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Abstract. Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the Boreal–Arctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 × 0.5∘ grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 × 106 km2 (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 × 106 km2. Bog, fen, and permafrost bog were the most abundant wetland classes, covering ∼ 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 × 106 km2 (6 % of domain). Low-methane-emitting large lakes (>10 km2) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km2) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval between 0.15 and 0.38 × 106 km2. Rivers and streams were estimated to cover 0.12  × 106 km2 (0.5 % of domain), of which 8 % was associated with high-methane-emitting headwaters that drain organic-rich landscapes. Distinct combinations of spatially co-occurring wetland and lake classes were identified across the BAWLD domain, allowing for the mapping of “wetscapes” that have characteristic methane emission magnitudes and sensitivities to climate change at regional scales. With BAWLD, we provide a dataset which avoids double-accounting of wetland, lake, and river extents and which includes confidence intervals for each land cover class. As such, BAWLD will be suitable for many hydrological and biogeochemical modelling and upscaling efforts for the northern boreal and arctic region, in particular those aimed at improving assessments of current and future methane emissions. Data are freely available at https://doi.org/10.18739/A2C824F9X (Olefeldt et al., 2021).

Current models and theories of the formation and maintenance of microtopography in ombrotrophic peatlands (bogs) assume autogenic feedbacks between vegetation composition, water table depth (WTD) and microtopography. A hypothesized outcome of autogenic feedbacks is a strong association among spatial variations in vegetation composition, WTD and microtopography. We tested and corroborated this hypothesis using fine spatial scale (<2 × 2 m 2 ) data from two 20 × 20 m 2 plots at Mer Bleue, a temperate bog. Furthermore, we partitioned the spatial variation of plant communities into portions explained by WTD as well as fine-scale and broad-scale spatial structures using distance-based Moran's eigenvector maps. We hypothesized that plant distributions are more strongly related to WTD than to microtopography and found that this hypothesis was supported in only one of the two sampled plots, suggesting that the feedbacks among WTD, vegetation and microtopography could be dependent on location within a bog. A plot closer to the centre (apex) of the bog showed stronger relationships among WTD-microtopography and vegetation than a plot closer to the margin. Our results support current models and theories of the development of bogs wherein plant communities, water table and microtopography are strongly associated because of underlying ecohydrological feedbacks but highlight that strength and direction of feedbacks may vary by location within a bog. Affirming the presence of these structural relationships and identifying variability in them is a key step towards better understanding peatland carbon cycling, especially in the context of increasing anthropogenic and natural disturbances to peatlands.Monte Carlo test for significance of all canonical axes suggested that the canonical correspondence analysis results were significant for plot A (Trace = 0.045, F-ratio = 2.7, p = 0.006) and plot B (Trace = 0.072, F-ratio = 4.0, p = 0.002). 1352A. MALHOTRA ET AL.

We would like to dedicate this paper to co-author Richard Payne. Richard was a member of a group of 8 climbers caught in an avalanche in the Himalayas at the end of May. Correspondence AbstractRecent studies show that soil eukaryotic diversity is immense and dominated by micro-organisms. However, it is unclear to what extent the processes that shape the distribution of diversity in plants and animals also apply to micro-organisms. Major diversification events in multicellular organisms have often been attributed to longterm climatic and geological processes, but the impact of such processes on protist diversity has received much less attention as their distribution has often been H I I I J J J J J J J J J K K K

Northern peatlands have cooled the global climate by accumulating large quantities of soil carbon (C) over thousands of years. Maintaining the C sink function of these peatlands and their immense long-term soil C stores is critical for achieving net-zero global carbon dioxide (CO 2 ) emissions by 2050 to mitigate climate warming. One-quarter of the world's northern peatlands are in Canada, with these mostly intact ecosystems providing a global C service that is increasingly recognized as a critical part of naturebased solutions to combat climate change. However, land-use change and other disturbances threaten these globally important stores of "irrecoverable C" (that is, soil C lost to disturbance that will take centuries to recover). Inadequate policy safeguards to avoid conversion and degradation, and the limited quantification and reporting of peatland greenhouse-gas emissions and removals, increase the vulnerability of these peatlands. Targeted policies from local to global scales will be needed for improved decision making and incentivizing long-term C management of northern peatlands.