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This literature review is focused on the potential for innovative
use of trees and other vegetation to reduce the odor associated with livestock
production. The goal is to examine available evidence to assess if trees
and shelterbelts may:
1) be able to help control odor through physical and biological means, and2) be an economically feasible technology for livestock producers as well as surrounding communities.
Shelterbelts have the potential to be an effective and inexpensive
odor control device particularly when used in combination with other control
methods for added effectiveness. The potential of shelterbelts is really
defined by the characteristics of livestock odors. These characteristics
(Smith, 1993) are:
There is compelling evidence that shelterbelts will work very well
within an agricultural landscape to provide odor control by affecting these
characteristics. Because the odor source is near the ground and the tendency
of the plume is to travel along the ground (Takle, 1983). Shelterbelts
of even modest heights (i.e. 20-30 ft) may be ideal for plume interception
and disruption (Heisler and DeWalle, 1988; Laird, 1997; Thernelius, 1997).
Shelterbelts can easily be designed as to fit the production situation
and expected/experienced odor plume shapes. Also, depending on the shelterbelt
design and species used, they can deal with the temporal characteristics
and provide year round plume/aerosol interception.
There are be four primary ways that shelterbelts can ameliorate livestock odors;
Shelterbelts create turbulence at the surface of the terrain that
intercept and disrupt odor plumes traveling in laminar flow helping to
push the plume into the lower atmosphere facilitating dilution (OCTF, 1998;
SOTF, 1995; Takle, undated). Lowering wind speeds over storage lagoons
can reduce convection of odorous compounds from the surface and allow for
slower release of the odor plume which also facilitates dilution (Bottcher
et al., 1999).
Pesticide drift mitigation research suggests that due to reduced
wind speeds drift pesticide will drop from the air stream. In broadleaf
species, downwind drift reductions of 70% (no leaves present) to 90% (with
leaves present) have been recorded (Porskamp et al., 1994). Numerical simulation
of the effects of tall barriers around manure lagoons predicted reductions
in downwind malodorous lagoon emissions of 26% to 92% (Liu et al., 1996).
Wind tunnel modeling of a three-row shelterbelt system has quantified reductions
of 35% to 56% in the downwind mass transport of odorous particulates (dust
and aerosols) (Laird, 1997; Thernelius, 1997).
Meister et al. (1984) suggests that a forest cleans the air of micro-particles
of all sizes by combing out twenty fold better than barren land. Leaves
with complex shapes and large circumference to area ratios collect particles
most efficiently, indicating that conifers may be more effective particle
traps than deciduous species (Smith, 1994) as well as having an “in leaf”
temporal advantage. Volatile Organic Compounds (VOC’s) have a distinct
affinity to the lipophilic membrane (the cuticle) that covers plant leaves
and needles. Research on this affinity is currently underway (Beattie et
al., undated) Researchers have quantified measurable quantities of anthropocentric
VOC’s that have accumulated at the surface of plants (adsorption) and within
the plants tissues (absorption) (Reischl et al., 1989; Reischl et al.,
1987; Gaggi et al., 1985) Micro-organisms dominate the surface of plants
(Preece and Dickenson, 1977). These organisms also adsorb and absorb VOC’s
and provide additional surface area for pollution collection. These organisms
also have the ability to metabolize and breakdown VOC’s (Screiber and Schonherr,
1992; Muller, 1992; Beattie et al, undated).
Economic analysis of a new shelterbelt planted around a 3000 head
hog facility, using scenarios of high” cost (10$/ Tree and shrub) and “higher”
cost ($25/ Tree and shrub), showed the following costs: for the “higher”
scenario: $0.68/pig for one year, capitalized over 20 years at 5% it comes
to just $0.09/pig These costs include maintenance costs. The relatively
low cost of a shelterbelt system would allow most producers to economically
utilize other odor control techniques (Hoff, 1998). Using multiple control
strategies increases the effectiveness of odor reduction (NPPC, 1995; Lorimor,
1998). Increased production costs are often the main barrier to reasonable
odor control. However, studies have shown that consumers may be willing
to pay for socially responsible animal production. Using contingent valuation
methods researchers have determined significant numbers of people who would
be willing to pay a premium for meat products produced in an “environmentally
friendly” manner, including odor control (Kliebenstein et al, 1998). The
Swine Odor Task Force out of North Carolina has recommended a certification
process for producers who control air and water pollution.
Penkala (1977) suggests the primary goal of odor mitigation is to minimize
or eliminate perceived odors. Achievement of this goal can be measured
by reductions in: 1) odor concentrations reaching populated areas, 2) number
of people affected by objectionable odors, 3) time duration of exposure
to odors, and 4) number of occurrences of odor events. The relationship
between odor perception and concentration of odorous chemicals is logarithmic.
This means that the concentration of odorous chemicals within a parcel
of air needs to be reduced significantly (i.e. sometimes > 99%) before
there is a noticeable change in perceived offensiveness. For example, in
laboratory studies, Misselbrook et al. (1993) determined that the average
concentration of odorous chemical emission following application of pig
slurry would need to be reduced between 94 % and 97.8% before the perceived
intensity (as determined by a human smell panel) went from a level 6 intensity
on a six level scale (6 = extremely strong odor) to a level 2 (2 = faint
odor). A typical concentration of odor from a poultry house ventilation
system would need to be reduced between 99.1% and 99.7% to get from perception
level 6 to level 2. As discussed earlier, legally defined separation distances
aid in the dispersion of odors. In Iowa, for example this distance is between
1250 and 2500 feet depending on the size of the facility and number of
head of animals (Lorimor, 1999). Since most of these distances are determined
based on protection of water sources, the distance is often not enough
to reduce odor concentrations to levels that eliminate odor nuisance. Shelterbelts
have the ability to reduce odor concentrations significantly (estimated
at > 56% (Thernelius , 1997; Laird, 1997) at or very near the source, which
greatly enhances the effectiveness of the separation distance. The 56%
reduction estimate above was achieved in a wind tunnel experiment modeling
a natural ventilated production building with minimal shelterbelt design
considerations. Proper shelterbelt and shelterbelt systems designs should
be able to decrease the concentration levels of odor plumes leaving production
sites even more and combined with legal separation distances effectively
reduce the odor perception levels reaching populated areas, reduce the
number of people affected, reduce the time duration of exposure to odors,
and allow for reductions in the number of occurrences of odor events. Unfortunately,
while several sources (Koelsch, 1999; WED, 1999; NPPC, 1999; Lorimer et
al., 1998; OCTF, 1998; Jacobson et al., 1998) list shelterbelts as odor
control devices, they provide little physical, biological, or economic
quantification as to effectiveness. Gassman (1995) concluded in a review
of available literature that shelterbelt and other vegetation impacts on
odor movement and abatement have yet to be studied in detail. However,
both laboratory and field work on the quantification of the effectiveness
of shelterbelts to mitigate odor is currently underway (Iverson, J., James,
W., and B. Munson, 1999-present; Beattie et al., 1999-present; Bottcher
et al, 1999). There are also currently 10 Iowa livestock producers who
are participating in Iowa State University’s Odor Control Demonstration
Project using landscaping that was planted in 1997. At least two other
Iowa livestock producers (both swine) have independently installed shelterbelt
systems for odor control within the last few years and one large scale
beef lot has made serious inquiries.
The use of shelterbelts for odor mitigation, and the diffusion of
this technology to livestock producers as well as communities affected
by odor issues, faces several barriers to fruition. The most pervasive
barriers are as follows:
Lack of technical information regarding shelterbelts:
Further quantification of effectiveness as odor control device needed.
Current studies are underway (Bottcher et al, 1999; Beattie et al, undated;
Iverson et al., undated). There often exist cultural barriers to erecting
“non-agricultural” structures within an agricultural setting. The following
are some common concerns:
Below is basic diagram of a shelterbelt design associated with a
swine production facility. The shelterbelt design shown is very generic.
The exact number of rows, species, and total number of trees are important
considerations not displayed. This generic design provides “buffering”
around the major sources of livestock odor. The design can easily be adapted
to fit other livestock confinement and /or feedlot systems. The wind in
Iowa primarily comes from the south and west during the summer months and
the north and west during the winter. The orientation of shelterbelts below
reflects this. The numbers next to the example shelterbelts on the diagram
correspond to the potential shelterbelt functions as listed below; the
numbers are in order of probable functional importance.
1) Turbulence - Dilution into lower atmosphere,
2) Dust deposition Off-field particulate elimination & overall particulate control Particulate deposition on the windward & lees sides,
3) Interception,4) Pollutant sink;Dust, bio-aerosols, gasses. Adsorption and absorption of odorous chemicals onto/into plants,
Microbial sink.
Figure 1. A hypothetical shelterbelt system design
for a typical swine production facility. The numbers refer to the functional
interaction and means by which the shelterbelt will mitigate livestock
odor. The number 1 refers to creation of air mixing turbulence, the number
2 refers to dust deposition, the number 3 refers to particulate interception,
and the number 4 refers to sites of air pollution sinks. Other important
design considerations include: livestock type, odor sources, air/wind patterns,
and the species of trees/shrubs used.
Figure 2. Planted in April 1999, this five row mixed conifer and hardwood species shelterbelt is located on the northwest corner of a swine confinement facility in central Iowa. This shelterbelt was planted specifically for odor control and improved aesthetics. Photograph by A. Holtz, Iowa State University.
Figure 3. Newly planted (April 1999) two row, mixed
conifer/hardwood species shelterbelt located along the east side of a manure
lagoon in the northeast corner of a swine production facility in central
Iowa. Photograph by A. Holtz, Iowa State University.
For more information, contact John Tyndall, Department of Forestry, Iowa State University, (515) 294-1167, jeeves@iastate.edu
Downloadable documents by John Tyndall:
(in Adobe Acrobat)
Shelterbelts and Odor
Final Report.pdf
Opportunities
for Agroforestry.pdf
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the files above.
It is free to download at:
http://www.adobe.com/products/acrobat/readstep2.html