Ground-Based Mobile Measurements to Track Urban Methane Emissions from Natural Gas in 12 Cities across Eight Countries.

To mitigate methane emission from urban natural gas distribution systems, it is crucial to understand local leak rates and occurrence rates. To explore urban methane emissions in cities outside the U.S., where significant emissions were found previously, mobile measurements were performed in 12 cities across eight countries. The surveyed cities range from medium size, like Groningen, NL, to large size, like Toronto, CA, and London, UK. Furthermore, this survey spanned across European regions from Barcelona, ES, to Bucharest, RO. The joint analysis of all data allows us to focus on general emission behavior for cities with different infrastructure and environmental conditions. We find that all cities have a spectrum of small, medium, and large methane sources in their domain. The emission rates found follow a heavy-tailed distribution, and the top 10% of emitters account for 60-80% of total emissions, which implies that strategic repair planning could help reduce emissions quickly. Furthermore, we compare our findings with inventory estimates for urban natural gas-related methane emissions from this sector in Europe. While cities with larger reported emissions were found to generally also have larger observed emissions, we find clear discrepancies between observation-based and inventory-based emission estimates for our 12 cities.

Potential to reduce methane production of using cultivated seaweeds supplementation to reshape the community structure of rumen microorganisms.

Methane is a short-lived greenhouse gas but has a far greater warming effect than carbon dioxide. At the same time, the livestock sector serves as a large contributor to global emissions of anthropogenic methane. Herein, this work aimed to use cultivated seaweed supplementation to reduce methane emissions and investigate the potential influencing mechanism. To evaluate the feasibility, two cultivated seaweeds, Laminaria japonica Aresch, and Porphyra tenera, along with the enzymatic hydrolysates derived from L. japonica, underwent in vitro trials, and they were both added into corn silage feed (CSF) with different concentrations (1%, 5%, and 10% of CSF) for methane reduction evaluation. The results indicated that >75% and 50% reductions in methane production were observed for the seaweeds and seaweed enzymatic hydrolysates in 9- and 30-day, respectively. Combined high-throughput sequencing and multivariate analysis revealed that supplementation with seaweed and seaweed enzymatic hydrolysates had a notable impact on the prokaryotic community structure. Mantel tests further revealed that significant correlations between the prokaryotic community and methane accumulation (P < 0.05), implying the prokaryotic community plays a role in reducing methane emissions within the rumen. Correspondingly, the networks within the prokaryotic community unveiled the crucial role of propionate/butyrate-producing bacteria in regulating methane emissions through microbial interactions. The predicted function of the prokaryotic community exhibited a significant reduction in the presence of the narB gene in seaweed-supplemented treatments. This reduction may facilitate an increased rate of electron flow toward the nitrate reduction pathway while decreasing the conversion of H2 to methane. These results indicated the supplementation of cultivated seaweeds and the enzymatic hydrolysates has the potential to reshape the community structure of rumen microbial communities, and this alteration appears to be a key factor contributing to their methane production-reduction capability.

Bio-manure substitution declines soil N2O and NO emissions and improves nitrogen use efficiency and vegetable quality index.

Substituting mineral fertilizer with manure or a combination of organic amendments plus beneficial soil microorganisms (bio-manure) in agriculture is a standard practice to mitigate N2O and NO emissions while enhancing crop performance and nitrogen use efficiency (NUE). Here, we conducted a greenhouse trial for three consecutive vegetable growth seasons for Spinach, Coriander herb, and Baby bok choy to reveal the response of N2O and NO emissions, NUE, and vegetable quality index (VQI) to fertilization strategies. Strategies included solely chemical nitrogen fertilizer (CN), 20 (M1N4) and 50% (M1N1) substitution with manure, 20 (BM1N4) and 50% (BM1N1) substitution with bio-manure, and no fertilization as a control and were organized in a completely randomized design (n = 3). Manure decreased N2O emissions by 24-45% and bio-manure by 44-53% compared to CN. Manure reduced NO emissions by 28-41% and bio-manure by 55-63%. Bio-manure increased NUE by 0.04-31% and yields by 0.05-61% while improving VQI, attributed to yield growth and reduced vegetable NO3- contents. Improvement of root growth was the main factor that explained the rise of NUE; NUE declined with the increase of N2O emissions, showing the loss of vegetable performance under conditions when denitrification processes prevailed. Under the BM1N1, the highest VQI and the lowest yield-scaled N-oxide emissions were observed, suggesting that substitution with bio-manure can improve vegetable quality and mitigate N-oxide emissions. These findings indicate that substituting 50% of mineral fertilizer with bio-manure can effectively improve NUE and VQI and mitigate N-oxides in intensive vegetable production.

Carbon footprint of farming practices in farmland ecosystems on the North and Northeast China plains.

Fast development of farming practices in China is projected to result in additional carbon emissions and thus affect farmland ecosystems' environmental performance. Based on 454 farm surveys on the North and Northeast China Plain, the carbon footprint (CF) of two farmland ecosystems (irrigated system for wheat and maize on the North China Plain and rainfed system for maize on the Northeast Plain) were assessed and emission reduction pathways explored by quantifying greenhouse gas emissions of agricultural inputs and farm practices during the entire crop growing seasons with an agricultural footprint model. The results demonstrated that the GHG emissions from wheat and maize rotation in the irrigated system were 7.63 t CO2 eq ha-1 and 3.17 t CO2 eq ha-1 for single season maize in the rainfed system. While energy consumption accounted for 12.5%-21.3% of the carbon footprint in both systems, the group assessment found that the largest difference in GHG emissions between the high and low emission groups came from mechanical energy consumption. Approximately 50.6% and 39.2% of the mechanical carbon footprint of wheat and maize, respectively, were caused by irrigation practices in the irrigated system. Regarding the rainfed system, where 46.6% of mechanical carbon emissions were generated by maize tillage operations. In addition, scenario analysis indicated that the mechanical carbon footprint could be reduced to 56 kg CO2 eq t-1 for NCP-wheat and 26 kg CO2 eq t-1 for NCP-maize, respectively, by optimizing yields and irrigation practices in irrigated systems and that the mechanical carbon footprint of NEP-maize could be reduced to 25 kg CO2 eq t-1 by optimizing yields and tillage practices in rainfed systems. Therefore, improvement in mechanization in irrigation and tillage practices can contribute to reduce GHG emissions in China. Water-saving irrigation technology is recommended in irrigated area and conservation tillage is recommended in rainfed agricultural area to reduce carbon footprints.

Greenhouse gas mitigation potential via a large-scale compulsory circular waste management system.

Municipal solid waste (MSW) is a major anthropogenic contributor to climate change due to the substantial quantities of greenhouse gas (GHG) emitted by landfills and incineration. Circular waste management has shown promise in reducing GHG emissions; however, it is still in its early stages and requires further optimization. In this study, support vector machine models were developed to determine the compositional dynamics of MSW, which were then integrated to examine the interactions among composition, disposal routes, and GHG emissions. The results from analyzing large-scale transitions from traditional to circular waste management practices showed that GHG mitigation potential will be significantly enhanced as the coverage of circular waste management increases from 35% in 2025 to 100% in 2035 in China. However, these reductions will eventually decrease as waste quantities decline in response to population shrinkage. The results reveal both the GHG mitigation potential and limitations of the circular waste management mode, assisting policymakers and researchers in maximizing its mitigation potential.

Interpreting contemporary trends in atmospheric methane.

Atmospheric methane plays a major role in controlling climate, yet contemporary methane trends (1982-2017) have defied explanation with numerous, often conflicting, hypotheses proposed in the literature. Specifically, atmospheric observations of methane from 1982 to 2017 have exhibited periods of both increasing concentrations (from 1982 to 2000 and from 2007 to 2017) and stabilization (from 2000 to 2007). Explanations for the increases and stabilization have invoked changes in tropical wetlands, livestock, fossil fuels, biomass burning, and the methane sink. Contradictions in these hypotheses arise because our current observational network cannot unambiguously link recent methane variations to specific sources. This raises some fundamental questions: (i) What do we know about sources, sinks, and underlying processes driving observed trends in atmospheric methane? (ii) How will global methane respond to changes in anthropogenic emissions? And (iii), What future observations could help resolve changes in the methane budget? To address these questions, we discuss potential drivers of atmospheric methane abundances over the last four decades in light of various observational constraints as well as process-based knowledge. While uncertainties in the methane budget exist, they should not detract from the potential of methane emissions mitigation strategies. We show that net-zero cost emission reductions can lead to a declining atmospheric burden, but can take three decades to stabilize. Moving forward, we make recommendations for observations to better constrain contemporary trends in atmospheric methane and to provide mitigation support.

Projecting the Impact of Socioeconomic and Policy Factors on Greenhouse Gas Emissions and Carbon Sequestration in U.S. Forestry and Agriculture.

Understanding greenhouse gas mitigation potential of the U.S. agriculture and forest sectors is critical for evaluating potential pathways to limit global average temperatures from rising more than 2° C. Using the FASOMGHG model, parameterized to reflect varying conditions across shared socioeconomic pathways, we project the greenhouse gas mitigation potential from U.S. agriculture and forestry across a range of carbon price scenarios. Under a moderate price scenario ($20 per ton CO2 with a 3% annual growth rate), cumulative mitigation potential over 2015-2055 varies substantially across SSPs, from 8.3 to 17.7 GtCO2e. Carbon sequestration in forests contributes the majority, 64-71%, of total mitigation across both sectors. We show that under a high income and population growth scenario over 60% of the total projected increase in forest carbon is driven by growth in demand for forest products, while mitigation incentives result in the remainder. This research sheds light on the interactions between alternative socioeconomic narratives and mitigation policy incentives which can help prioritize outreach, investment, and targeted policies for reducing emissions from and storing more carbon in these land use systems.

The role of biochars in sustainable crop production and soil resiliency.

Biochar is a promising soil additive for use in support of sustainable crop production. However, the high level of heterogeneity in biochar properties and the variations in soil composition present significant challenges to the successful uptake of biochar technologies in diverse agricultural soils. An improved understanding of the mechanisms that contribute to biochar-soil interactions is required to address issues related to climate change and cultivation practices. This review summarizes biochar modification approaches (physical, chemical, and biochar-based organic composites) and discusses the potential role of biochar in sustainable crop production and soil resiliency, including the degradation of soil organic matter, the improvement of soil quality, and reductions in greenhouse gas emissions. Biochar design is crucial to successful soil remediation, particularly with regard to issues arising from soil structure and composition related to crop production. Given the wide variety of feedstocks for biochar production and the resultant high surface heterogeneity, greater efforts are required to optimize biochar surface functionality and porosity through appropriate modifications. The design and establishment of these approaches and methods are essential for the future utilization of biochar as an effective soil additive to promote sustainable crop production.

Greenhouse gas mitigation potential of balanced fertilization cropland under double-cropping systems: a case study in Shaanxi province, China.

Reducing agricultural greenhouse gas (GHG) emissions is attracting increasing attention. Balanced fertilization (BF) of cropland has been widely promoted and applied and has great potential to reduce GHG emissions. This study assesses GHG mitigation of BF cropland systems including winter wheat and summer maize double-cropping system (wheat-maize) and winter oilseed rape (Brassica napus) and rice double-cropping system (rape-rice) in Shaanxi province, China. We determined the boundaries, scenarios, leakage, and sources of GHG mitigation and developed a measurement system for GHG mitigation under these cropping systems for BF farmland. In the measurement system, except for the changes in nitrogen fertilizer rates, soil carbon storage, mechanical fuel consumption, and fertilizer management mode (paddy), change in crop yield was recommended as a primary source of GHG mitigation. The BF cropland areas of wheat-maize and rape-rice were 2818.89 ha and 1671.73 ha, respectively. The use of BF reduced the GHG emissions of wheat-maize by 1.15 tCO2 equivalent (CO2e) ha-1 per year and the emissions of rape-rice by 1.05 tCO2e ha-1 per year. The BF cropland produced 5007.6 tCO2e per year. Our results do not only provide a reference for the assessment of GHG mitigation on BF cropland under double-cropping systems, but also will be helpful for improving the methodology of GHG mitigation on BF cropland.

Harnessing a methane-fueled, sediment-free mixed microbial community for utilization of distributed sources of natural gas.

Harnessing the metabolic potential of uncultured microbial communities is a compelling opportunity for the biotechnology industry, an approach that would vastly expand the portfolio of usable feedstocks. Methane is particularly promising because it is abundant and energy-rich, yet the most efficient methane-activating metabolic pathways involve mixed communities of anaerobic methanotrophic archaea and sulfate reducing bacteria. These communities oxidize methane at high catabolic efficiency and produce chemically reduced by-products at a comparable rate and in near-stoichiometric proportion to methane consumption. These reduced compounds can be used for feedstock and downstream chemical production, and at the production rates observed in situ they are an appealing, cost-effective prospect. Notably, the microbial constituents responsible for this bioconversion are most prominent in select deep-sea sediments, and while they can be kept active at surface pressures, they have not yet been cultured in the lab. In an industrial capacity, deep-sea sediments could be periodically recovered and replenished, but the associated technical challenges and substantial costs make this an untenable approach for full-scale operations. In this study, we present a novel method for incorporating methanotrophic communities into bioindustrial processes through abstraction onto low mass, easily transportable carbon cloth artificial substrates. Using Gulf of Mexico methane seep sediment as inoculum, optimal physicochemical parameters were established for methane-oxidizing, sulfide-generating mesocosm incubations. Metabolic activity required >∼40% seawater salinity, peaking at 100% salinity and 35 °C. Microbial communities were successfully transferred to a carbon cloth substrate, and rates of methane-dependent sulfide production increased more than threefold per unit volume. Phylogenetic analyses indicated that carbon cloth-based communities were substantially streamlined and were dominated by Desulfotomaculum geothermicum. Fluorescence in situ hybridization microscopy with carbon cloth fibers revealed a novel spatial arrangement of anaerobic methanotrophs and sulfate reducing bacteria suggestive of an electronic coupling enabled by the artificial substrate. This system: 1) enables a more targeted manipulation of methane-activating microbial communities using a low-mass and sediment-free substrate; 2) holds promise for the simultaneous consumption of a strong greenhouse gas and the generation of usable downstream products; and 3) furthers the broader adoption of uncultured, mixed microbial communities for biotechnological use.