Wetland methane emission response to last glacial maximum atmospheric carbon dioxide concentration

• Main Authors: Boardman, C., Gauci, V., Beerling, D.
• Format: Conference Object
• Language: unknown
• Published: 2008
• Subjects: Fid; ice core
• Online Access: https://oro.open.ac.uk/32784/; http://www.agu.org/cgi-bin/wais?mm=B11F-05

Ice core records show that the atmospheric concentration of methane (CH 4 ) during the Last Glacial Maximum (LGM) (~21,000 years ago) was 40% lower than the preindustrial Holocene. The contribution of natural wetlands to the global CH 4 budget during the LGM is determined by modelling their spatial extent and productivity. Although models provide an estimated flux of ~75-180 Tg yr -1 , they adopt present day physiological relationships to reconstruct past wetland emissions. Here we show that the LGM (180 ppm) carbon dioxide (CO 2 ) concentration lowers CH 4 emissions from peat cores incubated in controlled environments compared to cores maintained under a modern atmospheric CO 2 concentration (380 ppm). Peat cores (110 x 400 mm) collected from a UK minerotrophic fen and upland ombrotrophic bog were maintained either in a [CO 2 ] of 180 ppm or 380 ppm over 21 months. CH 4 fluxes were measured on a monthly/weekly basis using static chambers with [CH 4 ] measured via an LGR Fast CH 4 Analyser and GC-FID. Results show that total CH 4 flux from the minerotrophic fen was suppressed by 17 and 31% in season 1 and 2 respectively under LGM CO 2 starvation. The ombrotrophic bog cores were suppressed by 20% in year 1 and 10% in year 2. Both peat types exhibited a rapid initial response to the sub-ambient [CO 2 ] treatment with a change in CH 4 flux recorded 5 days into the experiment. We also measured the influence of an LGM [CO 2 ] atmosphere on CH 4 flux temperature response during years 1 and 2. These results suggest that both wetland plants, and the underlying biogeochemistry of the rhizosphere, are sensitive to a reduction in [CO 2 ] in the atmosphere and this has yet to be incorporated into global wetland CH 4 models.