The Importance of Lake Emergent Aquatic Vegetation for Estimating
Arctic-Boreal Methane Emissions
Abstract
Areas of lakes that support emergent aquatic vegetation emit
disproportionately more methane than open water but are
under-represented in upscaled estimates of lake greenhouse gas
emissions. These shallow areas are typically less than
~1.5 m deep and can be estimated through synthetic
aperture radar (SAR) mapping. To assess the importance of lake emergent
vegetation (LEV) zones to landscape-scale methane emissions, we combine
airborne SAR mapping with field measurements of vegetated and open-water
methane flux. First, we use Uninhabited Aerial Vehicle SAR (UAVSAR) data
from the NASA Arctic-Boreal Vulnerability Experiment (ABoVE) to map LEV
in 4,572 lakes across four Arctic-boreal study areas and find it
comprises ~16% of lake area, exceeding previous
estimates, and exhibiting strong regional differences (averaging 59
[50–68]%, 22 [20-25]%, 1.0 [0.8-1.2]%, and 7.0
[5.0-12]% of lake areas in the Peace-Athabasca Delta, Yukon Flats,
and northern and southern Canadian Shield, respectively). Next, we
account for these vegetated areas through a simple upscaling exercise
using paired methane fluxes from regions of open water and LEV. After
excluding vegetated areas that could be accounted for as wetlands, we
find that inclusion of LEV increases overall lake emissions by 21
[18-25]% relative to estimates that do not differentiate lake
zones. While LEV zones are proportionately greater in small lakes, this
relationship is weak and varies regionally, underscoring the need for
methane-relevant remote sensing measurements of lake zones and a
consistent criterion for distinguishing wetlands. Finally, Arctic-boreal
lake methane upscaling estimates can be improved with more measurements
from all lake zones.