B33B-0402
Recent Atmospheric Methane Growth: AGAGE and CSIRO Measurements and Optimal Estimation of Hemispheric Emission Rate Increases
After almost a decade with little change in the global atmospheric methane burden, measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) networks show a period of significant renewed growth at all measurement sites since late-2006. We use these data, with a simple model of atmospheric chemistry and transport, to optimally estimate the required change in emissions under both inter-annually repeating and inter-annually varying hydroxyl radical concentration. We find that if the annual mean hydroxyl radical concentration did not change, a substantial increase in emissions was required in both hemispheres during 2006-2007. However, if a small drop in the hydroxyl radical concentration did occur, consistent with AGAGE methyl chloroform measurements, the emissions increase is reduced overall and is more strongly biased to the Northern Hemisphere.
B33B-0403
Direct Measurements of Leaf Level CH4 and CO2 Exchange in a Boreal Forest
Reports of aerobic CH4 sources from leaves and litter of a variety of forests and plant functional types have added a potential mystery to our understanding of CH4 dynamics especially if these sources contribute enough to have a significant impact on the global budget. We have made direct measurements of leaf level CH4 and CO2 exchange using a quartz branch cuvette in a boreal forest in Norunda, Sweden since August of this year. The cuvette was temperature controlled and was designed to close for 5 minutes every 30 minutes. Air was circulated to a Los Gatos CH4/CO2 infrared absorption laser spectrometer. Air and cuvette temperatures, PAR and UV radiation (Kipp and Zonen, CUV4; spectral range 300-380 nm) were measured at the branch chamber. The study was made in the Norunda 100 years old stand consisting of a mixture of Scots pine (Pinus sylvestris L.) , Birch (Betula sp.) and Norway spruce (Picea abies (L.) Karst.). The cuvette was moved between trees at roughly 5 day intervals. A null empty cuvette period was included in the rotation. The initial data show the expected CO2 uptake correlated with incident PAR and low rates of emission at night. However, there was no clear pattern of emissions detectable in the CH4. We estimate that we should be able to resolve a change of 0.5 ppbv CH4 min- 1 with our analytical setup. Both the daytime (1000-1600) and nighttime (2200-0400) averages were less than our detection. Even on very sunny days with high PAR and UV flux values, no consistent pattern was detectable. The lack of a distinct signal may be due to the fact that the past month has been very rainy, it is late in the growth season at these latitudes and sun angles are increasing quickly. The trees were at the northern edge of a clearing and we were also measuring mid height (2-3 m) leaves and branches of young trees. The branch cuvette design can also be optimized to improve its sensitivity.
B33B-0404
Methane Emissions from Deciduous Trees
There is some disagreement today over whether terrestrial plants present a significant source of methane to the atmosphere. Even if the plants are recognized as a source, there is no clear method to extrapolate plant emissions to the global atmospheric budget of methane and estimates vary widely. There is also no consensus on a mechanism for methane production and/or plant-mediated transport to the atmosphere. Here, we present preliminary data showing a significant flux of methane to the atmosphere from three wetland deciduous tree species. Ash (Fraxinus latifolia), cottonwood (Populus deltoides L.), and willow (Salix fluviatillis) were grown in a greenhouse under inundated rice-cultivation conditions using a rice straw amendment equivalent to 3 t/ha to enhance below ground anaerobic methane production. Results of measurements of redox potential and methane concentrations in soil pore water show significant methane production similar to that observed in rice plots (Oryza sative L. 'M-103') and controls of the same treatment. Measurements of the stable carbon isotopic composition (δ13C) of methane dissolved in soil pore water show no significant difference from rice plots showing no discernable difference in bulk carbon substrate. Methane flux from trees, measured using static flux chamber and bag-tree enclosures, was found to be significantly higher than control treatments (i.e., no plants) but lower than rice plants overall. The carbon isotopic composition of emitted methane from tree species was found to be approximately 8‰ enriched in δ13C compared with methane emitted from rice. This difference in δ13C of emitted methane observed between rice and trees suggests the mechanisms contributing to regulating plant-mediated methane transport (e.g. transport, oxidation, carbon sources) may be quite distinct between diverse plant functional types. Identifying the mechanistic basis of this response will be a key development towards developing more accurate estimates of methane flux over local and regional scales.
B33B-0405
Methane Sources and Sinks in a High-Elevation Subalpine Forest Inferred from Canopy Tower Profiles
A thorough understanding of the biogeochemical sources and sinks of atmospheric methane is required to assess the current and future influence of greenhouse gases on climate. Recent work has suggested the possibility of aerobic methane emission from plants. There are conflicting conclusions in the literature, however, highlighting the need for a variety of experimental approaches to investigate this phenomenon. We examined the variability of methane in forest air at the Niwot Ridge AmeriFlux site in the Rocky Mountains of Colorado (3050 m elevation) during summer 2007. The site is an upland conifer forest dominated by Pinus contorta (lodgepole pine), Picea engelmannii (Engelmann spruce), and Abies lasiocarpa (subalpine fir). A fast-response optical methane analyzer was used to measure profiles of CH4 at 7 heights within and above the vegetation canopy. Profiles were measured in a 30-min time period and repeated every 2 h over 43 days. Observed CH4 varied over the study from 1780 to 1920 ppb, and the day to day variability was influenced by the urban plume from Denver, 60 km to the southeast. When profiles were examined relative to the top of the tower, there was a regular pattern of excess CH4 in the vegetation canopy at night, and a clear CH4 sink in the soil surrounding the tower. On the basis of wind direction analysis, the excess CH4 in the canopy at night appeared to be related to a nearby wetland source within the nocturnal tower footprint, and not to a source by local aerobic foliar emission. During the daytime, the soil sink persisted. Recent laboratory work by others has highlighted the importance of UV radiation for plant emission of CH4. The high elevation of our research forest is associated with high UV levels, which might be expected to enhance foliar emission rates. While daytime mixing may have obscured possible buildup of CH4 due to foliar emission, there was no evidence for higher emission in the canopy at high compared to low shortwave irradiation. These data will be used to provide bounds for the magnitudes of the soil methanotrophic sink and to assess the possible magnitude of foliar emission in this forest.
B33B-0406
Methane Uptake in Forest Soils is Driven by Diffusivity and Methane Oxidizer Community Size
Upland forest soils are the only known terrestrial biological sink of methane, but the mechanisms controlling methane uptake are poorly understood. Methane uptake is the result of bacterial and archaeal 'methane oxidizer' activity. Temperature, water content, and substrate availability have all been described as potential mechanisms governing methane uptake in soils. We measured methane uptake in soil across two ecological different gradients in an attempt to determine controls on methane uptake in semi-arid soils. We measured the uptake of atmospheric methane in situ across a gradient of northern Arizona, USA ponderosa pine forest disturbance. This gradient included an unthinned, unburned forest, a mechanically thinned forest, and a former forest site that completely burned 10 years prior to measurements. In laboratory incubations, we measured potential methane uptake across a soil chronosequence of basalt-cinder derived soils from 0.001 to 3 million years old by exposing soils to 10x ambient levels of methane. This chronosequence has a gradient of soil texture, which will influence the air filled pore space, and consequently methane diffusion. Both gradients experience distinct dry and wet seasons during the growing season. Our field measurements suggest that methane uptake is greatest when the forest floor is thinnest and the soil is most dry. Our laboratory incubations suggest that, during the dry season, potential methane uptake is driven by diffusion, but that during the wet season potential methane uptake is a function of methane oxidizer community size. Methane uptake patterns across both gradients demonstrates the importance of diffusion and methane oxidizer community size as codominant controlling factors.
B33B-0407
Comparison of Methods to Assess the Fate of Methane in a Landfill-Cover Soil
A substantial fraction of the greenhouse gas methane released into the atmosphere is produced in terrestrial environments such as wetlands, rice paddy fields, and landfills. However, the amount of methane that is emitted from these environments is often reduced by microbial methane oxidation, mediated by methanotrophic microorganisms. Methanotrophs are ubiquitous in soils and represent the largest biological sink for methane. We performed a series of field experiments in summer 2008 to compare several state-of- the-art methods to assess the fate of methane in a landfill-cover soil near Liestal (BL), Switzerland. Methods employed included eddy-covariance and field-chamber measurements to quantify net methane flux at the landfill surface. In addition, methane concentrations at the landfill surface were monitored using a portable methane detector. Methane fluxes within the cover soil were estimated from methane-concentration profiles in conjunction with radon measurements. Additionally, gas push-pull tests were employed for in-situ quantification of methane oxidation in the cover soil. Finally, methane stable-carbon-isotope measurements were conducted to corroborate methane oxidation in the cover soil. Preliminary results indicate that each method provides unique information, and when combined, the data provide detailed insight in the fate of methane in the cover soil. The investigated landfill-cover soil appears to be ordinarily a net sink for methane. However, it can quickly turn into a net source of methane under adverse meteorological conditions.
B33B-0408
Eddy Covariance Measurements of Methane Flux Using an Open-Path Gas Analyzer
Methane is an important greenhouse gas with a warming potential of about 23 times that of carbon dioxide over a 100-year cycle (Houghton et al., 2001). Measurements of methane fluxes from the terrestrial biosphere have mostly been made using flux chambers, which have many advantages, but are discrete in time and space and may disturb surface integrity and air pressure. Open-path analyzers offer a number of advantages for measuring methane fluxes, including undisturbed in- situ flux measurements, spatial integration using the Eddy Covariance approach, zero frequency response errors due to tube attenuation, confident water and thermal density terms from co-located fast measurements of water and sonic temperature, and remote deployment due to lower power demands in the absence of a pump. The prototype open-path methane analyzer is a VCSEL (vertical-cavity surface-emitting laser)-based instrument. It employs an open Herriott cell and measures levels of methane with RMS noise below 6 ppb at 10 Hz sampling in controlled laboratory environment. Field maintenance is minimized by a self-cleaning mechanism to keep the lower mirror free of contamination. Eddy Covariance measurements of methane flux using the prototype open-path methane analyzer are presented for the period between 2006 and 2008 in three ecosystems with contrasting weather and moisture conditions: (1) Fluxes over a short-hydroperiod sawgrass wetland in the Florida Everglades were measured in a warm and humid environment with temperatures often exceeding 25oC, variable winds, and frequent heavy dew at night; (2) Fluxes over coastal wetlands in an Arctic tundra were measured in an environment with frequent sub-zero temperatures, moderate winds, and ocean mist; (3) Fluxes over pacific mangroves in Mexico were measured in an environment with moderate air temperatures high winds, and sea spray. Presented eddy covariance flux data were collected from a co-located prototype open-path methane analyzer, LI-7500, and sonic anemometer at a 10 Hz rate. Data were processed using EdiRe software following standard FluxNet methodology, including stationarity tests, frequency response, and Webb- Pearman-Leuning density terms. Further details are provided in the extended conference paper at: ftp://ftp.licor.com/public/GBurba/AGU LI- 7700 Paper-2008.pdf
B33B-0409
An In situ Observing System for "Top-down" Studies of the Global Methane Budget
Atmospheric observations of CH4 are currently good enough to constrain its budget of sources and sinks reasonably well at global to hemispheric scales, but to quantify its budget at regional scales, a denser network is required. This will be necessary to assess the effectiveness of CH4 emission mitigation strategies, to validate emission inventories at national or regional scales, and to improve understanding of emission processes that are affected by changing climate. The current network poorly constrains natural emissions from wetland and permafrost regions in the Arctic, where there is the potential for strong climate feed-backs on CH4 emissions. The tropics are even more poorly constrained than the Arctic because of meteorology and a paucity of sampling sites. Scientific requirements for CH4 measurement repeatability are technically difficult, but achievable. WMO GAW recommends inter-laboratory comparability of 2 ppb; meeting this goal requires careful maintenance of a calibration scale closely tied to the WMO CH4 mole fraction scale, excellent analytical precision, and a detailed quality control strategy. The observing network itself should consist of multiple components. Discrete samples collected infrequently (e.g., weekly) at well-mixed background sites provide information on the CH4 budget over large spatial scales and provide boundary conditions for inverse model studies of fluxes over continents. Analysis of continuous measurements over continents is complicated by close proximity to sources and the diurnal changes in atmospheric mixing. These problems can be circumvented by measuring CH4 continuously from tall towers that are always above the nocturnal boundary layer. Additionally, vertical profiles of CH4 from aircraft are necessary to insure atmospheric chemistry and transport models adequately represent mixing. When discrete samples are used for the vertical profiles, multiple species, including stable isotopes of CH4, can be measured to help identify source signatures. This presentation will discuss measurement requirements in detail, assess the feasibility of using new measurement technologies, and describe a detailed quality assurance strategy for a network. If implemented, these observations can be combined with a high-resolution chemical transport model for a "top- down" assessment of the CH4 budget at regional scales.
B33B-0410
Flux Estimation of Methane using the Radon Flux Method
Radon has been continuously measured at the tall tower Cabauw (at 20 and 200 meters elevation) in the centre of the Netherlands since the beginning of 2006. CO2 and CH4 and a range of other gases have been measured for over a decade. Radon can serve as a useful tracer to study atmospheric transport processes because its sources are relatively uniform in space and time. Comparison with other species, e.g. CO2 or CH4, can therefore lead to more insight into (the spatial and temporal distribution of) their sources and sinks. Concentrations at Cabauw were modeled using the Lagrangian transport model COMET. Using a spatially varying radon flux field, derived from gamma radiation measurements, improves the average diurnal pattern, but not the overall correlation. The boundary layer height appears to be a dominant factor in explaining the error between modeled and measured concentrations. A modified radon flux method is employed to estimate the average regional flux of methane, using the COMET model to weigh the area of influence of the individual measurements.
B33B-0411
Chamber-Based Estimates of Methane Production in Coastal Estuarine Systems in Southern California
Wetland systems are believed to produce between 100 - 231 Tg CH4 yr-1 which is roughly 20% of global methane emissions. The uncertainty in methane emissions models stem from the lack of detailed information about methane gas production within regional wetland systems. The aim of this study is to report the range of methane fluxes observed along salinity gradients at two San Diego coastal wetland systems, the Tijuana Estuary (Tijuana River National Estuarine Research Reserve) and the Peñasquitos Lagoon (Torrey Pines State Park Reserve). Soil water samples are used to elucidate factors responsible for the observed variation in methane fluxes. Air samples were subsequently collected from the headspace of a static soil chamber and stored in pre- evacuated vials. Methane concentrations were analyzed within hours after collection by gas chromatography in the laboratory. The chemical and physical properties of the soil, including salinity, pH, redox potential and temperature are measured with a hand-held probe nearby soil collars. The biological properties of the soil, including dissolved organic carbon, nitrate, and ammonia levels are measured from soil water samples in the laboratory. We find that saline sites under direct tidal influence produced methane fluxes ranging from -3.10 to 9.10 (mean 2.18) mg CH4 m-2 day-1. We also find that brackish sites (0.6 to 3.2 ppt in salinity) with fresh water input from residential runoff at the Peñasquitos Lagoon produced methane fluxes ranging from 0.53 to 192.10 (mean 33.34) mg CH4 m-2 day-1. Sampling was done over the course of 5 weeks during August-September of 2008. We hypothesize that the contrasting methane fluxes found between the saline and the brackish sites is due primarily to the different salinity, and in turn sulfate levels found at the two sites. The reduction of sulfate to produce energy is more energetically favorable than the reduction of carbon dioxide to produce methane. Thus the presence of sulfate may act as a methanogensis inhibitor resulting in higher methane flux in low salinity conditions such as those found at the brackish sites.
B33B-0412
Methane and Sulfate Fluxes in Diffusion-controlled Marine Sediments: Consequences for the Global Carbon and Sulfur Cycles
We have established a comprehensive marine data base on methane and sulfate fluxes and on other relevant parameters in the seabed. The goal is to determine the global diffusive methane flux and the loss of methane within the sediment due to anaerobic oxidation of methane (AOM). The upward migrating methane exerts a major control on the depth of the sulfate/methane transition (SMT). The results of multivariate data analyses show, that the global relationship between sedimentary methane and sulfate fluxes is linear over several orders of magnitude. Yet, most flux ratios between methane and sulfate do not show a 1:1 relation, as would be expected from a simple stoichiometry (SO42- + CH4 + 2H+ → H2S + CO2 + 2H2O), but rather indicate a lower methane flux relative to the sulfate flux. Our first estimates of the global marine methane budget indicate that deep sea sediments play a larger role in sulfur and methane cycling than concluded in earlier studies. The compilation of data aims at a global dynamic methane budget for marine sediments which will be compared with available carbon data to reveal the role of AOM in the global carbon and sulfur cycles.
B33B-0413
Using 14C to investigate Methane Production and DOC Reactivity in Northern Peatlands
We found a consistent distribution pattern for radiocarbon in dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and methane replicated across spatial and temporal scales in northern peatlands from Minnesota to Alaska. The 14C content of DOC is relatively modern throughout the peat column, to depths of 3 meters. In sedge-dominated peatlands, the 14C content of the products of respiration, CH4 and DIC are essentially the same, and are similar to that of DOC. In Sphagnum-woody plant dominated peatlands with few sedges, however, the respiration products are similar but intermediate between the 14C content of the solid-phase peat and the DOC. Preliminary data indicates qualitative differences in the pore-water DOC depending on the extent of sedge cover, consistent with the hypothesis that the DOC in sedge-dominated peatlands is more reactive than DOC in peatlands where Sphagnum or other vascular plants dominate. These data are supported by molecular-level analysis of DOC by ultrahigh resolution mass spectrometry which suggests dramatic changes with depth in the composition of DOC in the sedge-dominated peatland porewaters but not in porewaters where Sphagnum dominates. The higher reactivity of DOC from sedge- dominated peatlands may be a function of either different source materials or environmental factors that are related to the abundance of sedges in peatlands. To further investigate the reactivity of peat DOC in anaerobic methane producing environments, we are conducting size fractionation experiments for both the bog and fen samples. We will analyze resulting size fractions of DOC for radiocarbon. Previous research has shown that microorganisms tend to prefer HMW DOC to LMW DOC. Due to this, we believe that LMW DOC from both the bogs and the fens will result in radiocarbon values that are more depleted in 14C relative to HMW DOC. We hypothesize that the HMW DOC from the bogs will show depletion in 14C relative to HMW DOC in the fens. We further hypothesize that the HMW DOC from the fens should be the most enriched in 14C as the DOC is being utilized by the bacteria before the 14C in this DOC pool has the chance to decay.
B33B-0414
Spatially Distributed Methane Flux Measurements for a Tropical Dambo Wetland Landscape in Uganda
Dambos are seasonal tropical wetlands that occupy up to 20% of the gently undulating land surface on the elevated plateaus of Central and Southern Africa and 1.3 to 2.3 million km2 throughout the African continent. Here, we present data from the first extensive field campaign to measure dambo CH4 fluxes in Africa. We selected measurement sites within a 2,214 km2 study area in central Uganda using a combination of stratified random selection and spatial clustering to: (1) facilitate the logistics of gas sampling and (2) identify representative sampling locations. Three watersheds were selected along a declining precipitation and topographic relief gradient from south to north. Within each watershed, we randomly selected four cluster centers with spatial inhibition, and then randomly selected five sites to represent the following dambo landscape classes from driest to wettest: (a) uplands; (b) margins; (c) floors; and (d) bottoms (two sites selected). At each site, we installed two replicate chamber bases with associated tube wells 10 m apart. In total, we measured CH4 emissions using static 1 m3 chambers at 60 sites (2 replicates each) five different times spanning the March-June, 2008 wet season in Uganda. We measured significant CH4 emissions from the dambo bottoms and floors only. The largest emissions came from inundated or nearly inundated dambo bottoms (37 and 230 mg m-2 day-1 median and max, respectively). The maximum emission measurement for floors was only 20 mg m-2 day-1, with an average flux during the wet season that was only slightly positive. The water table was never higher than 80 cm below the soil surface for margins and uplands, with an average emission of 1 mg m-2 day-1 for margins and average consumption of 2 mg m-2 day-1 for uplands. Accurate estimate of net regional CH4 fluxes for dambos will require high quality digital maps not just of dambos, but more importantly the wetter dambo bottoms.
B33B-0415
A Positive Feedback Loop For Global Warming: Methane Production And Microbial Diversity In Arctic Soils
As mean summer temperatures in the Arctic increase, the maximum depth of the annual thaw layer correspondingly increases. This warmed layer, also known as the active layer, is home to a wide diversity of microorganisms. As these microbes become metabolically active every summer, they respire anaerobically to produce carbon dioxide and methane, two powerful greenhouse gases. This study examines the diversity of microbial communities and the production of methane and carbon dioxide from successive layers of soil cores collected from a thaw-lake basin near Barrow, Alaska. The diversity of the microbial communities was determined by generating 16S rRNA gene libraries. A highly diverse community of Archaea and Bacteria was present throughout the soil core, and the structure of the community changed with depth. A novel Archaeal group was also discovered, and was a dominant presence in the microbial community at each depth within the soil core. In addition, the anaerobic production of carbon dioxide and methane from the soil was determined. Despite the fact that this was the first time some of the deepest layers of these cores have been defrosted in thousands of years, each layer was found to produce large volumes of methane and carbon dioxide. After 6 hours of incubation at 3°C, the total methane produced was found to increase with increasing depth, from near 340 ppm at the surface to 1800 ppm at the deepest layers of the cores (40-50 cm). Furthermore, carbon dioxide production was lowest in the top two layers (2500-3000 ppm, 0-20 cm), and highest in each of the lower layers (5000 ppm, 20-50 cm). These data indicate that the contribution of anaerobic respiration cannot be overlooked as a significant source of carbon dioxide into the atmosphere. Moreover, soils from this region of the Arctic are immediately capable upon thawing to convert ancient stores of organic carbon into methane and carbon dioxide. These data suggest that as the depth of the annual active layer increases, release of two of the most important greenhouse gases from this ecosystem will correspondingly increase, ultimately amplifying the greenhouse effect.
B33B-0416
Seasonal Patterns and Controls on Methane Fluxes during the Initiation of a Large-Scale Water Table Manipulation Experiment in the Alaskan Arctic Tundra
The 191.8 Pg C of Arctic soil organic mater is, or is at risk of, being released to the atmosphere as CO2 and/or CH4. Global warming will further alter the rate of emission of these gases to the atmosphere. Here we quantify the effect of major environmental variables affected by global climate change on CH4 fluxes in the Alaskan Arctic using eddy covariance integrating thousands of m2 in continuous measurements under differing environmental conditions. Soil temperature best predicts CH4 fluxes and explained 89% of the variability in CH4 emissions. Water table depth has a linear impact on CH4 efflux. Increasing water table height above the surface retards CH4 efflux. Decreasing water table depth below the surface has a minor effect on CH4 release once an aerobic layer is formed at the surface. In contrast with several other studies, we found that CH4 emissions are not driven by net ecosystem exchange (NEE) and are not limited by labile carbon supply. The temporal and spatial scale of these measurements begins to lay the ground work for regional estimation of current and future methane fluxes from Arctic tundra ecosystems.
B33B-0417
Assessing Biogenic Methane Content in Various Peatland Landforms Using GPR
Northern peatlands are known to be a source of biogenic methane, although efforts to accurately quantify their impact on the global carbon budget are ongoing. An important step towards a better understanding of the dynamics of methane releases to the atmosphere is to identify peatland landforms (i.e. raised bog, fen water track, open pools) where gas is accumulating in the subsurface compared to places where there is little subsurface methane. Additionally, it is important to identify areas of the vertical peat profile where high volumes of free-phase methane are present. In this study, we use ground penetrating radar (GPR) to acquire data on where free-phase gas (FPG) methane may be accumulating within the peat strata, and then make comparisons between various peatland landforms. 1-dimensional GPR common mid-point velocity analysis has been coupled with innovative subsurface gas sampling to identify the areas within northern peatlands that have significant gas trapped below confining layers in the subsurface. Gas samples are evaluated for total recovered volume and total methane concentration in order to support the GPR findings. Traditional 2-dimensional radar profiles were used to identify and estimate the depth at which laterally continuous woody confining layers are present, and therefore zones where gas can be expected to be found. By using 1-D, 2-D and direct sampling methods, it is now possible to identify potential areas of gas accumulation with a higher level of confidence.
B33B-0418
Methane Geogas Storages Discharge under Permafrost Degradation
High-latitude ecosystems are in the focus of global change studies. High-latitude ecosystems contribute up to 30% of all wetlands methane emissions according to AR4. High-latitude ecosystems are characterized with permafrost distribution. More than 107 km2 in the northern hemisphere is covered with permafrost. Permafrost soils were shown to contain layers enriched in methane and carbon dioxide as well as with pre- cursors needed for methane production and viable methanogenic microbial community. Thus the ancient methane itself, the substrate for its production and producers themselves are found in permafrost. They concentrated in various strata, geologic formations. For the North-Eastern Siberia a number of the strata were sampled for these components. More than 200 soil air samples from the cores of twenty 15-55 m boreholes were analyzed for methane and carbon dioxide concentration. The traces of acetate were also found in frozen soils. Labelled substrate experiments with soils in the laboratory gave the rates of methane production and lag phases of microbial communities for the various types of thawing permafrost soils. The volumes of the formations are calculated within the GIS based system according to state geological survey map of quaternary deposits of 1:1000000 scale. The land area was separated into three various morphologic levels dominating in the study area, as follows: Ice Complex covered watersheds, Alas Complex (Holocene Thaw Lake Depressions Deposits) and River Floodplains. The thickness and set of geologic formations for each morphologic level were specified. The study area was divided into 2.5 by 2.5 degrees Lat-Long grid to introduce to permafrost thawing model. Soil thermal characteristics were taken from the data available in literature or calculated on the basis of existing data on texture and iciness. The boundary conditions of ground surface temperature and water flow were controlled by the ensemble of GCMs models which ran under A1B and A2B emission scenarios to the year of 2100. The highest discharge of in situ methane is found for the Alas Complex covered layers occurring at 31% of the land area in the North-East Asia (the 68- 72°N, 147-162°E). The Ice Complex watersheds lacking the in situ methane and microbial community was found to support the high rates of methane production through assimilation of buried substrate by modern methanogenic communities of the active layer. Our assessment is based on the direct measurements of gas concentration within permafrost samples. The total assessment of possible efflux from permafrost of the studied area is somewhat lower than it was predicted by several studies on thermokarst conducted at Kolyma Lowland and in Alaska. Uncertainties in those assessments were analyzed.
B33B-0419
Methane Ebullition From a Thaw Lake During in-situ Incubations Simulating Thermokarst Erosion
Ebullition from Arctic thaw lakes is a major pathway of methane emission to the atmosphere. In regions of continuous permafrost, these lakes have been expanding due to thawing permafrost and thermokarst development, supplying large amounts of organic rich material to lake sediments where anaerobic decomposition can occur. Although increased methane emissions from thaw lake expansion would constitute a positive feedback to Arctic warming, we know very little about the time scales over which methane is released, or about the relative importance of permafrost vs. active layer sources of carbon for the observed ebullition. In order to reduce this uncertainty, we placed three tundra horizons (thawed active layer, frozen active layer and permafrost) into separate incubation chambers at the bottom of an Alaskan thaw lake, and we collected the gas bubbles that were emitted. The experiment ran from July 2007 until lake freeze-up in early October 2007 and resumed from June to August 2008. Despite the significant amount of organic material in the originally frozen layers (permafrost and frozen active layer), they emitted very little methane during the two seasons of monitoring. Instead, the active layer was the dominant source, exhibiting ebullition rates similar to "background ebullition" reported from Siberian thaw lakes. Ebullition from the active layer began the first week of incubation and increased during the first three to four weeks, reaching some of the highest rates of the entire incubation. Rates observed during the second season were similar to the first weeks of the first season. Overall carbon loss from methanogenesis represents less than 0.1% of the initial carbon content, suggesting that the observed rates of active layer methane ebullition are likely to be sustained for years.
B33B-0420
The Role of Sedges in Methane Production and Emission From a Temperate Fen
Northern peatlands are the largest single natural source of atmospheric methane (CH4) and thus any changes in these fluxes could have global consequences. Positive correlations have been observed between sedge biomass and high CH4 emissions from peatlands. We examined the effect that Carex rostrata has on methane production and transport in Sallie's Fen, Barrington, NH. During the summer of 2008, CH4 fluxes, pore-water CH4 concentrations, and C. rostrata biomass, along with temperature, net ecosystem CO2 exchange (NEE), and water table depth, were measured from both clipped and unclipped plots. In clipped plots, all C. rostrata were clipped below the peat surface and then sealed with petroleum jelly and plastic bags. Unclipped plots were left undisturbed. We observed a strong positive correlation between C. rostrata biomass and CH4 fluxes. Initial findings suggest that sedges have a strong effect on gas transport. The average 18 cm (C. rostrata rooting depth) pore water CH4 concentrations in the clipped plots (6141 ppm CH4) were significantly higher (p<0.001) than in the unclipped plots (3912 ppm CH4). The past 20 years of data at Sallie's Fen also show that plots with more C. rostrata have higher mid-season CH4 fluxes, on average, than shrub-dominated plots. Depth to water table, however, may be a stronger control on CH4 fluxes than vegetation.
B33B-0421
Using MODIS reflectance products to monitor wetness and methane fluxes and concentration in a managed temperate peatland in California
Compared to northern peatlands, managed temperate peatlands have generally received little attention from the climate change community. Many studies in northern peatlands have demonstrated the importance of wetness on atmospheric efflux and concentration of methane (CH4). In managed temperate peatlands such as Sherman Island located within the Sacramento-San Joaquin Delta, California, the monitoring of wetness poses a major challenge since hydrological input includes irrigation through a complex network of ditches and canals in addition to precipitation. The objective of this study is to investigate the capability of six spectral vegetation indices (SVI) to capture the seasonal dynamics of near surface wetness within the day- and nighttime CH4 concentration footprints of the EC tower located on Sherman Island, and ultimately to investigate the capability of these SVI to capture the seasonal dynamics of CH4 concentration and fluxes at this site. In addition to routinely applied normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI), we computed land surface water index (LSWI), shortwave infrared water stress index (SIWSI), and moisture stress index (MSI), all of which are related to wetness. These indices were derived from daily and 8-day composite MODIS surface reflectance products. We extracted information from the pixels that corresponded with the daytime footprint entirely located within a relatively "dry" area containing the EC tower, and for the nighttime footprint, which extends into adjacent relatively "wet" areas. For this purpose, the extents of day- and nighttime footprints were estimated with a 2-D version of an analytical footprint model. Preliminary results for the MODIS EC tower pixel show that especially the wetness-related SVIs compare favorably well with in situ near surface soil moisture measurements.
B33B-0422
Methane Emissions and Warming Potentials of Wetlands of the Great Lakes Region
Estimates of methane emissions from natural wetlands in the United States suggest that 28% of the source originates in the northern Great Lake States of Wisconsin, Minnesota, and Michigan (Potter et al., 2006). These estimates are based on a constant ratio of methane emissions to net ecosystem production during the growing season peak (0.033 mol CH4 mol-1 CO2, as observed by Whiting and Chanton, 1993), which is seasonally adjusted using air temperature response function (Q10=3.5). This model has not been tested in wetlands of the Great Lakes Region, and the simplified approach may not capture other factors controlling methanogenesis and methanotrophy (e.g., plant community composition, soil carbon and temperature profiles, and fluctuations in surface water table elevation). The objectives of this study were to evaluate models of methane emission and compute model uncertainty for three wetland types in northern Wisconsin (wet meadow, shrub fen, and ericaceous bog), with the overall goal of improving satellite-derived estimates of methane emissions in the Great Lakes Region of North America. In situ chambers were used to measure soil-atmosphere exchange of CO2 and CH4, and eddy covariance methods were used to measure net ecosystem exchange of CO2. These measurements were used to determine whether relationships between CH4 and CO2 exchange agree with Whiting and Chanton's observations, and whether seasonal variations in the CH4:CO2 ratio are reflected in air temperature observations. Markov Chain Monte Carlo methods were used to produce model parameter estimates and probability distributions. Factors contributing to the predictive uncertainty of CH4:CO2 and net warming potential of methane emissions will be discussed.
B33B-0423
Spatial and Temporal Variation in Methane Bubbling From a Stratified, Eutrophic Lake
Recent studies have suggested that significant amounts of methane can be released to the atmosphere from freshwater lakes, particularly through bubbling. However, spatial and temporal heterogeneity in ebullition has complicated efforts to accurately measure methane emissions from aquatic ecosystems. We have hypothesized that bubbling is triggered by variations in absolute water pressure at the lake bottom, and hence should be more or less synchronous from site to site within a small lake. In 2007, most of the bubbling in the eutrophic Upper Mystic Lake in Massachusetts occurred episodically, with peak fluxes approaching 200 ml/m2/d in late summer and early fall (comparable to wetland emissions), while average bubble fluxes were approximately 30-45 ml/m2/d. However the temporal resolution of these measurements was only of the order of a week. In 2008, under-water bubble traps were equipped with pressure sensors that measured the gas collected every 5 minutes, to determine the exact temporal pattern of ebullition. Early results suggest that synchronous lake-wide bubbling occurs during episodes lasting 2 to 4 days, and is in fact strongly linked with changes in the lake's water level, and to a lesser extent with variations in atmospheric pressure. Spatial variability in bubble fluxes was observed during both years, with shallower locations emitting 2 to 20 times less flux than deeper stations. The mixing ratio of methane present in the collected gas varied across stations and ranged from 30% to 90%.
B33B-0424
Assessing the role of different wetland methane emission pathways with a biogeochemistry model
One great challenge to estimate regional wetland CH4 emissions is due to the uncertain pathways of methane transport from wetland to the atmosphere. Here, we refine the algorithms of diffusion, bubbling, and plan-aided transport pathways in our existing biogeochemistry model, the Terrestrial Ecosystem Model (TEM). The revised TEM is tested at two peatland sites in Michigan, USA. For the site with plant communities dominated by Chamaedaphne calyculata, an ericaceous shrub, the model estimated CH4 fluxes agree well with observations at a daily time step, with a linear fitting of intercept 8.9 mg m-2 d-1 and slope 0.47 (R2=0.33). For the site with areas dominated by plants with aerenchymatous tissues, a linear fitting is of an intercept 99.8 mg m-2 d-1 and a slope 0.72 (R2=0.49) between model estimates and observations. At both sites, the model showed the diffusion is the major pathway for CH4 effluxes to the atmosphere, followed by plant aided transport and ebullition. Their relative contributions depend on the vegetation type. Next, we will apply the model to temperate wetlands in the United States to further assess the role of these pathways in determining methane emissions.
B33B-0425
Support for a New Mechanistic Hypothesis for the Effect of Nitrogen on Methane Flux
A new mechanistic hypothesis has emerged from natural and agrarian wetland environments concerning nitrogen (N) controls on ecosystem methane (CH4) flux, which may also be applicable to terrestrial soils: the ratio of CH4 to available N in the environment, when given sufficient oxygen, will determine whether CH4 uptake is inhibited or augmented by additional N. When the ratio of CH4 to available N is high, added N will be used by methanotrophs to metabolize available methane, thus stimulating methane uptake or decreasing methane release by the system. Once the ratio of methane to available N is low, any additional available N will begin attaching to the methane monooxygenase being produced by the methanotrophs, leading to decreased methane uptake or to increased methane release. This more mechanistic hypothesis may replace the older hypothesis, which suggests that differences in the structure of soil methanotrophic communities determine different responses to N addition across all ecosystems. Recent field CH4 flux data from N addition experiment, performed on temperate coastal pine forest soil, confirm this new mechanistic hypothesis. Ammonium nitrate was applied in solution with water to field plots. The applied N levels replicated both increased atmospheric deposition (low) and fertilization levels (high). Both N level and position relative to water table significantly affected CH4 uptake. Plots with low and high levels of N differed significantly from each other, but not from the control plots, which remained in between the two. Low N levels were found to stimulate CH4 uptake across plots, while high levels inhibited CH4 uptake or increased CH4 production. It is possible that this response may occur differently at different environmental ratios of methane to available N or in different microbial communities, and so further studies matching CH4 flux response to methanotrophic community composition should be performed.
B33B-0426
Methane and other Trace Gases in the Indian Summer Monsoonal Outflow as Measured by the Civil Aircraft Based Research Project CARIBIC
Monthly recurring flights between Europe and India with the CARIBIC aircraft (Civil Aircraft for the Regular
Investigation of the atmosphere Based on an Instrument Container, www.caribic-atmospheric.com) intercept
the easterly outflow over the Indian subcontinent in summer at the cruising altitude of 10-12 km. While the
route of the aircraft remains unchanged during the year, profound changes in the trace gas concentrations,
particularly methane, and aerosol number densities are observed when the monsoon plume is crossed. The
highly detailed information is used to estimate emission ratios for this continental type of emission plume, and
to understand the processes. On this basis source strengths can be estimated. Comparisons with results
from satellite observations and modeling are given.
http://www.caribic-atmospheric.com
B33B-0427
Train-borne Measurements of Enhanced Wet Season Methane Emissions in Northern Australia Implications for Australian Tropical Wetland Emissions
We present the first transect measurements of CH4, CO2, CO and N2O taken on the Ghan railway travelling on a N-S transect of the Australian continent between Adelaide (34.9°S, 138.6°E) and Darwin (12.5°S, 130.9°E). The Ghan crosses Australia from the mainly agricultural mid-latitude south through the arid interior to the wet-dry tropical savannah south of and around Darwin. In the 2008 wet season (February) we observed a significant latitudinal gradient of CH4 increasing towards the north. The same pattern was observed in the late 2008 wet season (March-April), with a smaller latitudinal gradient. These will be compared with a dry season transect, to be undertaken in September/October 2008. The Air Pollution Model (TAPM), a regional scale prognostic meteorological model, is used to estimate the surface methane source strength required to explain the observed latitudinal gradient in CH4 in the wet season, and investigate the source type. Fluxes from cattle and termites together contribute up to 25% of the enhancements seen, leaving wetlands as the major source of wet season methane in the Australian tropics. Wetlands are the largest natural source of methane to the atmosphere, and tropical wetlands are responsible for the majority of the interannual variation in methane source strength. We attempt to quantify the annual methane flux contributed by anaerobic organic breakdown due to wet- season flooding in tropical Northern Territory.
B33B-0428
Methane, carbon dioxide and carbon monoxide budgets for the Los Angeles area from September 2007 through June 2008
We will present an urban budget of methane, carbon dioxide and carbon monoxide, from nearly a year's worth of solar absorption measurements in Pasadena, a suburb of Los Angeles, California. The data were recorded by a high-resolution Fourier transform spectrometer that is part of the Total Carbon Column Observing Network (TCCON). Pasadena is a polluted urban site, and these high-precision measurements point to significant urban sources of methane. We will discuss the implications of these urban methane sources to the regional methane budget.
B33B-0429
Estimation for Global Terrestrial Methane Budget Using A Coupled Carbon and Nitrogen Cycles Model VISIT
Land-atmosphere exchange of methane (CH4) can exert considerable feedback effects on the human-
induced climatic change. However, there remain large uncertainties in our understanding and quantification
of the regional CH4 budget, owing to complexity and heterogeneity of terrestrial ecosystems. A process-
based model, Vegetation Integrative SImulator for Trace gases model (VISIT), was constructed by introducing
nitrogen cycle and methane exchange processes into a carbon-cycle model Sim-CYCLE , which provides an
observation-verified framework of ecosystem structure and carbon dioxide (CO2) exchange.
In this study, VISIT was applied on the global scale to evaluate the net budget of CH4 over terrestrial
ecosystems. The net budget of CH4 in terrestrial ecosystem is regulated by three different
biogeochemical mechanisms: (1) CH4 oxidation at upland soils (i.e. forests, grassland, deserts, and
croplands) estimated by NASA-CASA scheme, Ridgwellfs scheme, DelGrossofs scheme and Curryfs
scheme; (2) CH4 emission from wetland including paddy field estimated by Caofs scheme; and (3)
vegetation CH4 emission under aerobic condition (i.e. from tree and grass leaves) estimated by
Kirschbaumfs scheme.
Using historical climate data of CRU-TS2.1 from 1901 to 2000 and AOGCM climate projections from 2001 to
2100, we simulated temporal and spatial patterns of net CH4 budget at 0.5-deg x 0.5-deg resolution
under changing atmospheric composition, nitrogen deposition, climate, and land-use. As a result, total
CH4 oxidation by upland soils in 2000 was estimated as 35.9 Tg CH4 per year (25.8-35.9 Tg
CH4 per year by different schemes). Total CH4 emission from wetlands and paddy fields was
estimated as 235.3 Tg CH4 per year. Vegetation CH4 emission under aerobic condition was also
estimated as 91.8-137.4 Tg CH4 per year. Therefore, the net budget of CH4 for the global scale
was estimated as 291.2-336.8 Tg CH4 per year in greenhouse-effect gas source to atmosphere.
Preliminary results by VISIT is presented and compared with previous studies in terms of regional CH4
budget. Finally, we discuss potential uncertainties and collaboration with atmospheric observational and
inversion studies.
B33B-0430
Methane emissions estimated from atmospheric observations of methane and its carbon isotopes: MOZART - 2 modeling study
Methane is an important contributor to global warming with atmospheric concentrations nearly three times higher than the pre-industrial levels. Successful verifications of emission reductions from countries around the world depend on accurate modeling of atmospheric methane. Global model simulations of tropospheric methane, using the Model for Ozone and Related Chemical Tracers (MOZART-2), are presented. The magnitude of methane sources in the model is determined based on the a priori estimates of the source strengths, and the observed spatial distribution of atmospheric methane and its carbon isotopes. The results call for increased global emissions relative to the bottom-up source estimates. The significant increase in emissions in the Southern Hemisphere is required to match the observations. The proposed new set of methane emissions for MOZART-2 is consistent with the long-term global measurements of CH4 and 13C/12C.
B33B-0431
Transport model simulation of atmospheric CH4 - implications for surface flux estimation
We have used an AGCM (atmospheric general circulation model)-based Chemistry Transport Model (ACTM)
for the simulation of methane (CH4) in the lower and middle atmosphere. The model simulations are
compared with measurements at hourly, daily, monthly and interannual time scales at more than 50 surface
monitoring stations. From this comparison, we conclude that the recent (1990-present) trends in CH4 growth
rate and seasonal cycle at most measurement sites can be fairly successfully modeled by using existing
knowledge of CH4 flux trends and seasonality. Good model-observation comparison is achieved by optimizing
flux amplitudes with respect to the available hydroxyl radical (OH) distribution and model transport. Detailed
analysis of seasonal cycles, synoptic variations and diurnal cycles are shown to be useful for validating
regional flux distribution patterns and strengths. Our results, based on two emission scenarios, suggest
reduced emissions from temperate and tropical Asia region, and compensating increase in the boreal
Northern Hemisphere (NH) are indicated for improved model-observation agreement. The ACTM simulated
results are also compared with satellite observations (by UARS/HALOE) in the stratospheric altitudes to test
the validity of model chemistry scheme and role of quasi-biennial oscillation on CH4 profiles and trends. Next
we plan to use the ACTM forward transport for surface flux estimation of CH4 in a Bayesian synthesis
inversion framework.
http://www.jamstec.go.jp/frcgc/research/d4/prabir/papers/actm_ch4_jmsj.pdf