PARENT SESSION
Oral Session #76: Ecosystem Ecology: Larger scale processes, geomorphology, soils.
Presiding: W. Straw
Thursday, August 8. 9:00 AM to 11:30 AM. Gila Meeting Room, TCC.

Does dust matter? Geologic and eolian controls over ecosystem dynamics on the Colorado Plateau.

Neff, Jason^*,1, Reynolds, Richard¹, Lamothe, Paul¹, Moscato, Silvina¹, Belnap, Jayne², ¹ US Geological Survey, Denver, CO² US Geological Survey, Moab, UT

ABSTRACT- A number of studies have shown that dust delivers essential nutrients that sustain terrestrial productivity over millennia. Dust, however, contains a range of elements ranging from base cations, N and P, to heavy metals. Some of these elements will stimulate primary productivity over the time scale of soil development while others, such as metals, could inhibit biological activity. As dust accumulates, it also influences water flux and availability by altering soil texture. We are examining the ecological impacts of dust accumulation in Canyonlands National Park in Utah. Using magnetic susceptibility as a proxy for far-traveled dust, we have established transects in sandy surficial deposits (50-90% sand) in which dust contributes as much as 30% of the bulk fraction. Along these transects, we are measuring microbial decomposition, plant photosynthetic rates, soluble element concentrations, weathering rates, and hydrologic flux patterns. These studies indicate that water holding capacity does not linearly increase with silt content and that deep storage of water (> 40 cm depth) is similar in soils having either high sand or high-silt content. In contrast, soil textural (and dust accumulation) gradients show strong linear patterns in some soluble and weatherable elements (e.g., P, As, Sb, Mo). Microbial biomass and soil respiration are inversely correlated with soil silt (and dust) content. This negative relation appears more strongly linked to the geochemistry of silt and dust than to alterations in the texture and hydrology of desert soils. Plant foliar P and Mn and some heavy metal concentrations parallel soil concentrations. Plant photosynthetic rates are sensitive to variations in water content as influenced by soil silt/dust content. These results illustrate the multi-faceted role of dust in the geochemical and hydrologic controls over arid ecosystem productivity.

KEY WORDS: biogeochemistry, dust, arid, weathering