Intra- and Inter-Annual Variability in Wetland CH4 Emissions from a Sub-Boreal Peatland

Approximately half the global CH₄ flux originates from natural sources, and these are mostly located in wetland ecosystems. Understanding the climate sensitivities and temporal variability of wetland CH₄ emissions is thus key to constraining atmospheric CH₄ trajectories. Here we present a decade long dataset of ongoing CH₄ eddy covariance flux measurements from the Bog Lake Fen sub-boreal peatland in the Marcell Experimental Forest (47.505 N, -93.489 W, Minnesota, USA). Annual CH₄ fluxes between 2009 and 2018 ranged from 10 to 21 gCH₄ m^-2 yr^-1. Successive years differ by as much as 10 gCH₄ m^-2 yr^-1, revealing large inter-annual variability in wetland CH₄ emissions. We compared the observed fluxes to those predicted by the WetCHARTs (v.1.2.1) wetland emission model ensemble, and find that the model broadly captures the observed inter-annual variability, with up to 2.4-fold differences between successive years. High-emitting years were marked by cold seasons with shallow snow accumulation followed by warm seasons with extended periods of above-freezing peat temperatures plus high rainfall. Together these variables explained ~65% of the measured inter-annual flux variability. Within any particular year, CH₄ emissions remained elevated after the hottest day of the year and thus exhibited hysteresis with peat temperatures. The presentation will explore how the observed variability in CH₄ emissions can be understood in terms of watershed hydrology and peat/water redox potential.