and bottom‐up approaches, but sizable uncertainties remain in several flux terms. For example, the reported CO2 flux from land use and land cover change varies from a net source of more than 300 Tg CO2 yr−1 to a net sink of ∼−700 Tg CO2 yr−1. Although terrestrial ecosystems over East Asia is close to GHG neutral currently, curbing agricultural GHG emissions and additional afforestation and forest managements have the potential to transform the terrestrial ecosystems into a net GHG sink, which would help in realizing East Asian countries' ambitions to achieve climate neutrality.

Nitrous oxide inhibition of methanogenesis represents an underappreciated greenhouse gas emission feedback.

Methane (CH4) and nitrous oxide (N2O) are major greenhouse gases that are predominantly generated by microbial activities in anoxic environments. N2O inhibition of methanogenesis has been reported, but comprehensive efforts to obtain kinetic information are lacking. Using the model methanogen Methanosarcina barkeri strain Fusaro and digester sludge-derived methanogenic enrichment cultures, we conducted growth yield and kinetic measurements and showed that micromolar concentrations of N2O suppress the growth of methanogens and CH4 production from major methanogenic substrate classes. Acetoclastic methanogenesis, estimated to account for two-thirds of the annual 1 billion metric tons of biogenic CH4, was most sensitive to N2O, with inhibitory constants (KI) in the range of 18-25μM, followed by hydrogenotrophic (KI, 60-90μM) and methylotrophic (KI, 110-130μM) methanogenesis. Dissolved N2O concentrations exceeding these KI values are not uncommon in managed (i.e. fertilized soils and wastewater treatment plants) and unmanaged ecosystems. Future greenhouse gas emissions remain uncertain, particularly from critical zone environments (e.g. thawing permafrost) with large amounts of stored nitrogenous and carbonaceous materials that are experiencing unprecedented warming. Incorporating relevant feedback effects, such as the significant N2O inhibition on methanogenesis, can refine climate models and improve predictive capabilities.

Drivers and resilience of methane-derived carbon contribution to chironomid biomass in boreal lakes

General mechanisms underlying the pathways of methane (CH4)-derived carbon in aquatic food webs are often associated with eutrophication-driven anoxia. Yet, the influence of changing nutrient availability on CH4 cycling has been mainly investigated during the increasing phase (i.e. onset of anthropogenic eutrophication), thus leaving unclear whether nutrient reduction can lead to a simple reversion of the observed effects on CH4 cycling. We combined stable isotopes of chironomid remains (δ13CHC) and sedimentary ancient DNA of methanotrophic bacteria (MOB) to unravel the drivers of biogenic CH4 contribution to chironomid biomass in boreal lakes. Using a spatial dataset, our study shows that δ13CHC values were more depleted in hypoxic lakes and were positively associated with methanotrophic bacteria belonging to the γ-proteobacteria class (MOB type I), therefore supporting the view of higher utilization of CH4-derived carbon in anoxic environments. However, this space-for-time substitution approach failed to provide any reliable information on whether lake food webs follow the same pathway in forward and reverse directions. Using downcore reconstruction, our results show that despite a drastic mitigation-induced decrease in nutrient concentrations and strong evidence of biological recovery of algal and chironomid communities, chironomid biomass remained highly subsidized by methanotrophic bacteria throughout the study period. Results therefore suggest that mechanisms underlying the pathways of CH4-derived carbon in aquatic food webs are likely not the same during perturbation and recovery trajectories and that complex feedback mechanisms can stabilize lakes in this CH4-based food web state.

Characterization of atmospheric methane release in the outer Mackenzie River delta from biogenic and thermogenic sources

Abstract. 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 (CH4) emission from biogenic and thermogenic sources. Hotspots are known to have a significant contribution to summertime CH4 emissions in the region. Still, little research has been done to determine how often geologic or biogenic CH4 contributes to 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. Walking transects and point samples of atmospheric CH4 and CO2 concentrations were measured. 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 sources. A CH4 source was determined for eight hotspots, two of which were thermogenic in origin (−42.5 ‰, −44.7 ‰), four of which were biogenic in origin (−71.9 ‰ to −88.3 ‰), and two of which may have been produced by the oxidation of biogenic CH4 (−53.0 ‰, −63.6 ‰), 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.

Identifying Putative Subsurface Microbial Drivers of Methane Flux on Earth and Mars

On Earth microorganisms are critical drivers of the methane cycle, both producing and consuming methane (Boetius et al. 2000, Knittel and Boetius 2009, Orphan et al. 2001). Molecular and isotopic-based investigations of archaeal-bacterial consortia catalyzing the anaerobic oxidation of methane (AOM) in marine methane seeps identified the pivotal role of these microorganisms in mitigating the release of methane into the atmosphere (Knittel and Boetius 2009, Orphan et al. 2001). In the marine environment, AOM is predominantly carried out by closely associated consortia of methanotrophic archaea (ANME) and sulfate reducing bacteria (SRB) coupling methane oxidation to sulfate reduction in the absence of oxygen. Wolf Spring (WS), Axel Heiberg Island, Nunavut is a hypersaline cold spring methane seep and the only known terrestrial permafrost hosted methane seep known to host ANME-1 archaea associated with AOM (Niederberger et al. 2010, Magnuson et al. 2022). Wolf Spring is an unparalleled analogue for putative subsurface brines and sites of methane release on Mars. Enigmatic observations of methane in the near-surface Martian atmosphere remain a tantalizing potential biosignature. The combination of field site characterization, microbial microcosm experiments, and in situ methane monitoring represents a coordinated interdisciplinary effort to identify methane driven microbial metabolisms not only critical to understanding methane flux in the Arctic, but also as possible drivers to the methane cycle on Mars. Detailed microbial characterization of these springs has identified a chemotrophic community dominated by sulfur cycling (Altshuler et al. 2022, Niederberger et al. 2010). To date, microbial and geochemical characterization has been carried out on sediment samples to a few centimeters depth. This study expands on these initial studies, with the successful collection and analysis of deeper sediment cores at WS focusing on AOM activity to better understand the microorganisms involved and the methane cycling capacity at depth. Two decades of observing methane on Mars (Mumma et al. 2009) have generated data indicative of a dynamic, geochemical system characterized by a profile similar to the release of methane from seeps on Earth (Etiope and Oehler 2019) producing both distinct pulses known as plumes and slow background seepage. These observations suggest as of yet unknown geochemical and potentially geobiological methane sources and sinks. While methane can be produced abiotically (Etiope and Lollar 2013), on Earth most methane is biogenic. Determining the biogenicity of CH4 is non-trivial and requires a correlated approach including determination of carbon isotopes. In terrestrial systems, biogenic CH4 is 13C depleted. To characterize methane sources and sinks on Mars, near surface measurements at a frequency not possible with existing instrumentation are required. We are currently developing off-axis integrated cavity-enhanced output (OA-ICOS) spectrometry as a portable trace gas analyzer capable of obtaining high frequency measurements of methane at the sub-ppb level (Sapers et al. 2021). Optimizing OA-ICOS trace methane measurements at WS will help refine sensitivity and measurement cadence in a Mars-like environment as well as providing new remote methane monitoring capabilities for Arctic methane emissions. We are currently developing in situ 12CH4:13CH4 capabilities using OA-ICOS technology. The importance of δ 13C as a biosignature is summarized in Fig. 1.

Sources and controls of greenhouse gases and heavy metals in mine water: A continuing climate legacy

Water pollution arising from abandoned coal mines, is second only to sewage as a source of freshwater pollution and in coalfield catchments mine water can be the dominant pollutant, with oxidised iron smothering the bed of receiving rivers. This study measured greenhouse gases in mine water outflows from sixteen sites across the Midland Valley in Scotland. Radiogenic and stable carbon isotopes measurements (Δ14C and δ13C) were used to determine the sources of both methane (CH4) and carbon dioxide (CO2) produced within the flooded mine environment. Concentrations of CH4-C ranged from 20 to 215 μg l−1 and CO2-C from 30 to 120 mg l−1, with CO2 accounting for 97 % of the mine water global warming potential. Methane origins included 51 % modern biogenic, 41 % thermogenic and 8 % from hydrogenotrophic methanogenesis of coal. The most significant inverse impact on biogenic CH4 concentrations was sulphate, most likely due to sulphate reducing bacteria outcompeting methanogens. Carbon dioxide origins included 64 % from the dissolution of limestone, 21 % from terrestrial organic carbon and 15 % from coal. The limestone derived CO2 was positively correlated with high sulphate concentrations, which resulted in sulphuric acid and caused the dissolution of carbonate from limestone. The mine waters experienced significant carbonate buffering becoming only slightly acidic (pH 6–7), but with significant loss of inorganic carbon. The mine waters had low dissolved oxygen (6–25 %) and high dissolved iron (2 to 65 mg l−1) and manganese (0.5 to 5 mg l−1) concentrations. Dissolved greenhouse gases from abandoned mines were estimated as 0.27 +0.31−0.18% of Scotland's global warming potential. This novel work has contributed information about the sources and controls of greenhouse gas fluxes in mine waters and identified the need to quantify and report this emissions term.

Effects on global warming by microbial methanogenesis in alkaline lakes during the Late Paleozoic Ice Age (LPIA)

Abstract Methane (CH4) is an important greenhouse gas, but its behavior and influencing factors over geological time scales are not sufficiently clear. This study investigated the Late Paleozoic Ice Age (LPIA), which is thought to have experienced an interval of rapid warming at ca. 304 Ma, that may have been analogous to modern warming. To explore possible causes of this warming event, we investigated ancient alkaline lakes in the Junggar Basin, northwestern China. Results show that microbial CH4 cycling here was strong, as evidenced by carbonate δ13C (δ13Ccarb) values of >5‰, ~+0.6‰ offsets between pristane δ13C (δ13CPr) and phytane δ13C (δ13CPh) values, a 3β-methylhopane index of 9.5% ± 3.0%, and highly negative δ13C values of hopanes (–44‰ to –61‰). Low sulfate concentrations in the alkaline lakes made methanogenic archaea more competitive than sulfate-reducing bacteria, and the elevated levels of dissolved inorganic carbon promoted methanogenesis. Biogenic CH4 emissions from alkaline lakes, in addition to CO2, may have contributed to rapid climate warming.

Quantification of methane emissions in Hamburg using a network of FTIR spectrometers and an inverse modeling approach

Abstract. Methane (CH4) is a potent greenhouse gas, and anthropogenic CH4 emissions contribute significantly to global warming. In this study, the CH4 emissions of the second most populated city in Germany, Hamburg, were quantified with measurements from four solar-viewing Fourier transform infrared (FTIR) spectrometers, mobile in situ measurements, and an inversion framework. For source type attribution, an isotope ratio mass spectrometer was deployed in the city. The urban district hosts an extensive industrial and port area in the south as well as a large conglomerate of residential areas north of the Elbe River. For emission modeling, the TNO GHGco (Netherlands Organisation for Applied Scientific Research greenhouse gas and co-emitted species emission database) inventory was used as a prior for the inversion. In order to improve the inventory, two approaches were followed: (1) the addition of a large natural CH4 source, the Elbe River, which was previously not included in the inventory, and (2) mobile measurements were carried out to update the spatial distribution of emissions in the TNO GHGco gridded inventory and derive two updated versions of the inventory. The addition of the river emissions improved model performance, whereas the correction of the spatial distribution with mobile measurements did not have a significant effect on the total emission estimates for the campaign period. A comparison of the updated inventories with emission estimates from a Gaussian plume model (GPM) showed that the updated versions of the inventory match the GPM emissions estimates well in several cases, revealing the potential of mobile measurements to update the spatial distribution of emission inventories. The mobile measurement survey also revealed a large and, at the time of the study, unknown point source of thermogenic origin with a magnitude of 7.9 ± 5.3 kg h−1 located in a refinery. The isotopic measurements show strong indications that there is a large biogenic CH4 source in Hamburg that produced repeated enhancements of over 1 ppm which correlated with the rising tide of the river estuary. The CH4 emissions (anthropogenic and natural) of the city of Hamburg were quantified as 1600 ± 920 kg h−1, 900 ± 510 kg h−1 of which is of anthropogenic origin. This study reveals that mobile street-level measurements may miss the majority of total methane emissions, potentially due to sources located within buildings, including stoves and boilers operating on natural gas. Similarly, the CH4 enhancements recorded during the mobile survey from large-area sources, such as the Alster lakes, were too small to generate GPM emission estimates with confidence, but they could nevertheless influence the emission estimates based on total column measurements.

Temporal dynamics and controlling factors of CO2 and CH4 variability in the urban atmosphere of Wroclaw, Poland

Temporal and spatial distribution of both biogenic and anthropogenic components of atmospheric carbon dioxide (CO2) and methane (CH4) is crucial for understanding the environmental impacts of climate change over urban areas. This research focuses on applying stable isotope source-partitioning studies to determine the interactions between biogenic and anthropogenic CO2 and CH4 emissions in an average-sized city environment. Study signifies the weight of instantaneous variability and diurnal averaging as compared with seasonal records of variations of the atmospheric CO2 and CH4 at a variety of typical urban sites in the city of Wroclaw, conducted during a one-year period from June 2017 to August 2018.The findings reveal distinct temporal variations in atmospheric CO2 and CH4 mole fractions and their isotopic composition. The average atmospheric CO2 and CH4 mole fractions during the study period were 416.4 ± 20.5 ppm, and 1.95 ± 0.09 ppm, respectively. The study highlights the high variability of driving forces, including current energy use patterns, natural carbon reservoirs, planetary boundary layer dynamics, and atmospheric transport. Additionally, the relationship between the evolution of the convective boundary layer depth and the CO2 budget was analyzed using the CLASS model with input parameters based on field observations, resulting in insights such as an increase in the range of 25–65 ppm of CO2 during stable nocturnal boundary layers.The observed changes in stable isotopic signatures of air samples allowed for the identification of two main source categories in the city area: fuel combustion and biogenic processes. The δ13C-CO2 values of collected samples suggest that biogenic emissions dominate (up to 60 % of CO2 excess mole fraction) during the growing season, but are reduced by plant photosynthesis during summer afternoons. In contrast, local fossil-fuel CO2 contribution (up to 90 % of excess CO2 mole fraction) from domestic heating, vehicle emissions, and heat and power plants predominantly influence the urban GHG budget during winter. The δ13C-CH4 values indicate anthropogenic sources related to fossil fuel combustion during winter, with values ranging from −44.2 ‰ to −51.4 ‰, while slightly more depleted values, between −47.1 ‰ and −54.2 ‰, reflect a larger input of biological processes in the methane urban budget during summer.Overall, instantaneous and hourly variability of the above-mentioned readings of gas mole fraction and isotopic composition, have shown higher variability than seasonal amplitudes. Hence, respecting this granularity is the key to alignment and understanding significance of such localized atmospheric pollution studies. Additionally, the changing overprint of the system's framework, such as variability of wind and atmospheric layering patterns, weather events, provides context of sampling and data analysis at different frequencies.

Biogeochemical transformations after the emergence of oxygenic photosynthesis and conditions for the first rise of atmospheric oxygen.

The advent of oxygenic photosynthesis represents the most prominent biological innovation in the evolutionary history of the Earth. The exact timing of the evolution of oxygenic photoautotrophic bacteria remains elusive, yet these bacteria profoundly altered the redox state of the ocean-atmosphere-biosphere system, ultimately causing the first major rise in atmospheric oxygen (O2 )-the so-called Great Oxidation Event (GOE)-during the Paleoproterozoic (~2.5-2.2 Ga). However, it remains unclear how the coupled atmosphere-marine biosphere system behaved after the emergence of oxygenic photoautotrophs (OP), affected global biogeochemical cycles, and led to the GOE. Here, we employ a coupled atmospheric photochemistry and marine microbial ecosystem model to comprehensively explore the intimate links between the atmosphere and marine biosphere driven by the expansion of OP, and the biogeochemical conditions of the GOE. When the primary productivity of OP sufficiently increases in the ocean, OP suppresses the activity of the anaerobic microbial ecosystem by reducing the availability of electron donors (H2 and CO) in the biosphere and causes climate cooling by reducing the level of atmospheric methane (CH4 ). This can be attributed to the supply of OH radicals from biogenic O2 , which is a primary sink of biogenic CH4 and electron donors in the atmosphere. Our typical result also demonstrates that the GOE is triggered when the net primary production of OP exceeds >~5% of the present oceanic value. A globally frozen snowball Earth event could be triggered if the atmospheric CO2 level was sufficiently small (<~40 present atmospheric level; PAL) because the concentration of CH4 in the atmosphere would decrease faster than the climate mitigation by the carbonate-silicate geochemical cycle. These results support a prolonged anoxic atmosphere after the emergence of OP during the Archean and the occurrence of the GOE and snowball Earth event during the Paleoproterozoic.

Multi-Isotope Geochemical Baseline Study of the Carbon Management Canada Research Institutes CCS Field Research Station (Alberta, Canada), Prior to CO2 Injection

Carbon capture and storage (CCS) is an industrial scale mitigation strategy for reducing anthropogenic CO2 from entering the atmosphere. However, for CCS to be routinely deployed, it is critical that the security of the stored CO2 can be verified and that unplanned migration from a storage site can be identified. A number of geochemical monitoring tools have been developed for this purpose, however, their effectiveness critically depends on robust geochemical baselines being established prior to CO2 injection. Here we present the first multi-well gas and groundwater characterisation of the geochemical baseline at the Carbon Management Canada Research Institutes Field Research Station. We find that all gases exhibit CO2 concentrations that are below 1%, implying that bulk gas monitoring may be an effective first step to identify CO2 migration. However, we also find that predominantly biogenic CH4 (∼90%–99%) is pervasive in both groundwater and gases within the shallow succession, which contain numerous coal seams. Hence, it is probable that any upwardly migrating CO2 could be absorbed onto the coal seams, displacing CH4. Importantly, 4He concentrations in all gas samples lie on a mixing line between the atmosphere and the elevated 4He concentration present in a hydrocarbon well sampled from a reservoir located below the Field Research Station (FRS) implying a diffusive or advective crustal flux of 4He at the site. In contrast, the measured 4He concentrations in shallow groundwaters at the site are much lower and may be explained by gas loss from the system or in situ production generated by radioactive decay of U and Th within the host rocks. Additionally, the injected CO2 is low in He, Ne and Ar concentrations, yet enriched in 84Kr and 132Xe relative to 36Ar, highlighting that inherent noble gas isotopic fingerprints could be effective as a distinct geochemical tracer of injected CO2 at the FRS.

Methane Production by Facultative Anaerobic Wood-Rot Fungi via a New Halomethane-Dependent Pathway.

ABSTRACTThe greenhouse gas methane (CH4) is of pivotal importance for Earth’s climate system and as a human energy source. A significant fraction of this CH4 is produced by anaerobic Archaea. Here, we describe the first CH4 production by facultative anaerobic wood-rot fungi during growth on hydroxylated/carboxylated aromatic compounds, including lignin and lignite. The amount of CH4 produced by fungi is positively correlated with the amount of CH3Cl produced during the rapid growth period of the fungus. Biochemical, genetic, and stable isotopic tracer analyses reveal the existence of a novel halomethane-dependent fungal CH4 production pathway during the degradation of phenol and benzoic acid monomers and polymers and utilization of cyclic sugars. Even though this halomethane-dependent pathway may only play a side role in anaerobic fungal activity, it could represent a globally significant, previously overlooked source of biogenic CH4 in natural ecosystems.IMPORTANCE Here, we demonstrate that wood-rot fungi produce methane anaerobically without the involvement of methanogenic archaea via a new, halomethane-dependent pathway. These findings of an anaerobic fungal methane formation pathway open another avenue in methane research and will further assist with current efforts in the identification of the processes involved and their ecological implications.