Hot moments drive extreme nitrous oxide and methane emissions from agricultural peatlands

Agricultural peatlands are estimated to emit approximately one third of global greenhouse gas (GHG) emissions from croplands, but the temporal dynamics and controls of these emissions are poorly understood, particularly for nitrous oxide (N2O). We used cavity ring‐down spectroscopy and automated chambers in a drained agricultural peatland to measure over 70,000 individual N2O, methane (CH4), and carbon dioxide (CO2) fluxes over 3 years. Our results showed that N2O fluxes were high, contributing 26% (annual range: 16%–35%) of annual CO2e emissions. Total N2O fluxes averaged 26 ± 0.5 kg N2O‐N ha−1 y−1 and exhibited significant inter‐ and intra‐annual variability with a maximum annual flux of 42 ± 1.8 kg N2O‐N ha−1 y−1. Hot moments of N2O and CH4 emissions represented 1.1 ± 0.2 and 1.3 ± 0.2% of measurements, respectively, but contributed to 45 ± 1% of mean annual N2O fluxes and to 140 ± 9% of mean annual CH4 fluxes. Soil moisture, soil temperature, and bulk soil oxygen (O2) concentrations were strongly correlated with soil N2O and CH4 emissions; soil nitrate (NO3‐) concentrations were also significantly correlated with soil N2O emissions. These results suggest that IPCC benchmarks underestimate N2O emissions from these high emitting agricultural peatlands by up to 70%. Scaling to regional agricultural peatlands with similar management suggests these ecosystems could emit up to 1.86 Tg CO2e y−1 (range: 1.58–2.21 Tg CO2e y−1). Data suggest that these agricultural peatlands are large sources of GHGs, and that short‐term hot moments of N2O and CH4 are a significant fraction of total greenhouse budgets. We collected over 70,000 individual nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) fluxes over 3 years from an agricultural maize peatland. This system was a significant greenhouse gas source, with N2O alone contributing up to 35% of the annual CO2‐equivalent emissions. Both CH4 and N2O were driven by hot moments of extreme emissions, with