Annual CH4 Emissions Research Articles

Paddy–Upland Rotation Improves Rice Growth and Reduces Greenhouse Gas Emissions in Winter Paddy Fields

From May 2019 to May 2022, a field experiment was conducted to clarify the effects of paddy–upland rotations on rice yield and greenhouse gas emissions in winter paddy fields. Four types of rotation pattern, rice–oilseed rape, rice–radish, rice–faba bean, and rice–fallow (flooded), were investigated and the N2O, CH4, and CO2 emissions in situ and rice yield were determined. The results showed that the paddy–upland rotation mode required fertilization during the winter cropping season. Compared with the rice–fallow (flooded) mode, the flux rate and annual cumulative emissions of N2O were significantly higher in the paddy–upland rotation modes. The rice–radish mode had the highest flux rate and annual cumulative emissions of N2O. When the soil in each paddy–upland rotation mode was exposed to air in winter, the soil redox potential increased and reducing substances were oxidized. Compared with the rice–fallow (flooded) mode, the flux rate and annual cumulative emissions of CH4 significantly decreased in the paddy–upland rotation modes, with the rice–radish mode producing the lowest flux rate and annual cumulative emissions of CH4. Fertilization and crop planting were conducted in winter, and the soil moisture was low. Compared with the rice–fallow (flooded) mode, the flux rate of CO2 of the paddy–upland rotation modes increased significantly. The flux rate of CO2 in the rice–oilseed rape mode was the highest. Furthermore, the N2O and CH4 emissions produced during the rice season and annually were significantly positively correlated with those in the winter season, indicating that the winter season had a significant effect on greenhouse gas emissions from winter paddy fields. Because of the significantly higher annual cumulative emissions of CH4 and the significantly lower rice yield in the rice–fallow (flooded) mode than in the paddy–upland rotation modes, this mode’s global warming potential (GWP) and greenhouse gas intensity (GHGI) during the rice season are significantly higher than those of the paddy–upland rotation modes.

Environmental drivers of seasonal and hourly fluxes of methane and carbon dioxide across a lowland stream network with mixed catchment

Streams serve as open windows for carbon emissions to the atmosphere due to the frequent supersaturation of carbon dioxide (CO2) and methane (CH4) that originates from large carbon input during runoff and associated in-stream processes. Due to the high spatial and temporal variability of the underlying environmental drivers (e.g., concentrations of dissolved CO2 and CH4, turbulence, and temperature), it has remained difficult to address the importance and upscale the emissions to annual whole-system and regional values. In this study, we measured concentrations and calculated emissions of CO2 and CH4 at diel and seasonal scales at 15 stations in a 1.4 km2 stream network that drains a mixed lowland catchment consisting of agriculture (210 km2), forest (56 km2), and lakes, ponds, and wetlands (22 km2) in the upper River Odense, Denmark to evaluate environmental drivers behind the spatiotemporal variability. We used automatically venting floating chambers to calculate hourly diffusive fluxes of CO2 and CH4 and CH4 ebullition. We found: 1) highly supersaturated CO2 and CH4 concentrations (median: 175 and 0.33 µmol L−1, respectively) and high diffusive fluxes of CO2 and CH4 (median: 3,608 and 19 µmol m−2 h−1, respectively); 2) lower daytime than nighttime diffusive emissions of CO2 in spring and summer, but no diel variability of CH4; 3) higher concentrations and emissions of CH4 at higher temperatures; and 4) higher emissions of CH4 at stations located in sub-catchments with higher agricultural coverage. Ebullition of CH4 peaked at two stations with soft organic sediment and low summer flow, and their ebullition alone constituted 30% of total annual CH4 emissions from the stream network. Mean annual CO2 emissions from the hydrological network (37.15 mol CO2 m−2 y−1) exceeded CH4 emissions 100-fold (0.43 mol CH4 m−2 y−1), and their combined warming potential was 1.83 kg CO2e m−2 y−1. Overall, agricultural sub-catchments had higher CH4 emissions from streams, while lakes and ponds likely reduced downstream CH4 and CO2 emissions. Our findings demonstrate that CO2 and CH4 emissions data at high spatial and temporal resolution are essential to frame the heterogeneous stream conditions, understand gas emissions regulation, and upscale to annual values for hydrological networks and larger regions.

Sea Ice Modulates Air–Sea Methane Flux in the Southern Ocean

AbstractThe Southern Ocean (SO) is predicted to be a weak sink for atmospheric CH4, although the magnitude is uncertain due to a lack of observations of the marginal ice zone (MIZ). Using both eddy covariance and bulk formula flux measurements from the icebreaker R/V Xuelong2, we found that the eastern SO during an austral summer was a sink for CH4. The strongest downward CH4 fluxes occurred in areas of low sea ice concentration (10%–40%), where sea‐ice melting resulted in low temperature and salinity, increasing CH4 solubility. The CH4 fluxes are weak in regions of high sea ice concentration (>50%) due to the blocking effect of sea ice. We estimate that the uptake of CH4 during one summer month in the study region offsets 1.2%–2.6% of annual global oceanic CH4 emissions. Suggesting that the Antarctic MIZ is more important in the global CH4 budget than previously thought.

Methane emissions from the riverine sandy wetlands on the Mongolia Plateau.

Methane (CH4) processes and fluxes have been widely investigated in low-latitude tropical wetlands and high-latitude boreal peatlands. In the mid-latitude Mongolia Plateau, however, CH4 processes and fluxes have been less studied, particularly in riverine wetlands. In this study, in situ experiments were conducted in the riverine sandy wetlands of the Mongolia Plateau to gain a better understanding of CH4 emissions and their influencing mechanisms. Annual CH4 emissions were observed at 8.7mgm-2h-1 from the flowing water wetlands during November 2019 - October 2021, approximately 80% and 20% of which were emitted during the growing and non-growing seasons, respectively. In particular, CH4 emissions during the thawing period contributed < 5% to the annual total, contrary to the traditional idea that thawing plays an important role in annual CH4 emissions in boreal peatlands. CH4 emissions were significantly higher in the wetlands dominated by plant species than in that dominated by water body during the growing seasons; therefore, plant-mediated CH4 transport was explained as a favorable pathway for CH4 emissions from sandy soils to the atmosphere. Gene sequencing revealed differences in the phylogenies and taxonomies of methanogenic archaea and methanotrophs between the flowing and static water wetlands, suggesting that flowing water should bring oxygen and nutrients to microbial habitats and potentially affect the production, oxidation, and diffusion of CH4 in sandy wetlands.

Dissolved Nitrous Oxide and Methane in the Taiwan Strait: Distribution, Seasonal Variation, and Emission

AbstractThe global ocean plays an important role in the overall budgets of nitrous oxide (N2O) and methane (CH4), especially in continental estuaries and shelf areas. Four cruises were conducted between 2021 and 2022, covering the spring, summer, and fall seasons, to study the spatial and seasonal characteristics of N2O and CH4 distributions and emissions in the Taiwan Strait (TWS). The surface N2O and CH4 concentrations gradually decreased from the coast to the open sea, with maximum values (14.3 and 15.6 nmol L−1) occurring near the Jiulong and Minjiang estuaries, respectively. The mean surface N2O concentration (8.2 nmol L−1) was highest in the spring and approximately the same in the summer as in the fall. The mean surface concentrations of CH4 (8.8 nmol L−1) were greater in summer than in spring and fall, probably because of the high freshwater input in summer. Except for several stations in fall, surface waters were oversaturated with N2O and CH4 relative to the atmosphere in other seasons, and the TWS was a net source of atmospheric N2O and CH4 in the spring, summer, and fall. In situ production is the main source of N2O and CH4 in the TWS, with nitrification being the dominant mechanism of N2O production in the TWS. In contrast, physical influences (riverine inputs and water mass mixing) reshape the distributions of N2O and CH4. The annual emissions of N2O and CH4 from the TWS were estimated to be 0.9 × 10−3 ± 2.9 × 10−3 Tg yr−1 and 1.6 × 10−3 ± 3.0 × 10−3 Tg yr−1, respectively. Taken together, the TWS accounts for 0.025% of the surface area of the world's oceans and 0.022% ± 0.07% and 0.017% ± 0.033% of global oceanic N2O and CH4 emissions, respectively.

Quantifying Global Wetland Methane Emissions With In Situ Methane Flux Data and Machine Learning Approaches.

Wetland methane (CH4) emissions have a significant impact on the global climate system. However, the current estimation of wetland CH4 emissions at the global scale still has large uncertainties. Here we developed six distinct bottom-up machine learning (ML) models using in situ CH4 fluxes from both chamber measurements and the Fluxnet-CH4 network. To reduce uncertainties, we adopted a multi-model ensemble (MME) approach to estimate CH4 emissions. Precipitation, air temperature, soil properties, wetland types, and climate types are considered in developing the models. The MME is then extrapolated to the global scale to estimate CH4 emissions from 1979 to 2099. We found that the annual wetland CH4 emissions are 146.6±12.2TgCH4yr-1 (1Tg=1012g) from 1979 to 2022. Future emissions will reach 165.8±11.6, 185.6±15.0, and 193.6±17.2TgCH4yr-1 in the last two decades of the 21st century under SSP126, SSP370, and SSP585 scenarios, respectively. Northern Europe and near-equatorial areas are the current emission hotspots. To further constrain the quantification uncertainty, research priorities should be directed to comprehensive CH4 measurements and better characterization of spatial dynamics of wetland areas. Our data-driven ML-based global wetland CH4 emission products for both the contemporary and the 21st century shall facilitate future global CH4 cycle studies.

A Lake Biogeochemistry Model for Global Methane Emissions: Model Development, Site‐Level Validation, and Global Applicability

AbstractLakes are important sentinels of climate change and may contribute over 30% of natural methane (CH4) emissions; however, no earth system model (ESM) has represented lake CH4 dynamics. To fill this gap, we refined a process‐based lake biogeochemical model to simulate global lake CH4 emissions, including representation of lake bathymetry, oxic methane production (OMP), the effect of water level on ebullition, new non‐linear CH4 oxidation kinetics, and the coupling of sediment carbon pools with in‐lake primary production and terrigenous carbon loadings. We compiled a lake CH4 data set for model validation. The model shows promising performance in capturing the seasonal and inter‐annual variabilities of CH4 emissions at 10 representative lakes for different lake types and the variations in mean annual CH4 emissions among 106 lakes across the globe. The model reproduces the variations of the observed surface CH4 diffusion and ebullition along the gradients of lake latitude, depth, and surface area. The results suggest that OMP could play an important role in surface CH4 diffusion, and its relative importance is higher in less productive and/or deeper lakes. The model performance is improved for capturing CH4 outgassing events in non‐floodplain lakes and the seasonal variability of CH4 ebullition in floodplain lakes by representing the effect of water level on ebullition. The model can be integrated into ESMs to constrain global lake CH4 emissions and climate‐CH4 feedback.

Tree stem-atmosphere greenhouse gas fluxes in a boreal riparian forest

Tree stems exchange greenhouse gases with the atmosphere but the magnitude, variability and drivers of these fluxes remain poorly understood. Here, we report stem fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in a boreal riparian forest, and investigate their spatiotemporal variability and ecosystem level importance. For two years, we measured CO2 and CH4 fluxes on a monthly basis in 14 spruces (Picea abies) and 14 birches (Betula pendula) growing near a headwater stream affected by historic ditching. We also measured N2O fluxes on three occasions. All tree stems were net emitters of CO2 and CH4, while N2O fluxes were around zero. CO2 fluxes correlated strongly with air temperature and peaked in summer. CH4 fluxes correlated modestly with air temperature and solar radiation and peaked in late winter and summer. Trees with larger stem diameter emitted more CO2 and less CH4 and trees closer to the stream emitted more CO2 and CH4. The CO2 and CH4 fluxes did not differ between spruce and birch, but correlations of CO2 fluxes with stem diameter and distance to stream differed between the tree species. The absence of vertical trends in CO2 and CH4 fluxes along the stems and their low correlation with groundwater levels and soil CO2 and CH4 partial pressures suggest tree internal production as the primary source of stem emissions. At the ecosystem level, the stem CO2, CH4 and N2O emissions represented 52 ± 16 % of the forest floor CO2 emissions and 3 ± 1 % and 11 ± 40 % of the forest floor CH4 and N2O uptake, respectively, during the snow-free period (median ± SE). The six month snow-cover period contributed 11 ± 45 % and 40 ± 29 % to annual stem CO2 and CH4 emissions, respectively. Overall, the stem gas fluxes were more typical for upland rather than wetland ecosystems likely due to historic ditching and subsequent groundwater level decrease.

Global Wetland Methane Emissions From 2001 to 2020: Magnitude, Dynamics and Controls

AbstractThe large uncertainties in estimating CH4 emissions from wetland ecosystems, the leading natural source to the atmosphere, substantially hinder the quantification of the global CH4 budget. This study used the IBIS‐CH4 (Integrated BIosphere Simulator‐Methane) model, a process‐based model integrating microbial mechanisms associated with CH4 production and oxidation processes, to simulate global wetland CH4 emissions from 2001 to 2020. Initially, we employed the IBIS‐CH4 model to evaluate its performance across 26 diverse wetland sites worldwide. The results showed that the magnitude and seasonality of observed CH4 fluxes over various wetland sites were well reproduced. We then used this model to estimate the annual global wetland CH4 emissions from 2001 to 2020, averaging 152.67 Tg CH4 yr−1, with a range of 135.72–167.57 Tg CH4 yr−1. The estimated global wetland CH4 emissions are generally in agreement with the current bottom‐up estimates (117–256 Tg CH4 yr−1) and closely overlap with independent top‐down estimates (139–183 Tg CH4 yr−1). During 2001–2020, the estimated global wetland CH4 emissions initially showed an increasing trend, followed by a decline. The peak of CH4 emissions reached in 2010, coinciding with the peak of wetland area. The majority of global wetland CH4 emissions were concentrated in tropical regions, which exhibited a clear seasonality and had a peak in July. The impact of meteorological factors on wetland CH4 emissions was greater than that of leaf area index, indicating the importance of soil hydrothermal conditions on wetland CH4 emissions.

Temporal Variations in Methane Emissions from a Restored Mangrove Ecosystem in Southern China

The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide has been increasingly investigated in recent years. While studies have shown that mangroves are weak sources of methane (CH4) emissions, measurements of CH4 fluxes from these ecosystems remain scarce. In this study, we examined the temporal variation and biophysical drivers of ecosystem-scale CH4 fluxes in China’s northernmost mangrove ecosystem based on eddy covariance measurements obtained over a 3-year period. In this mangrove, the annual CH4 emissions ranged from 6.15 to 9.07 g C m−2 year−1. The daily CH4 flux reached a peak of over 0.07 g C m−2 day−1 during the summer, while the winter CH4 flux was negligible. Latent heat, soil temperature, photosynthetically active radiation, and tide water level were the primary factors controlling CH4 emissions. This study not only elucidates the mechanisms influencing CH4 emissions from mangroves, strengthening the understanding of these processes but also provides a valuable benchmark dataset to validate the model-derived carbon budget estimates for these ecosystems.

Identifying a sustainable rice-based cropping system via on-farm evaluation of grain yield, carbon sequestration capacity and carbon footprints in Central China

ContextRice-based cropping system is a major anthropogenic source of direct greenhouse gases (GHG) emissions, agricultural inputs also produces numerous indirect GHG emissions and environmental problems. Identification of rice cropping systems with lower GHG emissions and higher grain yields is of great significance to ensure food security while minimizing agricultural carbon footprint (CF). ObjectiveThis study aimed to identify the optimal rice-based cropping system with lower greenhouse effects and comparable annual yield in central China. MethodsUsed life cycle assessment, a two-year field experiment was performed to evaluate the direct and indirect GHG emissions, CF, and carbon sequestration capacity in the six rice-based cropping systems widely used in central China, which consisted of fallow-early rice-late rice, rapeseed-early rice-late rice, fallow-ratoon rice, rapeseed-ratoon rice (RRaR), fallow-middle rice, and rapeseed-middle rice. ResultsThe results showed that compared with the three systems with fallow season, the three systems with rapeseed had lower annual CH4 emissions. The two systems with ratoon rice had lower annual indirect and direct GHG emissions than the two systems with double rice. The three systems with rapeseed had higher annual biomass, grain yields, and fixed carbon in biomass and significantly lower CF than the three systems with fallow season, and RRaR had the highest value of fixed carbon in biomass. The systems with ratoon rice had lower average CF than those systems with double rice. CH4 emissions from paddy fields were the primary source of total annual GHG and the main component of CF. Compared with the three systems with fallow season, the three systems with rapeseed had significantly higher annual carbon sequestration capacity based on net ecosystem production (NEP). Ratoon rice systems had higher average NEP than double- and middle-rice systems. RRaR had the lowest CF per unit yield and highest NEP among all the six systems. ConclusionsThe results indicated that appropriate rice-based cropping systems may alleviate the greenhouse effect via reducing GHG emissions and enhancing paddy NEP, RRaR could achieve relatively higher annual grain yield and carbon sequestration capacity as well as lower CF. SignificanceThis study highlight conversion of double rice and middle rice systems to RRaR may help improve grain yield and mitigate greenhouse effect. The findings may provide a theoretical basis for selection of sustainable development of rice based cropping systems in central China.

To Harvest or not to Harvest: Management Intensity did not Affect Greenhouse Gas Balances of Phalaris Arundinacea Paludiculture

The cultivation of flooding-tolerant grasses on wet or rewetted peatlands is a priority in climate change mitigation, balancing the trade-off between atmospheric decarbonisation and biomass production. However, effects of management intensities on greenhouse gas (GHG) emissions and the global warming potential (GWP) are widely unknown. This study assessed whether intensities of two and five annual harvest occurrences at fertilisation rates of 200 kg nitrogen ha− 1 yr− 1 affects GHG exchange dynamics compared to a ‘nature scenario’ with neither harvest nor fertilisation. Fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), using opaque and transparent chambers, were measured on a wet fen peatland with a mean water table depth of -10 cm below soil surface. Overall, no treatment effect was found on biomass yields and GHG emissions. Annual cumulative CH4 emissions were low, ranging between 0.3 and 0.5 t CO2-C eq ha− 1 yr− 1. Contrary to this, emissions of N2O were high, ranging between 1.1 and 1.5 t CO2-C eq ha− 1 yr− 1. For magnitudes of CH4 and N2O, soil moisture conditions and electrical peat properties were critical proxies. Atmospheric uptake of CO2 by net ecosystem exchange was higher for the treatments with management. However, this benefit was offset by the export of carbon in biomass compared to the treatment without management. In conclusion, the results highlighted a near-equal GWP in the range of 10.5–11.5 t CO2-C eq t ha− 1 yr− 1 for all treatments irrespectively of management. In a climate context, a restoration scenario but also intensive paludiculture practices were equal land-use options.

Changing climatic controls on the greenhouse gas balance of thermokarst bogs during succession after permafrost thaw.

Permafrost thaw in northern peatlands causes collapse of permafrost peat plateaus and thermokarst bog development, with potential impacts on atmospheric greenhouse gas exchange. Here, we measured methane and carbon dioxide fluxes over 3 years (including winters) using static chambers along two permafrost thaw transects in northwestern Canada, spanning young (~30 years since thaw), intermediate and mature thermokarst bogs (~200 years since thaw). Young bogs were wetter, warmer and had more hydrophilic vegetation than mature bogs. Methane emissions increased with wetness and soil temperature (40 cm depth) and modelled annual estimates were greatest in the young bog during the warmest year and lowest in the mature bog during the coolest year (21 and 7 g C-CH4 m-2 year-1, respectively). The dominant control on net ecosystem exchange (NEE) in the mature bog (between +20 and -54 g C-CO2 m-2 year-1) was soil temperature (5 cm), causing net CO2 loss due to higher ecosystem respiration (ER) in warmer years. In contrast, wetness controlled NEE in the young and intermediate bogs (between +55 and -95 g C-CO2 m-2 year-1), where years with periodic inundation at the beginning of the growing season caused greater reduction in gross primary productivity than in ER leading to CO2 loss. Winter fluxes (November-April) represented 16% of annual ER and 38% of annual CH4 emissions. Our study found NEE of thermokarst bogs to be close to neutral and rules out large CO2 losses under current conditions. However, high CH4 emissions after thaw caused a positive net radiative forcing effect. While wet conditions favouring high CH4 emissions only persist for the initial young bog period, we showed that continued climate warming with increased ER, and thus, CO2 losses from the mature bog can cause net positive radiative forcing which would last for centuries after permafrost thaw.

Three years of CO2, CH4 and N2O fluxes from different sheepfolds in a semiarid steppe region, China

To better assess greenhouse gas (GHG) emissions from livestock folds in semi-arid steppe zones and reduce uncertainties in regional and national GHG emission inventories, we measured the fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from sheepfolds under contrasting management regimes (i.e., summer sheepfolds under continuous and rotational grazing strategies and the winter sheepfold) for 3 consecutive years. Our results showed that these GHG fluxes had high intra-annual and interannual variations, emphasizing the importance of multi-year measurement for achieving temporally representative annual budgets. Sheep presence and temperature appeared to be the key factors driving CH4, CO2 and N2O fluxes from sheepfolds, e.g., higher GHG emissions usually occurred in seasons with sheep presence. However, the sheepfold type exerted a distinct influence on the temperature sensitivity of GHG fluxes, i.e., the Q10 values for GHG fluxes were generally higher in summer sheepfolds than in winter sheepfold. The annual CH4, CO2 and N2O emissions for the 3 sheepfolds were estimated to be 1.5–16.5 kg C ha−1 yr−1 (or 1.9–2.6 g C yr−1sheep−1), 8.6–16.0 t C ha−1 yr−1 (or 5.1–6.6 kg C yr−1sheep−1) and 28.3–41.9 kg N ha−1 yr−1 (or 19.0–26.8 g N yr−1sheep−1), respectively. Averaging across the 3 years, the annual net GHG emissions (CH4 + CO2 + N2O) for all sheepfolds ranged from 47 to 71 t CO2-eq ha−1 yr−1 (or 27–36 kg CO2-eq yr−1 sheep−1), of which CO2 and N2O emissions contributed the most; moreover, the annual net GHG emissions had no significant differences between sheepfold types or grazing strategies. Given that local steppe soils have a lower magnitude of soil respiration (CO2) and N2O emissions and are also net sink for atmospheric CH4, the sheepfold sites in this region are undoubtedly one of the significant hotspots for GHG emissions and could be key areas to focus mitigation action.

Quantification of Methane Emissions from Cold Heavy Oil Production with Sand Extraction in Alberta and Saskatchewan, Canada.

Cold heavy oil production with sand (CHOPS) is an extraction process for heavy oil in Canada, with the potential to lead to higher CH4 venting than conventional oil sites, that have not been adequately characterized. In order to quantify CH4 emissions from CHOPS activities, a focused aerial measurement campaign was conducted in the Canadian provinces of Alberta and Saskatchewan in June 2018. Total CH4 emissions from each of 10 clusters of CHOPS wells (containing 22-167 well sites per cluster) were derived using a mass balance computation algorithm that uses in situ wind data measurement on board aircraft. Results show that there is no statistically significant difference in CH4 emissions from CHOPS wells between the two provinces. Cluster-aggregated emission factors (EF) were determined using correspondingly aggregated production volumes. The average CH4 EF was 70.4 ± 36.9 kg/m3 produced oil for the Alberta wells and 55.1 ± 13.7 kg/m3 produced oil for the Saskatchewan wells. Using these EF and heavy oil production volumes reported to provincial regulators, the annual CH4 emissions from CHOPS were estimated to be 121% larger than CHOPS emissions extracted from Canada's National Inventory Report (NIR) for Saskatchewan. The EF were found to be positively correlated with the percentage of nonpiped production volumes in each cluster, indicating higher emissions for nonpiped wells while suggesting an avenue for methane emission reductions. A comparison with recent measurements indicates relatively limited effectiveness of regulations for Saskatchewan compared to those in Alberta. The results of this study indicate the substantial contribution of CHOPS operations to the underreporting observed in the NIR and provide measurement-based EF that can be used to develop improved emissions inventories for this sector and mitigate CH4 emissions from CHOPS operations.

Effects of Ratoon Rice Cropping Patterns on Greenhouse Gas Emissions and Yield in Double-Season Rice Regions.

The ratoon rice cropping pattern is an alternative to the double-season rice cropping pattern in central China due to its comparable annual yield and relatively lower cost and labor requirements. However, the impact of the ratoon rice cropping pattern on greenhouse gas (GHG) emissions and yields in the double-season rice region requires further investigation. Here, we compared two cropping patterns, fallow-double season rice (DR) and fallow-ratoon rice (RR), by using two early-season rice varieties (ZJZ17, LY287) and two late-season rice varieties (WY103, TY390) for DR, and two ratoon rice varieties (YLY911, LY6326) for RR. The six varieties constituted four treatments, including DR1 (ZJZ17 + WY103), DR2 (LY287 + TY390), RR1 (YLY911), and RR2 (LY6326). The experimental results showed that conversion from DR to RR cropping pattern significantly altered the GHG emissions, global warming potential (GWP), and GWP per unit yield (yield-scaled GWP). Compared with DR, the RR cropping pattern significantly increased cumulative methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions by 65.73%, 30.56%, and 47.13%, respectively, in the first cropping season. Conversely, in the second cropping season, the RR cropping pattern effectively reduced cumulative CH4, N2O, and CO2 emissions by 79.86%, 27.18%, and 30.31%, respectively. RR led to significantly lower annual cumulative CH4 emissions, but no significant difference in cumulative annual N2O and CO2 emissions compared with DR. In total, the RR cropping pattern reduced the annual GWP by 7.38% and the annual yield-scaled GWP by 2.48% when compared to the DR cropping pattern. Rice variety also showed certain effects on the yields and GHG emissions in different RR cropping patterns. Compared with RR1, RR2 significantly increased annual yield while decreasing annual GWP and annual yield-scaled GWP. In conclusion, the LY6326 RR cropping pattern may be a highly promising strategy to simultaneously reduce GWP and maintain high grain yield in double-season rice regions in central China.

Life Cycle Greenhouse Gas Emissions in Maize No-Till Agroecosystems in Southern Brazil Based on a Long-Term Experiment

Life Cycle Greenhouse Gas Emissions in Maize No-Till Agroecosystems in Southern Brazil Based on a Long-Term Experiment

Effects of Controlled-release Blended Fertilizer on Crop Yield and Greenhouse Gas Emissions in Wheat-maize Rotation System

The increasing use of nitrogen fertilizers exerts extreme pressure on the environment (e.g., greenhouse gas emissions, GHGs) for winter wheat-summer maize rotation systems in the North China Plain. The application of controlled-release fertilizers is considered as an effective measure to improve crop yield and nitrogen fertilizer utilization efficiency. To explore the impact of one-time fertilization of controlled-release blended fertilizer on crop yield and GHGs of a wheat-maize rotation system, field experiments were carried out in Dezhou Modern Agricultural Science and Technology Park from 2020 to 2022. Five treatments were established for both winter wheat and summer maize, including no nitrogen control (CK), farmers' conventional nitrogen application (FFP), optimized nitrogen application (OPT), CRU1 (the blending ratio of coated urea and traditional urea on winter wheat and summer maize was 5:5 and 3:7, respectively), and CRU2 (the blending ratio of coated urea and traditional urea on winter wheat and summer maize was 7:3 and 5:5, respectively). The differences in yield, nitrogen fertilizer utilization efficiency, fertilization economic benefits, and GHGs among different treatments were compared and analyzed. The results showed that nitrogen application significantly increased the single season and annual crop yields of the wheat-maize rotation system (P &lt; 0.05). Compared with those of FFP, the CRU1 and CRU2 treatments increased the yields of summer maize by 0.4% to 5.6%, winter wheat by -5.4% to 4.1%, and annual yields by -1.1% to 3.9% (P &gt; 0.05). N recovery efficiency (NRE), N agronomic efficiency (NAE), and N partial factor productivity (NPFP) were increased by -8.6%-43.4%, 2.05-6.24 kg·kg-1, and 4.24-10.13 kg·kg-1, respectively. Annual net income increased by 0.2% to 6.3%. Nitrogen application significantly increased the annual emissions of soil N2O and CO2 in the rotation system (P &lt; 0.05) but had no effect on the annual emissions of CH4 (except for in the FFP treatment in the first year). The annual total N2O emissions under the CRU1 and CRU2 treatments were significantly reduced by 23.4% to 30.2% compared to those under the FFP treatment (P &lt; 0.05). Additionally, nitrogen application significantly increased the annual global warming potential (GWP) of the rotation system (P &lt; 0.05), but the intensity of greenhouse gas emissions was reduced due to the increase in crop yields. Compared with that under FFP, the annual GWP under the CRU1 and CRU2 treatments decreased by 9.6% to 11.5% (P &lt; 0.05), and the annual GHGs decreased by 11.2% to 13.8% (P &gt; 0.05). In summary, the one-time application of controlled-release blended fertilizer had a positive role in improving crop yield and economic benefits, reducing nitrogen fertilizer input and labor costs, and GHGs, which is an effective nitrogen fertilizer management measure to promote cleaner production of food crops in the North China Plain.

Methane emissions from residential natural gas meter set assemblies

Residential natural gas meter set assemblies (MSAs) emit methane (CH4), but reported emissions factors vary. To test existing emissions factors, we quantified CH4 emissions from 37 residential MSAs in Calgary, Alberta, Canada. A notable difference with previous studies is the targeted measurement of regulator vents in this study, which were measured with a static chamber, while fugitives were measured with a modified hi-flow sampler. Emissions were dominated by pressure regulator vents (emissions factor = 1.18 g CH4/h/MSA), but 7 fugitives were found (emissions factor = 0.018 g CH4/h/MSA). Six regulator vents were emitting at notably higher rates (≥ 1.79 g CH4/h/MSA). The total empirical emissions factor was 1.20 g CH4/h/MSA (95 % CI, 1.03 to 1.37 g/h/MSA). This is ∼7 times higher than the emissions factor for residential MSAs used in the U.S. EPA's Greenhouse Gas Inventory, which may not include emissions from regulator vents. Upscaling to annual CH4 emissions in Calgary indicates 3234.6 t CH4/yr (95 % CI, 2776.4 t to 3692.9 t CH4/yr) could be emitted from MSAs. This is equivalent to 4.1 % (95 % CI, 3.5 % to 4.7 %) of total city-level CH4 emissions as estimated with satellite data. Results suggest residential MSA emissions may be under-estimated and further study isolating root causes of regulator vent emissions is required to guide mitigation and improve emissions modeling.

Study of spatiotemporal variation and annual emission of CH4 in Shaoxing Yangtze River Delta, China, Using a portable CH4 detector on the UAV

Methane (CH4) is the second greenhouse gas and has a profound impact on global climate change due to its high global warming potential and concentration. By 2022, the CH4 concentration was approximately 1.9 ppm, which was 264% of the pre-industrial level. The spatiotemporal distribution of CH4 was investigated by a portable CH4 detector on an unmanned aerial vehicle and electric bicycles in Shaoxing, a city situated in the Yangtze River Delta, China. The vertical distribution revealed CH4 concentration generally decreased slowly with height. However, the inversion condition and low atmospheric boundary layer height (ABLH) leaded to the enhancement of CH4 with height. The highest CH4 concentration (2.2 ± 0.1 ppm, n = 1428) was observed in winter and the lowest (2.0 ± 0.2 ppm, n = 1530) in spring. Regarding the daily variation, CH4 concentration peaked at 5:00 local time (LT) and reached its lowest level at 14:00 LT, which was attributed to the daily variation of ABLH, lowest in the early morning and highest in the noon. In urban areas, CH4 concentrations showed higher levels near restaurants, natural gas stations and sewerage well, with a maximum value of 13.1 ppm, which was caused by CH4 emission and natural gas leakage from these places. The annual CH4 emission in Shaoxing were estimated to be approximately 69 ton/(km2·year) by the mass balance approach. Compared with other cities in the world, the CH4 emission is in higher level which imply some control measures should be conducted to reduce CH4 emission in Shaoxing.