Environmental Engineering Reference
In-Depth Information
required to install access roads and support facilities, there is a limited risk of
triggering geological hazards (e.g., landslides). Altering drainage patterns could
also accelerate erosion and create slope instability. Disturbed soil surfaces (crusts)
now cover vast areas in the western United States as a result of ever-increasing
recreational and commercial uses of these semi-arid and arid areas. Based on the
findings of several studies (Belnap and Gillette, 1997; McKenna-Neumann et al.,
1996; Williams et al., 1995), the tremendous land area currently affected by human
activity may lead to significant increases in regional global wind erosion rates.
Surface disturbance, heavy equipment traffic, and changes to surface runoff pat-
terns resulting from biomass energy construction activities could cause soil erosion
and impacts on special soils (e.g., cryptobiotic soil crusts; discussed below). Impacts
of soil erosion could include soil nutrient loss and reduced water quality in nearby
surface water bodies.
Cryptobiotic Soils Crust
With regard to disturbance of cryptobiotic soil crusts, this is an important but often
overlooked and not fully appreciated or understood soil disturbance problem, espe-
cially within the western and southwestern United States. Whether the renewable
energy source is solar, wind, hydro, or biomass, the western and southwestern states
are key players in harnessing and processing these energy sources. Cryptobiotic soil
crusts, consisting of soil cyanobacteria, lichens, and mosses, play an important eco-
logical role in the arid Southwest. In the cold deserts of the Colorado Plateau region
(parts of Utah, Arizona, Colorado, and New Mexico), these crusts are extraordi-
narily well developed, often representing over 70% of the living ground cover.
Cryptobiotic crusts increase the stability of otherwise easily eroded soils, increase
water infiltration in regions that receive little precipitation, and increase fertility in
soils often limited in essential nutrients such as nitrogen and carbon (Belnap, 1994;
Belnap and Gardener, 1993; Harper and Marble, 1988; Johansen, 1993; Metting,
1991; Williams et al., 1995).
Cyanobacteria occur as single cells or as filaments. The most common type
found in desert soils is the filamentous type. The cells or filaments are surrounded
by sheaths that are extremely persistent in these soils. When moistened, the cya-
nobacterial filaments become active, moving through the soils and leaving a trail
of the sticky, mucilaginous sheath material behind. This sheath material sticks to
surfaces such as rock or soil particles, forming an intricate webbing of fibers in the
soil. In this way, loose soil particles are joined together, and otherwise unstable and
highly erosion-prone surfaces become resistant to both wind and water erosion. The
soil-binding action is not dependent on the presence of living filaments. Layers of
abandoned sheaths, built up over long periods of time, can still be found clinging
tenaciously to soil particles at depths greater than 15 cm in sandy soils. This provides
cohesion and stability in these loose sandy soils even at depth.
Cyanobacteria and cyanolichen components of these soil crusts are important
contributors of fixed nitrogen (Mayland and McIntosh, 1966; Rychert and Skujins,
1974). These crusts appear to be the dominant source of nitrogen in cold-desert pin-
yon-juniper and grassland ecosystems over much of the Colorado Plateau (Evans
