101 Soil and Water Chemistry Characteristics of Thermo-Erosional Features in the Western Noatak River Basin, Alaska, USA Michael B. Flinn Murray State University, Murray, KY, USA William “Breck” Bowden University of Vermont, Burlington, VT, USA Andrew W. Balser, Jeremy B. Jones University of Alaska Fairbanks, USA Michael N. Gooseff Pennsylvania State University, University Park, PA, USA Abstract In 2007, 24 thermal-erosion and permafrost degradation features (hereafter “thermokarst”) were characterized in northwest Alaska, USA. Geomorphic assessments showed that active-layer detachments and thaw slumps had characteristic morphologies with permafrost thaw depths significantly deeper within these features (106 cm) than surrounding hillslopes and water tracks (86 cm). Characterization of soils and water associated with these features showed that reference transects above each feature were significantly different from feature transects (headwall, active surface, run-out). Water collected within the features showed significantly higher concentrations of nutrients (ammonium, nitrite), total dissolved nitrogen, dissolved organic and inorganic carbon, and anions (chloride and bromide) compared to the reference transect. Water samples from reference transects had higher soil electrical conductivity, calcium, and ratio of DOC:DON. Though thermokarst failures are a relatively rare spatial and temporal feature of the arctic landscape, they play an important role in the biogeochemical processing of terrestrial and aquatic resources of the Arctic. Keywords: active-layer detachment slide; biogeochemistry; permafrost degradation; thermal-erosion; thermokarst; retrogressive thaw-slump. Introduction Recent studies in the Arctic have shown increased temperatures in both air (Serreze et al. 2000, IPCC 2001, Hinzman et al. 2005) and permafrost (Pollack et al. 2003, Zhang et al 2006, Romanovsky et al. 2007). With increased temperatures, myriad effects have been documented for both terrestrial and aquatic ecosystems. These include changes in plant communities (Chapin et al. 2005, Tape et al. 2006), rates of nutrient cycling (Rastetter et al. 2004), solute and sediment fluxes in freshwaters (Hobbie et al. 1999, Bowden et al. 2008), and changes in fire regimes (Mack et al. 2011). The relationship between permafrost degradation and the initiation of thermokarst terrain has received increased attention over the last decade. Several studies have documented extensive changes across arctic landscapes in boreal forests and tundra (Osterkamp et al. 2000, U.S. Arctic Research Commission 2003, Jorgenson and Osterkamp 2005, Lewkowicz 2007, Bowden et al. 2008). Thermokarst features are a natural phenomenon of the Arctic. However, little is known about the rate and extent of their formation, the prevalence of different modes of failure, the frequency of their initiation, or their active longevity (Gooseff et al. 2009). The objective of this study was to characterize thermokarst features of the western Noatak Basin in an effort to understand their influence on biogeochemical processing, thaw depth variability, soil characteristics, and influence on water chemistry. Methods Study sites The Noatak River in northwest Alaska flows westerly at approximately 67.5°N latitude. The majority of the ~30,000 km 2 watershed is protected by a national park and preserve and is recognized as a UNESCO Biosphere Reserve. The area is underlain by continuous permafrost with land cover spanning a suite of arctic and alpine tundra types in headwaters areas. Ecotonal boreal forest cover appears at low elevations in the lower half of the Noatak Basin and coastal marshes at the mouth (Young 1974, Viereck et al. 1992, Jorgenson et al. 2010b). In late July and early August of 2007, we visited 24 thermokarst features located in the uplands of the Baird Mountains and in the adjacent upstream reaches of the Mission Lowlands in the western Noatak River Basin, approximately 100 km north of Kotzebue, AK (Fig.1). Geomorphic, soils, and water chemistry assessments Basic geomorphic measurements were calculated for 24 failure features that were selected from a conservative estimate of over 200 hillslope themokarst features. Only six of the 200 features, and none of the 24 surveyed, occurred within historic fire perimeters in the Alaska Fire Service GIS database (2010). Survey outlines were obtained by walking the perimeter of each feature using a Trimble GeoXH GPS. Roving survey data were recorded using Terrasync software logging at 1-second intervals. Due to topographic constraints, Wide Area