Geoscience Reference
In-Depth Information
While 85 % of natural desert surfaces have been described
as being not susceptible to wind erosion (Wilshire, 1980)
the area at risk may be greatly enhanced by human ac-
tivity (Prospero
et al.
, 1983; Tegen and Fung, 1995; Gill,
1996). Middleton (1989) describes two types of activity
that may enhance wind erosion in drylands: those that
break up naturally wind-resistant surfaces (such as stone
pavements) and those that remove a protective vegetation
cover. In the former category disturbance may be spatially
distinct in the form of off-road vehicle (ORV) use (Padgett
et al.
, 2008). Research suggests that ORV activity can
induce dust emissions equivalent to 564 kg/km in one
year for one vehicle used on a daily basis on an unpaved
road (Frazer, 2003). Compared to undisturbed surfaces,
Goossens and Buck (2009a) report typical dust emission
values for ORVs on dry desert soils varying between 300
and 800 g/km on mixed terrain, although they found much
higher values on silty soils (Goosens and Buck, 2009b).
However, much larger scale problems can be created
by dryland agricultural activity where stable vegetated
surfaces may be stripped and exposed to the power of
erosive winds, as occurred in the Dust Bowl era of the USA
in the 1930s (Worster, 1979; see Box 23.1). It has been
suggested that cultivated lands in drylands may produce
20 % more aeolian dust than uncultivated regions and
construction activity may double the amount of dust in
the atmosphere (Reheis and Kihl, 1995). Further, some
of the most intense human-induced dust hazards globally
result from the draining of inland water bodies such as
Owens Lake and the Aral Sea (Gill, 1996).
2007). Gill (1996) reports that the deposition of alkaline
dust from the drying Mono basin in California has the
potential to alter the downwind soil chemistry and veg-
etation structure, leading to a decrease in biodiversity in
the area and an increase in soil pH. Nearby, salt-laden
depositing dust that is blown out of Owens (dry) Lake is
noted to have a significant adverse environmental impact
on three surrounding national parks and numerous desig-
nated areas of critical environmental concern (Gill, 1996;
Reheis, 1997).
Third, the transportation of eroded sediment by high
winds can abrade buildings, crops and livestock and also
create visibility problems along roads and at airports. The
best-known example is the 1973 aviation accident at Kano,
Nigeria, when 183 people were killed in a crash-landing
widely attributed to Harmattan dust haze (Adefolalu,
1984; Adedokun, Emofurieta and Adedeji, 1989). More
chronically, however, the long-distance transport of dust-
sized particles (
<
62.5 µm) by suspension can create sig-
nificant health problems where fine material with aerody-
namic diameters of
one-seventh of the width
of a human hair), 5 µm and 2.5 µm (termed PM
10
,PM
5
and PM
2.5
, respectively) may be easily inhaled into the
lungs of people and animals. Epidemiological studies have
found that these fine particles can be drawn into the deep-
est portions of the human respiratory tract (Pope, Bates
and Raizenne, 1996; Griffin, 2007), where they may have
serious impacts on human respiratory and lung function
(Bennion
et al.
, 2007). These particles may be made up of
sulfates, carbonates, sodium and calcium and particular
health problems are evident where these fine, respirable
particles are contaminated with toxic agricultural fertilis-
ers and pesticides or waste residue that may contain trace
chemicals (e.g. arsenic, cadmium, lead, mercury; see Gal-
loway
et al.
, 1982; Griffin, 2007) that are associated with
the onset of asthma, cancers, interstitial lung disease, em-
physema and lung fibrosis (O'Hara
et al.
, 2000; Bennion
et al.
, 2007; Griffin, 2007). Furthermore, windborne dust
may contain high concentrations of organics composed of
microorganisms, which may include fungal spores, bacte-
ria, viruses and pollen (Prospero
et al.
, 2005; Kellog and
Griffin, 2006; Griffin, 2007). Inhalation of airborne spores
of the soil-dwelling
Coccidioides immitis
fungus, for ex-
ample, is known to cause 'valley fever' in the southwest
USA and Mexico where, during the epidemic from 1991
to 1995 the annual incidence of the infection rose from 50
to 500 per year (per 100 000 population) in Kern County,
California (Zender and Talamantes, 2006).
There is a wealth of evidence that inhalation of wind-
blown dryland dust has serious deleterious consequences
for human health. Hefflin
et al.
(1994) recorded a 3.5 %
<
10 µm(
∼
23.3
The aeolian dust hazard
Aeolian erosion is hazardous on three counts. First, wind
erosion can strip surfaces of soil nutrients so making them
much less able to preserve a protective vegetation cover.
Such erosion is particularly problematic in drylands where
the lack of moisture percolation through soils results in
nutrients lying very shallow beneath the surface and so
they are potentially easily removed, sometimes within
only one erosive event. Erosion of nutrient-rich topsoil
in this manner can seriously degrade semi-arid cropland
very quickly (Zobeck and Van Pelt, 2006). For example,
Larney
et al.
(1998) showed that spring wheat yields on
the Canadian prairies decreased linearly with increased
wind erosion severity. Second, the deposition of eroded
dust can bury plants, clog streams and drainage channels,
contaminate food and water resources and impact on veg-
etation growth, soil productivity and ecosystem dynamics
(Worster, 1979; Larney
et al.
, 1998; McTainsh and Strong,
