B51F-01 INVITED
Airborne measurements indicate large methane emissions from the Eastern Amazon Basin
Recent results from laboratory, field and remote sensing measurements suggest the presence of large methane emissions from the Amazon basin. In this talk, we will present regionally integrative, direct trace gas observations from two sites that confirm the presence of large fluxes of methane in eastern Amazonia. Air samples collected on aircraft near Santarem (2.9 deg. S, 55.0 deg W) and Manaus (2.6 deg S, 60.0 deg W) in eastern and central Amazonia show large enhancements of CH4 that are not seen at the NOAA/ESRL background sites in the tropical Atlantic Ocean. From the surface to about four km, enhancements averaging 34 ppb and up to 200 ppb occur throughout the year. Based on data from 2000 – 2007, we calculate emissions averaging 27 mg CH4/m2/day from upwind sources. This estimate is substantially larger than "bottom- up" source estimates for individual sources likely to be contributors. Our measurements represent a substantial gradient between South America and adjacent oceans and a tropical bulge in the global north-south methane gradient that are not captured by sampling sites in the marine boundary layer.
B51F-02
Airborne Remote-Sensing of Atmoshperic CH4 and CO2 Column Mixing Ratio With MAMap - First Results
The Methane Airborne Mapper (MAMap) performs quantitative CO2 and CH4 remote sensing measurements of the atmospheric column between an aircraft and the Earth's surface. Its two spectrometers cover wavelenghts of 1.59-1.62μm for CO2, 1.63-1.75μm for CH4 and 760nm for O2. A CH4 detection limit of <35ppbv and a resolution of <5% (at atmospheric background concentration of 1750ppbv) have been ascertained, which makes it possible to detect small changes within the atmospheric CH4 column at a local and regional scale. The atmospheric column mixing ratios of CH4 and CO2 were calculated using the WFM-DOAS algorithm which is known from the retrieval of CH4 and CO2 column concentrations from nadir measurements by SCIAMACHY. MAMap addresses the uncertainties in the current greenhouse gas emission budgets and provides a link between local ground-based small-scale and global satellite-based measurements. The aim of future MAMap research programs is the detection and quantification of CH4 and CO2 emission sources of both natural and anthropogenic origin. MAMap is designed for flexible operations at various planes, e.g. the DLR Dornier 228, the DLR 'Falcon' or the DLR Gulfstream 'HALO' aircraft. The results presented here were performed with a Cessna aircraft T207 at a flight height of 700m and a flight speed of 200km/h. The related ground pixel size covers 18m (across-track) x 10m (along track, albedo 0.18). The preliminary assessment of the sensor sensitivity under field campaign conditions includes measurements over a variety of natural and anthropogenic CH4 and CO2 emission sources, like coal-fired power plants, landfill sites, wetlands, a large number of different land surface types and a simulated CH4 source (CH4 released from a pressured gas bottle). First results will be reported.
B51F-03
Inverse Modeling of Atmospheric Methane Emissions Using 4D-Var
A four-dimensional variational (4D-Var) data assimilation system for inverse modeling of atmospheric CH4 emissions is presented. The system is based on the TM5 atmospheric transport model. It can be used for assimilating large volumes of CH4 measurements, in particular satellite retrievals, and at the same time it enables the optimization of a large number of model parameters. We present the results of global inversions and coupled global-regional inversions, exploiting the zooming capability of the TM5 model. We assimilate observations from both surface stations and the SCIAMACHY instrument aboard ENVISAT, measuring column-averaged CH4 mixing ratios globally with high sensitivity to near-surface CH4. After application of a bias correction to the satellite retrievals, the assimilation system is able to closely fit the SCIAMACHY measurements, while retaining consistency with the surface network. Reductions in the uncertainty of emissions achieved by the different observation types, as estimated by our 4D- Var system, are discussed. Specific attention is given to tropical South America, where SCIAMACHY generally measures higher methane concentrations than simulated a priori by the model. Particularly in the period September to November 2003, the inversions suggest almost a doubling of South American emissions relative to the prior estimate. Independent aircraft observations support the presence of large methane emissions but suggest that enhancements may be smaller than estimated from the assimilation of SCIAMACHY observations.
B51F-04
Trace Gas Fluxes From Through-Canopy Measurements in an Upland Forest of the Eastern Brazilian Amazon
Methane (CH4) is a radiatively active trace gas whose atmospheric budget has been perturbed by humans. Wetlands have been recognized as the main natural source of CH4 for the past 30 years. Current inverse models indicate that tropical sources account for the bulk of CH4 emissions. The largest sources are likely wetlands, agriculture and burning and that these sources may be underestimated. As part of the LBA experiment, we automatically sampled CH4 and carbon dioxide (CO2) mixing ratios in profiles through two forest canopies at sites 67 and 83 km south of Santarém, Pará. CH4 and CO2 can have a strong diurnal signal. CH4 mixing ratios correlated well with CO2. Both gases had column maxima in the early morning near dawn because of stable nocturnal conditions. However there were differences in the profiles. Highest CO2 mixing ratios tended to occur near the surface due to the strong respiration source of CO2. Often the lowest mixing ratios of CH4 were found near the surface which is consistent with a weak soil sink. Calculations of the CH4 flux of example periods from different seasons were made by correlating height weighted averages of the half hourly ambient mixing ratios of CH4 and CO2 and relating this correlation to the ratio of coincident nocturnal NEE CO2 eddy correlation fluxes made during windy nights at two towers at the same sites and automated chamber flux measurements made at the km67 site. Fluxes were calculated to be between 2.2 and 23.3 mg CH4 m-2 d-1. If the area of the upland forest area of the Amazon basin is 5 x 106 km2, we then estimate a CH4 source strength of 4 to 43 Tg y-1. This estimate is consistent with a flux of 4 to 38 Tg y-1 calculated from a survey of profile and flux measurements made during the dry and wet seasons at three other sites across the Amazon basin.
B51F-05 INVITED
News about methane emission from plant matter
Almost two years ago, Keppler et al. [2006] published results from laboratory experiments indicating that living plants, plant litter and the structural plant component pectin emit methane to the atmosphere under aerobic conditions. These findings contradict the accepted view that methane can be formed under oxygen-free conditions only, and in fact we still lack a fundamental understanding of the production process. They also have far-reaching implications since they imply a new and possibly important plant-climate feedback, since the global source strength estimated from those laboratory measurements was large. The scientific debate first concentrated on the up-scaling approach, and several other approaches have been suggested. However, since no up-scaling rule has been identified, also other up-scaling methods lack a solid scientific basis and the fundamental question at this stage is whether aerobic CH4 emissions from the biosphere do actually exist. Several possible experimental artifacts in the experiments of Keppler et al. have been suggested, and in fact one recent study has reported the absence of CH4 emissions from vegetation [Dueck, et al., 2007], but the discrepancy to the measurements of Keppler et al. could not be explained. In our follow up research we have aimed at proving that an aerobic CH4 production mechanism does indeed exist. Our new results – obtained with different analytical techniques – show that dry and fresh plant matter, as well as several structural plant components, emit significant amounts of methane upon irradiation with UV light and heating. Emissions from UV irradiation are almost instantaneous, indicating a direct photochemical process. The size of the methane-forming reservoir exceeds the size of suggested contamination sources by several orders of magnitude. A dry leaf of a pure 13C plant also produces 13CH¬4. References Dueck, T. A., R. de Visser, H. Poorter, S. Persijn, A. Gorissen, W. de Visser, A. Schapendonk, J. Verhagen, J. Snel, F. J. M. Harren, A. K. Y. Ngai, F. Verstappen, H. Bouwmeester, L. A. C. J. Voesenek, and A. van der Werf, No evidence for substantial aerobic methane emission by terrestrial plants: a 13C-labelling approach New Phytologist, doi : 10.1111/j.1469-8137.2007.02103.x, 2007. Keppler, F., J. T. G. Hamilton, M. Brass, and T. Röckmann, Methane emissions from terrestrial plants under aerobic conditions, Nature, 439, 187-191, doi:110.1038/nature04420, 2006.
B51F-06
Methane Evasion and Carbon Dynamics on the Amazon Floodplain
The fringing floodplain along the 2600 km reach of the Amazon River in Brazil inundates up to about 80,000 km squared of flooded forests, open water and floating macrophytes. These habitats outgas significant amount of carbon dioxide and methane as a result of autochthonous and allochthonous fixation and exchanges of carbon on the floodplain and with the neighboring uplands. Based on our measurements and those of others, we have assembled sufficient data to characterize the following fluxes and transformations in a representative central Amazon floodplain lake: inputs of litterfall, dissolved organic carbon (DOC) in rainfall, DOC and particulate organic carbon (POC) in streams, DOC in groundwater seepage; exchanges of DOC and POC with the mainstem river; net primary productivity of floating macrophyes, periphyton and phytoplankton; sedimentation; carbon dioxide and methane evasion. These data are the basis for models of carbon processing and methane evasion.
B51F-07
An Integrated Greenhouse Gas Assessment of an Alternative to Slash-and-Burn Agriculture in Eastern Amazonia
Fires set for slash-and-burn agriculture contribute to the current unsustainable accumulation of atmospheric greenhouse gases, and they also deplete the soil of essential nutrients, which compromises agricultural sustainability at local scales. Integrated assessments of greenhouse gas emissions have compared intensive cropping systems in industrialized countries, but such assessments have not been applied to common cropping systems of smallholder farmers in developing countries. We report an integrated assessment of greenhouse gas emissions in slash-and-burn agriculture and an alternative chop-and-mulch system in the Amazon Basin. The soil consumed atmospheric methane under slash-and-burn treatment and became a net emitter of methane to the atmosphere under the mulch treatment. Mulching also caused about a 50 percent increase in soil emissions of nitric oxide and nitrous oxide and required use of fertilizer and fuel for farm machinery. Despite these significantly higher emissions of greenhouse gases during the cropping phase under the alternative chop- and-mulch system, calculated pyrogenic emissions in the slash-and-burn system were much larger, especially for methane. The global warming potential CO2-equivalent emissions calculated for the entire crop cycles were at least five times lower in chop-and-mulch compared to slash-and-burn and were dominated by differences in methane emissions. The crop yields were similar for the two systems. While economic and logistical considerations remain to be worked out for alternatives to slash-and-burn, these results demonstrate a potential "win-win" strategy for maintaining soil fertility and reducing net greenhouse gas emissions, thus simultaneously contributing to sustainability at both spatial scales.
B51F-08
Trends and Patterns in a New Time Series of Natural and Anthropogenic Methane Emissions, 1980-2000
We report on a new time series of methane (CH4) emissions from anthropogenic and natural sources developed for a multi-decadal methane modeling study (see following presentation by Bruhwiler et al.). The emission series extends from 1980 through the early 2000s with annual emissions for all countries has several features distinct from the source histories based on IPCC methods typically employed in modeling the global methane cycle. Fossil fuel emissions rely on 7 fuel-process emission combinations and minimize reliance on highly-uncertain emission factors. Emissions from ruminant animals employ regional profiles of bovine populations that account for the influence of variable age- and size-demographics on emissions and are ~15% lower than other estimates. Waste-related emissions are developed using an approach that avoids using of data-poor emission factors and accounts for impacts of recycling and thermal treatment of waste on diverting material from landfills and CH4 capture at landfill facilities. Emissions from irrigated rice use rice-harvest areas under 3 water-management systems and a new historical data set that analyzes multiple sources for trends in water management since 1980. A time series of emissions from natural wetlands was developed by applying a multiple-regression model derived from full process-based model of Walter with analyzed meteorology from the ERA-40 reanalysis.