Abstract The greenhouse gas (GHG) balance of boreal peatlands in permafrost regions will be affected by climate change through disturbances such as permafrost thaw and wildfire. Although the future GHG balance of boreal peatlands including ponds is dominated by the exchange of both carbon dioxide (CO 2 ) and methane (CH 4 ), disturbance impacts on fluxes of the potent GHG nitrous oxide (N 2 O) could contribute to shifts in the net radiative balance. Here, we measured monthly (April to October) fluxes of N 2 O, CH 4 , and CO 2 from three sites located across the sporadic and discontinuous permafrost zones of western Canada. Undisturbed permafrost peat plateaus acted as N 2 O sinks (−0.025 mg N 2 O m −2 d −1 ), but N 2 O uptake was lower from burned plateaus (−0.003 mg N 2 O m −2 d −1 ) and higher following permafrost thaw in the thermokarst bogs (−0.054 mg N 2 O m −2 d −1 ). The thermokarst bogs had below‐ambient N 2 O soil gas concentrations, suggesting that denitrification consumed atmospheric N 2 O during reduction to dinitrogen. Atmospheric uptake of N 2 O in peat plateaus and thermokarst bogs increased with soil temperature and soil moisture, suggesting sensitivity of N 2 O consumption to further climate change. Four of five peatland ponds acted as N 2 O sinks (−0.018 mg N 2 O m −2 d −1 ), with no influence of thermokarst expansion. One pond with high nitrate concentrations had high N 2 O emissions (0.30 mg N 2 O m −2 d −1 ). Overall, our study suggests that the future net radiative balance of boreal peatlands will be dominated by impacts of wildfire and permafrost thaw on CH 4 and CO 2 fluxes, while the influence from N 2 O is minor.

Abstract Climate change and permafrost thaw may impact the mobilization of terrestrial dissolved organic carbon (DOC), mercury (Hg), and neurotoxic methylmercury (MeHg) into aquatic ecosystems; thus, understanding processes that control analyte export in northern catchments is needed. We monitored water chemistry for 3 years (2019–2021) at a peatland catchment (Scotty Creek) and a mixed catchment (Smith Creek) in the Dehcho (Northwest Territories), within the discontinuous permafrost zone of boreal western Canada. The peatland catchment had higher DOC and dissolved MeHg, but lower total Hg concentrations (mean ± standard deviation; 19 ± 2.6 mg DOC L −1 ; 0.08 ± 0.04 ng DMeHg L −1 ; 1.1 ± 0.3 ng THg L −1 ) than the mixed catchment (12 ± 4.4 mg DOC L −1 ; 0.05 ± 0.01 ng DMeHg L −1 ; 3.1 ± 2.2 ng THg L −1 ). Analyte concentrations increased with discharge at the mixed catchment, suggesting transport limitation and the flushing of near‐surface, organic‐rich flow paths during wet periods. In contrast, analyte concentrations in the peatland catchment were not primarily associated with discharge. MeHg concentrations, MeHg:THg, and MeHg:DOC increased with water temperature, suggesting enhanced Hg methylation during warmer periods. Mean open water season DOC and total MeHg yields were greater and more variable from the peatland than the mixed catchment (1.1–6.6 vs. 1.4–2.4 g DOC m −2 ; 5.2–36 vs. 6.1–10 ng MeHg m −2 ). Crucial storage thresholds controlling runoff generation likely drove greater inter‐annual variability in analyte yields from the peatland catchment. Our results suggest climate change may influence the production and transport of MeHg from boreal‐Arctic catchments as temperatures increase, peatlands thaw, and runoff generation is altered.