PARENT SESSION
Symposium 17: Biogeochemistry of Grassland and Shrubland Ecosystems: Local to Regional Linkages and Impacts of Land Use
Organized by: R Nowak and S Fuhlendorf
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Chatham Ballroom B.

Silver linings: Fertility gains and losses through dust redistribution at local, regional, and global scales.

Reheis, Marith^*,1, Sanford, Robert², Belnap, Jayne¹, Reynolds, Richard¹, Neff, Jason¹, ¹ U.S. Geological Survey, Denver, CO² University of Denver, Denver, CO

ABSTRACT- Wind erosion is commonly invoked as a chief cause of depletion of soil nutrients in arid and semiarid lands, especially those disturbed by land-use practices. Nevertheless, modern dust (both wetfall and dryfall deposition) is a source of macro- and micro-nutrients for soils and vegetation globally, and may be particularly important in organic-poor arid ecosystems. Dust is ubiquitous; modeled deposition rates are at least 10-100 kg/ha/yr throughout the continents and 100-1000 kg/ha/yr or more in the dry mid-latitudes. Example estimates of nutrient inputs in semiarid regions are P=0.03-6.0, N=0.5-9.0, and C=110-180 kg/ha/yr. In the southwestern U.S., deposition rates of micro-nutrients are Cu=5-90, Mn=18-160, and Mo=0.1-0.7 g/ha/yr. Aeolian dust is incorporated into surface sediments and redistributed downward into soil profiles by water infiltration. The dust component of soils can be distinguished from parent sediment by a particle size dominated by fine silt, different magnetite content, and different chemical composition. We focus on study sites having different grazing histories in the Canyonlands area of Utah and from desert areas of southern Nevada and California to (1) examine the composition and nutrient content of modern dust, (2) identify the dust component of soils, and (3) infer the contribution of dust to plant-nutrient availability, especially with respect to phosphorus. In general, modern dust samples have much more labile and biological P than soil samples. P contents, however, vary with season: in dust, total P and labile P are higher in winter than in summer, whereas labile P in soils increases dramatically in early summer. In A horizons and pothole sediments of our study sites, wind-deposited concentrations of such plant-critical trace elements as Cu, Mn, Mo, and Zn may be 25-100% greater than in some parent sediments or rocks. Conversely, wind erosion may have reduced concentrations of some elements in grazed soils.

Key words: eolian dust, soil fertility, wind erosion, southwestern U.S.