Beavers Impacting Tundra Ecosystems (BITE)

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By Alaska Science Center October 16, 2019

The range expansion of the North American beaver (Castor canadensis) has implications for water quality, aquatic ecosystems, and fisheries in Arctic streams.

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Beaver lodge and drained impoundment in tributary of the Noatak River, Noatak National Preserve.(Credit: Michael Carey, USGS. Public domain.)

Landscape change in the Arctic has altered the historical range and distribution of terrestrial mammals, including moose and snowshoe hares, which have moved northward into tundra ecosystems during the 20^th century. Recent field and remote sensing observations indicate that beavers (Castor canadensis) have also expanded their range from boreal forest to tundra ecosystems over the past 15 to 30 years. Extensive research from boreal and temperate regions show that beavers dramatically alter stream hydrology and water quality by building dams, creating impoundments, and modifying the transport of particulates and solutes downstream of the dam. However, little is known about beaver impacts to streams and rivers draining arctic tundra catchments, and how changing environmental conditions or management practices are driving beaver range expansion.

Compared to impacts in other regions and biomes, beaver range expansion in tundra ecosystems is unique as impoundments from beaver dams triggers rapid permafrost thaw due to inundation of valley bottom soils. Permafrost stores large reservoirs of organic carbon (C), nutrients, and mercury (Hg) in perennially frozen soils. Permafrost degradation will impact terrestrial and aquatic ecosystems by altering catchment hydrology, water temperatures and biogeochemical processes. Soil inundation increases wetland extent, which is critical for the production of dissolved organic C and the formation of toxic methylmercury. Further, enhanced hydrologic connectivity following inundation drives the mobilization of these constituents to surface waters and downstream ecosystems, where they can alter water quality and be taken up by stream food webs. Beaver dams may impact fish directly by restricting migration and movement or altering habitat for foraging and spawning, and indirectly by altering water quality through the release of C, nutrients and Hg from inundated permafrost soils. The more variable aquatic thermal habitat created by beavers may also have positive impacts on fish species. Ponded water may lead to warmer stream temperatures, providing greater unfrozen habitat in winter and warmer and more constant water temperatures throughout the year.