Abstract
Beavers are starting to colonize low arctic tundra regions in Alaska and Canada, which has implications for surface water changes and ice-rich permafrost degradation. In this study, we assessed the spatial and temporal dynamics of beaver dam building in relation to surface water dynamics and thermokarst landforms using sub-meter resolution satellite imagery acquired between 2002 and 2019 for two tundra areas in northwestern Alaska. In a 100 km2 study area near Kotzebue, the number of dams increased markedly from 2 to 98 between 2002 and 2019. In a 430 km2 study area encompassing the entire northern Baldwin Peninsula, the number of dams increased from 94 to 409 between 2010 and 2019, indicating a regional trend. Correlating data on beaver dam numbers with surface water area mapped for 12 individual years between 2002 and 2019 for the Kotzebue study area showed a significant positive correlation (R2 = 0.61; p < .003). Beaver-influenced waterbodies accounted for two-thirds of the 8.3% increase in total surface water area in the Kotzebue study area during the 17 year period. Beavers specifically targeted thermokarst landforms in their dam building activities. Flooding of drained thermokarst lake basins accounted for 68% of beaver-influenced surface water increases, damming of lake outlets accounted for 26%, and damming of beaded streams accounted for 6%. Surface water increases resulting from beaver dam building likely exacerbated permafrost degradation in the region, but dam failure also factored into the drainage of several thermokarst lakes in the northern Baldwin Peninsula study region, which could promote local permafrost aggradation in freshly exposed lake sediments. Our findings highlight that beaver-driven ecosystem engineering must be carefully considered when accounting for changes occurring in some permafrost regions, and in particular, regional surface water dynamics in low Arctic and Boreal landscapes.
Highlights
Arctic landscapes are in a state of transition due to changes in climate (Hinzman et al 2005, Rowland et al 2010, Vincent et al 2017)
The 5000% increase in the number of beaver dams between 2002 and 2019 was positively correlated (R2 = 0.61; p < .003) with an 8.3% increase in surface water area in a 100 km2 study area located near Kotzebue, Alaska
Beaver influenced waterbodies accounted for 66% of the observed increase in surface water area associated with various permafrost region landforms that included drained thermokarst lake basins, thermokarst lakes, and beaded streams
Summary
Arctic landscapes are in a state of transition due to changes in climate (Hinzman et al 2005, Rowland et al 2010, Vincent et al 2017). Summertime arctic lake area dynamics have been linked to long-term climate driven changes and permafrost degradation (Yoshikawa and Hinzman 2003, Smith et al 2005, Jones et al 2011, Nitze et al 2018), as well as to short-term weather events and annual patterns of precipitation and evaporation (Riordan et al 2006 , Cooley et al 2019, Swanson 2019). Jung et al (2017) noted the presence of a new beaver dam in 2015 near the Babbage River, located within 25 km of the Beaufort Sea coast on the Yukon Coastal Plain in northwestern Arctic Canada. Tape et al (2018) postulated that ongoing landscape-scale changes in the Arctic, combined with population rebound from over-trapping (Bockstoce 2009), are responsible for beavers recent colonization of Alaska tundra regions. The implications of beaver inhabitation in the Arctic and Boreal are unique relative to other ecosystems due to the presence of permafrost and its vulnerability associated with beaver dams and inundation
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