Effects of carbon dioxide and methane on methanogenesis

Summary A mixed microbial culture, enriched from sewage sludge, was cultivated on a glucose medium in a high turbulence fermentor at constant temperature, pH and loading rate. Effects of high pCO₂ (0.95 atm) and pCH₄ (0.90 atm) were compared to those of low pCO₂ (0.05 atm) and pCH₄ (0.05 atm). Generally, rapid in creases in pCO₂ resulted in rapid decreases in methane production and, conversely rapid decreases in pCO₂ by N₂-sparging resulted in rapid increases in methane production. Decreased values of methane production were also accompanied by acetic acid accumulation. No inhibiting effects of high pCH₄ were detected. A method to obtain low pCO₂ by gas recycling combined with CO₂-absorption is proposed.     

Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream

Streams draining peatlands export large quantities of carbon in different chemical forms and are an important part of the carbon cycle. Radiocarbon (¹⁴C) analysis/dating provides unique information on the source and rate that carbon is cycled through ecosystems, as has recently been demonstrated at the air–water interface through analysis of carbon dioxide (CO₂) lost from peatland streams by evasion (degassing). Peatland streams also have the potential to release large amounts of methane (CH₄) and, though ¹⁴C analysis of CH₄ emitted by ebullition (bubbling) has been previously reported, diffusive emissions have not. We describe methods that enable the ¹⁴C analysis of CH₄ evaded from peatland streams. Using these methods, we investigated the ¹⁴C age and stable carbon isotope composition of both CH₄ and CO₂ evaded from a small peatland stream draining a temperate raised mire. Methane was aged between 1617 and 1987 years BP, and was much older than CO₂ which had an age range of 303–521 years BP. Isotope mass balance modelling of the results indicated that the CO₂ and CH₄ evaded from the stream were derived from different source areas, with most evaded CO₂ originating from younger layers located nearer the peat surface compared to CH₄. The study demonstrates the insight that can be gained into peatland carbon cycling from a methodological development which enables dual isotope (¹⁴C and ¹³C) analysis of both CH₄ and CO₂ collected at the same time and in the same way.     

Methanofuran (carbon dioxide reduction factor), a formyl carrier in methane production from carbon dioxide in Methanobacterium

Methanofuran (carbon dioxide reduction factor) became labeled when incubated in cell extracts of Methanobacterium under hydrogen and 14CO2 in the absence of methanopterin. Proton NMR spectroscopy revealed that a formyl group was bound to the primary amine of methanofuran. [14C]Formylmethanofuran was enzymically converted to 14CH4 in the presence of CH3-S-CoM [2-(methylthio)ethanesulfonic acid], hydrogen, and methanopterin, establishing the formyl moiety as an intermediate in methanogenesis. In the absence of methanopterin, a substantial portion of the formyl label was oxidized to 14CO2 rather than reduced to 14CH4, consistent with a model in which the C1 intermediate is first bound to methanofuran and then to methanopterin, during its reduction. When CH3-S-CoM was replaced by HS-CoM (2-mercaptoethanesulfonic acid), most of the formyl label was oxidized to 14CO2, indicating that methyl group reduction by the CH3-S-CoM methylreductase is required for the conversion of formylmethanofuran to methane.     

舍饲绵羊甲烷和二氧化碳的日排放动态

运用密闭呼吸代谢箱系统,对3只舍饲绵羊24h(有间断)甲烷(CH4)和二氧化碳(CO2)日排放特征进行了研究.供试3只甘肃细毛羊体况相近(平均体重为(25±5)kg),其基础日粮为燕麦干草和玉米精料,粗精比为 6∶4.结果表明:供试绵羊CH4和CO2的平均排放量分别为11g/d和147 g/d,CH4排放的峰值分别出现在17:00和22:00左右,达0.4217g/h和0.8082 g/h,直到0:00降至最小为0.2993g/h;之后趋于平稳,次日8:00左右再次达到排放高峰,排放量为0.6587 g/h.而CO2在各个测定时间段内差异不显著(p＞0.05).因此,舍饲条件下绵羊CH4和CO2排放量动态(g/min)变化不同步.由此,推算出舍饲绵羊(25±5)kg年排放CH4和CO2总量分别约为4.38 kg和53.66 kg.     

Fluxes of methane and carbon dioxide from a small productive lake to the atmosphere

The fluxes of CH₄ and CO₂ to the atmosphere, and the relative contributions of ebullition and molecular diffusion, were determined for a small hypertrophic freshwater lake (Priest Pot, UK) over the period May to October 1997. The average total flux of CH₄ and CO₂ (estimated from 7 sites on the lake) was approximately 52 mmol m^–2 d^–1 and was apportioned 12 and 40 mmol m^–2 d^–1 toCH₄ and CO₂ respectively. Diffusion across the air-water interface accounted for the loss of 0.4and 40 mmol m^–2 d^–1 of CH₄ and CO₂ respectively whilst the corresponding figures for ebullition losses were 12.0 (CH₄) and 0.23 (CO₂) mmol m^–2 d^–1. Most CH₄ (96%) was lost by ebullition, and most CO₂ (99%) by diffusive processes. The ebullition of gas, measured at weekly intervals along a transect of the lake, showed high spatial and temporal variation. The CH₄ content of the trapped gas varied between 44 and 88% (by volume) and was highest at the deepest points. Pulses of gas ebullition were detected during periods of rapidly falling barometric pressure. Therelevance of the measurements to global estimates ofcarbon emission from freshwaters are discussed.     

Influence of drainage basin topography and elevation on carbon dioxide and methane supersaturation of stream water

The partial pressures of CO₂ (pCO₂) andCH₄ (pCH₄) in streams are not only governed byinstream processes, but also by transformations occurring in soil andgroundwater ecosystems. As such, stream water pCO₂ andpCH₄ can provide a tool to assess ecosystem respiration andanaerobic metabolism throughout drainage basins. We conducted three surveyssampling the gas content of streams in eastern Tennessee and western NorthCarolina to assess factors regulating ecosystem metabolism in catchmentswith contrasting geomorphologies, elevations and soil organic matterstorage. In our first survey, the influence of drainage basin geomorphologyon ecosystem respiration was examined by sampling streams drainingcatchments underlain by either shale or dolomite. Geomorphology isinfluenced by geology with shale catchments having shallower soils, broader,unconstrained valley floors compared with dolomite catchments.pCO₂ varied little between catchment types but increased froman average of 3340 ppmv in spring to 9927 ppmv in summer or 9.3 and 28 timesatmospheric equilibrium (pCO_2(equilib)), respectively. Incontrast, pCH₄ was over twice as high in streams drainingshale catchments (306 ppmv; pCH_4(equilib) = 116) compared withmore steeply incised dolomite basins (130 ppmv; pCH_4(equilib)= 51). Using the ratio of pCH₄:pCO₂ as an indexof anaerobic metabolism, shale catchments had nearly twice as muchanaerobiosis (pCH₄:pCO₂ = 0.046) than dolomitedrainages (pCH₄:pCO₂ = 0.024). In our secondsurvey, streams were sampled along an elevational gradient (525 to 1700 m)in the Great Smoky Mountains National Park, USA where soil organic matterstorage increases with elevation. pCO₂ did not vary betweenstreams but increased from 5340 ppmv (pCO_2(equilib) = 15) to8565 ppmv (pCO_2(equilib) = 24) from spring to summer,respectively. During spring pCH₄ was low and constant acrossstreams, but during summer increased with elevation ranging from 17 to 2068ppmv (pCH_4(equilib) = 10 to 1216). The contribution ofanaerobiosis to total respiration was constant during spring(pCH₄:pCO₂ = 0.017) but during summer increasedwith elevation from 0.002 at 524 m to 0.289 at 1286 m. In our last survey,we examined how pCO₂ and pCH₄ changed withcatchment size along two rivers (ca. 60 km stretches in both riverscorresponding to increases in basin size from 1.7–477km² and 2.5–275 km²). pCO₂and pCH₄ showed opposite trends, with pCO₂decreasing ca. 50% along the rivers, whereas pCH₄roughly doubled in concentration downstream. These opposing shifts resultedin a nearly five-fold increase of pCH₄:pCO₂along the rivers from a low of 0.012 in headwaters to a high of 0.266 65-kmdownstream. pCO₂ likely declines moving downstream asgroundwater influences on stream chemistry decreases, whereaspCH₄ may increase as the prevalence of anoxia in riversexpands due to finer-grained sediments and reduced hydrologic exchange withoxygenated surface water.     

Environmental controls on carbon dioxide flux from black spruce coarse woody debris

Carbon dioxide flux from coarse woody debris (CWD) is an important source of CO₂ in forests with moderate to large amounts of CWD. A process-based understanding of environmental controls on CWD CO₂ flux (R_CWD) is needed to accurately model carbon exchange between forests and the atmosphere. The objectives of this study were to: (1) use a laboratory incubation factorial experiment to quantify the effect of temperature (T_CWD), water content (W_C), decay status, and their interactions on R_CWD for black spruce [Picea mariana (Mill.) BSP] CWD; (2) measure and model spatial and temporal dynamics in T_CWD for a boreal black spruce fire chronosequence; and (3) validate the R_CWD model with field measurements, and quantify potential errors in estimating annual R_CWD from this model on various time steps. The R_CWD was positively correlated to T_CWD (R²=0.37, P<0.001) and W_C (R²=0.18, P<0.001), and an empirical R_CWD polynomial model that included T_CWD and W_C interactions explained 74% of the observed variation of R_CWD. The R_CWD estimates from the R_CWD model excellently matched the field measurements. Decay status of CWD significantly (P<0.001) affected R_CWD. The temperature coefficient (Q₁₀) averaged 2.5, but varied by 141% across the 5-42°C temperature range, illustrating the potential shortcomings of using a constant Q₁₀. The CWD temperature was positively correlated to air temperature (R²=0.79, P<0.001), with a hysteresis effect that was correlated to CWD decay status and stand leaf area index . Ignoring this temperature hysteresis introduced errors of -1% to +32% in annual R_CWD estimates. Increasing T_CWD modeling time step from hourly to daily or monthly introduced a 5-11% underestimate in annual R_CWD. The annual R_CWD values in this study were more than two-fold greater than those in a previous study, illustrating the need to incorporate spatial and temporal responses of R_CWD to temperature and water content into models for long-term R_CWD estimation in boreal forest ecosystems.     

Soil environmental variables affecting the flux of methane from a range of forest, moorland and agricultural soils

Measurements of the net methane exchange over a range of forest, moorland, and agricultural soils in Scotland were made during the period April to June 1994 and 1995. Fluxes of CH₄ ranged from oxidation –12.3 to an emission of 6.8 ng m^–2 s^–1. The balance between CH₄ oxidation and emission depended on the physical conditions of the soil, primarily soil moisture. The largest oxidation rates were found in the mineral forest soils, and CH₄ emission was observed in several peat soils. The smallest oxidation rate was observed in an agricultural soil. The relationship between CH₄ flux and soil moisture observed in peats (Flux_{CH 4} = 0.023 × %H₂O (dry weight) – 7.44, p > 0.05) was such that CH₄ oxidation was observed at soil moistures less than 325%( ± 80%). CH₄ emission was found at soil moistures exceeding this value. A large range of CH₄ oxidation rates were observed over a small soil moisture range in the mineral soils. CH₄ oxidation in mineral soils was negatively correlated with soil bulk density (Flux_{CH 4} = –37.35 × bulk density (g cm^–3) + 48.83, p > 0.05). Increased nitrogen loading of the soil due to N fixation, atmospheric deposition of N, and fertilisation, were consistently associated with decreases in the soil sink for CH₄, typically in the range 50 to 80%, on a range of soil types and land uses.     

农田生态系统CO_2通量的转换计算

通过冬小麦单叶CO2 通量与冠层CO2 通量的同步测定 ,发现不同日期净光合速率 (Pn)和冠层CO2 通量 (FCO2 )变化趋势相同 ,但峰值出现的时间不一致 .CO2 浓度差与FCO2 日变化趋势相反 ,CO2 浓度差最小时FCO2达到最大值 ;空气动力学法计算的FCO2 与采用积分法计算的冠层CO2 通量 (Ac)呈明显的倒“U”字型日变化趋势 ,而Ac日变化过程波动性小 ;采用积分法模拟的日同化量与空气动力学法计算日同化量有时相差很小 ,但有时误差大 ,由于模拟冠层通量Ac值只考虑了光强的变化 ,而实际上 ,温度、风速、土壤湿度等变化均对冠层CO2通量产生影响 .     

农田生态系统CO2通量的转换计算

通过冬小麦单叶CO2通量与冠层CO2通量的同步测定,发展不同日期净光合速率（Pn)和冠层CO2通量（Fco2)变化趋势相同,但峰值出现的时间不一致。CO2浓度差与Fco2日变化趋势相反,CO2浓度差最小时FCO2达到最大值;空气动力学法计算的FCO2与采用积分法计算的冠层CO2通量（Ac)呈明显的倒“U”字型日变化趋势,而Ac日变化过程波动性小;采用积分法模拟的日同化量与空气动力学法计算日同化量有时相差很小,但有时误差大,由于模拟冠层通量Ac值只考虑了光强的变化,而实际上,温度,风速,土壤湿度等变化均对冠层CO2通量产生影响。     

土壤有机碳和外源添加碳对水稻土土体呼吸的影响

土体呼吸输出碳来源于土壤固有有机碳和外源添加碳,而以往关于不同施肥措施对水稻土碳排放的研究少有区分碳的来源。本试验利用一个长达30年的水稻土定位试验,在保证原有定位试验继续正常开展的前提下变更部分施肥处理,得到继续施用高量有机肥(HOM)、施用常量有机肥30年后改施高量有机肥(N-H)、继续施用常量有机肥(NOM)、施用化肥30年后改施常量有机肥(C-N)、施用高量有机肥30年后改施化肥(H-C)、施用常量有机肥30年后改施化肥(N-C)、继续施用化肥(CF)等7种施肥处理。通过观测早稻生长期间原有施肥和改施肥处理土体CO2排放通量(FCO2),研究不同后续施肥对水稻土FCO2的影响,以期探讨土壤原始有机碳和外源添加碳对土壤FCO2的影响。结果表明:7种不同施肥处理土体CO2平均排放通量(F珔CO2)分别为85.34、69.10、51.27、49.15、14.89、12.92和11.59 mg C.m-2.h-1;对施用无机肥料和常量有机肥料的土体而言,土壤本身有机碳含量对F珔CO2无显著影响,但对施用高量有机肥的土体而言,土壤本身的高有机碳含量会增强F珔CO2;CO2排放通量(Y)与添加外源碳量(x)之间符合指数方程:Y=13.33e1.719 x(R2=0.967,n=21),施入的外源有机碳对土体FCO2产生极显著影响;当季外源添加碳以CO2-C矿化分解释放的碳占其总碳量的14%左右,且该分解率受土壤有机碳含量和有机物料添加量的影响较小。     

二氧化碳生物转化制甲烷技术研究进展

二氧化碳减量化与转化是当前业界关注及着手解决的重要问题,将二氧化碳作为资源转化为甲烷,有利于环境与社会的可持续发展。本文在分析二氧化碳转化为甲烷技术的基础上,重点介绍了国内外二氧化碳生物转化的研究与进展;总结了二氧化碳生物转化途径及其影响因素,分析了氢营养型、甲基营养型生物转化甲烷机理和生物转化能量来源;探讨了不同产甲烷菌微生物电合成产甲烷和氢气研究进展,总结了微生物电合成法、光合作用法和厌氧消化法等二氧化碳生物转化技术在反应器设计、电极材料选择、工艺条件优化及试验结果评估等方面取得的进展及存在的问题。重点就微生物电合成法的未来研究提出了增强微生物活性、提升氢气利用率、加快高效电极开发、提高能量效率、加强工业废气试验研究和强化光能转化等研究重点和发展方向,同时加强计算机模拟等交叉学科协同创新是促进二氧化碳生物转化技术进步的新方向。     

湿地碳排放及其影响因素

湿地生态系统在全球碳循环中起着重要作用.湿地独特的土壤、水文和植被条件,使得其在低氧环境下能不断累积碳,并同时释放大量温室气体——CH4和CO2,因此湿地的碳排放近年来成为全球气候变化研究关注的重点问题.湿地的土壤状况、水文条件及植被类型的不同导致湿地CH4和CO2的排放具有极强的时空变异性.土壤温度与CH4和CO2排放呈正相关关系;水位条件对湿地温室气体的排放有一定影响,在一定范围内,土壤的厌氧环境导致CH4排放量增大,CO2排放量减小;植被影响到温室气体产生、氧化和排放各个方面,因物种而异.     

Agriculture's impact on microbial diversity and associated fluxes of carbon dioxide and methane

Agriculture has marked impacts on the production of carbon dioxide (CO₂) and consumption of methane (CH₄) by microbial communities in upland soils—Earth''s largest biological sink for atmospheric CH₄. To determine whether the diversity of microbes that catalyze the flux of these greenhouse gases is related to the magnitude and stability of these ecosystem-level processes, we conducted molecular surveys of CH₄-oxidizing bacteria (methanotrophs) and total bacterial diversity across a range of land uses and measured the in situ flux of CH₄ and CO₂ at a site in the upper United States Midwest. Conversion of native lands to row-crop agriculture led to a sevenfold reduction in CH₄ consumption and a proportionate decrease in methanotroph diversity. Sites with the greatest stability in CH₄ consumption harbored the most methanotroph diversity. In fields abandoned from agriculture, the rate of CH₄ consumption increased with time along with the diversity of methanotrophs. Conversely, estimates of total bacterial diversity in soil were not related to the rate or stability of CO₂ emission. These combined results are consistent with the expectation that microbial diversity is a better predictor of the magnitude and stability of processes catalyzed by organisms with highly specialized metabolisms, like CH₄ oxidation, as compared with processes driven by widely distributed metabolic processes, like CO₂ production in heterotrophs. The data also suggest that managing lands to conserve or restore methanotroph diversity could mitigate the atmospheric concentrations of this potent greenhouse gas.     

Floods increase carbon dioxide and methane fluxes in agricultural streams

1. Changes in climate are causing floods to occur more often and more intensely in many parts of the world, including agricultural landscapes of southern Wisconsin (U.S.A.). How flooding and greater flood frequency affect stream carbon dioxide (CO₂) and methane (CH₄) fluxes and concentrations is not obvious. Thus, we asked how diffusive fluxes of CO₂ and CH₄ varied over time, particularly in response to floods, in agricultural streams, and what were likely causes for observed flood responses.
2. We measured concentrations and diffusive fluxes of CO₂ and CH₄ at 10 stream sites in mixed agricultural and suburban catchments in southern Wisconsin (U.S.A.) during the growing season (March–November) in a year that experienced multiple floods. Habitat, hydrologic, and water chemistry attributes were also quantified to determine likely drivers of changes in gas concentrations and fluxes.
3. Habitat and water chemistry, as well as CO₂ and CH₄ concentrations and fluxes were temporally erratic and lacked any seasonality. Carbon dioxide and CH₄ concentrations and fluxes were higher during floods along with increased water velocity, turbidity, and dissolved organic carbon and decreases in dissolved oxygen, soft sediment depth, and macrophyte cover.
4. Increased gas concentrations and fluxes were probably due to flushing of gases from soils, respiration of organic matter in the channel, and increased gas exchange velocities during floods.
5. Flooding alleviated both supply and transfer limits on CO₂ and CH₄ emissions in these agricultural streams, and frequent and prolonged flooding during the growing season led to sustained high emissions from these streams. We hypothesise that such persistent increases in emissions during floods may be a common response to high precipitation periods for many agricultural streams.

     

Bioconversion of carbon dioxide to methane using hydrogen and hydrogenotrophic methanogens

Biogas produced from organic wastes contains energetically usable methane and unavoidable amount of carbon dioxide. The exploitation of whole biogas energy is locally limited and utilization of the natural gas transport system requires CO₂ removal or its conversion to methane. The biological conversion of CO₂ and hydrogen to methane is well known reaction without the demand of high pressure and temperature and is carried out by hydrogenotrophic methanogens. Reducing equivalents to the biotransformation of carbon dioxide from biogas or other resources to biomethane can be supplied by external hydrogen. Discontinuous electricity production from wind and solar energy combined with fluctuating utilization cause serious storage problems that can be solved by power-to-gas strategy representing the production of storable hydrogen via the electrolysis of water. The possibility of subsequent repowering of the energy of hydrogen to the easily utilizable and transportable form is a biological conversion with CO₂ to biomethane. Biomethanization of CO₂ can take place directly in anaerobic digesters fed with organic substrates or in separate bioreactors. The major bottleneck in the process is gas-liquid mass transfer of H₂ and the method of the effective input of hydrogen into the system. There are many studies with different bioreactors arrangements and a way of enrichment of hydrogenotrophic methanogens, but the system still has to be optimized for a higher efficiency. The aim of the paper is to gather and critically assess the state of a research and experience from laboratory, pilot and operational applications of carbon dioxide bioconversion and highlight further perspective fields of research.