Net CH4 Production Research Articles

Assessing the efficacy of date-pits holocellulose as a novel additive candidate for ruminant feeding.

Holocellulose (HC) fraction extracted from date-pits was evaluated as a novel feed additive for ruminant feeding. This study was performed to investigate the effectiveness of the HC additive on rumen fermentation, methane (CH4) production, and diet degradability over 24h of in vitro incubation. Three independent incubation trials were conducted over three consecutive weeks, employing the same in vitro methodology to assess four treatment doses in a completely randomized design. The experimental diet incorporated four increasing doses of HC, containing HC at 0 (HC0), 10 (HC10), 20 (HC20), and 30 (HC30) g/kg dry matter (DM). In vitro gas production (GP) and CH4 production, volatile fatty acids (VFAs) concentration, protozoa accounts, degraded organic matter (DOM), metabolizable and net energy (ME and NE), and hydrogen (H2) estimates were measured. No significant differences in ruminal pH were observed as the HC doses gradually increased. All incremental doses of HC additive over 24h resulted in a linear increase in GP (P < 0.001), DOM (P < 0.001), total VFAs (P = 0.011), and propionate (P < 0.001) concentrations, as well as estimated energy (ME and NE) (P < 0.05) and microbial protein (P = 0.017) values. However, the inclusion of increasing doses of HC in the diet displayed linear reductions in the net CH4 production (ml/kg DOM; P = 0.002), protozoa abundance (P = 0.027); acetate (P = 0.029), and butyrate (P < 0.001) concentrations, the acetate-to-propionate ratio (P < 0.001), and the estimated net H2 production concentration (P = 0.049). Thus, the use of date-pits HC additive generated positive ruminal fermentability, including increased total VFAs and a reduction in the acetate-to-propionate ratio, leading to decreased CH4 output over 24h of in vitro incubation. Hence, HC could be considered a potent feed additive (at up to 30g/kg DM), demonstrating promising CH4-mitigating competency and thereby enhancing energy-use efficiency in ruminants.

S-containing molecular markers of dissolved organic carbon attributing to riverine dissolved methane production across different land uses

The emission of methane (CH4) from streams and rivers contributes significantly to its global inventory. The production of CH4 is traditionally considered as a strictly anaerobic process. Recent investigations observed a “CH4 paradox” in oxic waters, suggesting the occurrence of oxic methane production (OMP). Human activities promoted dissolved organic carbon (DOC) in streams and rivers, providing significant substrates for CH4 production. However, the underlying DOC molecular markers of CH4 production in river systems are not well known. The identification of these markers will help to reveal the mechanism of methanogenesis. Here, Fourier transform ion cyclotron mass spectrometry and other high-quality DOC characterization, ecosystem metabolism, and in-situ net CH4 production rate were employed to investigate molecular markers attributing to riverine dissolved CH4 production across different land uses. We show that endogenous CH4 production supports CH4 oversaturation and positively correlates with DOC concentrations and gross primary production. Furthermore, sulfur (S)-containing molecules, particularly S-aliphatics and S-peptides, and fatty acid-like compounds (e.g., acetate homologs) are characterized as markers of water-column aerobic and anaerobic CH4 production. Watershed characterization, including riverine discharge, allochthonous DOC input, turnover, as well as autochthonous DOC, affects the CH4 production. Our study helps to understand riverine aerobic or anaerobic CH4 production relating to DOC molecular characteristics across different land uses.

Fe(II)Cl2 amendment suppresses pond methane emissions by stimulating iron-dependent anaerobic oxidation of methane.

Aquatic ecosystems are large contributors to global methane (CH4) emissions. Eutrophication significantly enhances CH4-production as it stimulates methanogenesis. Mitigation measures aimed at reducing eutrophication, such as the addition of metal salts to immobilize phosphate (PO43-), are now common practice. However, the effects of such remedies on methanogenic and methanotrophic communities-and therefore on CH4-cycling-remain largely unexplored. Here, we demonstrate that Fe(II)Cl2 addition, used as PO43- binder, differentially affected microbial CH4 cycling-processes in field experiments and batch incubations. In the field experiments, carried out in enclosures in a eutrophic pond, Fe(II)Cl2 application lowered in-situ CH4 emissions by lowering net CH4-production, while sediment aerobic CH4-oxidation rates-as found in batch incubations of sediment from the enclosures-did not differ from control. In Fe(II)Cl2-treated sediments, a decrease in net CH4-production rates could be attributed to the stimulation of iron-dependent anaerobic CH4-oxidation (Fe-AOM). In batch incubations, anaerobic CH4-oxidation and Fe(II)-production started immediately after CH4 addition, indicating Fe-AOM, likely enabled by favorable indigenous iron cycling conditions and the present methanotroph community in the pond sediment. 16S rRNA sequencing data confirmed the presence of anaerobic CH4-oxidizing archaea and both iron-reducing and iron-oxidizing bacteria in the tested sediments. Thus, besides combatting eutrophication, Fe(II)Cl2 application can mitigate CH4 emissions by reducing microbial net CH4-production and stimulating Fe-AOM.

Anaerobic methane oxidation is quantitatively important in deeper peat layers of boreal peatlands: Evidence from anaerobic incubations, in situ stable isotopes depth profiles, and microbial communities

Boreal peatlands store most of their carbon in layers deeper than 0.5 m under anaerobic conditions, where carbon dioxide and methane are produced as terminal products of organic matter degradation. Since the global warming potential of methane is much greater than that of carbon dioxide, the balance between the production rates of these gases is important for future climate predictions. Herein, we aimed to understand whether anaerobic methane oxidation (AMO) could explain the high CO2/CH4 anaerobic production ratios that are widely observed for the deeper peat layers of boreal peatlands. Furthermore, we quantified the metabolic pathways of methanogenesis to examine whether hydrogenotrophic methanogenesis is a dominant methane production pathway for the presumably recalcitrant deeper peat. To assess the CH4 cycling in deeper peat, we combined laboratory anaerobic incubations with a pathway-specific inhibitor, in situ depth patterns of stable isotopes in CH4, and 16S rRNA gene amplicon sequencing for three representative boreal peatlands in Western Siberia. We found up to a 69 % reduction in CH4 production due to AMO, which largely explained the high CO2/CH4 anaerobic production ratios and the in situ depth-related patterns of δ13C and δD in methane. The absence of acetate accumulation after inhibiting acetotrophic methanogenesis and the presence of sulfate- and nitrate-reducing anaerobic acetate oxidizers in the deeper peat indicated that these microorganisms use SO42− and NO3− as electron acceptors. Acetotrophic methanogenesis dominated net CH4 production in the deeper peat, accounting for 81 ± 13 %. Overall, anaerobic oxidation is quantitatively important for the methane cycle in the deeper layers of boreal peatlands, affecting both methane and its main precursor concentrations.

Net Methane Production Predicted by Patch Characteristics in a Freshwater Wetland

AbstractMethane (CH4) dynamics in wetlands are spatially variable and difficult to estimate at ecosystem scales. Patches with different plant functional types (PFT) represent discrete units within wetlands that may help characterize patterns in CH4 variability. We investigate dissolved porewater CH4 concentrations, a representation of net CH4 production and potential source of atmospheric flux, in five wetland patches characterized by a dominant PFT or lack of plants. Using soil, porewater, and plant variables we hypothesized to influence CH4, we used three modeling approaches—Classification and regression tree, AIC model selection, and Structural Equation Modeling—to identify direct and indirect influences on porewater CH4 dynamics. Across all three models, dissolved porewater CO2 concentration was the dominant driver of CH4 concentrations, partly through the influence of PFT patches. Plants in each patch type likely had variable influence on CH4 via root exudates (a substrate for methanogens), capacity to transport gas (both O2 from and CH4 to the atmosphere), and plant litter quality which impacted soil respiration and production of CO2 in the porewater. We attribute the importance of CO2 to the dominant methanogenic pathway we identified, which uses CO2 as a terminal electron acceptor. We propose a mechanistic relationship between PFT patches and porewater CH4 dynamics which, when combined with sources of CH4 loss including methanotrophy, oxidation, or plant‐mediated transport, can provide patch‐scale estimates of CH4 flux. Combining these estimates with the distribution of PFTs can improve ecosystem CH4 flux estimates in heterogenous wetlands and improve global CH4 budgets.

Feeding Damascus goats humic or fulvic acid alone or in combination: in vitro and in vivo investigations on impacts on feed intake, ruminal fermentation parameters, and apparent nutrients digestibility.

In vitro and in vivo experiments were carried out to investigate the effects of the supplementation of different levels of humic and fulvic acids alone or their combination (2:1 ratio) on ruminal fermentation constituents, and nutrients digestibility in goats. The treatments in Exp. 1 were the following: (1) basal substrate (50% concentrate: 50% forage) was incubated humic at 0, 2, 4, and 6g/kg DM; (2) fulvic at 0, 1, 2, and 3g/kg DM; and (3) a combination of humic and fulvic (in a 2:1 ratio) at 0, 3, 6, and 9g/kg DM" of treatments. The results of Exp. 1 revealed that methane (CH4) production was linearly decreased (P < 0.001) upon increasing humic doses. Whereas, the combination of fulvic acid with humic acid resulted in a quadratic decrease (P < 0.001) in net CH4 production. Supplementing humic and fulvic acids, either separately or in combination, resulted in reduced (P < 0.05) ammonia nitrogen (NH3-N) and total volatile fatty acid (VFA) concentrations. In Exp. 2 to further examine the findings obtained in Exp. 1, forty Damascus non-lactating goats (2-3years of age and body weight 29 ± 1.5kg) were fed the same basal diet as in Exp. 1, plus one of four treatments. Treatments were the following: (1) control (no supplement); (2) basal diet plus 5g humic alone; (3) basal diet plus 2.5g fulvic alone, and (4) basal diet plus 7.5g their combination. Goats fed diets supplemented with humic acid, fulvic acid, either alone or in combination, increased concentrations of butyrate (P = 0.003), total VFA (P < 0.001), and improved (P < 0.001) digestibility of nutrients, but reduced (P < 0.001) ruminal NH3-N concentrations. In conclusion, applying humic and fulvic acids alone or in combination attenuated in vitro CH4 production, while improved intake and diet digestibility without adverse effect on rumen fermentation profiles in Damascus goats.

Potential of graded doses of neem (Azadirachta indica) seed oil on ruminal fermentation characteristics, degradability, and methane formation in vitro

Abstract Neem (Azadirachta indica) belongs to Meliaceae family, represented mainly by trees, and widely cultivated and adapted in many tropical regions. The objective of this study was to evaluate the effect of increasing doses of neem seed oil (NSO) on ruminal methane (CH4) formation, diet degradability, and fermentation characteristics after 24 h of in vitro incubation. Treatments were randomly designed to four doses of NSO supplemented to the basal diet (0, 20, 40, or 60 ml/kg DM). Increasing NSO dose resulted in a quadratic decrease (P &lt; 0.05) in net gas (expressed as ml/g DM and ml/g TDOM) and CH4 (expressed as ml/g TDNDF) production, while CH4 (expressed as ml/g TDOM), acetate and propionate proportions decreased linearly confirming a dose-related effect. A quadratic increase in TDOM and linear increase (P = 0.023) in DNDF, NH3-N concentrations, and total protozoal counts were observed. However, a linear increase (P = 0.009) was found in the ruminal butyrate proportion and partitioning factor as dietary NSO supplementation increased. In conclusion, dietary NSO supplementation mediated some desirable fermentation patterns, reducing ruminal NH3-N concentration and CH4 production with some adverse effects on fiber degradability. However, practical research under long-term conditions is required for further investigation.

Contribution of periphytic biofilm of paddy soils to carbon dioxide fixation and methane emissions

Rice paddies are major contributors to anthropogenic greenhouse gas emissions via methane (CH4) flux. The accurate quantification of CH4 emissions from rice paddies remains problematic, in part due to uncertainties and omissions in the contribution of microbial aggregates on the soil surface to carbon fluxes. Herein, we comprehensively evaluated the contribution of one form of microbial aggregates, periphytic biofilm (PB), to carbon dioxide (CO2) and CH4 emissions from paddies distributed across three climatic zones, and quantified the pathways that drive net CH4 production as well as CO2 fixation. We found that PB accounted for 7.1%–38.5% of CH4 emissions and 7.2%–12.7% of CO2 fixation in the rice paddies. During their growth phase, PB fixed CO2 and increased the redox potential, which promoted aerobic CH4 oxidation. During the decay phase, PB degradation reduced redox potential and increased soil organic carbon availability, which promoted methanogenic microbial community growth and metabolism and increased CH4 emissions. Overall, PB acted as a biotic converter of atmospheric CO2 to CH4, and aggravated carbon emissions by up to 2,318 kg CO2 equiv ha−1 season−1. Our results provide proof-of-concept evidence for the discrimination of the contributions of surface microbial aggregates (i.e., PB) from soil microbes, and a profound foundation for the estimation and simulation of carbon fluxes in a potential novel approach to the mitigation of CH4 emissions by manipulating PB growth.

Wetland microtopography alters response of potential net CO2 and CH4 production to temperature and moisture: Evidence from a laboratory experiment

Coastal wetlands store significant amounts of carbon (C) belowground, which may be altered through effects of rising temperature and changing hydrology on CO2 and CH4 fluxes and related microbial activities. Wetland microtopography (hummock-hollow) also plays a critical role in mediating plant growth, microbial activity, and thus cycling of C and nutrients and may interact with rising seas to influence coastal wetland C dynamics. Recent evidence suggests that CH4 production in oxygenated surface soils of freshwater wetlands may contribute substantially to global CH4 production, but comprehensive studies linking potential CH4 production to environmental and microbial variables in temperate freshwater forested wetlands are lacking. This study investigated effects of temperature, moisture, and microtopography on potential net CO2 and CH4 production and extracellular enzyme activity (β-glucosidase, xylosidase, phenol oxidase, and peroxidase) in peat soils collected from a freshwater forested wetland in coastal North Carolina, USA. Soils were retrieved from three microsites (hummock, hollow, and subsurface peat soils (approximately 20–40 cm below surface)) and incubated at two temperatures (27 °C and 32 °C) and soil water contents (65% and 100% water holding capacity (WHC)). Hummocks had the highest cumulative potential net CO2 (13.7 ± 0.90 mg CO2-C g soil−1) and CH4 (1.8 ± 0.42 mg CH4-C g soil−1) production and enzyme activity, followed by hollows (8.7 ± 0.91 mg CO2-C g soil−1 and 0.5 ± 0.12 mg CH4-C g soil−1) and then subsurface soils (5.7 ± 0.70 mg CO2-C g soil−1 and 0.04 ± 0.019 mg CH4-C g soil−1). Fully saturated soils had lower potential net CO2 production (50–80%) and substantially higher potential net CH4 production compared to non-saturated soils (those incubated at 65% WHC). Soils incubated at 32 °C increased potential net CO2 (24–34%) and CH4 (56–404%) production under both soil moisture levels compared to those incubated at 27 °C. The Q10 values for potential net CO2 and CH4 production ranged from 1.5 to 2.3 and 3.3–8.8, respectively, and did not differ between any microsites or soil water content. Enrichment of δ13CO2-C was found in saturated soils from all microsites (−24.4 to − 29.7 ‰) compared to non-saturated soils (−31.1 to − 32.4 ‰), while δ13CH4-C ranged from −62 to −55‰ in saturated soils. Together, the CO2 and CH4 δ13C data suggest that acetoclastic methanogenesis is an important pathway for CH4 production in these wetlands. A positive relationship (Adj. R2 = 0.40) between peroxidase activity and CH4 production was also found, indicating that peroxidase activity may be important in providing fermented C substrates to acetoclastic methanogenic communities and contribute to anaerobic C mineralization. These results suggest that changes in temperature and hydrology could stimulate CO2 and CH4 emissions from surface hummock soils, and to a lesser extent from hollow soils, and provide preliminary evidence that hummocks may be a spatially important and unrecognized hotspot for CH4 production.

Algal Organic Matter Drives Methanogen-Mediated Methylmercury Production in Water from Eutrophic Shallow Lakes.

Algal blooms bring massive amounts of algal organic matter (AOM) into eutrophic lakes, which influences microbial methylmercury (MeHg) production. However, because of the complexity of AOM and its dynamic changes during algal decomposition, the relationship between AOM and microbial Hg methylators remains poorly understood, which hinders predicting MeHg production and its bioaccumulation in eutrophic shallow lakes. To address that, we explored the impacts of AOM on microbial Hg methylators and MeHg production by characterizing dissolved organic matter with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and quantifying the microbial Hg methylation gene hgcA. We first reveal that the predominance of methanogens, facilitated by eutrophication-induced carbon input, could drive MeHg production in lake water. Specifically, bioavailable components of AOM (i.e., CHONs such as aromatic proteins and soluble microbial byproduct-like materials) increased the abundances (Archaea-hgcA gene: 438-2240% higher) and activities (net CH4 production: 16.0-44.4% higher) of Archaea (e.g., methanogens). These in turn led to enhanced dissolved MeHg levels (24.3-15,918% higher) for three major eutrophic shallow lakes in China. Nevertheless, our model results indicate that AOM-facilitated MeHg production could be offset by AOM-induced MeHg biodilution under eutrophication. Our study would help reduce uncertainties in predicting MeHg production, providing a basis for mitigating the MeHg risk in eutrophic lakes.

Trace Metal Availability Affects Greenhouse Gas Emissions and Microbial Functional Group Abundance in Freshwater Wetland Sediments.

We investigated the effects of trace metal additions on microbial nitrogen (N) and carbon (C) cycling using freshwater wetland sediment microcosms amended with micromolar concentrations of copper (Cu), molybdenum (Mo), iron (Fe), and all combinations thereof. In addition to monitoring inorganic N transformations (NO3–, NO2–, N2O, NH4+) and carbon mineralization (CO2, CH4), we tracked changes in functional gene abundance associated with denitrification (nirS, nirK, nosZ), dissimilatory nitrate reduction to ammonium (DNRA; nrfA), and methanogenesis (mcrA). With regards to N cycling, greater availability of Cu led to more complete denitrification (i.e., less N2O accumulation) and a higher abundance of the nirK and nosZ genes, which encode for Cu-dependent reductases. In contrast, we found sparse biochemical evidence of DNRA activity and no consistent effect of the trace metal additions on nrfA gene abundance. With regards to C mineralization, CO2 production was unaffected, but the amendments stimulated net CH4 production and Mo additions led to increased mcrA gene abundance. These findings demonstrate that trace metal effects on sediment microbial physiology can impact community-level function. We observed direct and indirect effects on both N and C biogeochemistry that resulted in increased production of greenhouse gasses, which may have been mediated through the documented changes in microbial community composition and shifts in functional group abundance. Overall, this work supports a more nuanced consideration of metal effects on environmental microbial communities that recognizes the key role that metal limitation plays in microbial physiology.

Methane emission offsets carbon dioxide uptake in a small productive lake

AbstractHere, we investigate the importance of net CH4 production and emissions in the carbon (C) budget of a small productive lake by monitoring CH4, CO2, and O2 for two consecutive years. During the study period, the lake was mostly a net emitter of both CH4 and CO2, while showing positive net ecosystem production. The analyses suggest that during the whole study period, 32% ± 26% of C produced by net ecosystem production was ultimately converted to CH4 and emitted to the atmosphere. When converted to global warming potential, CH4 emission (in CO2 equivalents) was about 3–10 times higher than CO2 removal from in‐lake net ecosystem production over 100‐yr and 20‐yr time frames, respectively. Although more work in similar systems is needed to generalize these findings, our results provide evidence of the important greenhouse gas imbalance in human‐impacted aquatic systems.

Evaluating biogeochemical indicators of methanogenic conditions and thermodynamic constraints in peat

Burial of organic matter in deep peat deposits has already been experimentally demostrated to slow down or even inhibit anaerobic decomposition due to lack of diffusive transport and end-product accumulation. However, so far little is known about potential biogeochemical or thermodynamic indicators for the observed inhibition of further decomposition. For example, theoretical energy yields for methanogenesis, hydrogen partial pressures, stable isotope fractionation factors between CO2 and CH4, and electrochemical properties of dissolved organic matter have been proposed as thermodyamic indicators for such inhibition. To test the applicability and explanatory power of these indicators to identify conditions inhibiting organic matter decomposition, we incubated homogenized ombrotrophic peat for 300 days at 20 °C under diffusive flux conditions as control, and compared the observed effects to a treatment with vertical advective transport by water circulation and to a treatment in which both the unsaturated and water-saturated zone of the peat profile were kept anoxic. Results of energy yields of acetoclastic and hydrogenotrophic methanogenesis were compared to hydrogen partial pressures, to 13C isotope fractionation factors and to redox properties of dissolved organic matter as obtained from mediated electrochemical oxidation and reduction. While CO2 and CH4 production slowed substantially in the deep peat profile, a concomitant decrease of Gibs free energy yields available to hydrogenotrophic and acetoclastic methanogensis and hydrogen and acetate concentrations over time supported a thermodynamic constraint on methanogenesis. Although, energy yields for the hydrogenotrophic pathway were close to or below the theoretical energy minimum levels already after 15 days. Transiently elevated H2 concentrations, not related to actual methanogenesis rates were observed for about 150–225 days. Thereafter, hydrogen concentrations diminished to levels below thresholds to thermodynamically support ongoing methanogenesis. Thus even on incubation timescales of 150–225 days, steady-state hydrogen concentrations as would be expected from thermodynamic considerations did not adjust on the bulk scale of observation. Gibbs free energy estimates for methanogenesis based on hydrogen partial pressures were consequently biased and did not reach the minimum required threshold despite ovious net CH4 production. Ratios between electron accepting (EAC) and donating (EDC) capacity of dissolved organic matter, however, turned out to provide suitable indicators of predominant redox conditions along gradients, stabilizing at low values upon onset of methanogenesis. Thus, our study demonstrated that the thermodynamically driven slow down of decomposition in deep peat deposits, preventing the peat to decompose further, cannot be easily identified based on a single indicator. However, constant and high concentrations of decomposition end-products, indicating zero net turnover and low energy yields, and constantly low EAC/EDC ratios, indicating no further availability of terminal electron acceptors, seem to be characteristic of the onset of conditions inhibiting further significant decomposition of peat.

Potentials of patchouli (Pogostemon cablin) essential oil on ruminal methanogenesis, feed degradability, and enzyme activities in vitro.

The effects of patchouli essential oil (PEO) as an alternative to antibiotics on ruminal methanogenesis, feed degradability, and enzyme activities were evaluated. The basal substrate was incubated without additives (control, CTL) and with monensin (MON, 6 μM/g DM) or patchouli essential oil (PEO, 90 μg/g DM) for 24 h. In three different runs, the gas production (GP) was recorded at 2, 4, 8, 12, and 24 h of incubation using a semi-automatic system. The results revealed that MON had decreased (P < 0.05) the net GP and CH4 production and digestible and metabolizable energy relative to PEO supplementation. The in vitro truly degraded organic matter was not influenced by PEO application, while was reduced (P = 0.027) with MON. Both PEO and MON had similar reducing effect on the activity of carboxymethylcellulase (P = 0.030), in vitro truly degraded neutral detergent fiber (P = 0.010), NH3-N concentrations (P = 0.012), acetate proportion (C2, P = 0.046), C2 to C3 ratio (P = 0.023), and total protozoal count (P = 0.017). Both additives recorded similar elevating potential on the α-amylase activity (P = 0.012), propionate (C3) proportion (P = 0.011), and microbial protein (P = 0.034) compared with CTL. Effects of MON and PEO on ruminal feed degradability, microbial enzyme activities, and total protozoa counts may be responsible for modifying rumen fermentation ecology. Addition of PEO may act as a desirable alternative rumen modifier for MON in ruminant diets.

Century-scale time since permafrost thaw affects temperature sensitivity of net methane production in thermokarst-lake and talik sediments.

Permafrost thaw subjects previously frozen soil organic carbon (SOC) to microbial degradation to the greenhouse gases carbon dioxide (CO2) and methane (CH4). Emission of these gases constitutes a positive feedback to climate warming. Among numerous uncertainties in estimating the strength of this permafrost carbon feedback (PCF), two are: (i) how mineralization of permafrost SOC thawed in saturated anaerobic conditions responds to changes in temperature and (ii) how microbial communities and temperature sensitivities change over time since thaw. To address these uncertainties, we utilized a thermokarst-lake sediment core as a natural chronosequence where SOC thawed and incubated in situ under saturated anaerobic conditions for up to 400 years following permafrost thaw. Initial microbial communities were characterized, and sediments were anaerobically incubated in the lab at four temperatures (0 °C, 3 °C, 10 °C, and 25 °C) bracketing those observed in the lake's talik. Net CH4 production in freshly-thawed sediments near the downward-expanding thaw boundary at the base of the talik were most sensitive to warming at the lower incubation temperatures (0 °C to 3 °C), while the overlying sediments which had been thawed for centuries had initial low abundant methanogenic communities (< 0.02%) and did not experience statistically significant increases in net CH4 production potentials until higher incubation temperatures (10 °C to 25 °C). We propose these observed differences in temperature sensitivities are due to differences in SOM quality and functional microbial community composition that evolve over time; however further research is necessary to better constrain the roles of these factors in determining temperature controls on anaerobic C mineralization.

Influence of water column stratification and mixing patterns on the fate of methane produced in deep sediments of a small eutrophic lake

AbstractMethane (CH4), a potent greenhouse gas, is produced in and emitted from lakes at globally significant rates. The drivers controlling the proportion of produced CH4 that will reach the atmosphere, however, are still not well understood. We sampled a small eutrophic lake (Soppensee, Switzerland) in 2016–2017 for CH4 concentrations profiles and emissions, combined with water column hydrodynamics to investigate the fate of CH4 produced in hypolimnetic sediments. Using a mass balance approach for the periods between April and October of both years, net CH4 production rates in hypolimnetic sediments ranged between 11.4 and 17.7 mmol m−2 d−1, of which 66–88% was stored in the hypolimnion, 13–27% was diffused to the epilimnion, and 6–7% left the sediments via ebullition. Combining these results with a process‐based model we show that water column turbulent diffusivity (K z) had a major influence on the fate of produced CH4 in the sediments, where higher K z values potentially lead to greater proportion being oxidized and lower K z lead to a greater proportion being stored. During fall when the water column mixes, we found that a greater proportion of stored CH4 is emitted if the lake mixes rapidly, whereas a greater proportion will be oxidized if the water column mixes more gradually. This work highlights the central role of lake hydrodynamics in regulating CH4 dynamics and further suggests the potential for CH4 production and emissions to be sensitive to climate‐driven alterations in lake mixing regimes and stratification.

Assessment of using dried vinasse rice to replace soybean meal in lambs diets: In vitro, lambs performance and economic evaluation

Effects of replacing soybean meal (SBM) with dried vinasse rice (DVR) as an alternative source of protein were evaluated under in vitro and in vivo conditions. Protein from SBM was partially replaced by DVR protein at the levels of zero (DVR0) control, 250 (DVR250), 500 (DVR500) and 750 g (DVR750) of the original concentration. An in vitro semi-automatic system was employed to evaluate gas production, feed degradability and fermentation profile of diets. The ANOVA and regression coefficients indicated that the DVR effective level was 500 g/kg DM. An in vivo experiment on twelve Texel lambs (BW; 30.48 ± 0.45 kg) kept individually in wooden pens and allotted into randomized complete block design with 6 blocks by 2 treatments as: control (diet without DVR) and DVR (500 g/kg DM) lasted for 60 days, and the subsequent 7 days were assigned for the digestibility trial. Upon increasing dietary DVR, net CH4 production decreased quadratically (P < 0.05). Ruminal NH3-N concentration and total protozoal count decreased linearly (P < 0.05) as DVR levels increased. In vitro microbial protein and propionate proportion (C3) increased quadratically (P = 0.027 and P = 0.034, respectively), while total short chain fatty acids, acetate (C2) butyrate, isobutyrate and C2:C3 ratio decreased quadratically (P = 0.036, P = 0.020, P = 0.029, P = 0.046 and P = 0.042, respectively). Lambs fed 500 g DVR/kg DM showed higher (P < 0.001) daily gain, body weight, feed efficiency and crude protein digestibility compared to control. The DVR diet showed higher (P < 0.05) digestible, metabolizable and net energy than control. DVR500 diet reduced (P < 0.001) feed costs and increased (P < 0.001) the net profit compared to control. The use of DVR provides a promising source of both protein and energy for growing lambs with extra potentials for economic advantages without adverse effects on growth performance.

Methane Cycling Contributes to Distinct Patterns in Carbon Stable Isotopes of Wetland Detritus

Increasing global temperatures are changing the balance between carbon sequestration and its microbial processing in wetlands, making the tracking of these processes important. We used detrital carbon stable isotopes (δ13C) to trace aerobic decomposition and CH4 production in two experiments conducted in Alaskan wetlands. In laboratory bottle incubations, larger decreases in detritus δ13C corresponded to higher net CH4 and CO2 production rates. Because net CH4 production was the stronger predictor and its effect was negative, we hypothesize that decreases in δ13C trace concurrent CH4 production and oxidation. In a field experiment, decreases in detritus δ13C were not correlated with aerobic decomposition rates, but were positively correlated with CH4 production potentials as estimated from bottle incubations. We hypothesize that the positive relationship reflects only CH4 production, rather than concurrent production and oxidation. Although CH4 production rates were correlated with changes in detrital δ13C in both experiments, the direction of this relationship differed between laboratory and field with important consequences for the scale of ecological experiments. Our study demonstrates that CH4 cycling can create distinct patterns in δ13C of wetland detritus. Future studies should conduct explicit mass balance experiments to clarify mechanisms and determine the importance of scale in shaping isotopic patterns.

Interannual Variability of Methane and Nitrous Oxide in the North Pacific Subtropical Gyre

AbstractThe temporal variability of two important greenhouse gases, methane (CH4) and nitrous oxide (N2O), is reported for the upper water column at Station ALOHA in the North Pacific Subtropical Gyre. Measured concentrations of N2O conform to predicted values with an increase in saturation during the summer period. In contrast, CH4 is less predictable and shows an approximate 2 year transition from a state of oversaturation in surface waters to equilibrium values in 2015, implying a change in net CH4 production. The decrease in CH4 followed on from fluctuations in phosphate concentrations supporting the hypothesized link between microbial metabolism of phosphorus and the global biogeochemical cycle of CH4. At this current time, future trends in the net CH4 production in the North Pacific Subtropical Gyre are uncertain and specifically whether the surface ocean will be a net source or sink for CH4.

An investigation of ultrasound effect on digestate solubilization and methane yield

In this study, different ultrasound power intensities of 0.05–0.21kW/L (4.13–16.52kWh/kg TS) were applied at a frequency of 20kHz and for durations of 5–20min to digestate obtained from a domestic wastewater treatment plant. The ultrasonic effect on digestate solubilization was revealed by increased levels of soluble Chemical Oxygen Demand (sCOD), soluble Total Organic Carbon (sTOC), and soluble Total Nitrogen (sTN) released into the solution. The highest material release was achieved at an ultrasonic energy intensity of 0.21kWh/L. Furthermore, the ultrasonic effect on CH4 production was studied using the anaerobic digestion process. The application of ultrasound at 0.05–0.21kWh/L provided 1.6–2.3-fold increase in net CH4 production. Analysis of the energetics of the system showed that only about 4 and 11% of the energy input was recovered in terms of additional CH4 production at 0.21 and 0.05kWh/L, respectively. A comprehensive cost-benefit analysis of the system is required for making a conclusion on the feasibility of the system, and such analysis should include environmental, economic, and societal benefits of the system, among others.