Browsing by Autor "David Lowry"

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δ 13 C methane source signatures from tropical wetland and rice field emissions
(Royal Society, 2021) James L. France; Rebecca Fisher; David Lowry; Grant Allen; Marcos Andrade; Stéphane Bauguitte; Keith Bower; Timothy J. Broderick; M. C. Daly; Grant L. Forster
The atmospheric methane (CH4) burden is rising sharply, but the causes are still not well understood. One factor of uncertainty is the importance of tropical CH4 emissions into the global mix. Isotopic signatures of major sources remain poorly constrained, despite their usefulness in constraining the global methane budget. Here, a collection of new δ13CCH4 signatures is presented for a range of tropical wetlands and rice fields determined from air samples collected during campaigns from 2016 to 2020. Long-term monitoring of δ13CCH4 in ambient air has been conducted at the Chacaltaya observatory, Bolivia and Southern Botswana. Both long-term records are dominated by biogenic CH4 sources, with isotopic signatures expected from wetland sources. From the longer-term Bolivian record, a seasonal isotopic shift is observed corresponding to wetland extent suggesting that there is input of relatively isotopically light CH4 to the atmosphere during periods of reduced wetland extent. This new data expands the geographical extent and range of measurements of tropical wetland and rice δ13CCH4 sources and hints at significant seasonal variation in tropical wetland δ13CCH4 signatures which may be important to capture in future global and regional models. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.
Isotopic signatures of methane emissions from tropical fires, agriculture and wetlands: the MOYA and ZWAMPS flights
(Royal Society, 2021) Euan G. Nisbet; Grant Allen; Rebecca Fisher; James L. France; James Lee; David Lowry; Marcos Andrade; Thomas J. Bannan; Patrick Barker; Prudence Bateson
We report methane isotopologue data from aircraft and ground measurements in Africa and South America. Aircraft campaigns sampled strong methane fluxes over tropical papyrus wetlands in the Nile, Congo and Zambezi basins, herbaceous wetlands in Bolivian southern Amazonia, and over fires in African woodland, cropland and savannah grassland. Measured methane δ13CCH4 isotopic signatures were in the range -55 to -49‰ for emissions from equatorial Nile wetlands and agricultural areas, but widely -60 ± 1‰ from Upper Congo and Zambezi wetlands. Very similar δ13CCH4 signatures were measured over the Amazonian wetlands of NE Bolivia (around -59‰) and the overall δ13CCH4 signature from outer tropical wetlands in the southern Upper Congo and Upper Amazon drainage plotted together was -59 ± 2‰. These results were more negative than expected. For African cattle, δ13CCH4 values were around -60 to -50‰. Isotopic ratios in methane emitted by tropical fires depended on the C3 : C4 ratio of the biomass fuel. In smoke from tropical C3 dry forest fires in Senegal, δ13CCH4 values were around -28‰. By contrast, African C4 tropical grass fire δ13CCH4 values were -16 to -12‰. Methane from urban landfills in Zambia and Zimbabwe, which have frequent waste fires, had δ13CCH4 around -37 to -36‰. These new isotopic values help improve isotopic constraints on global methane budget models because atmospheric δ13CCH4 values predicted by global atmospheric models are highly sensitive to the δ13CCH4 isotopic signatures applied to tropical wetland emissions. Field and aircraft campaigns also observed widespread regional smoke pollution over Africa, in both the wet and dry seasons, and large urban pollution plumes. The work highlights the need to understand tropical greenhouse gas emissions in order to meet the goals of the UNFCCC Paris Agreement, and to help reduce air pollution over wide regions of Africa. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.
Significant fluxes of methane over tropical wetlands and their associated &#948;13C isotopic source signatures
(2020) James L. France; A. E. Jones; Tom Lachlan‐Cope; A. H. Weiss; Marcos Andrade; Isabel Moreno; Rebecca Fisher; David Lowry; Mathias Lanoisellé; Euan G. Nisbet
&lt;p&gt;Tropical wetlands have been proposed as a potential driver for the recent rise in global atmospheric methane. However, direct access and quantification of emissions is difficult. In March 2019, a pilot study was given permission to overfly the Bolivian Llanos de Moxos wetlands to measure atmospheric mixing ratios of methane and collect spot samples for isotopic analysis. Combined with this was a short ground campaign to collect isotopic samples directly above the wetland edge to compare with the integrated atmospheric signature.&lt;/p&gt;&lt;p&gt;Atmospheric mixing ratios of methane reached a maximum of 2400 ppb (500 ppb above baseline concentrations) in the well mixed boundary layer flying at 400m above the wetland. Upwind and downwind transects were a maximum of 300 km, and methane mixing ratios increased roughly linearly with distance downwind. The isotopic data from the airborne surveys and ground surveys give a bulk isotopic signature for &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;CH4&lt;/sub&gt; of ~-59 &amp;#8240; &amp;#177; 4, which is less negative than Amazon floodplain work focusing on emission of methane through trees, but match well with bulk isotopic values from the Amazon Basin. Ground based wetland samples taken concurrently near Trinidad, Bolivia, gave a source signature of -56 &amp;#8240; &amp;#177; 4 re-enforcing the likelihood that the atmospheric enhancements measured are related to the wetland emissions. For comparison, tropical wetlands measured at ground level during a recent Ugandan and Zambian campaign gave heavier &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C&lt;sub&gt;CH4&lt;/sub&gt; isotopic source signatures of -50 to -54 &amp;#8240;. Based on this snap shot study, flux estimations suggest that the Bolivian wetlands could be emitting ~10mg CH&lt;sub&gt;4&lt;/sub&gt; m&lt;sup&gt;-2 &lt;/sup&gt;h&lt;sup&gt;-1&lt;/sup&gt;. The observed mole fractions will be compared to model simulations to determine how well the Bolivian wetland methane fluxes are represented.&lt;/p&gt;
Very large fluxes of methane measured above Bolivian seasonal wetlands
(National Academy of Sciences, 2022) James L. France; Mark F. Lunt; Marcos Andrade; Isabel Moreno; Anita L. Ganesan; Tom Lachlan‐Cope; Rebecca Fisher; David Lowry; Robert J. Parker; Euan G. Nisbet
Methane (CH4) mole fractions from the large semiseasonal Llanos de Moxos wetlands (∼70,000 km2) in northern Bolivia were measured by aircraft flights and ground sampling during early March 2019 (late wet season). Daily fluxes of CH4 determined from the measurements using box models and inverse modeling were between 168 (± 50) and 456 (± 145) mg CH4⋅m-2⋅d-1 for the areas overflown, very high compared with those of previous Amazon basin studies. If the seasonality of the CH4 emissions is comparable to other parts of the Amazon Basin, the region could contribute as much as 8% of annual Amazonian CH4 emissions.