Total CH4 Emissions Research Articles

Effects of moisture on emissions of methane, nitrous oxide and carbon dioxide from food and garden waste composting

Abstract Globally, waste generation is continually increasing, with landfill as the main destination for biological waste. Composting is a simple alternative for handling waste, but when poorly managed poses a risk of greenhouse gas emissions. The moisture content of substrate affects emissions of methane (CH4) and nitrous oxide (N2O) from composting, but the scale and mechanisms behind these effects are poorly understood. This study examined effects of different moisture levels (44–66%) on CH4, N2O and carbon dioxide (CO2) emissions during 20 days of composting food and garden waste under controlled conditions (55 °C, 16% oxygen) in a 200-L reactor. Total CO2 emissions were 400–500 g CO2-C kg−1 initial C. Total CH4 emissions were highest, 35 g CH4-C kg−1 initial C, for the wettest substrate (66% moisture) and decreased exponentially with declining moisture content, with the lowest total emissions, 0.04 g CH4-C kg−1 initial C, observed with the driest substrate. Total N2O emissions were negatively correlated with moisture content, decreasing from 1.2 g N2O-N kg−1 initial N at 44% moisture to 0.3 g N2O-N kg−1 initial N at 59%, but the wettest substrate (66% moisture) had the highest N2O emissions, 1.4 g N2O-N kg−1 initial N. NH4-N accumulated in the wettest material, suggesting that the increased N2O emissions were due to reduced oxygen availability. The results indicate potential to reduce greenhouse gas emissions from large-scale composting by adjusting the moisture content at different stages of composting, thus lowering its overall environmental impact. This finding can be used in guidelines for large-scale composting process to avoid moisture conditions causing large greenhouse gas emissions.

The energy input-output analysis of maize production in Sundarharaincha Municipality, Morang district, Nepal

Maize is the second largest crop grown in Nepal and is grown in all three geographic zones. The objective of this study is to analyse the energy input-output of maize production systems. The study is conducted in Sundarharaincha municipality of Morang district, Nepal, using direct questionnaires methods for the collection of primary data of varying landholding sizes farmers. The study revealed that total energy input and output for maize production system found about 10, 999.61 MJ/ha and 45, 501.52 MJ/ha, respectively, with the highest share by farmyard manure (FYM) about 50%. The energy use efficiency was found 4.14. Total CO2, N2O and CH4 emissions due to chemical inputs were found 163.24 kg/ha, 0.03 kg/ha and 0.33 kg/ha, respectively. The total Global warming potential was found 178.58 CO2 eq. per ha. The average cost of production were calculated USD 301.35/ha and profit USD 272.26/ha.

A Multiplatform Inversion Estimation of Statewide and Regional Methane Emissions in California during 2014-2016.

California methane (CH4) emissions are quantified for three years from two tower networks and one aircraft campaign. We used backward trajectory simulations and a mesoscale Bayesian inverse model, initialized by three inventories, to achieve the emission quantification. Results show total statewide CH4 emissions of 2.05 ± 0.26 (at 95% confidence) Tg/yr, which is 1.14 to 1.47 times greater than the anthropogenic emission estimates by California Air Resource Board (CARB). Some of differences could be biogenic emissions, superemitter point sources, and other episodic emissions which may not be completely included in the CARB inventory. San Joaquin Valley (SJV) has the largest CH4 emissions (0.94 ± 0.18 Tg/yr), followed by the South Coast Air Basin, the Sacramento Valley, and the San Francisco Bay Area at 0.39 ± 0.18, 0.21 ± 0.04, and 0.16 ± 0.05 Tg/yr, respectively. The dairy and oil/gas production sources in the SJV contribute 0.44 ± 0.36 and 0.22 ± 0.23 Tg CH4/yr, respectively. This study has important policy implications for regulatory programs, as it provides a thorough multiyear evaluation of the emissions inventory using independent atmospheric measurements and investigates the utility of a complementary multiplatform approach in understanding the spatial and temporal patterns of CH4 emissions in the state and identifies opportunities for the expansion and applications of the monitoring network.

Split N and P addition decreases straw mineralization and the priming effect of a paddy soil: a 100-day incubation experiment

The effect of mineral fertilization and its application pattern on microbial activity and the subsequent CO2 and CH4 emissions arising from soil organic matter (SOM) or added substrate remains unclear. We quantified the decomposition of 13C-labeled straw and the priming effect (PE) governed by the N and P fertilizer application pattern during a 100-day experiment in a flooded soil. Straw addition increased the total CO2 and CH4 emissions. Straw mineralization increased by 30% and decreased by 19% after full and split NP application, respectively, compared with only straw addition. However, application of NP fertilization (full or split) inhibited straw-derived CH4 emissions compared with only straw addition. SOM decomposition was increased by straw addition, yielding a positive PE for CO2 emission. The application of split NP fertilization along with straw addition improved microbial activity, yielding the highest positive PE for CO2 emission. In contrast, compared with the control (no addition), split NP application decreased the positive PE for CH4 emission. Therefore, the straw-C-derived total CO2 equivalent emission was decreased by split NP application. These results were mainly attributable to the increased Olsen P, microbial biomass, enzyme activity, and straw-derived C microbial use efficiency of split NP application, which negatively affected the PE for CH4 emission; this was supported by the results of standardized total effects determined from structural equation models. Overall, compared with full application, split NP fertilizer application significantly decreased the straw-C mineralization rate and PE for CH4 emission, thereby mitigating greenhouse gas emission and SOM storage in paddy soil.

The Importance of CH4 Ebullition in Floodplain Fens

AbstractUncertainty in estimates of CH4 emissions from peatlands arise, in part, due to difficulties in quantifying the importance of ebullition. This is a particular concern in temperate lowland floodplain fens in which total CH4 emissions to the atmosphere (often measured as the sum of diffusive and plant‐mediated fluxes) are known to be high, but few direct measurements of CH4 ebullition fluxes have been made. Our study quantified CH4 fluxes (diffusion, plant‐mediated, and ebullition) from two temperate floodplain fens under conservation management (Norfolk, UK) over 176 days using funnels and static chambers. CH4 ebullition was a major component (>38%) of total CH4 emissions over spring and summer. Seasonal variations in quantifiable CH4 ebullition fluxes were marked, covering six orders of magnitude (5 × 10−5 to 62 mg·CH4·m−2·hr−1). This seasonal variability in CH4 ebullition fluxes arose from changes in both bubble volume flux and bubble CH4 concentration, highlighting the importance of regular measurements of the latter for accurate assessment of CH4 ebullition using funnels. Soil temperature was the primary control on CH4 ebullition fluxes. Elevated water level was also associated with increased CH4 ebullition fluxes, with a distinct increase in CH4 ebullition flux when water level rose to within 10 cm of the peat surface. In contrast, CH4 ebullition flux decreased steadily with increasing plant cover (measured as vascular green area). Ebullition was both steady and episodic in nature, and drops in air pressure during the two‐day funnel deployments were associated with higher fluxes.

Mitigation of ammonia, nitrous oxide and methane emissions during solid waste composting with different additives: A meta-analysis

Composting of solid waste can be associated with a loss of the agronomic value (nutrient loss), as well as a source of environmental impact through the emission of the greenhouse gases (GHG) nitrous oxide (N2O) and methane (CH4) and volatilization of ammonia (NH3). Additives have been considered as a useful option to mitigate these environmental emissions, but the wider effects of using different additives on multiple gas emissions is still uncertain. Here, a global meta-analysis was conducted using 105 studies with 303 paired comparisons, to quantify the impact of different additives on NH3 and GHG emissions, considering different composting feedstock properties. On average, additives reduced the total nitrogen (TN) loss (46.4%), NH3 (44.5%), N2O (44.6%) and CH4 (68.5%) emissions, and total GHG emissions expressed as global warming potential (GWP) (54.2%) during composting. Chemical, physical and microbial additives all significantly reduced TN loss and NH3 emission; however, the strongest effect was observed for chemical additives under the condition of low moisture content (≤65%), low C/N ratios (≤20) or alkalinity (pH > 7.5). Specifically, PO43− and Mg2+ salt had the greatest mean mitigation for TN loss (68.0%) and NH3 emission (62.0%). In contrast, physical additives (e.g. biochar and zeolite) were more effective at reducing the total GHG emissions (67.2%) compared with chemical additives because of the greater mitigation of N2O emission. Low moisture content (≤65%) or low C/N ratios (≤20) enhanced the effectiveness of chemical additives in reducing TN loss and NH3 emission. Physical additives were suggested to be more effective in reducing N2O emission at low moisture content (≤65%) or high C/N ratios (>20 to ≤ 30). The magnitude of the mitigation of TN loss and NH3 emission increased as the dosage rate of PO43− and Mg2+ salt/superphosphate increased between 0 and 20%. This meta-analysis suggests that an optimized combination of chemical and physical additives tailored to feedstock characteristics and application dosage may be a promising approach for the synergistic mitigation of NH3 and GHG emissions.

A Case Study of Greenhouse-Gas-Emissions Measurements and Reduction-Potential Evaluation During Oil and Gas Production in China

Summary Reducing greenhouse–gas (GHG) emissions in oil and gas production could provide several benefits, including energy conservation, cost reduction, and economic returns. The direct–emissions measurements and reduction–potential evaluation are the prerequisites to achieve an effective reduction goal in GHG emissions. On the basis of the survey of production processes and related parameters, we identified and measured a series of GHG–emissions sources. The emissions sources were measured, including production processes and leakage–prone facilities such as dehydrators, boilers, heaters, associated gas–treatment plants, light–hydrocarbon–recovery units, storage tanks, and gas flaring. A series of leakage–detection/measurement instruments was applied as well, such as flow samplers, impeller flowmeter, gas detectors, and gas–flow probes. On the basis of the measured emissions data, we then used a simulation model to evaluate the specific forms, sources, and reduction potentials of the GHGs. The measured GHG emissions showed that evaporation and flashing losses from storage tanks were the largest source, accounting for 86% of the total methane (CH4) emissions and 42% of the total GHG emissions. The contribution of CH4 emissions from heaters and boilers during incomplete combustions was less than 1% of the total CH4 emissions and approximately 16% of the total GHG emissions. When controlling technology on storage–tank losses was applied, CH4 emissions could be reduced by 81.7% and the GHG emissions could be reduced by 39.9%. Furthermore, such controlling technologies also presented substantial economic benefits through the recovery of fuel gas. In this study, the recovery potentials of various GHG–emissions sources were analyzed. In addition, a preliminary cost/benefit analysis was performed per the emissions categories, reduction potentials, and the feasibility of reduction technologies. Finally, the probability of the application of such reduction technologies was evaluated.

Inventories of methane and nitrous oxide emissions from animal and crop farms of 69 municipalities in Alberta, Canada

Spatially explicit, accurate inventories of greenhouse gas (GHG) emissions are of primary importance when calculating the carbon footprint, identifying sources and sinks, pricing carbon pollution, and creating policy that is effective in reducing emissions. However, there are few reports available on methane and nitrous oxide emissions from each type of livestock and crop in all counties of the province due to a lack of statistical data of sub-categories, such as the different fertilizer quantities used in each crop in the county. Because fertilizer input is the most significant factor for N2O emissions from agricultural soils, how to best distribute the total fertilizer mass to a crop-specific fertilizer rate for each county is a major challenge in agricultural management. In this study, authors developed a crop-specific method correlating the recommended fertilizer rate and planted area of each crop for a reasonable distribution of total fertilizer mass to fertilizer rate. This is based on a balance between the sum of fertilizer used in all crops and the total fertilizer mass used by each municipality. Using this method, our calculations in 69 municipalities in the province of Alberta, Canada showed that the fertilizer rate for each crop was reasonably distributed from the total fertilizer mass of a municipality: less than 170 kg-N ha−1. The obtained fertilizer rates for each crop in 69 municipalities were used in GHG inventories using IPCC 2006 tier 1 and 2 methods. The total CH4 and N2O emissions from agriculture in all of Alberta in 2011 were 328 Gg CH4 yr−1 and 23.5 Gg N2O yr−1, respectively. The southeastern municipalities generally emitted more CH4 and N2O than northwestern municipalities. The southern municipality of Lethbridge emitted the largest amount of CH4 and N2O of all municipalities (25.3 Gg CH4 yr−1 (7.70% of total CH4 of entire Alberta) and 1.26 Gg N2O yr−1 (5.40% of total N2O of entire Alberta), respectively). This was due to its largest cattle population (414,627 head) and larger synthetic fertilizer input (32,111 ton-N) and planted area (206,077 ha). The second largest CH4 and N2O emission source was also located at the south. The Taber municipality emitted 15.8 Gg CH4 yr−1 (4.80% of total CH4 of entire Alberta) and 1.14 Gg N2O yr−1 (4.80% of total N2O of entire Alberta), respectively.

Multi-scale temporal variation in methane emission from an alpine peatland on the Eastern Qinghai-Tibetan Plateau and associated environmental controls

Most previous studies on methane (CH4) emissions from peatlands have focused on the boreal, subarctic, and tropical regions. Little is known about CH4 emissions from the alpine peatlands that are widely distributed in the eastern Qinghai-Tibetan Plateau (QTP), which are sensitive to climate change and human disturbance. To assess the magnitudes of daily and seasonal variations in CH4 flux in this area, and to identify the influential environmental factors, an eddy covariance (EC) tower with a LI-7700 open-path CH4 analyzer was established on Hongyuan Peatland. Total annual CH4 emission was 46.8 g CH4 m-2 in 2014, with emissions in the non-growing season accounting for 25% of the annual total. From May to September 2014, diurnal variation in CH4 emissions was observed, with CH4 fluxes varying between 0.15 and 0.25 μmol m-2 s-1. In contrast, during all other periods of 2014, no diurnal variation was observed, and CH4 flux varied below 0.05 μmol m-2 s-1. A clear seasonal pattern in CH4 exchange with small surges in CH4 emission appeared in soil thawing and freezing seasons. Wavelet analysis was applied to the continuous CH4 flux time series to explore temporal variation in ecosystem CH4 exchange during the growing season. On daily timescales, changes in CH4 flux are in phase with changes in air temperature, and influenced by friction velocity and vapor pressure deficit (VPD). On weekly-to-monthly timescales, soil temperature can explain most of the variation in CH4 exchange. Though CH4 fluxes had no apparent correlation with water table level, fluxes were significantly (R2 = 0.86) correlated with soil temperature measured at -25 cm depth, close to the water table level throughout the growing season, suggesting a synergistic effect of water table level and soil temperature on methane emission. This study highlights the need for continuous eddy covariance measurements and time series analysis approaches to adequately describe temporal variability in ecosystem CH4 exchange.

Methane formation and consumption by sediments in a cross-channel profile of a small river impoundment

Rivers are a natural source of methane (CH4) into the atmosphere and may contribute significantly to total CH4 emissions. Even though the details of sources of CH4 in rivers are not fully understood, weirs have been recognized as a hotspot of CH4 emissions. In this study, we investigated CH4 production and consumption in air-exposed river sediments along a cross-channel transect located upstream of a weir. Stable carbon isotopes were used for determination of individual methanogenic pathways. In order to understand the relationship between physicochemical and biological processes, additional parameters such as organic matter, grain median size, and carbon and nitrogen content were characterized as well. Generally, samples from the surface sediment layer (0-10 cm) had higher CH4 production than sediments from the deeper layer (10-20 cm) during the incubation experiments. Sediments near the bank zones and in the mid-channel were characterized by the highest organic carbon content (6.9 %) as well the highest methanogenic activity (2.5 mmol g-1 DW d-1). The CH4 production was predominated by H2/CO2 dependent methanogenesis in the surface sediment layer (0-10 cm), while the proportion of acetoclastic and hydrogenotrophic methanogenesis in the deeper sediment layer (10-20 cm) was balanced. The CH4 oxidation potential of sediments showed the same spatial pattern as observed for the CH4 production. Our results showed high spatial variability of sediment CH4 production and oxidation in the cross-channel profile upstream of the weir, whereas the highest CH4 dynamics were observed in the littoral zones. This variability was closely linked with the carbon and nitrogen content in the sediment samples.

The role of methane in future climate strategies: mitigation potentials and climate impacts

This study examines model-specific assumptions and projections of methane (CH4) emissions in deep mitigation scenarios generated by integrated assessment models (IAMs). For this, scenarios of nine models are compared in terms of sectoral and regional CH4 emission reduction strategies, as well as resulting climate impacts. The models’ projected reduction potentials are compared to sector and technology-specific reduction potentials found in literature. Significant cost-effective and non-climate policy related reductions are projected in the reference case (10–36% compared to a “frozen emission factor” scenario in 2100). Still, compared to 2010, CH4 emissions are expected to rise steadily by 9–72% (up to 412 to 654 Mt CH4/year). Ambitious CO2 reduction measures could by themselves lead to a reduction of CH4 emissions due to a reduction of fossil fuels (22–48% compared to the reference case in 2100). However, direct CH4 mitigation is crucial and more effective in bringing down CH4 (50–74% compared to the reference case). Given the limited reduction potential, agriculture CH4 emissions are projected to constitute an increasingly larger share of total anthropogenic CH4 emissions in mitigation scenarios. Enteric fermentation in ruminants is in that respect by far the largest mitigation bottleneck later in the century with a projected 40–78% of total remaining CH4 emissions in 2100 in a strong (2 °C) climate policy case.

Methane emissions responding to Azolla inoculation combined with midseason aeration and N fertilization in a double-rice cropping system.

Methane (CH4) is an important greenhouse gas (GHG), and paddy fields are major sources of CH4 emissions. This pot experiment was conducted to investigate the integrated effects of Azolla inoculation combined with water management and N fertilization on CH4 emissions in a double-rice cropping system of Southern China. Results indicated that midseason aeration reduced total CH4 emissions by 46.9%, 38.6%, and 42.4%, followed by N fertilization with 32.5%, 17.0%, and 29.5% and Azolla inoculation with 32.5%, 17.0%, and 29.5%, on average, during the early, late, and annual rice growing seasons, respectively. The CH4 flux peaks and total CH4 emissions observed in the late rice growing season were significantly higher than those in the early rice growing season. Additionally, CH4 fluxes correlated negatively to soil redox potential (Eh) and dissolved oxygen (DO) concentration. Azolla inoculation and N fertilization greatly increased the rice grain yields, whereas midseason aeration had distinct effects on grain yields in both rice seasons. The highest annual rice grain yields of approximately 110gpot-1 were obtained in the Azolla inoculation and N fertilization treatments. In terms of yield-scaled CH4 emission, Azolla inoculation combined with midseason aeration and N fertilization generated the lowest yield-scaled CH4 emissions both in the early and in the late rice growing seasons, as well as during the annual rice cycle. In contrast, the highest yield-scaled CH4 emission was obtained in the treatment employed continuous flooding, without Azolla and no N application. Our results demonstrated that Azolla inoculation, midseason aeration, and N fertilization practices mitigated total CH4 emissions by 18.5-42.4% during the annual rice cycle. We recommend that the combination of Azolla inoculation, midseason aeration, and appropriate N fertilization can achieve lower CH4 emissions and yield-scaled CH4 emissions in the double-rice growing system.

Dynamics of animal performance, and estimation of carbon footprint of two breeding herds grazing native neotropical savannas in eastern Colombia

The savannas of eastern Colombia located in the Orinoco river basin represent 18% of the Latin American neotropical savannas, and those areas that are tillable and closer to markets are subject to considerable anthropic pressure in the quest for intensification. Historically, and even today, beef cattle production constitutes the main land use, and much of it is subjected to extensive management. This paper describes for the first time, the use of cattle grazing experiments to assess methane (CH4) emissions from neotropical savanna-based beef breeding systems, and with the support of published research conducted next to them, estimates of the carbon (C) footprint in carbon dioxide equivalents (CO2-eq) for the whole system. Over 5 years and covering complete reproductive cycles, a conventional weaning (CW) herd system was compared to an early weaning (EW) herd system, that represented a modest degree of more intensive savanna management. Differences were found between the two management practices in total CH4 emissions, emission intensities [kg CH4 kg –1 calf born and kg CH4 kg –1 liveweight gain (LWG)] and emission efficiencies (kg CO2-eq kg –1 calf born and kg CH4 kg –1 LWG), that mostly associated with the different lactation lengths. When both herd systems were carried over until calves, later yearlings, reached to 25 months of age, the differences in favor of EW breeding herd system were diminished. The calculated C footprint in (CO2-eq) of both management practices was near neutral subjected to a number of assumptions and the use of limited published information on savanna C stocks and CH4 and nitrous oxide (N2O) emissions from soil, and it is posited that both herd systems were nearly in equilibrium. The available data and results show the need for further information on the neotropical savanna C stocks and C sequestration potential of soils of the Orinoco river basin. More reliable datasets regarding below-ground C inputs and CH4 and N2O emissions from soil are needed to provide a useful basal benchmark for, and approach to, future analyses of environmental impact of more intensive beef herd systems in the region.

Methane emissions of extensive grazing breeding herds in relation to the weaning and yearling stages in the Eastern Plains of Colombia

A substantial proportion of beef production in Colombia originates in its extensiveEastern Plains. However, in this scenario and in a global context, demand for cattleproduction increasingly requests that it satisfies social and environmental expectationsin addition to being economically efficient. A dataset containing five-year long recordsof cow-calf production systems collected at Carimagua Research Centre located in theMeta Department was retrospectively interrogated to understand the liveweight (LW)-derived flux matrix dynamics of methane (CH4) emissions. Estimated total CH4 (kg)emissions during the gestation period, were similar between conventional weaned (CW;37.86 ± 0.506 kg) and early weaned (EW; 37.47 ± 0.476 kg) cows. However, averagedover two lactations, total CH4 emissions were larger (p < 0.0001) in CW cows (38.67± 0.456 kg) than in their EW (14.40 ± 0.435 kg) counterparts. Total gas emissionsfrom birth to comparable commercial yearlings age were higher (p < 0.0001) for CW(43.11 ± 0.498 kg) calves than for EW (40.27 ± 0.472 kg) calves. It was concluded thatmid and long-term pastoral datasets and new concerns are well suited to understanddifferent contexts and adaptations to the contemporary weather conditions. Nevertheless,conventional farming systems will be less environmentally vulnerable if EWmanagement practices involve the strategic and temporal use of improved pastures. Theroles of veterinary medicine and animal sciences are briefly discussed in the context ofunprecedented climate variability to provide a guide to the uncertain future.

GLOBAL EMISSIONS: A NEW CONTRIBUTION FROM THE SHADOW ECONOMY

Based on the STIRPAT model and the EKC hypothesis, this study provides new evidences on the economic determinants of global emissions. The system-GMM estimations are used for the sample of 106 economies in the period of 1995-2012 to investigate the influences of income level, urbanization, industrialization, energy intensity, public expenditure, trade openness, FDI inflow, and especially shadow economy on total greenhouse emissions, CO2 emissions, CH4 emissions, and N2O emissions, respectively. This study contributes to the literature in three folds. First, the industrialization energy intensity are the main drivers for all emissions (excluding N2O). While, urbanization has positive effects on emissions excluding the case of CH4. Other drivers including public spending and economic integration (proxied by trade openness and FDI inflow) are also tested with interesting findings. Second, a higher level of shadow economy increases all emissions excluding CO2. Third, the determinants of emissions vary depending on the countries' income level. The study is supported by a battery of robustness checks and by various estimations in the short and long-run to identify the importance of emissions' drivers.Keywords: Emissions; CO2, CH4, N2O, Public expenditures, Economic integration, Shadow economy.JEL Classifications: F18, F64, O44, Q56, R11, O17DOI: https://doi.org/10.32479/ijeep.7244

Anthropogenic Methane Emission and Its Partitioning for the Yangtze River Delta Region of China

AbstractUrban areas are global methane (CH4) hotspots. Yet large uncertainties still remain for the CH4 budget of these domains. The Yangtze River Delta (YRD), China, is one of the world's most densely populated regions where a large number of cities are located. To estimate anthropogenic CH4 emissions in YRD, we conducted simultaneous atmospheric CH4 and CO2 mixing ratio measurements from June 2010 to April 2011. By combining these measurements with the Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport models and a priori Emission Database for Global Atmospheric Research emission inventories, we applied three “top‐down” approaches to constrain anthropogenic CH4 emissions. These three approaches included multiplicative scaling factors, flux ratio, and scale factor Bayesian inversion. The posteriori CH4 flux density estimated from the three approaches showed high consistency and were 36.32 (±9.17), 35.66 (±2.92), and 36.03(±14.25) nmol·m−2·s−1, respectively, for the duration of the study period (November 2010 to April 2011). The total annual anthropogenic CH4 emission was 6.52(±1.59) Tg for the YRD region based on the average of these three approaches. Our emission estimates were 30.2(±17.6)%, 31.5 (±5.6)%, and 30.8 (±27.4)% lower than the a priori Emission Database for Global Atmospheric Research v432 emission inventory estimate. The scale factor Bayesian inversion results indicate that the overestimate was mainly caused by two source categories including fuel exploitation and agricultural soil emissions (rice cultivation). The posteriori flux densities for agricultural soil and fuel exploitation were 10.68 and 6.34 nmol·m−2·s−1, respectively, and were 47.8% and 29.2% lower than the a priori inventory. Agricultural soil was the largest source contribution and accounted for 29.6% of the YRD CH4 budget during the study period.

Large Fine‐Scale Spatiotemporal Variations of CH4 Diffusive Fluxes From Shrimp Aquaculture Ponds Affected by Organic Matter Supply and Aeration in Southeast China

AbstractMariculture shrimp ponds are important CH4 sources to the atmosphere. However, the spatiotemporal variations of CH4 concentration and flux at fine spatial scales in mariculture ponds are poorly known, particularly in China, worlds largest aquaculture producer. In this study, the plot‐scale spatiotemporal variations of water CH4 concentration and flux, both within and among ponds, were researched in shrimp ponds in Shanyutan wetland, Min River Estuary, Southeast China. The average water CH4 concentration and diffusion flux across the water‐air interface in the shrimp ponds over the shrimp aquaculture period varied from 2.29 ± 0.29 to 50.48 ± 20.91 μM and from 0.09 ± 0.01 to 2.32 ± 0.95 mmol·m−2·hr−1, respectively. The CH4 emissions from the estuarine ponds varied greatly between seasons, with peaks in August and September, which was similar to the trend of water temperature and dissolved oxygen concentrations. There was no remarkable difference in CH4 concentration and flux between shrimp ponds but significantly spatiotemporal differences in CH4 concentration and flux within the ponds. Significantly higher emissions occurred in the feeding zone, accounting for approximately 60% of total CH4 emission flux, while much lower CH4 emissions appeared in aeration zone, contributing 14% to total flux. This study suggests the importance of considering spatiotemporal variation in the whole‐pond estimates of CH4 concentration and flux. In light of such high spatial variation within ponds, improving aeration and feed utilization efficiency would help to mitigate CH4 emissions from mariculture ponds.

Advancing CMM drainage, quality, and utilization with horizontal directional-drilled boreholes in Duanshi Coal Mine, southern Qinshui Basin, China

The Duanshi coal mine is a private, small-size producer and one of >1000 Chinese underground coal mines that pre-drain CMM prior to mining to prevent explosions, capture, and utilize fugitive gas. The coal mine opened in 2008 and employed in-seam auger-drilled boreholes to capture CMM and use as required by the China Emission Standard to curb CH4 emission, which is one of the most potent GHG. As drilling technology advanced, the coal mine used in-seam horizontal directional drilling in 2017 to boost capture of higher quality CMM for utilization but was hampered by technical and geological challenges. Deformation of Pennsylvanian–Permian coal-bearing rocks in the southern Qinshui Basin restricted horizontal directional drilling in the coal mine. The target No. 3 coal seam of the Permian Shanxi Formation is tightly folded into an asymmetrical, northward plunging syncline in the mine area, which requires designing innovative strategies for implementing drilling. Also, the “tight reservoir” (impermeable) property of the No. 3 coal makes recovery of high-volume and -quality CMM difficult. These technical and geological conditions were revealed as causes of the increasing trend in China's total CH4 emission, which is 1.1 ± 0.4 Tg CH4/yr from 2010 to 2015, specifically attributed to underground coal mining (Miller et al., 2019). The increase indicates that CMM drainage and utilization regulations have not curbed growing CH4 emission from underground coal mines. We conclude that our study of advancing CMM drainage technology and use in the Duanshi coal mine could serve as an example for China's small and medium mine operators of underground coal mines that suffer similar technical and geological challenges.

China's Urban Methane Emissions From Municipal Wastewater Treatment Plant

AbstractThe increased number and capacity of municipal wastewater treatment plants (WWTPs) in China has driven the emission of methane (CH4). Few studies have focused on quantification of CH4 emissions from municipal WWTPs of different cities and analysis of socioeconomic factors influencing the quantity of emissions. Here we estimated CH4 emissions from WWTPs in China for 229 prefectural‐level cities, based on data from 2,019 working municipal WWTPs. The results show the total CH4 emissions to be 1,169.8 thousand tons (29.2 MtCO2e) in 2014, which is over three times that of the municipal WWTPs in the United States in 2016. Large cities along the east coast regions had larger CH4 emissions in absolute and per capita terms. Correlation analysis shows that cities with higher gross domestic product, household food consumption expenditure, or household consumption expenditure produced more degradable organics in wastewater, thus more CH4 emissions. Measures to control the sources of degradable organics and regulate WWTP processes with less emission factor are key to mitigate CH4 emissions. In addition to aerobic or anaerobic wastewater treatment systems, factors such as wastewater temperature, length of sewer, and the addition of nitrate that influencing emission factor are suggested to be involved in CH4 emission modeling.

Is alternate wetting and drying irrigation technique enough to reduce methane emission from a tropical rice paddy?

ABSTRACT Combination of a pre-season wet soil condition and rice straw incorporation just before transplanting, which is typical for a tropical rice double cropping, can induce a flash of methane (CH4) emission shortly after the transplanting. The conventional practice of alternate wetting and drying (AWD) irrigation technique that typically starts at 21 days after transplanting (DAT) can hardly reduce this emission because the soil become methanogenic before the onset of AWD treatment. Field experiments were conducted in Central Luzon, Philippines, during the 2014–2017 dry rice seasons to examine the effects of the timing of rice straw/stubble incorporation on the efficacy of AWD in reducing the CH4 emission. Two treatments of the timing of stubble incorporation were stubbles incorporated during the start of wet land preparation (S1) and stubbles incorporated during the dry fallow tillage (S2). For the water management, we compared two treatments: continuous flooding (CF) and AWD with – 15 cm threshold for irrigation. The AWD under S2 was implemented earlier at 10 DAT. We observed a significant interaction (p < 0.01) between effects of AWD and straw management on CH4 emissions; the seasonal total CH4 emission was reduced by AWD compared with CF by 73% under S2, while the reduction was <20% under S1. The AWD significantly (p < 0.05) increased the nitrous oxide (N2O) emissions by 47 and 48% relative to CF under S1 and S2, respectively. The global warming potential (GWP, CH4 + N2O) and yield-scaled GWP were still substantially lower by 62 and 59%, respectively, in AWD than in CF under S2, but the reduction was not realized under S1 due to the relatively smaller CH4 reduction and increased N2O emission. The results confirm that pre-season aerobic stubble decomposition and earlier implementation of AWD enhanced AWD’s mitigation potential in reducing substantially the CH4 emission from the tropical rice double-cropping system.