Search

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 (CO2) and methane (CH4), disturbance impacts on fluxes of the potent GHG nitrous oxide (N2O) could contribute to shifts in the net radiative balance. Here, we measured monthly (April to October) fluxes of N2O, CH4, and CO2 from three sites located across the sporadic and discontinuous permafrost zones of western Canada. Undisturbed permafrost peat plateaus acted as N2O sinks (−0.025 mg N2O m−2 d−1), but N2O uptake was lower from burned plateaus (−0.003 mg N2O m−2 d−1) and higher following permafrost thaw in the thermokarst bogs (−0.054 mg N2O m−2 d−1). The thermokarst bogs had below‐ambient N2O soil gas concentrations, suggesting that denitrification consumed atmospheric N2O during reduction to dinitrogen. Atmospheric uptake of N2O in peat plateaus and thermokarst bogs increased with soil temperature and soil moisture, suggesting sensitivity of N2O consumption to further climate change. Four of five peatland ponds acted as N2O sinks (−0.018 mg N2O m−2 d−1), with no influence of thermokarst expansion. One pond with high nitrate concentrations had high N2O emissions (0.30 mg N2O 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 CH4 and CO2 fluxes, while the influence from N2O is minor. Plain Language Summary: The peatlands in the boreal biome of northwestern Canada have been a sink of the potent greenhouse gases (GHG) carbon dioxide (CO2) and nitrous oxide (N2O), and a source of methane (CH4) for many millennia. Now, climate change is transforming these boreal peat landscapes as more severe and frequent wildfires burn the forests and ground ice‐rich permafrost thaws. Wildfires and permafrost thaw alter soil biogeochemical conditions such as soil temperature, soil moisture, and water table depth. The changing conditions have immediate effects on GHG production, transport, and consumption in the soil, which are reasonably well understood for CO2 and CH4 but not for N2O. By measuring soil GHG concentrations at different depths and GHG exchange between soil and atmosphere with static chambers, we showed that N2O exchange from different peat surfaces responded differently depending on the two disturbance types. While burned peatland areas were close to neutral regarding N2O, the wet, thaw‐affected areas showed increased N2O uptake driven by high soil moisture contents, soil temperatures, and below‐atmospheric N2O soil gas concentrations. However, this minor N2O uptake can only offset less than 1% of the global warming potential of CH4 emissions from the thawing peatlands studied here. Key Points: Permafrost peatlands acted as sinks of nitrous oxide; thermokarst and wildfire caused increased and reduced uptake rates, respectivelyUptake of nitrous oxide in peat plateaus and thermokarst bogs increased with soil temperature, suggesting sensitivity to climate warmingImpacts of thermokarst and wildfire on nitrous oxide fluxes were minor compared to methane when expressed in carbon dioxide equivalents [ABSTRACT FROM AUTHOR]

Scotty Creek, Northwest Territories (NWT), Canada, has been the focus of hydrological research for nearly three decades. Over this period, field and modelling studies have generated new insights into the thermal and physical mechanisms governing the flux and storage of water in the wetland-dominated regions of discontinuous permafrost that characterises much of the Canadian and circumpolar subarctic. Research at Scotty Creek has coincided with a period of unprecedented climate warming, permafrost thaw, and resulting land cover transformations including the expansion of wetland areas and loss of forests. This paper (1) synthesises field and modelling studies at Scotty Creek, (2) highlights the key insights of these studies on the major water flux and storage processes operating within and between the major land cover types, and (3) provides insights into the rate and pattern of the permafrost-thaw-induced land cover change and how such changes will affect the hydrology and water resources of the study region. [ABSTRACT FROM AUTHOR]

Permafrost in peatlands strongly influences ecosystem characteristics, including vegetation composition, hydrological functions, and carbon cycling. Large amounts of organic carbon are stored in permafrost peatlands in northwestern Canada. Their possible degradation into permafrost-free wetlands including thermokarst bogs may affect carbon (C) stocks, but the direction and magnitude of change are uncertain. Using peat core reconstructions, we characterized the temporal and spatial variability in vegetation macrofossil, testate amoebae, C content, and peat decomposition along a permafrost thaw chronosequence in the southern portion of the Scotty Creek watershed near Fort Simpson, Northwest Territories. The accumulation of limnic and minerotrophic peat prevailed at the site until permafrost formed around 5000 cal. yr BP. Three distinct permafrost periods were identified in the permafrost peat plateau profile, while permafrost only aggraded once in the thermokarst bog profile. Permafrost thawed at ~550 and ~90 cal. yr BP in the thermokarst bog center and edge, respectively. Both allogenic (climatic shifts and wildfire) and autogenic (peat accumulation, Sphagnum growth) processes likely exerted control on permafrost aggradation and thaw. While apparent carbon accumulation rates (ACARs) were lower during present and past permafrost periods than during non-permafrost periods, long-term C accumulation remained similar between cores with different permafrost period lengths. Deep peat was less decomposed in the permafrost plateau compared with the thermokarst bog, which we speculate is due more to differences in peat type rather than differences in decomposition environment between these two ecosystem states. Our study highlights the importance of considering potential deep peat C losses to project the fate of thawing permafrost peat C stores. [ABSTRACT FROM AUTHOR]