Wind Erosion
Impacts on
Dryland Soils
Ted M. Zobeck, Research Soil Scientist
USDA, Agricultural Research Service
Lubbock, TX
Presentation Overview
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Defining the Scope
Soil Formation
Aeolian Processes
Characteristics of sediment
Local Effects
– Coppice dunes, islands of fertility
• Regional/Global Effects
– Proximity to source, loess, Terra Rossa Soils
Aeolian deposits occur over much of the globe. Their
origin and subsequent development widely varies. Today
I will focus on aeolian processes in arid and semi-arid
dryland regions.
Source FAO, 2002
Wind erosion is a significant aeolian process that
produces many effects on soils and landscapes in
dryland systems, comprising almost forty percent of the
Earth’s land surface. Although wind erosion occurs in
almost all climatic regions, it is a dominant process in
arid and semi-arid regions.
Source FAO, 2002
Wind erosion is active today!
Meadow, Texas September 3, 2011,
Photo: Ted Zobeck
A local man follows his sheep during a dust
storm on April 12, 2010 in Huailai county,
Hebei Province. Photo: CFP
Phoenix, Arizona July 5, 2011.
Photo: Assoc. Press
Queensland Australia October 2013
Photo: Karen Emmott in ABC Queensland
So how do aeolian processes affect
soils?
First, let’s have a very brief review of
the soil and wind erosion processes….
Wind erosion often occurs when soils are bare,
loose, dry and subjected to erosive winds.
Most prevalent in coarse-textured soils.
What we observe to
measure the impacts
of wind erosion
depends upon what
and where we
sample!
Effect of sampling height on particle
size
Mean diameter varied from 100 µm at 0.15 m to 50 µm at 2 m
Zobeck and Fryrear, 1986a
This impacts transport of minerals,
nutrients, organic matter, microbes…
Mean nutrient content and enrichment ratios for dust caught at
0.15 m to 2.0 m for 6 dust storms in west Texas
Na
K
Ca
Mg
CEC
OM
Amount
0.06
1.06
7.01
1.19
9.34
4.18
Enrichment
Ratio
2.1
1.6
2.0
1.2
2.1
2.0
Nutrients in cmole (+)/kg and OM in g/kg
From Zobeck & Fryrear, 1986b
Removal of soil can be quite
large…
During a field campaign from 1989-1997 at Big
Spring, Texas, observed soil loss due to wind erosion
on an agricultural field varied from about 40 to 290
Mg/Ha/Yr
The field was kept bare, smooth, and erodible.
Van Pelt & Zobeck, 2004
Creep and Saltation material is usually
trapped near the source and impacts
local vegetation and surface features
Van Pelt & Zobeck, 2004
Erosion of patchy vegetation in grasslands/shrublands
has significant impacts on soil properties and
redistribution of nutrients and sediment.
(Ravi at al., 2010)
Differences in soil properties under
plants and openings are often observed
• Compared with intershrub areas, the shrub
patches had a higher soil porosity, infiltration
capacity, water-holding capacity, hydraulic
conductivity, structural stability, and organic
matter content, and lower bulk density. (Stavi
et al, 2009).
• In another study, total and mineralizable soil
N, and total and respirable organic C in the
surface 5 cm were significantly greater for
soil under plants than soil from openings.
(Hook et al., 1991)
Let’s look at material that moves greater distances…
Where does all of the ‘dust’ go?
Well….That depends…..
Dust affects nearby ecosystems
and soils
A recent study by Hirmas and Graham (2011)
presented evidence for how the Fry
Mountains of California act as a topographic
‘baffle’ against the prevailing wind and
trapping aeolian sediment.
Studies have discovered how distance from
the source affects soils in many ways
A 390 km transect in west Texas showed
decreasing sand size with distance from the
hypothesized Pecos River source (E. M. Seitlheko
[with B.L. Allen], 1975)
There have been many other studies of the effects
of proximity to a source region when studying soils
with aeolian parent materials, particularly loess
soils.
But what about loess?
Much of the world’s loess occurs in mid-latitudes
associated with glaciation…
(Thomas and Wiggs, 2008)
Desert Loess Formation
Tsoar and Pye, 1987
• Loess mainly medium silt size transported near
the surface and so is relatively close to source
• Availability of silt source and wind needed
• Suitable dust trap very important
– Topographic obstacles
– Moist ground
– Vegetated surfaces
• Dust blown during glacial periods from certain
deserts (Sinai, Soviet Central Asia, China)
accumulated loess in neighboring semi-arid
areas
Observed Dust Deposition Rates
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Global 10 to over 200 t km-2 yr-1 (Pye, 1987)
Israel 57-217 t km-2 yr-1(Yaalon and Ganor, 1975)
Australia 5-10 t km-2 yr-1 (Tiller et al., 1987)
Nigeria 137-181 t km-2 yr-1 (McTainsh and Walker,
1982)
• Central and west (Edwards Plateau)Texas 12 t km-2
yr-1 (Rabenhorst et al, 1984)
• SHP West Texas 77-103 t km-2 yr-1 (Crabtree, 2005)
• S. Nevada and S. California 4 to 30 t km-2 yr-1
(Reheis and Kihl, 1995).
• SW California average of 78 t km-2 yr- (Hirmas and
Graham, 2011)
Dust affects distant ecosystems
and soils
• Saharan dust has
been identified as the
most important
parent material of
soils of the
Caribbean Islands
and Florida Keys as
shown by Al2O3/TiO2,
Ti/Y, Ti/Zr, Ti/Th
ratios
(Muhs, et al., 1990)
Dust affects distant ecosystems
and soils
Hawaiian rain forests receive nutrients from
Asia and sustains the productivity of these rain
forests (Chadwich et al, 1999).
– P is the main regulator of biological activity in oldest
sites
Rate of P loss from soil
Atmospheric
contribution of P
Dust affects distant ecosystems
and soils
• ‘Terra Rossa’ soils of Mallorca, Spain
developed from African dust (Muhs, et al.,
2010)
Aeolian processes do indeed
impact soil genesis, mineralogy,
fertility, and landscape evolution
in arid and semi-arid regions and
around the globe.
We have much more to learn and
invite you to join the fun.
www.aeolianprocesses.org
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