Permafrost Degradation and Soil Change in Temperature Sensitive Gelisols in Southwestern Alaska.

ASA-CSSA-SSSA Annual Meetings, Nov. 2-6, 2014 Long Beach, CA

Abstract

 

Title: Permafrost degradation and soil change in temperature sensitive

Gelisols in southwestern Alaska

C.L. Ping¹, M.H. Clark¹, S. Nield², and M. Woodgate¹

¹. Palmer Research Center, UAF

². Regional Soil Scientist, USDA-NRCS, Alaska State Office, Palmer

The dynamics of permafrost and soil formation was studied at Lower Mulchatna, MLRA 236 Bristol Bay and Northern Alaska Peninsula Lowlands. The study sites are on loess-mantled glaciofluvial plains and are somewhat poorly to very poorly-drained. There are three distinctly different land cover types identified. At the north part the land surface is characterized by turf hummocks with vegetation dominated by ericaceous shrubs. Based on vegetation composition and surface drainage, this land cover type is referred as moist acidic tundra (MAT). In the southern part of the study area, tussocks dominated the very poorly-drained site. This land cover type is identified a wet acidic tundra (WAT). Within the WAT unit, there are a series of stripe shaped frost mounds observed with the elongated direction parallel to the slope gradient. The land cover type of the frost mound is coined as “Dry Heath Mound” (DHM).The formation of these frost mounds is speculated as ice buildup due to moisture migration from the very poorly drained intermound areas along a thermal gradient toward the more exposed mounds which freeze faster.  Charcoal was noted in several of the pits and other data indicate that thawing of permafrost in the past was likely caused by a series of tundra fires dated from 350 to 1200 YBP. The position of the mounds on the landscape is noted as being linear downslope and concave across slope, resulting in the concentration of subsurface flow, providing a ready water supply for the mound building via cryogenic processes.  Presently, the frost mounds are in different stages of formation, from newly formed to the center-collapsed final stage, attesting to the dynamic nature of the permafrost and soil formation in this zone of discontinuous permafrost. The lack of mounded microtopography at the other sites is attributable to a more linear cross slope shape and better drainage.  Soils under the MAT are classified as Ruptic –Histic Aquiturbels or Turbic Haplogelolls and under WAT as Terric Hemistel. The soils under the frost mounds (DHM) have 20 – 40+ cm of organic horizon not meeting the criteria of histic epipedon, thus classified as Folistels-Aquiturbels.