Sponsored by the Geomorphology Specialty Group
Association of American Geographers 102nd Annual Meeting
Chicago, Illinois, March 7-11.
Geomorphology Specialty Group Graduate Student Paper Competition II
Paper Session 2250
Wednesday, 3/8/06, from 10:00 AM - 11:40 PM
Geomorphology Specialty Group
Susan W.S. Millar - Syracuse University
Susan W.S. Millar - Syracuse University
10:00 AM Author(s):
*Jennifer Horwath - University of Washington
Ronald S Sletten - University of Washington
Jeffrey M Welker - University of Alaska Anchorage
Abstract Title: Associations of Soil Organic Carbon with Non-Sorted Striped Patterned Ground in Northwest Greenland
Non-sorted stripes are a patterned ground feature that forms in permafrost terrain throughout the High Arctic. These cryogenic features are created by physical mixing and heaving (cryoturbation), and often result in transport and burial of soil organic carbon (SOC) to depth. In 2004, a 16 m long trench was excavated perpendicular to a series of non-sorted stripes near Thule Air Base, NW Greenland (76 deg N, 68 deg W). The stripes consist of alternating nearbarren ridges (1-2 m wide) and narrow vegetated troughs (0.5 m wide) that form on gentle to moderate slopes. The north wall of the trench wall was mapped in detail to study the association of SOC with the surface and subsurface morphology. The organic carbon content, 14C ages, and vegetative biomass were determined to obtain a complete view of the carbon pool. This study reveals that cryoturbation has a major affect on carbon accumulation and turnover in High Arctic soils. Pockets of SOC buried between 50 -70 cm had maximum 14C ages of 27,480 - 31,900 radiocarbon years, indicating that some soil carbon was stored prior to the Holocene. Total belowground SOC storage was estimated to be 10 kg/ m2. When combined with carbon data from our additional sites in NW Greenland, our estimates of SOC are an order of magnitude higher than previous studies of High Arctic SOC. These updated estimates should be incorporated into carbon cycling models if we are to fully understand the potential global feedback effects of warming in the Arctic.
Keywords: soil carbon, patterned ground, Greenland, climate change
- 10:15 AM Author(s):
*Robert H Gorcik - University of Wyoming
Abstract Title: Using Soil Stratigraphy to Reconstruct the Early Holocene Landscape at Barger Gulch, Colorado
Barger Gulch is a tributary of the Colorado River running through Middle Park, a high altitude basin in the Rocky Mountains near Kremmling, Colorado. Along the main axis of Barger Gulch, three Quaternary age alluvial terraces are present. The two younger terraces are composed of alluvial deposits with little evidence of past pedogenesis. The oldest and highest terrace, Qt3 displays more complex stratigraphy with a prominent buried soil, or paleosol. This soil formed shortly after Folsom Paleoindians were occupying the site. Understanding the landscape evolution of the site can aid in reconstructing the climate, vegetation, and topography. Modern elevation and buried soil elevation were compared to reconstruct the terrain at the time of pedogenesis. Data was gathered on the modern topography of the main axis, as well as the stratigraphy of the Qt3 surfaces. A total of twenty cross sections were set up and surveyed using standard surveying equipment. Soil augers were used to determine the depth to the buried soil horizon on Qt3 surfaces. Modern elevation data minus the depth to buried soil represents the elevation of the land surface during the early Holocene. Relief during the early Holocene appears to have a very gentle slope on the Qt3 surfaces. This was expected since the paleosol formed on terraces composed of point bar and overbank deposition. This is different from modern topography of the Qt3 surface, which has a steeper slope due to colluvial and slopewash deposits. Average rates of aggradation of Qt3 were between 0.2 and 0.3mm/year.
Keywords: Geomorphology, alluvial stratigraphy, Quaternary, environmental change, soils
- 10:30 AM Author(s):
*Linda L. Martin - University of Kentucky
Abstract Title: Changes in Epikarstal Vadose Properties Related to Fluviokarst Deforestation
Karst development in the inner Bluegrass region of Kentucky is typically confined to shallow, epikarstal dissolution by the interbedded limestones and shales of the Lexington Limestones. On the steeper (8-15°) slopes found along the escarpment of the Kentucky River, large storm events perch exfiltrating water and cause epikarstal conduit exhumation at the juncture of pastureland and downhill forests. Pits opened in the Bowman’s Bend region in forest and grass areas matched for elevation reveal that the highly irregular surface of the epikarst regulates water movement and clay content of lower horizons, and that near saturation flow tends to wick along both buried limestone slabs and large roots. Changes in soil properties over the last 200 years revealed by soil analysis, water content datalogging, and measurement of infiltration rates suggest that diffuse water entry taking place under grass cover tends to encourage lateral flow below the topsoil and above 55 cm depth, in contrast to direct bedrock entry mediated by discrete flow along tree roots in the forest. Clay translocation seals lower grass horizons and increases the tendency for water to emerge as downslope return flow or to concentrate in preferentially selected pre-existing conduits. Tree roots likely perform a critical system process in the thin residual soils of the crest and shoulders of the study area by entering the bedrock along weakened pathways, mechanically wedging rocks apart and increasing dissolution rates by introducing water and organics to deeper bedding planes.
Keywords: vadose properties, fluviokarst, biogeomorphology, human impacts
Session Description: This series of three special paper sessions are co-sponsored by the Coastal and Marine Geography (CoMa) and Geomorphology specialty groups. The research presented in the paper sessions cover a broad spectrum of spatial and temporal scales within aeolian geomorphology.