Size distribution of windblown sediment emitted from agricultural fields in the Columbia Plateau

Authors: Sharratt, Brenton

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2010
Publication Date: 4/22/2011
Citation: Sharratt, B.S. 2011. Size distribution of windblown sediment emitted from agricultural fields in the Columbia Plateau. Soil Science Society of America Journal. 75:1054–1060. doi:10.2136/sssaj2010.0337.

Interpretive Summary: Dust emitted from agricultural fields during high winds contributes to poor visibility and exceedance of air quality standards in eastern Washington. Strategies to control dust emissions from agricultural fields, however, necessitate an understanding of the size characteristics and modes of transport of windblown sediment. Although the soil was comprised of particles that had a mean diameter of 20-42µm, field measurements over seven years revealed that windblown sediment was largely composed of particles 11-32µm in diameter. In addition, windblown sediment >45µm in diameter was transported by saltation (bouncing along the soil surface) whereas sediment less than or equal to 32µm in diameter was transported by suspension (remain airborne) in the atmosphere. Since suspension-sized material appeared to constitute much of the windblown sediment, mitigation of wind erosion and poor air quality may be achieved by decreasing the amount of suspension-sized material at the soil surface which is exposed to the wind. Soil scientists and agronomists must therefore develop management strategies that either promote aggregation of the suspension component of the soil or shelter the suspension component at the soil surface from high winds.

Technical Abstract: Wind erosion of agricultural land in the Columbia Plateau has impaired visibility and threatened human health. Few land management practices have been developed to control erosion, but knowledge of the size distribution of windblown sediment is needed to develop effective control practices. Passive samplers were used to trap windblown sediment at various heights above eroding agricultural fields. Sediment collected during one high wind event in each of seven years was separated into less than or equal to 10, 11-32, 33-45, 46-100, and >100µm diameter size fractions. Windblown sediment trapped nearer the soil surface was more characteristic of the erodible portion of the in-situ parent soil. Vertical gradation in size of windblown sediment was evidenced by a decrease in the >100µm and 46-100µm size fractions and increase in the 11-32µm and less than or equal to 10µm size fractions with height from the soil surface. Trends in the sediment size distribution with height suggested that sediment less than or equal to 32µm in diameter is transported primarily by suspension, sediment 33-45µm in diameter is transported by saltation and suspension, and sediment >45µm in diameter is transported primarily by saltation. In addition, the size of windblown sediment observed at all heights above the soil surface was found to increase with an increase in wind velocity. A large fraction of windblown sediment was comprised of suspension-sized aggregates and particles, thus mitigation strategies to control wind erosion in the Columbia Plateau must promote aggregation of the suspension component (less than or equal to 32µm in diameter) of the parent soil or shelter the suspension component at the soil surface from high winds.