Atmospheric methane

About: Atmospheric methane is a research topic. Over the lifetime, 2034 publications have been published within this topic receiving 119616 citations.

Investigation of the effect of ammonium sulfate on populations of ambient methane oxidising bacteria by 13C-labelling and GC/C/IRMS analysis of phospholipid fatty acids

Abstract: The oxidation of atmospheric methane by methanotrophic bacteria residing in soils constitutes an important terrestrial methane sink with previous studies having revealed the inhibition of microbially mediated methane oxidation in the presence of salt ions. The bacteria responsible for ambient methane oxidation are not amenable to currently available methods of culturing, resulting in the need for a method of in situ analysis. A combination of phospholipid fatty acid (PLFA) analysis and stable isotopic labelling has been employed in this investigation as a means of cultivation-independent bacterial analysis. Soil samples were treated with an ammonium sulfate solution at a concentration that was known to inhibit methane oxidation or with distilled water, serving as a control, and incubated with 13C-labelled methane. PLFAs were analysed by GC/C/IRMS in order to determine their 13C content and, hence, the PLFA distribution of the methane oxidising bacteria. Ammonium sulfate treatment reduced the amount of 13C incorporated into the majority of PLFAs except the i17:0 PLFA in the presence of high concentrations of methane. These results implied a shift in the composition of the methane oxidising bacterial community in the soils treated with ammonium ions, with the treatment appearing to suppress one group of organisms more than another.

Effects of production and oxidation processes on methane emissions from rice fields

Abstract: The emission of methane from rice fields is the difference between the amount produced in the anaerobic zone below the soil and the amount oxidized in the root zone. Plants can also contribute to methane production by exuding organic compounds that may be utilized by methanogenic bacteria. We measured methane emissions from rice fields at Tu Zu in China between 1988 and 1994, which gave average emissions of about 30 mg m−2 h−1. We estimate that 45–60% of the methane produced was oxidized before reaching the atmosphere; and root exudates may have contributed of the order of 10% of the methane that was produced. The fraction of methane oxidized is low compared to experimental studies at other locations (60–85%). At Tu Zu, methane production is enhanced by continuously flooded fields and the use of large amounts of organic fertilizers; in addition, the lower oxidation rate may also contribute to the higher methane emissions observed compared to other locations. In the past, most of the attention has been devoted to the factors that affect methane production and transport, but it seems that the factors that affect methane oxidation are equally important in determining the flux, if not more so. The comparison of methane fluxes observed at different locations and the extrapolation of field measurements to accurately estimate global emissions will require a better understanding of the rate of methane oxidation in the soils and the factors that control it.

Interannual variation in methane emissions from tropical wetlands triggered by repeated El Niño Southern Oscillation

Abstract: Methane (CH4 ) emissions from tropical wetlands contribute 60%-80% of global natural wetland CH4 emissions. Decreased wetland CH4 emissions can act as a negative feedback mechanism for future climate warming and vice versa. The impact of the El Nino-Southern Oscillation (ENSO) on CH4 emissions from wetlands remains poorly quantified at both regional and global scales, and El Nino events are expected to become more severe based on climate models' projections. We use a process-based model of global wetland CH4 emissions to investigate the impacts of the ENSO on CH4 emissions in tropical wetlands for the period from 1950 to 2012. The results show that CH4 emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Nino periods and with positive anomalies occurring during La Nina periods. An approximately 8-month time lag was detected between tropical wetland CH4 emissions and ENSO events, which was caused by the combined time lag effects of ENSO events on precipitation and temperature over tropical wetlands. The ENSO can explain 49% of interannual variations for tropical wetland CH4 emissions. Furthermore, relative to neutral years, changes in temperature have much stronger effects on tropical wetland CH4 emissions than the changes in precipitation during ENSO periods. The occurrence of several El Nino events contributed to a lower decadal mean growth rate in atmospheric CH4 concentrations throughout the 1980s and 1990s and to stable atmospheric CH4 concentrations from 1999 to 2006, resulting in negative feedback to global warming.

A gas chromatography/combustion/isotope ratio mass spectrometry system for high‐precision δ13C measurements of atmospheric methane extracted from ice core samples

Abstract: Past atmospheric composition can be reconstructed by the analysis of air enclosures in polar ice cores which archive ancient air in decadal to centennial resolution. Due to the different carbon isotopic signatures of different methane sources high-precision measurements of δ13CH4 in ice cores provide clues about the global methane cycle in the past. We developed a highly automated (continuous-flow) gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique for ice core samples of ∼200 g. The methane is melt-extracted using a purge-and-trap method, then separated from the main air constituents, combusted and measured as CO2 by a conventional isotope ratio mass spectrometer. One CO2 working standard, one CH4 and two air reference gases are used to identify potential sources of isotope fractionation within the entire sample preparation process and to enhance the stability, reproducibility and accuracy of the measurement. After correction for gravitational fractionation, pre-industrial air samples from Greenland ice (1831 ± 40 years) show a δ13CVPDB of −49.54 ± 0.13‰ and Antarctic samples (1530 ± 25 years) show a δ13CVPDB of −48.00 ± 0.12‰ in good agreement with published data. Copyright © 2008 John Wiley & Sons, Ltd.