Aeolian dust in Colorado Plateau soils: Nutrient inputs and recent change in source

Aeolian dust (windblown silt and clay) is an important component in arid-la nd ecosystems because it may contribute to soil formation and furnish essen tial nutrients. Few geologic surfaces, however, have been characterized wit h respect to dust-accumulation history and resultant nutrient enrichment. W e have developed a combination of methods to identify the presence of aeoli an dust in arid regions and to evaluate the roles of this dust in ecosystem processes. Unconsolidated sandy sediment on isolated surfaces in the Canyo nlands region of the Colorado Plateau differs greatly in mineralogical and chemical composition from associated bedrock, mainly aeolian sandstone. Det rital magnetite in the surficial deposits produces moderately high values o f magnetic susceptibility. but magnetite is absent in nearby bedrock. A com ponent of the surficial deposits must be aeolian to account for the abundan ce of magnetite. which formed originally in far-distant igneous rocks. Part icle-size analysis suggests that the aeolian dust component is typically as much as 20-30%. Dust inputs have enriched the sediments in many elements, including P, Mg, Na, K, and Mo, as well as Ca, at sites where bedrock lacks calcite cement. Soil-surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades. Some of the recently fallen dust may result from human disturbance of land surfaces that are far from the Canyonlands. such as the Mojave Desert. Some land-use practices in the study area have the potential to deplete soil fe rtility by means of wind-erosion removal of aeolian silt.