Thermokarst failures are features of permafrost landscapes, which form due to collapse of soil structure with permafrost thaw.  Our broader collaborative project addressed hypotheses about how thermokarst failures influence the structure and function of the arctic landscape. Specifically we focused on geomorphology, composition of vegetation, distribution and processing of soil nutrients and organic matter, and exports of sediments and nutrients to stream and lake ecosystems. We hypothesized that a widespread and long-term increase in the incidence of thermokarst failures will have important impacts on the structure and function of arctic headwater landscapes.  At the University of Alaska Fairbanks, investigators focused on five components of the broader collaborative project: 1) the consequences of thermokarst failures for soil carbon and nutrients, 2) landscape scale characterization of modes of thermokarst failure, 3) thermokarst failure detection using remote sensing, 4) native Alaskan' perceptions of thermokarst failures in their landscape, and 5) outreach and education.

Soil respiration in thermokarst features was spatially heterogeneous with CO₂ flux from some areas significantly elevated above the flux from intact tundra, but depressed from exposed mineral soil.  Interestingly, at the scale of whole thermokarst failures, CO₂ flux to the atmosphere was not substantially different than from intact tundra.  Methane and nitrous oxide (greenhouse gases) concentrations were similarly heterogeneous.  Methane concentration was generally lower in thermokarst soil compared with undisturbed tundra, except in soil that had been re-vegetated.  Nitrous oxide was elevated in regions of the thermokarsts where soil drying had occurred.  This elevated nitrous oxide indicated that the microbial process of denitrification was occurring, which is thought to be low in tundra soil.  Recently formed thermokarst failures also influence soil water chemistry with dissolved organic carbon, dissolved organic nitrogen, and inorganic nutrient concentrations elevated compared to nearby water tracks.  However, the chemistry of water rapidly returned to pre-failure concentrations as thermokarst features stabilized.  Biodegradability of organic carbon released from thermokarst features was also significantly elevated.  At several sites, DOC biodegradability exceeded 60 % loss, making this some of the most bioavailable DOC ever reported in natural waters.

Ground ice morphology and volume were found to be fundamental factors affecting the type of thermokarst features at sites near Toolik Lake and in Noatak National Preserve.  The dominant types of ice were buried glacial ice associated with glacial thermokarst, and segregated ice in the intermediate layer of upper permafrost associated with active-layer detachment slides.  Differences in ground ice characteristics create unique patterns of differential thaw settlement and slumping.

Over 80% of active retrogressive thaw slumps examined in our study were first detected in remote sensing imagery in the summer 2004.  While 2004 was record-setting warm temperature for much of the state, weather data from the Noatak Basin indicate summer temperature and precipitation were close to average.  However, in summer 2004, the Noatak basin warmed rapidly in early summer and two two intense rainstorms occurred in May.  Snowmelt during spring 2004 was also early.

Community residents in Selawik and Anaktuvuk Pass with extensive knowledge of the local landscape guided us to sites that show evidence of thermokarst processes in and around each village.  Interviewees helped us to construct local knowledge maps showing patterns of local travel, subsistence activities, and features attributed to changing permafrost conditions.  ...

Please report errors in award information by writing to: awardsearch@nsf.gov.