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

Abstract

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 (N₂ O). We used cavity ring-down spectroscopy and automated chambers in a drained agricultural peatland to measure over 70,000 individual N₂ O, methane (CH₄ ), and carbon dioxide (CO₂ ) fluxes over 3 years. Our results showed that N₂ O fluxes were high, contributing 26% (annual range: 16%-35%) of annual CO₂ e emissions. Total N₂ O fluxes averaged 26 ± 0.5 kg N₂ O-N ha^-1 y^-1 and exhibited significant inter- and intra-annual variability with a maximum annual flux of 42 ± 1.8 kg N₂ O-N ha^-1 y^-1 . Hot moments of N₂ O and CH₄ emissions represented 1.1 ± 0.2 and 1.3 ± 0.2% of measurements, respectively, but contributed to 45 ± 1% of mean annual N₂ O 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 N₂ O and CH₄ emissions; soil nitrate ( ${\text{NO}}_3^{-}$ ) concentrations were also significantly correlated with soil N₂ O emissions. These results suggest that IPCC benchmarks underestimate N₂ O 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 CO₂ e y^-1 (range: 1.58-2.21 Tg CO₂ e y^-1 ). Data suggest that these agricultural peatlands are large sources of GHGs, and that short-term hot moments of N₂ O and CH₄ are a significant fraction of total greenhouse budgets.

Keywords: agricultural peatlands; drained peatlands; greenhouse gas flux; hot moments; methane; nitrous oxide.