PS 22-15 - Characterizing nitrous oxide fluxes and potential drivers across a permafrost gradient in a boreal peatland

Background/Question/Methods

Nitrogen (N) is limiting in boreal ecosystems, which shouldn’t allow for losses of N via leaching into waterways or via gaseous pathways. However, high concentrations of nitrate in streams, and extremely high ammonium in lakes and permafrost has been measured in permafrost influenced regions, indicating the potential for loses of N. One fate of N lost is as nitrous oxide (N₂O), a greenhouse gas (GHG) with a global warming potential ~265 times greater than carbon dioxide (CO₂), but N₂O is understudied at high latitudes leaving the true magnitude of emissions unknown. In late summer 2021, along 3 transects in a palsa-forming peatland near Kuujjuarapik, QC, we measured in-situ flux of N₂O, CO₂ and CH₄ using static chambers to calculate a linear flux, collected ancillary environmental data, and measured dissolved gas concentrations in thermokarst ponds and groundwater. In winter 2022, we will measure in-situ N₂O, CO₂ and CH₄ concentrations in the soil and snowpack using gas-wells, and measure dissolved gas concentrations in the ponds. We will also collect continuous soil temperature data for correlation with the gas-well data, measure snow density to calculate potential fluxes out of the snow, and collect winter water chemistry data for correlation with dissolved gases.

Results/Conclusions

We found no measurable N₂O production at most sites along our transects extending from a thermokarsting palsa (underlain by permafrost) to three thermokarst ponds (no permafrost). However, one site on the downstream side of a pond produced a low flux of N₂O, and we did find high linear production of CO₂ at every site indicating that our method was working. In the ponds, N₂O was undersaturated relative to atmospheric concentration (320 ppb), and concentrations declined at deeper depths suggesting denitrifiers were reducing N₂O to N₂. Extremely low nitrate and high ammonium concentrations in the ponds and groundwater, indicate that nitrification is likely not occurring. This means no N₂O emissions from “leaky” nitrification, and no denitrification reducing nitrate to produce N₂O. In most groundwater samples N₂O was undersaturated, but in an area of active permafrost thaw groundwater was oversaturated with N₂O (18.76 ppm_v) relative to atmospheric concentration, indicating permafrost thaw could contribute to high N₂O production by either nitrification or denitrification. However, we measured no N₂O emissions at the surface above this oversaturated groundwater, indicating that N₂O produced at depth is likely reduced to N₂ before it is emitted. Our results indicate some boreal peatlands are likely consuming, not producing, N₂O.