Mitigate CH4 Emissions Research Articles

Synergistic Effects of Essential Oil Blends and Fumaric Acid on Ruminal Fermentation, Volatile Fatty Acid Production and Greenhouse Gas Emissions Using the Rumen Simulation Technique (RUSITEC)

This study investigated the combined impact of essential oil blends (EOBs) and fumaric acid (FA) on ruminal fermentation in dairy cows using the rumen simulation technique (RUSITEC) system. Three rumen-cannulated, non-lactating Holstein Friesian cows served as inoculum donors. The substrate, a total mixed ration (TMR), comprised corn silage, alfalfa hay, and a concentrate mix in a 3:1:1 ratio. The four treatments evaluated were Control (TMR without additives), EFA1 (TMR + EOB1 + FA), EFA2 (TMR + EOB2 + FA), and EFA3 (TMR + EOB3 + FA). Sixteen fermentation chambers were randomly assigned to the treatments, each with four replicates, following a completely randomized design during a 9-day experimental period. EOBs and FA were added at 10 µL/g feed and 3% of TMR, respectively. After a 4-day adaptation, samples were collected for 5 days. Results revealed that EFA1 significantly reduced (p = 0.0351) CH4 emissions by 60.2% without negatively impacting dry matter disappearance, fiber fraction digestibility, pH, or gas volume. All EFAs increased (p < 0.001) the propionate molar proportion and decreased (p < 0.001) the acetate-to-propionate ratio. EFA2 decreased (p < 0.05) the acetate proportion by 3.3% compared to the control. In conclusion, EFA1 is recommended as an effective nutritional intervention to mitigate CH4 emissions and optimize ruminal fermentation in dairy cows.

Towards an integrated view on microbial CH4, N2O and N2 cycles in brackish coastal marsh soils: A comparative analysis of two sites

Coastal ecosystems, facing threats from global change and human activities like excessive nutrients, undergo alterations impacting their function and appearance. This study explores the intertwined microbial cycles of carbon (C) and nitrogen (N), encompassing methane (CH4), nitrous oxide (N2O), and nitrogen gas (N2) fluxes, to determine nutrient transformation processes between the soil-plant-atmosphere continuum in the coastal ecosystems with brackish water. Water salinity negatively impacted denitrification, bacterial nitrification, N fixation, and n-DAMO processes, but did not significantly affect archaeal nitrification, COMAMMOX, DNRA, and ANAMMOX processes in the N cycle. Plant species age and biomass influenced CH4 and N2O emissions. The highest CH4 emissions were from old Spartina and mixed Spartina and Scirpus sites, while Phragmites sites emitted the most N2O. Nitrification and incomplete denitrification mainly governed N2O emissions depending on the environmental conditions and plants. The higher genetic potential of ANAMMOX reduced excessive N by converting it to N2 in the sites with higher average temperatures. The presence of plants led to a decrease in the N fixers' abundance. Plant biomass negatively affected methanogenetic mcrA genes. Microbes involved in n-DAMO processes helped mitigate CH4 emissions. Over 93 % of the total climate forcing came from CH4 emissions, except for the Chinese bare site where the climate forcing was negative, and for Phragmites sites, where almost 60 % of the climate forcing came from N2O emissions. Our findings indicate that nutrient cycles, CH4, and N2O fluxes in soils are context-dependent and influenced by environmental factors and vegetation. This underscores the need for empirical analysis of both C and N cycles at various levels (soil-plant-atmosphere) to understand how habitats or plants affect nutrient cycles and greenhouse gas emissions.

Rice root Fe plaque increases paddy soil CH4 emissions via the promotion of electron transfer for syntrophic methanogenesis

Iron (Fe) plaque is a concentrated form of microbially available Fe oxide that coats rice plant root surfaces, representing a high density of Fe oxide and which potentially mediates paddy soil CH4 emissions. Using a combination of methods including Fe plaque induction, isotopic labeling, pure microbial strains, and Fe oxide addition experiments, we investigated the impact of Fe plaque on methane (CH4) emissions from paddy soils and explored the associated mechanisms underlying the influence of Fe plaque on CH4 emissions. A 13C–CH4 isotopic labeling experiment showed that Fe plaque did not significantly affect CH4 oxidation and associated gene expression, whereas Fe plaque significantly enriched methanogenic archaea and their expression of genes associated with methanogenesis. Pure microbial strain and Fe oxide addition experiments showed that the enhancement of CH4 production in the presence of Fe plaque was caused by the (semi) conductive minerals within the Fe plaque, specifically, hematite, which promoted the extracellular electron transfer between the methanogenic archaea and their syntrophic bacteria, resulting in enhancement of methanogenesis. Our results imply that the presence of Fe plaque will accelerate CH4 emissions from paddy soils and suppressing Fe plaque has the potential to mitigate CH4 emissions.

Paving the way for sustainable agriculture: An analysis of evolution and driving forces of methane emissions reduction in China

The agriculture sector in China faces the dual challenge of ensuring food security while reducing methane emissions. This study investigates the factors driving changes in methane emissions from rice cultivation, livestock manure, and enteric fermentation in the agricultural sector between 2010 and 2019. First, we use the extended Logarithmic Mean Divisia Index method to measure four effects—emission source structure, emission intensity, economic activity, and population effects. Second, Tapio's decoupling index is employed to analyze the association between export-induced methane emissions and economic growth over the entire period. The results show that (1) rice cultivation is the primary contributor to the overall increase in national CH4 emissions, particularly after 2014, while CH4 emissions from other sources have decreased; (2) economic activity is the key driver of rising methane emissions, while emission intensity has the opposite impact, albeit with a decreasing contribution; and (3) decoupling states exhibit weak and strong decoupling recently, indicating the preliminary performance of the transformation of farm management. Furthermore, we find heterogeneous and spatially imbalanced performance in CH4 emission mitigation among provinces. Although China is on the right track to reduce CH4 emissions and upgrade the domestic and international agricultural structure, this has not been achieved at the provincial level.

Effects of biochar application methods on greenhouse gas emission and nitrogen use efficiency in paddy fields

Biochar application in rice production reduces nitrogen loss and greenhouse gases. We conducted in situ experiments for 3 years, with N210B0 (210 kg N ha−1) as the control. Two biochar application methods (B1:15 t ha−1 biochar applied once and B2: biochar applied three times at 5 t ha−1 yr−1) combined with two nitrogen levels (N210: 210 kg N ha−1 and N168: 168 kg N ha−1) were used. Soil physicochemical properties, CH4 and N2O emissions, functional gene abundance, rice yield, and nitrogen use efficiency were analyzed. Both methods improved the physicochemical properties of the soil, however, B1 was less effective than B2 in increasing soil pH, bulk density, organic carbon, total nitrogen, and microbial biomass nitrogen in year 3. B1 had a higher CH4 emission mitigation effect than B2 in 3 consecutive years, mainly due to the higher pmoA gene abundance. B1 showed a higher reduction effect of N2O emissions compared to B2 in year 1, but the opposite was observed in years 2 and 3. B2 had a higher abundance of AOB, nirK, and nosZ genes compared to B1 in year 3. Compared with N210B0, rice yields were increased by 9.1 %, 9.6 %, and 3.6 % with N210B1, N210B2, and N168B2, respectively, over 3 years, while N168B1 improved yields in the previous 2 years. Biochar improved nitrogen use efficiency over 3 consecutive years directly due to increased use efficiency of panicle fertilizer; the effect of B1 was greater than that of B2 during years 1 and 2, while the opposite was observed in year 3. Both Biochar applied once and three times appeared to be promising practices to increase yield and mitigate GHGs. From the GHGI perspective, the biochar applied once combined with 168 kg N ha−1 can further improve nitrogen use efficiency, and reduce GHGs without hindering improvements in rice yield.

Comparison of the effects of alfalfa meal and sorghum distillery residue supplementation on the methane emissions in black-feathered Taiwan native chicken.

The issue of global warming, primarily fueled by anthropogenic greenhouse gas emissions, necessitates effective strategies to address methane (CH4) emissions from both ruminants and nonruminants. Drawing inspiration from successful approaches employed in ruminants, this study evaluates the impact of supplementing the diets of Taiwan's native black-feathered chickens with alfalfa meal and sorghum distillery residues (SDRs) on CH4 emissions. Using a respiration chamber the results reveal a significant reduction in CH4 emissions when incorporating either 30% alfalfa meal or 30% SDRs into the chicken diet, demonstrating a 59% and 49% decrease, respectively, compared to the control group (P < 0.05). Considering that alfalfa meal contains saponins and SDRs contain tannins, the study delves into the mechanism through which these components mitigate CH4 production in chickens. Incorporating saponins or tannins shows that groups supplemented with these components exhibit significantly lower CH4 emissions compared to the control group (P < 0.05), with a consistent linear decrease as the concentration of the feed additive increases. Further in vitro analysis of chicken cecal contents indicates a proportional reduction in CH4 production with increasing levels of added saponins or tannins (P < 0.05). These findings suggest that the CH4-reducing effects of alfalfa meal and SDRs can be attributed to their saponins and tannin content. However, caution is warranted as excessive alfalfa meal supplementation may adversely impact poultry growth. Consequently, sorghum distillery residue emerges as a more suitable feed ingredient for mitigating CH4 emissions in Taiwan's native black-feathered chickens compared to alfalfa. Additionally, substituting SDRs for conventional commercial chicken feed not only reduces CH4 emissions but also enhances the utilization of byproducts.

Effects of ratios of yak to cattle inocula on methane production and fiber digestion in rumen in vitro cultures1

Yaks are well-adapted to the harsh environment of the Tibetan plateau, and they emit less enteric methane (CH4) and digest poor-quality forage better than cattle. To examine the potential of yak rumen inoculum to mitigate CH4 production and improve digestibility in cattle, we incubated substrate with rumen inoculum from yak (YRI) and cattle (CRI) in vitro in five ratios (YRI: CRI): 0:100 (control), (2) 25:75, (3) 50:50, (4) 75:25 and (5) 100:0 for 72 h. The YRI: CRI ratios of 50:50, 75:25 and 100:0 produced less total gas and CH4 and accumulated less hydrogen (H2) than 0: 100 (control) at most time points. From 12 h onwards, there was a linear decrease (P < 0.05) in carbon dioxide (CO2) production with increasing YRI: CRI ratio. At 72 h, the ratios of 50:50 and 75:25 had higher dry matter (+7.71% and +4.11%, respectively), as well as higher acid detergent fiber digestibility (+15.5% and +7.61%, respectively), when compared to the 0:100 ratio (P < 0.05). Increasing the proportion of YRI generally increased total VFA concentrations, and, concomitantly, decreased the proportion of metabolic hydrogen ([2H]) incorporated into CH4, and decreased the recovery of [2H]. The lower [2H] recovery indicates unknown [2H] sinks in the culture. Estimated Gibbs free energy changes (∆G) for reductive acetogenesis were negative, indicating the thermodynamic feasibility of this process. It would be beneficial to identify: 1) the alternative [2H] sinks, which could help mitigate CH4 emission, and 2) core microbes involved in fiber digestion. This experiment supported lower CH4 emission and greater nutrient digestibility of yaks compared to cattle. Multi-omics combined with microbial culture technologies developed in recent years could help to better understand fermentation differences among species.

Equal importance of humic acids and nitrate in driving anaerobic oxidation of methane in paddy soils

Methane (CH4) is both generated and consumed in paddy soils, where anaerobic oxidation of methane (AOM) serves as a crucial process for mitigating CH4 emissions. Although the participation of humic acids (HA) and nitrate in AOM has been recognized, their relative roles and significance in paddy soils remain insufficiently investigated. In this study, we explored the potential activity of AOM driven by HA and nitrate, as well as the composition of archaeal communities in paddy soils across different rice growth periods and fertilization treatments. AOM activity ranged from 0.81 to 1.33 and 1.26 to 2.38 nmol of 13CO2 g−1 (dry soil) day−1 with HA and nitrate, respectively. No significant differences (p < 0.05) were observed between the AOM activity driven by HA and nitrate across the three fertilization treatments. According to AOM activity, the annual consumption of CH4 was estimated at approximately 0.49 ± 0.06 and 0.83 ± 0.19 Tg for AOM processes driven by HA and nitrate in Chinese paddy soils. Nitrate-driven AOM activity exhibited a positive (p < 0.05) correlation with the abundance of the ANME-2d mcrA gene but a negative (p < 0.05) correlation with the content of dissolved organic carbon. Intriguingly, HA-driven AOM activity was only correlated positively with the nitrate-driven AOM activity. Soil water content, soil organic carbon, nitrate and nitrite contents were significantly correlated with the relative abundance of methanogenic and methanotrophic archaea. These results identified the potential importance of HA and nitrate in driving AOM processes within paddy soils, providing a comprehensive understanding of the complex microbial processes regulating greenhouse gas emissions from paddy soils.

Impact of Reservoir Operation Policies on Spatiotemporal Dynamics of Sediment Methane Production and Release in a Large Reservoir

AbstractReservoir operation policies affect sediment methane (CH4) production and pathways through complex influence on hydrodynamic and biogeochemical processes in reservoir water and sediment. However, the underlying influencing mechanisms, especially the impact of operations on sediment CH4 production and pathways, remain poorly understood. This study combines a physical‐biogeochemical model with a reservoir operation model to evaluate operation impacts on spatiotemporal sediment CH4 production and release dynamics and to analyze affiliated processes and driving factors. Three typical operation policies (i.e., standard, hedging, eco‐friendly) are selected to create the operation scenarios, and a coupled physical‐biogeochemical model is adopted to simulate and compare sediment CH4 production, consumption, diffusion, and ebullition under these scenarios. The methods are applied in the second largest reservoir in China (i.e., Danjiangkou Reservoir) as a case study. Results show that annual total sediment CH4 production among the scenarios ranges from 285.9 to 298.3 Gg C year−1, while operation scenario outcomes significantly differ. Specifically, a significant CH4 percentage (34%–39%) is oxidized in surface sediment while the remaining escapes sediment through diffusion and ebullition. Although diffusion accounts for &gt;60% of the annual sediment CH4 release, sediment ebullition ultimately dominates atmospheric CH4 emissions. Annual total atmospheric CH4 emissions range from 42.8 to 71.1 Gg C year−1 and account for 14%–25% of the annual total sediment production among the three scenarios. The differences demonstrate that reservoir operations significantly impact CH4 pathways and atmospheric emissions. This study provides implications for reservoir managers to coordinate socioeconomic and ecological protection while mitigating CH4 emission targets.

Impact of Water Management on Methane Emission Dynamics in Sri Lankan Paddy Ecosystems

Paddy ecosystems constitute a dominant source of greenhouse gases, particularly of methane (CH4), due to the continuous flooding (CF) practiced under conventional paddy cultivation. A new management method, namely alternative wetting and draining (AWD) (i.e., flooding whenever surface water levels decline to 15 cm below the soil surface), is an emerging practice developed to mitigate CH4 emissions while providing an optimal solution for freshwater scarcity. Despite extensive paddy cultivation in Sri Lanka, no systematic research study has been conducted to investigate CH4 emissions under different water management practices. Thus, field experiments were conducted in Sri Lanka to investigate the feedback of controlled water management on seasonal and diel variation of CH4 emission, water consumption, and crop productivity. Adopting the same rice variety, two water management methods, continuous flooding (CF) and alternative wetting and draining (AWD), were compared with plants (W/P) and without plants (N/P) present. The emission of CH4 was measured using the static closed chamber method. The results show a 32% reduction in cumulative CH4 emission, on average, under AWD when compared to CF. The yield under the AWD was slightly higher than that of CF. Although it was not statistically significant (p &gt; 0.05) there was not any reduction in yield in AWD than in CF. The total water saving under AWD ranged between 27–35% when compared to CF. Thus, the results support (without considering the effect of nitrous oxide) AWD as a promising method for mitigating CH4 emissions while preserving freshwater and maintaining grain yield in paddy systems.

NZnO-based graphene/graphene oxide compounds inhibit methane metabolic pathways and lower the development of antibiotic resistance genes and virulence factors

Ruminant gastrointestinal fermentation produces a large amount of methane (CH4), antibiotic resistance genes (ARGs), and virulence factors (VFs) pose significant risks to human health. This study utilized metagenomic sequencing to investigate the effect of nZnO-based graphene (nZnOG) and nZnO-based graphene oxide (nZnOGO) on the archaeal community, CH4 metabolism, ARGs, VFs, and chemotaxis. Results indicated that the levels of zinc in manure were significantly lower in the nZnOG and nZnOGO groups compared to the nano zinc oxide (nZnO) group. The principal component analysis (PCA) of ARGs antibiotic class showed that there was an 80.13% variation between the three groups, suggesting that different zinc sources could influence ARGs related to various classes of antibiotics. The nZnO group exhibited considerably higher resistance levels to antimicrobial peptides and triclosan, in contrast to the nZnOG and nZnOGO groups. The copy number of ARGs followed the order of nZnO > nZnOG > nZnOGO, with a significant difference observed between the nZnO and nZnOGO groups. Moreover, the nZnOGO group displayed a significantly lower copy number of VFs compared to the nZnO group. Furthermore, the nZnOGO group demonstrated inhibition of CH4 metabolic and chemotaxis pathways, which were associated with reduced transfer of ARGs and VFs. The functional coexistence of ARGs and VFs was driven by the archaeal community, while chemotaxis regulated changes in the archaeal community. These findings suggest that nZnOGO has the potential to inhibit the expression of ARGs and VFs through the inhibition of CH4 metabolism and chemotaxis pathways. Consequently, feed supplementation with nZnOGO may offer a possible solution for mitigating CH4 emission and reducing the transmission of ARGs and VFs.

The mitigating effect of feeding lucerne hay cubes supplemented with an optimal combination of nitrate with l-cysteine on enteric methane emission in sheep

The combination of optimal nitrate and l-cysteine to safely mitigate rumen methane (CH4) emissions in ruminants was studied in an open-circuit respiration head-hood system using four rumen-fistulated Suffolk wethers in a 4 × 4 Latin square design. Four treatments were set up Control: fed on lucerne hay cubes without nitrate and l-cysteine, Nitrate: fed on lucerne hay cubes with 0.18 % NO3−-N in dry matter (DM)), N + Cys-H: fed on lucerne hay cubes supplemented with 0.18 % NO3−-N and 0.74 % l-cysteine (equivalent to half the upper limit of effective S requirement in DM), and N + Cys-Q: fed on lucerne hay cubes supplemented with 0.18 % NO3−-N and 0.37 % l-cysteine (equivalent to 1/4 of the upper limit of effective S requirement in DM). In this experiment, the ingested nitrate at a subclinical concentration/s (0.18 % in DM) increased by 11.2 % mean methemoglobin value and alleviated rumen methanogenesis by 47 %. Administration of l-cysteine set at 0.74 % and 0.37 % in DM reduced by 68 % and 58 % methemoglobin formed by nitrate alone, respectively (P < 0.05). However, daily mitigation of CH4 emissions decreased by 35 % with the addition of l-cysteine at both addition concentration/s compared with Control.The results of this study suggest that mitigation of enteric methane emissions by the combination of nitrate and l-cysteine can be achieved by feeding diets in which the nitrate content is maintained at around 0.18 % NO3−-N in DM and l-cysteine addition is adjusted to 0.37–0.74 % in DM. This method would be recommended as a safe, efficient, and practical way to mitigate enteric CH4 emissions leading to increased productivity while reducing the increased N excretion that causes N2O emissions.

Effect of ellagic and gallic acid on the mitigation of methane production and ammonia formation in an in vitro model of short-term rumen fermentation

Ruminant production is an important source of animal proteins for human nutrition. However, ruminants contribute to about 30% of anthropogenic methane (CH4) emissions worldwide. The reduction of CH4 emissions could represent an important strategy against climate warming. Tannins can play an important role in the mitigation of CH4 emissions from ruminants. However, their mode of action is not yet well known. Thus, the present study aimed to gain a better understanding of the effect of ellagic acid (EA) and gallic acid (GA) on rumen fermentation using a model of short-term in vitro rumen fermentation. The basal diet (hay) was supplemented with EA and GA in five treatments (mg/g dry matter): i) EA 75, ii) EA 150, iii) GA 75, iv) GA 150 and v) EA 75 + GA 75. After a 24 h incubation, pH, ammonia formation, gas production, short-chain fatty acids (SCFA), in vitro organic matter digestibility (IVOMD) and the microbial count were assessed. Total gas production and digestible organic matter (dOM) were decreased after all the treatments, except for GA 75. The treatments EA 150 and EA+GA significantly decreased CH4 production per unit of dietary DM, dOM, CO2 and SCFA. Ammonia production was significantly decreased by EA 150 and EA+GA. EA and GA differently affected the relative abundance of selected bacterial taxa in rumen microbiota. To conclude, EA 150 and EA+GA exerted a significant effect on the reduction of CH4 emissions and ammonia formation, but affecting also the rumen degradability of the diet and the total SCFA production, whereas EA 75 and GA 75 were not effective as EA 150 and EA+GA on CH4 and ammonia, but were less detrimental on feed degradability and SCFA. Further studies are needed to determine whether the beneficial and detrimental effects of tannins on rumen fermentation can be dissociated.

Higher rice grain yield and lower methane emission achieved by alternate wetting and drying in central Vietnam

Rice is the main staple food for more than half of the world’s population, but rice cultivation is a significant source of atmospheric methane (CH4). Alternate wetting and drying (AWD) reduces CH4 emission from paddy field, but the effect on rice yield remains unclear. Organic soil amendment increases grain yield but simultaneously increases CH4 emission. Therefore, the combination of AWD and organic amendment may compensate for each other’s shortcomings. The objective of this study was to assess whether AWD and organic amendment can increase rice yield while mitigating CH4 emission. The experiments were conducted in a farmer’s paddy field in Thua Thien Hue province, Vietnam, during five consecutive rice growing seasons in 2019–2021. Two water management practices, continuous flooding (CF) and AWD, with (+O) or without (−O) the application of a commercially available organic fertilizer were examined under normal cultivation conditions. Compared with CF, AWD significantly reduced CH4 emission by 34 %, increased nitrous oxide (N2O) by 46 %, and increased grain yield by 4.4 %. The +O treatment significantly increased the yield by 3.7 % relative to −O. Relative to CF−O by season, AWD+O significantly increased the yield. The integrated global warming potential of CH4 and N2O emissions was decreased by 33 % and irrigation water use was reduced by 33 % in AWD plots relative to that in CF plots. These results indicate that AWD by itself has the potential to increase rice yield as well as reduce CH4 emission, and the combination of AWD with organic amendment would ensure yield increase.

Retrospective and projected warming-equivalent emissions from global livestock and cattle calculated with an alternative climate metric denoted GWP.

Limiting warming by the end of the century to 1.5°C compared to pre-Industrial times requires reaching and sustaining net zero global carbon dioxide (CO2) emissions and declining radiative forcing from non-CO2 greenhouse gas (GHG) sources such as methane (CH4). This implies eliminating CO2 emissions or balancing them with removals while mitigating CH4 emissions to reduce their radiative forcing over time. The global cattle sector (including Buffalo) mainly emits CH4 and N2O and will benefit from understanding the extent and speed of CH4 reductions necessary to align its mitigation ambitions with global temperature goals. This study explores the utility of an alternative usage of global warming potentials (GWP*) in combination with the Transient Climate Response to cumulative carbon Emissions (TCRE) to compare retrospective and projected climate impacts of global livestock emission pathways with other sectors (e.g. fossil fuel and land use change). To illustrate this, we estimated the amount and fraction of total warming attributable to direct CH4 livestock emissions from 1750 to 2019 using existing emissions datasets and projected their contributions to future warming under three historical and three future emission scenarios. These historical and projected estimates were transformed into cumulative CO2 equivalent (GWP100) and warming equivalent (GWP*) emissions that were multiplied by a TCRE coefficient to express induced warming as globally averaged surface temperature change. In general, temperature change estimates from this study are comparable to those obtained from other climate models. Sustained annual reductions in CH4 emissions of 0.32% by the global cattle sector would stabilize their future effect on global temperature while greater reductions would reverse historical past contributions to global warming by the sector in a similar fashion to increasing C sinks. The extent and speed with which CH4 mitigation interventions are introduced by the sector will determine the peak temperature achieved in the path to net-zero GHG.

Potential of the Red Macroalga Bonnemaisonia hamifera in Reducing Methane Emissions from Ruminants.

Researchers have been exploring seaweeds to reduce methane (CH4) emissions from livestock. This study aimed to investigate the potential of a red macroalga, B. hamifera, as an alternative to mitigate CH4 emissions. B. hamifera, harvested from the west coast of Sweden, was used in an in vitro experiment using a fully automated gas production system. The experiment was a randomized complete block design consisting of a 48 h incubation that included a control (grass silage) and B. hamifera inclusions at 2.5%, 5.0%, and 7.5% of grass silage OM mixed with buffered rumen fluid. Predicted in vivo CH4 production and total gas production were estimated by applying a set of models to the gas production data and in vitro fermentation characteristics were evaluated. The results demonstrated that the inclusion of B. hamifera reduced (p = 0.01) predicted in vivo CH4 and total gas productions, and total gas production linearly decreased (p = 0.03) with inclusion of B. hamifera. The molar proportion of propionate increased (p = 0.03) while isovalerate decreased (p = 0.04) with inclusion of B. hamifera. Chemical analyses revealed that B. hamifera had moderate concentrations of polyphenols. The iodine content was low, and there was no detectable bromoform, suggesting quality advantages over Asparagopsis taxiformis. Additionally, B. hamifera exhibited antioxidant activity similar to Resveratrol. The findings of this study indicated that B. hamifera harvested from temperate waters of Sweden possesses capacity to mitigate CH4 in vitro.

Time-lag effects of flood stimulation on methane emissions in the Dongting Lake floodplain, China

Natural wetlands are the primary sources of CH4 emissions in the natural environment. However, the understanding of CH4 fluxes in floodplain wetlands remains limited. This study employed eddy covariance methods to observe CH4 fluxes over a three-year period in a subtropical wetland floodplain, specifically the Miscanthus sacchariflorus (M. sacchariflorus) ecosystem in Dongting Lake wetland. Our analysis focused on exploring the impact of flooding frequency on CH4 emissions, flood stimulation effect, time-lag effects, and the environmental factors influencing CH4 fluxes. The M. sacchariflorus ecosystem exhibited an annual CH4 emission rate of 14.54 g CH4C m−2 y−1. During the flood period, the average daily CH4 emissions reached 0.155 g CH4C m−2 d−1, contrasting with the pre-flood period's average of 0.014 g CH4C m−2 d−1. Moreover, the time-lag effect of flooding on CH4 emissions was found to be 10 days, representing the period between inundation and a substantial increase in CH4 emissions. Comparatively, in 2021, following three fluctuations in floodwaters, the average CH4 emission intensity during the flood period decreased by 46.2% and 48.9% when compared to the years 2019 and 2020 which both following one fluctuation, respectively. CH4 emissions during flooding are predominantly influenced by water depth (WD), wherein shallow WD corresponds to higher CH4 emissions. This correlation can be attributed to factors such as vegetation type, water-column pressure, and soil oxygen content. Therefore, increasing frequency of inundation and a higher WD hold promise as effective measures for mitigating CH4 emissions in floodplain wetlands.

Impact of temperature on the performance of compost-based landfill biocovers

Methane (CH4) emissions from landfills are a major contributor to global greenhouse gas emissions. Compost-based biocovers offer a viable approach to reduce CH4 emissions from landfills; however, the effectiveness in climates with varying temperatures is not well understood. The methane removal performances of two compost-based biocover materials (food and yard waste compost) were examined under different temperature conditions using laboratory column experiments. A reactive transport model was used to simulate the experimental results to develop a better quantitative understanding of the effect of temperature on overall methane removal efficiency. As expected, experimental results indicated that the oxidation rate was influenced by temperature, as it was reduced when the temperature decreased from 22 °C to 8 °C. However, some oxidation was observed at a lower temperature, which was confirmed by CO2 concentrations above the initial level and the observed temperatures above the exposure temperature along the height of biocover column. Furthermore, results showed that when the compost-based materials were subjected to 8 °C and then increased to 22 °C, methane oxidation within the material recovered quickly and returned to similar oxidation rates as observed before the temperature was reduced, suggesting that compost-based biocovers may not be affected by cyclic temperature variations when used in colder climates. Methane oxidation capacity was limited by the maximum oxidation rate, the biocover porosity, and the gas saturation profile that affects residence time and overall methane oxidation in the columns. The model results show that the CH4 oxidation rate was reduced by one order of magnitude when the temperature decreased from 22 °C to 8 °C. Therefore, the calculated Q10 values were 4.19 and 5.18 for the food and yard waste compost, respectively. Overall, compost-based landfill biocovers, such as food and yard waste compost, are capable of mitigate CH4 emissions from old and small landfills under different temperature conditions.

Impacts of production structure changes on global CH4 emissions: Evidences from income-based accounting and decomposition analysis

Globalization drives anthropogenic methane (CH4) emissions from upstream to downstream agents through global supply chains. However, previous studies have overlooked the indirect CH4 emissions enabled by primary suppliers. In this study, we use the Ghosh Multi-Regional Input-Output (MRIO) model and Structural Decomposition Analysis (SDA) to explore the temporal changes in global income-based CH4 emissions and decompose the socioeconomic drivers. Our results show that global income-based CH4 emissions increased by 17.21% from 2001 to 2014, with per capita primary inputs and technology being the two key drivers. Specifically, in China and India, income-based CH4 emissions were mainly from agriculture, and input structure was responsible for restraining the growth in CH4 emissions from their agricultural activities. On the other hand, service activities dominated the United States and the European Union, and production output structure was accountable for their emission growth related to service activities. To achieve global CH4 emission mitigation, key sectors of major economies with high income-based CH4 emissions should optimize their primary input structures, production output structure, and production technologies from the supply-side. It is crucial to reduce enabled CH4 emissions in emerging economies, particularly in Asia, through the adjustment of primary input activities.

Long-term fertilization enhances the activity of anaerobic oxidation of methane coupled to nitrate reduction and associated microbial abundance in paddy soils

Anaerobic oxidation of methane coupled to nitrate reduction (nitrate-coupled AOM) is performed by Candidatus Methanoperedens nitroreducens (M. nitroreducens)-related archaea, and is recently recognized as a crucial component of the global carbon cycle. The input of fertilizers is an essential agricultural practice that greatly impacts methane (CH4) production and emission. However, the significance of nitrate-coupled AOM in CH4 cycling and its response to fertilization in rice fields remain unclear. In this study, the potential nitrate-coupled AOM rates and the communities of M. nitroreducens-related archaea in rice fields were examined at different soil layers (0–10, 10–20, and 30–40 cm) at tillering, elongation, flowering, and ripening stages under three long-term fertilization treatments (CK-without fertilizer, CF-chemical fertilization, or CFS-chemical fertilization with straw incorporation). The results indicated that both CF (1.07 nmol 13CO2 g−1 d−1) and CFS (1.21 nmol 13CO2 g−1 d−1) treatments significantly promoted the potential nitrate-coupled AOM rates compared to CK (0.53 nmol 13CO2 g−1 d−1). A greater response of potential activity to fertilization was observed at plough layer (upper 20 cm) and during elongation stage. The abundance of M. nitroreducens-related archaea under CF (1.12 × 107 copies g−1) and CFS (1.62 × 107 copies g−1) treatments was significantly greater than that under CK (6.93 × 106 copies g−1). Conversely, the growth response of these archaeal to fertilization was stronger at deeper layer (30–40 cm). Moreover, no significant change was observed in the community composition of M. nitroreducens-related archaea among treatments. Correlation analysis suggested that the variations of soil organic carbon, NH4+, and NO3− contents caused by fertilization were key factors influencing the potential nitrate-coupled AOM rates and M. nitroreducens-related archaeal abundance. Our findings provide the first evidence for positive response of nitrate-coupled AOM to long-term fertilization, demonstrating its potential to act as an important process for mitigating CH4 emission in rice fields.