Beavers and the Arctic carbon cycle

Methane hotspots are more common near beaver ponds (51% greater) compared to non-beaver bodies of water. Methane is the second-most abundant greenhouse gas in the atmosphere, after carbon dioxide, and is more effective than carbon dioxide in trapping heat and warming the planet.

Beavers are rapidly expanding their range in northwest Alaska, moving beyond the northern extent of the boreal forest into Arctic tundra ecosystems. As beavers build dams and create ponds, they flood soils adjacent to streams and rivers, which can thaw underlying permafrost. Permafrost soils store large amounts of carbon, which can be released to the atmosphere as carbon dioxide or methane gas upon thaw. Wet soils adjacent to beaver-impacted streams favor methane production. In a new study, scientists from the University of Alaska Fairbanks, NASA, and the National Park Service used airborne imagery to detect methane emission “hotspots” adjacent to beaver ponds in the lower Noatak River basin, within and adjacent to Noatak National Preserve in northwest Alaska. Findings from this study indicate that methane hotspots are more common near beaver ponds (51% greater) compared to non-beaver bodies of water (lakes, streams). Future work will involve taking ground-based measurements of methane release from beaver-impacted soils to compliment the airborne imagery. Still, these initial observations highlight the importance of beaver pond inundation on carbon cycling and permafrost feedbacks to Earth’s climate.

Do beaver ponds increase methane emissions along Arctic tundra streams?

Abstract

Beaver engineering in the Arctic tundra induces hydrologic and geomorphic changes that are favorable to methane (CH₄) production. Beaver-mediated methane emissions are driven by inundation of existing vegetation, conversion from lotic to lentic systems, accumulation of organic rich sediments, elevated water tables, anaerobic conditions, and thawing permafrost. Ground-based measurements of CH₄ emissions from beaver ponds in permafrost landscapes are scarce, but hyperspectral remote sensing data (AVIRIS-NG) permit mapping of 'hotspots' thought to represent locations of high CH₄ emission. We surveyed a 429.5 km² area in Northwestern Alaska using hyperspectral airborne imaging spectroscopy at ∼5 m pixel resolution (14.7 million observations) to examine spatial relationships between CH₄ hotspots and 118 beaver ponds. AVIRIS-NG CH₄ hotspots covered 0.539% (2.3 km²) of the study area, and were concentrated within 30 m of waterbodies. Comparing beaver ponds to all non-beaver waterbodies (including waterbodies >450 m from beaver-affected water), we found significantly greater CH₄ hotspot occurrences around beaver ponds, extending to a distance of 60 m. We found a 51% greater CH₄ hotspot occurrence ratio around beaver ponds relative to nearby non-beaver waterbodies. Dammed lake outlets showed no significant differences in CH₄ hotspot ratios compared to non-beaver lakes, likely due to little change in inundation extent. The enhancement in AVIRIS-NG CH₄ hotspots adjacent to beaver ponds is an example of a new disturbance regime, wrought by an ecosystem engineer, accelerating the effects of climate change in the Arctic. As beavers continue to expand into the Arctic and reshape lowland ecosystems, we expect continued wetland creation, permafrost thaw and alteration of the Arctic carbon cycle, as well as myriad physical and biological changes.

Clark, J. A., K. D. Tape, L. Baskaran, C. Elder, C. Miller, K. Miner, J. A. O'Donnell, and B. M. Jones. 2023. Do beaver ponds increase methane emissions along Arctic tundra streams? Environmental Research Letters 18: 075004.