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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]

Simple and robust hydrological modelling is critical for peat studies as water content (θ) and water table depth (dWT) are key controls on many biogeochemical processes. We show that near-surface θ can be a good predictor of θ at any depth and/or dWT in peat. This was achieved by further developing the formulae of an existing model and applying it for Mer Bleue bog (Ontario, Canada) and a permafrost peat plateau at Scotty Creek (Northwest Territories, Canada). Simulated θ dynamics at various depths in hummocks and hollows at both sites matched observations with R2, Willmott's index of agreement (d), and normalized Nash-Sutcliffe efficiency coefficient (NNSE), reaching 0.97, 0.95, and 0.86, respectively. Simulated bog WT dynamics matched observations with R2, d, and NNSE reaching 0.67, 0.87, and 0.72. Our approach circumvents the difficulties of measuring subsurface hydrology and reveals a perspective for large spatial scale estimation of θ and dWT in peat. [ABSTRACT FROM AUTHOR]

In the discontinuous permafrost zone of the Northwest Territories (NWT), Canada, snow covers the ground surface for half the year. Snowmelt constitutes a primary source of moisture supply for the short growing season and strongly influences stream hydrographs. Permafrost thaw has changed the landscape by increasing the proportional coverage of permafrost‐free wetlands at the expense of permafrost‐cored peat plateau forests. The biophysical characteristics of each feature affect snow water equivalent (SWE) accumulation and melt rates. In headwater streams in the southern Dehcho region of the NWT, snowmelt runoff has significantly increased over the past 50 years, despite no significant change in annual SWE. At the Fort Simpson A climate station, we found that SWE measurements made by Environment and Climate Change Canada using a Nipher precipitation gauge were more accurate than the Adjusted and Homogenized Canadian Climate Dataset which was derived from snow depth measurements. Here, we: (a) provide 13 years of snow survey data to demonstrate differences in end‐of‐season SWE between wetlands and plateau forests; (b) provide ablation stake and radiation measurements to document differences in snow melt patterns among wetlands, plateau forests, and upland forests; and (c) evaluate the potential impact of permafrost‐thaw induced wetland expansion on SWE accumulation, melt, and runoff. We found that plateaus retain significantly (p < 0.01) more SWE than wetlands. However, the differences are too small (123 mm and 111 mm, respectively) to cause any substantial change in basin SWE. During the snowmelt period in 2015, wetlands were the first feature to become snow‐free in mid‐April, followed by plateau forests (7 days after wetlands) and upland forests (18 days after wetlands). A transition to a higher percentage cover of wetlands may lead to more rapid snowmelt and provide a more hydrologically‐connected landscape, a plausible mechanism driving the observed increase in spring freshet runoff. [ABSTRACT FROM AUTHOR]

Permafrost degradation in the peat‐rich southern fringe of the discontinuous permafrost zone is catalysing substantial changes to land cover with expansion of permafrost‐free wetlands (bogs and fens) and shrinkage of forest‐dominated permafrost peat plateaux. Predicting discharge from headwater basins in this region depends upon understanding and numerically representing the interactions between storage and discharge within and between the major land cover types and how these interactions are changing. To better understand the implications of advanced permafrost thaw‐induced land cover change on wetland discharge, with all landscape features capable of contributing to drainage networks, the hydrological behaviour of a channel fen sub‐basin in the headwaters of Scotty Creek, Northwest Territories, Canada, dominated by peat plateau–bog complexes, was modelled using the Cold Regions Hydrological Modelling platform for the period of 2009 to 2015. The model construction was based on field water balance observations, and performance was deemed adequate when evaluated against measured water balance components. A sensitivity analysis was conducted to assess the impact of progressive permafrost loss on discharge from the sub‐basin, in which all units of the sub‐basin have the potential to contribute to the drainage network, by incrementally reducing the ratio of wetland to plateau in the modelled sub‐basin. Simulated reductions in permafrost extent decreased total annual discharge from the channel fen by 2.5% for every 10% decrease in permafrost area due to increased surface storage capacity, reduced run‐off efficiency, and increased landscape evapotranspiration. Runoff ratios for the fen hydrological response unit dropped from 0.54 to 0.48 after the simulated 50% permafrost area loss with a substantial reduction of 0.47 to 0.31 during the snowmelt season. The reduction in peat plateau area resulted in decreased seasonal variability in discharge due to changes in the flow path routing, with amplified low flows associated with small increases in subsurface discharge, and decreased peak discharge with large reductions in surface run‐off. [ABSTRACT FROM AUTHOR]

Abstract: Evapotranspiration (ET) is a key component of the water cycle, whereby accurate partitioning of ET into evaporation and transpiration provides important information about the intrinsically coupled carbon, water, and energy fluxes. Currently, global estimates of partitioned evaporative and transpiration fluxes remain highly uncertain, especially for high‐latitude ecosystems where measurements are scarce. Forested peat plateaus underlain by permafrost and surrounded by permafrost‐free wetlands characterize approximately 60% (7.0 × 107 km2) of Canadian peatlands. In this study, 22 Picea mariana (black spruce) individuals, the most common tree species of the North American boreal forest, were instrumented with sap flow sensors within the footprint of an eddy covariance tower measuring ET from a forest–wetland mosaic landscape. Sap flux density (JS), together with remote sensing data and in situ measurements of canopy structure, was used to upscale tree‐level JS to overstorey transpiration (TBS). Black spruce trees growing in nutrient‐poor permafrost peat soils were found to have lower mean JS than those growing in mineral soils. Overall, TBS contributed less than 1% to landscape ET. Climate‐change‐induced forest loss and the expansion of wetlands may further minimize the contributions of TBS to ET and increase the contribution of standing water. [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]

We present the first survey of the vascular flora of Scotty Creek, a peatland-dominated watershed with discontinuous permafrost about 60 km south of Fort Simpson, Northwest Territories (NWT). Of the 140 vascular plant taxa found at Scotty Creek, two are additions to the boreal flora of NWT: Arethusa bulbosa (Dragon's-mouth, Orchidaceae) and Carex pauciflora (Few-flowered Sedge, Cyperaceae). The occurrence of Arethusa bulbosa extends the known range of this species 724 km to the northwest, making this purportedly eastern American plant almost pan-Canadian. Two other major range extensions (> 200 km) are reported for Carex brunnescens subsp. sphaerostachya (Round-spike Brownish Sedge) and Platanthera dilatata var. dilatata (Tall White Bog Orchid). Furthermore, 15 other rare NWT species are reported, including three species known from a single other locality in the NWT. The flora of Scotty Creek is dominated by circumpolar (55%) and widespread North American (34%) elements. Despite the absence of exposed alkaline rocks and the dominance of deep organic soil almost throughout Scotty Creek, a number of limeindicator plants were found in lakes and minerotrophic wetlands. [ABSTRACT FROM AUTHOR]

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Abstract: The Sacramento-San Joaquin Delta in California was drained and converted to agriculture more than a century ago, and since then has experienced extreme rates of soil subsidence from peat oxidation. To reverse subsidence and capture carbon there is increasing interest in converting drained agricultural land-use types to flooded conditions. Rice agriculture is proposed as a flooded land-use type with CO2 sequestration potential for this region. We conducted two years of simultaneous eddy covariance measurements at a conventional drained and grazed degraded peatland and a newly converted rice paddy to evaluate the impact of drained to flooded land-use change on CO2, CH4, and evaporation fluxes. We found that the grazed degraded peatland emitted 175–299g-Cm−2 yr−1 as CO2 and 3.3g-Cm−2 yr−1 as CH4, while the rice paddy sequestered 84–283g-Cm−2 yr−1 of CO2 from the atmosphere and released 2.5–6.6g-Cm−2 yr−1 as CH4. The rice paddy evaporated 45–95% more water than the grazed degraded peatland. Annual photosynthesis was similar between sites, but flooding at the rice paddy inhibited ecosystem respiration, making it a net CO2 sink. The rice paddy had reduced rates of soil subsidence due to oxidation compared with the drained peatland, but did not completely reverse subsidence. [Copyright &y& Elsevier]

Abstract: We report on methane (CH4) concentrations and efflux densities that were measured over a drained and grazed, peatland pasture in the Sacramento-San Joaquin River Delta of California over a three year period. The site was ideal for micrometeorological flux measurements due to its very flat topography, its exposure to vigorous winds and its extended fetch along the predominant wind direction. Nevertheless, the interpretation of methane fluxes with eddy covariance proved to be extremely complicated by a number of geographical, biophysical, biogeochemical and site management factors. Initial inspection of the data revealed unexpected results—methane concentrations and efflux densities were greatest during the night rather than during the day. To explain this odd diurnal behavior in methane efflux densities and concentration, we tested two hypotheses. The prime hypothesis presupposed that the stable stratification of the nocturnal boundary layer elongated the flux footprint and enabled the flux tower to sense wetter fields at the western edge of the pasture, flooded drainage ditches, and/or a tidal marsh upwind of the pasture—these land forms emitted methane at rates 10–100 times greater than the drained portion of the peatland. And, this methane was emitted into a shallower volume of the atmosphere due to the collapse of the nocturnal boundary layer, causing methane concentrations to rise faster. The alternative hypothesis attributed the higher nocturnal methane fluxes to cattle, as they may have congregated near the tower at night. We investigated these hypotheses with: (1) a series of micrometeorological field measurements at companion sites upwind and downwind of the pasture; (2) a series of chamber-based flux measurements on the representative land classes; (3) through the lens of a one-dimensional planetary boundary layer (pbl), box model; and (4) via inspection of digital camera images for the presence or absence of cattle. Together, these pieces of data suggest that elevated methane fluxes and concentrations at night were due to the combined correlation between: (1) the collapse of the nocturnal boundary layer; (2) the elongation of the flux and concentration footprints; and (3) the preferential sampling of an elevated methane source, be it the cattle, wet proportions of the field or some combination. On the other hand, our flux measurements were not perturbed by methane emanating from the tidal marsh that was several kilometers upwind of the peatland pasture site. [Copyright &y& Elsevier]

Abstract: Northern hemisphere peatlands play an important role in the global carbon (C) cycle, accounting for about 30% of global soil C and ~10–25% of global natural methane (CH4) emissions. Satellite remote sensing has the potential for extracting continuous information related to C exchange rates at regional and global extents, yet, few studies have focused on peatlands. In this study we examined the potential of moderate resolution imaging spectroradiometer (MODIS) vegetation indices (normalized difference vegetation index, NDVI and simple ratio, SR), MODIS light use efficiency (LUE) based gross primary production (GPP) and a MODIS derived phenological index (annual peak photosynthetic rate) for the estimation of eddy covariance (EC) flux-derived GPP and net ecosystem production (NEP) at four contrasting northern peatlands. At the four sites of this study MODIS NDVI and SR explained between 39% and 71%, and between 42% and 69% of the variation in EC-derived GPP, respectively; and between 25% and 53%, and between 29% and 39% of the variation in EC-derived NEP, respectively. The relationships were mostly consistent across sites and within sites, suggesting that data may be pooled across years and sites, which could simplify the prediction of gross and net C dioxide (CO2) uptake over large areas dominated by northern peatlands based on MODIS data. MODIS GPP explained between 68% and 89% of the variation in EC-derived GPP at the four study sites. The root mean square errors ranged between 0.62 and 1.16gCm−2 d−1 and were similar to errors from ecosystem process model estimates reported in the literature. Annual peak MODIS GPP, NDVI and SR rates explained up to 50% of the variations in annual cumulative EC-derived GPP and NEP at two of the study sites. Our results show the potentials and limitations of MODIS data to monitor the C dynamics of northern peatlands; among the three studied approaches the MODIS LUE-based GPP approach showed better performance as a predictor of GPP and NEP. The other approaches (VIs and phenology) can provide important input data for LUE models. [Copyright &y& Elsevier]