Annual CH4 Research Articles (Page 1)

Lateral and air-water inorganic carbon and methane fluxes in a small Arctic river: Seasonal variations and the connections with local hydrology.

Spatial and temporal methane emissions from urbanized subtropical estuaries in the northwest Gulf of Mexico.

Comprehensive analysis of greenhouse gases emissions and microbial dynamics in glacier-fed lakes across various ablation stages.

Dynamic variability of methane and controlling mechanisms in the northern North Yellow Sea.

Temporal-spatial characteristics and environmental controls of annual CH4 fluxes in a Tibetan alpine landscape

Abstract Wetland ecosystems are the dominant natural source of atmospheric methane (CH4) in the global methane cycle, yet significant uncertainties remain. Along with the warming climate system, CH4 emissions from these ecosystems are projected to increase, presenting challenges for accurate CH4 budget accounting and climate mitigation efforts. This study assessed CH4 emissions and controlling factors in wetlands across East, South, and Southeast Asia (EA, SA, and SEA) for 2010–2020, using a regional Earth system model coupled online with a microbial functional‐group‐based CH4 model (RegESM‐Microbe). The results from the RegESM‐Microbe model were evaluated against 11 offline wetland models from the Global Carbon Project and revealed consistent hotspots for wetland CH4 emissions, including the Yangtze River floodplain, the Ganges and Brahmaputra River basins, and the Mekong River basin. The annual total wetland CH4 emissions in Asia estimated (34.69 ± 2.55 Tg CH4 yr−1) by the RegESM‐Microbe model was close to the bottom‐up wetland model ensemble (36.66 ± 1.19 Tg CH4 yr−1). The time series of emissions showed a decreasing trend before 2014. Meanwhile, the weakening of anaerobic CH4 oxidation between 2014 and 2020 contributed to increased CH4 flow in the three transport sub‐processes, driving the enhanced CH4 emissions. Most wetlands in the region exhibited an upward trend in CH4 emission, with precipitation and radiation as the primary driver, followed by rising atmospheric CO2. Our study highlighted the critical role of climate change‐induced wetland CH4 emissions in shaping long‐term greenhouse gas mitigation strategies.

Rice-crayfish farming represents a typical green and low-carbon alternative to rice monoculture. It is important to investigate the carbon sequestration and emission reduction effect of rice-crayfish farming to improve paddy soil quality, ensure food security, and address climate change challenges. In this study, we systematically evaluated the carbon sequestration and emission reduction effects of rice-crayfish farming through field experiment, carbon footprint assessment, and the DeNitrification-DeComposition (DNDC) model. Compared with rice monoculture, rice-crayfish farming increased the soil organic carbon (SOC) storage, and reduced the annual CH4 emissions, annual N2O emissions, and global warming potential (GWP) by 6.4, 2.4 and 6.2%, respectively. Field engineering, nutrient management and regional variations contributed to differences in carbon emissions and carbon footprints associated with rice-crayfish farming. Moreover, reduction of CH4 emissions was pivotal for decreasing carbon footprint in rice-crayfish farming. DNDC model simulation revealed that the carbon sequestration potential of the rice-crayfish system is influenced by agronomic practices (planting pattern, area proportion of culture ditch, proportion of straw returning, nitrogen fertilizer application, tillage depth, and irrigation regime) and regional climate, landform, and soil. Optimized rice-crayfish farming exhibited varying carbon sequestration effects across different regions. Conversion from rice monoculture to optimized rice-crayfish farming altered the regional carbon sequestration and source dynamics. This study provides a rationale for developing tailored strategies to maximize carbon sequestration and minimize carbon emissions at the regional or farm scales.

Green roofs are a key solution for increasing green spaces in urban areas covered with impervious surfaces. In recent years, there has been growing interest in the ability of green spaces to reduce greenhouse gas (GHG) emissions and enhance carbon sequestration. To investigate whether green roofs contribute to GHG reduction, it is essential to quantify both carbon sequestration and GHG fluxes. However, few studies have investigated GHG fluxes from green roofs over the long term. To address this gap, this study measured and quantified the annual GHG (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O)) fluxes from a thin-layer rooftop lawn using clear acrylic automatic open/close chambers. In addition, we calculated CO2 sequestration based on the difference between total carbon contents in rooftop lawns (soil and turf) at the beginning and end of the experiment. The annual CO2, CH4, and N2O fluxes were calculated to be −1762 g-CO2• m-2• year-1, 92.33 mg-CH4• m-2• year-1, and 0.53 mg-N2O•m-2• year-1 respectively, and CO2 sequestration by plants and soil was estimated to be −2,626 g-CO2•m-2•year-1 during the first year after construction. The CH4 and N2O fluxes from the rooftop lawn were significantly lower than those reported in other studies conducted on ground-level lawns. Based on these results, annual GHG emission (total of CO2, CH4, and N2O) from the rooftop lawn were calculated to be −1759 to −2,623 g-CO2e (CO2 equivalents). m-2• year-1, indicating that the rooftop lawn acts as GHG sink.

Abstract. Shallow ponds can occur either in a clear-water state dominated by macrophytes or a turbid-water state dominated by phytoplankton, but it is unclear if and how these two alternative states affect the emission of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to the atmosphere. We measured the dissolved concentration of CO2, CH4, and N2O from which the diffusive air–water fluxes were computed, in four urban ponds in the city of Brussels (Belgium): two clear-water macrophyte-dominated ponds (Silex and Tenreuken), and two turbid-water phytoplankton-dominated ponds (Leybeek and Pêcheries) on 46 occasions over 2.5 years (between June 2021 and December 2023). Ebullitive CH4 fluxes were measured with bubble traps in the four ponds during deployments in spring, summer, and autumn, totalling 48 d of measurements. Measured ancillary variables included water temperature, oxygen saturation level ( %O2), concentrations of chlorophyll-a (Chl-a), total suspended matter (TSM), soluble reactive phosphorus (SRP), nitrite (NO2-), nitrate (NO3-), and ammonium (NH4+). The turbid-water and clear-water ponds did not differ significantly in terms of diffusive emissions of CO2 and N2O. Clear-water ponds exhibited higher values of ebullitive CH4 emissions compared to turbid-water ponds, most probably in relation to the delivery of organic matter from macrophytes to sediments, but the diffusive CH4 emissions were not significantly different between clear- and turbid-water ponds. Across seasons, CH4 emissions increased with water temperature in all four ponds, with ebullitive CH4 fluxes having a stronger dependence on water temperature (Q10) than diffusive CH4 fluxes. The temperature sensitivity of ebullitive CH4 fluxes decreased with increasing water depth, implying that shallow sediments would respond more strongly to warming (e.g. heat waves). Total annual CH4 emissions (diffusive + ebullitive) in CO2 equivalents equalled those of CO2 in turbid-water ponds and exceeded those of CO2 in clear-water ponds, while N2O emissions were negligible compared to the other two GHGs. Total annual GHG emissions in CO2 equivalents from all four ponds increased from 2022 to 2023 due to higher CO2 diffusive fluxes, likely driven by higher annual precipitation in 2023 compared to 2022 (leading putatively to higher inputs for organic or inorganic carbon from run-off), possibly in response to the intense El Niño event of 2023. The findings of this work suggest that it might be necessary to account for the presence of submerged macrophytes when extrapolating ebullitive CH4 fluxes in ponds at a larger scale (regional or global) (particularly if Chl-a is used as a descriptor), although it might be less critical for the extrapolation of diffusive CH4, CO2, and N2O fluxes.

Tibetan alpine grasslands (AG) serve as critical methane (CH4) sinks, yet face degradation from anthropogenic and climatic disturbances that promote subterranean rodents (e.g., Plateau zokor [Myospalax baileyi] and pika [Ochotona curzoniae]) activities. Although rodent bioturbation (e.g., burrowing, foraging and excreting) alters soil structure, soil physico-chemical properties and productivity from AG, its impacts on CH4 uptake remain poorly understood. Among the first, we combined paired year-round CH4 flux measurements from Plateau zokor mounds (ZM) and surrounding healthy meadow (HM) patches in Tibetan alpine meadow with collated CH4 fluxes from meta- and synthetic analyses across Tibetan AG, temperate grasslands (TG) and tropical grasslands (TrG) globally. We observed that rodent bioturbation significantly (p < 0.001) doubled annual CH4 uptake (HM: -0.91 ± 0.08 kg C ha-1 vs. ZM: -1.80 ± 0.19 kg C ha-1, mean ± standard error, negative values indicate uptake). Notably, 67% of this net increase (-0.89 ± 0.10 kg C ha-1 year-1) due to rodent bioturbation occurred during the growing season. Meta-analysis results revealed this phenomenon associated with significantly (p < 0.001) decreased topsoil moisture and increased functional gene abundances of pmoA for methanotrophs. Non-growing season (NGS) CH4 uptake contributed 45% and 39% to annual CH4 uptake for HM and ZM, respectively, falling into the ranges of 12%-64% NGS CH4 uptake contributions from TG to AG of China. The TrG showed significant (p < 0.001) lower annual CH4 uptake than TG and AG globally, due to the fact that significant (p < 0.05) greater precipitation and soil moisture from the former than the latter. Our findings elucidate mechanisms underlying rodent-mediated CH4 flux changes and highlight soil moisture as a key driver for global CH4 sink variations. These results emphasise the need for long-term monitoring to better assess the ecological consequences of bioturbation in climate-sensitive alpine ecosystems.

Wetlands are the largest natural source of atmospheric methane (CH4), but substantial uncertainties remain in the global CH4 budget, partly due to a mismatch in spatial scale between detailed insitu flux measurements and coarse-resolution land surface models. In this study, we evaluated the importance of capturing small-scale spatial heterogeneity within a patterned bog to better explain seasonal variation in ecosystem-scale CH4 emissions. We conducted chamber-based flux measurements and pore water sampling on vegetation removal plots across different microtopographic features (microforms) of Siikaneva bog, southern Finland, during seasonal field campaigns in 2022. Seasonal and spatial patterns in CH4 fluxes were analyzed in relation to key environmental and ecological drivers. High-resolution (6 cm ground sampling distance) drone-based land cover mapping enabled the extrapolation of microscale (< 0.1 m2) fluxes to the ecosystem scale (0.75 km2). Methane emissions from wetter microforms (mud bottoms and hollows) closely followed seasonal changes in peat temperature and green leaf area of aerenchymatous plants, while emissions from drier microforms (high lawns and hummocks) remained seasonally stable. This constancy was attributed to persistently low water tables, which moderated environmental fluctuations and reduced seasonality of CH4 production, CH4 oxidation and plant-mediated transport. The strong spatial pattern in CH4 emissions and their seasonal dynamics made both the magnitude and seasonal cycle of ecosystem-scale emissions highly sensitive to the areal distribution of microforms. Our findings underscore the need to integrate microscale spatial variability into CH4 modelling frameworks, as future shifts in peatland hydrology due to climate change may alter the balance between wet and dry microforms-and with it, the seasonal and annual CH4 budget.

Abstract. This study focuses on direct measurements of CO2 and CH4 turbulent eddy covariance fluxes in tundra ecosystems on the Svalbard islands over a 2-year period. Our results reveal dynamic interactions between climatic conditions and ecosystem activities such as photosynthesis and microbial activity. During summer, pronounced carbon uptake fluxes indicate increased photosynthesis and microbial methane consumption, while during the freezing seasons very little exchange was recorded, signifying reduced activity. The observed net summertime methane uptake is correlated with the activation and aeration of soil microorganisms, and it declines in winter due to the presence of snow cover and because of the negative soil temperature which triggers the freezing process of the active layer water content but then rebounds during the melting period. The CH4 fluxes are not significantly correlated with soil and air temperature but are instead associated with wind velocity, which plays a role in the speed of soil drying. Non-growing-season emissions accounted for about 58 % of the annual CH4 budget, characterized by large pulse emissions. The analysis of the impact of thermal anomalies on CO2 and CH4 exchange fluxes underscores that high positive (&gt;5 °C) thermal anomalies may contribute to an increased positive flux in both summer and winter periods, effectively reducing the net annual uptake. These findings contribute valuable insights to our understanding of the dynamics of greenhouse gases in tundra ecosystems in the face of evolving climatic conditions. Further research is required to constrain the sources and sinks of greenhouse gases in dry upland tundra ecosystems in order to develop an effective reference for models in response to climate change.

Despite tropical and subtropical aquatic systems suffering from increasing invasion of floating plants, the effects of floating plants invasion on aquatic greenhouse gas (GHG) emissions remain poorly understood. In this study, CO2 and CH4 fluxes were measured in water lettuce (Pistia stratiotes) and open water areas in Huixian wetland in Guangxi, Southwest China, from November 2020 to November 2021. Our results indicated that CO2/CH4 emissions showed obvious seasonal variations, CO2 fluxes for the water lettuce and open water zones showed a significant CO2 sink in winter, and CH4 fluxes for the water lettuce showed a maximum emission in September 2021. The annual cumulative CO2 fluxes for the water lettuce zone were 5,578.63 ± 957.99 g m−2 yr−1, which were significantly higher than that from the open water area (2,551.77 ± 482.49 g m−2 yr−1). Likewise, the annual cumulative CH4 emissions from the water lettuce area (693.39 ± 142.88 g m−2 yr−1) were significantly higher than those from the open water zone (119.17 ± 4.45 g m−2 yr−1). CO2 fluxes were significantly positively correlated with air and water temperature, and significantly negatively correlated with TN and DO. CH4 fluxes were significantly negatively correlated with HCO3 −. This study indicated that the increased invasion of water lettuce may enhance GHG emissions from a subtropical lake, thus contributing to global warming. More attention should be paid to the invasion of floating plants into subtropical karst lakes because geological conditions and aquatic plants might significantly influence greenhouse gas emissions.

Effective action for climate change mitigation requires an accurate understanding of global greenhouse gas budgets, including those of methane (CH4). Atmospheric measurement data provide key constraints for estimating the magnitudes and distributions of sources and sinks and are utilized in atmospheric chemistry transport modeling studies. Long-term atmospheric measurement networks have revealed decadal, interannual, and seasonal variations in atmospheric CH4. In 2020, a record-breaking annual CH4 increase was recorded, but its cause is still unknown. This study analyzes atmospheric CH4 variations using data from the National Institute for Environmental Studies (NIES) and its collaborative observation networks. Datasets from ground, mobile, and satellite platforms, employing diverse measurement techniques, confirmed past episodes, recent remarkable increases, and spatial distributions of atmospheric CH4. Our data clearly showed a sustained CH4 increase from 2020 to 2022, with the highest annual increase in 2021. The atmospheric CH4 increase was pronounced in the northern mid-to-high latitudes in 2020, but the enhancement shifted south in 2021 and 2022. This study demonstrates the capability of observational data from the NIES and collaborative networks in accurately characterizing spatiotemporal variations in atmospheric CH4 regularly, supporting the improvement of our estimates of the global CH4 budget.

Invasive primary producers modulate carbon fluxes and associated carbon budgets in temperate shallow lakes.

Climate change mitigation through irrigation strategies during rice growing season is off-set in fallow season.

ABSTRACTRewetting is considered a strategy for mitigating carbon dioxide (CO2) emissions from drained peatlands, with associated climate benefits often derived by applying emission factors (EFs). However, data from rewetted sites are lacking, particularly for boreal peatland forests established on drained nutrient‐poor fens. Instead, their EFs have been developed primarily based on data from natural mires, implying similar carbon (C) cycles. In this study, we integrated eddy covariance measurements of ecosystem CO2 and methane (CH4) exchanges with dissolved C export estimates to compare the net ecosystem C balance (NECB) of a recently rewetted minerogenic peatland and two nearby undisturbed fen‐type mires in northern Sweden. We found that the rewetted peatland was an annual C source with a mean NECB of +77 ± 34 g C m−2 year−1 (±SD) over the initial 3 years following rewetting. In comparison, the mires were nearly C neutral or a C sink with their 3‐year mean NECB ranging between +11 and −34 g C m−2 year−1. The net CO2 emission of the rewetted peatland declined to about half by the third year coinciding with an increase in gross primary production. Annual CH4 emissions from the rewetted peatland steadily increased but remained at 32% and 49% in the first and third year, respectively, relative to the mires. We further noted differences in key environmental response functions of CO2 and CH4 fluxes between the rewetted and natural peatlands. Relative to the mires, the dissolved C loss was significantly greater in the rewetted peatland during the first year, but similar in subsequent years. Thus, our study demonstrates that the C balance of a recently rewetted minerogenic peatland may not immediately resemble that of natural mires. This further highlights the need for separate and dynamic EFs to improve estimates of the short‐term climate benefit of rewetting measures.

Benthic methane fluxes and oxidation over the Western Indian Shelf: No evidence of pelagic methanotrophic denitrification.

Permafrost thaw increases the bioavailability of ancient organic matter, facilitating microbial metabolism of volatile organic compounds (VOCs), carbon dioxide, and methane (CH4). The formation of thermokarst (thaw) lakes in icy, organic-rich Yedoma permafrost leads to high CH4 emissions, and subsurface microbes that have the potential to be biogeochemical drivers of organic carbon turnover in these systems. However, to better characterize and quantify rates of permafrost changes, methods that further clarify the relationship between subsurface biogeochemical processes and microbial dynamics are needed. In this study, we investigated four sites (two well-drained thermokarst mounds, a drained thermokarst lake, and the terrestrial margin of a recently formed thermokarst lake) to determine whether biogenic VOCs (1) can be effectively collected during winter, and (2) whether winter sampling provides more biologically significant VOCs correlated with subsurface microbial metabolic potential. During the cold season (March 2023), we drilled boreholes at the four sites and collected cores to simultaneously characterize microbial populations and captured VOCs. VOC analysis of these sites revealed "fingerprints" that were distinct and unique to each site. Total VOCs from the boreholes included > 400 unique VOC features, including > 40 potentially biogenic VOCs related to microbial metabolism. Subsurface microbial community composition was distinct across sites; for example, methanogenic archaea were far more abundant at the thermokarst site characterized by high annual CH4 emissions. The results obtained from this method strongly suggest that ∼10% of VOCs are potentially biogenic, and that biogenic VOCs can be mapped to subsurface microbial metabolisms. By better revealing the relationship between subsurface biogeochemical processes and microbial dynamics, this work advances our ability to monitor and predict subsurface carbon turnover in Arctic soils.

Streams serve as open windows for carbon emissions to the atmosphere due to the frequent supersaturation of carbon dioxide (CO2) and methane (CH4) that originates from large carbon input during runoff and associated in-stream processes. Due to the high spatial and temporal variability of the underlying environmental drivers (e.g., concentrations of dissolved CO2 and CH4, turbulence, and temperature), it has remained difficult to address the importance and upscale the emissions to annual whole-system and regional values. In this study, we measured concentrations and calculated emissions of CO2 and CH4 at diel and seasonal scales at 15 stations in a 1.4 km2 stream network that drains a mixed lowland catchment consisting of agriculture (210 km2), forest (56 km2), and lakes, ponds, and wetlands (22 km2) in the upper River Odense, Denmark to evaluate environmental drivers behind the spatiotemporal variability. We used automatically venting floating chambers to calculate hourly diffusive fluxes of CO2 and CH4 and CH4 ebullition. We found: 1) highly supersaturated CO2 and CH4 concentrations (median: 175 and 0.33 µmol L−1, respectively) and high diffusive fluxes of CO2 and CH4 (median: 3,608 and 19 µmol m−2 h−1, respectively); 2) lower daytime than nighttime diffusive emissions of CO2 in spring and summer, but no diel variability of CH4; 3) higher concentrations and emissions of CH4 at higher temperatures; and 4) higher emissions of CH4 at stations located in sub-catchments with higher agricultural coverage. Ebullition of CH4 peaked at two stations with soft organic sediment and low summer flow, and their ebullition alone constituted 30% of total annual CH4 emissions from the stream network. Mean annual CO2 emissions from the hydrological network (37.15 mol CO2 m−2 y−1) exceeded CH4 emissions 100-fold (0.43 mol CH4 m−2 y−1), and their combined warming potential was 1.83 kg CO2e m−2 y−1. Overall, agricultural sub-catchments had higher CH4 emissions from streams, while lakes and ponds likely reduced downstream CH4 and CO2 emissions. Our findings demonstrate that CO2 and CH4 emissions data at high spatial and temporal resolution are essential to frame the heterogeneous stream conditions, understand gas emissions regulation, and upscale to annual values for hydrological networks and larger regions.