Mean CH4 Research Articles

Methane and carbon dioxide evasion from a mosaic of Amazon lakes, river channels, and inundated forests

Seasonally inundated forests are the largest type of wetland in the Amazon basin. Here we provide new data from inundated forests, a lake, and river channels during high water in the forested Anavilhanas archipelago (Negro River, Brazil). Evasion pathways of CH4 in flooded forests include tree trunks, diffusion from the water, and ebullition. Within flooded forest sites, diffusive CH4 fluxes were lowest (mean, 6.2 µmol m-2 h-1), ebullitive fluxes averaged 50 µmol m-2 h-1, and fluxes from the trees had the highest fluxes when expressed per inundated surface area (83 µmol m-2 h-1). The lake and river channels usually had higher CH4 and CO2 fluxes than inundated forests. Overall, mean CH4 fluxes from inundated forests in our study were lower than fluxes measured in nutrient-rich inundated forests. Our results contribute to understanding the heterogeneity of C fluxes from inundated forests. Water levels, currents and extent of inundated habitats contribute to variability in gas fluxes. Outgassing rates are expected to become more variable with projected periods of especially high and low water levels as the climate changes.

The aeration and dredging stimulate the reduction of pollution and carbon emissions in a sediment microcosm study

Sediment dredging and aeration are used as important technical measures to remediate internal loading of sediment in polluted rivers. However, previous studies have overlooked the impact of dredging and aeration on Greenhouse gases (GHGs) emission. We established three aeration rate(six different aeration intervals), one dredging treatment to investigate the effect of aeration and dredging on pollutant removals and CO2, CH4 and N2O emissions. The results indicated the pollutants and GHGs at 2.4, 3.4, 4.4 L min−1 aeration rates reached collaborative emission reduction after more than 3 h or within 1.5 h. Meanwhile, the GHGs fluxes after aeration decreased with the increasing aeration rate, with the mean CO2, CH4 and N2O fluxes of 69.74, 0.16, 7.53 mg m−2 h−1 and 33.64, 0.09, 4.17 mg m−2 h−1 before and after aeration, respectively. With respect to dredging, the pollutants and N2O reached synergic effects between reduction of pollution and carbon emissions after 1 h dredging. Specifically, the CO2 and CH4 emissions after dredging was lower than those of before dredging, but the N2O emissions was higher than those of before dredging. In addition, our analysis revealed that the dissolved oxygen (DO), oxidation-reduction potential (ORP), available potassium (AK) and ammoniacal nitrogen (NH4+-N) in the sediment influenced GHGs fluxes at the water-air interface in the aeration. Our study indicated moderate aeration and dredging can achieve the synergistic effect in reducing pollution and carbon emissions.

Foliar methane and nitrous oxide fluxes in tropical tree species

Methane (CH₄) and nitrous oxide (N₂O) are critical biogenic greenhouse gases (GHGs) with global warming potentials substantially greater than that of carbon dioxide (CO₂). The exchange of these gases in tropical forests, particularly via foliar processes, remains poorly understood. We quantified foliar CH₄ and N₂O fluxes among tropical tree species and examined their potential association with the leaf economics spectrum (LES) traits. Sampling within Lawachara National Park, Bangladesh, we used in-situ measurements of foliar CH₄ and N₂O fluxes employing off-axis integrated cavity output spectroscopy (CH₄, CO₂ and H₂O) and optical feedback–cavity enhanced absorption spectroscopy (N₂O) analyzers. Leaves were measured under dark, low, and high (0, 100, and 1000 μmol·m−2·s−1) light conditions. Surveyed tree species exhibited both net foliar uptake and efflux of CH₄, with a mean flux not different from zero, suggesting negligible net foliar emissions at the stand level. Plant families showed differences in CH₄, but not N₂O fluxes. Consistent efflux was observed for N₂O, with a mean of 0.562 ± 0.060 pmol·m−2·s−1. Pioneer species exhibited a higher mean N₂O flux (0.81 ± 0.17 pmol·m−2·s−1) compared to late-successional species (0.37 ± 0.05 pmol·m−2·s−1). Pioneer species also showed a trend toward a higher mean CH₄ flux (0.24 ± 0.21 nmol·m−2·s−1) compared to mid-successional (−0.01 ± 0.26 nmol·m−2·s−1) and late-successional species (−0.05 ± 0.28 nmol·m−2·s−1). Moreover, among all leaf traits within the leaf economic spectrum, a significant positive relationship was observed between leaf N₂O flux and total leaf nitrogen. Our results suggest that pioneer tree species significantly contribute to net CH₄ and N₂O emissions, potentially counteracting the carbon sequestration benefits in regenerating tropical forests. These findings indicate that accurate GHG budgeting should include direct measurements of foliar CH₄ and N₂O fluxes. Moreover, the results suggest that forest conservation and management strategies that prioritize late successional species will better mitigate GHG emissions.

PSLBII-28 Effects of dietary protein manipulation on greenhouse gases and ammonia emissions from feedlot beef steers

Abstract Black Angus steers [n = 112; body weight (BW) = 401 ± 3.6 kg] were used in a randomized incomplete block design to evaluate the effects of 3 rumen available protein to microbial crude protein ratios (RAP:MCP) on growth performance, and gaseous emissions from feedlot steers. Steers were blocked by initial BW and randomly assigned to 1 of 3 treatment rations. Diets were fed rations either Deficient (-150 gּ animal-1ּ d-1; DEF), Balanced (0 gּ animal-1ּ d-1; BAL), or Excess (+150 gּ animal-1ּ d-1; EXS) in RAP: MCP. Steers were allocated and housed in cattle pen enclosures (CPE), and treatment diets were delivered daily as a total mixed ration. The present study consisted of two 42-d periods. Refusals were collected weekly and BW every 14 d. Gas measurements were obtained daily in sequential order from all CPE. Data were analyzed with R statistical software (4.2.3). The linear mixed effect model procedure within the “lme4” package was used with CPE as the experimental unit, treatment and week as fixed effects, and block and period as random effects. A contrast coefficient matrix was constructed to test for linear and quadratic effects. Initial, intermediary and final BW were not different for steers receiving the varying RAP:MCP (P ≥ 0.239). A treatment effect (P = 0.004) was observed for mean dry matter intake (DMI) where EXS steers consumed 0.46 kg more DM compared with BAL steers, but DEF steers had similar DMI to those fed EXS and BAL (P = 0.189). Average daily gain (ADG) was only affected by treatment (P = 0.007) on d 0 to 14 where steers receiving DEF gained 0.6 kg more than those fed BAL (P = 0.010), but those fed EXS had similar ADG. Similar to ADG, gain to feed (G:F) was affected by treatment (P = 0.012) only during d 0 to 14. Mean CH4 production from steers fed DEF and EXS were 20% and 13% greater (P = 0.010) compared with those fed BAL, respectively; however, CH4 from EXS vs. DEF steers was not different (P = 0.149). Mean cumulative NH3 emissions increased linearly by treatment with EXS steers emitting up to 52% more NH3 compared with those receiving DEF (P < 0.001). Similarly, EXS steers had increased SO2 emissions by up to 44% compared with those fed DEF (P < 0.001). Emissions of CO2, N2O, and H2S were similar (P > 0.100). The manipulation of RAP:MCP in the diets of feedlot steers can drastically reduce NH3 emissions without affecting growth performance and may be a valuable tool to reduce air pollution from beef production systems.

453 Fluxes of greenhouse gases from pastures and methane emissions from beef cattle in Australia

Abstract The carbon footprint of beef cattle production may need to consider both the fluxes of greenhouse gases (GHG) of pasture ecosystems and cattle enteric emissions because these are the largest contributors to the carbon balance. The objective of the present study was to measure the fluxes of greenhouse gases from pastures and enteric methane (CH4) emissions from cattle throughout long periods of time under commercial conditions. The fluxes of CH4, carbon dioxide (CO2), and nitrous oxide (N2O) were measured throughout a period of 3 yr in multiple pasture types ranging from native to sown, and from temperate to summer pastures in New South Wales, Australia. A set of 8 dynamic chambers that automatically close for 10 min every 1.5 h were used for this purpose. The chambers measured the change in the concentration of GHG to allow for the estimation of emissions (positive flux) or sinks (negative flux). All data was then summarized to estimate daily fluxes and the global warming potential (CO2e) was calculated multiplying CH4 by 28 and N2O by 265. The final dataset contained 2,709 d of measurements across the 8 chambers. The GreenFeed system was used to measure CH4 production from cattle under varying conditions fed various diets throughout the same period. Cattle categories included weaners, heifers and steers, bulls and cows under both grazing or pen conditions. Cattle were fed a variety of diets ranging from low quality forages to high quality forages, grain supplementation, and grain-based diets. Data were averaged across many days for each animal and the final dataset contained 1,014 measurements. The CO2 flux from pastures ranged from -855 (uptake) to +339 kg CO2ּ ha-1ּ d-1 with a mean of -10.4 ± 2.19 kg CO2ּ ha-1ּ d-1. The minimum, mean and maximum CH4 fluxes were -192 (uptake), 0.015 ± 0.488, 434 g CH4 ּha-1ּ d-1, respectively, whereas NO2 values -146 (uptake), 17.1 ± 1.23, 1,293 g N2O ּ ha-1ּ d-1, respectively. These fluxes resulted in a GWP ranging from -855 (uptake), -5.83 ± 2.222, 445 kg CO2e ּha-1ּ d-1suggesting that pastures were on average a net sink of GHG throughout the present study. The CH4 production from cattle ranged from 43.6 to 404.6, with an average CH4 production of 192 ± 90.3 g CH4ּ animal-1ּ d-1, which is equivalent to 5.37 kg CO2eqּ animal-1ּ d-1. These results suggest that a hectare of livestock pastures offsets more than the CH4 produced by the average beef cattle in the present study. The fluxes of GHG from vegetation may need to be considered when estimating the contribution of livestock production to global warming.

Assessing methane emissions and soil carbon stocks in the Camargue coastal wetlands: Management implications for climate change regulation

Coastal wetlands are crucial in climate change regulation due to their capacity to act as either sinks or sources of carbon, resulting from the balance between greenhouse gas (GHG) emissions, mainly methane (CH4), and soil carbon sequestration. Despite the paramount role of wetlands in climate regulation few studies investigate both aspects. The Camargue is one of the largest wetlands in Europe, yet the ways in which environmental and anthropic factors drive carbon dynamics remain poorly studied. We examined GHG emissions and soil organic carbon (SOC) stocks and accumulation rates in twelve representative wetlands, including two rice fields, to gain insights into the carbon dynamics and how it is influenced by hydrology and salinity. Mean CH4 rates ranged between – 87.0 and 131.0 mg m−2 h−1and the main drivers were water conductivity and redox, water table depth and soil temperature. High emission rates were restricted to freshwater conditions during summer flooding periods whereas they were low in wetlands subjected to summer drought and water conductivity higher than 10 mS cm−1. Nitrous oxide emissions were low, ranging from – 0.5 to 0.9 mg N2O m−2 h−1. The SOC stocks in the upper meter ranged from 17 to 90 Mg OC ha−1. Our research highlights the critical role of low-saline wetlands in carbon budgeting which potentially are large sources of CH4 but also contain the largest SOC stocks in the Camargue. Natural hydroperiods, involving summer drought, can maintain them as carbon sinks, but altered hydrology can transform them into sources. Artificial freshwater supply during summer leads to substantial CH4 emissions, offsetting their SOC accumulation rates. In conclusion, we advocate for readjusting the altered hydrology in marshes and for the search of management compromises to ensure the compatibility of economic and leisure activities with the preservation of the inherent climate-regulating capacity of coastal wetlands.

Methane and nitrous oxide emissions in the rice-shrimp rotation system of the Vietnamese Mekong Delta

Rice-shrimp rotation systems are one of the widespread farming practices in the Vietnamese Mekong Delta coastal areas. However, greenhouse gas (GHG) emissions in the system have remained unclear. This study aimed to examine methane (CH4) and nitrous oxide (N2O) emissions from the system, including (i) land-based versus high-density polyethylene-lined (HDPE) nursery ponds and (ii) conventional versus improved grow-out ponds inoculated with effective microorganisms (EM) bioproducts. The results showed that CH4 flux in land-based and HDPE-lined nursery ponds were 1.04 and 0.25 mgCH4 m−2 h−1, respectively, while the N2O flux was 8.37 and 6.62 μgN2O m−2 h−1, respectively. Global warming potential (GWP) from land-based nursery ponds (18.3 g CO2eq m−2) was approximately 3 folds higher than that of the HDPE-lined nursery pond (6.1 g CO2eq m−2). Similarly, the mean CH4 and N2O fluxes were 15.84 mg CH4 m−2 h−1 and 7.17 μg N2O m−2 h−1 for the conventional ponds, and 10.51 mg CH4 m−2 h−1 and 7.72 μg N2O m−2 h−1 for the improved grow-out ponds. Conventional practices (2388 g CO2eq m−2) had a higher 1.5-fold GWP compared to the improved grow-out pond (1635 g CO2eq m−2). The continuation of the land-based nursery pond and conventional aquacultural farming practices increase CH4 emission and GWP, while applying HDPE-lined nursery ponds combined with improved grow-out ponds could be a promising approach for reducing GHG emissions in rice-shrimp rotation systems. This study recommends further works in the rice-shrimp rotation systems, including (i) an examination of the effects of remaining rice stubbles in the platform on the availability of TOC levels and GHG emissions and (ii) ameliorating dissolved oxygen (DO) concentration on the effectiveness of GHG emission reduction.

The response of soil carbon mineralization losses to changes in rainfall frequency is seasonally dependent in an estuarine saltmarsh

Altered rainfall distribution patterns resulting from climate change have substantial effects on soil carbon (C) cycling in terrestrial ecosystems particularly in water-limited regions. However, how rainfall redistribution affects soil C mineralization (CO2 and CH4 fluxes) in humid regions such as of the coastal saltmarshes remain unclear. We conducted mesocosm experiments in an estuarine saltmarsh in the Yellow River Delta of China, where we simulated three rainfall frequency scenarios (high-frequency, medium-frequency and low-frequency) with the same total rainfall amount in the dry and wet seasons, respectively. Soil CO2 and CH4 fluxes were measured before and after rain frequency treatment during a 40-day period for each season. The decrease in rainfall frequency significantly reduced the mean soil CO2 and CH4 fluxes during the dry season, but had no effect on either flux during the wet season. The seasonal variation in the response of soil C mineralization to rainfall frequency changes could be explained by the changes in antecedent soil water and salinity conditions, soil C substrate, microbial activities and diversity. Thus, the effects of changes in rainfall frequency on soil C mineralization are regulated by season, and should be considered when predicting the future C balance of coastal wetland ecosystems. Furthermore, the shift in precipitation frequency distribution towards increasing heavy rainfall events during the dry season in this region will have a great effect on soil C losses, potentially feeding back into the soil C budget and stability in this estuarine saltmarsh.

Soil greenhouse gas fluxes and net global warming potential from two maize farming practices in the Bamenda highlands, Cameroon

Farming practices used in maize crop production are thought to modify greenhouse gas (GHG) emissions from the soil particularly methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). The quantities of these GHG fluxes have rarely been estimated from smallholder farms in Sub-Saharan Africa. We estimated the quantities of GHG fluxes and Global Warming Potential (GWP) from the Push-Pull Technology (PPT) and Tillage with the Formation of Ridges (TFR) farming systems at the University of Bamenda, Cameroon. Greenhouse gases were sampled bi-monthly from April to Early August 2020 using the static chamber technique. The experiment followed a split-plot randomized complete block design with two replicates and three planting distances (1 m, 1.5 m, and 2 m) used as treatments. Mean cumulative CH4 (5.39 kgCH4-Cha−1) and N2O (1.03 kgN2O-Nha−1) emissions under TFR were significantly higher (P < 0.05) than mean CH4 (3.59 kgCH4-Cha−1) and N2O (0.52 kgN2O-Nha−1) emissions under PPT system. Mean net-GWP under PPT followed the trend 2 m (−267.61 tCO2-eqha−1) < 1.5 m (−75.76 tCO2-eqha−1) < 1 m (−24.95 tCO2-eqha−1) while under TFR, net-GWP was ordered 1 m (0.38 tCO2-eq ha−1) < 1.5 m (85.29 tCO2-eq ha−1) < 2 m (288.41 tCO2-eq ha−1) with significant differences between them. Maize grain yields under PPT were in the trend 1 m (0.81 tha−1) < 2 m (0.85 tha−1) < 1.5 m (0.92 tha−1) with a significant difference (P < 0.05) between 1 m and 1,5 m treatments. While under TFR, the trend was 2 m (0.56 tha−1) < 1 m (0.77 tha−1) < 1.5 m (0.80 tha−1) with significant difference between 1.5 m and 2 m (P < 0.05). On average, PPT was a sink to GWP (−122.77 tCO2-eqha−1) and revealed higher (P < 0.05) yields (0.86 tha−1) than TFR (0.71 tha−1) which was a source of GWP (124.69 tCO2-eqha−1). Therefore, a PPT practice of 1.5 m planting distance is recommended in Sub-Saharan Africa to enhance food productivity while mitigating global warming by minimizing soil greenhouse gas emissions.

Variations in Greenhouse Gas Fluxes at the Water–Gas Interface in the Three Gorges Reservoir Caused by Hydrologic Management: Implications for Carbon Cycling

The Three Gorges Project is the largest hydraulic hub project in the world, and its hydrological management has altered the hydrological environment of the reservoir area, affecting the carbon emission and absorption of the reservoir water. In this study, representative hydrological stations in the Three Gorges Reservoir area were selected as research sites to monitor the CO2 and CH4 fluxes of the reservoir water and nine environmental factors during the drainage and impoundment periods in 2022. The study aimed to explore the mechanisms of hydrological management and environmental factors on greenhouse gas emissions. The results showed that the mean CO2 fluxes of the reservoir water during the drainage and impoundment periods were (103.82 ± 284.86) mmol·m−2·d−1 and (134.39 ± 62.41) mmol·m−2·d−1, respectively, while the mean CH4 fluxes were (1.013 ± 0.58) mmol·m−2·d−1 and (0.571 ± 0.70) mmol·m−2·d−1, respectively, indicating an overall “carbon source” characteristic. Through the evaluation of the characteristic importance of environmental factors, it was found that the main controlling factors of CO2 flux during the drainage period were total phosphorus (TP) and chlorophyll a (Chl_a), while total nitrogen (TN) was the main controlling factor during the impoundment period. Dissolved organic carbon (DOC) was the main controlling factor of CH4 flux during the different periods. Based on these findings, a “source-sink” mechanism of CO2 and CH4 in the Three Gorges Reservoir water under reservoir regulation was proposed. This study is of great significance for revealing the impact of reservoir construction on global ecosystem carbon cycling and providing scientific support for formulating “emission reduction and carbon sequestration” plans and achieving “dual carbon” goals.

Winter harvesting reduces methane emissions and enhances blue carbon potential in coastal phragmites wetlands

Enhancing the ability of coastal blue carbon to accumulate and store carbon and reduce net greenhouse gas emissions is an essential component of a comprehensive approach for tackling climate change. The annual winter harvesting of Phragmites is common worldwide. However, the effects of harvesting on methane (CH4) emissions and its potential as an effective blue carbon management strategy have rarely been reported. In this study, the effects of winter Phragmites harvesting on the CH4 and carbon dioxide (CO2) fluxes and the underlying mechanisms in coastal Phragmites wetlands were investigated by comparing the eddy covariance flux measurements for three coastal wetlands with different harvesting and tidal flow conditions. The results show that harvesting can greatly reduce the CH4 emissions and the radiative forcing of CH4 and CO2 fluxes in coastal Phragmites wetlands, suggesting that winter Phragmites harvesting has great potential as a nature-based strategy to mitigate global warming. The monthly mean CH4 fluxes were predominantly driven by air temperature, gross primary productivity, and latent heat fluxes, which are related to vegetation phenology. Additionally, variations in the salinity and water levels exerted strong regulation effects on CH4 emissions, highlighting the important role of proper tidal flow restoration and resalinization in enhancing blue carbon sequestration potential. Compared with the natural, tidally unrestricted wetlands, the CH4 fluxes in the impounded wetland were less strongly correlated with hydrometeorological variables, implying the increased difficulties of predicting CH4 variations in impounded ecosystem. This study facilitates the improved understanding of carbon exchange in coastal Phragmites wetlands with harvesting or impoundment, and provides new insights into effective blue carbon management strategies beyond tidal wetland restoration for mitigating the effects of climate change.

Magnitude of and Hydroclimatic Controls on CO2 and CH4 Emissions in the Subtropical Monsoon Pearl River Basin

AbstractRivers are important ecosystems for carbon emissions and play a crucial role in the global carbon cycle. However, CO2 and CH4 emissions from subtropical rivers are substantially under‐represented in global‐scale estimates. Here, we explored the regional patterns of riverine CO2 and CH4 dynamics in the Pearl River basin with a subtropical monsoon climate. We found that its CO2 and diffusive CH4 emissions showed a decreasing trend with increasing stream order. Seasonality in CO2 and diffusive CH4 emissions was primarily driven by variations in partial pressure of CO2 (pCO2) and CH4 (pCH4) and gas transfer velocities, which were strongly regulated by hydrology and climate. We further estimated the basin‐wide CO2 and diffusive CH4 fluxes at 17.8 ± 7.4 Tg C yr−1 and 191.5 ± 139.9 Gg C yr−1, respectively. When normalized to the water surface, the mean diffusive fluxes were 790.1 and 8.5 mmol m−2 d−1 for CO2 and CH4, respectively, which were 1.3 and 2.5 times higher than the global mean riverine CO2 and CH4 fluxes, respectively. This suggests that the global significance of subtropical rivers is probably underestimated because their substantially higher CH4 fluxes are unaccounted for. Furthermore, compared with measured pCO2, the alkalinity‐based pCO2 could introduce significant errors by 20% at ∼30% of the sampling sites, underscoring the necessity of direct measurements to reduce uncertainty. This study provides the first estimate of basin‐wide CO2 and diffusive CH4 emissions in the PRB through direct pCO2 and pCH4 measurements, and highlights the role of hydrologic and climatic factors in governing riverine carbon emissions.

Comparison of greenhouse gas emissions from sheep measured using both respiration and portable accumulation chambers

Methane (CH4) is a potent gas produced by ruminants, and new measurement techniques are required to generate large datasets suitable for genetic analysis. One such technique are portable accumulation chambers (PAC), a short-term sampling method. The objectives of the current study were to explore the relationship between CH4 and carbon dioxide (CO2) output measured using both PAC and respiration chambers (RC) in growing lambs, and separately investigate the relationship among CH4, CO2 and measured ad libitum DM intake (DMI). Methane, CO2 and DMI were measured on 30 Suffolk and 30 Texel ewe lambs (age 253 ± 12 days) using the RC and PAC sequentially. The experiment was conducted over a 14-day period, with DMI measured from days 1 to 14; measurements in RC were conducted from days 10 to 12, while measurements in PAC were taken twice, the day immediately prior to the lambs entering the RC (day 9; PAC Pre-RC) and on the day lambs exited the RC (day 13; PAC Post-RC). Greater CH4 and CO2 output was measured in the RC than in the PAC (P < 0.01); similarly mean CH4 yield was greater when measured in the RC (15.39 ± 0.452 g CH4/kg DMI) compared to PAC (8.01 ± 0.767 g CH4/kg DMI). A moderate correlation of 0.37 was found between CH4 output measured in PAC Pre-RC and the RC, the corresponding regression coefficient of CH4 output measured in the RC regressed on CH4 output measured in PAC Pre-RC was close to unity (0.74; SE 0.224). The variance of CH4 and CO2 output within the measurement technique did not differ from each other (P > 0.05). Moderate to strong correlations were found between CH4 and CO2 per kg of live weight and CH4 and CO2 yield. Results from this study highlight the suitability of PAC as a ranking tool to rank animals based on their gaseous output when compared to the RC. However, repeated measurements separated by several days may be beneficial if precise rankings are required. Given the close to unity regression coefficient of CH4 output measured in the RC regressed on CH4 output measured in PAC Pre-RC suggests that PAC could also be potentially used to estimate absolute CH4 output; however, further research is required to substantiate this claim. When DMI is unknown, CH4 and CO2 per kg of live weight are a suitable alternative to the measurement of CH4 and CO2 yield.

A pilot study to capture methane from the exhausted air of dairy cows using a cryogenic approach

In the agricultural sector, ruminants are the largest methane (CH4) emission source and many efforts have been undertaken to reduce these greenhouse gas emissions, while compromising animal health and physiology. On the other hand, ruminal CH4, which is biomethane, is in high demand, especially in its liquid form (LBM) that can be used as high energy density fuel. However, CH4 released from a ruminant is immediately mixed with air and highly diluted (<0.1%), challenging CH4 capture technologies. Here we aimed to construct a cryogenic pilot system to capture and liquefy enteric CH4 released from dairy cows kept in respiration chambers. To approach this aim, the outlet air from the chambers was directed through a two-step cooling trap to capture CO2 (−120 to −130 °C) as a solid in the first and CH4 and O2 as liquids in the second cooler (−160 to −180 °C). Warming the second cooler resulted in the evaporation of O2, thereby separating O2 and CH4. LBM purity was in average 90% and was lowest at warming rates higher than 0.88 °C/min. The mean CH4 capture efficiency was 92% and found to be independent of sequestration time and flow rate. However, an increase in CH4 concentration to 0.6%, as it occurs directly at the muzzle of a cow, reduced the sequestration time for CH4. These results show that cryogenic technology can be used to obtain LBM from the air containing ultra-low CH4 concentrations as it is found in cattle barns with high efficiency and purity.

Hourly methane and carbon dioxide fluxes from temperate ponds

AbstractPonds are regarded as greenhouse gas (GHG) emission hot spots, but how hot are they? We examined this question by measuring methane (CH4) and carbon dioxide (CO2) fluxes in six forest and open land ponds on grasslands in Denmark during summer and winter. We used floating chambers with do-it-yourself sensors and automated headspace venting, allowing for 7404 hourly measurements. We found highly variable gas fluxes within ponds and between seasons and pond types. Ebullitive CH4 fluxes were more variable than diffusive CH4 fluxes. Ebullition was absent when total CH4 fluxes were lowest (15 µmol m−2 h−1), dominant (&gt; 90%) at the highest fluxes (&gt; 400 µmol m−2 h−1), and increased with water temperature. In summer, a minor daily increase in diffusive fluxes was found on days with high wind speed, while CH4 ebullition remained constant. CO2 fluxes paralleled the day-night balance of photosynthesis and respiration. Mean CH4 ebullition in open and forest ponds exceeded CH4 diffusive fluxes 4.1 and 7.1-fold in summer (avg. 22.5 °C) and 2.3 and 2.5-fold in winter (9.6 °C), respectively. CO2 emissions were higher on a molar basis than CH4 emissions, both in summer and winter, while their annual global warming potentials were similar. Mean annual gas emissions from open and forest ponds (1092 and 2527 g CO2e m−2 y−1) are naturally high due to extensive external input of dissolved CO2 and organic carbon relative to pond area and volume.

Effect of cubicle hood system on methane concentrations around the lying area in cold climate dairy cattle buildings

There is scarcity of data on methane (CH4) concentration levels and other gas compositions around animals in commercial cattle barns, especially for developing technology for gaseous CH4 treatment. Consequently, use of biofiltration and catalytic combustion strategies as alternative enteric CH4 mitigation techniques remain concepts yet to be validated in real cattle barns. One of the major barriers to implementing these techniques is that they require close buildings, which is not the case for most cattle barns. Open cattle barns are frequently associated with excessive ventilation, resulting in low CH4 concentrations, which can reduce the cost effectiveness of CH4 treatment techniques. With the development of low-cost, low-CH4-concentration enrichment technologies still in their infancy, developing local ventilation systems at the animal level capable of collecting breath CH4 from cows prior to air mixing could be an option. Therefore, the effect of a cubicle hood system (CHS) with different air extraction techniques on increasing CH4 concentrations at the lying area were evaluated in natural and mechanically ventilated dairy cattle buildings during the winter in Norway. In both barns, the use of CHS increased CH4 concentrations under the hood at the lying area by 14-25 % compared to without CHS. The results obtained depended on the height of the CHS from the floor and effect of outdoor temperature on air exchange rate in the barns. In the naturally ventilated barn, the hourly mean CH4 concentrations under the cubicle hood ranged from 14-225 ppm, and 31-322 ppm in the mechanically ventilated building.

Neighbouring effect of land use changes and fire emissions on atmospheric CO2 and CH4 over suburban region of India (Shadnagar)

The present study investigated the effects of land use/land cover (LU/LC) changes on atmospheric carbon dioxide (CO2) and methane (CH4) concentrations over the sub-urban region of India (Shadnagar) using continuous decadal CO2 and CH4in-situ data measured by the greenhouse gas analyser (GGA). Data was collected from 2013 to 2022 at a 1 Hz frequency. Analysis of the current study indicates that during pre-monsoon, the seasonal maximum of CO2 was 409.91 ± 9.26 ppm (μ ± 1σ), while the minimum during monsoon was about 401.64 ± 7.13 ppm. Post-monsoon has a high seasonal mean CH4 concentration of 2.08 ± 0.06 ppm, while monsoon has a low seasonal mean CH4 concentration of 1.88 ± 0.03 ppm. The primary classes, such as forest, crop, and built-up, were considered to estimate the effect of LU/LC changes on atmospheric CO2 and CH4 concentrations. Between 2005 and 2021, the study's results show that the built-up area at radii of 10 km, 20 km, and 50 km increased by 0.17 %, 0.10 %, and 0.4 %, respectively. While other LU/LC categories declined by 30 %, agriculture areas increased by 30 % on average. As a result, the CO2 and CH4 concentrations at the study site are increased by 6 % (26 ppm) and 6.5 % (140 ppb), respectively. The present study utilised the fire-based carbon emissions data from the Global Fire Emissions Database (GFED) to understand the impact on atmospheric CO2 and CH4. Analysis of the present work investigated the influence of transported airmass on CO2 and CH4 during the pre-monsoon and post-monsoon seasons using the HYSPLIT trajectories and found emissions were from the northwest, southeast, and northeast of the study site. Further, in-situ CO2 and CH4 records are compared against the MIROC4-ACTM simulation, and strong agreement was found with bias of 1.80 ppm and 0.98 ppb for CO2 and CH4, respectively.

Bubbles dominated the significant spatiotemporal variability and accumulation of methane concentrations in an ice-covered reservoir

Climate-sensitive ice-covered reservoirs are critical components of methane (CH4) release. However, the mechanisms that influence CH4 dynamics during ice-covered periods remain poorly studied. To investigate the effects of bubbles on CH4 dynamics, we conducted intensive field and incubation experiments in an ice-covered reservoir (ice growth, stability, and melt period) in Northeast China. We found that the mean dissolved CH4 concentrations in the ice (625.9 ± 2419.7 nmol L−1) and underlying water (1218.9 ± 2678.9 nmol L−1) were high, making them atmosphere CH4 sources. The visible bubble bands (bubble area) in the riverine zone and the vertical profile of the CH4 concentration in the ice reflect the distribution of trapped bubbles. The mean CH4 concentration in the ice of the bubble area (1674.8 ± 3926.8 nmol L−1) was 2 orders of magnitude higher than that of no-bubble area (53.7 ± 9.2 nmol L−1). Moreover, a large amount of CH4 accumulated under the ice in the bubble area. These findings suggest that bubbles determine the CH4 storage in ice and CH4 accumulation in the underlying water. Ice growth increases CH4 storage in ice and the underlying water because of the entrapment and re-dissolution of CH4 bubbles. However, ice melting releases the CH4 accumulated in the ice and underlying water. A comparison of the field and incubation experiments indicated that the deep-water environment of the reservoir had a CH4 burial effect. Stepwise regression analysis revealed that higher sediment organic matter content, median particle size, and porosity increased the production and release of CH4 bubbles, trapping more CH4 bubbles in ice. Overall, this study improves the mechanistic understanding of CH4 dynamics and predictability of CH4 emissions during ice-covered periods.

Driving and limiting factors of CH4 and CO2 emissions from coastal brackish-water wetlands in temperate regions

Abstract. Coastal wetlands play a fundamental role in mitigating climate change thanks to their ability to store large amounts of organic carbon in the soil. However, degraded freshwater wetlands are also known to be the first natural emitter of methane (CH4). Salinity is known to inhibit CH4 production, but its effect in brackish ecosystems is still poorly understood. This study provides a contribution to understanding how environmental variables may affect greenhouse gas (GHG) emissions in coastal temperate wetlands. We present the results of over 1 year of measurements performed in four wetlands located along a salinity gradient on the northeast Adriatic coast near Ravenna, Italy. Soil properties were determined by coring soil samples, while carbon dioxide (CO2) and CH4 fluxes from soils and standing waters were monitored monthly by a portable gas flux meter. Additionally, water levels and surface and groundwater physical–chemical parameters (temperature, pH, electrical conductivity, and sulfate concentrations of water) were monitored monthly by multiparametric probes. We observed a substantial reduction in CH4 emissions when water depth exceeded the critical threshold of 50 cm. Regardless of the water salinity value, the mean CH4 flux was 5.04 gm-2d-1 in freshwater systems and 12.27 gm-2d-1 in brackish ones. In contrast, when water depth was shallower than 50 cm, CH4 fluxes reached an average of 196.98 gm-2d-1 in freshwater systems, while non-significant results are available for brackish/saline waters. Results obtained for CO2 fluxes showed the same behavior described for CH4 fluxes, even though they were statistically non-significant. Temperature and irradiance strongly influenced CH4 emissions from water and soil, resulting in higher rates during summer and spring.

Grazing reduced greenhouse gas fluxes in Inner Mongolia grasslands: A meta-analysis

Grazing exerts a significant influence on greenhouse gases (GHGs) fluxes within temperate grasslands. While previous studies have explored the impact of varying grazing intensities on GHGs fluxes in meadow steppe, typical steppe, and desert steppe, there remains a knowledge gap regarding how grazing intensities affect GHGs fluxes across different grassland types and seasonal variations. In this study, we conducted a meta-analysis of Inner Mongolia grasslands involving 38 published reports and aggregating 143, 160, and 118 records for the CO2, CH4, and N2O, respectively. Our results demonstrated that grazing reduced annual mean CO2 emission, CH4 uptake, and N2O emission by 15.29%, 10.56%, and 24.73%, respectively (P < 0.05). Specifically, during the freeze-thaw period, grazing induced a decrease of 28.06% and 58.41% in CH4 uptake and N2O emissions, respectively, compared to ungrazed treatments (P < 0.05). Further dissecting the impact, we found that grazing reduced CO2 emissions in desert steppe, typical steppe, and meadow steppe by 20.28%, 15.54%, and 11.79%, respectively. In addition, grazing decreased CH4 uptake in typical steppe by 15.14% and decreased N2O emission in typical steppe, meadow steppe, and sown pasture by 20.25%, 24.18%, 52.91%, respectively. Crucially, the alteration in plant biomass due to grazing-induced changes underlying drivers that govern the responses of GHGs fluxes. These results furnish compelling evidence that grazing, particularly in non-growing season, holds the potential to mitigate grassland GHGs fluxes in temperate grasslands. Our results can deepen the understanding of the grazing effects on GHGs and offer valuable insights for refining grazing management strategies in pastoral regions.