Reduce CH4 Emissions Research Articles

A meta-analysis of ecological functions and economic benefits of co-culture models in paddy fields

The co-culture of rice and poultry/aquatic animals has become a popular strategy to ensure the critical ecological functions and economic benefits of this ecosystem in recent years. Yet, quantitative synthetic effects of co-culture models on ecological functions and economic benefits in paddy fields are poorly understood. This study conducted a meta-analysis of 4707 observations from 224 published papers on the outcomes of co-culture models in paddy fields. On aggregate, co-culture models significantly reduced CH4 emissions by 14.8 % as compared with rice monoculture, but did not affect rice yields, N2O emissions, and greenhouse gas intensity (GHGI). However, significant differences in rice yields, CH4 emissions, GHGI, and economic benefits were observed among various co-culture models and rice-growing regions. Particularly, the co-culture models in East Asia significantly increased rice yields (+2.2 %), reduced CH4 emissions (–22.1 %), and GHGI (–9.4 %). Importantly, co-culture models improved rice grain quality. Furthermore, co-culture models increased soil fertility (7.8–16.2 %), nutrients content in paddy water (26.2–87.0 %), and net ecological and economic benefits (31.7–71.1 %), while decreasing diseases, pests, and weeds (37.0–84.6 %) in paddy fields. Additionally, we suggest that the production of poultry or aquatic animals that alters input and output would increase net income, and it is necessary to develop co-culture models in paddy fields according to regional differences in the agricultural environment. Therefore, our study provides a reference for maximizing ecological and economic benefits of suitable co-culture models in rice-planted areas.

Modeling CH4 and N2O emissions for continuous and noncontinuous flooding rice systems

CONTEXTNoncontinuous flooding irrigation is an important means of reducing water use, mitigating greenhouse gas emission, and maintaining crop yield in rice production systems. Quantifying the CH4 and N2O emissions in continuous and noncontinuous flooding irrigation systems is crucial to the exploration of sustainable water management practices in rice systems. OBJECTIVEIn this study, a simple “anaerobic ball” method was incorporated into the WHCNS (soil Water Heat Carbon Nitrogen Simulator) model to simulate and evaluate the CH4 and N2O emissions under continuous and noncontinuous flooding irrigation conditions. METHODSThis model considers the processes of dissolved organic carbon (DOC) release and transport in the soil profile, CH4 production, oxidation, and transport, and N2O production, reduction, and transport. Three years of field experiment data, including soil and environment variables (e.g., ponding water depth, soil water content, and soil temperature) and daily CH4 and N2O emission fluxes under different irrigation practices were collected to test the improved WHCNS model. RESULTS AND CONCLUSIONSResults show that the model performs well in simulating soil and environment variables, with performance indices IA, NSE, and Pearson's r varying from 0.772 to 0.966, 0.530–0.853, and 0.780–0.934, respectively. Furthermore, the daily dynamics of CH4 and N2O emissions were captured under different rice irrigation systems, with average IA, NSE, and Pearson's r values of 0.857, 0.476, and 0.763, respectively. The observed and simulated results indicate that noncontinuous irrigation reduces CH4 emission but increases N2O emission. Compared with continuous flooding irrigation, noncontinuous flooding irrigation significantly decreased the accumulated CH4 emission by 82.1%, but significantly increased the N2O emission by 129.4%, resulting in the global warming potential reduction of 23.5%. SIGNIFICANCEThe improved model reflects the effects of continuous and noncontinuous flooding practices on CH4 and N2O emissions, and exhibits great potential for the development of sustainable water management for rice production systems.

Land use intensification significantly reduced CH4 emissions while increasing N2O emissions: Taihu Lake region, China

Land use intensification is becoming increasingly common in China’s Taihu Lake region because of economic interests. Frequent intensification is the conversion from natural wetlands (NW) to conventional rice-wheat rotation fields (RW), and from conventional RW to greenhouse vegetable fields (GH). However, the impact of land use intensification on greenhouse gas emissions in this area is still unknown. In our study, we chose typical NW, RW, and GH to compare and measure methane (CH4) and nitrous oxide (N2O) emissions from the three land use types through two-year in-situ field experiments. The results showed that land use intensification significantly reduced CH4 emissions, and NW, RW, and GH emissions were 970.66 ± 100.09, 896.71 ± 300.44, and −71.23 ± 63.62 kg C ha-1. Land use intensification significantly increased N2O emissions, and NW, RW, and GH emissions were 3.35 ± 0.44, 14.38 ± 4.09, and 81.62 ± 4.89 kg N ha-1. The global warming potential of CH4 and N2O under different land use types was in the order of RW (28,137.98 ± 9077.12 kg eq-CO2 ha-1) > NW (27,123.76 ± 2703.34 kg eq-CO2 ha-1) > GH (20,360.44 ± 2651.51 kg eq-CO2 ha-1). Overall, we observed that the comprehensive greenhouse effect of CH4 and N2O was enhanced by conversion from NW to RW and weakened by conversion from RW to GH. Our study provides a predictive understanding of how land use intensification changes greenhouse gas emissions in the Taihu Lake region and in regions with similar land use types.

Effects of N-enriched biochar on ecosystem greenhouse gas emissions, rice yield, and bacterial community diversity in subtropical rice paddy soils

Nitrogen (N)-enriched biochar is a novel type of biochar prepared by mixing biomass with N-rich sources at a higher temperature via pyrolysis. Although the agronomic benefits of N-enriched biochar are reportedly positive, its effects on GHG emissions, crop yields, and soil bacterial communities in rice paddy fields remain undefined. This study examines the short-time effects of adding different rates of N-enriched biochar (0, 4, and 8 t ha−1) to subtropical early and late rice cropping soils on GHG emissions – namely carbon dioxide (CO2) and methane (CH4), rice yields, and soil bacteria communities. Across the two seasons, cumulative CO2 emissions increased under both biochar treatments while cumulative CH4 emissions declined with the application of biochar at 8 t ha−1. Early rice's global warming potential increased by 86 and 21% following application of biochar at 4 and 8 t ha−1, respectively, and by 43 and 41%, respectively, in late rice. Rice yields significantly (P < 0.05) increased with the application of 4 t N-enriched biochar ha−1 while rates at 8 t ha−1 had no effect. Application of N-enriched biochar altered the relative abundance of dominant bacterial taxa related to N and C cycling, particularly of denitrifying Rhodanobacter and Sphingomona in early and late rice soils, respectively. Furthermore, both rates of N-enriched biochar raised the relative abundance of Thiobacillus and Lysobacter in early and late rice-the latter associated with rice yields-while reducing Streptomyces and H16 taxa. Overall, findings suggest that the application of 4t ha−1 nitrogen-enriched biochar can increase rice yield and reduce CH4 emissions while increased soil cumulative C emissions GWP caused by CO2 emission increase, in part via biochar-induced changes on the plant growth characteristics and soil's bacterial community. This study reflects that the application of moderate doses of biochar can become an important sustainable soil management method for rice fields in subtropical regions, and the application of exogenous organic nutrients can promote crop yields and reduce GHC emissions. Now, a long-term experiment would be required to assess what is the optimal yearly frequency of application of these moderate doses of biochar.

Characteristics and effect factors of CH4 emissions in single-family treatment wetlands

Single-family treatment wetland (SFTW) is increasingly used in developing countries to treat rural domestic sewage. But they can emit CH4, which will affect the global carbon balance. However, a detailed understanding of CH4 emissions in SFTW under long-term real operating conditions is still lacking. To understand the emission characteristics of CH4 from SFTW, a 50-month CH4 flux measurement was conducted in six SFTWs (namely ZHANG, HU, LUO, WEEC, WANG, GAO) of Anlong village, Chengdu, China. The results show that the monthly fluxes of CH4 ranged from −81.35 to 223.13 mg·m−2·h−1, with an average value of 37.41 ± 60.97 mg·m−2·h−1. Generally, CH4 emissions were higher in spring and summer than other seasons (p < 0.05). Besides, the mean annual CH4 flux of 2016 had a significant increase compared to 2014 and 2015 in SFTW (p < 0.05). On the other hand, the mean CH4 fluxes from HU (P < 0.05) and WEEC were lower in the influent tank than in the effluent tank. Moreover, precipitation, air temperature, and sunshine duration were three key factors of CH4 emissions from SFTW. Illumina sequencing shows that Methanoregula and Methanobacterium were dominant methanogenic populations in SFTW (accounting for 96.97%), and were both hydrogenotrophic archaea. A high level of CH4 global warming potential (GWP) was found in SFTW, with an average value of 9.63 kg·CO2-eq·m−2·year−1. WANG wetland was the most environmentally friendly SFTW, acted as a “carbon sink” of CH4 from 2013 to 2016. This study provides a foundational reference for future research on CH4 emission reduction in constructed wetlands (CWs).

Interactive effects of water management and liming on CH4 emissions and rice cadmium uptake in an acid paddy soil.

Rice agriculture is both an important source of the potent greenhouse gas methane (CH4) and a bioaccumulator of cadmium (Cd), which is hazardous to human health. Avoiding flooding during rice production is effective for reducing CH4 emissions, but it increases rice Cd uptake. Although lime application decreases Cd concentration in rice grains, it is not clear whether combining appropriate water management with liming can simultaneously reduce CH4 emissions and Cd uptake in rice paddies. Thus, a pot experiment was performed to investigate the interactive effects of water management (F: continuous flooding, FDF: flooding - midseason drainage - flooding, FDI: flooding - midseason drainage - intermittent irrigation) and lime application on CH4 emissions and rice Cd uptake in an acid paddy soil spiked with Cd. Results showed that neither water management nor liming significantly affected grain yield. Overall, liming reduced CH4 emissions by 42.2%. Compared to F, the FDF and FDI treatments reduced CH4 emissions by 43.5% and 54.2%, respectively. Liming reduced CH4 emissions by 32.6% under F, but with a greater decrease of 48.6% and 52.7% under FDF and FDI, respectively. Overall, liming reduced rice Cd uptake by an average of 47.3%. Compared to FDI, F and FDF significantly reduced Cd uptake by 84.0% and 75.1%, respectively, but there was no significant difference between F and FDF. Liming did not significantly affect Cd uptake under F and FDF, whereas liming reduced Cd uptake by 55.9% under FDI. These results suggest that maintaining flooding following midseason drainage can help in reducing rice Cd uptake, though slightly promoting CH4 emissions. Therefore, we recommend FDF combined with liming to mitigate CH4 emissions without increasing rice Cd uptake in acid paddy soils.

Life cycle environmental impact assessment of methane emissions from the biowaste management strategy of the United Kingdom: Towards net zero emissions

Waste-related methane (CH4) emissions could account for 31% of total UK CH4 emissions. Waste management strategies in the UK have recently changed as more waste is diverted from landfills to anaerobic digesters (AD) and composting facilities, which can be significant sources of CH4. In this study, we combined mobile CH4 emissions data from waste treatment facilities to perform a life cycle assessment of current biowaste treatment and potential future mitigation, including AD, in-vessel composting, incineration, and landfilling scenarios. We found that diverting biowaste from landfill to AD is an effective strategy, but it is not enough to eliminate emissions. The fugitive CH4 emissions from anaerobic digesters have a significant impact on the environmental sustainability of waste management strategies, with upgrading the biogas into biomethane being the best option for climate change mitigation, in the case where natural gas is replaced. A change in the biowaste strategy can also reduce CH4 emissions from the waste sub-sector analysed, from 58.2 to 30.3 kilotonnes per year, an emissions saving of approximately 52%. However, with these technologies, net-zero emissions is challenging unless the absolute minimum emissions from the treatment technologies is consistently achieved. Therefore, we strongly recommend a focus on mitigating CH4 emissions from AD to achieve the goal of net-zero waste management.

Greenhouse Gas Emissions from Salt-Affected Soils: Mechanistic Understanding of Interplay Factors and Reclamation Approaches

Salt-affected soils contain high levels of soluble salts (saline soil) and exchangeable sodium (alkali soil). Globally, about 932 million ha (Mha), including 831 Mha of agricultural land, is salt-affected. Salinity and sodicity adversely affect soil microbial diversity and enzymatic activities, and thereby carbon and nitrogen dynamics and greenhouse gas (GHG) emissions from soils. In this review article, we synthesize published information to understand the impact of salinity and sodicity on GHG production and emissions from salt-affected soils, and how various reclamation amendments (gypsum, phosphogypsum, organic manure, biochar, etc.) affect GHG emissions from reclaimed soils. Nitrous oxide (N2O) and methane (CH4) emissions are of greater concern due to their 298 and 28 times higher global warming potential, respectively, compared to carbon dioxide (CO2), on a 100-year time scale. Therefore, CO2 emissions are given negligible/smaller significance compared to the other two. Generally, nitrous oxide (N2O) emissions are higher at lower salinity and reduced at higher salinity mainly due to: (a) higher ammonification and lower nitrification resulting in a reduced substrate for denitrification; (b) reduced diversity of denitrifying bacteria lowered down microbial-mediated denitrification process; and (c) dissimilatory nitrate reduction to ammonium (DNRA), and denitrification processes compete with each other for common substrate/nitrate. Overall, methane (CH4) emissions from normal soils are higher than those of salt-affected soils. High salinity suppresses the activity of both methanogens (CH4 production) and methanotrophs (CH4 consumption). However, it imposes more inhibitory effects on methanogens than methanotrophs, resulting in lower CH4 production and subsequent emissions from these soils. Therefore, reclamation of these soils may enhance N2O and CH4 emissions. However, gypsum is the best reclamation agent, which significantly mitigates CH4 emissions from paddy cultivation in both sodic and non-sodic soils, and mitigation is higher at the higher rate of its application. Gypsum amendment increases sulfate ion concentrations and reduces CH4 emissions mainly due to the inhibition of the methanogenesis by the sulfate reductase bacteria and the enhancement of soil redox potential. Biochar is also good among the organic amendments mitigating both CH4 and N2O emission from salt-affected soils. The application of fresh organic matter and FYM enhance GHG emissions for these soils. This review suggests the need for systematic investigations for studying the impacts of various amendments and reclamation technologies on GHG emissions in order to develop low carbon emission technologies for salt-affected soil reclamation that can enhance the carbon sequestration potential of these soils.

Liming modifies greenhouse gas fluxes from soils: A meta-analysis of biological drivers

Acidic soils cover about 30% of the world’s land. Liming is a management practice applied worldwide to reduce the negative effects of acidification on soil fertility and plant growth. Liming also affects the biotic and abiotic soil properties controlling the production and consumption of the greenhouse gases (GHGs) carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Although our understanding of how liming regulates net GHG emissions is increasing, the impact of liming on soil biological drivers of GHG emissions has not been quantitatively synthesized. Here we conducted a global meta-analysis using 1474 paired observations from 124 studies to explore the responses of GHG emissions to liming, with a focus on soil biological factors. We show that the N2O mitigation capacity of liming could be linked to (i) increases in bacterial abundance of N2O reductase genes (NosZ) and decreases in fungi:bacteria ratio, both contributing to a lower N2O:N2 product ratio of denitrification; and (ii) reductions in soil mineral nitrogen (N) via stimulation of plant N uptake. The limited evidence available indicates that liming reduced CH4 emissions and the abundance of methanogens, but it had no effect on CH4 uptake and abundance of methanotrophs. Liming-induced increases in soil CO2 emissions can be explained by higher heterotrophic and/or autotrophic respiration. The strong coupling between liming effects on GHG emissions and on soil microbial communities involved in GHG production and consumption can be used to identify strategies to reduce GHGs in response to liming, and to improve process-based models for better predictions of soil GHG emissions.

Product Type, Rice Variety, and Agronomic Measures Determined the Efficacy of Enhanced-Efficiency Nitrogen Fertilizer on the CH4 Emission and Rice Yields in Paddy Fields: A Meta-Analysis

Enhanced-efficiency nitrogen fertilizer (EENF) is a recommend nitrogen fertilizer for rice production because of its advantage on improving nitrogen use efficiency. However, its efficacy on CH4, the dominant greenhouse gas, emission from rice fields showed great variation under field conditions. And the factors influencing its efficacy are still unclear. We synthesized the results of 46 field studies and analyzed the impact of product type, rice variety, and primary agronomic measures (rice cropping system, nitrogen (N) application rate, and water management options) on the effectiveness of EENF on the CH4 emission and rice yield. Overall, EENF, including inhibitors (IS) and slow/control-released fertilizer (S/CRF), significantly reduced CH4 emission by 16.2% and increased rice yield by 7.3%, resulting in a significant reduction in yield-scaled CH4 by 21.7%, compared with conventional N fertilizer. Nitrapyrin, DMPP (3,4-dimethylpyrazole phosphate), and HQ (Hydroquinone) + Nitrapyrin showed relative higher efficacy on the mitigation of CH4 emission than other EENF products; and HQ showed relative lower efficacy on rice yield than other EENF products. The reduction in CH4 emission response of hybrid rice varieties to IS and S/CRF was greater than that of inbred rice varieties. IS significantly reduced the CH4 emission and increased the rice yield under all three rice cropping systems, and showed the highest efficacy in the late rice season of double rice cropping system. Whereas, S/CRF did not significantly reduce the CH4 emission from rice seasons of single rice cropping system and rice-upland crops rotation system. IS did not reduce the CH4 emission when N application rate less than 100 kg ha−1, and S/CRF did not affect the CH4 emission when N application rate less than 100 kg ha−1 or above 200 kg ha−1. Continuous flooding was unfavorable for IS and S/CRF to mitigate CH4 emission and enhance rice yield. These results emphasized the necessary to link EENF products with rice varieties and agronomic practices to assess their efficacy on CH4 emissions and rice yield.

A steady-state analytical model for coupled methane transport and oxidation in vegetated landfill cover soil

The biologically active soils covered by plants are widely applied in landfill final covers for controlling the emission of methane from municipal solid waste. The current study focuses on developing alternative formulations of steady-state analytical modeling for coupled methane transport and oxidation in vegetated landfill cover systems considering the effect of mass exchange via plants’ roots. The proposed analytical frameworks are validated by a set of experimental data. The varied examples of coupled methane transport and oxidation are evaluated by the proposed solution to discuss the effects of the properties of roots and soils on the overall performance of vegetated landfill covers. It was shown that the increment of the root depth or root density can effectively contribute to the reduction of CH4 emission from landfill cover systems while coupled effects of advection/diffusion and oxidation rate may influence the overall performance of CH4 transport. For example, increasing root density from 100 m/m3 to 3 × 103 m/m3 can lead to a reduction of CH4 emission rate by a factor of 1.3. This is mainly attributed to the increase of aerobic zone with the root density growing. It is found that the methane removal efficiency is more sensitive to variations of the saturation outside the root zone (S2) than that in the root zone (S1) as gases inlet fluxes are largely reduced and the role of the plant is weakened for a larger S2. The present analytical models may provide an easy-to-use tool for performance evaluation of cover systems, benchmark studies, parameter identification and sensitivity analysis.

Contrasting effects of different field-aged biochars on potential methane oxidation between acidic and saline paddy soils

There is recognition that biochar addition is an appropriate measure to mitigate methane (CH4) emissions by promoting potential methane oxidation (PMO) in the field. However, the mechanism for different field-aged biochars and effective duration after field application are not well documented. Based on a long-term field experiment, biochar was field aged and separated from two contrasting acidic (Ba) and saline (Bs) paddy fields. Then, the effects of different aged biochars on PMO in acidic and saline paddy soils were explored by incubation experiment. There were five treatments for each soil group: soil without biochar (CK), biochar-enriched paddy soil (2 or 6 years) (NB), fresh biochar amendment (Bf), aged biochar separated from acidic paddy soil amendment (Ba), and aged biochar separated from saline paddy soil amendment (Bs). Results showed that saline paddy soils had a significantly higher PMO than acidic paddy soils under treatment without biochar, and that PMO in acidic paddy soil was enhanced by various biochar amendments, whereas those biochar amendments had no significant effects on PMO in saline paddy soil. PMO was positively correlated with pmoA abundance, N consumption rate and pH of soil-biochar mixture. Aged biochar separated from different fields had conflicting influences on soil pH, N consumption rate and PMO. Ba lost its initial effect on changing PMO as compared to Bf treatment when added back into acidic paddy soil. To the contrary, the acidic paddy soil NB treatment containing biochar added six years before possessed the highest value of PMO among all ten treatments. This study suggested that acidic paddy soil with biochar amendment could mitigate CH4 emissions by promoting PMO for a prolonged period, though aged biochar separated from the same field had a limited impact on reducing CH4 emissions.

Discrepant impact of polyethylene microplastics on methane emissions from different paddy soils

Microplastics (MPs) can affect soil organic carbon (C) cycling in paddy soil by changing microbial function and soil properties. In this study, a laboratory incubation experiment was applied to explore the effect of polyethylene (PE) MP on methane (CH4) and carbon dioxide (CO2) emissions from paddy soils after rice straw addition. Moreover, the microbial functional genes encoding CH4 oxidation and production and organic C degradation were measured. MP addition significantly (p < 0.05) affected the release of CH4, but this effect varied with soil type. The amendment of PE MPs significantly (p < 0.05) reduced CH4 emission by 16.9 % for the acidic soil (pH = 5.0) and 16.1 % for the alkaline soil (pH = 8.2), which was probably due to these plastic particles inhibiting CH4 production by reducing the abundance of the mcrA gene or stimulating CH4 oxidation with the increasing number of pmoA gene copies, respectively. For the neutral soils, the presence of PE MPs did not significantly (p > 0.05) alter CH4 emissions and their associated microbial functional genes. Across the experimental paddy soils, the response of CH4 emissions to MPs was negatively and positively correlated with those of soil ammonium (NH4+) content and mcrA gene abundance, respectively, suggesting that the change in these variables may control the release of CH4 in the presence of MPs. In addition, PE MPs had a negligible effect on soil CO2 emissions and the abundances of all functional genes encoding starch, hemicellulose, and lignin degradation. Our results demonstrated that the presence of MPs affects the release of CH4, probably by regulating NH4+ substrates and methanogens, and this emerging environmental factor should be considered when estimating CH4 emissions from paddy fields.

Effects of ruminal protozoa on methane emissions in ruminants—A meta-analysis

The effects of different ruminal protozoa (RP) on CH4 emissions from ruminants were evaluated in a meta-analysis, using 64 publications reporting data from 79 in vivo experiments. Experiments included in the database reported CH4 emissions (g/d) and total RP (TRP, log10 cells/mL) from the same group of animals. The relationship between CH4 emissions and RP (TRP, entodiniomorphids, and isotrichids), and TRP-, entodiniomorphid-, and isotrichid-based CH4 emission prediction models, were evaluated as mixed models with experiment as a random effect and weighted by the reciprocal of the standard error of the mean and centered around one. Positive associations existed between TRP and isotrichids with CH4 emissions but not between entodiniomorphids and CH4 emissions. A reduction in CH4 emissions was observed, averaging 7.96 and 4.25 g/d, per log unit reduction in TRP and isotrichid concentrations, respectively. Total RP and isotrichids were important variables in predicting CH4 emissions from ruminants. Isotrichid CH4 prediction model was more robust than the TRP, evidenciated by lower predicted sigma hat study (%), and error (%), and with higher concordance correlation coefficient. Both TRP and isotrichid models can accurately predict CH4 emissions across different ruminant types, as shown by the low square root of the mean square prediction error, with 6.59 and 4.08% of the mean of root of the mean square prediction error in the TRP and isotrichid models, respectively. Our results confirm that isotrichids are more important than entodiniomorphids in methanogenesis. Distinguishing these 2 populations yielded a more robust CH4 prediction model than combining them as total protozoa.

A case for ensuring reductions in CO2 emissions are given priority over reductions in CH4 emissions in the near term

A case for ensuring reductions in CO2 emissions are given priority over reductions in CH4 emissions in the near term

Comparisons of Ramie and Corn Stover Silages: Effects on Chewing Activity, Rumen Fermentation, Microbiota and Methane Emissions in Goats

The study aimed to investigate the nutritional value of ramie (Boehmeria nivea) silage, and its consequences for chewing activity, rumen fermentation, and enteric methane (CH4) emissions in goats, by comparing it with corn stover (CS) silage. An in vitro ruminal experiment was firstly performed to investigate the substrate degradation and fermentation of CS and ramie silage. The ramie silage diet was formulated by replacing 60% of CS silage with ramie silage (dry matter (DM) basis). Eight female Xiangdong Black goats (a local breed in Southern China, 1 to 1.2 years of age) with BW of 21.0 ± 1.05 kg were used for this experiment and were randomly assigned to either one of the two dietary treatments in a cross-over design. The ramie silage had higher crude protein (CP) and ash content and lower hemicellulose content, together with decreased (p &lt; 0.05) nutrient degradation and methane production and increased (p &lt; 0.05) acetate molar percentage and acetate to propionate ratio through in vitro ruminal fermentation. Feeding the ramie silage diet did not alter feed intake (p &gt; 0.05), decreased (p &lt; 0.05) nutrient digestibility, and increased (p &lt; 0.05) chewing activity and rumination activity, with reductions (p &lt; 0.05) in eating activity and idle activity. Although feeding the ramie silage diet caused a greater (p &lt; 0.05) molar percentage of acetate and lower molar percentage of propionate, it decreased the rumen-dissolved CH4 concentration and enteric CH4 emissions (p &lt; 0.05). Feeding the ramie silage diet did not alter (p &gt; 0.05) the population of bacteria, protozoa, and fungi; it increased the 16S rRNA gene copies of Ruminococcus flavefaciens (p &lt; 0.05). Further 16SrRNA gene amplicon analysis indicated a distinct bacterial composition between the two treatments (p &lt; 0.05). Feeding the ramie silage diet led to a lower abundance of genera Lawsonibacter, Sedimentibacter, Saccharofermentans, Sediminibacterium, and Bifidobacterium (p &lt; 0.05). Ramie can be an alternative forage resource to stimulate chewing activity and reduce CH4 emissions in ruminants.

Dynamics and controls of inland water CH4 emissions across the Conterminous United States: 1860-2019

Inland waters (rivers, lakes, and reservoirs) have been recognized as hotspots of methane (CH4) emissions. However, the magnitude and spatiotemporal pattern of CH4 emissions and their underlying mechanisms remain largely unknown due to a lack of process-based quantification of CH4 production, consumption, and evasion within the aquatic ecosystem. Here we developed a process-based aquatic CH4 module within the framework of the Dynamic Land Ecosystem Model (DLEM) to explicitly simulate inland water carbon fluxes and the associated CH4 processes. We further applied this model to assess the inland-water CH4 emissions across the conterminous United States (CONUS) as affected by the climate variability, land use, fertilizer nitrogen (N) application, atmospheric N deposition, and rising atmospheric CO2 concentration during 1860-2019. The inland water CH4 emissions across the CONUS had doubled from the 1860s (1.65±0.18 Tg CH4-C∙yr−1) to the 2010s (3.73±0.36 Tg CH4-C∙yr−1). In the 2000s, inland water accounts for 8% of the regional CH4 budget that offsets 11∼14% of the terrestrial C uptake across the CONUS. Our study showed that the small headwater streams (1st –3rd order) account for 49% of the diffusive CH4, and reservoirs constitute 50% of the ebullitive CH4 emissions during the 2010s. Climate change and variability played a dominant role in the increased CH4 emissions from rivers and lakes. This study implies that effective mitigation strategies to reduce CH4 emissions should pay much attention to global climate change and headwater stream management.

Lowering water table reduces carbon sink strength and carbon stocks in northern peatlands.

Peatlands at high latitudes have accumulated >400 Pg carbon (C) because saturated soil and cold temperatures suppress C decomposition. This substantial amount of C in Arctic and Boreal peatlands is potentially subject to increased decomposition if the water table (WT) decreases due to climate change, including permafrost thaw-related drying. Here, we optimize a version of the Organizing Carbon and Hydrology In Dynamic Ecosystems model (ORCHIDEE-PCH4) using site-specific observations to investigate changes in CO2 and CH4 fluxes as well as C stock responses to an experimentally manipulated decrease of WT at six northern peatlands. The unmanipulated control peatlands, with the WT <20 cm on average (seasonal max up to 45 cm) below the surface, currently act as C sinks in most years (58 ± 34 g C m-2 year-1 ; including 6 ± 7 g C-CH4 m-2 year-1 emission). We found, however, that lowering the WT by 10 cm reduced the CO2 sink by 13 ± 15 g C m-2 year-1 and decreased CH4 emission by 4 ± 4 g CH4 m-2 year-1 , thus accumulating less C over 100 years (0.2 ± 0.2 kg C m-2 ). Yet, the reduced emission of CH4 , which has a larger greenhouse warming potential, resulted in a net decrease in greenhouse gas balance by 310 ± 360 g CO2-eq m-2 year-1 . Peatlands with the initial WT close to the soil surface were more vulnerable to C loss: Non-permafrost peatlands lost >2 kg C m-2 over 100 years when WT is lowered by 50 cm, while permafrost peatlands temporally switched from C sinks to sources. These results highlight that reductions in C storage capacity in response to drying of northern peatlands are offset in part by reduced CH4 emissions, thus slightly reducing the positive carbon climate feedbacks of peatlands under a warmer and drier future climate scenario.

Mechanism of slag-based silicate fertilizer suppressing methane emissions from paddies

The addition of electron acceptors to boost soil microbes competitive to methanogens could minimize methane (CH4) emissions from paddy soils. To study the microbiological mechanisms underlying the suppression of CH4 emissions, silicate fertilizer made from blast furnace slag that contains electron acceptors, such as Fe, was applied to Japonica and Indica rice at a rate of 2 Mg ha−1. We found that silicate fertilization significantly reduced CH4 emissions from Japonica and Indica rice by 21.1% and 25.7%, respectively, and the decrease in CH4 emissions coincided with an increase in iron reduction in paddy soils. Silicate fertilization markedly suppressed several methanogens and abundance of genes involved in acetoclastic and hydrogenotrphic methanogenesis, albeit the suppression of acetoclastic gene abundance was larger. Conversely, it increased methanotrophs, their gene abundance, and CH4 oxidation potential of paddy soils, which could be explained by an increase in root oxidation potential. Iron-reducing and oxidizing microbes, and their gene abundance significantly increased by silicate fertilization. Structural equation modeling showed that the suppression of CH4 emissions was mainly due to the competitive inhibition of methanogens by iron-reducing bacteria and the proliferation of methonotrophs. These findings have implications for understanding the CH4 biogeochemistry under silicate fertilization, as it has the potential to mitigate CH4 emissions from paddies.

Investigating detection probability of mobile survey solutions for natural gas pipeline leaks under different atmospheric conditions

The 2015 Paris agreement aims to cut greenhouse gas emissions and keep global temperature rise below 2 °C above pre-industrial levels. Reducing CH4 emissions from leaking pipelines presents a relatively achievable objective. While walking and driving surveys are commonly used to detect leaks, the detection probability (DP) is poorly characterized. This study aims to investigate how leak rates, survey distance and speed, and atmospheric conditions affect the DP in controlled belowground conditions with release rates of 0.5–8.5 g min−1. Results show that DP is highly influenced by survey speed, atmospheric stability, and wind speed. The average DP in Pasquill–Gifford stability (PG) class A is 85% at a low survey speed (2–11 mph) and decreases to 68%, 63%, 65%, and 60% in PGSC B/C, D, E/F, and G respectively. It is generally less than 25% at a high survey speed (22–34 mph), regardless of stability conditions and leak rates. Using the measurement data, a validated DP model was further constructed and showed good performance (R2: 0.76). The options of modeled favorable weather conditions (i.e., PG stability class and wind speed) to have a high DP (e.g., >50%) are rapidly decreased with the increase in survey speed. Walking survey is applicable over a wider range of weather conditions, including PG stability class A to E/F and calm to medium winds (0–5 m s−1). A driving survey at a low speed (11 mph) can only be conducted under calm to low wind speed conditions (0–3 m s−1) to have an equivalent DP to a walking survey. Only calm wind conditions in PG A (0–1 m s−1) are appropriate for a high driving speed (34 mph). These findings showed that driving survey providers need to optimize the survey schemes to achieve a DP equivalence to the traditional walking survey.