Low CH4 Research Articles

Effect of Ru-promotion on the catalytic performance of a cobalt-based Fischer-Tropsch catalyst activated in syngas or H2

This research demonstrated the effect of Ru addition on the structure-performance relationships of Co/SiO2 catalysts reduced in either syngas or H2. The activity results show that the syngas reduced Co-Ru/SiO2 catalyst afforded better product selectivity (high C5+ = 86.8% and low CH4 = 8.45%) but low activity (CO conversion = 15.2%) compared to the H2 reduced Co-Ru/SiO2 catalyst (C5+ = 78.9%, CH4 = 10.5%, CO conversion = 44.8%) at 120 h TOS. Furthermore, the activity of the unpromoted H2-reduced Co/SiO2 catalyst (C5+ = 82%, CH4 = 9.19%, CO conversion = 25%) was comparable to that of syngas catalyst Co-Ru/SiO2 catalyst. Ru improved the reducibility and subsequent dispersion of the Co sites leading to enhanced catalytic activity for the catalyst reduced by H2-reduction. However, the addition of Ru suppressed the CO hydrogenation for the syngas reduced Co-Ru/SiO2 catalyst. This strongly reflects on the superiority of H2 as a reducing agent for Ru-promoted Co-based catalysts. XRD and XPS analysis of the spent catalysts points out at the formation of Co2C species, which suppressed the FT activity and stimulated the formation of olefinic products over the syngas-reduced catalysts. While there is a potential for syngas reduction for unpromoted Co-based catalysts, in small FTS plants, this system in not favorable for Ru-promoted catalysts.

Conservation Agriculture With Optimum Fertilizer Nitrogen Rate Reduces GWP for Rice Cultivation in Floodplain Soils

Wetland rice cultivation contributes significantly to global warming potential (GWP), an effect which is largely attributed to emissions of methane (CH4). Emerging technologies for wetland rice production such as conservation agriculture (CA) may mitigate greenhouse gas (GHG) emissions, but the effects are not well defined. Investigations were carried out in an irrigated rice (Boro rice) field in the fifth crop after conversion of conventional tillage (CT) to strip tillage (ST). Two crop residue levels (low versus high, LR versus HR) and three nitrogen (N) application rates (N1 = 108, N2 = 144, and N3 = 180 kg N ha−1) were laid out in a split-plot experiment with three replicates. Yield-scaled GHG emissions and GWP were estimated to evaluate the impacts of CA on mitigating CH4 and N2O emissions in the rice paddy field. There was a 55% higher N2O emission in ST with HR coupled with N3 than that in CT with LR coupled with N1. The N2O emission factors ranged from 0.43 to 0.75% in ST and 0.45 to 0.59% in CT, irrespective of the residue level and N rate. By contrast, CH4 emissions were significantly lower in CA than in the conventional practices (CT plus LR). The ST with LR in N2 reduced the GWP by 39% over the GWP in CT with HR in N1 and 16% over the conventional practices. Based on our investigation of the combination of tillage, residue, and N rate treatments, the adoption of CA with high and low residue levels reduced the GWP by 10 and 16%, respectively, because of lower CH4 and N2O emissions than the current management practices. The relatively high N2O emission factors suggest that mitigation of this GHG in wetland rice systems needs greater attention.

Pyrolysis gas from biomass and plastics over X-Mo@MgO (X = Ni, Fe, Co) catalysts into functional carbon nanocomposite: Gas reforming reaction and proper process mechanisms

The metal catalysts X-Mo@MgO (X = Ni, Fe, Co) was studied as excellent catalyst for catalytic pyrolysis conversion of biomass and plastics into functional carbon nanocomposite. The proper reaction mechanism of the process was explored through the gas composition, and explored the bactericidal performance of functional carbon nanocomposite. The results showed that the Ni, Fe and Co-based catalysts elevated H2 gas yield reached to 57%, 34% and 44% as the addition of Mo, due to Mo or its oxide species for scission of small molecule compound. The introduction of NiMo@MgO catalyst produced lower CH4, and higher H2 and MWCNTs, which indicated that the formation of MWCNTs is mainly attributed to CH4 dehydrogenation. As a comparison, FeMo@MgO catalyst for CO disproportionation reaction could generate more MWCNTs and lower H2. The functional carbon nanocomposite from FeMo@MgO catalyst were comprehensively evaluated by multiple characterizations. TPO and Raman results confirmed that FeMo@MgO catalyst can provide an excellent carrier to generate MWCNTs with few defects and high graphitization. The functional carbon nanocomposite were initially applied to E.coli extinguishing. The core-shell structure catalyst not only has excellent bactericidal performance, but also has strong resistance to metal leaching.

Integrated evaluation for advanced removal of nitrate and phosphorus in novel PHBV/ZVI-based biofilters: Insight into functional genes and key enzymes

Effective control of nitrogen and phosphorus simultaneously is of great significance to satisfy the strict requirement of the ecological health of receiving waters. In this study, PHBV/ZVI composites made from solid carbon (poly-3-hydroxybutyrate-cohyroxyvelate, PHBV) and zero-valent iron (ZVI) were proposed to be functional fillers in biofilters for advanced wastewater treatment. Results showed that high-rate treatment performance was obtained with nitrate and phosphorus removal efficiencies of 79–97% and 97–98% in the biofilters packed with PHBV/ZVI composites. Lower N2O and CH4 emission (56.3–129.2 μg m−2 h−1) were also achieved simultaneously, further indicating the superiority of PHBV/ZVI composites applied in the wastewater treatment. High-throughput quantitative-PCR (HT-qPCR) results uncovered that the existence of ZVI could enrich carbon-degradation genes (manA, gam and mxa) and facilitate denitrifier utilize organic matters more efficiently, as evidenced by up-regulations of genes involved in nitrate reduction (nirS and nosZ). Meanwhile, higher Fe concentration and less functional genes inducing lower activities of phosphate metabolism and in PHBV/ZVI systems indicated ZVI corrosion and coprecipitation were the main pathway of phosphorus removal. Network and redundancy analysis highlighted the role of ZVI in the removal of pollutants with keystone genes changed (pox and napA) and genes distribution remodeled compared to single PHBV fillers. Further, the activities of dehydrogenase (DHA) and nitrite reductase (Nir) enzymes also increased by the modulation of microbes, which explicitly interpreted the synergistic promotion of PHBV and ZVI on the denitrification process. These findings provided an alternative for the advanced treatment of wastewater and improve the understanding of C, N and P cycling in the co-occurrence of PHBV and ZVI.

Separation of methane and nitrogen using ionic liquidic zeolites by pressure vacuum swing adsorption

AbstractThe separation of methane (CH4) and nitrogen (N2) is a significant challenge to the enrichment and utilization of low concentration CH4 due to the similarity in the physical and chemical properties of the two molecules. In this work, we investigated the separation of CH4 from N2 using 100 kg of a new ionic liquidic zeolite (ILZ) material in a 6‐bed pilot‐scale pressure swing adsorption process. Feed gases with CH4 concentrations of 5.0% and 16.1% were upgraded to 11.5% and 34.6%, respectively, with CH4 recoveries higher than 80%. The pilot test results were used to anchor a numerical model that then allowed the efficient investigation of multiple operational parameters including desorption pressure and feed gas flow rates. The numerical model produced CH4 concentrations for both product streams consistent with those measured in the pilot experiments, with root mean square deviations below 2%. The modeling results revealed that sufficiently low desorption pressures can unexpectedly lead to lower heavy product purities under limited feed gas flow conditions. Furthermore, the optimum feed gas flow rate under which maximum heavy product purity is achieved increases with lower desorption pressure. The maximum CH4 concentrations increased from 31.8% to 41.5%, as desorption pressures decreased from 22.8 to 12.2 kPa for optimum feed flow rates between 78.2 and 105.5 mol/h. We also demonstrate a method of process optimization based on the bed capacity ratio, ℂ, which provides a scale‐independent measure of the degree to which the column is being used effectively. By varying feed flow rate and/or desorption pressure, ℂ values between 0.2 and 0.8 were explored, with maxima in the combined separation performance metric (methane recovery) × (methane purity) occurring for values of ℂ in the range 0.29–0.36. This separation performance optimization by adjusting ℂ provides an effective strategy for integrating and understanding the impact of multiple operating parameters.

Synthesis gas and H2 production by chemical looping reforming using bio-oil from fast pyrolysis of wood as raw material

• CLR of pine wood bio-oil has been demonstrated in a 1 kW th continuous unit. • Complete conversion of bio-oil was found during 60 h of operation. • Carbon deposition can be minimized and controlled in the continuous CLR unit. • Maximum H 2 production and H 2 /CO ratio were found at 650 °C with very low C deposition. • Auto-thermal H 2 production at 650 °C was 13.6 g/100 g of bio-oil with H 2 O/bio-oil = 6. The interest of using bio-oil produced by biomass fast pyrolysis to generate H 2 and high value chemicals is growing up in order to reduce CO 2 emissions by the use of biomass. In the present work, bio-oil Chemical Looping Reforming was demonstrated in a 1 kW th continuous unit during 60 h of operation using a Ni-based oxygen carrier to produce syngas/H 2 . No agglomeration of the oxygen carrier was detected. Complete conversion of the bio-oil was obtained in all cases, obtaining as main products H 2 , CO, CO 2 and in much lower concentration CH 4 . Carbon deposition in the bed appeared in almost all the experiments carried out during the bio-oil reforming, and CO 2 was found in the air reactor outlet, although did not affect to the process performance when oxygen carriers were used. This fact only let to a reduction of the CO 2 capture efficiency. Fuel reactor temperature was a key factor for the H 2 production, the H 2 /CO ratio and the carbon accumulated in the CLR unit. The maximum H 2 production together with the maximum H 2 /CO ratio of 6 were found at the lowest temperature used, 650 °C. In addition, the carbon formed in the fuel reactor was reactive enough so that it could be burnt in the air reactor with minimum accumulation in the continuous unit. The autothermal H 2 production was 13.6 g/100 g of bio-oil without water at 650 °C with a H 2 O/bio-oil = 6, which corresponds to 68 mol H 2 /kg of bio-oil without water. Therefore, the CLR process of bio-oil allows obtaining high H 2 production with low carbon deposition at 650 °C using less amount of water than in conventional bio-oil reforming.

The influence of closed pores and stacked coal grains on gas transport in CO2 injection enhanced CH4 recovery process

CO2 injection enhanced coalbed methane (CH4) recovery technology can achieve the enhancement of CH4 production and the effective geological storage of carbon dioxide in coal seams. A coal seam is composed of matrix and fractures. Matrix has open pores and closed pores and fractures may have stacked coal grains. However, the influences of closed pores in matrix and stacked coal grains in fractures on CO2 injection enhanced CH4 recovery have rarely been studied. This paper develops a numerical simulation model to explore the hydraulic-mechanical coupling responses in CO2 injection enhanced coalbed methane (CO2-ECBM) recovery process. This model considers the binary gas displacement and transport in ternary pores, the deformation of coal with different porosity, and fractal stacked coal grains in fractures. After verification with the data available from literature, this model is used to simulate a field trial in the Qinshui Basin. The simulation results show that the contribution of gas in closed pores to the total CH4 production enhanced by CO2 injection is more than 60% in high-rank coal and is proportional to the volume fraction of closed pores. The stacked coal grains in fractures affect the effective roughness and can be expressed by three structural parameters. Higher effective roughness induces lower cumulative CO2 injection and lower cumulative CH4 production and the conical bottom diameter of cone-like element has the largest influence. These findings can promote our understanding for the influence of closed pores and stacked coal grains on gas transport in coalbed gas reservoirs from a multi-scale perspective.

Treating tropical grass with fibrolytic enzymes from the fungus Trichoderma reesei: Effects on animal performance, digestibility and enteric methane emissions of growing lambs

Food security and climate change concerns are pressing livestock production industry to seek sustainable practices to increase productivity while reducing the intensity of enteric methane (CH4) emissions. In this scenario, the use of enzyme products in ruminant nutrition may be an important alternative to meet future increased demands for animal products with reduced environmental impacts. The objective of this study was to evaluate the effects of treating forage with a fibrolytic enzymes extract (FEE), produced by Trichoderma reesei, on animal performance, blood biochemical parameters, nutrient digestibility, ruminal fermentation, and enteric CH4 production of growing lambs. Nineteen Santa Inês growing lambs were divided into two groups: control (CTL) and enzyme (ENZ). The animals were fed with 700 g/kg of tifton-85 hay and 300 g/kg (as fed basis) of concentrate mixture for 73 days. The FEE was manually applied 24 h before each feed supply. Initially, animals were kept in individual pens for the growth performance trial (15 days of adaptation plus 45 for data collection), then were taken to metabolic cages (seven days) and to gas measurement chambers (six days) for the metabolism assay and determination of CH4 production, respectively. No effects (P > 0.05) were observed on dry matter intake (DMI), average daily gain (ADG), and feed conversion ratio. However, ENZ animals showed higher proportion of body weight gain (PBWG) when considering the entire growth performance period (P < 0.05). Analysis of blood parameters indicated that FEE did not impair animals’ health. Lambs fed forages treated with FEE showed 12% higher acid detergent fiber (ADF) digestibility (P < 0.05) and 20% lower enteric CH4 yield (i.e. per kg of digestible organic matter intake) (P < 0.05). Microbial protein synthesis, pH, ammonia nitrogen, short-chain fatty acids concentration and protozoa population were not affected by the addition of FEE (P > 0.05). The results indicated that FEE can be used in diets of lambs, leading to higher PBWG, improving ADF digestibility and reducing CH4 yield, suggesting its potential suitability as a strategy to increase animal productivity and contribute to the mitigation of enteric CH4 production, especially when animals are fed poor-quality forages.

Low N2O and variable CH4 fluxes from tropical forest soils of the Congo Basin

Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (N2O) and sink for methane (CH4). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ N2O and CH4 flux measurements are scarce. Here, we provide multi-year data derived from on-ground soil flux (n = 1558) and riverine dissolved gas concentration (n = 332) measurements spanning montane, swamp, and lowland forests. Each forest type core monitoring site was sampled at least for one hydrological year between 2016 - 2020 at a frequency of 7-14 days. We estimate a terrestrial CH4 uptake (in kg CH4-C ha−1 yr−1) for montane (−4.28) and lowland forests (−3.52) and a massive CH4 release from swamp forests (non-inundated 2.68; inundated 341). All investigated forest types were a N2O source (except for inundated swamp forest) with 0.93, 1.56, 3.5, and −0.19 kg N2O-N ha−1 yr−1 for montane, lowland, non-inundated swamp, and inundated swamp forests, respectively.

Water level changes in Lake Erie drive 21st century CO2 and CH4 fluxes from a coastal temperate wetland

Wetland water depth influences microbial and plant communities, which can alter the above- and below-ground carbon cycling of a wetland. Wetland water depths are likely to change due to shifting precipitation patterns, which will affect projections of greenhouse gas emissions; however, these effects are rarely incorporated into wetland greenhouse gas models. Seeking to address this gap, we used a mechanistic model, ecosys, to simulate a range of water depth scenarios in a temperate wetland, and analyzed simulated predictions of carbon dioxide (CO2) and methane (CH4) fluxes over the 21st century. We tested our model using eddy covariance measurements of CO2 and CH4 fluxes collected at the Old Woman Creek National Estuarine Research Reserve (OWC) during 2015 and 2016. OWC is a lacustrine, estuarine, freshwater, mineral-soil marsh. An empirical model found that the wetland water depth is highly dependent on the water depth of the nearby Lake Erie. Future wetland surface water depths were modeled based on projection of Lake Erie's water depth using four separate NOAA projections, resulting in four wetland water-depth scenarios. Two of the four 21st century projections for Lake Erie water depths used in this study indicated that the water depth of the wetland would remain nearly steady; however, the other two indicated decreases in the wetland water depth. In our scenario where the wetland dries out, we project the wetland's climatological warming effect will decrease due to smaller CH4 fluxes to the atmosphere and larger CO2 uptake by the wetland. We also found that increased water level can lower emissions by shifting the site towards more open water areas, which have lower CH4 emissions. We found that decreased water depths would cause more widespread colonization of the wetland by macrophyte vegetation. Using an empirical relationship, we also found that further drying could result in other, non-wetland vegetation to emerge, dramatically altering soil carbon cycling. In three of our four projections, we found that in general the magnitude of CO2 and CH4 fluxes steadily increase over the next 100 years in response to higher temperatures. However, in our driest simulations, we projected a different response due to increased oxidation of soil carbon, with CH4 emissions decreasing substantially from an annual cumulative peak of 224.6 to a minimum of 104.7 gC m−2 year−1. In that same simulation, net cumulative flux of CO2 changed from being a sink of 56.5 gC m−2 year−1 to a source of 369.6 gC m−2 year−1 over the same period, despite a temperature increase from 13.7 °C to 14.2 °C. This temperature shift in our other three cases with greater water depths increased the source strength of CH4 and the sink strength of CO2.We conclude that the magnitude of wetland greenhouse-gas fluxes depended on the water depth primarily as it affected the areal percentage of the wetland available for plant colonization, but dramatic decreases in water depths could cause significant reductions in the wetland CH4 fluxes, while simultaneously altering the wetland vegetation.

Response of CO2 and CH4 transport to damming: A case study of Yulin River in the Three Gorges Reservoir, China

The growing number of dams in the Three Gorges Reservoir (TGR) make tributaries of TGR into spatially complex and temporally dynamic systems. To assess the influence of damming on the carbon emission in the tributary of TGR, we investigated the spatial heterogeneity of CO2, CH4, organic carbon, inorganic carbon, and evaluated the transport mechanisms of CO2 and CH4 within water column during different TGR operation periods. We found that mean CO2 and CH4 concentrations in water downstream (44.04 and 0.44 μmol L−1 for CO2 and CH4, respectively) were lower than upstream (48.36 and 1.63 μmol L−1 for CO2 and CH4, respectively) in the impoundment period of TGR, which was consistent with the spatial variations of organic carbon. In the drainage period of TGR, the mean CO2 concentration of upstream (58.71 μmol L−1) was significantly lower than that of downstream (88.92 μmol L−1). The higher CO2 concentration downstream was attributed to terrestrial input and higher microbial diversity of the water column, while the lower CO2 concentration upstream was due to the photosynthesis of phytoplankton. Furthermore, low CH4 concentrations (less than 0.1 μmol L−1) of both upstream and downstream were detected in the drainage period. Based on results of 16s rRNA sequencing, quantitative PCR, and functional prediction, it was indicated that aerobic CH4 oxidation predominantly in the bottom water layer reduced CH4 of the water column in drainage period. Our results expand the theory of CO2 and CH4 transport within the water column in complex river systems and provide theoretical references for the distribution of carbon in the dammed tributaries of TGR.

Impacts of eucalyptus biochar application on greenhouse gas emission from an upland rice–sugarcane cropping system on sandy soil

Summary An on-farm field experiment was conducted in northeastern Thailand to assess the effects of different eucalyptus biochar (BC) application rates, in combination with mineral fertilizers, on upland rice and a succeeding crop of sugarcane on sandy soil. Soil mineral N and greenhouse gas emissions were also evaluated. The field experiment consisted of three treatments: no biochar (BC0), 3.1 Mg ha−1 of biochar (BC1), and 6.2 Mg ha−1 of biochar (BC2). All treatments received the same recommended fertilizer rate. Soil mineral N, and emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored after BC application. The results revealed that the BC2 treatment caused lower soil mineral N content than that of the BC0 treatment during the upland rice period. During the sugarcane period, the BC2 treatment induced a greater soil mineral N content than the BC1 treatment but had no significant difference from the BC0 treatment. The BC2 treatment resulted in significantly lower cumulative CH4 and N2O emissions than the BC0 treatment during the upland rice period. In conclusion, we found that the BC2 treatment alleviated the global warming potential from CH4 and N2O emissions throughout the experiment, causing slight changes in soil N availability in the upland rice–sugarcane cropping system.

Comparisons of Varying Dosages of Chloral Hydrate-Hydroxyzine with and without Meperidine for Managing Challenging Pediatric Dental Behavior: A Retrospective study of 35 years of Sedation Experiences.

This retrospective study compares the efficacy and safety of variable dosing of Chloral Hydrate - Hydroxyzine with and without Meperidine (Mep)for managing varying levels of anxiety and uncooperative behavior of young pediatric dental patients over a 35-year period. Reviews of the sedation logs of 2,610 children, 3-7 years were compared in search of what dosing proves safe and effective for differing levels of challenging behavior. Variable dosing of CH with and without Mep were judged using a pragmatic approach which defined sedation success as optimal, adequate, inadequate, or over-dosage using oneway analysis of variance. Descriptive analyses of behavior and physiologic assessment was included with regard to the extent to which physical restraint occurred to control interfering behavior. Arousal levels requiring stimulation, oxygen desaturation, and adverse reactions were included as indications of safety. Where Mep was used, success rates were consistently higher; need for higher-end dosing of CH was not found beneficial when Mep was included. Significantly less need for physical restraint accompanied the addition of Mep. There appears to be strong basis for the safety and efficacy of the use of CH-H-Mep in combination at lower dosing than historically used. Addition of Mep was observed to enhance sedations, permit lower CH dosing, lessen or eliminate the need for physical restraint and adverse reactions.

Microstructure, mechanical and electrochemical properties of Ti3AlC2 coatings prepared by filtered cathode vacuum arc technology

Ti3AlC2 MAX phases have attracted increasing attention due to their unique properties. However, high synthesis temperatures of Ti3AlC2 bulk materials limit their further development. In this work, Ti3AlC2 coatings were prepared by a two-step method with filtered cathode vacuum arc (FCVA) deposition at room temperature and annealing at 800 °C for 1 h. The structure and properties of coatings were investigated. The results showed that the formation of Ti3AlC2 phase in the annealed coating depended on the C2H2 flow rate during deposition. At low C2H2 flow rates (≤ 9 sccm), almost no Ti3AlC2 phase was formed. As the C2H2 flow rate increased, the annealed coatings mainly exhibited Ti3AlC2 phases, the texture of which transformed from (104) to (105) planes. Meantime, the hardness of Ti3AlC2 coatings continuously increased to a maximum of 20.7 GPa, and the corrosion resistance first increased and then decreased with the increase of C2H2 flow rate.

Chemical and in vitro evaluation of Leucaena (Leucaena leucocephala) Leaves as a Substitute of Alfalfa (Medicago sativa L.) with/without Rejected Green Banana Fruits (Musa paradisiaca)

Leucaena leaves and rejected green banana fruits can be promising to cope with feed gaps in arid and semi-arid Mediterranean regions. The present study evaluated the feeding value and secondary active compounds of Leucaena leaves and rejected green banana fruits for ruminants using a semi-automated gas production (GP) system. Comparisons were made with the traditional feeds as alfalfa, and Dichanthium spp. grass hay. Analysis of HPLC was performed for the feed ingredients to characterize the main phenolic components. The in vitro evaluation was carried out for the experimental feed ingredients and diets. Four diets were formulated as the first diet consisted of alfalfa and grass hay at a ratio of 35:65 (AG), the second diet composed of alfalfa, grass hay, and green banana fruits at a ratio of 35:55:10 (AGB), third and fourth diets were prepared by replacing alfalfa in AG and AGB with Leucaena leaves to be LG and LGB, respectively. Leucaena leaves showed a high content of valuable phenolic components that have antioxidant and anti-inflammatory properties, such as gallic acid, ellagic acid, and naringenin. Moreover, Leucaena leaves and diet had higher crude protein, total phenols, and total tannins than alfalfa, which was reflected on the chemical composition of diets, and recorded the lowest total accumulative GP at 24 hours leading to low CH4 and CO2 production. Banana fruits recorded the lowest ruminal pH, ammonia concentration, and degraded neutral detergent fiber, compared to other feed ingredients, while it had the highest GP and degraded organic matter. Therefore, it is highly recommended to use Leucaena leaves in animals’ diets with/without rejected green banana fruits as an alternative feed resource with potential environmental and animal health benefits.

Vegetation and hydrology stratification as proxies to estimate methane emission from tidal marshes

Direct measurement of methane emissions is cost-prohibitive for greenhouse gas offset projects, necessitating the development of alternative accounting methods such as proxies. Salinity is a useful proxy for tidal marsh CH4 emissions when comparing across a wide range of salinity regimes but does not adequately explain variation in brackish and freshwater regimes, where variation in emissions is large. We sought to improve upon the salinity proxy in a marsh complex on Deal Island Peninsula, Maryland, USA by comparing emissions from four strata differing in hydrology and plant community composition. Mean CH4 chamber-collected emissions measured as mg CH4 m−2 h−1 ranked as S. alterniflora (1.2 ± 0.3) ≫ High-elevation J. roemerianus (0.4 ± 0.06) > Low-elevation J. roemerianus (0.3 ± 0.07) = S. patens (0.1 ± 0.01). Sulfate depletion generally reflected the same pattern with significantly greater depletion in the S. alterniflora stratum (61 ± 4%) than in the S. patens stratum (1 ± 9%) with the J. roemerianus strata falling in between. We attribute the high CH4 emissions in the S. alterniflora stratum to sulfate depletion likely driven by limited connectivity to tidal waters. Low CH4 emissions in the S. patens stratum are attributed to lower water levels, higher levels of ferric iron, and shallow rooting depth. Moderate CH4 emissions from the J. roemerianus strata were likely due to plant traits that favor CH4 oxidation over CH4 production. Hydrology and plant community composition have significant potential as proxies to estimate CH4 emissions at the site scale.

Geochemical Characteristics of Hydrothermal Volatiles From Southeast China and Their Implications on the Tectonic Structure Controlling Heat Convection

Hot springs and igneous rocks are present widely in southeast China, influenced by the subduction of the Western Pacific and Philippine Sea Plates. This study reports on new data of chemical compositions and He–Ne–C isotopes for gas samples from representative hot springs and wells in the Guangdong and Fujian provinces to identify the origin of hydrothermal volatiles and provide insight into geothermal tectonic affinities. The primary hydrothermal volatile component from southeast China is atmospheric N2, with a volumetric percentage of 82.19%–98.29%. It indicates medium-low temperature geothermal systems where geothermal fluids suffered a shallow circulation in closed fracture systems. Low CO2 and CH4 contents and their depleted δ13C values confirmed the small number of deep-derived components in the study area. However, spatially discernible geochemical characteristics imply enhanced hydrothermal fluid convection in the adjacent area of the two provinces, including the Fengshun, Zhangzhou, Longyan, and Sanming geothermal fields. Specifically, the He–Ne isotopes from this area exhibit mantle He contribution of more than 10% and mantle heat flow accounts for more than half of the total heat flow. Moreover, according to the thermal background calculations, the highest heat flow value of 77.7 mW/m2 is indicated for the Zhangzhou geothermal area and the lowest value of 54.7 mW/m2 is indicated for the Maoming geothermal area. Given the epicenter distributions and the corresponding earthquake magnitudes, the NE-trending faults are heat-control tectonic structures and their intersections with the NW-trending faults provided expedite channels for geothermal fluids rising to the surface. Therefore, the preferred development potential of geothermal resources can be expected in the adjacent area of the two provinces where two sets of active faults crossed. This study provides critical information on understanding the geothermal distribution controlled by the tectonic structure in southeast China.

Impact of forage diversity on forage productivity, nutritive value, beef cattle performance, and enteric methane emissions.

Greenhouse gas emissions from the beef industry are largely attributed to the grazing sector, specifically from beef cattle enteric methane emissions. Therefore, the study objective was to examine how forage diversity impacts forage productivity, nutritive value, animal performance, and enteric methane emissions. This study occurred over three consecutive grazing seasons (2018 to 2020) and compared two common Midwest grazing mixtures: 1) a simple, 50:50 alfalfa:orchardgrass mixture (SIMP) and 2) a botanically diverse, cool-season species mixture (COMP). Fifty-six steers and heifers were adapted to an Automated Head Chamber System (AHCS) each year (C-Lock Inc., Rapid City, SD) and stratified into treatment groups based on acclimation visitation. Each treatment consisted of four pastures, three 3.2-ha and one 1.6-ha, with eight and four animals each, respectively. Forage production was measured biweekly in pre- and postgrazed paddocks, and forage nutritive value was analyzed using near-infrared reflectance spectroscopy. Shrunk body weights were taken monthly to determine animal performance. Forage availability did not differ between treatments (P = 0.69) but tended lower in 2018 (P = 0.06; 2.40 t dry matter ha−1) than 2019 (2.92 t dry matter ha−1) and 2020 (P = 0.10; 2.81 t dry matter ha−1). Crude protein was significantly lower for COMP in 2018 compared with SIMP. Forage acid detergent fiber content was significantly lower for the COMP mixture (P = 0.02). The COMP treatment resulted higher dry matter digestibility (IVDMD48) in 2018 and 2019 compared with the SIMP treatment (P < 0.01). Animal performance did not differ between treatments (P > 0.50). There was a tendency for the COMP treatment to have lower enteric CH4 production on a g d−1 basis (P = 0.06), but no difference was observed on an emission intensity basis (g CH4 kg−1 gain; P = 0.56). These results would indicate that adoption of the complex forage mixture would not result in improved forage productivity, animal performance, or reduced emission intensity compared with the simple forage mixture.

The Effect of Multi-Years Reclaimed Water Irrigation on Dryland Carbon Sequestration in the North China Plain

Reclaimed water is an alternative water source which could alleviate the shortage of water resources in agricultural systems. Many researchers have studied the effect of reclaimed water on soil environment, crop yield, etc. However, carbon sequestration in reclaimed water irrigated agricultural systems is less studied. This study investigates methane uptake and photosynthesis in reclaimed water irrigation systems contributing to carbon sequestration estimation and analyzes the important factors impacting them. The results show that CH4 uptake is related to soil water-filled pore space (WFPS) with a quadratic and it has the highest uptake when WFPS is between 40 and 50%. Long-term reclaimed water irrigation could significantly decrease (p &lt; 0.05) CH4 uptake and macroaggregate stability in the topsoil. However, reclaimed water had no significant impact on photosynthesis in comparison. The type of fertilizer is an important factor which impacts CH4 emission from soil; urea had a lower CH4 uptake and a higher CO2 emission than slow-released fertilizer. Overall, reclaimed water irrigation could effectively decrease soil carbon sequestration. A soil wetted proportion level of 40–50% was recommended in this study for favorable methane oxidation. Slow-released fertilizer in reclaimed water irrigated agriculture could better control soil carbon emission and soil carbon absorption.

Simulating the Long-Term Effects of Fertilizer and Water Management on Grain Yield and Methane Emissions of Paddy Rice in Thailand

Rice is an important economic crop in Thailand. However, paddy rice fields are one of the largest anthropogenic sources of methane (CH4) emissions. Therefore, suitable crop management practice is necessary to reduce CH4 emissions while rice grain yield is maintained. This study aimed to evaluate appropriate options of fertilizer and water management practices for Thai rice cultivation with regards to improving rice grain yield and reducing CH4 emissions. The Denitrification–Decomposition (DNDC) model was used to simulate grain yield and the emission of CH4 under the three fertilizer options (chemical fertilizer (F), manure (M) and chemical fertilizer + manure (F + M)) with three water management options (continuous flooding (CF), mid-season drainage (MD) and alternate wet and dry (AWD)) during the years 2011–2050. Rain-fed and irrigated rice cropping systems were used. A total of 24 sites distributed in 22 provinces were studied. The data sets of daily climate, soil properties, and rice management practices were required as inputs in the model. Model validation with observation data in a field experiment indicated that simulated grain yields (R2 = 0.83, slope = 0.98, NRMES = 0.30) and cumulative seasonal CH4 emissions (R2 = 0.83, slope = 0.74, NRMES = 0.43) were significantly and positively correlated with the observation. At the end of the simulation period (2046–2050), fertilizer management options of F and F + M gave more grain yield than the M management option by 1–44% in rain-fed rice cropping and 104–190% in irrigated rice cropping system, respectively. Among options, the lower CH4 emissions were found in AWD water management options. The appropriate options with regard to maintaining grain yield and reducing CH4 emissions in the long term were suggested to be F + M with AWD for the rain-fed rice, and F with AWD for the irrigated rice cropping systems.