Effect of Drought and Heavy Precipitation on CH 4 Emissions and δ 13 C–CH 4 in a Northern Temperate Peatland

Shifting precipitation patterns due to climate change may impact peatland methane (CH 4 ) emissions, as precipitation affects water table level which largely controls CH 4 cycling. To investigate the impact of variable precipitation on peatland CH 4 emissions, we measured CH 4 fluxes and their 13 C isotope composition ( δ 13 C–CH 4 ) across two summers marked by drought (2020) and heavy precipitation (2021) in a northern temperate poor fen in New Hampshire, USA. Monthly variation in CH 4 fluxes and δ 13 C–CH 4 was larger than interannual variation and variation between peatland microforms. While the seasonal pattern of CH 4 emissions was not significantly different between years, the magnitude of seasonal changes in CH 4 flux and δ 13 C–CH 4 provided insight regarding the processes controlling CH 4 emissions. Between July and August 2020, water table levels dropped > 15 cm, CH 4 emissions decreased by an order of magnitude, and δ 13 C–CH 4 increased ~ 10‰, suggesting lower water table levels promoted CH 4 oxidation and reduced emissions in late summer. Rainstorms in July 2021 caused flooding and stimulated high CH 4 emissions, but the impact of increased water table levels due to heavy precipitation on CH 4 fluxes was transient and did not have an apparent effect on emitted δ 13 C–CH 4 . While drought conditions had a clear impact on CH 4 fluxes and δ 13 C–CH 4 , our results suggest rainstorms and subsequent flooding do not have a sustained impact on CH 4 emissions from temperate peatlands.