Office of Acid Deposition,
Environmental Mcfhitoring, and Quality Assurance
ACID DEPOSITION
RESEARCH PROGRAM
Prepared by
ICAIR
£f( Systems, he.
Under Contract
No. 68-02-4193
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Atmospheric Sciences
45019891
Policy Questions
• What are emissions in designated base years for policy-
development and implementation purposes? f'.-
• How much does it cost to control these emissions?
• What are the current patterns of acid deposition?
• What is the quantitative relationship between the
distribution, rate, and form of emission and the distribu-
tion, rate, and form of deposition?
The objective of the Atmospheric Sciences Research Pro-
gram is to develop a scientific understanding of the
cause/effect relationship between sources of emissipns
and acid deposition in sensitive receptor areas.
Understanding the distribution, rate, and form of emis-
sions is a critical first step to developing an under-
standing of cause/effect relationships between emission
sources and receptors of acid deposition.
What are emissions in designated base years for policy
development and implementation purposes?
The first policy-related question is: What are emissions in
designated base years for policy development and im-
plementation purposes?
Emissions that contribute to acid deposition include a
number of trace gases, of which oxides of sulfur and
nitrogen are the most important. Sulfur dioxide (SC>2),
nitrogen oxide and nitrogen dioxide (considered together
as NOX) oxidize in the atmosphere after they are emitted
to form sulf uric acid and nitric acid, respectively, or acidic
salts. Volatile organic compounds (VOCs) can enhance
the production of oxidants as can NOX. These oxidants
hasten the atmospheric transformation of SC>2 and NOX
into their respective acids. Ammonia and alkaline dust
emissions are also of interest for determining the acidity
of atmospheric deposition. The fraction of emissions for
each of these chemical species for which man-made
sources are. responsible varies from very high for S02
(more than 95% in the eastern United States) to relatively
low (about half) for ammonia and alkaline dust.
About two-thirds of the S02 in the eastern United States
is emitted by coal-fired electric utility plants. Most of the
remainder of S02 emissions in the East come from in-
dustrial combustion of fossil fuels in boilers and process
heaters. The S02 emissions in the West come principally
from primary metal smelters, predominantly copper. The
highest concentration of SO2 emissions is in the Ohio
River basin which has a high concentration of high-sulfur
coal-fired power plants.
Principal sources of NOX are highway vehicles, power
plants and industrial combustion. Although these
sources are more concentrated in the Midwest and North-
east, they are also concentrated in large metropolitan
areas throughout the United States and Canada.
Historically, emissions of SO2 have risen irregularly since
the beginning of the century, reaching a maximum in the
early 1970s. They have fallen by about one-fourth since
then. The NOX emissions have risen more steadily and
sharply, beginning in the early 1940s, and have only
declined by about 5% since reaching a maximum in the
late 1970s. It has been estimated that emissions of VOCs
Increased by about 50% between 1940 and 1970, and have
gradually declined since then to about the same levels
found in the mid-1950s.
It is important to note that there are regional differences
in emissions and that different emission trends exist in
each region. For example: emissions have decreased in
the Northeast primarily as a result of the implementation
of emission controls; growth in industry and population in
the Southeast during the 1970s has resulted in increases
in emissions in that region; and labor strikes, emission
controls, and changes in Western smelter operations
have resulted in emissions fluctuations in the West.
In 1986, a final 1980 emissions data base and ^inventory
and a preliminary 1985 point source emission filets ex-
pected to be completed. A preliminary 1985 emissions in-
ventory is expected to be completed in 1987. In'l988. a
final 1985 emissions data base and a final 1985 emissions
inventory are expected to be completed.
How much does it cost to control these emissions?
Emissions change as changes occur in demand for power
and products, sources of fuels utilized, proposed emis-
sion control strategies and emission control technology.
This leads to the next policy-related question: How much
does it cost to control these emissions?
Emission projection and cost-of-control models are cur-
rently under development. These models are capable of
projecting emission trends over the next several decades
for alternative sets of future conditions and control re-
quirements. The models are also capable of indicating the
cost of additional control requirements.
In 1986, an initial version of the Advanced Utility Simula-
tion Model (AUSM) is expected to be delivered. Testing of
initial versions of AUSM, the Volatile Organic Compounds
Model (VOCM), the PROcess Modeling Projection Techni-
que (PROMPT), and the Industrial Combustion Emissions
(ICE) emission models are expected to be completed in
1987. In 1988, testing and assessment of refined emis-
sions models is expected to be completed.
What are the current patterns of acid deposition?
The previous policy questions addressed the distribution.
rate, and form of emissions. It is also necessary to discern
the distribution, rate, and form of acid deposition. The wet
and dry components of deposition and trends of deposi-
tion need to be determined. This leads to the next policy-
related question: What are the current patterns of acid
deposition?
Estimates from existing linear models suggest that 25%
of total sulfur emissions in North America comes down
as wet deposition; that is, in precipitation as rain or snow.
A roughly equivalent amount (30%) comes down as dry
deposition; that is, deposition in the form of particulates
that fall out of the atmosphere or gasses that are adsorb-
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ed by surfaces. The remainder (45%) blows out over the
Atlantic to be deposited elsewhere. These estimates do
not address either the non-linearities or the regional dif-
ferences that occur. What is important to note from these
estimates is that dry deposition can be of the same impor-
tance as wet. Therefore, it is important to measure both
wet and dry deposition.
Wet deposition alone is now being monitored at 150 sta-
tions in the National Trends Network (NTN) which
reached full-scale operation in 1982. The samples are col-
lected on a weekly basis. The precipitation samples are
sent for analysis to a central laboratory located at the Il-
linois State Water Survey Laboratory in Champaign-
Urbana, Illinois where they are analyzed for: hydrogen ion
(H + ), ammonium ion (NH,)"1"), calcium ion (Ca2 + ),
magnesium ion (Mg2 +), sodium ion (Na +), potassium ion
(K + ), sulfate ion (SO,,2'), nitrate ion (N03~), chloride ion
(Cl~), pH and conductivity.
Based upon very limited measurements as reported in the
National Academy of Sciences (NAS) Report, "Acid
Deposition Long-Term Trends":
• Sulfate and nitrate in the eastern half of the United
States and southeastern Canada are in general a factor
of five greater than those in remote areas of the earth.
This suggests that sulfate and nitrate levels in this area
have increased by this amount since sometime before
the 1950s.
• Precipitation is currently more acidic in parts of the
eastern United States than it was in the 1950s, or
mid-1960s.
• Precipitation sulfate concentrations and possibly acidi-
ty have increased in the southeastern United States
since the mid-1950s.
• For Hubbard Brook in New England, since 1964:
hydrogen ion shows no trend; sulfate has decreased 2 %
per year; sodium, chloride, calcium, magnesium, and
potassium have shown strong decreases with time; and
nitrate appears to have increased until about 1970-1971
and subsequently leveled off.
Dry deposition requires much more complex monitors
than wet deposition. Because methods of direct measure-
ment are very complicated, dry deposition generally must
be inferred or calculated from measurements of ambient
concentrations and other variables (i.e., meteorological
conditions, surface type and condition, time of day, etc.).
Installation of the first 30 dry deposition sites is to be in-
itiated late in 1986.The first 30 monitors will be sited in the
Northeast where sensitive receptor areas are located and
significant acid deposition concentrations are expected.
These sites will also provide data necessary for model
evaluation. An additional 15 dry deposition monitoring
sites are to be installed in 1987, with five sites in the
Southeast and ten in the western United States. The dry
deposition measurements are planned to include: SO2,
N02, 03, HNO3, particulate SO42~, and particulate NO3~.
By the end of 1988, one year of data from the first 30 dry
deposition sites and five years of data from 150 NTN wet
deposition sites are expected to be available.
What is the quantitative relationship between the
distribution, rate, and form of emission and the distribu-
tion, rate, and form of deposition?
The programs and policy-related questions associated
with the distribution, rate, and form of emission, and the
distribution, rate and form of acid deposition have been
previously addressed. It is also necessary to understand
the atmospheric processes that provide the link between
sources of emissions and the deposition of acidic
substances in sensitive receptor areas. Understanding of
the atmospheric chemical and physical processes is re-
quired to be able to quantitatively describe source/recep-
tor relationships. This leads to the next policy question:
What is the quantitative relationship between the
distribution, rate, and form of emission and the distribu-
tion, rate, and form of deposition?
The greatest density of SO2 emission is along the Ohio
River valley with 50% of the total United States emissions
coming from eight states (Ohio, Indiana, Pennsylvania. Il-
linois, Missouri, Kentucky, West Virginia, and Tennessee).
The NAS has concluded that, "...in eastern North America
a causal relationship exists between anthropogenic
sources of emissions of S02 and the presence of sulfate
aerosol, reduced visibility and wet deposition of sulfate.
The wet deposition of SO42~ conforms with the distribu-
tion of S02 emissions and climatic air mass transport.
This correspondence provides a qualitative understand-
ing that the high density of S02 emissions in the Ohio
River valley is the source of sulfate measured in precipita-
tion samples in the northeastern United States.
Although we have a qualitative understanding of this
source/receptor link, we do not have an adequate quan-
titative understanding. We do not know that reducing
emissions will result in a proportionate reduction in acid
deposition. Thus, we have a need for numerical
source/receptor models as assessment tools to address
large potential changes in emissions, and numerous dif-
ferent proposed emissions control scenarios. Regional
models are needed to provide national/state levels of
resolution. Mesoscale models are needed to address
local versus distant source/receptor relationships (e.g.,
assessment of material damage in eastern cities and
other urban areas, conducting Prevention of Significant
Deterioration (PSD) permitting analyses for Western
sources or other assessments in areas of complex ter-
rain, and evaluating aquatic and terrestrial ecological ef-
fects and determining the relative importance of local ver-
sus distant sources of emissions).
Existing models (such as the models that were used to
estimate the relative amounts of wet and dry deposition
resulting from North American SO2 emissions) do not
have the capacity to address non-linear processes or
represent the state-of-the-science understanding of the
atmospheric chemistry and physics cause/effect
source/receptor relationships. In order to handle pro-
posed control strategies involving large changes in emis-
sions, it is extremely important to have a model that works
for the right reasons, i.e., properly simulates the at-
mospheric chemistry and physics. Thus, such models
need to be able to simulate non-linear atmospheric pro-
cesses including: multi-layers transport, chemical
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transformation, dry deposition, precipitation scavenging
processes, and the interactions between these compo-
nent processes.
The conversion of SO2 to SO42" is limited by available ox-
idants. If oxidants are limited, not all S02 can be con-
verted to S042"; therefore, a reduction in SO2 would not
result in a proportionate reduction in S042". The question
becomes: When are oxidants limited with respect to SO2
emissions?
Linearity is expected over continental and annual time
scales; however, non-linearity is expected over small
spatial and temporal scales. A key question is: What are
the smallest spatial and temporal scales over which pro-
cesses are linear? In order to address these needs,
regional and mesoscale acid deposition models are cur-
rently being developed with frameworks to accommodate
non-linear processes and state-of-the-science
understanding of atmospheric processes. These models
are expected to be tested and evaluated by a planned
model evaluation field program.
In 1987, a regional model for calculating sulfur deposition
is expected to be completed. A regional model fordeposi-
tion of all acid substances and one year of surface
monitoring for evaluation of atmospheric models are ex-
pected to be available by the end of 1988.
Outputs
•1986
- Final 1980 emissions data base and inventory com-
pleted
- Preliminary 1985 point source emission file com-
pleted
- Initial version of Advanced Utility Simulation Model
delivered
•1987
- Preliminary 1985 emissions inventory completed
- Testing of initial versions of emission models com-
pleted
- Regional model for sulfur deposition delivered
• 1988
- Final 1985 emissions data base completed
- Final 1985 emissions inventory completed
- Refined versions of emission models completed
- Testing and model assessment of refined emission
models completed
- One year of data from first 30 dry deposition sites
delivered
- Five years of data from 150 National Trends Network
wet deposition sites delivered
-Advanced version of regional model for acidic
deposition delivered
- Completion of first year of surface monitoring for
evaluation of atmospheric models
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Aquatic Effects
Policy Questions
• How extensive is the current damage?
• What are the anticipated rate and extent of damage in
the future?
• What rates of deposition will provide various levels of
protection for sensitive surface waters?
Suspected acidification in the lakes in the northeastern
regions of the United States was crucial in initiating
EPA's focus on acidic deposition. The recent MAS report
on long-term trends found considerable evidence to show
that acidic deposition has been influential in changing the
nature of lakes in the Northeast. A major question, left
unanswered in that report and in a 1984 report on lake
acidification, is whether many more lakes and streams
will become acidic in the next few years, or whether any
damage now visible is all we will see for a few decades,
because short-term ecological resistance to acidic inputs
has been overcome, leaving longer-term (30 to 100 years)
resistances in place.
Acid deposition raises the hydrogen ion concentration,
which by definition results in lower pH. As pH decreases,
effects on aquatic ecosystems increase, so that below pH
five, sport fish populations do not generally exist. The pH
of rain in the Northeast is now in the low fours, but the pH
of lake water is usually higher than rainfall pH; for exam-
ple, the median pH of lakes in the Adirondack Mountains
is 6.8.
Alkalinity, or more properly, acid neutralizing capacity
(ANC), is related to pH; it is the ability of the system to buf-
fer acidic inputs. An ANC less than zero means the water
has no ability to neutralize acids. Lakes with ANC less
than zero and pH less than five are classified as acidic.
Early in our research experience, the United
States/Canada Memorandum of Intent concluded that
long-term and short-term acidification of some low
alkalinity waters had occurred in Canada and the United
States in areas receiving acidic deposition. Although the
relative importance of various acidification mechanisms
has not been demonstrated, we now know that many fac-
tors in a lake's surrounding watershed contribute to its
overall sensitivity.
How extensive is the current damage?
To measure the current extent of acidic surface waters,
the National Surface Water Survey was initiated in 1983.
Using a map of alkalinities of surface waters compiled
from existing data as a general guide to areas of interest,
a statistically sound plan was designed to yield a
regionally representative picture of the current status of
aquatic resources. The survey is divided into smaller pro-
jects: the Eastern Lake Survey, the Stream Survey, and the
Western Lake Survey.
The Eastern Lake Survey, Phase I, sampled the Northeast,
Southeast and Upper Midwest regions. Lakes with a sur-
face area greater than four hectares were identified on
topographical maps and statistically sampled to yield
results that could be regionalized. A single sample taken
near fall turnover serves as an index to the chemical
status of each lake.
The results of the Eastern Lake Survey indicate that the
largest estimated number of lakes with pH less than five
are in the Adirondacks, Michigan's Upper Peninsula, and
Florida. Other potentially sensitive areas contain few
lakes with pH less than five. The largest estimated
number of lakes with ANC less than zero are in the same
regions. The overall estimated percentages of lakes in
these regions with pH less than five are: Adirondacks,
10%; Michigan's Upper Peninsula, 9%; and Florida, 12%.
These percentages are smaller when expressed on a lake
area basis.
To give the current status of surface waters a useful
perspective, EPA funded the NAS to assess historical
acidity trends over time. They studied historical data on
surface water chemistry, sediments, and fish popula-
tions. Trends analysis by NAS led to the conclusion that
surface waters in the Northeast, and some in the upper
Midwest, respond quickly to changes in acidic deposi-
tion, with statistically significant declines in surface
water ANC and pH for some lakes over the past 50 years.
Paleolimnologic study also showed increased surface
water acidification between 1955 and 1970 for the North-
east. Analysis of fish populations showed that acidifica-
tion has caused the decline of a number of fish com-
munities in the Adirondacks.
Other studies done to address the extent question in-
clude: (1) the First Interim Assessment (a comprehensive
assessment of the latest research), (2) a survey of
precipitation-affected drinking water systems, and (3) the
effect of storm events and snowmelt or "episodes" on
aquatic chemistry.
Liming is being studied to determine whether it is an ef-
fective mitigation strategy for acidic lakes. Future study
will helpdetermine the long-term effectiveness and risks,
as well as cost/benefit relationships. The Fish and
Wildlife Service has the lead in this area of research.
What are the anticipated rate and extent of damage in the
future?
At first, Scandinavians, North Americans, and others
thought that acidification of sensitive waters would be
detectable within one or two decades where rainfall pH
was 4.6 or below. In 1981, the NAS concluded that of the
options available, only control of emissions of sulfur and
nitrogen oxides could significantly reduce the rate of
degradation of aquatic ecosystems. They concluded that
in some areas where rainfall pH approximates 4.1, reduc-
tions of 50% in deposited hydrogen ions might be
necessary.
Now the NAS recognizes a new hypothesis and has iden-
tified two major mechanisms that control the rate of sur-
face water acidification and lead to different watershed
response rates even within the same region. These pro-
cesses, which occur in the terrestrial portion of the water-
shed, are: (1) the ability to supply bases to neutralize
acids, and (2) the ability of the watershed to retain sulf ate,
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which thereby limits the transport of hydrogen ions and
potentially toxic aluminum to surface waters. When both
processes are high, a capacity-protected system results.
As these factors decrease, systems increasingly respond
to acidic deposition. If at current deposition loadings, a
system responds within a 100-year period, it is called a
delayed-response system. When both processes are very
low, a direct-response system results that is either acidic
now or will become acidic within ten years.
To learn more about how surface waters respond to
chronic acidic deposition, the Direct/Delayed Response
Project (DDRP) was initiated in 1984. This project
sampled a range of lake/watershed systems that should
exhibit the above response time differences. One hundred
and forty-five watersheds in the Northeast and 35 water-
sheds in the Southeast have been sampled, permitting
regionalization of results for making population
estimates.
Research in the DDRP includes collecting data to model
watershed processes that affect water chemistry. These
processes have been modeled to create a predictive tool
for answering questions about future acidification and
the acidification of other areas. The tools from this pro-
gram will also enable the program to address the third
policy area, target loadings for deposition.
What rates of deposition will provide various levels of pro-
tection for sensitive surface waters?
Deposition monitoring indicates loads are currently in-
creasing in the Southeast and West and decreasing in the
Northeast. The effect of changing rates of deposition is
being studied by the Watershed Manipulation Project
(WMP). The WMP will combine catchment, large plot, and
laboratory experimentation to corroborate DDRP models
and assumptions, and determine the relative importance
of acidification processes. The data from the WMP will be
used in combination with the models from the DDRP to
address questions about target loadings for several
regions.
The aquatic effects research program has maintained a
trends-detection project since 1983 to assess trends in
surface water acidification. Data from the long-term
monitoring project will validate the research of the other
projects.
By 1990, major strides will have been taken toward fully
addressing the three main policy questions that provide
the motivation for the aquatic effects research program.
Outputs
•1986
- First Interim Assessment
- Eastern and Western Lake Survey reports (Phase I)
- Results from Pilot Stream Survey
•1987
- Results from Stream Survey
- Results from Cistern Survey
- Direct/Delayed report for Northeast
•1988
- Direct/Delayed report on Southern Blue Ridge Pro-
vince
- Report on manipulation field trials
•1989
- Results from Episodic Response Project
- Damage estimates for episodic events
- Report on Watershed Manipulation Project
- Report on watershed sulfur budgets and deposition
monitoring comparisons
- Long-term Monitoring Trends Assessment
- Direct/Delayed report on Middle Atlantic region
(pending)
•1991
- Direct/Delayed report on West (pending)
•1992
- Integration report for all Direct/Delayed Response
Project results with Watershed Manipulation results
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Materials Effects
Policy Questions
• What is the geographical extent of materials-at-risk?
• What are the quantitative relationships between the
various forms of acidic deposition and the resulting
damage rates to materials?
• What are the benefits of reducing the rate of acidic
damage to materials?
Precursors to acidic deposition, especially SOX, NOX, and
oxidants such as ozone, have long been known to be
damaging to some classes of materials, with statuary and
cathedrals being most noticeable. The relationship be-
tween materials degradation and acidic deposition itself
is much less clear, and the question of how extensive the
cultural, commercial, and personal resources that might
be at risk specifically to acidic deposition is largely
unknown. The policy questions that need to be addressed
follow logically.
What is the geographical extent of materials-at-risk?
The research for the first policy question is directed
toward developing inventories of residential and non-
residential materials. These two classes were chosen
because materials at risk characteristically follow these
two divisions, e.g, residences are often made of wood,
while high rises are more often glass or concrete. The
residential inventory is developed from a statistical
analysis of data collected from ground surveys, while the
non-residential inventory can be compiled from aerial
photography, analysis of existing records, and other data.
Some data have been collected for the residential inven-
tory of four cities in the Northeast. This data will be in-
dependently validated, and mathematical models will be
developed to extrapolate the data to other cities. Work on
the non-residential inventory is just beginning. By 1990,
the two inventories will be completed and merged.
What are the quantitative relationships between the
various forms of acidic deposition and the resulting
damage rates to materials?
In addition to identifying the materials at risk, we must
also know the incremental damage to each material due
to acid deposition. Both laboratory and field studies are
being conducted which will lead to the development of
damage functions. A damage function shows the quan-
titative relationship between materials damage and acid
deposition variables. In the laboratory, the materials
specimens are exposed to a variety of air pollutants at
known concentrations, providing individual damage
mechanisms. Field exposure studies, conducted at five
sites in the Northeast, aid in assessing the significance of
the individual damage process is the context of all other
environmental variables. Materials studied at these sites
include metal alloys, carbonate stone, and painted wood
and metal. The damage function for galvanized steel will
be completed within the next year and the damage func-
tion for carbonate stone in the next two to three years.
What are the benefits of reducing the rate of acidic
damage to materials?
Calculation of the economic benefits of reducing damage
due to acidic deposition requires determination of the in-
.ventory of materials at risk and damage functions.
However, to complete the calculation, other data are need-
ed to define further material service lives, cost data and
consumer response. Thus, surveys are planned that will.
answer these questions by 1990.
Outputs
•1986
- Residential materials inventory data base (North-
east)
• 1987
- Residential materials inventory model
- State-of-science report
- Uncertainty analysis report
•1988
- Non-residential inventory data base (Northeast)
•1989
- Reinforced concrete damage survey report
- Brick and mortar damage survey report
- Consumer response report
•1990
- Complete materials inventory
- Dose-response reports:
- Galvanized steel
- Weathering steel
- Copper
- Painted wood
- Painted metal
- Assessment of acid deposition on materials report
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Forest Effects
Policy Questions
• Is there a significant problem of forest damage in the
United States that might be attributed to acid deposi-
tion, alone or in combination with associated
pollutants?
• If so, what is the causal relationship between acid
deposition and associated pollutants and forest decline
in the United States?
• If there is a causal relationship, what is the dose-
response relationship between acid deposition and
associated pollutants and forest damage in the United
States?
Beginning in the early 1970s, extensive damage was
reported for silver fir at high elevations in southern
regions of the Federal Republic of Germany. This was
followed by reports of similar damage to Norway spruce
and European beech. In conifers, one of the most obvious
and most extensive symptoms of damage was premature
loss of older needle sets; another common symptom was
chlorosis, or yellowing, of older needles.
Similar symptoms have been observed at high elevations
in the northeastern United States. Various changes in
forest conditions have been observed in the United States
since the early 1980s. Apparently increased mortality has
been observed in high elevation stands of red spruce and
balsam fir. Also, there is some indication that annual in-
crement growth is reduced in these stands.
In both central Europe and the United States, the ob-
served symptoms are non-specific; they could be caused
by a number of different factors or combinations of fac-
tors. Acid deposition and air pollutants have been im-
plicated as causal factors. A joint EPA-Forest Service
research program, the Forest Response Program (FRP)
has been established to study these factors.
Several different forest types exist throughout the United
States and will be studied. The FRP has established four
research cooperatives to study problems associated with
these forest types:
• The Spruce/Fir Cooperative—to study northeastern
and high elevation southeastern spruce and fir forests.
• The Southern Commercial Cooperative—to study com-
mercially important species in the Southeast, such as
loblolly, slash, and shortleaf pines.
• The Eastern Hardwoods Cooperative—to study various
species of hardwood and Eastern white pine in the East.
• The Western Conifer Cooperative—to study important
coniferous species in the West, such as Douglas fir and
ponderosa pine.
In addition to these research cooperatives, three suppport
groups will provide necessary information to the research
cooperatives. These are:
• The National Vegetation Survey—toexamine the extent
and severity of damage.
• Deposition Monitoring—to provide air quality and
deposition data.
• The Synthesis and Integration Team—to track activities
of the cooperatives and assimilate the information for
the generation of program-wide outputs.
Is there a significant problem of forest damage in the
United States that might be attributed to acid deposition,
alone or in combination with associated pollutants?
The first policy question to be addressed involves the ex-
tent and severity of forest damage. By the end of 1988, we
can expect an evaluation of this problem that will come
primarily from projects of the National Vegetation Survey
and from exploratory research of the Eastern Hardwoods
and Western Conifers cooperatives.
If so, what is the causal relationship between acid deposi-
tion and associated pollutants and forest decline in the
United States?
The second policy question concerns the possible
cause/effect relationship between acid deposition (and
associated pollutants) and forest damage in the United
States. In the Northeast, most damage is observed at high
elevations, which are characterized by frequent exposure
to clouds of low pH and high chemical loading. An impor-
tant aspect of the Deposition Monitoring effort is the
Mountain Cloud Forest Exposure Project, which will in-
vestigate this phenomenon at intensive study sites in the
eastern United States.
A number of hypotheses have been proposed to explain
observed damage. The main hypotheses include:
• Alteration of plant physiology leading to change in tree
growth.
• Impact of gaseous air pollutants and leaching of
nutrients from foliage.
• Over-fertilization with nitrogen through atmospheric
deposition leading to increased winter injury through
early break in dormancy or delayed cold hardening.
• Soil mediated mechanisms, including nutrient leaching
and mobilization of toxic metal ions.
• The impact of natural factors such as drought, pests
and pathogens.
Research in the cooperatives will test these hypotheses.
The first-stage experiments involve studies in chambers
in which experimental conditions can be closely
regulated. This allows the study of very complex
physiological processes under controlled conditions.
Studies will also be carried out in open-top chambers,
which allow less control over experimental conditions,
but can include larger plants under more natural en-
vironmental conditions. Field experiments will be carried
out under natural conditions of deposition, climate and
stand dynamics. All of these types of experiments will be
used to test the postulated mechanisms of damage.
These efforts will contribute information for an evaluation
of the roles of sulfur and nitrogen compounds in forest
damage. This evaluation can be expected in the early
1990s.
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If there is a causal relationship, what is the dose-
response relationship between acid deposition and
associated pollutants and forest damage in the United
States?
The final policy question involves quantification of tree
responses and projection of responses under different
deposition conditions. The primary responsibility for ad-
dressing this question lies with the Synthesis and In-
tegration Team and involves development of a stand-level
forest response model based on individual tree models.
Data from the research cooperatives will be used to
develop these models, which will ultimately allow predic-
tions of health, growth and general forest condition.
Results of this effort will lead to quantification of current
responses of trees to sulfur and nitrogen compounds and
to models which will allow decisions and predictions
related to changes in deposition conditions. We expect
these results in the early 1990s.
Outputs
•1988
- Evaluation of reported forest damage
• 1989
-'Preliminary evaluation of the roles of sulfur and
nitrdgen;in forest damage
•1990
- Quantitative estimates of current forest response to
sulfur and nitrogen
• 1991
- Final evaluation of the roles of sulfur and nitrogen in
forest damage
- Projected role of atmospheric deposition in forests
of the United States
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