HR: 11:50h
AN: B11F-06    [PDF]
TI: Distribution of Aeolian Dust Determined From Magnetic and Chemical Properties in Surficial Substrates of Grassland and Shrubland, Central Colorado Plateau (Utah)
AU: * Reynolds, R L
EM: rreynolds@usgs.gov
AF: U.S. Geological Survey, Box 25046 MS 980, Denver, CO 80225 United States
AU: Neff, J
EM: neffjc@colorado.edu
AF: Univ. of Colorado, Dept. of Geological Sciences, Boulder, CO 80309 United States
AU: Reheis, M
EM: mreheis@usgs.gov
AF: U.S. Geological Survey, Box 25046 MS 980, Denver, CO 80225 United States
AU: Goldstein, H
EM: hgoldstein@usgs.gov
AF: U.S. Geological Survey, Box 25046 MS 980, Denver, CO 80225 United States
AU: Lamothe, P
EM: plamothe@usgs.gov
AF: U.S. Geological Survey, Box 25046 MS 980, Denver, CO 80225 United States
AB: Rock-derived nutrients in soils originate from both local bedrock and atmospheric dust. Distinction between sediment derived from local bedrock and from dust provides better understanding of nutrients and the processes responsible for their distributions across landscapes. Sandy surficial deposits overlying dominantly sandstone substrates cover vast upland areas of the central Colorado Plateau. These deposits typically contain 5-40% fines (silt and clay measured using laser-diffraction methods), depending on geomorphic setting and slope (excluding drainages and depressions). Far-traveled aeolian dust in the deposits is indicated by the presence of titanium-bearing magnetite grains that are absent in the sedimentary rocks of the region. Thus, the quantity of dust can be estimated from magnetic properties that primarily reflect magnetite content, such as isothermal remanent magnetization acquired at 0.3 Tesla (IRM3). IRM3 was measured on bulk ($<$2 mm) sediment samples (IRMsoil; 0-10 cm depth) from a transect in surficial sediment (10 samples, each separated by 20-30 m) down a 2-3 degrees slope away from an exposure of Cedar Mesa Sandstone. The mass proportion (f) of aeolian fines in each sample was calculated using values of IRMsoil, IRMrock (average of 19 samples of regionally distributed Cedar Mesa Sandstone), and IRMdust (on sediment deposited over four months in nearby dust collectors at 2-m height determined on sand-free and organic matter-free bases): f=(IRMsoil-IRMrock)/(IRMdust-IRMrock). Very small magnetic contributions from hematite are responsible for the IRMrock value, which is 6 to 60x less than IRMsoil values. IRM-based calculations show a systematic down-slope increase in aeolian dust (2-18%), similar to the down-slope increase in total fines (18-40%). Aeolian dust calculated by the same method using titanium and vanadium contents closely matches the IRM-based results (6-20% and 5-19%, respectively). IRM-based dust estimates of soils correlate much more strongly with P, Na, K, Mn, Fe, Zn, and Mg (r$^{2}$$>$0.8) than do amounts of total fines. The combination of substantial aeolian dust contributions to soil fines and high concentrations of rock-derived nutrients in dust relative to local parent materials suggests that dust is a major source of potential plant nutrients in this setting.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0400 Biogeosciences
DE: 1512 Environmental magnetism
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting