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OCR for page 171
Impacts of Air Pollution on Agriculture
in North America
WALTER W. HECK
Agricultural Research Service
U.S. Department of Agriculture
This chapter highlights our current understanding of the effects of
anthropogenic air pollutants on agriculture in the United States and assesses
their impact on crop productivity. Information from a cross section of
crop-oriented review articles has been used to help define the problem
(Altshuller and Linthurst, 1984; Dochinger and Seliga, 1976; Evans, 1984;
Guderian, 1985; Heck 1984; Heck and Brandt, 1977; Heck et al., 1977,
1982a, 1982b, 1983a, 1984a, 1984b, 1984c, 1986; Irving, 1987; Jager and
Klein, 1980; National Academy Sciences, 1977; Roberts, 1984; Shupe et
al., 1983; Shriner et al., 1980; Reshow, 1984; Unsworth and Ormrod, 1982;
U.S. EPA, 1978, 1982a, 1982b, 1986; and Winner et al., 1986~.
Air pollution effects from point sources were first recognized in the
early 1900s. Research was directed at recognizing injury symptoms and
assessing losses in productivity in accordance with the severity of symptom
development. Since that time, many chemicals have been identified as
atmospheric contaminants that can injure or damage crops at some range
of exposure concentration and time Able 1~.
Sulfur dio~de (SO2) and fluoride (generally as hydrogen fluoride or
HF) gases from point sources caused injury to vegetation around the
turn of the century. Ducktown (Copper Hill), Tennessee in the United
States, and SudbuIy, Ontario in Canada still show marked effects from
SO2 releases from early smelter operations. Today, the installation of
emission control systems and the use of high stacks has generally eliminated
extensive injury to vegetation near sources of SO2. However, high-capacity
power stations with tall stacks have increased the distribution of lower
SO2 concentrations over larger areas. Thus, SO2 is now considered a
regional problem, although direct effects on agricultural production are
poorly defined.
171
OCR for page 172
172
TABS F 1 Phytoto~cic air pollutants, in order of importance to crop systems.a
ECOLOGICAL RISKS
Primary or
Pollutant Secondary
Form Major Source(s)
. .
o
so2
NO2
HF
PAN-Oxid.C
NO
C12
HO
Toxic elements
NH3
SO4
NO3-
H2S
co2
UV-B!
Secondary
Primary
Primary and
secondary
Primary
Primary
Secondary
Primary
Primary
Primary
Primary
Primary
Secondary
Secondary
Primary
Primary
Primary
Gas
(;as
Gas
Gas -
particulate
Gas
Gas
Gas
Gas
Gas
Particulate
Gas
Aerosol
Aerosol
Gas
Gas
Radiation
Atmospheric transformation (associated with
automotive emissions, NO2, hydrocarbons)
Power generation, smelter operations
From direct release and atmospheric
transformation ~igh-temperature com-
bustion, from NO); fertilizer production
Superphosphate, aluminium
smelters
Combustion, natural
Atmospheric transformation (automotive
emissions, NO2, hydrocarbons)
Combustion, natural
Spills, manufacture
Buming of plastics
Smelters, combustion processes
Feedlots, natural
Atmospheric transformation (SO2)
Atmospheric transformation (;N02)
Paper production, natural, geothermal
Combustion, natural
Natural, stratospheric O3 depletion
a This list is not meant to be complete but represents the most unportant air pollutants with
respect to terrestrial plant systems. Several of dose low on the list have been poorly studied
and may be more important than currently thought.
b Ethylene
c Peroxyace~1 nitrate~xidant
SOURCE: Heck, 1982.
Fluoride (as HF) injury to vegetation was described by the turn of the
century, but did not become a major problem until aluminum smelting and
super-phosphate production increased in the 1940s. Fluoride symptoms are
well characterized and a spectrum of sensitivities both between and within
species is known. Foliar analysis is an acceptable diagnostic tool since fluo-
ride accumulates in plant tissues. However, natural distribution of fluoride
complicates the diagnosis. Shupe et al. (1983) present a comprehensive
treatment of fluoride research.
Photochemical air pollution injury was first described in the Los Ange-
les area in 1944 and was evident over large segments of California by 1950.
Components of photochemical oxidants (primarily ozone or 03) injure and
damage crops in many areas of North America. Ozone, peroxyacetyl ni-
trate (PAN), and nitrogen dioxide (NO2) are phytotoxic components of the
photochemical complex.
Ethylene is a major petrochemical and a by-product of combustion and
of plant metabolism. It is a phytotoxic hydrocarbon gas and contributes
OCR for page 173
HUMAN EFFECTS ON THE TE~ST~ E~RONME~
173
to the formation of photochemical oxidants. Ethylene from anthropogenic
sources probably contributes to crop losses.
EFFECTS OF AIR POLLUTANTS OTlIER THAN OZONE
ON AGRICULTURAL PRODUCTIVITY
Many phytotoxic air pollutants have caused serious damage around
point sources. Others are ubiquitous across the continent of North Amer-
ica and are perceived as major problems. Fluoride is one of the most
phytotoxic of the first group, while hydrogen chloride and hydrogen sulfide
are less toxic. PAN is more phytotoxic than O3 and is widespread (in
low concentrations) around metropolitan areas. Nitrogen dioxide has been
studied principally in combination with O3 and SO2 because alone it is not
particularly phytotoxic at current ambient concentrations. However, it is a
primary actor in ozone formation.
The air pollutants currently of greatest national concern are O3, SO2,
NO2, and the transformed products of SO2 and NO2 (SO42- and NO3-)
that are largely responsible for acidic precipitation. In North America, O3
has the greatest effect on agricultural productivity because it is found in
damaging concentrations in most sections of the continent. Sulfur dioxide
is released from point sources and may, over weeks or months, injure
sensitive vegetation. Its primary impact may occur when it is associated
with O3 or NO2. The importance of NO2 in terrestrial ecosystems is as an
ingredient in photochemical reactions (forming 03) and when present in
association with SO2 or O3. These three pollutants (03, SO2, and NO2)
are critical components in the formation of acidic precipitation.
Space does not permit a discussion of the many air pollutants that
have damaged plants due to accidental releases or on a fairly local basis.
However, a brief discussion of NO2, acidic deposition, and SO2 are included
in this section. The importance of ozone is recognized and treated in a
separate section along with assessment methods.
Nitrogen Dioxide (NO2)
Nitrogen dioxide can be used as a nitrogen source by plants. The
first published study using ambient levels of i5NO2 (0.097, 0.152, or 0.325
ppm NO: for three hours) reported a linear relation between exposure
concentration and uptake for snapbean; essentially all the nitrogen was
metabolized (Rogers et al., 1979~. Although several studies have reported
greater NO2 uptake at night, Yoneyama et al. (1979) found that night
absorption was only about 14% of that absorbed during the day.
Both nitrogen oxide (NO) and NO2, which are associated with the
production of high levels of greenhouse CO2, substantially decreased growth
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174
ECOLOGICAL RISKS
and productivity of greenhouse crops (Mansfield et al., 1982~. This raises
serious concern for greenhouse operators who add CO2 in the greenhouse.
Acidic Deposition
The effects on crops of acidic precipitation (often incorrectly called
"acid rain," but encompassing all forms of precipitation) was highlighted
in the United States in an international symposium (Dochinger and Seliga,
1976~. Acidic deposition includes both wet and dry deposition of acidifying
substances such as SO2 and NO2. Acidic precipitation is used to separate
the transformed products (SO42- and NO3-) from gaseous SO2 and NO2;
the term "acid rain" denotes only that specific form of acidic precipitation.
Vegetation growing where acidic fogs or clouds are common may also be
affected.
The pollution control strategy of using tall stacks to reduce ground-
level concentrations of sulfur and nitrogen oxides near fossil fuel combus-
tion sources is a contributing factor to the long-range transport of acidic
substances. The transformed products may be deposited hundreds of kilo-
meters downwind in precipitation.
Acidic precipitation may affect the growth, reproduction, quality,
and/or yield of agricultural crops (Heck et al., 1984a). Direct effects
include changes in leaf surface morphology, foliar nutrient leaching, up-
take of additional sulfur or nitrogen, or changes in metabolic function or
reproductive processes; with perennial plants, the effect may be cumulative
across growing seasons. Indirect effects include altered physicochemical
characteristics of soils (e.g., water-holding capacity), nutrient availability,
availability of toxic elements, and susceptibility of plants to biotic and other
stresses.
Research efforts in the early 1980s developed around field studies
utilizing rain exclusion systems to permit growth of plants under field
conditions. Evans et al. (1986) reported significant acidic rain effects on
'Amsoy 71' over five consecutive growing periods; but no effects on other
soybean cultivars were reported. DuBay and Heagle (1987) reported no
effects on growth or yield from rain acidities as low as pH 2.7 (using
similar field protocol) for the cultivar 'Forrest.' Banwart et al. (1987) found
no effect on two field corn cultivars at present acidity levels, although a
significant reduction in yield was found in one cultivar at a pH of 3.0. Fell
et al. (1987) detected no effects on two potato cultivars at pH treatments
as low as 2.8.
Acidic precipitation may affect plant systems, but the evidence is lim-
ited. It seems safe to suggest that we have not succeeded in developing an
experimental approach that will permit the identification of small impacts.
OCR for page 175
HUAf 4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT
175
Likewise, the presence of increasing nitrogen and sulfur with decreasing
pH (increasing H+) probably confounds experimental results.
Sulfur Dioxide (SO2)
Sulfur dioxide was extensively studied in the first half of the century
(Heck and Brandt, 1977~. Interest was renewed by the increase in power
generation and the subsequent increase in SO2 emissions. In addition,
results of long-term assessments around point sources convinced scientists
that earlier perceptions of SO2 thresholds needed to be reexamined.
The effects of SO2 may be visible or subtle. Acute injury results in cell
plasmolysis with foliar lesions, often bleached white; chlorosis may occur.
Chronic injury may initially disrupt cellular activity, followed by chlorosis or
other pigment changes that may lead to cell death. Chronic injury patterns
are generally not characteristic of SO2 and may be confused with symptoms
caused by diseases, insects. other stresses, as well as normal leaf senescence.
The mechanism of crop response to SO2 has been studied in several
ways. Sensitivity differences in four cultivars of cucumber were related to
SO2 uptake (stomata! activity), but leaves of different sensitivity on the
same plant involved a biochemical or developmental resistance mechanism
related to the formation and loss of hydrogen sulfide (H2S) (Bressan et al.,
1978; Sekiya et al., 1982~. Evidence for the photodetoxification of SO2 was
associated with increased injury to plants on which stomata remained open
during dark exposures to SO2; a strong case was presented for sulfite as
the primary phytotoxicant for acute plant injury (Olszyk and Tingey, 1984~.
Plant physiological and biochemical processes are probably more important
controllers of plant resistance to SO2 (tolerance) than is control of gas
entry via the stomata (avoidance).
Many biological and physical factors affect the response of plants to
SO2, including genetic, biological, environmental, and chemical. Research
of a genetic nature has concentrated on the determination of relative sen-
sitivities of species and their genotypes, and on the effects on pollen and
pollen germination (Heck et al., 1986~. Mexican bean beetle larva fed
preferentially on soybean foliage exposed to chronic concentrations of SO2
(Hughes et al., 1983~. Environmental factors include light, temperature,
humidity, CO2, freezing, soil moisture, and soil nutrition. Several of these
have been studied in combination. Plants are generally more sensitive to
SO2 as light intensity, wind speed, temperature, and humidity increase; ele-
vated CO2 levels protect plants; and freezing may increase plant sensitivity,
while low soil moisture tends to make plants more resistant.
The effect on plants of mixtures of pollutants (i.e., SO2 and 03) is
due primarily to the O2 component and is discussed below. Research
has shown that mixtures of SO2 and NO2 can cause interactive effects
OCR for page 176
176
ECOLOGICAL RISgS
TABLE 2 Growth and yield of selected crop species in response to sulfur dioxide exposures.
Test Sulfur Dioxide
Plant Exposure Characteristics
Results
Six species Constant and stochastic
concentration, 0-0.20
ppm (Greenhouse)
Barley
Barley
Rice
(3cvs)
L~liw?~
Constant SO2 concentration underestimated
effects compared to the time series treat-
ments; excellent discussion of time series
concept; interpretation of results difficult.
0.010, 0.023, 0.038 and
0.058 ppm mean over
growing season (Field,
open release system)
0.04 to 0.20 ppm mean
concentration across
growing season; a
two year field study;
open release of SO2
0.05 to 0.20 ppm, 24 hr
per day, 5 da per week,
15 weeks; in pots in
open-top chambers
0.012 to 0.029 ppm
perenne winter mean at 4
selected sites with
differing SO2
concentrations
(field-correlational)
Controls not defied but three lowest SO2
concentrations gave about 5, 20, and 12%
yield increase respectively; the high SO2
reduced yield about 18% (McLeod et al., 1986).
Yield reduction found in both years;
when average SO2 during fumigation
was used in regression analysis found
a 2.2% loss per 0.01 ppm of SO2
(Baker et al., 1986).
Yield at highest SO2 compared to
lowest was reduced from 11 to 29%
in the three cultivars
(Kats et al., 1985~.
Two sites with lowest mean SO2 showed
same total dry wt yields; two highest
sites showed a -19 and -54% reduction
respectively. Me site with highest
SO2 also suffered winter injury
(Ashenden, 1987).
SOURCE: Heck et al., 1986. Individual references, not included here, are found in the
original table.
On sensitive plant types. An interesting biochemical explanation for the
synergistic action of SO2 and NO2 on several grass species involves the
inability of the plant to detoxify nitrite in the presence of SO2 (Wellburn
et al., 1981~.
Examples of the effects of SO2 on carbon translocation and partitioning
and on plant growth and yield are shown in Able 2. Generally, assimilates
move to developing leaves rather than to roots under low SO2 stress.
Root growth is generally reduced more than shoot growth and occurs at
relatively low SO2 concentrations. The results support the contention that
plants are sensitive to low SO2 concentrations (< 0.10 ppm), when exposed
continuously.
Dose/response studies using an open-air SO2 release system have sim-
ulated exposures of soybean to SO2 near point sources. Soybean yield was
decreased by periodic SO2 exposures after flowering to doses of approx-
imately 10 to 15 ppm-hours (Sprugel et al., 1980~. These dose statistics
OCR for page 177
HUAL4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT
J 120
o
at
0 1 tO
o
~ 100
90
~ -80
o
o
177
CULTIVAR YEAR
~ WELLS 1977
O WELLS 1978
~K- S 1492 1980
K-S 1492 1981
' ~ WILLIAMS Iseo
~ ~ CORSOY 1980
- ° an
on
~ 0
.
· ~ so ~
I I l
o
5 10 ~ 65 20 2S 50 :55
SULFUR Dl OX I DE DO SE ( ~ pm - H R )
FIGURE 1 Effects of periodic SO2 exposures in open air on the yield of soybeans (Heck
et al., 1986~.
were products of mean exposure durations of 2.5 to 4.2 hours, mean con-
centrations of 0.12 to 0.31 ppm, and 19 to 25 exposures. Doses in the 5
ppm-hour range were either stimulators or inhibitory. Maximum peak-to-
mean SO2-concentration ratios were about 2.5. Figure 1 shows results of
these studies.
Daily four- or seven-hour exposures of cotton and tomato (Heck et
al., 1983b) or soybeans (Heagle et al., 1983) in open-top field chambers
demonstrated that SO2 concentrations, which are likely to occur regionally
in the United States, probably do not cause decreased yield. A similar
conclusion was reached in a review by Roberts (1984) on the effects of
SO2 on plant productivity, which included results from open-air studies.
However, emissions of SO2 near point sources can cause decreased yield
. . . .
in sensitive crop species.
EFFECTS OF OZONE ON AGRICULTURAL PRODUCTIVITY
This section presents summary information on the effects of O3 on
crop growth and productivity. It also provides background information on
plant response, including some review of field research that supports efforts
to assess O3 dose, and crop yield responses for assessment purposes.
OCR for page 178
178
ECOLOGICAL RISKS
Symptomatology
The effects of O3 on crops are either visible (i.e., morphological,
pigmented, chlorotic, or necrotic foliar patterns resulting from major phys-
iological disturbances in plant cells) or subtle (i.e., measurable growth or
physiological changes Without visible injury that may affect yield, or re-
productive or genetic crop systems). Ozone injury often appears as flecks
(small, bleached necrotic areas) or stipple (small pigmented areas) on up-
per foliar surfaces. Chlorosis may be associated with acute exposure to
O3. Chronic injury may cause chlorosis or other color or pigment changes
that may eventually lead to cell death; early senescence with or without
leaf abscission may occur. Chronic injury patterns are easily confused
with symptoms caused by diseases, insects, other stresses, and normal leaf
senescence.
From a practical standpoint, visible foliar injury is the only conclusive
way to identify O3 injury in the field. Research has shown relationships
between visible injury and growth and yield for many plant species (Heck
et al., 1977~.
Physiological and Biochemical Effects
Ozone enters leaves through stomata. Any stress causing stomata!
closure reduces O3 uptake and thus protects the plant by avoidance. The
fate of O3 after entry into plant leaves is not known. Some fraction of
O3 may pass through the cell membrane (Mudd et al., 1984~; O3 may
react with protein or lipid membrane components (Heath, 1980~; or free,
radical products of O3 activity within the substomatal cavity may react
with membrane components (Grimes et al., 1983~. Regardless of the exact
mechanism of action, the cell membrane is probably the site of initial O3
reaction.
Factors Affecting Plant Response
Many biological and physical factors are known to affect the response
of plants to 03, including genetic (e.g., cultivar and species differences,
effects on reproductive structures, inheritance of sensitivity); biological
(e.g., plant diseases, insects); environmental (e.g., climatic [temperature,
light, humidity] and edaphic [nutrition, soil moistures; and chemical (e.g.,
herbicides, insecticides, special additives), as well as other factors.
Genetic
Research of a genetic nature has concentrated on the determination
of relative sensitivities of species and their genotypes, and on the effects on
OCR for page 179
HUMAN EFFECTS ON THE TERRESTRIAL ENVIRONMENT
179
pollen and pollen germination. Studies on the heritability of O3 resistance
suggest that O3 resistance is heritable. Results of cultivar screening suggest
that, when dealing with extremes of sensitivity, cultivars maintain the same
relative separations when longer-term exposures are performed under both
field and controlled conditions (Heck et al., 1988c).
Biological
Interrelationships between biological stresses (e.g., insects and dis-
eases) and plant response to O3 must be understood as part of a crop-loss
assessment effort. Available information regarding effects of O3 on plant
parasites suggest that obligate fungal parasitism is generally inhibited and
that some facultative parasites may benefit; these effects are probably indi-
rect through the host. Foliar parasites may provide localized protection of
the host from O3 injury. Review articles by Heagle (1982) and Lawrence
(1981) cover much of the research on plant/parasite interactions.
Environmental
Relationships between climatic or edaphic factors and plant response
to pollutant exposure are discussed in several O3 reviews (Heck et al.,
1977; U.S. EPA' 1986~. Generalizations on the modifications of plant
response to O3 by climatic factors are difficult because of the known
exceptions. Evidence suggests that lower light intensity during growth,
higher light intensity during exposure, higher growth temperatures, and
higher growth and exposure humidities increase the sensitivity of many
species to O3. Information suggests that increased O3 sensitivity, although
related to stomata! conductance, reflects changed physiological conditions
within the plant. Environmental conditions in the field can affect stomata!
control of plant response the same day, and physiological control of plant
response will start the following day. A two- to four-day period is usually
necessary before physiological conditions that affect plant response to 0
will completely reflect the changed environmental conditions.
Tingey et al. (1982), using a uniform water stress, reported that O3
sensitivity in bean decreased with increasing plant water stress; protection
occurred in one day at the highest stress, and recovery occurred within
six days. Beans treated with a chemical to induce stomata! opening in
water-stressed plants were as sensitive to O3 as non-water-stressed plants
(Tingey and Hogsett, 1985~. Results suggest that O3 protection in water-
stressed plants is caused by stomata! control and not biochemical control.
Heggestad et al. (1985) found that soybean growing in open-top chambers
were more sensitive to ambient concentrations of O3 under a small soil-
moisture stress than when adequate moisture was available. Because of the
OCR for page 180
180
TABLE 3 Plant response to O3 and -SO2 mixtures.
ECOLOGICAL RISKS
Test Exposure
Plant Information
Plant Response to
the Mixture
Bean,
snap
Bean,
field
0.20 ppm each gas; 7 hours/
day, 4 days; varied
. .
sa Duty
0.05-0.30 ppm O3; 0.04
ppm SO2; 4 hours
Tomato 0.005 to 0.468 pprn SO2; 0.015
pprn or 0.056 ppm O3; 5 hr/
day, 5 da/wk, 57 days; field
study with open top chambers
Lettuce, 0.4 ppm O3, 0.8
radish ppm SO2; 6 hours
Potato
Soybean
Four O3 concentrations filter-
ing of ambient O3; 0.1 ppm
SO2; for 6 hours/day, 255 hours
0.06 or 0.08 ppm O3, 0.06 or
0.11 ppm SO2; 5 hours/day,
days; in open field facility
Soybean 0.04 to 0.08 mean ppm 03,
0.00 to 0.11 mean ppm SO2;
5 hr/day, 16 days, during
pod fill, linear gradient
system in field.
Stomatal conductance: synergistic (variable);
foliar injury: antagonistic; growth:
additive; effect changed with salinity.
Net photosynthesis: additive or antag-
onistic, depending on O3 concentration.
Ripe fruit decreased 16% by O3 Cow SO2
treatment), 18% by SO2 (low O3 treatment);
32% in high O3 - high SO2 treatment;
additive response (Heggestad et al., 1986).-
Use of covariates increased precision for
lettuce and radish; lettuce growth and injury
effects antagonistic; radish was additive.
Reductions in various growth and yield
parameters were additive.
Both O3 and SO2 caused decreases in a
number of yield measures; mixture
responses were additive.
Ozone caused 26% seed yield
reduction, SO2 a 6% reduction
. . a. . .
Wit n no slgnlIlcant interactions
(Reich and Amundson, 1984).
SOURCE: Heck et al., 1986. Individual references, not included here, are found in the
onginal table.
importance of soil water stress in agricultural areas, it is imperative that we
try to understand this interaction and include it in any assessment effort.
Pollutant Interactions
Plants are often more severely affected by mixtures of O3 with other
pollutants than by O3 alone (Lefohn and Ormrod, 1984; Reinert, 1984~. In
general, mixtures tend to give a greater-than-additive (synergistic) response
when the concentrations are below those causing visible effects from pol-
lutants singly; concentrations around the injury threshold tend to produce
an additive response; and concentrations above threshold tend to cause a
less-than-additive (antagonistic) response. The term synergistic, although
statistically appropriate, is not necessarily biologically appropriate since
response functions may not be linearly related to pollutant concentration.
Table 3 is a summary of results from selected studies using O3 with SO2.
OCR for page 181
HUMAN EFFECTS ON THE TERRESTRIAL ENVIRONMENT
TABLE 4 Growth and yield of selected crop species in response to ozone exposure.
181
Test Ozone Exposure
Plant Characteristics
Results
Bean, lima Comparison of charcoal filtered
(8 genotypes) (< 0.02 ppm mean daily max)
and non-filtered (< 0.06 ppm
mean daily max) greenhouses.
Yield reductions of 3.4 to 68.5%
were found across the 8 geno-
types (Meredith et al., 1986).
Bean, snap 0.30, 0.60 ppm; 1.5 hour, 2 Reduced relative and absolute
times; 6 growth stages; growth rates, pod production,
harvest 7 days after exposure modulation, and fixed nitrogen;
or at fresh harvest (con- magnitude varied with O3 concentra-
trolled) lion and growth stage.
Tomato, 0.08-0.10 ppm; 5 hours/day, 5 86% reduction in fruit number,
Tusy Ton days/week, 5 weeks (green- 91% reduction in fruit weight.
house)
Soybean 0.02 to 0.097 ppm; 341 hours, Yield was +15%, -34%, and -40% at
intermittent over 113 days; 0.046, 0.070 and 0.097 ppm in com-
greenhouse parison to 0.02 ppm. The increase
at 0.046 ppm was not significant
(Endress and Greenwald, 1985).
Cotton, 0.20 ppm; 6 hours, 2 times/ Vegetative biomass and boll production
Acala SJ-2 week, 1 group started at 8 day, reduced; greatest reduction in boll
1 at 42 days from seed and root weights; 48% reduction in
(greenhouse) boll number.
Clover, 0.03, 0.05, 0.08 ppm; 7 hours/ Total forage and forage regrowth
Ladino day, 6 months Field: pots) reduced for clover and clover-
fescue mixture in relation to O3
concentration; fescue unaffected.
Rice (3 cvs) 0.05 to 0.20 ppm, 5 hr per Yield at highest O3 lowest
day, compared to 5 da per wk. was reduced front 12 to 29%
15 wks; in pots in open in the three cultivars
top chambers (Kats et al., 1985).
SOURCE: Heck et al., 1986. Individual references, not included here, are found
in the original table.
Growth, Biomass, and Yield Effects
Greenhouse and controlled-environment research were used in early
assessments of O3 effects. These studies underestimated the effects of O3
found in later field studies, but the estimates were reasonable. The effects
of O3 on growth and yield are briefly summarized in Able 4. Research
results have generally shown that:
· O3 affects crop growth and productivity;
· cultivar differences are usually observed;
· root growth is affected more than shoot growth;
OCR for page 185
HUAI4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT
1.0
08
en
~ 0.S
e_
-
~ 0.4
-
o
~0.2
185
—Corn
Wheot
,
Cot ton
Soybeans
Peats
'Ng
~ .,
O~ 1 1 1 1 1
=:
0 0.02 0.04 0 06
- _~
—_~_
\
-
-
_ ~
0.08 0.
Ozore Concentration (ppn`)
FIGURE 2 Effects of chronic O3 exposures on the proportional yield loss of five crop
species as predicted by the Weibull model, using results Mom open-top chambers. The O3
concentration is the seasonal 7-hr/day mean (Heck et al., 1986~.
Ozone Functions for Use in Crop Loss Assessments
The N CLAN program determined that the Weibull function had a
number of redeeming features and accepted its relative response portion
for use in assessment efforts. The Weibull permitted the assessment either
to utilize a homogeneous response function for a species (i.e., a single
or several cultivars) developed from experimental designs across years or
sites, or to use a heterogeneous response function if such a function showed
no apparent inconsistencies. In the assessment of yield effects Cable 6,
Figure 2), many of the combined data sets were homogeneous; in the 1988
economic assessment, however, heterogeneous data sets were used where
necessary to describe the effects on a single species (Adams et al., 1988~.
Ozone dose/crop yield response functions can take on a variety of forms
depending upon the dose statistic used. There is no preferred function,
OCR for page 186
186
110 _
o Im
c
o
-
y
.*
60
50
90
80
70
ECOLOGICAL RISKS
_
Of
.
\
O iA
~ -
·~Q
·\
~ or
~ Cordon Argo~,11 t980
· toys. aweigh, NC 1981
G Hods -Ithaca, NY 19 81
· Dovi. Ro~h,NC 1982
O Ems Bet? - lie, - 1982
OWiIIi~ -8~1~'vilb, Ad 1982
· Isis—Raleigh, NC 1983
C4ttivor Locotbn
'9
· \ O
002 0.~ 0." 0.~ 0~ 0.12 0 ~ O.K
Ozone C4=entraton- Seasonal 7 How/Doy Meon (pen)
FIGURE 3 Effects of chronic O3 exposures in open-top field chambers on yield of
soybeans. The seasonal O3 concentrations for the control treatment ranged from 0.02 to
0.03 ppm, depending on the year and location (Heck et al., 1986~.
but it should utilize an exposure statistic that adequately describes the
biological response to O3. The N CLAN program used 7-hr/day and 12-
hr/day seasonal mean O3 values because they adequately described the
yield responses of the crops tested. These functions were used by Adams
et al. (1988) in their final economic assessment for NCLAN.
Interpolations of Ozone Data to a County Level
The NCLAN program utilized data from the U.S. Environmental Pro-
tection Agency (EPA) Storage and Retrieval of Aerometric Data (SAROAD)
system for interpolation processes. In the SAROAD system most monitor-
ing sites are urban, with few in rural crop-growing areas, and many areas
of the United States have only a few monitoring sites. Several factors
enhanced our ability to interpolate O3 data across broad areas. First, O3
precursors are transported over great distances. Second, O3 is more stable
as air masses move into rural areas because concentrations of reactive
chemical species are reduced (Heck et al., 1984b). NCLAN used the krig-
ing spatial interpolation process to develop county-level seasonal (7-hr/day,
OCR for page 187
HUAL41V EFFECTS ON THE TERRESTRIAL ENVIRONMENT
BOO
-
1
.00
300
>
o
t00
o
187
SOt LEVEL
· ·.000
o ·.C;26
· · .O~ 5
O · .367
1
to
. . , , . , .
o o ~
o
0 02 0.0. 0.06 0.08 0.10 0.12 O. 1.
B
7H d~' SEASONAL - CAN 0. CONCE~rRAT'oN (ppm )
FIGURE 4 Yield response of 'Davis' soybean to combinations of O3 and SO2 at Raleigh,
NC in 1982. Curve was estimated by polynomial analysis using combined SO2 data (Heagle
et al., 1988~.
12-hr/day) mean O3 concentrations for use in crop-loss assessment (Heck
et al., 1983b, 1984b). This technique was fully reviewed by an outside
group and found to be a reasonable approach to estimate county-level O3
concentrations (Heck et al., 1985; Lefohn et al., 1987~. However, it should
be noted that this technique does not handle mountainous terrain well, and
it is weak where monitoring points are too far apart, as in much of the
western United States.
Crop Census
The Census of Agriculture, conducted by the U.S. Department of
Agriculture, provides a county-level yield statistic for crops of interest
(Heck et al., 1982b; Shriner et al., 1984; Adams et al., 1988~. It involves an
extensive national inventory of crops (not broken down by cultivars) and
acreage grown. Data are obtained by analyzing responses to questionnaires
mailed out approximately every five years. County estimates are adjusted
for nonrespondents.
Analysis of Crop Yield Reductions
Ozone dose/crop yield response functions, crop yields at the county
level, and seasonal 7-hr/day mean O3 concentrations at the county level are
OCR for page 188
188 ECOLOGICAL RISKS
Z I.0 ~ - Ve
~ o.a \ `N
~ o.e \
° of
o
0 0.2 _
~ B
o.o . 1 . I I , , ,
002 004 0C>6 008 0 10 012 014
12 ~ 6~' SŁaSONa~ - ~~N as cot~cE~TR^rio~ I Pam )
FIGURE 5 Proportional yield response to O3 of cotton grown with intermittent periods
of soil-moisture stress (WS) or grown with well-watered conditions (WOO) for 'McNair 235'
at Raleigh, NC in 1985. Curves were derived using Weibull analyses with the a value set
at 100 (Heagle et al., 1988~.
used to calculate crop losses related to reductions in yield. The impacts
of O3 are reflected in the yield data found in the Census of Agriculture.
Using the county-level O3 values and the response function for the crop of
interest, the expected percent yield reduction of the crop in the county is
calculated. The yield reduction is based on comparing the yield found at
the observed county-level O3 values with the expected yield at an 0.025 ppm
O3 concentration (seasonal 7-hr/day mean O3 concentration in clean air).
Increases in yield with different percentage improvements in air quality can
then be calculated. Values for each crop and each county where a given
crop is grown are then used to calculate national yield losses for each crop
of interest.
This approach was first used for an analysis with four species (i.e.,
corn, peanut, soybean, and wheat) by Heck et al. (1982b) as part of a
larger assessment by Shriner et al. (1984~. The assessment was done to
show the value of the selected approach in documenting regional and
national losses of crops due to O3. Nine NCLAN type data sets (i.e.,
1 corn, 1 peanut, 3 soybean, and 4 wheat) obtained from two N CLAN
and seven pre-NCLAN studies at North Carolina State University were
utilized in the assessment effort. County O3 and crop inventory data for
1978 were used. Kriging of the 1978 O3 data was first attempted and used
OCR for page 189
HUAf4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT
189
on a national basis by James Reagan (EPA) to predict county-wide yield
losses (Heck et al., 1983a). The data sets were used with the 7-hr/day
seasonal mean O3 statistic in calculating yield reductions using a linear
response function. Results were calculated for county units, and tables and
maps were developed to summarize and show patterns of the O3 effects
on soybean, corn, wheat, and peanuts. The assessment estimated that an
approximate $3 billion of productivity in the four crops would be gained
if current maximum 7-hr/day seasonal O3 concentrations were reduced to
0.025 ppm. Soybean represented 64% of the impact, corn 17%, wheat 12%,
and peanut 7%. The methodology is sound but the assessment of dollar
losses cannot be considered an economic analysis.
The same basic approach was utilized by Adams et al. in develop-
ing yield reduction/increase estimates for their interim (1984) and final
(1988) NCLAN economic assessment efforts. In the interim assessment,
the Weibull model was used for the response function. Into O3 data sets
were utilized: the kriged 1980 O3 data on a county basis and the 1978-82
five-year average O3 data base kriged to the county level. Crop inventory
data were used and losses were based on 1980 dollars. Six crops (i.e.,
barley, corn, cotton, sorghum, soybean, and wheat) were used in this as-
sessment. The final assessment utilized a similar approach, incorporated
three additional crops (i.e., alfalfa, hay, and rice) and used 1982 as the base
year for O3.
The Economic Erects of Ozone on Agriculture
Based on crop response data from many experimental designs, a num-
ber of regional and national economic assessments have been made since
1980 (Table 7~. Regional estimates ranged from about $30 million (Min-
nesota) to about $670 million (Corn Belt). National estimates were based
on different groups of crops but ranged from $1.2 to 3.0 billion; corn and
soybean were included in all estimates. The national economic assessments
by NCLAN (Adams et al., 1988) was in good agreement, showing about
$2.7 billion surplus with a 40% reduction in seasonal O3 concentrations
(Table 8~. A summary of economic estimates suggests that current seasonal
O3 concentrations are causing in excess of $3 billion annual loss in crop
productivity (Adams et al., 1988~.
CONCLUSIONS
The information presented here supports the thesis that O3 has a major
impact on crop production in North America. Assessment methodologies
are developed along with results of field research that are critical to the
prediction of O3 effects on crop productivity.
OCR for page 190
190
ECOLOGICAL RISKS
TABLE 7 Summary results of several regional and national economic
assessment using NCLAN data.a
Assumptions of
Region O3 Concentration Crops
Benefits
($ tic 106)
California Reduce to 0.04 18 $ 45
ppm (seasons)
Com Belt Reduce NAAQS from Coin, Soybean $ 668
0.12 to 0.08 ppm Wheat
Illinois logo reduciion Com, Soybean $ 226
U.S. Reduce to 0.04 ppm Com, Soybean $ 2,400
Cotton, Wheat
U.S. Reduce to 0.04 ppm Sene + Peanut $ 1,300
a Reports from 1984/1985; results in 1980 U.S. dollars.
SOURCE: Adams et al., 1988.
TABLE 8 National economic assessment from NCLAN.a
Total Surplus
O3 Assumption (millions in 1982 dollars)
1984 Model 25% increase
109to reduciion
25% reduciion
4~o reduciion
1988 Model 25% increase
logo reduciion
25% reduciion
40% reduciion
-2,165
699
1,828
2,637
-2,053
808
1,890
2,780
a Reports from 1984 and 1988; results in 1982 dollars.
SOURCE: Adams et al., 1988
Summary of Current Knowledge on the Effects of Ozone
(and Other Air Pollutants)
· Ozone is responsible for most of the crop-yield losses from air
pollutants on both a regional and national scale within North America.
· Losses from other pollutants are minimal, relative to O3, and
primarily source related or related to joint effects with O3.
· Pollutant dose/crop yield response functions are essential for pre-
dicting yield losses; non-linear models give the best fit to available field
data for O3.
· Based on available technology, the open-top chamber system is the
best approach for the development of predictive models for O3, but open
release systems may function well for other pollutants.
OCR for page 191
HUMAN EFFECTS ON THE TERRESTRL4L ENVIRONMENT
191
· The extrapolation of O3 data on a regional basis, using the interpo-
lation technique of kriging, is a useful and necessary part of an assessment
effort. However, the technique is not suitable with SO2 or other point
source related pollutants.
Foliar symptoms on crops under field conditions often appear as
early senescence and -may be difficult to assess.
· Although the mechanism of plant response to air pollutants is not
understood, the cell membrane is probably the site of initial impact for O3.
· Ozone and SO2 affect photosynthesis and carbon allocation in
plants; reduced allocation to roots and reproductive structures is usually
found. Similar effects may be true for other pollutants.
Differences in both species and cultivars within species response to
air pollutants is found in all crops.
Interactions between air pollutants (02, S02, and HF) and both
biotic and abiotic factors on plant responses are documented.
· The response of many crop species to O3 iS affected by the presence
of other pollutants (specifically SO2 and NOT.
· Most crops show growth, biomass and yield reduction when grown
under current ambient air concentrations of O3. These responses may be
true for SO2 and acidic precipitation, but the data are equivocal.
· The NCLAN data base has permitted a reasonable first estimate
of crop yield losses associated with O3 as an air pollutant of national and
international importance.
Areas of Uncertainty in Assessing the Effects of
Air Pollutants on Crop Production
· The available data base is small and thus is not fully representative
of North America. For 03, only 10 field crops were studied in the N CLAN
program; five had four or more experimental designs. Data for other
pollutants is not as strong.
· Potential effects of field methodology have not been fully addressed
for any pollutant.
· Ozone dose/crop yield response models are empirical and not based
on mechanistic considerations. Models for other pollutants are weak.
· The effect of soil moisture on crop yield response to air pollutants
has been studied for O3 and SO2, but the results are not definitive.
· The effects of other biotic or abiotic stresses on crop response to
air pollutants are not understood and are not included in predictive models.
· The importance of exposure dynamics (i.e., peak O3 values) occur-
ring throughout the growing season is not well understood.
OCR for page 192
192
ECOLOGICAL RISKS
· There are insufficient rural monitoring sites to corroborate the
knging interpolative process for 03; interpolation for other pollutants is
not feasible.
· The estimates of economic loss from O3 would probably range
from $1-7 billion or more if all crops were considered; losses will vary from
year to year depending on both O3 concentrations and meteorological
conditions.
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Representative terms from entire chapter:
primary primary primary
