Abstract. Methane (CH4) emissions from the boreal and arctic
region are globally significant and highly sensitive to climate change.
There is currently a wide range in estimates of high-latitude annual
CH4 fluxes, where estimates based on land cover inventories and
empirical CH4 flux data or process models (bottom-up approaches)
generally are greater than atmospheric inversions (top-down approaches). A
limitation of bottom-up approaches has been the lack of harmonization
between inventories of site-level CH4 flux data and the land cover
classes present in high-latitude spatial datasets. Here we present a
comprehensive dataset of small-scale, surface CH4 flux data from 540
terrestrial sites (wetland and non-wetland) and 1247 aquatic sites (lakes
and ponds), compiled from 189 studies. The Boreal–Arctic Wetland and Lake
Methane Dataset (BAWLD-CH4) was constructed in parallel with a
compatible land cover dataset, sharing the same land cover classes to enable
refined bottom-up assessments. BAWLD-CH4 includes information on
site-level CH4 fluxes but also on study design (measurement method,
timing, and frequency) and site characteristics (vegetation, climate,
hydrology, soil, and sediment types, permafrost conditions, lake size and
depth, and our determination of land cover class). The different land cover
classes had distinct CH4 fluxes, resulting from definitions that were
either based on or co-varied with key environmental controls. Fluxes of
CH4 from terrestrial ecosystems were primarily influenced by water
table position, soil temperature, and vegetation composition, while CH4
fluxes from aquatic ecosystems were primarily influenced by water
temperature, lake size, and lake genesis. Models could explain more of the
between-site variability in CH4 fluxes for terrestrial than aquatic
ecosystems, likely due to both less precise assessments of lake CH4
fluxes and fewer consistently reported lake site characteristics. Analysis
of BAWLD-CH4 identified both land cover classes and regions within the
boreal and arctic domain, where future studies should be focused, alongside
methodological approaches. Overall, BAWLD-CH4 provides a comprehensive
dataset of CH4 emissions from high-latitude ecosystems that are useful
for identifying research opportunities, for comparison against new field
data, and model parameterization or validation. BAWLD-CH4 can be
downloaded from https://doi.org/10.18739/A2DN3ZX1R (Kuhn et al., 2021).
