EGU2020-9660
https://doi.org/10.5194/egusphere-egu2020-9660
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Significant fluxes of methane over tropical wetlands and their associated δ13C isotopic source signatures

James L. France1,2, Anna Jones1, Tom Lachlan-Cope1, Alex Weiss1, Marcos Andrade3, Isabel Moreno3, Rebecca Fisher2, Dave Lowry2, Mathias Lanoiselle2, Euan Nisbet2, and Mark Lunt4
James L. France et al.
  • 1British Antarctic Survey, Cambridge, United Kingdom of Great Britain and Northern Ireland (jamfra@bas.ac.uk)
  • 2Royal Holloway University, Earth Sciences, Egham, United Kingdom of Great Britain and Northern Ireland
  • 3Campus Universitario Cota-Cota, Universidad Mayor de San Andres, La Paz, Bolivia
  • 4School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom of Great Britain and Northern Ireland

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.

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 δ13CCH4 of ~-59 ‰ ± 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 ‰ ± 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 δ13CCH4 isotopic source signatures of -50 to -54 ‰. Based on this snap shot study, flux estimations suggest that the Bolivian wetlands could be emitting ~10mg CH4 m-2 h-1. The observed mole fractions will be compared to model simulations to determine how well the Bolivian wetland methane fluxes are represented.

How to cite: France, J. L., Jones, A., Lachlan-Cope, T., Weiss, A., Andrade, M., Moreno, I., Fisher, R., Lowry, D., Lanoiselle, M., Nisbet, E., and Lunt, M.: Significant fluxes of methane over tropical wetlands and their associated δ13C isotopic source signatures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9660, https://doi.org/10.5194/egusphere-egu2020-9660, 2020.

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