Higher CH4 Emissions Research Articles

Effect of improved nitrogen management on greenhouse gas emissions from intensive dairy systems in the Netherlands

Dairy systems in Europe contribute to the emissions of the greenhouse gases (GHGs) nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2). In this paper, the effects of improved nitrogen (N) management on GHG emissions from Dutch dairy farms are determined. The GHG emissions are calculated using the panel on climate change (IPCC) methodology for the Netherlands, an updated and refined IPCC methodology, and a full accounting approach. The changes in dairy farming over the last 20 years, and the consequences for N management are described using detailed farm-level data, collected in 1985, 1997 and 2002. The selected years represent distinct stages in the implementation of N policies. The changes in N management have reduced the GHG emissions. A reduction of the N surplus per kilogram milk with 1 g N reduced the GHG emissions per kilogram milk with approximately 29 g CO2-equivalents. The reduction of the N surpluses was mainly brought about by reduced fertilizer use and reduced grazing time. The use of updated and refined emission factors resulted in higher CH4 emissions and lower N2O emissions. On average, the overall emission was 36% higher with the refined method. Full accounting, including all direct and indirect emissions of CH4, N2O and CO2, increased the emission with 36% compared with the refined IPCC methodology. We conclude that the N surplus at farm level is a useful indicator of GHG emissions. A full accounting system as presented in this study may effectively enable farmers to address the issue of emissions of GHGs in their operational management decisions. Both approaches serve their own specific objectives: full accounting at the farm level to explore mitigation options, and the IPCC methods to report changes in GHG emissions at the national level

Greenhouse gas fluxes during rewetting of peatlands by use of effluents – a lysimeter study

The present study aims at assessing the effect of using the effluent of a wastewater treatment plant as an alternative measure for rewetting nutrient-rich fen soils over the growing season on the emission of greenhouse gas (GHG) and at discussing possible changes in the greenhouse potential as a result of this practice. In order to allow a discussion on GHG based on integrated CH4, N2O, and CO2 flux rates, fluxes were measured in our lysimeter study using the chamber methodology from May to December in 2003 and 2004. The study compares the gaseous fluxes of fen soils in lysimeters treated with the effluent and/or freshwater for rewetting. Only freshwater was applied to the control lysimeter. The source of water hardly had any statistically significant effect on trace gas fluxes. However, there was a trend towards higher CH4 emissions at the effluent lysimeters compared to the control lysimeter. Effluent usage did not decrease the greenhouse effect at the same rate, which could be observed at the control. Nevertheless, regarding gaseous emissions the use of effluents could prove to be a solution to the current problem of today's major peat oxidation and fen soil loss by drainage.

Enteric methane emissions from backgrounded cattle consuming all-forage diets

To quantify enteric methane (CH4) emissions of growing cattle consuming allforage diets, a field study utilizing 144 British × Continental crossbred steers (262 ± 4 kg) was conducted during an 84-d overwintering period followed by a 56-d grazing period in one of two, grass-based pastures. Enteric CH4 emissions were quantified using the sulphur hexaflouride (SF6) tracer gas technique. During the overwintering period, four qualities of chopped alfalfa-grass silage, ranging in NDF content from 46.4 to 60.8%, DM basis, were utilized. Steers fed the lowest quality forage (60.8% NDF) had lower DMI, (6.8 ± 0.4 kg head-1, P = 0.0075) and lower ADG (0.83 ± 0.03 kg d-1, P = 0.0028) compared with those fed higher quality forage whose intake ranged from 8.2 to 9.1 ± 0.4 kg d-1, with gains ranging from 1.00 to 1.06 ± 0.03 kg d-1. Enteric emissions (% GE intake) were not influenced by forage quality across this range of NDF values; however, CH4 losses did decrease from 6.8 to 4.7 ± 0.3% GE intake as the winter period progressed. Increased DMI, accompanied by a decrease in the proportion of feed energy lost as enteric CH4 emissions, suggests that utilization of the lower-quality forage improved as steers reached higher body weights. Emissions were influenced by pasture quality and availability, as highest CH4 emissions (11.3% GE intake, P = 0.0005) were observed when quality was low and DM availability was limited (738 kg ha-1). This study demonstrates that growing cattle consuming all-forage diets typical of those utilized in Western Canada during the winter feeding period will lose 5.1 to 5.9% of feed energy as CH4. Further, it has shown that emissions from growing cattle on grass-based pastures may exceed 10% GE intake – a value that is greater than those previously reported for growing cattle grazing legume-based pastures. Key words: Enteric methane emissions, cattle, forage, backgrounding, pasture

Effect of improved nitrogen management on greenhouse gas emissions from intensive dairy systems in the Netherlands

AbstractDairy systems in Europe contribute to the emissions of the greenhouse gases (GHGs) nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2). In this paper, the effects of improved nitrogen (N) management on GHG emissions from Dutch dairy farms are determined. The GHG emissions are calculated using the panel on climate change (IPCC) methodology for the Netherlands, an updated and refined IPCC methodology, and a full accounting approach.The changes in dairy farming over the last 20 years, and the consequences for N management are described using detailed farm‐level data, collected in 1985, 1997 and 2002. The selected years represent distinct stages in the implementation of N policies. The changes in N management have reduced the GHG emissions. A reduction of the N surplus per kilogram milk with 1 g N reduced the GHG emissions per kilogram milk with approximately 29 g CO2‐equivalents. The reduction of the N surpluses was mainly brought about by reduced fertilizer use and reduced grazing time. The use of updated and refined emission factors resulted in higher CH4 emissions and lower N2O emissions. On average, the overall emission was 36% higher with the refined method. Full accounting, including all direct and indirect emissions of CH4, N2O and CO2, increased the emission with 36% compared with the refined IPCC methodology.We conclude that the N surplus at farm level is a useful indicator of GHG emissions.A full accounting system as presented in this study may effectively enable farmers to address the issue of emissions of GHGs in their operational management decisions. Both approaches serve their own specific objectives: full accounting at the farm level to explore mitigation options, and the IPCC methods to report changes in GHG emissions at the national level.

A comparison of methane flux in a boreal landscape between a dry and a wet year

We used field measurements of methane (CH4) flux from upland and wetland soils in the Northern Study Area (NSA) of BOREAS (BOReal Ecosystem‐Atmosphere Study), near Thompson, Manitoba, during the summers of 1994 and 1996 to estimate the overall CH4 emission from a 1350 km2 landscape. June–September 1994 and 1996 were both drier and warmer than normal, but summer 1996 received 68 mm more precipitation than 1994, a 40% increase, and had a mean daily air temperature 0.6°C warmer than 1994. Upland soils consumed CH4 at rates from 0 to 1.0 mg m−2 d−1, with small spatial and temporal variations between years, and a weak dependence on soil temperature. In contrast, wetlands emitted CH4 at seasonal average rates ranging from 10 to 350 mg CH4 m−2 d−1, with high spatial and temporal variability, and increased an average of 60% during the wetter and warmer 1996. We used Landsat imagery, supervised classification, and ground truthing to scale point CH4 fluxes (<1 m2) to the landscape (>1000 km2). We performed a sensitivity analysis for error terms in both areal coverage and CH4 flux, showing that the small areas of high CH4 emission (e.g., small ponds, graminoid fens, and permafrost collapse margins) contribute the largest uncertainty in both flux measurements and mapping. Although wetlands cover less than 30% of the landscape, areally extrapolated CH4 flux for the NSA increased by 61% from 10 to16 mg CH4 m−2 d−1 between years, entirely attributed to the increase in wetland CH4 emission. We conclude that CH4 fluxes will tend to be underestimated in areas where much of the landscape is covered by wetlands. This is due to the large spatial and temporal variability encountered in chamber‐based measurements of wetland CH4 fluxes, strong sensitivity of wetland CH4 emission to small changes in climate, and because most remote sensing images do not adequately identify small areas of high CH4 flux.

Emission and oxidation of methane in Equisetum fluviatile stands growing on organic sediment and sand bottoms

Methane emission and rhizospheric CH4 oxidation were studied in stands of Equisetum fluviatile, a common cryptogam in boreal lakes. The experiment was performed in mesocosms with organic sediment or sand bottoms under natural variation of temperature and light using the light-oxic – dark-anoxic chamber (LO/DA) technique. Net CH4 emission from the organic sediment during the growing season varied between 3.4 and 19.0 mg m−2 h−1, but from sand the net CH4 emission was only 3–10% of that measured from the organic sediment. In the organic sediment net CH4 emission was very significantly correlated with sediment temperature (r2 = 0.92). In the sand mesocosms the variation of net CH4 emission was better correlated with the shoot biomass than with sediment temperature variation during the growing season, indicating that methanogens were severely limited by substrate availability and were probably dependent on substrates produced by E. fluviatile. The proportion of the methane oxidized of the potential CH4 emission in summer did not differ significantly between the bottom types. The net CH4 emission during the growing season as a proportion of the seasonal maximum of the shoot biomass was significantly higher in the organic sediment mesocosms (6.5%) than in sand (1.7%). The high CH4 emissions observed from dense well-established E. fluviatile stands in the field appear to be more related to temperature-regulated turnover of detritus in the anaerobic sediment and less to CH4 oxidation and seasonal variation in plant growth dynamics

Carbon dynamics of wetland in the Sanjiang plain

Methane (CH4) and carbon dioxide (CO2) emission was measured from mires in the Sanjiang Plain, Northeast China, by using a static chamber technique during free snow-covered periods. The seasonal mean emission of CH4 was 12.4mg/(m2·h) and the emission range of CO2 was 8.7–16.6g/(m2·d) (gross CO2 flux) during plant growth period. CO2 emission rate in the day was stronger than that at night, and the daily peak appears at 19:00. The mire plants in the Sanjiang Plain begin to sprout at the end of April. The aboveground biomass of the mire plants increased from zero to the peak from July to September and showed single peak form. The aboveground biomass of Carex lasiocarpa (464.8g/m2) was lower than that of Deyeuxia platyphylla (530.8g/m2), but the underground biomass was higher than that of Deyeuxia platyphylla. Gross CO2 flux showed the significance positive correlation relationship with plant biomass. Gross CO2 flux and CH4 emission were also correlated with soil temperature (0–5cm) and water temperature. However, the highest CH4 emission rate lagged behind the highest soil temperature in the root area during plant growth period. The data also indicated that wet and warm conditions during the early spring led to greater value of CH4 emission flux. Inundation is the necessary condition for the existence of methane bacteria, but there is no significant positive correlation between the inundation depth and CH4 emission rate in this region. Within the same growing season and under the same inundation condition, the variations of CH4 emission rate could be markedly different.

Optimizing grain yields reduces CH4 emissions from rice paddy fields.

Microbial production in anoxic wetland rice soils is a major source of atmospheric CH4 the most important non-CO2 greenhouse gas. Much higher CH4 emissions from well managed irrigated rice fields in the wet than in the dry season could not be explained by seasonal differences in temperature. We hypothesized that high CH4 emissions in the wet season are caused by low grain to biomass ratios. In a screenhouse experiment, removing spikelets to reduce the plants' capacity to store photosynthetically fixed C in grains increased CH4 emissions, presumably via extra C inputs to the soil. Unfavorable conditions for spikelet formation in the wet season may similarly explain high methane emissions. The observed relationship between reduced grain filling and CH4 emission provides opportunities to mitigate CH4 emissions by optimizing rice productivity.

Effects of rice cultivars on methane fluxes in a paddy soil

CH4 emission and its relevant processes involved (i.e. CH4 production, rhizospheric CH4 oxidation and plant-mediated CH4 transport) were studied simultaneously to comprehensively understand how rice cultivars (Yanxuan, 72031, and 9516) at growth stages (early and late tillering, panicle initiation, ripening, and harvest stage) affect CH4 emission in a paddy soil. Over the entire rice-growing season, Yanxuan had the highest CH4 emission flux with 5.98 μg CH4 m−2 h−1 followed by 72031 (4.48 μg CH4 m−2 h−1) and 9516 (3.41 μg CH4 m−2 h−1). The highest CH4 production rate of paddy soils planted to Yanxuan was observed with 18.0 μg CH4 kg{ (d.w.soil)} h−1 followed by the soil planted to 9516 (17.5 μg CH4 kg{ (d.w.soil)} h−1). For each cultivar, both rhizospheric CH4 oxidation ability and plant-mediated CH4 transport efficiency varied widely with a range of 9.81–76.8% and 15.5–80.5% over the duration of crop growth, respectively. Multiple regression analyses showed that CH4 emission flux was positively related with CH4 production rate and rice plant-mediated CH4 transport efficiency, but negatively with rhizospheric CH4 oxidation (R 2=0.425 for Yanxuan, P<0.01; R 2=0.426 for 72031, P<0.01; R 2=0.564 for 9516, P<0.01). The contribution of rice plants to CH4 production seems to be more important than to rhizospheric CH4 oxidation and plant-mediated transport in impact of rice plants on CH4 emission.

Effect of rice plants on CH4 production, transport, oxidation and emission in rice paddy soil

To understand the integrated effects of rice plants (variety Wuyugeng 2) on CH4 emission during the typical rice growth stage, the production, oxidation and emission of methane related to rice plants were investigated simultaneously through laboratory and greenhouse experiments. CH4 emission was significantly higher from the rice planted treatment than from the unplanted treatment. In the rice planted treatment, CH4 emission was higher at tillering stage than at panicle initiation stage. An average of 36.3% and 54.7% of CH4 produced was oxidized in the rhizosphere at rice tillering stage and panicle initiation stage, respectively, measured by using methyl fluoride (MF) technique. In the meantime, CH4 production in the planted treatments incubated under O2-free N2 condition was reduced by 44.9 and 22.3%, respectively, compared to unplanted treatment. On the contrary, the presence of rice plants strongly stimulated CH4 production by approximately 72.3% at rice ripening stage. CH4 emission through rice plants averaged 95% at the tillering stage and 89% at the panicle initiation stage. Based on these results, conclusions are drawn that higher CH4 emission from the planted treatment than from unplanted treatment could be attributed to the function of rice plants for transporting CH4 from belowground to the atmosphere at tillering and panicle initiation stage, and that a higher CH4 emission at tillering stage than at panicle initiation stage is due to the lower rhizospheric CH4 oxidation and more effective transport mediated by rice plants.

Estimation of regional methane emission from rice fields using simple atmospheric diffusion models

Two atmospheric diffusion models, the box model and the ATDL (Atmospheric Turbulent and Diffusion Laboratory) model, were used to calculate regional methane (CH4) emissions of rice fields in the Beijing area. Compared with conventional closed chamber measurements, the box model overestimated CH4 emission because of meteorological conditions—the ground inverse layer was not favorable for the application of the model during the rice-growing season. The ATDL model, on the other hand, handled this unfavorable meteorological condition and gave reasonable CH4 emission estimates (about 6.1—8.5 mg m-2h-1) close to conventional measurements (about 0.314.3 mg m-2h-1) in June, a period generally characterized by significant CH4 emission from rice fields. In September, CH4 emission as measured with closed chambers was negligible (about 0–0.3 mg m-2h-1), but the ATDL model still calculated it to be about 2.8–5.3 mg m-2h-1albeit at a low level and considerably below the June emission level. This discrepancy cannot be explained at present and needs further study. Most likely causes are measurement artifacts and/or the presence of minor local CH4 sources (ditches, field depressions) in the study area. The application of atmospheric diffusion models for regional CH4 emission estimation depends greatly on meteorological conditions. Moreover, the models tend to give much more reliable results during periods of rather high CH4 emission. This coincides with the time that such regional CH4 emission estimates are most valuable. The atmospheric diffusion models complement the closed chamber method by providing integrated CH4 emission estimates from 1-100-km2 rice areas. Detailed information about agricultural management of rice fields and other potential CH4 sources within the study region are necessary to better understand the integrated regional emission estimates.

CH4 emission from a hollow-ridge complex in a raised bog: The role of CH4 production and oxidation

The aim of this study was to correlate magnitude andcontrols of CH4 fluxes with the microtopographyand the vegetation in a hollow-ridge complex of araised bog. High CH4 emission rates were measuredfrom hollows and mud-bottom hollows, while hummocksconsumed atmospheric CH4 at a low rate. Thehighest emissions were measured from plots with Eriophorum vaginatum and Scheuchzeriapalustris. CH4 emission ceased after Scheuchzeria had been clipped below the water table,indicating the importance of this aerenchymatic plantas a conduit for CH4. Peat in the upper catotelm of hollows was younger andless decomposed than in hummocks. Potential CH4production in vitro was higher and themethanogenic association was better adapted to highertemperatures in hollow than in hummock peat. Highertemperatures in hollows resulted in a strongerCH4 source in hollows than in hummocks. Negativefluxes from hummocks indicated that even in wetlandsmethanotrophic bacteria exist that are able to oxidizeCH4 at atmospheric mixing ratios, and thatoxidation controls CH4 emission completely. TheCH4 mixing ratio was low in the acrotelm, but itincreased within the catotelm. Comparing fluxesmeasured in static chambers with fluxes calculatedfrom the porewater CH4 profiles it was deducedthat the zone of methane oxidation was located closeto the water table. In hollows, CH4 production at in situtemperature was far higher than emission into theatmosphere, corresponding to an oxidation rate ofnearly 99%. The CH4 flux between the catotelmand the acrotelm of hollows was also higher than theemission, indicating the importance of CH4oxidation in the aerobic acrotelm, too. CH4microprofiles showed that CH4 oxidation inmud-bottom hollows was confined to the topmost 2 mm,and that in Sphagnum-covered hollows CH4oxidation occurred at the lower edge of green Sphagnum-parts.

Methane transport capacity of rice plants. I. Influence of methane concentration and growth stage analyzed with an automated measuring system.

A major portion (60–90%) of the methane (CH4) emitted from rice fields to the atmosphere is transported through the aerenchyma of the rice plants. However, a rapid and accurate method to study the CH4 transport capacity (MTC) of rice plants is not available. We developed a gas sampling and analytical device based on a closed two-compartment chamber technique and analyzed the enrichment of the CH4 mixing ratio inside the shoot compartment of cylindrical cuvettes enclosing individual rice plants under ambient conditions. The computer-controlled analytical system consists of a gas chromatograph (GC) and a pressure-controlled autosampler for eight cuvettes (seven for plants and one for CH4-calibration gas). The system automates closure and opening of plant cuvettes using pneumatic pressure, air sample collection and injection into the GC, and CII, analysis. It minimizes sources of error during air sampling by continuously mixing headspace air of each cuvette, maintaining pressure and composition of the headspace inside the cuvettes, purging the dead volumes between the sampler induction tube and GC, and running a reference CH4-calibration gas sample in each cycle. Tests showed that the automated system is a useful tool for accurate sampling of headspace air of cylindrical cuvettes enclosing individual rice plants and enables rapid and accurate fully automated analysis of CH4 in the headspace air samples. A linear relationship was obtained between CH4 transported by rice plants of two cultivars (1872, a high-yielding dwarf, and Dular, a traditional tall cultivar) and concentration of CH4 up to 7,500 ppm used for purging the nutrient culture solution surrounding the roots in the root compartment of the chamber. Further increase in CH4 emission by shoots was not observed at 10,000 ppm CH4 concentration in the root compartment of the chamber. The MTC of 1872 was measured at six development stages; it was lowest at seedling stage, increasing gradually until panicle initiation. There was no further change at flowering, but a marked decrease at maturity was noted. These results suggest that the plants have 45–246% greater potential to transport CH4 than the highest CH4 emission rates reported under field conditions, and plants would not emit CH4 at early growth and at a reduced rate close to ripening.

Factors influencing nitrous oxide and methane emissions from minerotrophic fens in northeast Germany

At two field sites representing northeastern German minerotrophic fens (Rhin-Havelluch, a shallow peat site; Gumnitz, a partially drained peat site) the influence of different factors (N fertilization, groundwater table, temperature) on N2O and CH4 emissions was investigated. The degraded fens were sources or sinks of the radiatively active trace gases investigated. The gas fluxes measured were much higher than those found in other terrestrical ecosystems such as forests. Lowering the groundwater table increased the release of N2O and the oxidation of CH4. High CH4 emission rates occurred when the groundwater tables and soil temperatures were high (>12 °C). N fertilization stimulated the release of N2O only when application rates were very high (480 kg N ha–1). A moderate N supply (60 or 120 kg N ha–1) hardly increased the release of N2O in spite of high soluble soil NO3 – contents.

Methane and hydrogen production in a termite‐symbiont system

Methane and hydrogen emission rates and the δ13C of CH4 were observed for various termites in Australia, Thailand and Japan. Combined with the already reported emission rates of CH4 in the literature, the phylogenetic trend was examined. Emission rates of the observed termites were categorized into five groups: group I with high CH4 and low H2 emission rates with a CH4/H2 ratio of typically 10/1; group II with high CH4 and high H2 emissions with a CH4/H2 ratio of 4/1–1/2; group III with low emission rates of CH4 and H2; group IV with high H2 and insignificant CH4 emissions; and group V with insignificant emissions for both CH4 and H2. In lower termites, there are both colonies infected and uninfected with methanogens even in the same species, and no specific trend in CH4 and H2 emissions was observed within a genus. Whether protozoa in the hindgut of termites are infected with methanogens or not and the differences in species compositions of protozoa are possibly responsible for the inter‐colonial variations. The proportions of infected colonies were possibly small for the family Kalotermitidae (dry wood feeders), and relatively large for families of wet or damp wood feeders. The hydrogen emission rate possibly depends on the locality of methanogens: namely, whether they are intracellular symbionts of protozoa or whether they are attached to the hindgut wall. Emission rates of higher termites were classified into groups according to genera and the diet. Most species of soil or wood/soil interface feeders classified into group I, while the soil feeders Dicuspiditermes in Thailand and Amitermes in Australia were classified into groups with high H2 emission rates. Typical wood‐feeding termites and fungus‐growing termites were classified into group III. The results indicate that higher termites tend to increase the CH4 emission rate during dietary evolution from wood‐ to soil‐feeding, and two types of the system with different efficiencies of interspecies transfer of H2 have been formed. The δ13C of CH4 was discernible with a difference in the decomposition process in the termite–symbiont system among lower termites, fungus‐growing termites and other higher termites.

Emissions of porewater compounds and gases from the subaquatic sediment disposal site “rodewischhafen”, hamburg harbour

In the year 1993 a confined and unused harbour basin was used to store 290,000 m3 of fine-grained dredged material from Hamburg harbour. About 70% of the deposit surface was water covered. The edge areas were above the water table and covered with reed. Emissions of dissolved compounds into the groundwater, as well as surface gas emissions were measured from 1994 to 1996. As indicators for water fluxes from the deposit we used NH4+ and HCO3− because of their high concentrations in mud porewater in comparison to groundwater. The average concentrations of NH4+ and HCO3− in the porewater increased during 2 years from 85 to 250 mg NH4+ 1−1 and from 2.0 to 3.1 g HCO3− 1−1, while the groundwater samples showed constant values of 8 mg NH4+ 1−1 and 0.7 g HCO3− 1−1. Furthermore, the average gas emissions over the water surface were 3.2 g CH4 m−2 d−1 and 0.8 g CO2 m−2 d−1. In contrast, no methane and 3.0 g CO2 m−2 d−1 were emitted from land areas. The results indicated, that there were no significant emissions of mud porewater compounds into the groundwater but high CH4-emissions over the water covered surface of the mud deposit.

Emissions of porewater compounds and gases from the subaquatic sediment disposal site “Rodewischhafen”, Hamburg harbour

In the year 1993 a confined and unused harbour basin was used to store 290,000 m3 of fine-grained dredged material from Hamburg harbour. About 70% of the deposit surface was water covered. The edge areas were above the water table and covered with reed. Emissions of dissolved compounds into the groundwater, as well as surface gas emissions were measured from 1994 to 1996. As indicators for water fluxes from the deposit we used NH4+ and HCO3− because of their high concentrations in mud porewater in comparison to groundwater. The average concentrations of NH4+ and HCO3− in the porewater increased during 2 years from 85 to 250 mg NH4+ 1−1 and from 2.0 to 3.1 g HCO3− 1−, while the groundwater samples showed constant values of 8 mg NH4+ 1−1 and 0.7 g HCO3 1−1. Furthermore, the average gas emissions over the water surface were 3.2 g CH4 m−2 d−1 and 0.8 g CO2 m−2 d−1. In contrast, no methane and 3.0 g CO2 m−2 d−1 were emitted from land areas. The results indicated, that there were no significant emissions of mud porewater compounds into the groundwater but high CH4-emissions over the water covered surface of the mud deposit.

Methane emissions from wetlands in the zone of discontinuous permafrost: Fort Simpson, Northwest Territories, Canada

We examined the influence of water table position, temperature, vegetation, and CH4 storage on CH4 flux at 22 wetland sites located in the zone of discontinuous permafrost, near Fort Simpson, Northwest Territories. Sites ranged from frozen peat plateaux and palsas with collapse scars to fens and bogs and ponds. Mean summer CH4 emissions ranged from −1.3 to 255 mg m−2 d−1, and the variation among sites was best explained by mean water table position (r2 = 0.62, n = 19). Large CH4 fluxes (&gt;30 mg m−2 d−1) and high water tables occurred in ponds and graminoid sites, whereas small fluxes (&lt;30 mg m−2 d−1) and low water tables occur in shrub and woody sites. These relationships were upheld across several northern boreal regions, based on water table depth and broad ecological criteria. CH4 turnover times were generated by comparing surficial fluxes and storage within the saturated portion of the peat profile. Graminoid sites had CH4 turnover times from 1 to 4 days, whereas shrub or woody sites had longer turnover times, ranging from weeks to years. We estimated an overall flux of ∼18 mg m−2 d−1 for the landscape around Fort Simpson. This CH4 flux may increase with the onset of global warming, owing to the fragility of permafrost, resulting in the formation of collapse scars with high CH4 emission rates.

Atmosphere‐wetland carbon exchanges: Scale dependency of CO2 and CH4 exchange on the developmental topography of a peatland

Measurement of the spatial variability of CH4 emissions and net CO2 ecosystem exchange were made in a boreal peatland in northern Sweden in the summers of 1992 and 1993. Variability was monitored at the microscale (hummocks and hollows), mesoscale (ridges, lawns and pools), and macroscale (landforms) to assess the role of peatland topography on the magnitude and variability of the fluxes. The general trend is for topographically lower areas, such as hollows, pools, or peatland margins, to have higher CH4 emissions and lower CO2 uptake than the adjacent topographically higher areas such as hummocks, ridges, and plateaus. However, the greatest difference occurs at the microtopographic scale because the maximum differences in water table position and temperature occur at the microscale. The CH4 flux at the margins of the peatland was three to four times greater than that observed at the central plateau sites. Net CO2 uptake was also greatest at the margin sites. A combined meso‐macro topographic model (MMF) was used to estimate the total peatland CH4 and CO2 exchange. The model indicates that a failure to measure the exchange of carbon from peatland pools can result in a large overestimate of the total peatland NEE and therefore carbon accumulation rates.

Spatial and seasonal variation of methane emission from an Amazon floodplain lake

Methane (CH4) emission from a floodplain lake in central Amazonia was measured during a complete annual cycle using a static chamber method. The results show significant differences in the CH4 flux rates from different habitats in the lake: open water, floating vegetation (mainly the aquatic grass Paspalum repens) and floodplain forest. The highest CH4 emission rates (10–198 mg CH4 m−2 d−1) were recorded during inundation in the seasonally flooded forest. Lower emission rates occurred in the floating vegetation (3–79 mg CH4 m−2 d−1), which is found in areas with a short subaerial phase and in the permanently aquatic part of the lake (4–65 mg CH4 m−2 d−1) free of macrophytes and with the lowest productivity. Seasonal fluctuations in water level resulted in distinct seasonal patterns in CH4 release at different sites in the lake. The permanently aquatic part of the lake had lowest emission rates during periods of water inflow and subsurface oxygen replenishment into the lake. At the periodic aquatic...