Total CH4 Emissions Research Articles

Greenhouse gas emissions and soil bacterial community as affected by biochar amendments after periodic mineral fertilizer applications

In a 338-d microcosm incubation experiment, greenhouse gas emissions (GHG) and bacterial diversity were studied in a clayey soil amended with 5% (w/w) biochar in the presence or absence of 4% (w/w) peat- and shrimp-based compost used as an additional C source. Two maple biochars produced at 400 °C (M400) or 700 °C (M700) and pine chips produced at 700 °C (P700) were tested. In comparison with soil supplemented or not with compost, the addition of any biochar resulted in lower total cumulative N2O emission (90% to 97%). The low porosity of M400 and M700 increased soil anaerobic conditions and resulted in higher total cumulative CH4 emission compared to the other soil treatments. In addition, the lowest total cumulative CO2 emission was observed with M700, probably due to its low-priming effect on native soil C decomposition. In all treatments, compost addition had the highest impact on both soil bacterial richness and community composition, particularly on bacteria of the class Anaerolineae. At day 338, results showed that modification of soil properties by maple biochars reduced bacterial diversity and induced shifts in the taxonomic composition of their community. In fact, heterotrophic bacteria involved in denitrification, such as genera Haliangium, Hyphomicrobium, Opititus, and Pedomicrobium, increased in abundance in response to the amendment with maple biochars. We conclude that the nature of biochar feedstock can impact soil bacterial diversity by changing soil physicochemical properties, thus influencing C dynamics, porosity, and pH, and by mitigating total cumulative GHG emissions.

Emission factors and carbon emissions of methane from enteric fermentation of cattle produced under different management systems in South Africa

Production of livestock is important for sustainability of human nutrition and overall livelihoods. Demand for livestock products is increasing due to the growing global human population. Cattle production plays an important role in South Africa’s socio-economics and largely benefits from vast rangelands available for grazing. Similarly, cattle and their management are significant emitters of greenhouse gases. Quantification of past cattle emissions in the country is, however, affected by unreliable activity data and emission factors. This study therefore aims to calculate emission factors for methane (CH4) produced by cattle during enteric fermentation and the related historical CH4 carbon emissions. The emission factors are developed for each cattle subcategory and management system. Feeding practices are collated from the survey conducted in 2015 and the literature. Dairy cattle have the highest emission factors, followed by subsistence beef and commercial beef cattle. However, the large population of commercial beef cattle results in the highest total emissions by category whilst dairy cattle are the smallest producers of CH4. Of the total CH4 emissions from enteric fermentation of 0.87 million tonnes in 2018, commercial beef cattle contributed 48% while subsistence beef cattle and dairy cattle accounted for 36% and 17% respectively. Declining population particularly of commercial beef cattle results in a reduction in emissions with time. Trends of implied emission factors and emissions per energy-corrected milk and animal carcass weight for beef cattle show that cattle production efficiencies are improving in South Africa. Despite relatively lower meat prices for beef compared to poultry, poultry consumption in the country is higher than that of beef and is still growing. This pattern will out-market beef consumption and ultimately cause the emissions to decline.

Sheep Methane Emission on Semiarid Native Pasture-Potential Impacts of Either Zinc Sulfate or Propylene Glycol as Mitigation Strategies.

Simple SummaryFeed availability for small ruminant production in the Brazilian semi-arid region is characterized by the seasonality of forage production over the year. Large variations of methane (CH4) production have been reported among forage types and are mainly explained by the rate of fermentation of plant cell contents and the presence of various plant secondary compounds, notably in heterogeneous pasture. The aim of this study was to evaluate the effects of Zinc sulfate and propylene glycol (PG) on CH4 emission, nutrient intake, digestibility, and production in sheep grazing on a native Caatinga (Brazilian semi-arid savannah) pasture during the rainy season (from March to June 2014). Fifteen mixed Santa Inês sheep were distributed into three treatments (control, Zn, and propylene glycol supplement) in this 112-day study. CH4 emission was measured using the SF6 tracer gas technique. Across the months of the trial, organic matter (OM) and neutral detergent fiber (NDF) intakes were greater in March, while the greatest emission of CH4 (g/day) was observed in May. Total CH4 emission (kg) from March to June (112 days of evaluation) was greater in PG. In conclusion, our results indicate that Zn and PG have no beneficial effects in mitigating sheep CH4 emission when grazing Caatinga-native pasture in the rainy season.The aim of this study was to evaluate the effects of Zinc sulfate and propylene glycol (PG) on methane (CH4) emission, nutrient intake, digestibility, and production in sheep grazing on a native Caatinga (Brazilian semi-arid savannah) pasture during the rainy season (from March to June 2014). Fifteen mixed Santa Inês sheep, all non-castrated males, with initial body weight of 19.8 ± 1.64 kg, and 4 ± 0.35 months of age, were distributed in a complete randomized design into three treatments: control (CT)—concentrate supplemented at 0.7% of body weight; CT + 300 mg of Zn/day; and CT + 2.5 mL of propylene glycol/kg LW0.75/day. Measurements were done in four periods during the rainy season, with 28 days of interval between each measurement. CH4 emission was measured using the SF6 tracer gas technique. CH4 emission per day was greater in PG than in CT and Zn (p < 0.05). However, no additive effect was observed on the intakes of organic matter (OM) and neutral detergent fiber (NDF), or on CH4 emission expressed as a function of OM and NDF intakes (p > 0.05). Across the months of the trial, OM and NDF intakes were greater in March, while the greatest emission of CH4 (g/day and g by g/OM intake) was observed in May (p < 0.05). Total CH4 emission (kg) from March to June (112 days of evaluation) was greater in PG compared with CT and Zn (p < 0.05). Zinc and PG had no effect on total CH4 emission when it was expressed per unit of body weight gain or carcass production (p > 0.05). The results of this study indicate that Zinc sulfate and propylene glycol have no beneficial effects in mitigating sheep CH4 emission. The CH4 emissions originated from sheep grazing native Caatinga pasture change throughout the rainy season due to fluctuations in availability and quality of pasture biomass. Moreover, the inclusion of zinc sulfate or propylene glycol did not improve animal feed intake, nutrient digestibility, and animal performance.

Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions.

Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era1. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate2,3. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century4,5. Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year)2,3 between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year6,7. Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago8, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core 14CH4 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)-an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions9,10.

Magnitude and drivers of integrated fluvial network greenhouse gas emissions across the boreal landscape in Québec

Streams and rivers are now recognized to be sites of intense carbon (C) emissions, yet the lack of C emission estimates that integrate beyond individual river systems has slowed their inclusion in landscape C budgets. Here we apply empirical models of CO2 and CH4 concentrations and gas exchange continuously along entire fluvial networks to derive the total fluvial CO2 and CH4 emissions in large (3000 to 30,000 km2) watersheds located across the boreal biome of Québec (Canada). We assess how total fluvial network C emissions vary with landscape and climate properties, and compare their magnitude to other components of the landscape C budget. The total fluvial network emissions expressed as per unit watershed area ranged from 0.7 to 29.2 g C m−2 yr−1 for CO2, and 4–1780 mg C m−2 yr−1 for CH4, and neither was related to watershed area or drainage density. Rather, watershed slope and terrestrial net productivity were major drivers of the integrated network fluvial emissions. We also show that steeper watersheds had a greater proportion of emissions relative to downstream export of C from the watershed. Integrated fluvial emissions are of the same magnitude as the terrestrial C sink, yet these two fundamental components of the boreal landscape C budget are not tightly coupled.

Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions.

We demonstrate direct eddy covariance (EC) observations of methane (CH4) fluxes between the sea and atmosphere from an icebreaker in the eastern Arctic Ocean. EC-derived CH4 emissions averaged 4.58, 1.74, and 0.14 mg m-2 day-1 in the Laptev, East Siberian, and Chukchi seas, respectively, corresponding to annual sea-wide fluxes of 0.83, 0.62, and 0.03 Tg year-1. These EC results answer concerns that previous diffusive emission estimates, which excluded bubbling, may underestimate total emissions. We assert that bubbling dominates sea-air CH4 fluxes in only small constrained areas: A ~100-m2 area of the East Siberian Sea showed sea-air CH4 fluxes exceeding 600 mg m-2 day-1; in a similarly sized area of the Laptev Sea, peak CH4 fluxes were ~170 mg m-2 day-1. Calculating additional emissions below the noise level of our EC system suggests total ESAS CH4 emissions of 3.02 Tg year-1, closely matching an earlier diffusive emission estimate of 2.9 Tg year-1.

Comparing methane ebullition variability across space and time in a Brazilian reservoir

AbstractThe potent greenhouse gas methane (CH4) is readily emitted from tropical reservoirs, often via ebullition (bubbles). This highly stochastic emission pathway varies in space and time, however, hampering efforts to accurately assess total CH4 emissions from water bodies. We systematically studied both the spatial and temporal scales of ebullition variability in a river inflow bay of a tropical Brazilian reservoir. We conducted multiple highly resolved spatial surveys of CH4 ebullition using a hydroacoustic approach supplemented with bubble traps over a 12‐month and a 2‐week timescale to evaluate which scale of variation was more important. To quantify the spatial and temporal variability of CH4 ebullition, we used the quartile coefficients of dispersion at each point in space and time and compared their frequency distributions across the various temporal and spatial scales. We found that CH4 ebullition varied more temporally than spatially and that the intra‐annual variability was stronger than daily variability within 2 weeks. We also found that CH4 ebullition was positively related to water temperature increase and pressure decrease, but no consistent relationship with water column depth or sediment characteristics was found, further highlighting that temporal drivers of emissions were stronger than spatial drivers. Annual estimates of CH4 ebullition from our study area may vary by 75–174% if ebullition is not resolved in time and space, but at a minimum we recommend conducting spatially resolved measurements at least once during each major hydrologic season in tropical regions (i.e., in dry and rainy season when water levels are falling and rising, respectively).

Estimation of agricultural greenhouse gases emission in interprovincial regions of China during 1996–2014

Agriculture is an important component of national economy in China, and agricultural production is also an important source of greenhouse gas emission. Based on the methods of IPCC, this paper has improved the method with the researches of a large number of scholars. Then, according to the agricultural production data of interprovincial regions of China from 1996 to 2014, the CO2, CH4 and N2O emissions from agriculture were carefully estimated. Then, based on the theory of club convergence in the field of economics, the estimation results are normalized and further analyzed. The results showed that the total CO2 emission has increased from 143.10 Tg in 1996 to 210.67 Tg in 2014, with an average annual growth rate of 2.17%. The largest emission source is the coal for thermal power, accounting for 30% of total emission. The total CH4 emission fell from 23.44 Tg in 1996 to 20.99 Tg in 1997 and then showed a slight fluctuation tendency; the rice field is found to hold major position, accounting for 59% of total emission. The total N2O emission has increased from 337.5 Gg in 1996 to 405.3 Gg in 2014, with an average annual growth rate of 1.02%. The main emission source is fertilizer, accounting for 59% of total emission. The total agricultural greenhouse gas emission in China shows an upward trend, increases from 915.09 Tg CO2 Eq. in 1996 to 965.90 Tg CO2 Eq. in 2014, with an average annual growth rate of 0.3%. The fastest growing area is Heilongjiang, followed by Xinjiang.

Methane flux measurements in rice by static flux chamber and eddy covariance

AbstractUnderstanding methane (CH4) fluxes from rice (Oryza sativa L.) at the field scale is paramount to reducing environmental impacts while ensuring global food security. Greenhouse gas (GHG) measurements at the plot scale using static flux chambers (SFC) have long informed the understanding of flux dynamics and have largely been the basis of global flux estimates. However, in many parts of the world, the landscapes where agricultural fluxes are generated come from larger fields. Eddy covariance (EC) can measure trace gases on larger fields, but there are few studies available quantifying CH4 emissions under typical practices at a field scale. Furthermore, few of these studies are from the U.S. Midsouth, the largest producer of U.S. rice. This study compares and quantifies field‐scale SFC and EC flux measurements on a large commercial system in northeastern Arkansas during the 2015 and 2016 growing seasons, following typical producer practices. Daily measured SFC CH4 fluxes did not differ from EC‐daily CH4 fluxes (p = .108). Total season CH4 emissions, calculated as the sum of daily fluxes ranged from 50 to 156 kg CH4 ha−1 season−1, with SFC reporting greater emissions than EC. Although SFC and EC‐daily flux measurements were similar early (p = .382) and late (p = .543) in the season, they differed mid‐season (p &lt; .001) with SFC consistently reporting greater fluxes than EC. The findings of this study help unify season long plot‐scale and field‐scale flux measurements and signify an advancement of our understanding of GHG fluxes from rice systems.

Can integrated rice-duck farming reduce CH4 emissions?

Integrated rice-duck farming (IRDF) has proven to decrease methane (CH4) emissions due to increased dissolved oxygen caused by duck bioturbation. The duck bioturbation, however, also causes many bubbles of CH4 that were overlooked in previous studies. Therefore, it is uncertain whether IRDF could decrease CH4 emissions. We hypothesize that the effect of IRDF on CH4 emissions is related with the intensity of duck bioturbation. We simulated duck's disturbance (trampling and foraging) by stirring and aerating the surface soil in flooded rice fields. Three treatments were disturbed with an interval of 12h (D12), 24h (D24), and 48h (D48), respectively, with non-disturbance as the control (CK). CH4 emissions as bubbles during the disturbance period (CH4-A) were investigated. Besides, CH4 emissions were investigated every 2h (CH4-B), which lasted for 4days during the rice elongation stage. Compared with CK, D12, D24, and D48 decreased CH4-B emissions by 17.1%, 14.0%, and 10.1%, respectively. However, the CH4-A emissions under D12, D24, and D48 were equivalent to 14.2%, 14.0%, and 11.9% of CH4 emissions under CK, respectively. On the whole, simulated duck bioturbation had limited effects on the reduction of total CH4 emissions.

Beyond-the-Meter: Unaccounted Sources of Methane Emissions in the Natural Gas Distribution Sector.

The United States Environmental Protection Agency maintains an inventory of greenhouse gas emissions in accordance with the Intergovernmental Panel on Climate Change. Methane (CH4), a potent gas with a global warming potential 86-125× that of carbon dioxide (CO2) over a twenty-year period, is the main component of natural gas (NG). As NG becomes an increasingly larger percentage of the energy resources used in the United States, it is ever more important to evaluate the CH4 emissions inventory. However, the inventory also does not account for all possible sources of CH4 leaks, contributing to uncertainty in the national CH4 inventory. Discrepancies between top-down and bottom-up inventories of CH4 emissions imply that there are significant unaccounted-for sources of CH4 leaks, especially over cities. Diffuse CH4 plumes above cities that are not attributable to distribution pipelines or other NG infrastructure suggest many small beyond-the-meter leaks together contribute to large emissions. Here, we evaluate the distribution sector of the CH4 emissions inventory and make suggestions to improve the inventory by analyzing end-user emissions. Preliminary research into beyond-the-meter emissions suggests that while individually small, the appliances and buildings that make up the residential sector could contribute significantly to national scale emissions. Furnaces are the most leak-prone of appliances, contributing to 0.14% of total CH4 emissions from the NG sector in the United States. Combining measurements from whole house emissions and steady-state operation of appliances, we estimate that residential homes and appliances could release 9.1 Gg CH4 yearly in the United States, totaling over 2% of the CH4 released from the NG sector. While factors such as appliance age and usage, climate, and residential setting could influence the emissions profile of individual appliances, these preliminary estimates justify further exploration of beyond-the-meter emissions.

The opportunity of direct seeding to mitigate greenhouse gas emission from paddy rice field

Direct seeded rice (DSR) is one of the options to reduce CH4 emission because it uses less water during initial cropping but it sometimes has side effects such as increasing N2O emissions. The trade-off N2O and CH4 production in rice soils makes a real challenge to reduce the gas production. Nonetheless, few studies have observed the effect of DSR to GHG emission. This study aims to investigate the option of agriculture strategy used to reduce GHG emission without any yield loss through DSR. The study was conducted during rainy season at experimental field of Indonesian Agricultural Environment Research Institute (IAERI), Central Java, Indonesia. We compared the emission of CH4 and N2O, yield and yield components that affected by DSR and TPR practices. Total CH4 emission in TPR was from 352 kg ha−1 season−1 and, it ranged from 187 kg ha−1 season−1 in the DSR. The CH4 emissions were 47% lower for DSR than for TPR during a rice growing season. No significant differences were observed among crop establishments on N2O emissions. GWP were reduced by 46.4% under DSR compare to TPR. Crop-establishment did not influence grain yield, indicating the potential of DSR as alternative methods of establishing lowland rice with low GHG emissions.

Nitrous oxide (N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O) and methane (CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;) in rivers and estuaries of northwestern Borneo

Abstract. Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles in the climate and atmospheric chemistry of the Earth. However, little is known about their emissions from rivers and estuaries, which seem to contribute significantly to the atmospheric budget of both gases. To this end concentrations of N2O and CH4 were measured in the Rajang, Maludam, Sebuyau and Simunjan rivers draining peatland in northwestern (NW) Borneo during two campaigns in March and September 2017. The Rajang River was additionally sampled in August 2016 and the Samunsam and Sematan rivers were additionally sampled in March 2017. The Maludam, Sebuyau, and Simunjan rivers are typical “blackwater” rivers with very low pH (3.7–7.8), very high dissolved organic carbon (DOC) concentrations (235–4387 mmol L−1) and very low O2 concentrations (31–246 µmol L−1; i.e. 13 %–116 % O2 saturation). The spatial and temporal variability of N2O and CH4 concentrations (saturations) in the six rivers or estuaries was large and ranged from 2.0 nmol L−1 (28 %) to 41.4 nmol L−1 (570 %) and from 2.5 nmol L−1 (106 %) to 1372 nmol L−1 (57 459 %), respectively. We found no overall trends of N2O with O2 or NO3-, NO2- or NH4+, and there were no trends of CH4 with O2 or dissolved nutrients or DOC. N2O concentrations showed a positive linear correlation with rainfall. We conclude, therefore, that rainfall is the main factor determining the riverine N2O concentrations since N2O production or consumption in the blackwater rivers themselves seems to be low because of the low pH. CH4 concentrations were highest at salinity = 0 and most probably result from methanogenesis as part of the decomposition of organic matter under anoxic conditions. CH4 in the concentrations in the blackwater rivers showed an inverse relationship with rainfall. We suggest that CH4 oxidation in combination with an enhanced river flow after the rainfall events might be responsible for the decrease in the CH4 concentrations. The rivers and estuaries studied here were an overall net source of N2O and CH4 to the atmosphere. The total annual N2O and CH4 emissions were 1.09 Gg N2O yr−1 (0.7 Gg N yr−1) and 23.8 Gg CH4 yr−1, respectively. This represents about 0.3 %–0.7 % of the global annual riverine and estuarine N2O emissions and about 0.1 %–1 % of the global riverine and estuarine CH4 emissions. Therefore, we conclude that rivers and estuaries in NW Borneo – despite the fact their water area covers only 0.05 % of the global river/estuarine area – contribute significantly to global riverine and estuarine emissions of N2O and CH4.

Estimation of greenhouse gas emissions in the agro-industrial system of sugarcane in Piauí, Brazil

The present study presents an estimate of greenhouse gas emissions throughout the production process of ethanol and sugar originated from sugarcane in Piauí. The field research was carried out in a mill with an attached distillery, where the harvest was conducted manually, from January to December 2015. Life Cycle Assessment principles were considered in the quantification of total CO2, CH4 and N2O emissions in the stages of agriculture, industrialization and distribution, converting them according to their global-warming potential into carbon-equivalent (CO2eq). The use of fuels, agriculture inputs, sugarcane burning, manufacture of machinery and physical structure of the mill, application of pesticides, seeds, use of chemical reagents in the production process and human labor were considered in this study. The results show a total emission of 2,413.3 kg CO2eq /ha.year, and the main key sources were sugarcane burning (48%) and use of chemical products (29.6 %). The industrial and distribution stages contributed with 2% of the emissions each. There was an emission of 29.9 kg CO2eq per ton of sugarcane processed and it was estimated that there would be a net reduction of 83% of emissions if the harvesting could be thoroughly conducted mechanically.

Reduction of methane emissions from manganese-rich constructed wetlands: Role of manganese-dependent anaerobic methane oxidation

The considerable amount of methane (CH4) emitted from constructed wetlands (CWs) during wastewater treatment has the potential to intensify global climate change. Reducing CH4 emissions from CWs is, therefore, an important step in mitigating global warming. In this study, we compared CH4 emission fluxes from long-term operated pilot-scale vertical-flow CWs with natural manganese ore (Mn-CW) and gravel (Gr-CW, control) as a substrate without any seeding sludge or sediment added. The CH4 emission from the Mn-CW (3.01 ± 0.38 g C/m2/day) was significantly lower than the emission from the Gr-CW (5.50 ± 0.24 g C/m2/day). Mn(IV)-dependent anaerobic oxidation of CH4 (Mn-AOM) occurred in the Mn-CW, and was estimated to account for 66% of the total CH4 emissions reduction. The anaerobic methanotrophic archaea lineage ANME-2d present in the Mn-CW was considered the likely methanotroph that mediated Mn-AOM. Anaerobic fermentation, dissimilatory Mn reduction, and hydrogenotrophic methanogenesis were the main processes responsible for the degradation of organics in the Mn-CW. The acetoclastic methanogen archaea were suppressed in the Mn-CW. For the first time, Mn-AOM was demonstrated to be spontaneously present in the freshwater CWs. Our findings also demonstrated a novel approach to mitigate CH4 emissions from CWs, and indicate potential strategies against global climate change.

Global ocean methane emissions dominated by shallow coastal waters

Oceanic emissions represent a highly uncertain term in the natural atmospheric methane (CH4) budget, due to the sparse sampling of dissolved CH4 in the marine environment. Here we overcome this limitation by training machine-learning models to map the surface distribution of methane disequilibrium (∆CH4). Our approach yields a global diffusive CH4 flux of 2–6TgCH4yr−1 from the ocean to the atmosphere, after propagating uncertainties in ∆CH4 and gas transfer velocity. Combined with constraints on bubble-driven ebullitive fluxes, we place total oceanic CH4 emissions between 6–12TgCH4yr−1, narrowing the range adopted by recent atmospheric budgets (5–25TgCH4yr−1) by a factor of three. The global flux is dominated by shallow near-shore environments, where CH4 released from the seafloor can escape to the atmosphere before oxidation. In the open ocean, our models reveal a significant relationship between ∆CH4 and primary production that is consistent with hypothesized pathways of in situ methane production during organic matter cycling.

Methane emissions from oil and gas production on the North Slope of Alaska

Recent warming of the Arctic has motivated assessments of methane (CH4) release from the North Slope Region of Alaska (NSRA). This study examines the contributions of thermogenic emissions from the Prudhoe Bay Oil Field (PBOF) to the elevated concentrations of atmospheric CH4 observed across the NSRA. We report high precision atmospheric measurements of CH4 and ethane (C2H6) within and downwind of the PBOF. Biogenic CH4 emissions, due to methanogenic processes within the Arctic tundra, are not co-emitted with C2H6. We show that the thermogenic gas emanating from oil and gas extraction point sources contains on average 1 mol of C2H6 for every 16 mol of CH4. We use a mass balance approach to estimate total emissions of thermogenic CH4 from two days in the summer of 2016 and find 2–5 times greater emissions than the sum of all sources in the PBOF reported to the EPA Greenhouse Gas Reporting Program in 2016. Although higher than reported, these emissions are much smaller than estimates of CH4 emissions from other oil and natural gas production areas in the US, and they make a very small contribution to total CH4 emissions from the North Slope.

Greenhouse gas emissions from gradually-filled liquid dairy manure storages with different levels of inoculant

Liquid dairy manure storages emit large amounts of methane (CH4), nitrous oxide (N2O) and ammonia (NH3). Gradually filling manure storages is a standard practice, however, most studies have batch filling approaches. Gradual manure filling may emit different GHGs when inoculum is present, as it changes the substrate/microorganism ratio, manure temperature, and distribution of solids. This study compared CH4, N2O and NH3 emissions from gradually-filled and batch-filled 11.9 m3 capacity liquid dairy manure tanks with 0%, 10% or 20% inoculum over 122 day of storage. On average, gradually-filled tanks had 1.8 °C higher manure temperature, which may have contributed to a 12% increase in total CH4 emissions to 6.26 kg m−3 and 28% increase in total NH3 emissions to 328 g m−3. The absence of inoculum reduced CH4 emissions by 25% and 23% compared to the 10% inoculum tanks (6.48 kg m−3) and 20% inoculum tanks (6.31 kg m−3), respectively. Absence of inoculum had no effect on N2O and NH3 emissions. Gradual filling of tanks containing inoculum increased CH4 emissions by 27% to 7.38 kg m−3, while in the absence of inoculum CH4 emissions were reduced by 29% to 4.03 kg m−3. Our results suggest that research using inoculant in batch-filled manure storage systems may underestimate GHG emissions. Future research should further characterize the effects of gradual filling on solids and temperature profiles, and substrate availability linked to production of GHGs.

Quantifying global CH4 and N2O footprints

This study aims to quantify global CH4 and N2O footprints in 2012 in terms of 181 economies and 20 world regions based on the official national emission accounts from the UNFCCC database and the global multi-region input-output accounts from the EORA database. Global total CH4 and N2O emissions increased by 15.0% in 2012 compared to 1990, mainly driven by increasing demands of agricultural and energy products. Mainland China, Western Europe, the USA, Southeast Asia and Sub-Saharan Africa were identified as the largest five CH4 footprint contributors (55.6% of the global total), while Mainland China, the USA, Western Europe, Brazil and Sub-Saharan Africa as the largest N2O footprint contributors (59.2% of the global total). In most developed economies, the CH4 and N2O footprints were much higher than their emissions on the production side, but opposite picture is observed in emerging economies. 36.4% and 24.8% of the global CH4 and N2O emissions in 2012 were associated with international trade, respectively. Substantial energy-related CH4 and agricultural CH4 and N2O emissions were transferred from developed countries to developing countries. Several nations within Kyoto targets have reduced their CH4 and N2O emissions significantly between 1990 and 2012, but the generally-believed success is challenged when viewing from the consumption side. Mainland China, Southeast Asia, Sub-Saharan Africa, Brazil, Middle East and India witnessed prominent increase of CH4 and N2O footprints in the same period. The structure and spatial patterns of global CH4 and N2O footprints shed light on the role of consumption-side actions and international cooperation for future non-CO2 GHG emission reduction.

Methane emissions from contrasting urban freshwaters: Rates, drivers, and a whole‐city footprint

Global urbanization trends impose major alterations on surface waters. This includes impacts on ecosystem functioning that can involve feedbacks on climate through changes in rates of greenhouse gas emissions. The combination of high nutrient supply and shallow depth typical of urban freshwaters is particularly conducive to high rates of methane (CH4 ) production and emission, suggesting a potentially important role in the global CH4 cycle. However, there is a lack of comprehensive flux data from diverse urban water bodies, of information on the underlying drivers, and of estimates for whole cities. Based on measurements over four seasons in a total of 32 water bodies in the city of Berlin, Germany, we calculate the total CH4 emission from various types of surface waters of a large city in temperate climate at 2.6±1.7GgCH4 /year. The average total emission was 219±490mgCH4 m-2 day-1 . Water chemical variables were surprisingly poor predictors of total CH4 emissions, and proxies of productivity and oxygen conditions had low explanatory power as well, suggesting a complex combination of factors governing CH4 fluxes from urban surface waters. However, small water bodies (area <1ha) typically located in urban green spaces were identified as emission hotspots. These results help constrain assessments of CH4 emissions from freshwaters in the world's growing cities, facilitating extrapolation of urban emissions to large areas, including at the global scale.