Coupled Landscape and Ecosystem Response to Permafrost Loss and Disturbance

Authors

Joel Rowland1* (jrowland@lanl.gov), Evan Thaler1, Baptiste Dafflon2, Sebastian Uhlemann2, Sylvain Fiolleau2, Amy Breen3, and Lauren Thomas1, Colleen Iversen4

Institutions

1Los Alamos National Laboratory, Los Alamos, NM; 2Lawrence Berkeley National Laboratory, Berkeley, CA; 3University of Alaska–Fairbanks, AK; 4Oak Ridge National Laboratory, Oak Ridge, TN

URLs

Abstract

The rapid and catastrophic erosion of soil on hillslopes underlain by permafrost has been attributed to rapid deepening of seasonally thawed surface material and the loss of near-surface permafrost. These erosional events both redistribute sediment, reshape hillslopes, and have the potential to abruptly release globally significant quantities of soil carbon (C) from previously stable sinks. At a series of small watersheds on the southern Seward Peninsula in Alaska, researchers have documented a range of soil movement processes affected by the presence and recent loss of permafrost. These movements range from steady creep-like behavior to rapid and repetitive failures. Based on direct field measurements and geophysical imaging of the subsurface conducted over multi-year campaigns, researchers produced high-resolution maps showing the presence and absence of near-surface permafrost across these watersheds. A comparison of the permafrost map to the spatial patterns of annual ground surface displacement and failures suggests that regions of recent and/or active permafrost loss exhibit the greatest rates of movement measured from 2017 to 2022. Despite topographic evidence of past failures, regions without permafrost have the lowest rates of present-day movement. Regions of relatively stable and continuous permafrost have intermediate rates of soil creep and lack catastrophic erosional features.

The loss of permafrost drives both an increase the heterogeneity in microtopography and the diversity and spatial complexity of vegetation. Topographic heterogeneity arises from local ground subsidence, Earth flows, and retrogressive failures propagating across recently thawed hillslopes with topographic connectivity to rapidly eroding stream hollows. Vegetation heterogeneity associated with disturbance is evidenced by shrubification of stream hollows experiencing active gullying, on the margins of solifluction and Earth flow lobes, and in active layer detachment scars. Despite steep hillslopes, Earth flow scars create areas of relatively flat topography that route and capture surface water runoff, leading to emergent patches of graminoids Eriophorum vaginatum, Carex aquatilis, and Equisetum hyemale.

Overall, the team’s observations suggest that the greatest hillslope instability occurs in the transitional regions of watersheds undergoing rapid permafrost loss. Both the rates and extent of propagation of failures appears to be influenced by the topographic connectivity of failures to the network of established channels and developing gullies. If the small watersheds are representative of larger swathes of permafrost landscapes, then researchers expect to see an acceleration of hillslope processes and release of soil organic C during and immediately following permafrost loss followed by a reduction in soil transport rates and a stabilization of the landscape.