Anthropogenic Methane Sources Research Articles

Limited impact of El Niño–Southern Oscillation on variability and growth rate of atmospheric methane

Abstract. The El Niño–Southern Oscillation (ENSO) has been suggested as a strong forcing in the methane cycle and as a driver of recent trends in global atmospheric methane mole fractions [CH4]. Such a sensitivity of the global CH4 budget to climate events would have important repercussions for climate change mitigation strategies and the accuracy of projections for future greenhouse forcing. Here, we test the impact of ENSO on atmospheric CH4 in a correlation analysis. We use local and global records of [CH4], as well as stable carbon isotopic records of atmospheric CH4 (δ13CH4), which are particularly sensitive to the combined ENSO effects on CH4 production from wetlands and biomass burning. We use a variety of nominal, smoothed, and detrended time series including growth rate records. We find that at most 36 % of the variability in [CH4] and δ13CH4 is attributable to ENSO, but only for detrended records in the southern tropics. Trend-bearing records from the southern tropics, as well as all studied hemispheric and global records, show a minor impact of ENSO, i.e. < 24 % of variability explained. Additional analyses using hydrogen cyanide (HCN) records show a detectable ENSO influence on biomass burning (up to 51 %–55 %), suggesting that it is wetland CH4 production that responds less to ENSO than previously suggested. Dynamics of the removal by hydroxyl likely counteract the variation in emissions, but the expected isotope signal is not evident. It is possible that other processes obscure the ENSO signal, which itself indicates a minor influence of the latter on global CH4 emissions. Trends like the recent rise in atmospheric [CH4] can therefore not be attributed to ENSO. This leaves anthropogenic methane sources as the likely driver, which must be mitigated to reduce anthropogenic climate change.

Methane and Global Environmental Change

Global atmospheric methane concentrations have continued to rise in recent years, having already more than doubled since the Industrial Revolution. Further environmental change, especially climate change, in the twenty-first century has the potential to radically alter global methane fluxes. Importantly, changes in temperature, precipitation, and net primary production may induce positive climate feedback effects in dominant natural methane sources such as wetlands, soils, and aquatic ecosystems. Anthropogenic methane sources may also be impacted, with a risk of enhanced emissions from the energy, agriculture, and waste sectors. Here, we review the global sources of methane, the trends in fluxes by source and sector, and their possible evolution in response to future environmental change. We discuss ongoing uncertainties in flux estimation and projection, and highlight the great potential for multisector methane mitigation as part of wider global climate change policy.

Holistic Assessment of Rumen Microbiome Dynamics through Quantitative Metatranscriptomics Reveals Multifunctional Redundancy during Key Steps of Anaerobic Feed Degradation.

Ruminant livestock is a major source of the potent greenhouse gas methane. The complex rumen microbiome, consisting of bacteria, archaea, and microbial eukaryotes, facilitates anaerobic plant biomass degradation in the cow rumen, leading to methane emissions. Using an integrated approach combining multidomain quantitative metatranscriptomics with gas and volatile fatty acid (VFA) profiling, we aimed at obtaining the most comprehensive picture of the active rumen microbiome during feed degradation to date. Bacterial, archaeal, and eukaryotic biomass, but also methane emissions and VFA concentrations, increased drastically within an hour after feed intake. mRNA profiling revealed a dynamic response of carbohydrate-active enzyme transcripts, transcripts involved in VFA production and methanogenesis. While the relative abundances of functional transcripts did not mirror observed processes, such as methane emissions, transformation to mRNA abundance per gram of rumen fluid echoed ruminant processes. The microbiome composition was highly individual, with, e.g., ciliate, Neocallimastigaceae, Prevotellaceae, Succinivibrionaceae, and Fibrobacteraceae abundances differing between cows. Microbiome individuality was accompanied by inter- and intradomain multifunctional redundancy among microbiome members during feed degradation. This likely enabled the robust performance of the anaerobic degradation process in each rumen. Neocallimastigaceae and ciliates contributed an unexpectedly large share of transcripts for cellulose- and hemicellulose-degrading enzymes, respectively. Methyl-reducing but not CO2-reducing methanogens were positively correlated with methane emissions. While Methanomassiliicoccales switched from methanol to methylamines as electron acceptors, Methanosphaera became the dominating methanol-reducing methanogen. This study for the first time linked rumen meta-omics with processes and enabled holistic insights into the contribution of all microbiome members to feed degradation. IMPORTANCE Ruminant animals, such as cows, live in a tight symbiotic association with microorganisms, allowing them to feed on otherwise indigestible plant biomass as food sources. Methane is produced as an end product of the anaerobic feed degradation in ruminants and is emitted to the atmosphere, making ruminant animals among the major anthropogenic sources of the potent greenhouse gas methane. Using newly developed quantitative metatranscriptomics for holistic microbiome analysis, we here identified bacterial, archaeal, and eukaryotic key players and the short-term dynamics of the rumen microbiome during anaerobic plant biomass degradation and subsequent methane emissions. These novel insights might pave the way for novel ecologically and economically sustainable methane mitigation strategies, much needed in times of global climate change.

Neglecting the fallow season can significantly underestimate annual methane emissions in Mediterranean rice fields.

Paddy rice fields are one of the most important sources of anthropogenic methane. Improving the accuracy in the CH4 budget is fundamental to identify strategies to mitigate climate change. Such improvement requires a mechanistic understanding of the complex interactions between environmental and agronomic factors determining CH4 emissions, and also the characterization of the annual temporal CH4 emissions pattern in the whole crop cycle. Hence, both the growing and fallow seasons must be included. However, most of the previous research has been based on single-factor analyses that are focused on the growing season. In order to fill this gap, a study was conducted in a Mediterranean rice agrosystem (Ebre Delta, Catalonia) following a farm-to-farm approach with the purpose of 1) evaluating the cumulative and temporal pattern of CH4 emission, and 2) conducting a multi-variate analyses to assess the associative pattern, relative contribution and temporal variation of the main explanatory variables concerning the observed CH4 emissions. Measurements of CH4 emissions and agronomic and environmental parameters in 15 commercial rice fields were monitored monthly, during a whole crop field cycle. The temporal pattern of CH4 emission followed a bi-modal distribution peaking in August and October. The cumulative annual CH4 emissions from rice fields amounted 314 kg CH4 kg ha-1, of which ca. 70% were emitted during the fallow season. The main controlling factors of the CH4 emission rate in the growing season were positive related to water level and plant cover, while soil redox was negatively related. The main controlling factors in the fallow season were water level (negatively related, conversely to the growing season), as well as straw incorporation and soil temperature (positively related). The results of this study highlight the importance of the often neglected fallow season in the accurate estimation of CH4 emissions and, thus, the necessity of measurement programs that cover the whole crop field cycle. This information is the first step for setting effective mitigation strategies based on straw and water management.

Inventory of methane emissions from livestock in China from 1980 to 2013

Livestock is the largest anthropogenic methane (CH4) source at the global scale. Previous inventories of this source for China were based on the accounting of livestock populations and constant emission factors (EFs) per head. Here, we re-evaluate how livestock CH4 emissions have changed from China over the last three decades, considering increasing population, body weight and milk production per head which cause EF to change with time, and decreasing average life span (ALS) of livestock. Our results show that annual CH4 emissions by livestock have increased from 4.5 to 11.8 Tg CH4 yr−1 over the period 1980–2013. The increasing trend in emissions (0.25 Tg CH4 yr−2) over this period is ∼12% larger than that if using constant EFs and ALS. The increasing livestock population, production per head and decreasing ALS contributed +91%, +28% and −19% to the increase in CH4 emissions from livestock, respectively. This implies that the temporal changes in EF and ALS of livestock cannot be overlooked in inventories, especially in countries like China where livestock production systems are experiencing rapid transformations.

Lime application lowers the global warming potential of a double rice cropping system

Liming is a common practice to alleviate soil acidification in agricultural systems worldwide. Because liming affects soil microbial activity and soil carbon (C) input rates, it can affect soil greenhouse gas (GHG) emissions as well. However, little is known about the effect of liming on GHG emissions from rice agriculture, one of the main sources of anthropogenic methane (CH4). Here, we report on the first experiment to measure the effect of liming on GHG emissions from rice paddy fields. We studied a double rice cropping system in an acid paddy for two years and measured the impacts of liming on GHG emissions and rice growth with or without straw incorporation. We found that liming reduced CH4 emissions in the early rice season, but it did not affect nitrous oxide (N2O) emissions. Over the two-year study, lime application reduced total CH4 emissions by 12.5% and 15.4% in plots without and with straw incorporation, respectively. Lime application significantly enhanced rice aboveground biomass, while reducing the area- and yield-scaled global warming potential of CH4 and N2O emissions. Lime application stimulated soil respiration during the fallow season and reduced the abundance of methanogens during the early rice growing season. Together, these results suggest that liming reduces CH4 emissions by promoting the decomposition of organic matter during the fallow season, thereby reducing C availability for methanogens. We conclude that in the short term, liming is an effective practice to reduce greenhouse gas emissions from acidic paddy soils.

Vista-LA: Mapping methane-emitting infrastructure in the Los Angeles megacity

Abstract. Methane (CH4) is a potent greenhouse gas (GHG) and a critical target of climate mitigation efforts. However, actionable emission reduction efforts are complicated by large uncertainties in the methane budget on relevant scales. Here, we present Vista, a Geographic Information System (GIS)-based approach to map potential methane emissions sources in the South Coast Air Basin (SoCAB) that encompasses Los Angeles, an area with a dense, complex mixture of methane sources. The goal of this work is to provide a database that, together with atmospheric observations, improves methane emissions estimates in urban areas with complex infrastructure. We aggregated methane source location information into three sectors (energy, agriculture, and waste) following the frameworks used by the State of California GHG Inventory and the Intergovernmental Panel on Climate Change (IPCC) Guidelines for GHG Reporting. Geospatial modeling was applied to publicly available datasets to precisely geolocate facilities and infrastructure comprising major anthropogenic methane source sectors. The final database, Vista-Los Angeles (Vista-LA), is presented as maps of infrastructure known or expected to emit CH4. Vista-LA contains over 33 000 features concentrated on < 1 % of land area in the region. Currently, Vista-LA is used as a planning and analysis tool for atmospheric measurement surveys of methane sources, particularly for airborne remote sensing, and methane hotspot detection using regional observations. This study represents a first step towards developing an accurate, spatially resolved methane flux estimate for point sources in SoCAB, with the potential to address discrepancies between bottom–up and top–down methane emissions accounting in this region. The Vista-LA datasets and associated metadata are available from the Oak Ridge National Laboratory Distributed Active Archive Center for Biogeochemical Dynamics (ORNL DAAC; https://doi.org/10.3334/ORNLDAAC/1525).

Quantitative analysis of the methane gas emissions from municipal solid waste in India

Increased emissions of greenhouse gases have altered the global ambient temperature and adversely affected global climatic conditions. The municipal solid waste (MSW) generated by households is considered the third largest anthropogenic source of methane (CH4) emissions, constituting 11% of all global CH4 emissions. The current study derived total MSW CH4 emission estimates using the IPCC default method (DM), modified triangular method (MTM) and first order decay method (FOD). The estimated CH4 emission was higher for the DM than the other methods, and was comparable to estimates from other studies. This study observed that the net annual emission of CH4 from landfills in India increased from 404 Gg in 1999–2000 to 990 Gg and 1084 Gg in 2011 and 2015, respectively. We also found that CH4 emissions were highly correlated (R2 = 0.8) with the gross state domestic product (GSDP) of states and the gross domestic product (GDP) of the country, which is an indicator of human well-being. The MSW management policy of India needs to be reviewed in a current policy context, as the management and efficient utilization of MSW technologies might help increase the use of CH4 as an energy source and thereby improve its sustainable and cost-effective management.

Estimates and Predictions of Methane Emissions from Wastewater in China from 2000 to 2020

Methane accounts for 20% of the global warming caused by greenhouse gases, and wastewater is a major anthropogenic source of methane. Based on the Intergovernmental Panel on Climate Change greenhouse gas inventory guidelines and current research findings, we calculated the amount of methane emissions from 2000 to 2014 that originated from wastewater from different provinces in China. Methane emissions from wastewater increased from 1349.01 to 3430.03 Gg from 2000 to 2014, and the mean annual increase was 167.69 Gg. The methane emissions from industrial wastewater treated by wastewater treatment plants (EIt) accounted for the highest proportion of emissions. We also estimated the future trend of industrial wastewater methane emissions using the artificial neural network model. A comparison of the emissions for the years 2020, 2010, and 2000 showed an increasing trend in methane emissions in China and a spatial transition of industrial wastewater emissions from eastern and southern regions to central and southwestern regions and from coastal regions to inland regions. These changes were caused by changes in economics, demographics, and relevant policies.

‘Frontline research in mitigating greenhouse gas emissions from paddy fields’

Paddy fields are recognized to be a major anthropogenic source of atmospheric methane (CH4), a potent greenhouse gas with a relatively short lifetime in the atmosphere. Like other biogenic sources,...

Intercontinental comparison of greenhouse gas emissions from irrigated rice fields under feasible water management practices: Brazil and Japan

ABSTRACTFlooded rice fields are a significant anthropogenic source of methane (CH4) and nitrous oxide (N2O) from agriculture in Asia, Latin America, and the Caribbean regions. In this work, we comparatively assessed the potential of intermittent irrigation and continuous rice flooding for reducing soil CH4 and N2O emissions, partial global warming potential (pGWP), and its yield-scaled version (YpGWP) in northwestern Japan and southern Brazil. Seasonal CH4 emissions under continuous flooded soils were slight higher in Japan (738 ± 87 kg ha−1) than in Brazil (623 ± 197 kg ha−1), and they were probably related to the higher level of soil organic C and the longer period under flooding in the seedling transplanting system in the Japanese site. Intermittent irrigation had similar efficiency in decreasing soil CH4 emissions in both study areas, with the maximum mitigation potential of 71% in northwestern Japan and of 62% in southern Brazil. No significant difference in seasonal soil N2O emissions (−0.17 ± 0.05 to −0.24 ± 0.06 kg N2O ha−1 in Japan and 0.32 ± 0.08–1.16 ± 0.40 kg ha−1 in Brazil) or rice yield (7328–8064 kg ha−1 in Japan and 9391–10,231 kg ha−1 in Brazil) between irrigation systems was observed in either area. The potential of intermittent irrigation for reducing pGWP was around three times higher than that of continuous flooding in both sites. Thus, a reduction by 47–63% and 62–80% in yield-scaled pGWP was observed in southern Brazil and northwestern Japan, respectively. Like the well-established labor-intensive rice transplanting systems used in Asia, the introduction of feasible irrigation suppression systems in mechanized direct seeding rice fields in southern Brazil and other countries of Latin America and the Caribbean region is an effective choice for reducing greenhouse gas emissions with no adverse impact on rice yield.

Stratification of Diversity and Activity of Methanogenic and Methanotrophic Microorganisms in a Nitrogen-Fertilized Italian Paddy Soil.

Paddy fields are important ecosystems, as rice is the primary food source for about half of the world’s population. Paddy fields are impacted by nitrogen fertilization and are a major anthropogenic source of methane. Microbial diversity and methane metabolism were investigated in the upper 60 cm of a paddy soil by qPCR, 16S rRNA gene amplicon sequencing and anoxic 13C-CH4 turnover with a suite of electron acceptors. The bacterial community consisted mainly of Acidobacteria, Chloroflexi, Proteobacteria, Planctomycetes, and Actinobacteria. Among archaea, Euryarchaeota and Bathyarchaeota dominated over Thaumarchaeota in the upper 30 cm of the soil. Bathyarchaeota constituted up to 45% of the total archaeal reads in the top 5 cm. In the methanogenic community, Methanosaeta were generally more abundant than the versatile Methanosarcina. The measured maximum methane production rate was 444 nmol gdwh-1, and the maximum rates of nitrate-, nitrite-, and iron-dependent anaerobic oxidation of methane (AOM) were 57 nmol, 55 nmol, and 56 nmol gdwh-1, respectively, at different depths. qPCR revealed a higher abundance of ‘Candidatus Methanoperedens nitroreducens’ than methanotrophic NC10 phylum bacteria at all depths, except at 60 cm. These results demonstrate that there is substantial potential for AOM in fertilized paddy fields, with ‘Candidatus Methanoperedens nitroreducens’ archaea as a potential important contributor.

Methane emissions from a Californian landfill, determined from airborne remote sensing and in situ measurements

Abstract. Fugitive emissions from waste disposal sites are important anthropogenic sources of the greenhouse gas methane (CH4). As a result of the growing world population and the recognition of the need to control greenhouse gas emissions, this anthropogenic source of CH4 has received much recent attention. However, the accurate assessment of the CH4 emissions from landfills by modeling and existing measurement techniques is challenging. This is because of inaccurate knowledge of the model parameters and the extent of and limited accessibility to landfill sites. This results in a large uncertainty in our knowledge of the emissions of CH4 from landfills and waste management. In this study, we present results derived from data collected during the research campaign COMEX (CO2 and MEthane eXperiment) in late summer 2014 in the Los Angeles (LA) Basin. One objective of COMEX, which comprised aircraft observations of methane by the remote sensing Methane Airborne MAPper (MAMAP) instrument and a Picarro greenhouse gas in situ analyzer, was the quantitative investigation of CH4 emissions. Enhanced CH4 concentrations or CH4 plumes were detected downwind of landfills by remote sensing aircraft surveys. Subsequent to each remote sensing survey, the detected plume was sampled within the atmospheric boundary layer by in situ measurements of atmospheric parameters such as wind information and dry gas mixing ratios of CH4 and carbon dioxide (CO2) from the same aircraft. This was undertaken to facilitate the independent estimation of the surface fluxes for the validation of the remote sensing estimates. During the COMEX campaign, four landfills in the LA Basin were surveyed. One landfill repeatedly showed a clear emission plume. This landfill, the Olinda Alpha Landfill, was investigated on 4 days during the last week of August and first days of September 2014. Emissions were estimated for all days using a mass balance approach. The derived emissions vary between 11.6 and 17.8 kt CH4 yr−1 with related uncertainties in the range of 14 to 45 %. The comparison of the remote sensing and in situ based CH4 emission rate estimates reveals good agreement within the error bars with an average of the absolute differences of around 2.4 kt CH4 yr−1 (±2. 8 kt CH4 yr−1). The US Environmental Protection Agency (EPA) reported inventory value is 11.5 kt CH4 yr−1 for 2014, on average 2.8 kt CH4 yr−1 (±1. 6 kt CH4 yr−1) lower than our estimates acquired in the afternoon in late summer 2014. This difference may in part be explained by a possible leak located on the southwestern slope of the landfill, which we identified in the observations of the Airborne Visible/Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) instrument, flown contemporaneously aboard a second aircraft on 1 day.

Shallow Gas Migration along Hydrocarbon Wells–An Unconsidered, Anthropogenic Source of Biogenic Methane in the North Sea

Shallow gas migration along hydrocarbon wells constitutes a potential methane emission pathway that currently is not recognized in any regulatory framework or greenhouse gas inventory. Recently, the first methane emission measurements at three abandoned offshore wells in the Central North Sea (CNS) were conducted showing that considerable amounts of biogenic methane originating from shallow gas accumulations in the overburden of deep reservoirs were released by the boreholes. Here, we identify numerous wells poking through shallow gas pockets in 3-D seismic data of the CNS indicating that about one-third of the wells may leak, potentially releasing a total of 3-17 kt of methane per year into the North Sea. This poses a significant contribution to the North Sea methane budget. A large fraction of this gas (∼42%) may reach the atmosphere via direct bubble transport (0-2 kt yr-1) and via diffusive exchange of methane dissolving in the surface mixed layer (1-5 kt yr-1), as indicated by numerical modeling. In the North Sea and in other hydrocarbon-prolific provinces of the world shallow gas pockets are frequently observed in the sedimentary overburden and aggregate leakages along the numerous wells drilled in those areas may be significant.

Maintaining rice production while mitigating methane and nitrous oxide emissions from paddy fields in China: Evaluating tradeoffs by using coupled agricultural systems models

China is the largest rice producing and consuming country in the world, accounting for more than 25% of global production and consumption. Rice cultivation is also one of the main sources of anthropogenic methane (CH4) and nitrous oxide (N2O) emissions. The challenge of maintaining food security while reducing greenhouse gas emissions is an important tradeoff issue for both scientists and policy makers. A systematical evaluation of tradeoffs requires attention across spatial scales and over time in order to characterize the complex interactions across agricultural systems components. We couple three well-known models that capture different key agricultural processes in order to improve the tradeoff analysis. These models are the DNDC biogeochemical model of soil denitrification-decomposition processes, the DSSAT crop growth and development model for decision support and agro-technology analysis, and the regional AEZ crop productivity assessment tool based on agro-ecological analysis. The calibration of eco-physiological parameters and model evaluation used the phenology and management records of 1981–2010 at nine agro-meteorological stations spanning the major rice producing regions of China. The eco-physiological parameters were calibrated with the GLUE optimization algorithms of DSSAT and then converted to the counterparts in DNDC. The upscaling of DNDC was carried out within each cropping zone as classified by AEZ. The emissions of CH4 and N2O associated with rice production under different management scenarios were simulated with the DNDC at each site and also each 10×10km grid-cell across each cropping zone. Our results indicate that it is feasible to maintain rice yields while reducing CH4 and N2O emissions through careful management changes. Our simulations indicated that a reduction of fertilizer applications by 5–35% and the introduction of midseason drainage across the nine study sites resulted in reduced CH4 emission by 17–40% and N2O emission by 12–60%, without negative consequences on rice yield.

Controls on Methane Occurrences in Aquifers Overlying the Eagle Ford Shale Play, South Texas.

Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo-Wilcox Aquifer (250-1200 m depth range) and Queen City-Sparta Aquifer (150-900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ13 Cmethane (>-55‰) and δDmethane (>-180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ13 Cmethane and δDmethane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs.

On Methane Leaks from Pipelines in Bryan and College Station, Texas, USA

Methane is the second most important anthropogenically emitted greenhouse gas after carbon dioxide. Anthropogenic methane sources in the US are dominated by emissions from domestic ruminants and from fossil fuel exploration, storage and transmission. The fossil fuel source is primarily due to natural gas leaks along the production to distribution chain, and pipeline leaks in urban areas have been identified as a significant contributor. In this study, we evaluated possible leaks in three neighborhoods of a midsize Texas metropolitan region surrounding Texas A&amp;M University through mobile measurements using a fast response, high precision methane analyzer. Neighborhoods were selected by age and land use, and each predetermined driving route was evaluated three times. Methane spikes exceeding 2.5 ppm were identified as leaks, and approximately one leak per mile of urban road was discovered. The largest leaks were found around the Texas A&amp;M natural gas plant and in the oldest neighborhood to its north, while fewer leaks were found in a slightly younger neighborhood. No leaks were found in the youngest, less than 20-year old neighborhood suggesting that pipeline system age is a strong determinant of current and future leaks from the natural gas distribution system.

Water management reduces greenhouse gas emissions in a Mediterranean rice paddy field

Rice paddy fields are one of the largest anthropogenic sources of methane (CH4), the second most important anthropogenic greenhouse gas (GHG) after carbon dioxide (CO2). For this reason most studies on the GHG budget in these agricultural systems focus on the evaluation of CH4 production. However, these systems also exchange other GHGs with the atmosphere, such as CO2 and nitrous oxide (N2O). To estimate the total global warming potential (GWP) of rice cultivation, a field experiment was carried out in a Mediterranean rice paddy field in the Po Valley (Italy), the largest rice producing region in Europe. For two consecutive years, ecosystem CO2 and CH4 fluxes were assessed using the eddy covariance technique and CH4 and N2O fluxes were measured with closed chambers. The net biome productivity indicated a nearly carbon (C) neutral system in 2009 while it accumulated C in 2010, due to the application of organic fertilizers and the midseason drainage of the otherwise flooded field, the latter having the additional benefit of leading to lower water consumption. The rice paddy field acted as a strong GHG source with a GWP of 1148g CO2-eqm−2yr−1 in 2009 and decreased four-fold in 2010 (289g CO2-eqm−2yr−1). In both years, the site was a large CH4 source. Differences in the GHG budget between the two years of measurements were mainly caused by the lower CH4 emissions in 2010 (21.0g CH4 m−2 compared to 37.4gCH4m−2 in 2009), probably driven by drainage of the otherwise flooded field in the middle of the growing season during 2010 and moderately larger CO2 uptake. The increased N2O fluxes (29%), had a marginal contribution to the GWP. However, midseason drainage, which needs to be evaluated in combination with the concurrent application of organic fertilizers, resulted in small decreases of yield. Our results therefore suggest that an adequate management of the water table level reduces CH4 fluxes and has the potential to decrease the GWP and water losses through evapotranspiration of rice paddy fields, confirming that full GHG budgets should be assessed in combination with yields in order to develop and evaluate effective mitigation strategies.

Projection of methane emissions from livestock through enteric fermentation: A case study from India

Livestock is one of the major sources of anthropogenic methane (CH4) emissions. India has the world's largest number of livestock and thus CH4 emissions from the Indian livestock sector are very significant. Any long-term CH4 emissions mitigation strategies would require the precise projection of livestock growth, followed by implementation of appropriate policy mechanisms. However, livestock related long-term CH4 emissions projection studies are currently lacking in India. In this study, a dynamic approach based on the STELLA software in combination with mathematical models was developed to assess livestock population growth and CH4 emissions in India for a 25 year period (2007–2032) under baseline (BS: BS-I, BS-II, BS-III) and modified (MS: MS-I, MS-II, MS-III) scenarios. Standard Indian livestock database and IPCC emission guidelines were followed to estimate CH4 emissions. The results indicate that under the baseline scenarios, CH4 emissions range from 14.08 Tg (296 Tg CO2e CH4) in 2007 to 68.49 Tg (1438 Tg CO2e CH4) in 2032 and for modified scenarios, emissions range from 13.85 Tg (291 Tg CO2e CH4) in 2007 to 16.62 Tg (349 Tg CO2e CH4) in 2032. At the state level, the highest CH4 emissions from livestock has been observed in Uttar Pradesh (15% of total emissions in India) followed by Madhya Pradesh (9.41%) and Andhra Pradesh (9.20%). The lowest emission per head livestock has been observed in goats and sheep (105kg CO2e CH4 head−1 yr−1) followed by cattle (672kg CO2e CH4 head−1yr−1) and buffalo (1155kg CO2e CH4 head−1yr−1) in all the scenarios. However, while considering livestock populations, cattle contribute the highest CH4 emissions (more than 50%) trailed by buffalo, goat, and sheep. Substantial reduction in emissions would be possible if livestock population growth could be stabilized according to the modified scenarios. Different approaches (like dietary management, livestock product demand optimization, and population stabilization) for CH4 emissions reduction are also discussed in this paper. A comparison of modeled v/s estimated emissions using actual recent livestock census data from year 2012 has also been presented in this paper. The findings of the present study are expected to help policy makers to adopt appropriate policy mechanisms to reduce CH4 emissions from the Indian livestock sector.

메타게놈 분석을 이용한 돈분뇨 처리에 의한 논토양에서 메탄대사에 미치는 영향 조사

Under flooded rice fields, methanogens produce methane which comes out through rice stalks, thus rice fields are known as one of the anthropogenic sources of atmospheric methane. Studies have shown that use of manure increases amount of methane emission from rice. To investigate mechanisms by which manure boosts methane emission, comparative soil metagenomics between inorganically (NPK) and pig manure fertilized paddy soils (PIG) were conducted. Results from taxonomy analysis showed that more abundant methanogens, methanotrophs, methylotrophs, and acetogens were found in PIG than in NPK. In addition, BLAST results indicated more abundant carbohydrate mabolisetm functional genes in PIG. Among the methane metabolism related genes, PIG sample showed higher abundance of methyl-coenzyme M reductase (mcrB/mcrD/mcrG) and trimethylamine-corrinoid protein Co-methyltransferase (mttB) genes. In contrast, genes that down regulate methane emission, such as trimethylamine monooxygenase (tmm) and phosphoserine/homoserine phosphotransferase (thrH), were observed more in NPK sample. In addition, more methanotrophic genes (pmoB /amoB / mxaJ ), were found more abundant in PIG sample. Identifying key genes related to methane emission and methane oxidation may provide fundamental information regarding to mechanisms by which use of manure boosts methane emission from rice. The study presented here characterized molecular variation in rice paddy, introduced by the use of pig manure.