John E. Stout

The Wolfforth field experiment : A wind erosion study

The goal of this field study was to obtain a detailed account of wind erosion processes within a single agricultural field during a regional dust storm in the Southern High Plains of West Texas. The field, located in Wolfforth, Texas, was observed as the wind grew in strength, peaked, and later weakened. Sediment transport was monitored by an array of samplers spaced across the field, and meteorological information was obtained from a 10-m tower erected within the field. Erosion activity was monitored by a piezoelectric sensor that responded to the impact of saltating grains and provided a means for detecting the threshold of soil movement. Attempts were made to relate the observed temporal and spatial variations of sediment transport to meteorological factors and surface conditions. The results indicate that at the beginning of the storm, threshold was around 7 to 8 m/s. As the storm progressed, threshold appeared to slowly shift downward with time, suggesting a surface that was becoming increasingly erodible. Mass flux measurements showed substantial temporal variations that reflected changes of wind strength and changes in surface erodibility. The pattern of mass flux variation across the field was dependent on the height of measurement. The near surface flow of saltating grains (z < 0.25 m) was found to vary according to surface conditions, especially surface roughness. At greater heights, the flow of fine dust was less affected by surface conditions immediately beneath the point of measurement. Within the fully developed surface layer (z < 0.25 m), the mass flux profile was found to follow a modified powerlaw function. The near surface mass flux consisted of a broad range of particle sizes ranging from 50 μm to 300 μm, whereas farther from the surface the mode shifted distinctly toward smaller particle sizes with few particles larger than 100 μm. We show that it is possible to display graphically the relative contribution of the various grain sizes to the mass flux at each height in a way that makes it possible to visualize the zones of saltation and suspension, and the region of transition between these regimes.

Validation of the wind erosion stochastic simulator (WESS) and the revised wind erosion equation (RWEQ) for single events

Abstract The wind erosion stochastic simulator (WESS) is a single event wind erosion model that is the core of the wind erosion submodel of the environmental policy integrated climate (EPIC) erosion model. WESS uses inputs of soil texture, erodible particle diameter, soil roughness, soil water content, crop residue, and 10 min average wind speeds to predict the erosion at several user-selected distances within a given field. The revised wind erosion equation (RWEQ) makes annual or period estimates of wind erosion based on a single event wind erosion model that includes factors for wind and rainfall, soil roughness, the erodible fraction of soil, crusting, and surface residues. In this study, we compared estimates of wind erosion at multiple points in a field for 24 events at Big Spring, Texas with the predictions of WESS and compared estimates of maximum sediment transport capacity (Qmax), critical field length at which Qmax is attained ( S ), and soil loss (SL) calculated from field measured data collected at six locations and 41 events with the predictions of RWEQ. Compared to observed estimates of erosion for the 24 events, WESS under-predicted 9 events, accurately predicted 8 events, and over-predicted 7 events. In general, RWEQ underestimated Qmax and SL and overestimated S .

Indirect evidence of wind erosion trends on the Southern High Plains of North America

Abstract Detecting and quantifying changing regional patterns of wind erosion activity is complicated by a lack of long-term records of direct wind erosion measurements. Here, we attempt to piece together indirect evidence of changing wind erosion activity on the Southern High Plains. Sources of indirect evidence include visibility-based observations of blowing dust as well as past measurements of ambient particulate matter concentration. Both the visibility record and particulate matter record suggest independently that there have been significant declines in blowing dust during the last 40 years. There are three key factors that may have contributed to the observed reduction of blowing dust—natural climatic variations, changing land use, and improved agricultural practices. Historical climatic records suggest that there have been no appreciable climate shifts that could account for the observed decline in blowing dust. Although it is not possible to rule out land use as a factor in the reduction of blowing dust, one can point to periods when land use changed very little while annual dust levels decreased significantly. Overall, the relatively minor changes in land use, including the removal of land from production, cannot fully account for the magnitude of the observed reduction of ambient dust levels on the Southern High Plains. We are left to conclude that the adoption of improved agricultural practices has played a crucial role in reducing wind erosion activity and dust emissions on the Southern High Plains.

Seasonal Variations of Saltation Activity on A High Plains Saline Playa: Yellow Lake, Texas

The Southern High Plains region of West Texas and eastern New Mexico is often described as a flat elevated tableland. Spaced across this vast and otherwise featureless plain are 21 large closed basins containing approximately 40 irregularly shaped saline playas. Yellow Lake, located on the Yellow House Ranch northwest of Lubbock, Texas, is among the largest of the High Plains saline playas. This paper represents the first report of a 4-yr. study of saltation activity at Yellow Lake. From December 30, 1998, to January 1, 2003, a fast-response piezoelectric saltation sensor was used to collect a continuous record of aeolian activity at a point on the playa surface. Since saltation activity is often associated with dust emissions, the saltation record also provides information regarding seasonal patterns of dust emissions from the Yellow House Basin. Results suggest that blowing events can occur at any time of the year when conditions are favorable; however, the necessary conditions are rarely satisfied. As a result, the saltation record is characterized by many hours of inactivity punctuated with brief periods of occasionally intense aeolian activity. From December 30, 1998, to January 1, 2003, saltation activity was detected for only 7% of the hours measured. Although there can be substantial deviations from one year to the next, it was found that saltation activity tends to peak during winter months when winds are moderately strong and precipitation is at a minimum. Hourly saltation activity values occasionally approached unity during intense winter blowing events, indicating nearly continuous sediment transport over a one-hour period. Saltation activity is at a minimum during summer months when winds are often weak and wet conditions prevail. Although winds are typically strongest during the spring season, the playa is relatively stable due to high threshold values produced by significant spring precipitation. This contrasts sharply with the surrounding cropland, which tends to be most active during the spring season.

Validation of the Revised Wind Erosion Equation (RWEQ) for Single Events and Discrete Periods

The Revised Wind Erosion Equation (RWEQ) makes annual or period estimates of wind erosion based on a single event wind erosion model that includes factors for wind and rainfall, soil roughness, the erodible fraction of soil, crusting, and surface residues. In this study we measured wind erosion and the factors used in RWEQ for 41 storm events at six locations. The maximum sediment transport (Qmax), critical field length (S) and field soil loss (SL) were calculated from the field measured data and estimated using the equations provided by RWEQ. RWEQ under-estimated Qmax and SL and over-estimated S. Simple linear regressions between observed and estimated Qmax, S and SL revealed significant (P<0.05) correlations for Qmax and SL. The correlation coefficients for Qmax and SL were 0.70 and 0.62, respectively. The calculated S was not significantly related to the estimated S.

Composition and Characteristics of Aerosols in the Southern High Plains of Texas (USA)

Aerosol samples on polycarbonate filters were collected daily for several years in the Southern High Plains region of western Texas. Selected samples representing a variety of size modes, locations, and air quality conditions were analyzed by PIXE. Silicon and other crustal elements dominated during dust storms and in the coarse mode; sulfur dominated during anthropogenic pollution episodes and in the fine mode. A mixture of both aerosol types was present even during “clear” conditions. The Al/Si ratio in dust events increases with wind speed. These data provide an initial assessment of aerosol chemistry in the West Texas plains.