Boreal peatlands cover approximately 350 Mha from which about 50 % is found in North America. These ecosystems are substantial carbon sinks and constitute one of the most important natural source of methane (CH4) to the atmosphere. Annual release of CH4 to the atmosphere has been estimated to range between 20 and 50 Tg yr-1. A strong relationship between water table depth (WTD), plant community and CH4 fluxes is well documented, fluxes being more important as the WTD is closer to the peatland surface. Given their sensibility to peatland surface moisture changes, testate amoebae and plant macrofossils assemblages constitute valuable paleohydrological proxy indicators from which robust WTD reconstruction can be obtained. When coupled to modern CH4 fluxes, WTD fluctuation can potentially yield to holocene CH4 estimates.

Based on these assumptions, late-holocene CH4 fluxes from boreal peat bog in the Eastmain-1 region (James Bay, Québec, Canada) were reconstructed. Modern CH4 fluxes were measured using static chambers over different vegetation types following a hydrologic gradient between 2005 and 2006 growing seasons. Two 1m-long peat cores were sampled at 2-cm intervals for macrofossil and testate amoebae analyses, and transfer functions were applied to the latter assemblages in order to estimate past WTD changes. Peat chronologies were controlled by AMS radiocarbon dates and 210Pb dates. Based on modern CH4 emissions, past fluxes were derived paleohydrological reconstruction and transfer to CH4 values throughout the Late-Holocene period.

This research highlights the need for a better understanding of the role played by past CH4 emissions from peatlands in atmospheric CH4 concentration.

Late-Holocene reconstruction of methane fluxes for the last 3000 years based on testate amoebae assemblages: application to a Canadian boreal peat bog