Mitigate CH4 Emissions Research Articles

Beyond CO2 equivalence: The impacts of methane on climate, ecosystems, and health

In this article we review the physical and chemical properties of methane (CH4) relevant to impacts on climate, ecosystems, and air pollution, and examine the extent to which this is reflected in climate and air pollution governance. Although CH4 is governed under the UNFCCC climate regime, its treatment there is limited to the ways in which it acts as a “CO2 equivalent” climate forcer on a 100-year time frame. The UNFCCC framework neglects the impacts that CH4 has on near-term climate, as well its impacts on human health and ecosystems, which are primarily mediated by methane’s role as a precursor to tropospheric ozone. Frameworks for air quality governance generally address tropospheric ozone as a pollutant, but do not regulate CH4 itself. Methane’s climate and air quality impacts, together with its alarming rise in atmospheric concentrations in recent years, make it clear that mitigation of CH4 emissions needs to be accelerated globally. We examine challenges and opportunities for further progress on CH4 mitigation within the international governance landscapes for climate change and air pollution.

Global anthropogenic CH4 emissions from 1970 to 2018: Gravity movement and decoupling evolution

In recent years, the growth rate of global non-CO2 greenhouse gas (GHG) emissions has exceeded carbon dioxide (CO2) emissions, among which methane (CH4) emissions gradually attracted increasing attention. Compared with CO2 emissions, the sources of CH4 emissions are more complex. Based on the gravity theory and decoupling analysis, this study aims to explore the long-term time-series characteristics of global anthropogenic CH4 emissions from 1970 to 2018. The results showed that the overall gravity center of global CH4 emissions moved towards the east after 2000. The main driving forces could be attributed to the emissions from solid fuel production in China and the oil & gas exploitation in the United States. Specifically, the gravity center of CH4 emissions from animal husbandry and rice cultivation exhibited a southward shift. Besides, most of the countries and economies were in a decoupling state, driving the gravity center of these countries to the east. Among them, most of the developed countries including Australia, Germany, France, Poland, the United Kingdom, the United States, and Japan showed a strong decoupling state between CH4 emissions and economic development. However, some developing countries such as Angola, Venezuela, Brazil, Argentina, Libya, and Iran showed a negative decoupling state. By identifying the gravitational movement and decoupling evolution from 1970 to 2018, this study provides practical strategies and implications towards CH4 emission mitigation worldwide.

Impacts of combined water-saving irrigation and controlled-release urea on CH4 emission and its associated microbial communities and function

Water-saving irrigation and controlled-release nitrogen fertilizer are used in rice farming. The aim of this study was to understand the effects of water-saving irrigation and controlled-release urea on methane (CH4) emission and its associated microbial communities and function. A field experiment was conducted with two nitrogen treatments (NU 100% normal urea, CU 60% normal urea and 40% controlled-release urea, total N amount was the same) and three irrigation modes (CI continuous flooding irrigation, AI alternate wetting and drying irrigation, RI ridge irrigation). CH4 fluxes, organic acid contents and enzyme activities were measured, and soil microbial communities and function were investigated by whole-genome shotgun sequencing analysis, and then their relationships were analyzed by Spearman correlation analysis, redundancy analysis and mantel test. Compared to CI, AI and RI decreased cumulative CH4 emissions by 43.5% and 25.8% in NU, and 64.9% and 13.3% in CU, respectively. Among all treatments, AICU had the lowest CH4 emission and reduced it by 72.2% compared to CINU. AI and RI had higher contents of some organic acids than CI. Compared to CINU, AICU decreased the relative abundance of Methanosarcina barkeri and associated genes in the CO2-reduction methanogenesis pathway by 83.4% and 91.0%. Both abundance of methanogens and associated genes in the CO2-reduction methanogenesis pathway were positively correlated with cumulative CH4 emission, but negatively correlated with most soil organic acids. Thus AICU can mitigate CH4 emission by decreasing the abundance of methanogens and associated genes in the CO2-reduction methanogenesis pathway.

Potential methane emission reduction strategies from rice cultivation systems in Bangladesh: A critical synthesis with global meta-data

Methane (CH4) is one of the dominant greenhouse gases (GHG) that is largely emitted from rice fields and thus, significantly contributes to global warming. Significant efforts have been made to find out suitable strategies to mitigate CH4 emission from rice culture. However, the effectiveness of these management practices is often diverse with negative, no, or positive impacts making it difficult to adopt under a particular condition. The diversity of rice cultivation in terms of agro-climatic conditions and cultivation practices makes it difficult for providing specific recommendations. Here, we collected data from a total of 198 studies reporting 1052 observations. The management practices are categorized into five different management practices i.e., water, organic and inorganic fertilizer management, crop establishment method, and agronomic practices while major categories were subdivided into different classes. To test statistically significant differences in the effectiveness between major management practices, an analysis of variance (ANOVA) was applied. The Gaussian and bootstrapping model were applied to find out the best estimate of the effectiveness of each practice. In addition, mechanisms controlling the CH4 emission reductions were synthesized. Next, the adoption potentials of these practices were assessed based on the existing rice cultivation systems in Bangladesh. Our results showed that water and organic matter management were the most effective methods irrespective of the growing conditions. When these technologies are customized to Bangladesh, water management and crop establishment methods seem most feasible. Among the rice-growing seasons in Bangladesh, there is a larger scope to adopt these management practices in the Boro season (December to May), while these scopes are minimal in the other two seasons due to their rain-fed nature of cultivation. Altogether, our study provides fundamental insights on CH4 reductions strategies from rice fields in Bangladesh.

Decreasing ruminal methane production through enhancing the sulfate reduction pathway

Methane (CH4) production from ruminants accounts for 16% of the global greenhouse gas emissions and represents 2% to 12% of feed energy. Mitigating CH4 production from ruminants is of great importance for sustainable development of the ruminant industry. H2 is the primary substrate for CH4 production in the processes of ruminal methanogenesis. Sulfate reducing bacteria are able to compete with methanogens for H2 in the rumen, and consequently inhibit the methanogenesis. Enhancing the ruminal sulfate reducing pathway is an important approach to mitigate CH4 emissions in ruminants. The review summarized the effects of sulfate and elemental S on ruminal methanogenesis, and clarified the related mechanisms through the impacts of sulfate and elemental S on major ruminal sulfate reducing bacteria. Enhancing the activities of the major ruminal sulfate reducing bacteria including Desulfovibrio, Desulfohalobium and Sulfolobus through dietary sulfate addition, elemental S and dried distillers grains with solubles can effectively decrease the ruminal CH4 emissions. Suitable levels of dietary addition with different S sources for reducing the ruminal CH4 production, as well as maintaining the performance and health of ruminants, need to be investigated in the future.

Evaluation of biochar products at two inclusion levels on ruminal in vitro methane production and fermentation parameters in a Timothy hay-based diet

This study evaluated the effects of seven biochar products at two levels of inclusion [2.25% or 4.50% diet dry matter (DM)] on DM disappearance (DMD), cumulative gas and methane (CH4) production, ammonia-nitrogen, and volatile fatty acid (VFA) production from Timothy grass hay over 48 h of incubation. Biochar did not affect gas and CH4 production (P ≥ 0.17) nor the DMD or ruminal fermentation (P ≥ 0.12). In conclusion, the biochar, irrespective of level of inclusion, did not exhibit potential to mitigate CH4 emission in a grass hay diet.

CS2 increasing CH4-derived carbon emissions and active microbial diversity in lake sediments

Lakes are important methane (CH4) sources to the atmosphere, especially eutrophic lakes with cyanobacterial blooms accompanied by volatile sulfur compound (VSC) emissions. CH4 oxidation is a key strategy to mitigate CH4 emission from lakes. In this study, we characterized the fate of CH4-derived carbon and active microbial communities in lake sediments with CS2 used as a typical VSC, based on the investigation of CH4 and VSC fluxes from Meiliang Bay in Lake Taihu. Stable isotope probing microcosm incubation showed that the efficiency of CH4-derived carbon incorporated into organic matter was 21.1% in the sediment with CS2 existence, which was lower than that without CS2 (27.3%). SO42--S was the main product of CS2 oxidation under aerobic condition, accounting for 59.3–62.7% of the input CS2–S. CS2 and CH4 coexistence led to a decrease of methanotroph and methylotroph abundances and stimulated the production of extracellular polymeric substances. CS2 and its metabolites including total sulfur, SO42− and acid volatile sulfur acted as the main drivers influencing the active microbial community structure in the sediments. Compared with α-proteobacteria methanotrophs, γ-proteobacteria methanotrophs Methylomicrobium, Methylomonas, Crenothrix and Methylosarcina were more dominant in the sediments. CH4-derived carbon mainly flowed into methylotrophs in the first stage. With CH4 consumption, more CH4-derived carbon flowed into non-methylotrophs. CS2 could prompt more CH4-derived carbon flowing into non-methanotrophs and non-methylotrophs, such as sulfur-metabolizing bacteria. These findings can help elucidate the influence of VSCs on microorganisms and provide insights to carbon fluxes from eutrophic lake systems.

Effects of calcium salt of linseed oil fatty acid with different oil adsorbents on in vitro gas production and ruminal fermentation characteristics.

We investigated the effects of supplementary calcium salt of fatty acid (CSFA) from linseed oil with different oil adsorbents on in vitro gas production and rumen fermentation characteristics in barley substrate condition. A non-supplementation treatment (CONT) and treatments of six products, CSFA without oil adsorbent (2.1 fatty acid/Ca molar ratio) and CSFAs with silica gel, zeolite, bentonite, diatomite, and vermiculite (2.8 fatty acid/Ca molar ratio), were prepared. The supplementary 2% and 4% CSFA with silica gel (+S) in the substrate reduced CH4 production 56% and 79%, respectively, compared with that in CONT (p < 0.01). The products, except for +S, did not decrease CH4 production. The dry matter (DM) disappearance in CSFAs with oil adsorbents was lower than that in the CSFA without oil adsorbent (74.8%-77.3% vs. 79.3%, p < 0.01), and crude protein (CP) disappearance in +S supplementation was lower than that of the other products (53.5% vs. 57.2%-59.1%, p < 0.01). The +S supplementation decreased acetate proportion and increased propionate proportion (p < 0.01). Our study indicated that although the disappearance of DM and CP might decrease, using silica gel as an oil adsorbent of linseed oil calcium salt with high fatty acid/Ca molar ratio has the potential to mitigate CH4 emissions from ruminants.

Global Trade Networks Bring Targeted Opportunity for Fugitive Ch4 Emission Mitigation

Global Trade Networks Bring Targeted Opportunity for Fugitive Ch4 Emission Mitigation

Integrated assessment of carbon footprint and economic profit from paddy fields under microbial decaying agents with diverse water regimes in central China

Numerous studies have reported effects of straws with microbial decaying agents on greenhouse gas emissions from rice fields. However, studies regarding the effects of microbial decaying agents on carbon footprint and economic profit under diverse water regimes remained unclear. A two-factor field experiment was adopted to assess effects of different straw treatments (straw returning alone abbreviated as S, and straw returning with microbial decaying agent abbreviated as SMD) on CH4 and N2O emissions, rice yield, carbon footprint, economic profit and net ecosystem economic profit (NEEP) from paddy field under different water regimes (continuous flooding abbreviated as F, and alternation of wetting and drying abbreviated as AWD) in central China. Compared with S treatment, SMD treatment significantly enhanced the crop water productivity by 7.9%−8.4% and the rice yield by 7.3%−7.7%. Though SMD treatment increased the economic profit by 9.9%−18.5%, and the NEEP by 9.6%−18.0% relative to S treatment, it also resulted in higher the CH4 emissions by 12.7%−32.4% and global warming potential by 11.2%−21.5% regardless of water regimes. Water regimes had significant effects on the crop water productivity, rice yield, CH4 and N2O emissions, global warming potential, economic profit, NEEP and carbon footprint. Compared with F treatment, AWD treatment improved the crop water productivity by 51.7%−79.4%, maintained rice yield, increased N2O emissions by 17.7%−40.0%, and mitigated CH4 emissions by 33.2%−75.1%, which therefore resulted in lower global warming potential by 31.5%−69.8% and carbon footprint by 32.7%−66.0%. Moreover, AWD treatment significantly increased the economic profit by 25.4%−41.9% and the NEEP by 28.8%−46.6% relative to F treatment. Overall, the straw incorporated with microbial decaying agents is not an environmental friendly practice for the tradeoff of mitigation of CH4 emissions and increase in economic profit. It is necessary to further optimize straw treatment for mitigating CH4 emissions in order to develop rice sustainable production.

Elevation of NO3−-N from biochar amendment facilitates mitigating paddy CH4 emission stably over seven years

Biochar application into paddy is an improved strategy for addressing methane (CH4) stimulation of straw biomass incorporation. Whereas, the differentiative patterns and mechanisms on CH4 emission of straw biomass and biochar after long years still need to be disentangled. Considering economic feasibility, a seven-year of field experiment was conducted to explore the long-term CH4 mitigation effect of annual low-rate biochar incorporation (RSC, 2.8 t ha−1), with annual rice straw incorporation (RS, 8 t ha−1) and control (CK, with no biochar or rice straw amendment incorporation) as a comparation. Results showed that RSC mitigated CH4 emission while RS stimulated CH4 significantly (p < 0.05) and stably over 7 experimental years compared with CK. RSC mitigated 14.8–46.7% of CH4 emission compared with CK. In comparison to RSC, RS increased 111–950.5% of CH4 emission during 7 field experimental years. On the 7th field experimental year, pH was significantly increased both in RS and RSC treatment (p < 0.05). RSC significantly (p < 0.05) increased soil nitrate (NO3−-N) compared with RS while RS significantly (p < 0.05) increased dissolved carbon (DOC) compared to RSC. Soil NO3−-N inhibition on methanogens and promotion on methanotrophs activities were verified by laboratory experiment, while soil pH and DOC mainly promoted methanogens abundance. Significantly (p < 0.05) increased DOC and soil pH enhanced methanogens growth and stimulated CH4 emission in RS treatment. Higher soil NO3−-N content in RSC than CK and RS contributed to CH4 mitigation. Soil NO3−-N and DOC were identified as the key factors differentiating CH4 emission patterns of RS and RSC in 2019. Collectively, soil NO3−-N impacts on CH4 flux provide new ideas for prolonged effect of biochar amendment on CH4 mitigation after years.

Contribution of periphytic biofilm of paddy soils to carbon dioxide fixation and methane emissions

Rice paddies are major contributors to anthropogenic greenhouse gas emissions via methane (CH4) flux. The accurate quantification of CH4 emissions from rice paddies remains problematic, in part due to uncertainties and omissions in the contribution of microbial aggregates on the soil surface to carbon fluxes. Herein, we comprehensively evaluated the contribution of one form of microbial aggregates, periphytic biofilm (PB), to carbon dioxide (CO2) and CH4 emissions from paddies distributed across three climatic zones, and quantified the pathways that drive net CH4 production as well as CO2 fixation. We found that PB accounted for 7.1%–38.5% of CH4 emissions and 7.2%–12.7% of CO2 fixation in the rice paddies. During their growth phase, PB fixed CO2 and increased the redox potential, which promoted aerobic CH4 oxidation. During the decay phase, PB degradation reduced redox potential and increased soil organic carbon availability, which promoted methanogenic microbial community growth and metabolism and increased CH4 emissions. Overall, PB acted as a biotic converter of atmospheric CO2 to CH4, and aggravated carbon emissions by up to 2,318 kg CO2 equiv ha−1 season−1. Our results provide proof-of-concept evidence for the discrimination of the contributions of surface microbial aggregates (i.e., PB) from soil microbes, and a profound foundation for the estimation and simulation of carbon fluxes in a potential novel approach to the mitigation of CH4 emissions by manipulating PB growth.

MITIGATION YIELD SCALED METHANE EMISSION FROM RICE GROWN IN WATER STRESS CONDITIONS WITH BIOCHAR AND SILICATE AMENDMENTS

Climate change and water scarcity may badly affect existing rice production system in Bangladesh. With a view to sustain rice productivity and mitigate yield scaled CH4 emission in the changing climatic conditions, a pot experiment was conducted under different soil water contents, biochar and silicate amendments with inorganic fertilization (NPKS). In this regard, 12 treatments combinations of biochar, silicate and NPKS fertilizer along with continuous standing water (CSW), soil saturation water content and field capacity (100% and 50%) moisture levels were arranged into rice planted potted soils. Gas samples were collected from rice planted pots through Closed Chamber technique and analyzed by Gas Chromatograph. This study revealed that seasonal CH4 emissions were suppressed through integrated biochar and silicate amendments with NPKS fertilizer (50–75% of the recommended doze), while increased rice yield significantly at different soil water contents. Biochar and silicate amendments with NPKS fertilizer (50% of the recommended doze) increased rice grain yield by 10.9%, 18.1%, 13.0% and 14.2%, while decreased seasonal CH4 emissions by 22.8%, 20.9%, 23.3% and 24.3% at continuous standing water level (CSW) (T9), at saturated soil water content (T10), at 100% field capacity soil water content (T11) and at 50% field capacity soil water content (T12), respectively. Soil porosity, soil redox status, SOC and free iron oxide contents were improved with biochar and silicate amendments. Furthermore, rice root oxidation activity (ROA) was found more dominant in water stress condition compared to flooded and saturated soil water contents, which ultimately reduced seasonal CH4 emissions as well as yield scaled CH4 emission. Conclusively, soil amendments with biochar and silicate fertilizer may be a rational practice to reduce the demand for inorganic fertilization and mitigate CH4 emissions during rice cultivation under water stress drought conditions.

Creating new value of blast furnace slag as soil amendment to mitigate methane emission and improve rice cropping environments

Blast furnace slag (BFS), a by-product of iron making, has been utilized as silicate fertilizer in Korean and Japanese rice paddy. Silicate fertilizer, which has high contents of active iron and manganese as electron acceptor, was newly known to suppress methane (CH4) emission in flooded rice paddies, but the effect of its long-term application on rice cropping environment is still debatable. To evaluate the effect of silicate fertilization on suppressing CH4 emissions, the changes of CH4 index, indicating the ratio (%) of seasonal CH4 flux at the silicate fertilization treatment to that at the control, were generalized using the global investigation data (42 observations from 8 fields in Bangladesh, China, and Korea). Seasonal CH4 fluxes significantly decreased with increasing silicate fertilization levels. In CH4 index changes, 1.5 Mg ha−1 of silicate fertilizer application (the recommended level of rice cultivation in Korea) decreased by 15% of seasonal CH4 fluxes. Rice grain yield highly increased with increasing silicate fertilization rates and maximized at approximately 4 Mg ha−1 with 18% higher than no-silicate fertilization due to overall improvement of soil properties. To evaluate the long-term silicate fertilization effect on rice cropping environments, silicate (1.5 Mg ha−1 year−1) and non-silicate fertilization treatments were installed in a typical temperate-monsoon climate paddy field in South Korea in 1990. Periodic silicate fertilization significantly increased rice grain productivity by an average of 14% over the control for the last 28 years. This fertilization evidently improved rice quality without changes in chemical quality. Consecutive silicate fertilization effectively improved soil physical and chemical properties but did not increase any acid extractable heavy metal concentration in soil. In conclusion, BFS as silicate fertilizer could be a beneficial amendment to mitigate CH4 emission in the rice paddy and improve soil properties and rice productivity and quality without hazardous material accumulation.

Modeling temporal variability in the surface expression above a methane leak: The ESCAPE model

Leaks in natural gas distribution networks are often initially detected by odor and then localized during operators' walking surveys. The size of the enhancement detected and the leak's proximity to infrastructure are used to determine leak severity of the leak and how quickly it is repaired. Methane (CH4) enhancements on the surface above the leak change with atmospheric conditions, but currently the leak severity assessment is made without considering the environmental conditions and could result in misdiagnosis of the leak. This study has developed the “ESCAPE” model, a tool that can be used to estimate CH4 enhancements on the surface above a leak using meteorological and leak data as input. Surface CH4 concentrations calculated using the ESCAPE model agrees well with measurements made during controlled experiments (m = 0.95 and R2 = 0.95). This study highlights the effect of micrometeorology on gas transport from the surface to the atmosphere, where the surface and the atmospheric conditions have the largest effect on the flux. Here, recommendations are made to improve industry best practices, including recording the meteorological conditions at the time of the leak detection, avoiding walking surveys on days where there are strong winds or strong solar irradiance and that known leak locations should be revisited and measured in different conditions. Mitigating CH4 emissions from the gas distribution network is a cost-effective and economically realistic target. Distribution operators can be directed by the output of ESCAPE model to correctly identify and repair the largest distribution leaks and could reduce annual CH4 emissions by 0.69 Tg, this may go some way to reducing energy sector emissions in accordance with the Paris Agreement.

Mitigation of CH4 emissions in sanitary landfills: an efficient technological arrangement to reduce Greenhouse gas emission

Problems related to the solid waste have been shown a relevant subject, by contributing to global warming and climate change. The MSW is one of the main sources of Greenhouse Gases (GHG) emissions, especially the methane gas (CH4). Towards this concern, the general objective of this research is to estimate CH4 emissions produced at the Dom Antonio Barbosa II Sanitary Landfill, situated in the City of Campo Grande, state of MS. Its aim, specifically, is to verify the gravimetric composition of these residues, as well as measure the amount of the MSW already existing and also the volume placed in the mentioned sanitary landfill. The CH4 emissions were estimated in an accumulated total of 2,364,556.28 tCO2eq. It was obtained a total reduction of 1,479,693.87 tCO2eq by methane burning, transforming it into CO2, thus it was possible mitigating the emissions of 62.65% of CH4 generated in DAB II landfill. It is expected that the results from this research contribute to the attenuation of the problems related to the MSW impact on the environment, as well as reflect on the effectiveness of the current adopted technological model.

Integrated effects of microbial decomposing inoculant on greenhouse gas emissions, grain yield and economic profit from paddy fields under different water regimes

Few studies have comprehensively evaluated the impacts of microbial decomposing inoculants on greenhouse gas emissions and economic profit from paddy fields under different water regimes. Here, this study evaluated the effects of microbial decomposing inoculant treatments (straw returning without or with microbial decomposing inoculants (S and SMD)) on rice yield, CH4 and N2O emissions, economic profit and net ecosystem economic profit (NEEP) from paddy fields under different water regimes (continuous flooding (CF) and alternate wetting and drying irrigation (AWD)) in central China with a two-year field experiment. Compared with S treatment, SMD treatment significantly increased the rice yield and crop water productivity by 6.6–7.2% and 5.6–7.9%, respectively. AWD treatment significantly enhanced the crop water productivity by 56.9–73.7% while did not affect rice yield relative to CF treatment. Regardless of water regimes, SMD treatment did not affect N2O emissions, but significantly increased CH4 emissions by 13.8–39.6% relative to S treatment, resulting in a remarkable enhancement of global warming potential by 13.5–32.5%. Compared with S treatment, SMD treatment improved the economic profit and NEEP. By contrast, AWD treatment significantly increased N2O emissions by 19.1–64.8% compared with CF treatment, but significantly reduced CH4 emissions by 35.3–79.1%. Accordingly, AWD treatment significantly decreased the global warming potential by 33.4–73.9% compared with CF treatment. In addition, AWD treatment resulted in 39.9–96.4% higher economic profit and 48.0–124.4% higher NEEP relative to CF treatment. In summary, AWD treatment is a sustainable water regime that can maintain rice yield, mitigate global warming potential, and increase economic income. However, regardless of water regimes, SMD treatment led to higher rice yield and economic profit, as well as higher global warming potential than S treatment, suggesting that other appropriate treatments of crop straw are needed to mitigate CH4 emissions while improving economic profit for rice sustainable production.

A new approach to suppress methane emissions from rice cropping systems using ethephon

Rice is the main staple food for more than half of the world's population. Yet, rice cultivation is subjected to criticism because of its important role in methane (CH4) emissions. Although several agronomic practices such as controlled irrigation and conservation tillage have been widely adopted to mitigate CH4 emissions from rice cultivation, the benefits gained by these practices are highly dependent on site-specific soil and climate conditions, and often offset by yield reduction. The use of plant growth regulating compounds having the potential to increase the crop yield and mitigate CH4 emissions may be an innovative approach to sustainable agriculture. Ethylene (C2H4), a plant growth regulator is known to have a strong inhibitory effect on methanogenesis. However, due to gaseous form and low water solubility, C2H4 has not been used to suppress methanogenesis in paddy fields. To develop C2H4 as a prospective soil amendment for reducing methane (CH4) emissions, ethephon (2-Chloroethylphosphonic acid), a precursor of C2H4 was tested. We found that ethephon reduced CH4 formation by 43%, similar to other well known methanogenic inhibitors (2-Bromoethanesulfonate, 2-Chlomoethanesulfonate, 2-Mercaptoethanesulfonate). However, ethephon rapidly hydrolyzed to C2H4 and methanogenic activity recuperated completely after C2H4 removal. To slow down the release of C2H4, ethephon was mixed with bio-degradable polymers such as cellulose acetate and applied to paddy soils. We found that compared with the control, the C2H4 release of ethephon slowed down to 90 days, and the CH4 emissions were reduced by 90%. The application of ethephon at lower concentrations did not significantly alter bacterial communities, their relative abundance, and the abundance of methanotrophs, but it significantly reduced archaeal communities and the relative abundance and expression level of methanogens in paddy soils. Results suggest that cellulose acetate-mixed ethephon has great promise to suppress CH4 emissions in rice paddies while ensuring sustainable yields.

Global trade network and CH4 emission outsourcing

The intensifying globalization contributes to the anthropogenic methane (CH4) emissions outsourcing, a strong greenhouse gas and harmful air pollutant, through the increasingly complex global trade network. However, the CH4 flow patterns embodied in global traded goods and services have not been interpreted from the perspective of a complex network. In this paper, we integrate global CH4 emission inventory from the EDGAR (the Emission Database for Global Atmospheric Research) databases, global multi-regional input-output model from the GTAP database, and complex network analysis to reveal the structural characteristics of the global CH4 flow network (GCFN). In the GCFN, more than one quarter of the global anthropogenic CH4 emissions in 2014 are associated with international trade. The top 20 economies contribute to about 70% of the total embodied CH4 emission flows. The GCFNs mainly consist of tripartite patterns centered on China, the USA and Russia. Some emerging countries, such as Thailand and Brazil, also exhibit dominated positions in different kinds of GCFNs. Moreover, the core-periphery structure of the GCFN confirms the existence of a few hub economies associated with a large amount of CH4 emissions. The results emphasize the multinational cooperation on global CH4 emission mitigation, and well-focused mitigation policies should be implemented on some key economies.

Cattle biogas effluent application with multiple drainage mitigates methane and nitrous oxide emissions from a lowland rice paddy in the Mekong Delta, Vietnam

Household biogas production from livestock manure is popular in Vietnam. Effluent from the biogas production can be effectively used as organic fertilizer for rice cultivation. However, there is concern about enhanced methane (CH4) emission from the flooded soil under reductive conditions because the effluent contains labile organic carbon, the substrate for microbial CH4 production. We therefore combined multiple drainage with “cattle biogas effluent” (BE) application to mitigate CH4 emission by ameliorating the reductive soil conditions while obtaining grain yields comparable to the conventional practice, a combination of synthetic fertilizers (SY) application and continuous flooding (CF). We performed a 1-year experiment on a lowland (0 m a.s.l.) paddy field in the Mekong Delta, Vietnam, under a triple cropping system. We examined the effects of fertilizer type (SY and BE) and water management (CF, alternate wetting and drying [AWD], and midseason drainage followed by intermittent irrigation [MiDi]) on rice growth and yield and on CH4 and nitrous oxide (N2O) emissions. For AWD, a surface water level of −15 cm was used as the threshold for re-irrigation after natural drainage, whereas MiDi used a fixed irrigation schedule with one-time forced drainage during the midseason drainage period. Surface water level did not drop sufficiently in either AWD or MiDi due to the lowland conditions, and both practices caused similar seasonal changes in water level except for the forced drainage in MiDi. A significant (P = 0.05) interaction between fertilizer type and water management on grain yield was found only in dry season (winter–spring) with the highest yield level. Despite the poorly drained conditions, CH4 emission was significantly reduced by AWD and MiDi (by 27–30%), and both practices offset the significant CH4 emission enhancement by BE application. N2O emission was significantly reduced by BE application, whereas it was not affected by water management because flooded conditions were maintained during every nitrogen fertilizer application. Our results indicate that the combination of BE application and multiple drainage can mitigate CH4 and N2O emissions from a lowland rice paddy in the Mekong Delta without yield loss.