Professional Writing Service http://StudyHub.vip/Acid-Rain-Effects-Research-A-Status-Rep 👈

1. Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=uawm20
Journal of the Air Pollution Control Association
ISSN: 0002-2470 (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/uawm16
Acid Rain Effects Research—A Status Report
Allen S. Lefohn & Robert W. Brocksen
To cite this article: Allen S. Lefohn & Robert W. Brocksen (1984) Acid Rain Effects Research—A
Status Report, Journal of the Air Pollution Control Association, 34:10, 1005-1013, DOI:
10.1080/00022470.1984.10465847
To link to this article: https://doi.org/10.1080/00022470.1984.10465847
Published online: 08 Mar 2012.
Submit your article to this journal
Article views: 4935
View related articles
Citing articles: 11 View citing articles

2. Acid Rale Effects Research—-A Status Report
Allen S. Lefohn
A.S.L. & Associates
Helena, Montana
Robert W. Brocksen
University of Wyoming
Laramie, Wyoming
International concern about acidic precipitation as a
possibly serious, widespread pollution problem with
severe ecological consequences has increased the pace
of acid rain research in the United States. Accompa-
nying this increased activity has been a consonant in-
crease in results that directly relate to clarifying many
of the hypotheses that were proposed in the middle
1970s. This paper focuses on these key working hy-
potheses and summarizes, from the most current
knowledge base, the available information on possible
impacts of acid precipitation on the aquatic and ter-
restrial ecosystem. Based on the finer resolution now
available, research questions are provided to help guide
the testing of new and refined hypotheses.
In the 1970s and early 1980s, considerable effort was made to
publicize the potential danger that acidic deposition might
cause to ecosystems in the United States.1
"9
Concern for the
ecosystem has focused primarily on aquatic and forest eco-
systems.10
"12
To assess possible impacts associated with acidic deposition,
several hypotheses have been proposed. Some of the more
important of these hypotheses are:
• Concentrations of hydrogen ions observed in wet depo-
sition are mostly associated with strong mineral acids.
• The amount of sulfate in atmospheric precipitation can
be used as a substitute for predicting the amount of hy-
drogen ion contained in precipitation.
• Episodic pH declines observed in surface waters result
from: a) snowmelt runoff that has been acidified by at-
mospheric deposition and b) heavy rains that wash dry
deposited acidifying material to surface waters.
• Forest ecosystems in the northeastern United States may
have been impacted as a result of acidic deposition.
• Agricultural crops may be at risk as a result of exposures
to acidic deposition and gaseous air pollutants.
• Aquatic ecosystems have been impacted by acidic depo-
sition.
• Mitigation strategies are available to ameliorate the
possible ecosystem effects of acidic deposition.
The physical and biological parts of the ecosystem interact
in a synergistic manner. For example, the transport of anions
such as sulfate and nitrate through the various soil horizons
is a function of the physical soil characteristics, ion exchange
rates, chemical valence state, biological uptake, and micro-
bially-mediated transformations. To properly describe cause
and effect relationships, it may be necessary to focus on the
complex ecological factors that require researchers to combine
broad scale terrestrial and aquatic survey activities with in-
dividual process oriented laboratory and field work. Ecosys-
tem level research may be required to properly place into
perspective the natural ecological processes that are perturbed
by man's actions. This insight can provide us with an estimate
of the elasticity of the natural ecosystem and its ability to
respond to ecological perturbations.
Assessing the effects of acidic deposition on the ecosystem
requires an understanding of the cycling of each of the im-
portant nutrients through the ecosystem. The nutrient
chemical form, its concentration, and spatial and temporal
distribution are important considerations that may require
quantification. Without this additional understanding, it may
be difficult to use field survey results to separate perceived
anthropogenically caused environmental effects from those
resulting from natural changes in nutrient cycling pro-
cesses.
This article focuses on these key working hypotheses and
summarizes, from the most current knowledge base, the
available information on possible impacts of acid precipitation
on the aquatic and terrestrial ecosystem and proposes addi-
tional research questions to help guide the testing of new and
refined hypotheses. Specific attention is directed at the pos-
sible importance of natural ecological processes in controlling
many of the environmental observations that have been at-
tributed to acidic deposition.
Wet Deposition
The definition of the natural pH for atmospheric precipi-
tation is an important consideration. Some confusion is evi-
dent when trying to define the natural pH of atmospheric rain
in the absence of anthropogenic emissions. Galloway et al.,13
in an attempt to define the chemistry of unpolluted rain, an-
alyzed chemical precipitation data fromfiveremote sites. Data
analyses were based on precipitation event samples taken
from December 3,1979 through May 1,1981. Average volume
weighted pH precipitation data indicated acidity that ranged
from pH values of 4.78 to 4.96. Charlson and Rodhe14
and
Guiang et al.15
have confirmed that background atmospheric
rainfall pH values for other sites range from 4.5 to above 5.6.
Galloway et al.,1
^ Keene et al.,16
and Keene et al.17
attributed
the measured acidity at the remote locations to both weak
organic (e.g., acetic and formic) and strong mineral (e.g., sul-
furic and nitric) acids derived from sources that are a result
of natural and anthropogenic processes.
Copyright 1984-Air Pollution Control Association
October 1984 Volume 34, No. 10 1005

3. "At present, scientific results support the conclusion that no direct
evidence exists that acidic deposition currently limits forest growth
in North America. However, results indicate that tree growth
reductions are occurring in widespread areas in regions where
rainfall acidity is generally high on a volume weighted annual
average."
Keene and Galloway18
have emphasized that the pH of at-
mospheric precipitation at a specific site depends upon the
chemical nature and relative proportions of acids (i.e., strong
versus weak) and bases in solution. Temporal changes in
precipitation pH are related to variation in concentrations of
alkaline materials (e.g., Ca2+
) in the atmosphere, relative to
acid content. To use pH 5.6 to represent the hydrogen ion
concentration of wetfall for all sites not heavily influenced by
anthropogenic sources, and then compare this value to pH
values recorded at geographic locations thought to be in-
fluenced by anthropogenic emissions, is inappropriate. A clear
understanding of anthropogenic contributions and the natural
pH variation in deposition acidity resulting from weak at-
mospheric acids and soil sources is required.
Sulfate in Precipitation as a Surrogate for Hydrogen in
Rainfall
The acidic deposition discussion has mostly focused on the
direct and indirect effects of atmospheric hydrogen ion de-
positions on vegetation, soils, and surface waters. However,
because of 1) the difficulty associated with developing
transport models for predicting regional hydrogen ion depo-
sition and 2) the assumption that atmospherically deposited
sulfate is equivalent to atmospherically deposited hydrogen
ion, much of the discussion about reducing atmospheric
loading of hydrogen ion has centered on sulfate reduc-
tion.10
Several authors have commented on using either sulfur or
hydrogen ion loading in precipitation for estimating the im-
pact of acidic deposition. Coote et al. ,19
while focusing on the
applicability of using these two chemicals for predicting
possible soil impacts, have commented "when sulfur alone is
used, then the neutrality of calcium, magnesium, sodium, and
other such salts of sulfur is ignored." Results reported by
Krupa and Pratt,20
-21
Pratt et al. ,22
and Sequeira23
'24
bring
into question the hypothesis that sulfate can be used as a
substitute for predicting possible precipitation acidity effects
on both the aquatic and terrestrial environments.
Pratt et al.22
collected rain samples during the summers of
1977 through 1980 at seven sites in the vicinity of a coal-fired
power plant in central Minnesota. The authors' analyses in-
dicated that the major anions (sulfate and nitrate) appeared
to be more closely associated with calcium, magnesium, so-
dium, and ammonium ions than with hydrogen ions. They also
indicated that the sulfate concentration was dependent upon
the concentration of the cations present in precipitation.
Sequeira24
analyzed chemical composition data from at-
mospheric precipitation for three high altitude World Mete-
orological Organization stations (Monte Cimone, Italy; Mauna
Loa, Hawaii; and Alamosa, Colorado). Simple linear and
multiple linear regression analyses indicated that sulfate was
strongly associated with alkali/alkaline earth elements (cal-
cium, potassium, and sodium). Of the three sites, hydrogen
and total sulfate were highly correlated only at Mauna Loa,
Hawaii.
Data reported by Gorham et al.25
for 33 National Atmo-
spheric Deposition Program (NADP) stations in 1980 and 49
in 1981 (sites east of 95° W), indicate that hydrogen ions in
precipitation are more closely associated with sulfate than
with nitrate and that a reduction in sulfate ions would result
in a reduction in hydrogen in wetfall. The investigators ex-
amined correlations between volume-weighted, mean annual
ionic concentrations in wet deposition across sites. Caution
should be exercised in using the results because the authors
did not calculate the variability between sulfate and hydrogen
and nitrate and hydrogen at each of the monitoring sites.
Using annually averaged wet chemistry monitoring data to
address the surrogate question appears inappropriate. To test
this hypothesis, statistical analyses should be performed using
weekly (NADP) or event (MAP3S/UAPSP) wet chemistry
data collected at each site.
The implications of the work by Krupa and Pratt,20
-21
Pratt
et al. ,22
and Sequeira23
'24
are that sulfate in wetfall at some
sites is associated with cations other than hydrogen. The
National Research Council26
noted that not all sulfates in the
air or in precipitation contribute to the acidity measured.
However, the assumption that sulfate ion deposition can be
equated with hydrogen ion deposition over large geographic
areas has been made by several groups.10
'27
Caution should
be exercised when attempting to apply the hypothesis over
large geographic areas to predict surface water chemical
changes resulting from atmospherically deposited sulfate.
Surface Water Episodic pH Depressions
One of the important observations associated with possible
acidic deposition effects on the aquatic system is the episodic
increase in hydrogen ion concentration in surface waters
during snowmelt and heavy runoff. It has been hypothesized
that 1) during the winter, acidic deposition in rainfall and
snow is collected by the snowpack and released during spring
runoff periods and 2) heavy storms cause flushing events that
result in acidic materials deposited on the soil (derived from
dry atmospheric deposition) being carried to surface wa-
ters.10
However, recent reports and articles by Everett et al.,28
Brocksen and Lefohn,29
Jones et al.,30
Krug and Frink,31
Richter,32
U.S./Canada,10
CARP,33
and Lefohn and Klock,34
Noggle et al.,35
and Krug et al.,36
have rekindled the possi-
bility that natural soil processes have a more important role
in defining stream water chemistry than generally acknowl-
edged. Lefohn and Klock34
reviewed data and reports derived
from ten watershed sites across the U.S. and found that nat-
ural soil processes appeared to play an important role at most
of the sites in defining the seasonal episodic activity and
aluminum concentrations measured in many of the surface
waters. Noggle et al.35
have shown that forest soils in the
Raven Fork and Straight Fork, North Carolina watershed play
an important role in defining surface water chemistries. Re-
sults from applying pH 5.7 simulated rain showed that Raven
Fork forest soils contributed weak acids, strong acids, and
aluminum to percolating water in the absence of acidic de-
position in precipitation.
Further support for the importance of naturally produced
hydrogen in soils is derived from work of Seip et al.37
The
authors studied the changes in concentrations of chemical
components in snowpack and runoff in several mini-catch-
ments in Telemark, Norway. In 1979, the investigators neu-
tralized snow with sodium hydroxide before the snow melting
period. When the H+
concentrations in runoff in 1978 and
1979 were compared, the authors reported that the average
hydrogen ion concentrations were similar, despite the neu-
tralization of snow in 1979. Rosenqvist et al.38
have estimated
1006 Journal of the Air Pollution Control Association

4. that the atmospheric acids in excess of carbonic acids in the
Numedal area (Norway) contributed about 5-15% ofthe total
acid formed in soil.
There is mounting evidence supporting the thesis that ad-
ditional research is necessary before scientists can ascertain
whether the pH events observed during snowmelt and heavy
autumn rains can be attributed to internal H+
sources or a
mixture of both internal and anthropogenic sources. Works
by Chen et al.39
and Newton and April40
stress the importance
of soils in defining lake chemistry. For specific sites, if the
observed pH events in surface water are a result of a combi-
nation of natural and anthropogenic sources, then an effort
must be made to quantify the relative contribution associated
with each.
Forest Decline
There has been concern that acidic deposition has damaged
forest systems. Recent surveys of forests in the eastern U.S.
have shown that there are symptoms of measurable decline.
The slowing growth indicates a broad regional phenomenon
observed in both young and old trees of several species. In
some high elevation areas, visible dieback of certain coniferous
tree species has also occurred.
Johnson et al.n
have reported possible acidic precipitation
effects on a forest ecosystem in the New Jersey Pine Barrens
area. Johnson and Siccama41
have suggested that the rela-
tionship between loss of vigor and drought is clear. Surveys
of vegetation effects, conducted in the 1970s, reflected levels
of ozone in the vicinity of the Pine Barrens that were capable
of causing impacts to vegetation.42
-43
Lefohn44
recently re-
viewed the EPA air quality data for a monitoring site in the
area and has reported that elevated levels of hourly averaged
ozone concentrations do exist during the spring and summer
months.
In the Northeast, work by Vogelmann12
has been cited as
possible evidence that acidic deposition has caused the decline
of red spruce on Camel's Hump Mountain, Vermont. Johnson
and Siccama41
do not support this hypothesis. The authors
conclude instead that current evidence suggests conifers are
primarily affected by drought. The authors believe that acidic
deposition could exacerbate drought stress, but that no con-
vincing evidence is available to show that acidic deposition
can be linked to the observed mortality. Siccama et al.45
have
concluded that the cause of the decline of red spruce is not
known.
To explain the reduced growth phenomenon, the following
set of working hypotheses has been proposed:46
• Gaseous air pollutants, such as ozone, are causing damage
to tree foliage, and either alone or by interacting with acid
deposition, affecting tree growth.
• Deposition of metals, alone or interactively with acid de-
position, is directly or indirectly affecting tree growth.
• Acid deposition is increasing the leaching of nutrients
from the foliage of trees at a rate rapid enough that uptake
and recycling of lost nutrients cannot maintain adequate
supplies of nutrients in the tree foliage.
• Acid deposition is acidifying soil water, increasing alu-
minum concentrations, and ultimately affecting root
growth and nutrient and water uptake.
• Nitrogen saturation of forest soils is changing the bene-
ficial relationship between trees and soil microorganisms
either directly or indirectly, resulting in nutrient and
water imbalances.
Krug and Frink31
have pointed out that soils beneath forest
stands proceeding through succession toward climax generally
become more acidic over time. The authors stated that the
recovery of landscapes in New England from earlier distur-
bances, such as tree harvesting, can result eventually in in-
creasing acid surface soil horizons and thickening and acidi-
fication of forest floors. Evidence to support such a hypothesis
has been provided by Troedsson.47
The investigator analyzed
soil pH data from 13,000 arbitrarily selected test plots from
the National Forest Survey in Sweden and found a strong
correlation between increasing forest age and increasing soil
acidity. The author concluded that the relationship between
the age of coniferous trees and soil pH was stronger than the
relationship between atmospheric depositions.
In addition to the change in soil environment, Krug and
Frink31
have discussed land use practices as a possible per-
turbing agent in affecting the natural nutrient cycling pro-
cesses that influence forest growth. Man's destruction of the
"old growth" forest environment tends to diminish soil pod-
zolization. In contrast, fire protection of forest stands may
enhance podzolization. Therefore, land use practices have the
potential for significantly influencing podzolization activity
and consequently, the soil environment in which trees grow.
Placing the comments of Krug and Frink into perspective, a
second set of hypotheses might be:
• Changes in soil chemistry that result from natural suc-
cession result in forest decline for specific species.
• Land use practices (e.g., tree harvesting and fire man-
agement) have impacted the soil environment in which
trees grow. Changes in soil chemistry are manifested by
modifying tree succession patterns.
While scientists attempt to identify the causes of the forest
decline, survey work is continuing. McLaughlin et al.48
have
described two large scale surveys sponsored by the federal
government. The first is a study of dieback of red spruce over
its entire range of occurrence in the eastern U.S. Approxi-
mately 32 stands of spruce have been sampled to document
the geographical extent of dieback, the degree to which die-
back was preceded by declining growth of both spruce and
associate species, and the association of these responses with
the past history of growth of these species at these sites. A
second program was initiated in 1982 to examine the combined
effects of acid rainfall and chronic gaseous pollution stress on
a variety of forest species distributed throughout the eastern
U.S. The project, entitled FORAST (Forest Responses to
Anthropogenic Stress), is assessing forest effects and the re-
sults will be incorporated into the 1985 National Acid Pre-
cipitation Program Assessment.
At present, scientific results support the conclusion that no
direct evidence exists that acidic deposition currently limits
forest growth in North America. However, results indicate that
tree growth reductions are occurring in widespread areas in
regions where rainfall acidity is generally high on a volume
weighted annual average.33
It is possible that through a
comprehensive environmental characterization effort, a
quantification of anthropogenically caused effects will be
documented.
October 1984 Volume 34, No. 10 1007

5. "Although liming does not always work as predicted, it is currently
the most well understood and applicable management tool for
enhancing fisheries in acidic waters."
Agricultural Crops
Simulated acid precipitation experimental studies on ag-
ricultural crops show positive, negative, and no effects.49
"52
Using artificial exposures, effects symptoms have been ob-
served.53
"64
At this time, it appears that rain with pH values
above 4.0 applied in a routine manner to the vegetation, does
not cause detrimental effects.
The frequency of occurrence of rain events below pH 4.0 is
important. Many investigators have commented on the epi-
sodic nature of rain chemistry.13
-14
'22
-24
'65
-68
The annual
volume weighted concentration of a specific ion may not
necessarily correlate with possible ecological impacts. John-
ston et al.57
have compared differences between plants grown
in greenhouses exposed to rain at a constant pH 3.2 level and
those exposed to rain that increased in pH from 2.8 to 4.0 with
a pH 3.2 mean. Results indicate a tendency for rain events
with a high peak level of acidity to cause greater deleterious
effects on bush bean plants (Phaseolus vulgaris L. cv 'Blue
Lake 274') than those rain events characterized by a constant
pH level.
Using actual rain chemistry data, Lefohn69
and Lefohn and
Benedict70
have evaluated the frequency of weekly reported
pH values for wet chemistry monitoring sites. For the majority
of events, even at sites experiencing annual volume weighted
pH values of 4.16, the pH values are mostly above 4.0. Sites
in the northeastern U.S. experienced a greater percentage of
precipitation events below 4.0 than did sites in other parts of
the country. However, weekly NADP samples varied over a
large pH range. Jacobson,52
after reviewing the U.S. Depart-
ment of Energy's MAP3S data for the Ithaca, New York and
Pennsylvania sites, states that"... a reasonable conclusion
is that there is a low risk of foliar injury to field-grown vege-
tation from exposure to current levels of acidity in precipita-
tion in the U.S." While these conclusions are preliminary in
nature, Lefohn and Brocksen,71
Irving,51
and Jacobson52
have
emphasized that additional research should include other
considerations such as exposure patterns and chemical con-
stituent identification (e.g., nitrate and sulfate).
Concern has been expressed about the possible effects on
crops from simultaneous exposures of gaseous air pollutants
(e.g., ozone) and acid precipitation. Results by Jacobson et
al.,72
Troiano et al.,5S
and Troiano et al.73
show that under
simulated acid rain and filtered and nonfiltered ambient ox-
idant conditions, ozone and acid rain tended to show inter-
active effects. Work by Norby and Luxmoore74
showed that
simulated acid rain and sulfur dioxide/ozone exposures did
not affect the response of soybeans to extremely low pH (2.6)
simulated acid rain exposures. Lefohn and Tingey75
have re-
cently summarized the frequency of the number of co-occur-
rences of SO2/O3, SO2/NO2, and O3/NO2 under ambient
conditions and state that vegetation research using gaseous
air pollutant mixtures should focus on the sequential ap-
pearance of the pollutants. It appears reasonable to propose
that combined acidic deposition and gaseous air pollutant
mixture exposures should stress the sequential patterns of
occurrence.
Aquatic Ecosystems
The question of acid rain affecting aquatic systems has been
shrouded in confusion. While much of what we do know is
based on circumstantial evidence,27
there are some specific
statements that can be made concerning the possible impact
of acidic deposition on streams, rivers, and lakes. Work Group
I reviewed the empirical data available for assessing possible
acidic deposition impacts to the aquatic ecosystem.10
The
Work Group has identified the following geographic areas as
examples that can be cited for illustrating acidic deposition
chemical and biological effects: Algoma (Ontario), Mus-
koka-Haliburton (Ontario), Laurentide Park (Quebec), Nova
Scotia, Adirondack Mountains of New York, the Hubbard
Brook Ecosystem (New Hampshire), and Maine and New
England.
Some headwater lakes in the Algoma district of Ontario
have elevated sulfate, aluminum, and lead concentrations.10
The Work Group has examined fish surveys conducted in the
area and has indicated that the numbers of fishless lakes in-
crease with decreasing alkalinity. This district begins about
100 km from Sudbury, Ontario (a significant local point source
of sulfate and heavy metal emissions). Because elevated lead
concentrations have been observed, the elevated sulfate levels
observed in the lakes may have originated from Sudbury
emissions. In addition, the number of fishless lakes may be
associated with possible elevated levels of heavy metals de-
rived from Sudbury.76
Data for the Muskoka-Haliburton area of Ontario show a
loss of alkalinity for one lake. However, the Work Group
mentioned pH depressions in a number of lakes and streams.
A fish kill, moreover, was observed once during spring snow-
melt in one lake. Although acidification was the suspected
cause, the actual cause of the fish kill was not determined. As
discussed by CARP,33
it is possible that pH depression events
occurring during the spring snowmelt and during the fall rains
could consist of natural (internally generated hydrogen ions
in the soil) and, secondarily, anthropogenic sources. Jones et
al.30
discuss this possibility in their description of the Raven
Fork, North Carolina, investigation. The Work Group has
stated that it is difficult to include natural acid formation
criteria in regional sensitivity assessments because the data
base is so limited.10
Thus, at this time, it is impossible to at-
tribute the fish kill to an anthropogenically derived source.
Work by Evans, and Dillon76
suggests that elevated con-
centrations of lead in the sediments of lakes in the Mus-
koka-Haliburton region of southern Ontario originated from
the burning of fossil fuels in North America; elevated con-
centrations of lead are also found in lakes in the Algoma dis-
trict. Both regions, however, are relatively close to a large point
source of sulfate and heavy metal emissions at Sudbury, On-
tario (200 km from the Muskoka-Haliburton region and 100
km from the Algoma district). Nriagu et al.77
report that
230,000 kg of lead are emitted annually from the Sudbury
smelters; in comparison, Turner and Strojan78
report that
total atmospheric emissions of lead from coal combustion in
the U.S. amount to 54,000 kg annually. The maximum lead
concentrations reported in the sediments of lakes in the
Muskoka-Haliburton region, reported by Dillon and Evans79
and presented by the Work Group,10
are about 2.5 to 5.0 times
greater than those found in Adirondack lake sediments (128
fig lead per gram of sediment) by Davis et al.80
Thus, if lead
concentrations provide an indication of the origin of the lakes'
anthropogenically derived sulfates, local emitting sources in
Canada may be important in explaining some of the obser-
vations.
1008 Journal of the Air Pollution Control Association

6. Data for Laurentide Park, Quebec, have been reviewed by
Work Group I, who found that sulfate concentrations in sur-
face waters in Quebec decrease toward the east and north,
parallel with the deposition pattern. As discussed by Lefohn
et al.,81
sulfate concentrations did not correlate well with
calcium + magnesium — alkalinity concentrations. Most im-
portantly, there is no evidence of effects to fish populations
from elevated sulfate concentrations in Quebec lakes.10
Historical salmon catch records from Nova Scotian rivers
reportedly show reductions over the past 40 years.10
The At-
lantic Salmon Review Task Force,82
relying on commercial
Canadian salmon catch data for the years 1910 through 1977,
report that many Atlantic salmon stocks production areas in
Nova Scotia, New Brunswick, and St. John have been affected
by over-harvesting and industrial development. For example,
the Task Force reported that Atlantic salmon in the southwest
Nova Scotia area have been impacted by over-harvesting,
while in the southern New Brunswick-St. Johns area, the
salmon have been impacted by the "construction of the
massive Mactaquac hydro-electric development just above
tide-head ..." The Task Force appears to believe that the
development created additional demands on much of the
salmon's freshwater habitat or lifeline and that by the late
1960s, thereiwas little optimism for rehabilitation of stocks
in the river.
In addition to development activities, local air pollution and
natural hydrogen sources may be an important aspect of the
problem. The findings of Shaw83
-84
suggest that a substantial
part of the hydrogen concentration in the Nova Scotian
waterbodies appears to be related to local point sources. Results
reported by Watt et al.85
and Farmer et al.86
show that many
of the Nova Scotian rivers contain humic and/or fulvic acids
and that the contribution of these organic acids to total acidity
may be significant.10
Data for the Adirondack Mountains in New York have been
reviewed by the Work Group.10
The Group infers that losses
in fish populations at 180 lakes are attributable to acid rain
because a comparison of data from the 1930s with data from
recent surveys has shown that more lakes have become acid-
ified. Recent reviews of the problems associated with com-
paring data derived from two distinct time periods87
con-
cluded that there are many more questions that need to be
answered before one can consider the comparisons valid and
reliable. Retzsch et al.88
have suggested several possible al-
ternative explanations for the reported observations. The
authors report that the numbers of lakes and ponds stocked
have shown a relatively continuous decline. This decline, ac-
cording to the authors, may be the result of the closing of
stocking waters found to be unsatisfactory for long-term fish
survival.
While no biological impacts associated with aquatic or-
ganisms have been documented at the Hubbard Brook study
area in New Hampshire, Work Group I did state that the area
has experienced pH depressions of 1 to 2 units in streams
during snowmelt.10
Brocksen and Lefohn29
and Lefohn and
Klock34
have discussed possible reasons that pH depressions
could be attributed to natural occurrences. The authors stress
that additional research is necessary to separate the natural
from the anthropogenic contribution of hydrogen ion during
spring snowmelt and heavy runoff.
In the Maine and New England areas, the Work Group10
reported lake water pH declines based on comparisons with
historical information.80
'89
-90
No effects have been observed
on Atlantic salmon populations, nor have effects been ob-
served on fish in inland lakes. Marcus et al.87
have pointed out
that Davis et al.91
noted that cultural eutrophication had
apparently increased the daytime pH of a small but significant
portion of the surveyed lakes and that although the earlier
measurements were made using colorimetric methods, the
more recent values were determined with potentiometric
methods. Lefohn et al.92
have pointed out the problems as-
sociated with comparing pH values using different measure-
ment techniques. The work by Norton et al.89
examined
changes in surface water pH between the periods 1939-1946
and 1978-1980. The authors concluded that 85% of the lakes
appeared to be more acidic in the period 1978-1980 than in
1939-1946. Marcus et al.81
and Brown and Brocksen93
pointed
out that since the study only compared two points in time over
extended intervals, it was unclear whether the results obtained
represented actual trends or were artifacts of normal temporal
variations in surface water pH. Linthurst et a/.94
state that
lake acidification trends, as described for the above examples,
cannot be unequivocably related to acidic deposition.
In contrast to the suggested acidification of New England
surface waters reported by the above cited authors, Norvell
and Frink95
concluded that the pH and alkalinity in sensitive
(alkalinity less than 200 neq L"1
) lakes of Connecticut had not
changed significantly from 1937 to 1973. Inspection of the
atmospheric deposition maps presented by the Work Group10
shows similar deposition rates of hydrogen and sulfate ions
in Connecticut and other parts of New England. Thus, care
must be exercised when discussing the possibility of extrap-
olating the results from a local observation in order to predict
regional scale effects.
Both chemical and biological processes within a forest
ecosystem soil appear to play an important role in determining
the chemistry of surface waters. Swank and Fitzgerald96
have
shown that the metabolism of inorganic sulfate to organic
forms can be a major process in the sulfur cycle that influences
sulfate soil accumulation and mobility in forest ecosystems.
Vitousek and Matson97
have reported that measurements of
nitrogen-15 retention in the field demonstrated that microbial
uptake of nitrogen during the decomposition of residual or-
ganic material was one of the most important processes in
retaining nitrogen in the soil. Results reported by Johnson and
Todd98
showed that irrigation with sulfuric and nitric acid at
two and ten times the current annual hydrogen inputs over
a period of one year had no statistically significant lasting
effect on nitrogen in the soil or Al availability or P avail-
ability.
Using sulfate concentration measured in surface waters as
an indication of acidic deposition effects may be misleading.
Parnell99
showed that where bedrock sulfide concentrations
are significant, naturally derived sulfuric acid may cause ac-
celerated chemical weathering rates and low pH values in local
streams. The author stressed that where sulfidic rocks crop
out, this contribution may have previously been underesti-
mated by some investigators. The author stresses that caution
should be used in interpreting acid precipitation leaching and
weathering data from New England drainage basins underlain
by sulfidic schists. As discussed by Everett et al. ,28
sulfate
measured in surface waters may be more correlated to the
sulfur contained in minerals than the sulfate deposited from
atmospheric wetfall and dryfall.
October 1984 Volume 34, No. 10 1009

7. "Science is the search for truth. Our efforts may lead us down
several different paths, but our challenge is to search for data that
will provide a clearer picture of how the ecosystem responds to
both natural and man-made perturbations."
Mitigation Strategies
Acidic surface waters generally have unproductive fisheries
or, in some cases, are incapable of supporting any fish popu-
lations. This results from both the oligotrophic (nutrient poor)
status of these waters and the low tolerances ofmany desirable
fish species to the acidity.
Liming is defined as the addition of lime, limestone, or other
alkaline materials to acidic surface waters for neutralization.
Finely ground calcium carbonates and basic slags of the mono-
and dicalcium silicate types have been found particularly
useful in pH adjustments of acid lakes because their relatively
intermediate solubilities tend to extend the period of neu-
tralization.100
Historically, liming has been used to establish, restore, or
enhance fish production in acidified waters. As a fisheries
management technique, liming was first used in naturally acid,
brown water lakes.101
Subsequently, the technique has been
applied to reclaimed lakes impacted by acid mine drainages.
And more recently, liming has been applied to surface waters
in regions receiving acidifying depositions.102
'103
Liming reduces adverse effects of acidification on fish
populations by increasing pH, hardness, and alkalinity levels
of surface waters. These increases reduce the toxicity of acid
waters by 1) reducing toxic hydrogen ion concentrations; and
2) complexing, precipitating, changing chemical speciation,
and inhibiting uptake of metals that are often enriched in
acidified waters. As a result, liming has been very beneficial
in restoring and enhancing the fishery potential of some
acidified waters.
The utility of liming is best illustrated by the Swedish ex-
perience.104
Sweden is undertaking an extensive lake program
to preserve and protect salmon, perch, and pike fisheries
threatened by acidification. During 1977 to 1979, about 700
lakes and rivers were limed. During the 1982 fiscal year, 1000
lakes were to be limed at a cost of six million dollars. The
program is expected to expand to an annual budget of 40
million dollars by fiscal year 1986 to include the liming of
20,000 lakes and streams.
Liming programs in North America have been much less
extensive. Liming was used to increase pH levels in several
acidic lakes near Sudbury, Ontario. However, fish introduc-
tions into these lakes failed because high toxic metal con-
centrations, derived from local smelter emissions, remained
in lake waters. New York state has used liming since the late
1950s to maintain trout populations in some acidic lakes.
Concurrently, considerable research on liming and its use-
fulness for protecting or restoring fisheries is being conducted
by a number of governmental and private institutions.
Although liming does not always work as predicted, it is
currently the most well understood and applicable manage-
ment tool for enhancing fisheries in acidic waters. Much po-
tential exists for increasing its usefulness, especially by com-
bining it with some of the alternative strategies that may be
available.
Liming is not a viable mitigative strategy for every surface
water. Where the inaccessibility of some acidic water bodies
may greatly increase costs or where liming may not reduce the
episodic aspects of snowmelts, etc., other alternative strategies
may be appropriate. And, in some instances, more than one
strategy may be applied to the same waters. Certainly there
is a need for evaluation and development of additional strat-
egies for restoring and enhancing the fisheries of acidic wa-
ters.
Modern agriculture, animal husbandry, and forestry
practices may provide insight into ways of accomplishing this.
Through selective breeding, introduction of new species, and
fertilization coupled with changes in land use practices, it may
be possible to increase the pH and alkalinity of acidic waters
and establish fisheries where they were once absent.
While liming is a proven management tool in some cases,
there remain questions with respect to toxic metal bioaccu-
mulation by fish, longer term chemical alterations, and the
need to lime with relative frequency. As stated previously,
there is currently a large research effort examining problems
associated with liming and if this mitigative strategy is to be
implemented, consideration must be given to the site specific
characteristics of the water body and its watershed.
Future Research Directions
Much effort has been directed toward surveying the nation's
aquatic and terrestrial resources. To separate perturbations
associated with anthropogenic sources from those derived
from natural occurrences, it will be necessary for researchers
to blend survey activities with process oriented efforts. To
assist in this endeavor, the following series of fundamental
questions are proposed:
• What will happen to the pH concentration in rainfall in
the amount of sulfate and nitrate in rainfall is modi-
fied?
• How much do natural acidification soil processes con-
tribute to the pH depressions that are observed in surface
waters during heavy rainfall and snowmelt events?
• What are the important pollutants (e.g., acidic deposition,
ozone, sulfur dioxide, etc.) in combination with natural
factors (e.g., forest succession, drought, infestation, etc.)
that may contribute to the observed forest decline?
• Do combinations of pollutants (e.g., acidic deposition,
sulfur dioxide, and ozone) adversely affect agricultural
crops?
• How many lakes are acidic because of acidic deposi-
tion?
• How many lakes are incapable of supporting fish because
of acidic deposition?
• How many lakes will become supportive of fish if acidic
deposition can be reduced?
• What other remedial measures (or combinations of mea-
sures) will make a lake supportive of fish?
The ecosystem may have the potential for ameliorating
anthropogenically derived stresses if a pollutant's concen-
tration, frequency of occurrence, time between occurrences,
and temporal exposure occur in a pattern that provides for a
homeostasis or hysteresis feedback response. For researchers
to provide answers to the questions raised, it will be necessary
for "alternative" hypotheses to be identified and seriously
addressed. The talents of an eclectic set of scientists will be
needed to probe beyond the obvious.
Conclusion and Recommendation
Recent publications underscore the tenuous nature of the
acid deposition effects data base. Based upon the most current
evidence the following conclusions may be drawn:
1010 Journal of the Air Pollution Control Association

8. • If the hydrogen ion that is deposited on a watershed is
believed to be the primary source of ecosystem pertur-
bation (recognizing that mobile aluminum is a secondary
product of the soil acidification process), then it is unclear
whether a reduction in atmospherically deposited sulfate
or nitrate would result in a similar reduction in deposited
hydrogen ion.
• While hot being able to quantify their contribution at this
time, naturally produced acids that are internally gener-
ated within the soil ecosystem may play a considerably
more important role in determining the acidification of
surface water bodies than previously believed. The acid-
ification process may involve a combination of natural and
anthropogenically derived acid sources.
• While reductions in tree growth are occurring in North
America and Europe, no direct evidence exists to link
acidic deposition with these observations. In fact, recent
hypotheses tend to focus on many factors as possible
agents that might significantly contribute to the observed
forest decline.
• Evidence is mounting that ambient exposures of acidic
deposition may not injure or reduce the growth of agri-
cultural crops.
• Aquatic waterbodies identified by Work Group I (based
on empirical observation) as having been acidified by acid
rain may be more affected by local point sources (e.g.,
Sudbury, Ontario) or naturally derived acid sources con-
tained within the soil.
• Mitigation techniques are presently under review, but
caution should be exercised so that possible biological
modifications resulting from chemical alteration can be
avoided.
Over the next several years, the pace of acid rain research
will be increasing. However, it is unclear whether the quality
of the data produced from this increased pace will show a
consonant increase. Increased federal spending is not neces-
sarily synonymous with obtaining answers more quickly. The
entropy of the universe tends to increase and with it, maxi-
mum randomness. Therefore, additional energies within our
funding institutions will have to be found to organize and in-
terpret new information. Science is the search for truth. Our
efforts may lead us down several different paths, but our
challenge is to search for data that will provide a clearer pic-
ture of how the ecosystem responds to both natural and
man-made perturbations.
As Resnick105
has stated:
"Successful problem-solving requires a substantial
amount of qualitative reasoning. Good problem-sol-
vers dp not rush in to apply a formula or an equation.
Instead they try to understand the problem situation;
they consider alternative representations and rela-
tions among the variables. Only when they are satis-
fied that they understand the situation and all the
variables in it in a qualitative way do they start to
apply the quantification that we often mistakenly
identify as the essence of 'real' science of mathe-
matics."
Careful work will be required to clarify our knowledge of
how acidic deposition may be impacting ecosystems. With well
founded hypotheses that are designed to lead to greater un-
derstanding of the complex processes associated with this
problem, we hope to learn more about those important pro-
cesses that affect our biosphere.
References
1. G. E. Likens, F. H. Bormann, N. M. Johnson, "Acid rain," En-
vironment 14: 33 (1972).
2. G. E. Likens, "Acid precipitation," Chem. Eng. News 54: 29
(1976).
3. C. V. Cogbill, G. E. Likens, "Acid precipitation in the north-
eastern United States," Water Resources Res. 10: 1133
(1974).
4. C. L. Schofield, "Acid precipitation: effects on fish," Ambio. 5:
228(1976). .
5. J. N. Galloway, G. E. Likens, "Calibration of collection proce-
dures for the determination of precipitation chemistry," Water,
Air, Soil Pollut. 6: 241 (1976).
6. J. N. Galloway, E. B. Cowling, E. Gorham, W. W. McFee, "A
national program for assessing the problem of atmospheric de-
position (acid rain)," National Atmospheric Deposition Pro-
gram, Natural Resources Ecology Laboratory, Fort Collins, CO,
1978.
7. G. E. Likens, R. F. Wright, J. N. Galloway, T. J. Butler, "Acid
. rain," Sci. Am. 241:43 (1979).
8. G. E. Likens, T. J. Butler, "Recent acidification in precipitation
in North America," Atmos. Environ. 15:1103 (1981).
9. E. B. Cowling, "Acid precipitation in historical perspective,"
. Environ. Sci. Technol. 16:110A (1982).
10. "United States—Canada Memorandum of Intent on Trans-
boundary Air Pollution," Final Report, prepared by the Impact
Assessment Work Group 1,1983, (Draft).
11. A. H. Johnson, T. C. Siccama; D. Wang, R. S. Turner, T. H.
Barringer, "Recent Changes in Patterns of Tree Growth Rate
in the New Jersey Pinelands: A Possible Effect of Acid Rain,"
University of Pennsylvania, Philadelphia, PA, 1981.
12. H. W. Vogelmann, "Catastrophe on Camel's Hump," Natural
History, November 1982.
13. J. N. Galloway, G. E. Likens, W. C. Keene, J. M. Miller, "The
composition of precipitation in remote areas of the world," J.
Geophys. Res. 87:8771 (1982).
14. R. J. Charlson, H. Rodhe, "Factors controlling the acidity of
natural rainwater," Nature 295: 683 (1982).
15. S. F. Guiang, III, S. V. Krupa, G. C. Pratt, "Measurements of
S(IV) and organic anions in Minnesota rain," Atmos. Environ.
(1984), in press.
16. W. C. Keene, J. N. Galloway, J. D. Holden, Jr., "Measurement
of weak organic acidity in precipitation from remote areas of the
world," J. Geophys. Res. 88: 5122 (1983).
17. W. C. Keene, J. N. Galloway, J. D. Holden, Jr., "Organic Acidity
in Precipitation from Remote Areas of the World," in Pro-
ceedings of the 3rd Annual National Symposium on Recent
Advances in Measurements of Pollutants in Ambient Air and
Stationary Sources, U.S. EPA, Research Triangle Park, NC,
1984.
18. W. C. Keene, J. N. Galloway, "Organic acidity in precipitation
of North America," Atmos. Environ. (1984), in press.
19. D. R. Coote, D. Siminoyitch, S. Shah Singh, C. Wang, "The
Significance of Acid Rain to Agriculture in Eastern Canada,"
Land Resource Research Institute, Contribution No. 119,
1981.
20. S. V. Krupa, G. C. Pratt, "Rainfall Chemistry in Minnesota and
West-Central Wisconsin—Final Report 1981," prepared for
Minnesota/Wisconsin Power Suppliers Group, 1983.
21. S. V. Krupa, G. C. Pratt, "Rainfall and Aerosol Chemistry in
Minnesota and Wisconsin—Final Report 1982," prepared for
Minnesota/Wisconsin Power Suppliers Group, 1983.
22. G. C. Pratt, M. Coscio, D. W. Gardner, B. I. Chevone, S. V.
Krupa, "An analysis of the chemical properties of rain in Min-
nesota," Atmos. Environ. 17: 347 (1983).
23. R. Sequeira, "Acid rain: an assessment based on acid-base
considerations," JAPCA 32: 241 (1982).
24. R. Sequeira, "Chemistry of precipitation at high altitudes:
inter-relation of acid-base components," Atmos. Environ. 16:
329 (1982).
25. E. Gorham, F. B. Martin, J. T. Litzau, "Acid rain: ionic corre-
lations in the Eastern United States, 1980-1981," Science 225:
407 (1984).
October 1984 Volume 34, No. 10 1011

9. 26. Acid Deposition Atmospheric Processes in Eastern North
America—A Review of Current Scientific Understanding,
National Academy of Sciences Press, National Research Council,
Washington, DC, 1983.
27. Atmosphere-Biosphere Interactions: Toward a Better Un-
derstanding of the Ecological Consequences of Fossil Fuel
Combustion, National Academy Press, National Research
Council, Washington, DC, 1981.
28. A. G. Everett, W. C. Retzsch, J. R. Kramer, I. P. Montanez, P.
F. Duhaime, "Hydrbgeochemical Characteristics of Adirondack
Waters Influenced by Terrestrial Environments," in Proceed-
ings of the Second National Symposium on Acid Rain, Greater
Pittsburgh Chamber of Commerce, 1983.
29. R. W. Brocksen, A. S. Lefohn, "Lake Acidification: Sources of
Surface Water Acidification—Anthropogenic and Natural,"
presented at the AIAA 21st Aerospace Sciences Meeting, Reno,
NV, 1983.
30. H. C. Jones, J. C. Noggle, R. C. Young, J. M. Kelly, H. Olem, R.
J. Ruane, R. W. Pasch, G. J. Hyfantis, W. J. Parkhurst, "In-
vestigation of the Cause of Fish Kills in Fish-Rearing Facilities
in Raven Fork Watershed," Tennessee Valley Authority, Office
of Natural Resources, Division of Air and Water Resources,
TVA/ONR/WR-83/9,1983.
31. E. C. Krug, C. R. Frink, "Acid rain on acid soils: a new perspec-
tive," Science 221: 520 (1983).
32. D. D. Richter, "Comments on 'Acid Precipitation in Historical
Perspective' and 'Effects of Acid Precipitation,' " Environ. Sci.
Technol. 17:568 (1983).
33. "The Acidic Deposition Phenomenon and its Effects," in Critical
Assessment Review Papers, Volume II Effects Sciences, Public
Review Draft, EPA 600/8-83-016B, 1983.
34. A. S. Lefohn, G. 0. Klock, "The Possible Importance of Natu-
rally Occurring Soil Processes in Defining Short-Term pH De-
pressions Observed in United States' Surface Waters," prepared
for the U.S. Environmental Protection Agency, 1983, (Draft).
35. J. C. Noggle, H. C. Jones, J. D. Joslin, Jr., R. W. Garber, J. M.
Kelly, H. Olem, P. F. Brewer, "Investigations of the Role of In-
ternally Generated H+
and Al+++
on Soil and Surface Water
Acidification," presented at the 77th Annual Meeting of the Air
Pollution Control Association, San Francisco, CA, June 1984.
36. E. C. Krug, P. J. Isaacson, C. R. Frink, "Appraisal of Some
Current Hypotheses Describing Acidification of Watersheds,"
presented at the 77th Annual Meeting of the Air Pollution
Control Association, San Francisco, CA, June 1984.
37. H. M. Seip, S. Anderson, B. Halsvik, "Snowmelt Studied in a
Minicatchment with Neutralized Snow," SNSF Project, Internal
Report IR 65/80, ISBN 83-90153-96-1,1980.
38. I. T. Rosenqvist, P. Jorgenson, H. Rueslatten, "The Importance
of Natural H+
Production for Acidity in Soil and Water," in D.
Drablos, A. Tollan, eds., Proceedings of an International Con-
ference on the Ecological Impact of Acid Precipitation," SNSF
Project, Acid Precipitation—Effects on Forest and Fish, Oslo,
Norway, 1980, pp. 240-241.
39. C. W. Chen, J. D. Dean, S. A. Gherini, R. A. Goldstein, "Acid rain
model: hydrologic module," J. Environ. Eng. Div. ASCE
108(EE3): 455 (1982).
40. R. M. Newton, R. H. April, "Surficial geologic controls on the
sensitivity of two Adirondack lakes to acidification," N.E. En-
viron. Sci. 1:143 (1982).
41. A. H. Johnson, T. G. Siccama, "Acid deposition and forest de-
cline," Environ. Sci. Technol. 17: 294 (1983).
42. A. Feliciano, "1971 Survey and Assessment of Air Pollution
Damage to Vegetation in New Jersey," prepared for the U.S.
Environmental Protection Agency, Contract No. 68-02-0078,
1972.
43. E. J. Pell, "1972 Survey and Assessment of Air Pollution Damage
to Vegetation irk New Jersey," prepared for the U.S. Environ-
mental Protection Agency, Contract No. 68-02-0078,1973.
44. A. S. Lefohn, "The Availability and Analysis of Ozone Air
Quality Data," in Proceedings of the Symposium of Air Pollu-
tion and the Productivity of the Forest, prepared for the Izaak
Walton League of America, 1983, in press.
45. T. G. Siccama, M. Bliss, H. W. Vogelmann, "Decline of red
spruce in the Green Mountains of Vermont," Bull. Torrey
Botan. Club 102:162 (1981).
46. Annual Report 1983 to the President and Congress, National
Acid Precipitation Assessment Program, Washington, DC,
1984.
47. T. Troedsson, "Ten Years Acidification of Swedish Forest Soils,"
in D. Drablos, A. Tollan, eds., Proceedings of an International
Conference on the Ecological Impacts of Acid Precipitation,
SNSF Project, Acid Precipitation—Effects on Forest and Fish,
Oslo, Norway, 1980.
48. S. B. McLaughlin, T. J. Biasing, L. K. Mann, D. N. Duvick,
"Effects of acid rain and gaseous pollutants on forest produc-
tivity: a regional scale approach," JAPCA 33:1042 (1983).
49. D. S. Shriner, "Effects of simulated acidic rain on host-parasite
interactions in plant diseases," Phytopathology 68: 213
(1978).
50. J. S. Jacobson, "The Influence of Rainfall Composition on the
Yield and Quality of Agricultural Crops," in D. Drablos, A.
Tollan, eds., Proceedings of an International Conference on the
Ecological Impact of Acid Precipitation, SNSF-Project, San-
defjord, Norway, 1980.
51. P. M. Irving, "Acidic precipitation effects on crops: a review and
analysis of research," J. Environ. Qual. 12:442 (1983).
52. J. S. Jacobson, "Effects of Acidic Aerosol, Fog, Mist, and Rain
on Crops and Trees," in Ecological Effects ofDeposited Sulfur
and Nitrogen Compounds, Royal Society, London, 1984.
53. I. J. Hindawai, J. A. Rea, W. L. Griffis, "Response of bush bean
exposed to acid mists," J. Botany 67:168 (1980).
54. L. S. Evans, K. R. Lewin, in D. S. Shriner, C. R. Richmond, S.
E. Lindberg, eds., Potential Environmental and Health Effects
of Atmospheric Deposition, Ann Arbor Press, Ann Arbor, MI,
1980.
55. P. M. Irving, J. E. Miller, "Productivity of field-grown soybeans
exposed to acid rain and sulfur dioxide alone and in combina-
tion," J. Environ. Qual. 10:473 (1981).
56. J. J. Lee, G. E. Neely, S. C. Perrigan, L. C. Grothaus, "Effect of
simulated sulfuric acid rain on yield, growth, and foliar injury
of several crops," Environ. Exp. Botany 21:171 (1981).
57. J. W. Johnston, D. S. Shriner, C. I. Klarer, D. M. Lodge, "Effect
of rain pH on senescence, growth, and yield of bush bean," En-
viron. Exp. Botany 22: 329 (1982).
58. J. Troiano, L. Heller, J. S. Jacobson, "Effect of added water and
acidity of simultated rain on growth of field-grown radish,"
Environ. Pollut. (Series A) 29:1 (1982).
59. C. J. Cohen, J. C. Grothas, S. C. Perrigan, "Effects of Simulated
Sulfuric and Sulfuric-Nitric Acid Rain on Crop Plants: Results
of 1980 Crop Survey," Special Report 670, Agricultural Exper-
iment Station, Oregon State University, Corvallis, OR, 1982.
60. L. S. Evans, N. F. Gmur, D. Mancini, "Effects of simulated acidic
rain on yields oiRaphanus sativus," Environ. Exp. Botany 22:
445 (1982).
61. J. T. A. Proctor, "Effect of simulated sulfuric acid rain on apple
tree foliage, nutrient content, yield and fruit quality," Environ.
Exp. Botany 23:167 (1983).
62. P. O. Forsline, R. C. Musselmann, W. J. Kender, R. J. Del, "Ef-
fects of acid rain on apple productivity and fruit quality," J. Am.
Soc. Hort. Sci. 10: 70 (1983).
63. G. J. Keever, J. S. Jacobson, "Response of Glycine max (L.)
Merrill to simulated acid rain. Environmental and morphological
influences on the foliar leaching of 86
Rb," Field Crops Res. 6:
241 (1983).
64. L. S. Evans, K. F. Lewin, M. J. Patti, "Effects of simulated acid
rain on yields of field-grown soybeans," New Phytologist 96:207
(1984). .
65. M. A. Tabatabai, J. M. Laflen, "Nutrient content of precipitation
over Iowa," Water, Air, Soil Pollut. 6: 361 (1976).
66. R. Sequeira, "Acid rain: Some preliminary results from global
data analysis," Geophys. Res. Lett. 8:147 (1981).
67. J. Chamberlain, H. Foley, D. Hammer, G. MacDonald, O. Ro-
thaus, M. Ruderman, "The Physics and Chemistry of Acid
Precipitation," SRI Technical Report JSR-81-25,1981.
68. D. H. Pack, "Precipitation chemistry probability—the shape
of things to come," Atmos. Environ. 16:1143 (1982).
69. A. S. Lefohn, "Dose Response Considerations Associated with
Acid Precipitation Effects on Vegetation," in Proceedings of the
Second National Symposium on Acid Rain, Greater Pittsburgh
Chamber of Commerce, 1982.
70. A. S. Lefohn, H. M. Benedict, "The development of mathe-
matical indices that describe gaseous pollutant exposure, fre-
quency, and duration," Atmos. Environ. 16: 2529 (1982).
71. A. S. Lefohn, R. W. Brocksen, "A Status Report: What is Cur-
rently Known about the Effects of Acid Rain on the Environ-
ment," in Proceedings of the 43rd Annual Meeting of the
Montana Academy of Sciences, Bozeman, MT, 1984.
72. J. S. Jacobson, J. Troiano, L. J. Colavito, L. J. Heller, D. C.
McCune, in M. W. Miller, P. E. Marrow, eds., Polluted Rain,
1980, pp. 219-305.
73. J. Troiano, L. Colavito, L. Heller, D. C. McCune, J. S. Jacobson,
"Effects of acidity of simulated rain and its joint action with
ambient ozone on measures of biomass and yield in soybean,"
Environ. Exp Botany 23:113 (1983).
74. R. J. Norby, R. J. Luxmoore, "Growth analysis of soybean ex-
posed to simulated acid rain and gaseous air pollutants," New
1012 Journal of the Air Pollution Control Association

10. Phytologist 95:277 (1983).
75. A. S. Lefohn, D. T. Tingey, "The co-occurrence of potentially
phytotoxic concentrations of various gaseous air pollutants,"
Atmos. Environ. (1984), in press.
76. L. S. Evans, P. J. Dillon, "Historical changes in anthropogenic
lead fallout in southern Ontario, Canada," Hydrobiologia 91:
131 (1982).
77. J. 0. Nriagu, H. K. T. Wong, R. D. Coker, "Deposition and
chemistry of pollutant metals in lakes around the smelters at
Sudbury, Ontario," Environ. Sci. Technol. 16:551 (1982).
78. R. B. Turner, C. L. Strojan, "Coal Combustion, Trace-Element
Emissions, and Mineral Cycles," in D. C. Adriano, I. L. Brisbin,
Jr., eds., Processes, National Technical Information Service,
CONF-760429,1978.
79. P. J. Dillon, R. D. Evans, "Whole-lake lead burdens in sediments
of lakes in southern Ontario, Canada," Hydrobiologia 91:121
(1982).
80. A. O. Davis, J. N. Galloway, D. K. Nordstrom, "Lake acidifica-
tion: its effect on lead in the sediment oftwo Adirondack lakes,"
Limnol. Oceanogr. 27:163 (1982).
81. A. S. Lefohn, M. D. Marcus, B. P. Parkhurst, "Comments on
Work Group I Impact Assessment Final Report," prepared for
the Utility Air Regulatory Group, 1983.
82. Atlantic Salmon Review Task Force, Biological Conservation
Subcommittee Report, 1978.
83. R. W. Shaw, "Acid precipitation in Atlantic Canada," Environ.
Sci. Technol. 13:406 (1979).
84. R. W. Shaw, "Deposition of atmospheric acid from local and
distant sources at a rural site Nova Scotia," Atmos. Environ. 16:
337 (1982).
85. W. D. Watt, D. Scott, W. J. White, "Evidence of acidification
in some Nova Scotia rivers and of impact on Atlantic salmon,
Salmo Salar," Can. J. Fish. Aquat. Sci. 40:462 (1983).
86. J. Farmer, D. Swan, M. Baxter, "Records and sources of metal
pollutants in a dated Loch Lomond sediment core," Sci. Tot.
Environ. 16:131 (1983).
87. M. D. Marcus, B. R. Parkhurst, F. E. Payne, "An Assessment
of the Relationship among Acidifying Depositions, Surface
Water Acidification and Fish Populations in North America,"
prepared for the Electric Power Research Institute, EA Research
Project #1910-2,1983.
88. W. C. Retzsch, A. G. Everett, P. F. Duhaime, R. Nothwanger,
"Alternative Explanations for Aquatic Ecosystems Effects At-
tributed to Acidic Deposition," prepared for the Utility Air
Regulatory Group, 1982.
89. S. A. Norton, R. B. Davis, D. F. Brakke, "Responses of Northern
New England Lakes to Atmospheric Inputs ofAcids and Heavy
Metals," Land and Water Resources Center, University of Maine
at Orono, ME, 1981.
90. T. A. Haines, J. Akielaszek, "A Regional Survey of Chemistry
of Headwater Lakes and Streams in New England: Vulnerability
to Acidification," U.S. Fish and Wildlife Service, Kearneysville,
WV, 1982.
91. R. B. Davis, M. O. Smith, J. H. Bailey, S. A. Norton, "Acidifi-
cation of Maine (U.S.A.) lakes by acid precipitation," Verh. Int.
Verein. Limnol. 20:532-537 (1978).
92. A. S. Lefohn, M. D. Marcus, B. R. Parkhurst, "The Effects of
Acid Rain on Terrestrial and Aquatic Ecosystems—A Status
Report—A Review of the Joint Canadian and United States
Impact Assessment Report," prepared for the Utility Air Reg-
ulatory Gnoup, October 1982.
93. B. J. A. Brown, R. W. Brocksen, "An Analysis of the Relationship
between Acid Deposition, Surface Water Acidification, and Loss
of Fisheries," in Atmospheric Deposition, Air Pollution Control
Association, Pittsburgh, PA, 1983.
94. R. A. Linthurst, J. Baker, A. M. Bartuska, "Effects of Acidic
Deposition: A Brief Review," North Carolina State University,
Raleigh, NC, 1983.
95. W. A. Norvell, C. R. Frink, "Water Chemistry and Fertility of
Twenty-Three Connecticut Lakes," Bull. Conn. Agric. Exp. Sta.,
# 759, New Haven, CT, 1975.
96. W. T. Swank, J. W. Fitzgerald, "Microbial transformation of
sulfate in forest soils," Science 223:182-184 (1983).
97. P. M. Vitousek, P. A. Matson, "Mechanisms of nitrogen reten-
tion in forest ecosystems: a field experiment," Science 225:51-52
(1984).
98. D. W. Johnson, D. E. Todd, "Effects of acid irrigation on carbon
dioxide evolution, extractable nitrogen, phosphorus, and alu-
minum in a deciduous forest soil," Soil Sci. Soc. Am. J. 48:664
(1983).
99. R. A. Parnell, Jr., "Weathering processes and pickeringite for-
mation in a sulfidic schist: a consideration in acid precipitation
neutralization studies," Environ. Geol. 4:209(1983).
100. O. Grahn, H. Hultberg, "The neutralizing capacity of 12 different
lime products used for pH-adjustment of acid water," Vatten
31:120 (1975).
101. W. E. Johnson, A. D. Hasler, "Rainbow trout production in
dystrophic lakes," J. Wildlife Manag. 18:113(1954).
102. P. J. Dillon, N. D. Yan, W. A. Scheider, N. Conroy, "Acidic lakes
in Ontario, Canada: characterization, extent and responses to
base and nutrient additions," Arch. Hydrobiol. Beih. Ergn.
Limnol. 13:317 (1979).
103. B. Bengtsson, W. Dickson, P. Nyberg, "Liming acid lakes in
Sweden," Ambio 9:34 (1980).
104. J. Fraser, D. Hinckley, R. Burt, R. R. Severn, J. Wisniewski, "A
Feasibility Study to Utilize Liming as a Technique to Mitigate
Surface Water Acidification," Report No. 1238-03-81-CR,
General Research Corporation, McLean, VA, 1981.
105. L. B. Resnick, "Mathematics and science learning: a new con-
ception," Science 220: 477 (1983).
Dr. Lefohn is President and Founder of A.S.L. & Asso-
ciates, 111 North Last Chance Gulch, Helena, MT 59601. Dr.
Brocksen is Director of the Wyoming Water Research Center
and Professor of Zoology at the University of Wyoming.
October 1984 Volume 34, No. 10 1013