HR: 1340h
AN: B43D-0307    [Abstracts]
TI: Hillslope Chromatography in Savannas
AU: * Hartshorn, A
EM: tony@geog.ucsb.edu
AF: University of California, Department of Geography, Santa Barbara, CA 93106-4060 United States
AU: Khomo, L
EM: lesegok@gmail.com
AF: University of the Witwatersrand, APES, Johannesburg, 2050 South Africa
AU: Chadwick, O
EM: oac@geog.ucsb.edu
AF: University of California, Department of Geography, Santa Barbara, CA 93106-4060 United States
AU: Rogers, K
EM: kevinr@gecko.biol.wits.ac.za
AF: University of the Witwatersrand, APES, Johannesburg, 2050 South Africa
AU: Kurtz, A
EM: kurtz@bu.edu
AF: Boston University, Department of Earth Sciences, Boston, MA 02215 United States
AU: Heimsath, A
EM: arjun.heimsath@dartmouth.edu
AF: Dartmouth College, Department of Earth Sciences, Hanover, NH 03755 United States
AB: In semiarid ecosystems, vegetation patterns are controlled in part by soil water availability. Along hillslopes in Kruger National Park, South Africa, water availability is strongly dependent on soil texture and textural differences with depth, which are a function of landscape position (convergent or divergent crests, midslopes, and footslopes) and parent material. We are studying weathering and landscape development on the western side of the park, which is underlain by granitic gneisses. Hillslopes in the park are often described as catenas, where rainfall catalyzes chemical weathering and drives the downslope transport of clays and weathering products, forming a predictable sequence of soil types. Sandy crest soils grade to midslope soils where sandy surface horizons overlie clayey subsurface horizons; footslopes generally have higher volumetric clay contents. The boundary between the sandy and clayey soils is of ecological significance because this is the location where run-on from upslope landscape positions is diverted to the surface, initiating overland flow and reducing infiltration. In a geochemical sense these hillslopes can be thought of as chromatographic columns that accentuate differential solute mobility along the long (~1-2 km) potential flowpaths. We use the compound topographic index (a terrain attribute that indexes soil wetness by dividing the upslope contributing area by the slope) to predict the redistribution of clays across these semiarid hillslopes and hope to demonstrate that landscape positions occupying comparable plan and profile curvatures contain clay and organic carbon in proportion to contributing area. Thus far, we have derived contributing area values for 40 soil pits using LiDAR-based digital elevation models and then tested how well contributing area and other terrain attributes predicted clay and carbon content for 218 horizons at these 40 locations. Depth-weighted soil clay ranged from 3 to 25% and total soil carbon ranged from 0.1 to 2.1%. Our preliminary results suggest that greater contributing area only produces greater soil clay content up to a threshold clay content, after which clay illuviation and in situ clay production slows following the diversion of water to the surface.
DE: 0400 BIOGEOSCIENCES
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005