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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #319938

Research Project: MANAGEMENT TECHNOLOGIES FOR CONSERVATION OF WESTERN RANGELANDS

Location: Range Management Research

Title: Threshold wind velocity dynamics as a driver of aeolian sediment mas flux

Author
item Webb, Nicholas - New Mexico State University
item Galloza, Magda
item Zobeck, Teddy
item Herrick, Jeffrey - Jeff

Submitted to: Aeolian Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2015
Publication Date: 3/1/2016
Citation: Webb, N., Galloza, M.S., Zobeck, T.M., Herrick, J.E. 2016. Threshold wind velocity dynamics as a driver of aeolian sediment mas flux. Aeolian Research. 20:45-58.

Interpretive Summary: Sediment transported in saltation by the wind is an important driver of dust emission. Model estimates of the saltation mass flux determine estimates of the global dust emission and influence our understanding of the dust cycle and its interactions. Current equations for predicting saltation mass flux are based on limited field data. They are also constrained to representing saltation under wind energy-limiting conditions. This can result in large overestimation of the mass of transported sediment. In this paper we compare measurements of the soil entrainment threshold, horizontal mass flux, and their temporal variability for five undisturbed dryland soils to explore the role of threshold in controlling the magnitude of the mass flux. Average and median entrainment threshold showed relatively small variability among sites and relatively small variability between seasons, despite significant differences in soil surface conditions. Physical and biological soil crusts had little effect on the threshold value, and threshold appeared to play a minor role in determining the magnitude of the mass flux. Our results suggest that sediment transport was controlled more by the supply limitation and abrasion efficiency of saltators present as loose erodible material or originating from neighboring soil sources. The omission of sediment supply and explicit representation of saltation bombardment from horizontal flux equations is inconsistent with the process representation in dust emission models and contributes to uncertainty in model predictions. We suggest that this uncertainty can be reduced by modifying wind erosion models to predict sediment transport under both supply- and transport-limited conditions.

Technical Abstract: Horizontal (saltation) mass flux is a key driver of aeolian dust emission. Estimates of the horizontal mass flux underpin assessments of the global dust budget and influence our understanding of the dust cycle and its interactions. Current equations for predicting horizontal mass flux are based on limited field data and are constrained to representing transport-limited equilibrium saltation, driven by the wind momentum flux in excess of an entrainment threshold. This can result in large overestimation of the sediment mass flux. Here we compare measurements of the soil entrainment threshold, horizontal mass flux, and their temporal variability for five undisturbed dryland soils to explore the role of threshold in controlling the magnitude of the mass flux. Average and median entrainment threshold showed relatively small variability among sites and relatively small variability between seasons, despite significant differences in soil surface conditions. Physical and biological soil crusts had little effect on the threshold value, and threshold appeared to play a minor role in determining the magnitude of the mass flux. Our results suggest that horizontal mass flux was controlled more by the supply limitation and abrasion efficiency of saltators present as loose erodible material or originating from neighboring soil sources. The omission of sediment supply and explicit representation of saltation bombardment from horizontal flux equations is inconsistent with the process representation in dust emission schemes and contributes to uncertainty in model predictions. This uncertainty can be reduced by developing greater process fidelity in models to predict horizontal mass flux under both supply- and transport-limited conditions.