Temporal and Spatial Variation of Episodic Wind Erosion in Unburned and Burned Semiarid Shrubland

Abstract

Redistribution of soil, nutrients, and contaminants is often driven by wind erosion in semiarid shrublands. Wind erosion depends on wind velocity (particularly during episodic, high-velocity winds) and on vegetation, which is generally sparse and spatially heterogeneous in semiarid ecosystems. Further, the vegetation cover can be rapidly and greatly altered due to disturbances, particularly fire. Few studies, however, have evaluated key temporal and spatial components of wind erosion with respect to (i) erosion rates on the scale of weeks as a function of episodic high-velocity winds, (ii) rates at unburned and burned sites, and (iii) within-site spatial heterogeneity in erosion. Measuring wind erosion in unburned and recently burned Chihuahuan desert shrubland, we found (i) weekly wind erosion was related more to daily peak wind velocities than to daily average velocities as consistent with our findings of a threshold wind velocity at approximately 7 m s(-1); (ii) greater erodibility in burned vs. unburned shrubland as indicated by erosion thresholds, aerodynamic roughness, and nearground soil movement; and (iii) burned shrubland lost soil from intercanopy and especially canopy patches in contrast to unburned shrubland, where soil accumulated in canopy patches. Our results are among the first to quantify post-fire wind erosion and highlight the importance of accounting for finer temporal and spatial variation in shrubland wind erosion. This finer-scale variation relates to semiarid land degradation, and is particularly relevant for predictions of contaminant resuspension and redistribution, both of which historically ignore finer-scale temporal and spatial variation in wind erosion.

Aeolian Processes and the Biosphere

“…More recently, fast‐response instruments to measure wind characteristics (e.g., sonic anemometers) are widely used to measure threshold shear velocity [ van Boxel et al , 2004]. These instruments can be deployed in the field along with active or passive dust aerosol samplers to investigate dust movement in the entrainment, transport, and deposition phases over large landscapes [ Whicker et al , 2002; Breshears et al , 2003; Mikami et al , 2006].…”

“…Over time, the redistribution of soil from source to sink areas may reinforce patterns of wind and water erosion, leading to further degradation of source areas and additional enrichment of sink areas. Arid regions are particularly susceptible to increases in rates of wind and water erosion after disturbance such as fire or livestock grazing [ Whicker et al , 2002; Ludwig et al , 2005; Field et al , 2011] (see also section 4.5). For example, proxy records of dust deposition from high‐elevation lakes in the southwestern United States indicate that dust load levels have increased by 500% above the late Holocene average, likely due to land use change and disturbance associated with the expansion of livestock grazing in the early twentieth century [ Neff et al , 2008].…”

“…Arid and semiarid regions are affected by disturbances like fires and grazing, which may render soils in these regions more susceptible to aeolian erosion with important impacts on crop productivity and regional dust emissions [ Whicker et al , 2002; Ravi et al , 2009b; Neff et al , 2008; Sankey et al , 2009a; Field et al , 2011]. Fires are known to affect wind erosion and subsequent dust emission from these landscapes [ Whicker et al , 2002; Breshears et al , 2009; Ravi et al , 2009b; Sankey et al , 2009b]. Fires increase the susceptibility to erosive action of wind by destruction of surface vegetation cover and microbial soil crusts.…”

Source reconciliation of atmospheric dust causing visibility impairment in Class I areas of the western United States

“…Dust emissions from travel on paved and unpaved roads are related to traffic characteristics and the quality of the road [ Etyemezian et al , 2003]. Windblown dust emissions generally occur over larger spatial scales and the magnitude of dust emissions during these events can eclipse the comparatively smaller, but more regular road dust emissions [ Okin and Gillette , 2001; Reynolds et al , 2001; Breshears and Allen , 2002; Whicker et al , 2002; Mahowald et al , 2007]. On a transcontinental scale, dust from regional wind storms in the Saharan and Chinese/Mongolian deserts can be transported across continents and impact areas in North America [ Prospero , 1999; VanCuren and Cahill , 2002; Darmenova et al , 2005].…”

Fire and the Land Surface

“…There have been some observations but few measurements. Whicker et al (2002) undertook measurements near Carlsbad, New Mexico, and found that erosion was three times greater over several months and 70 times greater during strong winds for recently burned compared with unburned sites. Whicker et al (2002) undertook measurements near Carlsbad, New Mexico, and found that erosion was three times greater over several months and 70 times greater during strong winds for recently burned compared with unburned sites.…”