Effect of Drought and Heavy Precipitation on CH₄ Emissions and ¹³C-CH₄ in a Northern Temperate Peatland

Shifting precipitation patterns due to climate change may impact peatland methane (CH4) emissions, as precipitation affects water table level which largely controls CH4 cycling. To investigate the impact of variable precipitation on peatland CH4 emissions, we measured CH4 fluxes and their C-13 isotope composition (delta C-13-CH4) across two summers marked by drought (2020) and heavy precipitation (2021) in a northern temperate poor fen in New Hampshire, USA. Monthly variation in CH4 fluxes and delta C-13-CH4 was larger than interannual variation and variation between peatland microforms. While the seasonal pattern of CH4 emissions was not significantly different between years, the magnitude of seasonal changes in CH4 flux and delta C-13-CH4 provided insight regarding the processes controlling CH4 emissions. Between July and August 2020, water table levels dropped > 15 cm, CH4 emissions decreased by an order of magnitude, and delta C-13-CH4 increased similar to 10 parts per thousand, suggesting lower water table levels promoted CH4 oxidation and reduced emissions in late summer. Rainstorms in July 2021 caused flooding and stimulated high CH4 emissions, but the impact of increased water table levels due to heavy precipitation on CH4 fluxes was transient and did not have an apparent effect on emitted delta C-13-CH4. While drought conditions had a clear impact on CH4 fluxes and delta C-13-CH4, our results suggest rainstorms and subsequent flooding do not have a sustained impact on CH4 emissions from temperate peatlands.