Abstract:

Lake methane emissions are commonly upscaled from lake area, with recognition that smaller, non-inventoried lakes emit more per unit area. There is also growing awareness of the importance of lake aquatic vegetation and potential “double-counting” with wetlands, but lack of consensus on which is most impactful. Here, we combine high-resolution data with the comprehensive lake inventory HydroLAKES to rank these three variables based on emissions sensitivity. Including non-inventoried small lakes <0.1 km2 (+30 [range: 9.0 to 82]% change) is greatest, followed by double-counting (−20 [−11 to −34]%) and lake aquatic vegetation (+14 [2.7 to 43]%). Significantly, emissions from non-inventoried lakes contribute far less than the ∼40% previously determined globally through statistical area extrapolation. We produce a first pan-Arctic estimate of lake aquatic vegetation in 1.37 million km2 of lakes, but after correcting for persistent double-counting, its net effect is to decrease emissions estimates by 9%. Thus, previous global emissions estimates are likely too high.