2024 Abstracts

Soils of the Arctic Foothills of Alaska: Composition and Degradation State


Roser Matamala1* (matamala@anl.gov), Chien-Lu Ping2, Francisco Calderón3, Nicolas Jelinski4, Irfan Ainuddin4, Julie Jastrow1


1Argonne National Laboratory, Lemont, IL; 2University of Alaska–Fairbanks, AK; 3Columbia Basin Agricultural Research Center, Oregon State University, OR; 4University of Minnesota–Twin Cities, Minneapolis/St. Paul, MN



The Arctic Foothills of Alaska are characterized by rounded hills and plateaus with continuous permafrost soils covered in tundra vegetation. The region undergoes permafrost- affected processes, such as solifluction and other lateral mass movements, cryoturbation, and patterned-ground formation, impacting soil organic matter (SOM) accumulation, composition, and degradation. Anthropogenic activities and climate change have intensified press and pulse thaw disturbances, potentially leading to downstream soil movement and exposure of SOM that has been cold-stabilized for thousands of years. However, information is limited on the composition of the SOM that might be mobilized by these processes. Here, researchers investigated the composition and degradation state of SOM across landscape positions in the Arctic Foothills.

Two toposequences, formed on land surfaces of differing ages, were examined, encompassing seven hillslope positions: summit, shoulder, upper- and lower-back slopes, upper- and lower-foot slopes, and basin. Researchers used mid-infrared spectroscopy to examine variations in organic functional groups and minerals across soil horizon types and slope positions. The ratio of aromatics to polysaccharides was calculated as an indicator of SOM degradation state. Researchers identified 14 influential wavelength bands across toposequences, horizons, and slope positions. The abundance of organic functional groups, associated with phenolic OH, aliphatics, and polysaccharides were lowest in mineral horizons and varied between organic and mixed organic-mineral horizons. These organic groups also differed between toposequences and across slope positions. Conversely, bands characteristic of amides and aromatics were consistent across toposequences, horizons, or slope positions. Spectral bands indicating clays varied across toposequences and slope positions but not among horizon types, whereas general silicate bands were more pronounced in mineral horizons. The ratio of aromatics to polysaccharides indicated consistently more degraded SOM occurred in mineral horizons. In summary, slope position significantly influenced SOM composition (particularly phenolics, aliphatics, and polysaccharides) and clay content, with mineral horizons containing more degraded SOM.