vvEPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
EPA-
May
600 3-80-044
1980
Research and Development
Impacts of Airborne
Pollutants on
Wilderness Areas
Along the
Minnesota-Ontario
Border
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RESEARCH REPORTING SERIES
Research reports of the Office ct Researon and Development U S Environmental
Protection Agency have been grouped into nine series These nine broad cate-
gories were established to lac'hta'e further development and application of en-
vironmental technology Elim nation of traditional grouping was consciously
planneo to ?oster technology tra::sfer and a maximum mterface in related fields
The nine series are
1 Environmental Heailr Effects Research
Env ron ne'>tai Protec^on Technology'
Ecological Research
Environmental Monitorinq
Socioeronomic En^'Onmental Studies
3c'e-!t'f ; jr '1 r-c'in>i,ai Assessment Reports (STAR)
interage-.: y Energy-Environment Research ana Development
Speoia: Reports
Mi3f>?Hanecus Fieo('r!s
This report has been assigned to the ECOLOGICAL RESEARCH series This series
describes reseaicri on the effects of pollution on humans, plant and animal spe-
cies, and materials Problems are assessed for their long- and short-term influ-
ences Investigations include formation transport and pathway studies to deter-
mine the fate ot pollutants and their effects This work provides the technical bas s
for setting stancards to minimise undesirable changes in living organisms in the
aquat.c terrestnal and atmospheric environments
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United States Environmental Research EPA-600 380044
Environmental Protection Laboratory May 1980
Agency Duluth MN 55804
Research and Development
&EPA Impacts of Airborne
Pollutants on
Wilderness Areas
Along the
Minnesota-Ontario
Border
-------
RESEARCH REPORTING SERIES
Research reports of trie Office ot Research arid Development U S Environmental
Protection Agency have been grouped into nine series These nine broad cate-
gories were established to tac'htate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to toster technology 'ranker and a maximum interface in related fields
The Cine series are
1 Environmental He. aitn Effects Research
2 Env.ronmeMai Protect on Tecnnoiogy
3 E c c! c ;'j > i' a I R e search
4 Environmental Monitoring
5 Soci^eoonomic E:,,' r )nmental Studies
6 Sc'er-'itu ar'd TVciinu:ai Assessment Reports (STAR)
•7 Interface- ,< Energy-Environment Research and Development
8 Special ReooHb
9 Miscellaneous Reocns
This report has been assigned to the ECOLOGICAL RESEARCH series This series
describes research on the effects of pollution on humans plant and animal spe-
cies, and rnatena.s Problems are assessed for their long- and short-term influ-
ences Investigations mcluae formation transport and pathway studies to deter-
mine the fate o* pollutants and the^r ejects This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic terrestrial and atmospheric environments
-------
&EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
EPA-GOO 3-80-044
May 1980
Research and Development
Impacts of Airborne
Pollutants on
Wilderness Areas
Along the
Minnesota-Ontario
Border
EP 600/3
-------
EPA-600/3-80-044
May 1980
IMPACTS OF AIRBORNE POLLUTANTS ON WILDERNESS AREAS ALONG THE
MINNESOTA-ONTARIO BORDER
Edited by
Gary E. Glass
Environmental Research Laboratory-Duluth
and
Orie L. Loucks
The Institute of Ecology-Indianapolis
Project Coordinator
Gary E. Glass
Environmental Research Laboratory-Duluth
Duluth, Minnesota 55804
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
DULUTH, MINNESOTA 55804
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory-
Duluth, U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commerical products does not constitute endorsement
or recommendation for use.
11
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FOREWORD
Many of the objectives that drive efforts to improve our environment are
local in nature and can be viewed as improvements in the quality of life.
For example, the opportunities to swim in rivers and lakes, to catch sport
fish in a beautiful lake, or to camp in a wilderness area are certainly
valuable. But these objectives are not necessary for our biological
requirements.
Other efforts for environmental protection are driven by the necessity
to sustain the very existence of mankind. Examples of such efforts are the
protection of the ozone layer, preservation of our soil for food
productivity, the maintenance of our forest lands for production of wood
products, and the protection of terrestrial vegetation to assure gas balance
in the atmosphere.
This report presents evidence to suggest that the deposition of
atmospheric pollutants is not only threatening a huge, beautiful wilderness
area of the continent, but is also giving rise to another large geographical
area where forests may be endangered for wood production and sustaining the
atmospheric life-supporting systems.
Donald I. Mount, Director
Environmental Research Laboratory
Duluth, Minnesota
ill
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ABSTRACT
The goal of this study was to examine previously unanswered questions
concerning potential effects of the proposed Atikokan, Ontario power plant on
ecosystems in the Boundary Waters Canoe Area Wilderness (BWCA) and Voyageurs
National Park (VNP) of Minnesota by using the most relevant data and
analytical methods. The principal steps were to focus on: (1) the ultimate
deposition of emissions from the plant (rather than only on pollutant
concentrations), (2) the use of a time-varying grid model with provision for
atmospheric transformations, and (3) a detailed review of all available data
from the region on atmospheric deposition of pollutants, water quality, and
effects. The results are considered in relation to a review of responses by
terrestrial and aquatic organisms to changes in the chemistry of this
environment.
The sensitive aquatic and terrestrial receptors in the BWCA-VNP region
are described quantitatively, and this information is assessed in terms of
what is currently known about the impacts of atmospheric pollutants.
Specific conclusions based on factual information, probable consequences, and
possible impacts of the proposed coal-fired power generating station at
Atikokan are presented.
The study supports, in part, the conclusions reached previously
concerning the predicted air concentrations of sulfur dioxide, but differs
significantly with the conclusions concerning the significance of future
impacts. When, the total emissions from the proposed power plant are
considered, the increased loadings of sulfuric and nitric acids, fly ash, and
mercury as an addition over and above other regional sources will, with high
probability, have significant consequences for the sensitive receptors in the
BWCA-VNP region, especially for the future of sport fisheries and other
aquatic resources.
IV
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CONTENTS
Foreword iii
Abstract iv
Figures vii
Tables ix
Acknowledgments x
1. Introduction 1
Background 1
Uniqueness of the BWCA 3
Structure of the study 5
2. Summary of Results and Conclusions 6
Air-Quality Impacts 6
Conclusions of fact 6
Probable consequences 7
Terrestrial Impacts 7
Conclusions of fact 7
Probable impacts 8
Possible impacts 9
Aquatic Impacts 9
Conclusions of fact 9
Probable impacts 10
Possible impacts 11
3. Air Quality in the Boundary Waters Canoe Area (BWCA) 12
Introduction 12
Background Air-Quality Data Near the BWCA 14
Atikokan Emissions 16
Atmospheric Dispersion, Transformation, and Deposition ... 18
Plume chemistry 19
Dry deposition 20
Wet deposition 20
Description of the Three-Dimensional Dispersion Model .... 27
Model formulation 27
Numerical solution of the plume model 31
Meteorological data used in the model 33
Plume Model Results for Atikokan 35
Atmospheric loadings in the Quetico area 45
Validation of the Model 46
Summary Discussion of the Atikokan Modeling Results 48
4. Potential Effects of Coal-Combustion Emissions on the Terrestrial
Biota of the BWCA 49
Introduction and Goals 49
Biological and Temporal Characteristics of the Boundary
Waters Canoe Area 50
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Plant community types 50
Long-term stability of the BWCA landscape 54
Biotic Responses to Coal-Fired Power-Plant Emissions 55
Residuals of concern 57
Conifers (pines) and aspen 59
Lichens and Bryophytes (sphagnum) 65
Arthropods (insects) 69
Amphibians 73
Soils 73
Nutrient Cycling 79
Influence of affected trees on insect populations 82
Bioaccumulation 83
Application of Research Findings to the Boundary Waters Canoe Area 90
Significance for pines 91
Significance for lichens 91
Significance for insects 92
Potential for the bioaccumulation of toxic materials .... 92
Significance for nutrient cycles 93
Lake and watershed chemistry in relation to BWCA soils ... 93
5. Impacts of Acidification on Aquatic Ecosystems of the Boundary
Waters Canoe Area (BWCA) and Voyageurs National Park (VNP) .... 98
Introduction 98
Characteristics of Lakes Vulnerable to Acidification .... 99
Physical factors in the characterization of vulnerable
lakes 99
Chemical characteristics and responses of vulnerable
lakes 104
Atmospheric acidification of BWCA-VNP lakes 106
Impacts Upon Aquatic Communities 113
Effects on microbiota 117
Effects on benthic plants 119
Effects on phytoplankton 121
Effects on invertebrates 121
Effect on vertebrates-fish 123
Effects on other vertebrates 127
Summary 127
References 129
Appendices
A. Wet Removal Rates for S02 Gas and S0£ Aerosol 154
B. Simple Model Calculations of Emissions Applied to Atikokan .... 167
C. Representative Analysis of Coal and Fly Ash for Major and Trace
Components 172
D. Data Pertinent to the Aquatic Ecosystems of the Boundary Waters
Canoe Area 173
VI
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FIGURES
Number Page
1 Map of the study area showing grid for computer model ......... 13
2 Qualitative description of synoptic situations envisioned for
the model .............................. 22
3 Washout ratio as a function of precipitation rate. Curve 1
represents predictions for intense convective storms or from
clouds where tops are warmer than 0°C; curve 2 represents
predictions for storms where rain develops without the
assistance of an ice-growth stage; curve 3 is for storms where
the ice-growth process is necessary for initiating precipitation . . 25
4 Sulfate concentrations in surface precipitation at Pennyslvania State
University, September 1976 through January 1978. The curve is
an eyeball fit to individual data points .............. 26
5 Schematic diagram of the parameters used in the grid model ...... 28
6 Computed annual average concentrations due south of Atikokan
for SC>2> SO^, fly ash, and mercury ................. 38
7 Computed 24-h worst-case concentrations due south of Atikokan
for S02> S0£, fly ash, and mercury ................. 39
8 Computed 3-h worst-case concentrations due south of Atikokan
for S02> SO^, fly ash, and mercury ................. 40
9 Computed annual and seasonal dry deposition flux due south of
Atikokan for SC^j SO^, fly ash, and mercury. There are only
two seasons: summer and winter. Summer is defined as the time
when the snow is not on the ground ................. 43
10 Computed annual and seasonal. wet deposition flux due south of
Atikokan for SC^, SO^, fly ash, and mercury. There are two
seasons: summer is rain, and winter is snow ............ 44
11 Results of the sensitivity tests of the grid model showing
the influence on SC>2 concentration for a worst-case day ....... 47
12 Distribution of vegetation types in the BWCA-VNP area and vicinity . . 53
vii
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13 Schematic diagram of regional material exchange system and
biological response processes that may be anticipated in response
to coal-fired power-plant emissions 56
14 General exchange relationships between pH and cations 78
15 Outline map of the areas of sensitive soils (shaded) within the
Kawishiwi Area Soils Map 94
16 Sample sheet of the soil map of the Kawishiwi Area showing
sensitive soil areas (shaded) and the location of six potentially
sensitive lakes (arrows) 95
17 Regions of North America containing lakes that are sensitive
to acidification by acid precipitation, based on bedrock geology.
Calcareous overburden will modify this picture somewhat 100
18 Rainy Lake drainage basin emphasizing major watershed areas and
river-flow patterns toward U.S./Canadian border lakes. Water-
flow direction of Lake Superior, Hudson Bay, and Lake of the
Woods watersheds is indicated 101
19 Profile of waters along the international boundary, Lake Superior to
Rainy Lake Reservoir 102
20 Park boundaries outlined on the Rainy Lake drainage basin. November
1978 EPA sampling sites 103
21 Percentage distribution of 85 BWCA-VNP lakes based on the water
alkalinity observed in November 1978 105
22 Relationship between pH and alkalinity in 85 BWCA-VNP lakes 108
23 Relationship between acid Loading and pH change for lakes in Sweden
in very sensitive and somewhat less sensitive surroundings .... 110
24 Effect of acid addition on the pH of water from selected BWCA-
VNP lakes 112
25 Relationship between frequency and mercury concentrations of walleye
and northern pike taken from selected BWCA-VNP area lakes .... 115
26 Regressions of log mercury concentration against total length for
brook trout sampled from acid drainage lakes and limed, seepage,
and bog lakes in the Adirondacks 116
Vlll
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TABLES
Number
1 Summary of Available Data on Air Pollutants in the Boundary
Waters Canoe Area and Adjacent Ontario 15
2 Atikokan Power Plant Emissions 17
3 Wind and Diffusivity Profiles 30
4 Model Parameters that are Species Dependent 34
5 Average Meteorological Data, International Falls, Minn., 1970-74 . 36
6 Number of Periods Per Year When the S02 Concentration in the
BWCA is Calculated to be in a Given Range due to the Atikokan
Plume 41
7 Virgin Upland Communities in the BWCA and the Importance of
Stands, Types, Species, and Families 52
8 Effects of S02 in Combination with Other Pollutants on Native
Vegetation 62
9 Summary of Native Insect Responses to S02 and Other Pollutants . . 84
10 Potentially Sensitive Headwater Lakes in the BWCA 97
11 The pH of Precipitation on the Laurentian Shield of Eastern North
America 107
12 Calcite Saturation Indices (CSl) for 85 BWCA-VNP Lakes 109
13 Snow-meltwater Enrichment by Dissolved Components - Concentrations
and Percentage of Total Mass Found in Melted Snow as a Function
of the Percentage Melted (Average of Three Sites in BWCA-VNP). . 114
14 Approximate pH at which fish in the LaCloche Mountain Lakes,
Ontario, Stopped Reproduction 126
IX
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ACKNOWLEDGMENTS
Air Quality and Modeling
This section was written primarily by Dr. K. W. Ragland (University of
Wisconsin-Madison) and Dr. B. C. Scott (Battelle, Pacific Northwest
Laboratories). It does not indicate endorsement by EPA or Battelle. K.
Wilkening, C. Donovan, and H. Hull (University of Wisconsin-Madison) did much
of the computer work. The cooperation of J. Bowman (Minnesota Copper-Nickel
Study) was most helpful.
Terresterial Impacts
Edited by S. S. Smith and 0. L. Loucks, University of Wisconsin-Madison,
and E. Preston, EPA Laboratory, Corvallis, Oregon from contributions provided
by a panel including J. Bromenshenk, University of Montana, Missoula; J.
Chilgren, EPA Laboratory, Corvallis, Oregon; S. Eversman, Montana State
University, Bozeman; C. C. Gordon, University of Montana, Missoula.
Additional help was provided by J. Lieberman and B. Patterson of the Minnesota
Copper-Nickel Study Group and P. Juneau, Environmental Research Laboratory-
Duluth.
Aquatic Impacts
Edited by J. Eaton, Environmental Research Laboratory-Duluth, and B.
Coffin, Minnesota Department of National Resources, from contributions provided
by a panel including E. Gorham, University of Minnesota, Minneapolis; H.
Harvey, University of Toronto, Toronto, Ontario; G. R. Hendrey, Brookhaven
National Laboratory, Upton, N.Y.; D. W. Schindler, Freshwater Institute,
Winnipeg, Manitoba; C. L. Schofield, Cornell University, Ithaca, N.Y.; G. E.
Glass, L. J. Heinis, L. Anderson, C. Sandberg, T. Roush, J. Use, J. Rogalla,
S. Kohlbry, and M. Brilla, Environmental Research Laboratory, Duluth,
Minnesota; S. Eisenreich, University of Minnesota, Minneapolis; and members of
the Minnesota Copper-Nickel Study Group.
1978 Data Report (Appendix D) - and Manuscript
Compiled by G. E. Glass, L. J. Heinis, L. Anderson, F. Boettcher, C.
Sandberg, B. Halligan, and T. Roush, with acknowledgments of assistance from
the staff of the following organizations:
USEPA Environmental Research Laboratory-Corvallis, D. Krawczyk
USEPA Environmental Research Laboratory-Duluth, T. Highland, P. Gray, and
B. Halligan
USDA Forest Service-Duluth, J. M. Ramquist, E. Marsolek, and B.
Dovenmuehl
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Freshwater Institute Winnipeg
Minnesota Pollution Control Agency, J. Pegors and T. Musick
University of Wisconsin-Madison, A. Andren
University of Minnesota-Duluth, Lake Superior Basin Study Center
Laboratory
USDC Voyageur's National Park Director
Comments and suggestions contributed by manuscript reviewers; W. Dickson,
W. R. Effer, J. H. Gibson, D. Lang, G. E. Likens, C. S. Mathias, J. Moody, G.
Robitaille, B. Smith (reviewer and editor), and R. F. Wright are gratefully
recognized. The reviewers are, of course, not responsible for any data or
information contained in the report.
XI
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SECTION 1
INTRODUCTION
The Boundary Waters Canoe Area Wilderness (BWCA), a wilderness unit
within the Superior National Forest (Minnesota) and located along 176 km (110
miles) of the Minnesota-Ontario border, occupies 439,093 ha (1,085,000 acres)
of characteristic northwoods terrain. The area varies from 16 to 48 km (10
to 30 miles) in width. Over 1,900 km (1,200 miles) of streams, portages, and
foot trails connect the hundreds of pristine, island-studded lakes that make
up approximately one-third of the total area. Few wilderness areas have been
the focus of as much persistent concern for protection from human impacts as
has the BWCA.
The 1976 proposal by Ontario Hydro to build and operate a major
coal-fired power plant north of the Quetico-BWCA wilderness complex has led
to concern that air quality and ecosystems in the area could be inadvertently
degraded, in spite of the years of effort and the legislation designed to
protect them. Because of the important natural resources represented by the
waters, forests, and air of the BWCA, many individuals, legislators, and
environmental organizations have been concerned with possible deficiencies in
the available data, methodology, and scope of the assessments carried out
since the plant was first proposed. These concerns have led to the decision
by the U.S. Environmental Protection Agency, in cooperation with State
agencies, universities, and other Federal agencies, to proceed with the
present comprehensive study of potential impacts on the biota, air, and
water. Additional data and new analytical tools, including a grid model that
computes pollutant transformation and deposition, were available and
appropriate for a second-level analysis.
BACKGROUND
Ontario Hydro, a crown corporation established by the Ontario govern-
ment, requested in 1976 and received in 1977 Provincial approval to build an
800-MW, coal-fired electric generating station near Atikokan, Ontario. The
site is approximately 20 km (12 miles) from the northern boundary of Quetico
Provincial Park and about 55 km (38 miles) from that portion of the
U.S.-Canadian border which forms the northern edge of the BWCA in Minnesota.
Criticism of the project from Canadian and U.S. environmental
organizations and individual scientists has centered on the proposed plant's
proximity to the Quetico-BWCA wilderness complex, and on the omission from
the structure of any scrubber technology. Concern also has been addressed to
the Ontario Hydro environmental analysis document, which, critics said,
failed either to give substantial evidence for its claim that no vegetation
damage would result from S02 emissions or to treat adequately the problems
of acid precipitation and deposition of pollutants in the Quetico-BWCA
environment.
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The Atikokan facility is to be staged in four 200-MW units, one of which
is to be in service during 1984. The boilers for these units would burn
either low sulfur subbituminous coal from Alberta or lignite from
Saskatchewan. The proposed facility would feature electrostatic
precipitators to control particulate emissions, but no scrubbers would be
used to minimize SC>2 emissions. Planning for the Atikokan generating
station began in 1974; in 1976 Ontario Hydro published an environmental
analysis and supplementary report dealing with the project. The regulations
of the recent Environmental Assessment Act of Ontario were not applied
retroactively to the Atikokan generating station.
United States-Canadian international negotiations on the Atikokan plant
began in August 1977. At that time the Canadian participants agreed to
provide the U.S. Department of State with additional information for a more
precise evaluation of the project's potential transboundary effects.
Technical studies were undertaken in each country of the S02 concentrations
expected to originate from this plant. The results were exchanged in late
December 1977. With the additional Canadian information and in consultation
with the Department of State, the U.S. Environmental Protection Agency
proceeded with its initial review of the Atikokan proposal.
During this period Minnesota congressional representatives and several
environmental organizations urged the Department of State to ask Canadian
officials (1) to refer the matter to the International Joint Commission
(IJC), with a moratorium on plant construction (to allow a comprehensive
study of the plant and its impacts), or (2) to ask for installation of the
best available scrubbers (90% efficient) similar to those already used
extensively in Minnesota for new sources.
The Department of State presented the results of the EPA initial review
at a second international negotiations meeting held on January 11, 1978. The
EPA review included a literature survey on acid rain problems and projections
of S02 dispersal based on the standard Gaussian plume dispersion model.
At this January meeting the U.S. team noted that results of both
Canadian and U.S. modeling studies indicated that the concentrations of S02
entering the BWCA from the Atikokan plant occasionally may be in excess of
the Class I air quality standards permitted under the U.S. Prevention of
Significant Deterioration Criteria. (Covering classified wilderness, Class I
is the most stringent standard.) Also using the studies from both countries,
the Canadians concluded at the January meeting that the predicted
transboundary impact of S02 emissions from the Atikokan generating station
was below the threshold at which injurious environmental effects are known to
occur. Canadian officials confirmed that the plant would meet all Canadian
environmental requirements.
The U.S. negotiating team initially requested the installation of 50-
percent-efficient scrubbers. The Canadian representatives indicated that
they could not, at that time, accept such a requirement. The negotiators
then focused on discussing a referral to the IJC'that would not include a
construction moratorium, but would feature a program to monitor effects of
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the plant. The Department of State submitted proposed wording for such an
IJC reference, and the Canadian Office of Foreign Affairs agreed to consider
the proposal.
The U.S. team, lead by officials of the Department of State, included
representatives from the State of Minnesota, the Environmental Protection
Agency, and the USDA Forest Service, which manages the BWCA. The Canadian
team, headed by officials from the Bureau of USA Affairs of the Department of
External Affairs, included representatives of the Province of Ontario,
Environment Canada, the Canadian Embassy in Washington, and the Canadian
consulate in Minneapolis.
On February 22, 1978, some members of the U.S. negotiating team met in
Chicago to discuss additional potential air quality impacts such as acid
fallout. Also present were staff of the EPA Office of International
Activities, EPA Region 5; scientists from the EPA Environmental Research
Laboratory-Duluth (Minnesota), and Environmental Research Laboratory-
Corvallis (Oregon), and several universities; and representatives from
conservation organizations (National Parks and Conservation Association,
Friends of the Boundary Waters Wilderness, and National Clean Air Coalition).
At this meeting the data, methodology, and scope of the initial EPA study
were reviewed in detail, especially the following: (1) the lack of realistic
simulation of meteorological and chemical transport and deposition processes
by a Gaussian plume model over the distance involved in the Quetico-BWCA
study; (2) the omission of data on existing conditions covering sensitive
water quality, water-flow direction, and high mercury levels in fish; and (3)
the necessity that contributions made by the Atikokan plant be assessed
against present background levels and all planned future sources in the area.
The consensus of those attending was that the Atikokan generating station had
the potential to be a significant addition to the pollutants in the BWCA area
for both air and water and that a much more comprehensive study to assess its
significance should be undertaken.
On March 20 the Canadian Embassy issued a diplomatic note rejecting any
International Joint Commission reference, citing as its reason "the lack of
indiction of any potential injury" to the U.S. side, such injury potential
being "the traditional basis for considering transboundary pollution
questions" by the IJC. The Canadian team also concluded that since the
existing studies predicted that concentrations of the pollutant of major
concern in the United States, sulphur dioxide, would be far below injurious
levels, there was no basis for considering the installation of scrubbers.
Subsequently, the U.S. Environmental Protection Agency agreed to support
a limited additional study of potential impacts of the proposed Atikokan
power plant, for which this report details results. This latest study was to
be supported also in part by the Department of State; the USDA Forest Service;
and the Minnesota Pollution Control Agency; and was to be coordinated by the
EPA Environmental Research Laboratory-Duluth.
UNIQUENESS OF THE BWCA
The Boundary Waters Canoe Area has been recognized as a unique resource
for many decades. In 1930 the Shipstead-Newton-Newland Act was passed to
3
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protect its shorelines and water levels from dam building and drainage. In
1948 passage of the Thye-Blatnik Act allowed condemnation and purchase by the
Federal government of private lands in the "roadless area," as it was then
called. President Truman issued an air ban in 1950, stopping the floatplane
flights into the "roadless area" which had allowed over-fishing of many
lakes. The 1964 Wilderness Act designated the Boundary Waters Canoe Area as
part of the National Wilderness Preservation System, thus recognizing it as a
national resource of outstanding quality that should be preserved in an
unimpaired condition so that the forces .of nature rather than those of man
could predominate. The act contained specific provisions allowing certain
logging and motorized activity within portions of the BWCA, but otherwise
mandated specific wilderness protection. Recently passed legislation in the
1977-78 Congress now further limits nonwilderness uses of the BWCA.
It is difficult to describe adequately the BWCA's significance to the
American public as a conservation, scientific, and recreation resource for
the present and future. It is the only lakeland canoe unit of the U.S.
wilderness system and one of the system's largest units of any kind.
Embracing the largest remaining virgin forest in the east, it attracts more
recreationists than any other wilderness area in the nation and lies within
2 days' travel of nearly 50 million people. As the last large, unmodified
northern coniferous forest ecosystem in the eastern United States, it has
become the focus of much education and demonstration management in wilderness
ecology, animal behavior, vegetation history, nutrient cycling, and aquatic
ecosystems.
The attraction of the area appears to be not any single factor, but a
combination of related ones: fishing and camping in a sought-for atmosphere
of wild, unpolluted landscape. However, the evergreen forests, clear water
and air, rock outcrops, and shallow soils that are the conspicuous
ingredients of the BWCA landscape are all also unusually sensitive to
regionally transported pollutants. The expansive and relatively unspoiled
terrestrial and aquatic ecosystems in the BWCA are the major reasons for its
recognition as a unique resource in the United States. This recognition and
uniqueness have led to a protective degree of legislative and citizen
vigilence, and, indirectly, to recent monitoring of air quality in
northeastern Minnesota. Since August 8, 1977, the BWCA has been protected by
U.S. Clean Air Act amendments that guarantee maximum "Class I" protection for
parks and wilderness areas. The intent of a Class I status is to assure
long-term maintenance of air quality over an area at essentially the 1974-75
levels. Class I applies to areas such as the BWCA in which practically any
change in air quality would be regarded as signficant.
Complementing the BWCA is Ontario's adjacent Quetico Provincial Park,
453,258 ha (1,120,000 acres) where logging, snowmobiles, and motorboats are
banned. In 1973 the Ontario Provincial Government determined that Quetico
did not fit into any of the usual classifications for provincial parks and
declared it a "primitive wilderness." The importance of the BWCA to the
United States has been greatly augmented by the forward-looking decisions
made by Canadians in regard to the Quetico Park, established simultaneously
in 1909 with the Superior National Forest to create an international
sanctuary. Approximately 90% of the people who visit and enjoy the resources
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of Quetico are U.S. citizens, and over the years the Quetico-Superior (BWCA)
area has come to be viewed as a single air, water, biological, and
recreational resource.
STRUCTURE OF THE STUDY
This study has been structured to capitalize on, rather than duplicate,
any of the previous assessments of the Atikokan power plant. New data and
modeling approaches were available from two major energy-impact studies
sponsored by the EPA, and results of an intensive study in the northern
Minnesota area by the State of Minnesota also were becoming available. These
results, together with the previously available literature, could be used in
conjunction with the issues identified during reviews of the previous
assessments to set a new standard of analysis and evaluation.
Thus, the analysis and assessment process incorporated in this report is
divided into three areas: (1) air-quality modeling (with multiple modeling
approaches for predicting air-pollutant concentrations and deposition); (2)
terrestrial effects (emphasizing transformation products of the S02 and the
receptors within the BWCA); and (3) aquatic effects (considering acid inputs,
due to all substances leaving the stacks at Atikokan, as well as existing
conditions including high levels of mercury in fish and water flow to the
border from both countries). Each area involved participants from the two
principal research sites, Madison (Wisconsin), and Colstrip (Montana), and
other technical consultants and required the assessment data from sources
throughout the region.
The task of the air-quality modeling group was (1) to determine what can
be predicted regarding the route and deposition of the proposed emissions in
the region, by using a regional grid model with provisions for chemical
transformations and deposition; (2) to draw together information on current
background levels of air pollutants and all of the emission sources in the
northwestern Minnesota region and adjacent Canada; and (3) to model all
current and proposed emissions so that the contribution of all regional
inputs could be analyzed in relation to the total loadings in the region.
The goals of the groups studying terrestrial and aquatic effects were
(1) to characterize the sensitivity of the components of the terrestrial and
aquatic ecosystems to the gaseous and particulate pollutants; and (2) to
summarize research results available on the responses of sensitive species as
well as to summarize the overall sensitivity of these associated ecosystems
to the current and expected levels of pollutants reaching the BWCA.
The assessment by these groups proceeded around two principal workshops
and the preparations and follow-up for each workshop. Materials were
prepared for study prior to a problem-definition workshop on each of the
three tasks (held in April 1978). Detailed data summaries and first drafts
of the final reports were prepared during the spring and early summer,
leading to an assessment workshop (August 1978) where the findings of the
model output, assessment of existing conditions, and a review of existing
literature were evaluated by participants from all groups.
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SECTION 2
SUMMARY OF RESULTS AND CONCLUSIONS
The goal of this study was to use the most relevant data and analytical
methods to examine previously unanswered questions of potential effects from
the Atikokan power plant on ecosystems in the Boundary Waters Canoe Area
(BWCA) and Voyageurs National Park (VNP) of Minnesota. The approach has
been to focus on the ultimate deposition of emissions from the plant (rather
than only on pollutant concentrations), to use a time-varying grid model with
provision for atmospheric transformations, and to review in detail all
available data from the region on atmospheric deposition of pollutants and on
water quality. The results are considered in relation to a review of
responses by terrestrial and aquatic organisms to changes in the chemistry of
this environment.
The study supports, in part, the conclusions reached previously
concerning the predicted air concentrations of sulfur dioxide, but differs
significantly with the conclusions concerning the significance of future
impacts. When the total emissions from the proposed power plant are
considered, the increased loadings of sulfuric and nitric acids, fly ash, and
mercury as an addition over and above other regional sources will, with high
probability, have significant consequences for the sensitive receptors in the
BWCA-VNP region, especially for the future of sport fisheries and other
aquatic resources. Additional research will be required to specify these and
other possible impacts in detail.
AIR-QUALITY IMPACTS
A time-varying grid model has been developed and applied to the plume
from the proposed Atikokan generating station. Preliminary validation steps
on the model have been carried out, and a number of outside reviewers have
examined the model assumptions and output. Within the limits of the
available data and the design specifications available to the study, the
model performance provides a basis for reasonable confidence in the projected
concentrations and deposition fluxes.
Conclusions of Fact
1. By using the coal type (western Canadian), sulfur content (0.8%), ash
content (12%), and operating conditions agreed upon by previous
assessment studies, the emissions from the 800-MW Atikokan generating
station were computed to be 70,307 metric tons/yr (77,500 tons/yr) of
sulfur dioxide, 2,358 metric tons/yr (2,600 tons/yr) of fly ash, 41,630
metric tons/yr (45,900 tons/yr) of nitrogen oxides, and 0.9 metric
tons/yr (1 ton/yr) of mercury. Other volatile components of coal, such
-------
as fluoride, arsenic, selenium, etc., will be emitted, and the amounts
will vary depending on the source of coal.
2. The plume from the proposed Atikokan generating station will be carried
over the BWCA by NW to NE winds persisting for 3-6 h. For the base
study-year, 1964, such conditions occurred during 49 time-periods, which
totaled 910 h or 10.3% of the year.
Probable Consequences
1. Model computations indicate that emissions from the proposed Atikokan
stack reaching the 80-120 km BWCA region contained in the 35° south sector
will increase atmospheric deposition of sulfate by about 0.9-1.4
kg/hectare-year (ha-yr), fly ash by 18 g/ha-yr, and mercury by 0.0016
g/ha-yr. These values will be added to the present 7-yr average atmospheric
loading of 11 kg/ha-yr for sulfates. Fly ash deposition in the region has
not been measured, and mercury deposition based on snow cores is at most
0.013 g/ha per snow season.
2. The planned operation of the Atikokan facility represents a potential 30
percent increase over probable unbuffered acid deposition even after the
prospective closing of the Steep Rock iron ore processing facility. If
the iron mining operation is closed, and only half of the Atikokan
generating station is constructed (400-MW), unbuffered acid deposition in
the BWCA is expected to increase by 15 percent.
3. The grid-model computations indicate that the 3-h S02 concentration
would exceed the U.S. air-quality Class I regulations for protection of a
wilderness area two times per year; the 24-h standard would be exceeded
three times per year. The annual average S02 standard would not be
exceeded.
4. Two-thirds of the particulate matter reaching the BWCA from the Atikokan
plume will be as SO^ rather than fly ash; and most of the sulfate
deposition in the region will have been deposited initially as S02,
followed by transformation in situ.
5. Approximately half of the SC^-plus-SO^ and fly ash and two-thirds of
the mercury deposition will occur during the snow season.
6. The amount of sulfur leaving the 100-x 100-km region by atmospheric
transport would be as much as 70% of the total emitted from the proposed
Atikokan power plant.
TERRESTRIAL IMPACTS
Conclusions of Fact
1. The terrestrial ecosystems of the BWCA and VNP are dominated by
short-season species, two of which, white pine (Pinus strobus) and
trembling aspen (Populus tremuloides), are known to be particularly
sensitive to the gaseous emissions of coal-fired generating stations.
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The white pine is the largest and most long-lived of species in the BWCA
(a lifespan often over 250 yr), and is essential to the lake-edge and
skyline features.
2. Soils of the BWCA-VNP region are mostly shallow (0-46 cm), of glacial
origin, coarse textured, derived from granites and other acid bedrock
types, low in cations and available nitrogen, and low in percentage base
saturation.
3. Geochemical weathering of rocks and soils has, throughout the earth's
history, been dominated by the weak carbonic acid formed from carbon
dioxide and water. The nitric and sulfuric acid components of
atmospheric deposition now being measured in the BWCA-VNP are sufficient
to modify the normal carbonic acid weathering of these soils and create a
geochemical cycle in which dilute nitric and sulfuric acid are
important.
4. A number of lichen species are among the plants that are most sensitive
to gaseous coal-combustion emissions and acid particulates. Lichens are
an important part of the BWCA-VNP biota and make up the principal plant
cover on 5% of the land area. Lichen species also have been shown to be
an important source of nitrogen (through N fixation) in a number of
nitrogen-limited coniferous forest areas.
5. A number of insect groups with strong sensory systems, particularly
saprophagous and predaceous beetles, social bees (pollinators), and
parasitic wasps, have been shown to be reduced in abundance at very low
concentrations of air pollutants, apparently because of pollutant
avoidance or disorientation. Several plant-feeding insect groups have
been shown to increase rapidly when the activity of parasites or
predatory control insects is reduced, or the vigor of host-plant species
is reduced, both of which have been shown to occur from gaseous pollutant
emissions.
Probable Impacts
1. Given what is presently known on mobilization of toxic elements by acid
fallout, the increase in fallout of sulfuric and nitric acid deposition
from operation of the Atikokan generating station must be viewed with
considerable concern. Some of the mobilized elements are toxic to
terrestrial vegetation after relatively small changes in concentration
are induced by additional acid fallout. The projected additions of H+
through nitrate and sulfate represent an increase of more than 25% over
the presently unbuffered atmospheric acid deposition and appear likely to
exceed soil buffering capacities. These mechanisms lead to effects, as
well, on small lakes that could begin to receive increasing amounts of
nutrient and toxic elements within a few years. Detailed watershed
geochemistry and mass balance studies will be required to document such a
response.
2. Small additions of acidity to the thin, rocky soils common in the BWCA,
coupled with the geochemical weathering changes that are probable, can be
expected to have relatively rapid and irreversible effects on outputs
8
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from the nutrient cycles of these ecosystems. These changes will affect
groundwater quality and produce soil-mediated changes in cycling rates
within the ecosystems. Although the net changes in cation leaching due
to lowered soil pH are difficult to predict, H+ additions to some soils
will facilitate leaching of essential plant nutrients.
Possible Impacts
1. The projected ambient concentrations of total suspended particulates,
S02> ozone, and acid particulates from the proposed Atikokan plant may
directly affect the growth and reproductive rates of sensitive pine
species. The presence of phytotoxic elements by leaching of cations
could produce similar effects. The possibility of such effects increases
as other major point sources of gaseous emissions are developed in the
region. Over periods of 100-200 yr (the lifespan of much of the
vegetation) even small effects on growth rates affect survival of
the dominant species and could have important consequences on the
composition of the region's vegetation. Such plant responses could be
assessed as part of long-term watershed monitoring.
2. Although visible effects on lichens that would be measurable within 5 yr
are not anticipated at the projected pollutant levels, slowing of growth
rates for a number of species is probable and could change the species
composition over a period of a few decades, leading to detrimental
effects on nitrogen fixation.
3. The lower pH of the forest soils could amplify trace-element effects by
making these elements more available in the food chain, and hence in
small herbivores, fish, and birds at the top of the food chain.
Long-term monitoring will be needed to assess these effects.
4. Effects on insects at the proposed concentrations have not yet been
documented because work on the insect groups is sparse and has not
focused on the threshold for response. Additional emissions and higher
concentrations can be expected in the area in the next few years, and
effects are known for the concentrations expected in the future.
Mobilization of toxic elements through insect food chains to small
mammals and birds is possible. Since pollutant injury to sensitive pine
species also is possible, increased insect damage may occur. Additional
studies of the effects of low concentrations of S(>2 on the olfactory
systems of pollinating and parasitic Hymenoptera, predatory beetles, and
decomposer insects are urgently needed.
AQUATIC IMPACTS
Conclusions of Fact
1. The BWCA and VNP are in a region comparable in vulnerability to others
that have already been severely affected by acid precipitation in Europe
and North America. Most BWCA-VNP surface waters have a poor buffering
capacity, and many have a low pH (below 6.5) as well.
-------
2. Precipitation in the near vicinity of the BWCA-VNP is strongly acid on
occasion, and the mean annual pH of precipitation is near the level where
damage begins.
3. Atmospheric acid sulfate loadings in the near vicinity of the BWCA-VNP
are at levels associated with the onset of severe lake acidification in
Scandinavian countries.
4. Mercury levels in fish, which increase as lakes acidify, are already high
in some lakes in and near the BWCA-VNP.
5. Most of the area within a 100-km (62-mile) radius of Atikokan is in the
Rainy Lake watershed and drains into the international waters of the
BWCA, VNP, and Quetico lakes.
6. The varied, valuable fishery resource of the BWCA-VNP includes many
species that have been reduced or eliminated by acid precipitation
elsewhere in the United States and Canada.
7. Increased metal concentrations, sufficient themselves to cause problems,
often accompany reduced pH. As the pH is lowered, the forms of metals
present also become more toxic in most cases.
Probable Impacts
1. It is likely that vulnerable lakes in the BWCA-VNP and Quetico areas
(poorly buffered headwater lakes with small watersheds and shallow soils
of low buffering capacity) are already being affected by acidity from
atmospheric sources.
2. Although present atmospheric loadings of acid-producing material are
probably affecting some BWCA-VNP-Quetico lakes, additional loadings from
Atikokan will accelerate the rate of acidification in vulnerable lakes
and endanger other lakes not presently being acidified. Long-term
studies of lake-water and stream-water chemistry in the BWCA are needed.
Special attention should be given to accurate hydrological and chemical
budgets of inputs, outputs, and storage in ecosystems susceptible to
damage by acidification to define the timing and magnitude of the
effects.
3. Given the probable changes in the existing pH levels of lake water, we
can project likely responses in the aquatic biota: reduction in
decomposition of organic matter; undesirable accumulation of certain
nuisance algae; decreases in phytoplankton species numbers, diversity,
biomass, and production per unit volume; elimination of some species and
simplification of zooplankton communities; alterations in benthic plant
and animal communities; and the loss of fish species preceded by
reproductive failure. These changes will occur over different time
spans: for some lakes, several years; for others, several decades.
4. Likely increases in the acidity of the water will increase the severity
of seasonal events such as acid flushing in the spring due to snow melt.
Even moderately buffered lakes may form a shallow, but highly acid layer
10
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of water from acid meltwater. This condition will result in a reduction
in the variety of insect species emerging in the spring and cause death
of exposed fish embryos.
A reconnaissance survey of the biota and productivity at all trophic
levels should be carried out. It would be followed by detailed, long-
term monitoring of population dynamics and lake metabolism, with special
attention to organisms and processes sensitive to acidification, in a
series of lakes of differing sensitivity to acid precipitation. Studies
currently going on in Scandinavia and the Adirondacks can serve as
models.
5. Increased acidity is likely to result in detrimental levels of aluminum
and of other trace elements in the lake water by increasing leaching and
creating more toxic forms of these elements. Detailed studies of
precipitation chemistry in the BWCA-VNP are needed on a long-term basis
(10-20 yr) . Special attention should be given to loadings of acid,
sulfate, nitrate, and heavy metals to define these changes.
6. The projected additions of mercury and of acid to the Rainy River water-
shed are very likely to aggravate an existing problem of mercury levels
in fish tissues. Additional data will be required to define the precise
changes and sources.
Possible Impacts
1. Fish populations in the most susceptible lakes of the BWCA-VNP and
Quetico could be eliminated by acid precipitation. Some populations may
be lost within a few years, and in many other lakes within a few
decades.
2. The productivity and biotic diversity of the aquatic communities in these
lakes is likely to be severely reduced over a period of one to several
decades. Some of the most vulnerable lakes may already have experienced
reductions in pH levels and undergone corresponding biological changes.
The paucity of historical base-line data makes such an analysis very
difficult to perform at this time.
3. It is possible that these changes and others (e.g. ground-water quality),
will not be reversible within the foreseeable future, even if the acidity
of precipitation is substantially reduced.
11
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SECTION 3
AIR QUALITY IN THE BOUNDARY WATERS CANOE AREA (BWCA)
INTRODUCTION
Air quality in the BWCA of Minnesota can be degraded by a combination of
large emission sources within 80-160 km (50-100 miles) of the area and
long-distance transport of pollutants which are accumulated during certain
periods in the Midwestern United States and Canada. Degradation may occur by
increasing ambient air concentrations of air pollutants and by the resulting
flux of these pollutants to the ground either by dry deposition or by removal
via rain or snow.
The air-pollutant concentrations or deposition, or both, may cause
damage to vegetation and animal groups such as insects and degrade
visibility. The deposition fluxes potentially may cause damage to fish and
animals via the water and soil. If the concentrations and deposition rates
are low enough (i.e., within some theoretical assimilative capacity for the
region), no significant damage will occur. Since the BWCA is a U.S.
wilderness area, the most sensitive effects must be considered. To assess
the effects of future increased pollutant loadings and concentrations,
careful estimates of the emissions near the BWCA, the transport, and the
deposition are needed.
The objective of this section on air quality, therefore, is to develop
and utilize a grid-type model of air pollution dispersion to assess the
ambient air concentrations and deposition fluxes in the BWCA due to emissions
from the proposed Atikokan generating station. Attention will be focused on
sulfur dioxide, sulfate aerosol, total fly ash particulates, and mercury.
The study area contains the BWCA and the Quetico Provincial Park (Figure
1). The Atikokan generating station will lie 80-120 km north of the BWCA.
Sources of pollutant emissions due to present electric power generation,
mining activity, and industrial and municipal sources that may have an impact
on the BWCA are considered as regional contributors to the current air
quality and atmospheric loadings. Most of these sources are outside the grid
considered in this report.
The BWCA-Quetico area has a cool continental climate characterized by
short, warm summers and long, cold winters: mean annual temperature 2°C
(36°F); mean July temperature, 17°C (63°F); mean January temperature, -15°C
(6°F). The average annual precipitation is 71 cm (28 in.), 64% of which
occurs as rain from May through September, the growing season. Annual mean
snowfall is about 152 cm (60 in.), and the ground is usually snow covered
from mid-November to mid-April.
12
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The BWCA's landscape has a generally slight but locally rugged relief
left by preglacial erosion of the Canadian Shield. Elevations above sea
level range from 341 m (1,119 ft) at Crane Lake to 680 m (2,232 ft) in the
Misquah Hills; local differences in elevation range from 30 to 150 m. The
land is heavily wooded, and 16.7% of the BWCA consists of lakes and streams.
BACKGROUND AIR-QUALITY DATA NEAR THE BWCA
The BWCA currently has especially clean air. The available monitoring
data near the BWCA are summarized in Table 1. The Fernberg Road site,
presented in the table, is a remote site at the edge of the BWCA that has
been monitored by the Minnesota copper-nickel study. Monitoring data for
sulfur dioxide, suspended particulates, and bulk deposition are available
from February to December 1977 and ozone from May to December (Valentine,
Minnesota Pollution Control Agency, personal communication, 1978).
The sulfur dioxide levels at Fernberg during 1977 never exceeded the
threshold level of the instrument, which was 10 yg/m^ (4 ppb), and only
once exceeded this level during 1978.
The suspended particulate matter, as measured by a high volume sampler,
yielded an annual arithmetic average of 15 yg/nr* and an annual geometric
average of 11 yg/m . There were 53 days of data, taken approximately once
per week. The maximum 24-h reading was 66 yg/m , which occurred on May 1,
1977.
The ozone data were recorded at Fernberg for 5,384 h from May to
December 1977. The arithmetic average of all hourly values was 0.030 ppm,
and the geometric average was 0.027 ppm. The maximum hourly readings were
0.100 ppm and 0.101 ppm, which occurred during the afternoons of May 28 and
July 19, 1977.
Since the ozone concentrations are due to long-distance transport, it is
instructive to compare the Fernberg site with another site at Cloquet, Minn.,
west of Duluth. At Cloquet the ozone readings followed a pattern similar to
that at the Fernberg site, but were slightly lower. The peak reading on July
19 was 0.070 ppm rather than 0.10 ppm, for example. The highest reading was
0.097 ppm on August 20. The Cloquet site probably records lower ozone
readings than Fernberg because of scavenging of the ozone by local sources of
nitric oxide from automobiles.
The ozone measurements indicate that the Fernberg site is probably
representative of the region. It is assured that the SC>2 -and particulate
readings are representative. These data indicate that the ambient SC^ from
regional sources is converted to sulfates, or the SC>2 is deposited out
before it reaches the Fernberg site instrument. The total deposition of
sulfate (wet plus dry) measured by the Minnesota copper-nickel study south of
the BWCA was 10-15 kg/ha-yr during the 2-yr period 1976-78.
In addition, Ontario Hydro has monitored air and precipitation quality
at five sites near Atikokan. Continuous monitoring of S02> Og, and NOX
started in July 1975 (Ontario Hydro 1976). The Nym Lake site, which is
14
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TABLE 1. SUMMARY OF AVAILABLE DATA ON AIR POLLUTANTS IN THE BOUNDARY WATERS
CANOE AREA AND ADJACENT ONTARIO
Pollutant
Location
Level
recorded
Averaging
period
MINNESOTA (near BWCA)
S02
°3
03
Suspended
particulates
Bulk 804
deposition
Bulk 804
deposition
Fernberg Road3
Superior Nat'l Forest
Fernberg Road3
Superior Nat'l Forest
Cloquet, Minn.3
Fernberg Road3
Superior Nat'l Forest
BWCAb
Minnesota Copper-Nickel3
Project Area
< 10 Mg/m3
~ (4 ppb)
0.10 ppm
0.03 ppm
0.097 ppm
66 Mg/m3
15 Mg/m3
11 Mg/m3
1.5 kg/ha
10-15 kg/ha-yr
Individual hourly
readings Feb. -Dec. 197
Hourly maximum
May-Dec. 1977
Average May-Dec. 1977
Hourly maximum
May-Dec. 1977
24- hr maximum
Feb. -Dec. 1977
Annual arithmatic
average Feb. -Dec. 1977
Annual geometric
average Feb. -Dec. 1977
Average 304 snow
loading, 65 sites,
March 1978
Range 1976-78
ONTARIO (near Atikokan)
S02
°3
NOX
NOX
NOX
Bulk 804
deposition
Bulk 504
deposition
Nym Lakec
Nym Lakec
Nym Lakec
Nym Lakec
Nym Lake0
0.02 ppm
(50 Mg/m3)
0.10 ppm
0.01 ppm
0.03 ppm
0.10 ppm
Atikokan Region0 4 and 7
kg/ha-yr
Experimental Lakes'1 7-14 kg/ha-yr
Region (Kenora) (10.9 kg/ha-yr)
Hourly maximum
1975-76
Hourly maximum
1975-76
Summer average
1975
24-h maximum
1975
Hourly maximum
6/75-4/76
1971-77
Average
a Minnesota Pollution Control Agency (1978).
b Glass, G. E., L.
unpublished data
J. Heinis , L. Anderson, C
(1979).
. Sandberg, and
F. Boettcher,
c Ontario Hydro (1976).
d Schindler, D. W., unpublished data, ELA Research Station (1978).
15
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located 17 km SSW of the generating station site near the Quetico boundary,
is the most remote site from the Steep Rock mines and will be briefly
reviewed (see Table 1). The total deposition of sulfate measured at two
sites was 4 and 7 kg/ha-yr.
The minimum detectable SC>2 level of 10 ppb was observed for short
times on 25 different days, and the levels never exceeded 25 ppb (50 yg/m^)
during the 10-month period reported. Ozone levels reached maximum levels of
0.100 ppm on 2 consecutive days during July 1975 and were generally similar
to those at the Fernberg site. When the ozone was high, the sulfur dioxide
was usually not above threshold level of the instrument. The NOX levels
typically averaged 5 ppb during June and 10 ppb during July, August, and
September. On occasion the concentration reached an hourly value of 0.100
ppm; however, these high values did not correspond to either high 03 or
high S02 levels. It appears that the S02 is due primarily to local
mining activities, and that the 0^ levels are due to long-distance
transport. The elevated NOX levels may be due to local sources.
Measurements of bulk deposition of sulfate, wet-plus-dry fall, have been
carried out at three locations in the vicinity of the BWCA (Table 1). The
longest record, at the Experimental Lakes Area (ELA) lakes 180 km northwest
of Atikokan, shows an average recent sulfate deposition of 10.9 kg/ha-yr.
The average pH of the rainfall here during 1974-77 is 4.86. The
presettlement pH for rainfall in this area appears to have been 5.7 (cf.
carbonic acid equilibrium and data for 1955-56 shown by Galloway and Cowling
(1978). Data from the ELA show that 70% of the nitrate and sulfate in the
current rainfall is in a neutralized form. Thirty percent is in the acid
form, and the H+ ions were assumed to divide between SO^ and N03 on
a 2:1 ratio. This information yields an estimate of 7.6 kg/ha-yr of
neutralized sulfate and 3.1 kg/ha-yr of acid sulfate producing the net
depression in pH. Thus, depending on the historic potential of atmospheric
constituents to neutralize anthropogenic acid, presettlement loadings of
sulfate must lie between 0 and 7.6 kg/ha-yr. For purposes of further
comparison a value of 4 kg/ha-yr will be used.
ATIKOKAN EMISSIONS
The proposed Atikokan generating station consists of four 200-MW units
burning sub-bituminous or lignite coal from Saskatchewan with a sulfur
content not to exceed 0.8% and a maximum ash content of 12% .
Electrostatic precipitators for fly ash removal are to be employed. The
potential emissions were calculated with the assumption of an overall thermal
efficiency of 36% and a full load (Table 2). The emission factors were
obtained as follows. For sulfur dioxide 38S is the current EPA handbook
(EPA-AP-42) value for pulverized coal boilers. The sulfate emission factor
of 1.2 corresponds to the assumption that 2% of the sulfur is emitted
directly as sulfate. Mercury is assumed to go entirely up the stack
(Billings et al. 1973). The nitrogen oxide emission factor is based on the
Fry, R.J. (Manager of Air Pollution and Environmental Contaminants
Division, Environmental Protection Service, Ontario). Letter I.M.
Goklany, U.S. Environ. Prot. Agency, Region V, Chicago, Oct. 14, 1977.
16
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TABLE 2. ATIKOKAN POWER PLANT EMISSIONS3
Item
High
Low
Heating value (BTU/lb)
Sulfur content (% weight)
Ash content (% weight)
Mercury content (% weight)
Sulfur dioxide emission factor (Ib/ton)
Sulfate emission factor (Ib/ton)
Total particulate emission factor0 (Ib/ton)
Mercury emission factor (Ib/ton)
Coal rate (full load) (tons/h)
Sulfur dioxide emissions (g/s)
Sulfur dioxide emissions (tons/yr)
Sulfate emissions (g/s)
Sulfate emissions (tons/yr)
Total particulate emissions (g/s)
Total particulate emissions (tons/yr)
Mercury emissions (g/s)
Mercury emissions (tons/yr)
NOX emission factor (lb/lb6 BTU)
NOX emissions (g/s)
NOX emissions (tons/yr)
7,500
0.8
12.0
2 x 10~5
38 Sb
1.2S
0.085A
20Hg
583
2,230
77,500
67
2,325
75
2,600
0.029
1.01
1.2
1,323
45,900
6,500
0.4
6.5
2 x 10~5
38S
1.2S
0.085A
20Hg
506
969
33,700
29
1,010
35
1,226
0.025
0.89
1.2
955
34,500
a If 36% thermal efficient and a full load at 800-MW are assumed, the heat
input rate is 7.59 x 109 BTU/h.
b S, A, and Hg are percentage by weight, e.g., S = 0.8.
c Assuming 99.5% removal in precipitator.
17
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current U.S. emission standard, which reflects current boiler technology.
There are to be four stacks each 198 m high with a 3.8-m exit diameter. The
stack gas-flow rate is 288 m^/s and the exhaust temperature is 408°K.
Representative coal analysis is given in Appendix C.
In addition, the Steep Rock Iron Mines at Atikokan currently emit an
estimated 14-27,000 metric tons/yr (15-30,000 tons/yr) sulfur dioxide and
10-18,000 metric tons/yr (10-20,000 tons/yr) particulates. The Caland Ore
Company at Atikokan emits an estimated 254 metric tons/yr (280 tons/yr)
sulfur dioxide and 1,490 tons/year particulates. Only the main stack of the
Steep Rock Iron Mine facility, which is 91 m high, will possibly influence
the BWCA directly, since the other stacks are short. These emission sources
are reportedly being closed in the near future and hence are not considered
in this modeling effort.
ATMOSPHERIC DISPERSION, TRANSFORMATION, AND DEPOSITION
A realistic air-quality model to meet the objective of this study must
consider a number of physical and chemical processes. Consider a parcel of
air emitted from a tall stack. The advection caused by the wind diffuses
laterally and vertically at a rate that depends on the amount of turbulence
in the air. The turbulence depends on the wind speed and net heat flux. The
vertical spread is constrained by an inversion layer which moves up or down
depending on the net heat flux and overall pressure patterns in the
atmosphere. If the inversion is low, the plume will rise above the
inversion, and pollutants will not reach the ground unless there is
precipitation. The wind speed, wind direction, and heat flux are continually
changing as the parcel of air is dispersing within the region, and hence a
time-dependent model is more appropriate than a steady-state model.
Certain pollutants within the plume can undergo chemical reaction as
they are being transported, such as the conversion of sulfur dioxide into
sulfate aerosol. The reaction rate depends on the concentration of the
reacting species as well as other species in the air and on the intensity of
the sunlight. As part of the parcel diffuses to the ground, it is partially
removed by dry deposition at the surface depending on the type of surface and
type of pollutant. When precipitation occurs, pollutants are scavenged at a
rate related to the amount and type of precipitation. The precipitation,
which is usually more acidic because of the pollutants, is deposited on the
ground.
Plume modeling is often done with a so-called Gaussian plume model, such
as the EPA CRSTER (Guldberg 1977) model. Since this type of model is not
time dependent and does not include pollutant transformation, or wet and dry
deposition processes, the Gaussian plume models are more appropriate to
smaller regions. For a study such as this a grid-type model based on
numerical solution of the general, time-dependent diffusion equation is more
appropriate because the meteorological, chemical, and deposition processes
can be more realistically simulated.
Before describing the modeling work, a general discussion of chemical
reactions in the plume and dry deposition processes is presented.
18
-------
Plume Chemistry
The primary gases emitted from the stack of a power-plant plume are
nitrogen, carbon dioxide, and water vapor. The release of these gases from
the regional sources will not have a direct known effect on the BWCA. Carbon
monoxide and low molecular weight hydrocarbon emissions are considered to be
small and thus will not be considered. Sulfur oxides, nitrogen oxides, total
particulate matter, halogens, and mercury will be discussed below.
Most of the sulfur in the combustion chamber is oxidized to SC^ although
a small percentage is oxidized to 803 in the combustion chamber and reacts
with water vapor in the stack to form sulfuric acid. Approximately 2% of the
sulfur is in sulfate form in the plume close to the stack (Forrest and Newman
1977a, b) . There is general agreement that SC>2 continues to react in the
plume and form sulfate aerosol as the plume diffuses (Gillani et al. 1978,
Schwartz and Newman 1978). Recent studies by Husar et al. (1978) found that
during noon hours the S02 conversion rate was 1-4% per hour, whereas at night
the conversion rate was below 0.5% per hour in the Labadie plume, which is from
a 2,400-MW coal-fired power plant near St. Louis. The sulfate aerosol which is
formed is primarily in the light-scattering size range (0.1-1 ym) so that
visibility is reduced by sulfate formation. The mechanism for sulfate
conversion can be photochemical or heterogeneous reactions in combination with
particulate matter in the plume. Although theories exist for rapid conversion
of SC>2 to sulfates in the plume, the exact mechanisms have not been
established.
Nitrogen oxide (NO) is formed in the combustion chamber from nitrogen in
the supply air and nitrogen bound in the coal. Nitrogen oxide is generally
converted to nitrogen dioxide (N02) in the plume as ambient ozone
diffuses into the plume.
The NO/N02 ratio in a plume is difficult to model, and hence it is
customary to model NOX, which is NO plus N02 weighted as N02.
Particulate matter in the form of fly ash is emitted from the stack in
mostly submicron size. The fly ash serves as condensation nuclei for aerosol
formation. The particulate matter can also serve as a catalyst for sulfur
dioxide reactions. In our modeling work we assume that the particulate
matter represents the fly ash only; the sulfate aerosol is modeled separately.
Mercury in coal is believed to be vaporized in the combustion chamber
and emitted as a vapor. It is possible that part of the mercury may condense
on the fly ash as the plume cools. For modeling purposes, however, mercury
should be considered in the vapor phase. Coal also contains trace amounts of
chlorine, fluorine, and bromine, which can form the acids HCl, HF, and HBr and
particulates containing these elements. These components were not considered
in detail because of lack of information concerning their environmental
behavior.
19
-------
Dry Deposition
Dry deposition of gases occurs by absorption and adsorption on
vegetation, soil, and surface water. Dry deposition of particulates occurs
by impaction onto the surface material. The dry deposition flux of any
species can be determined by multiplying the concentration of that species
near the ground by the effective deposition velocity. The deposition
velocities have been determined experimentally and have been shown to depend
on the rate of diffusion and the characteristics of the underlying surface.
Frequently a deposition resistance is used, which is the inverse of the
deposition velocity. The total resistance is the sum of the aerodynamic
resistance and the surface resistance.
Calculation of the aerodynamic resistance will be discussed later. For
S02 the surface resistance of tall forest lands, which is the majority of
the surface in the BWCA during summer, is generally agreed to be about
0.5 s/cm (Chamberlain 1966, Shepherd 1974). The surface resistance of snow
to SC>2 is about 3 s/cm (Whelpdale and Shaw 1974, Dovland and Eliassen 1976).
Also, the atmosphere tends to be more stable over snow, and hence the
deposition velocity of SC>2 to snow is considerably lower than to summer
vegetation.
The dry deposition velocity of particles is strongly dependent on
particle size. Most of the sulfate mass lies in the 0.1- to 1-ym-diameter
range for which the deposition velocity is not expected to exceed 0.1 cm/s
(Anon. 1978). Hence we have used a surface resistance of 5 s/cm for both
winter and summer for sulfate aerosol. Fly ash emitted from the stack is
also predominantly in this size range, and hence a deposition velocity of 0.1
cm/s has been used.
Wet Deposition
The concentration of sulfate in precipitation is a consequence of
several cumulative processes occurring within and beneath the clouds.
Brownian motion, phoretic attachment, inertial impaction, and nucleation all
serve to remove the sulfate aerosol from the air and attach it to the cloud
and precipitation elements. However,_Brownian and phoretic attachment
mechanisms cannot place sufficient SO^ mass into the cloud water to
account for observed concentrations, and inertial impaction of subcloud
sulfate is of second-order importance when compared to other removal
mechanisms (Scott and Laulainen 1979).
Since sulfate particles are generally soluble and are quite small, and
the majority of mass is distributed over particles with diameters less than
1.0 pm (Harrison et al. 1976), they should be effective as cloud condensation
nuclei. Indeed, if as Weiss et al. (1977) claim, the major portion of the
aerosol with diameters between 0.1 and 1.0 pm is sulfate, then the airborne
sulfate aerosol could be responsible for nearly all of the cloud droplets
appearing in continental clouds.
Sulfate may be generated within the cloud and precipitation water
through the oxidation of absorbed SC>2 • The oxidation processes appear to
20
-------
be temperature dependent and often appear to rely on the presence of metal
catalysts. Laboratory and theoretical work also suggests that oxidants such
as 02> O-j, and ^02 are capable of producing substantial quantities
of sulfate in cloud water (see e.g., Levy et al. 1976 for an extensive
literature survey).
Both the oxygen and ozone transformation mechanisms are pH dependent and
begin to decrease substantially in importance as the pH decreases to less
than 6 for G£ reactions and 4.5 for 63 reactions. The hydrogen peroxide
mechanism is relatively insensitive to acidity, but few measurements of
tropospheric ^2^2 exist to determine the contribution to S0£ by this
oxidant. Ammonia can also play an important role in aqueous phase S02
oxidation by neutralizing some of the ^SO^ that is formed and reducing the
acidity. However, recent solubility measurements by Drewes and Hales (1979)
imply that oxidation mechanisms based upon the presence of ammonia proceed more
slowly than previously thought.
Fortunately some evidence is beginning to accumulate suggesting that it
is not necessary to consider in-cloud conversion of SC>2 to SO^ in order
to predict the sulfate concentration in precipitation. Recent observations
by Scott and Laulainen (1979), and modeling efforts by Scott (1978) have
suggested that for certain precipitation events, the sulfate concentration in
precipitation is determined largely by the sulfate concentration in the air
flowing into the storm system. Scott suggests that the sulfate concentration
in precipitation is inversely proportional to the precipitation rate and
strongly dependent upon the type of storm system producing the precipitation.
The removal of soluble, submicron, pollutant aerosol from clouds appears
to be accomplished primarily by large collector particles, such as snowflakes
or raindrops, sweeping downward through the cloud and capturing the small
cloud droplets containing high concentrations of the aerosol. The final
concentration in the precipitation reaching the ground is dependent upon two
features; first, the initial concentration in the collector particles as they
start their descent through the region of the cloud where accretion of cloud
droplets is the primary growth mechanism, and secondly, the concentration of
pollutant in the cloud water accreted by the collector particles.
The solubility of sulfate particles makes them extremely effective as
cloud condensation nuclei. The sulfate concentration in the collected cloud
droplets depends upon the amount of cloud water condensed about each
activated sulfate particle which, in turn, depends upon the number of
available aerosol, their size, and the intensity of the updraft velocity
within the cloud.
The model of sulfate removal by Scott (1978), considers the three basic
precipitation systems illustrated in Figure 2. In the first case (Figure
2a), the Bergeron or ice growth process is primarily responsible for
precipitation development. Ice crystals nucleate in the upper portions of
the cloud, grow rapidly to precipitation sized particles, aggregate with each
other, and accrete tiny cloud droplets. Even if melting should occur before
the ice particles reach cloud base, the hydrometeors are large enough so that
accretion of small cloud droplets continues to be the primary growth
21
-------
la) BERGERON CLOUD
IE
o
2 -•
0 -L
0UC
7
POO
/« o ?••.••£
v
(b) WARM OR MARITIME CLOUD
—V"
*
x
o
#**•- o°09o
, trajectory
of air flowing into the storm (solid lines); — ->, motion
of hydrometeors relative to the storm (dashed lines). The
vertical scale represents typical cloud depths.
22
-------
mechanism*. The sulfate incorporated into the precipitation is assumed to be
predominantly that advected through the cloud base. This first case
represents a situation where the collector particle (snow) is relatively
pollutant free when it begins to accumulate liquid water. The ice nucleation
is in an environment subsaturated with respect to water and upon nuclei with
lattice structures similar to ice, such as silicas and clays (McDonald 1964).
Sulfate aerosol are not activated as cloud condensation nuclei in the upper
portions of the cloud and are not initially incorporated into the hydrometeor
water. Sulfate pickup comes primarily through incorporation of the dirty
cloud water in the lower portions of the cloud. Surface precipitation from
this type of cloud may be snow or rain.
The Bergeron or cold cloud is felt to be responsible for the majority of
precipitation falling from layer-type clouds over the continents (Mason
1971). The precipitation from continuous rain or snow storms over northern
Minnesota almost certainly relies upon a Bergeron process for its
development.
In the second situation (Figure 2b) the ice-growth process is assumed to
be ineffective in initiating precipitation. Rain develops entirely through
warm phase mechanisms. Gentle uplift (0.1-0.5 m/s) is implied, and long
times are available for precipitation-sized drops to develop by condensation
and coalescence. A major fraction of the moisture and pollutants is assumed
to be transported through the sides of the storm. For this second case,
sulfate aerosol flowing into the storm at the higher levels are activated in
environs saturated with respect to water. The collector particles therefore
have an initial sulfate concentration when they begin their descent through
the lower portions of the cloud. Net sulfate pickup is equal to the sum of
the sulfate material activated in the collector particles at their formation
altitude and the sulfate accumulated by accretion of the dirty cloud droplets
near cloud base. Thus, this warm cloud is capable of removing more sulfate
than the cold cloud.
The third case (Figure 2c) considers precipitation development in
convective storms. Here strong updrafts produce large supersaturations and
large liquid water contents which enable combined condensation and
coalescence to produce precipitation-sized drops faster than they can be
removed by hydrometeors falling from above. The mass flux of moisture and
pollutants is assumed to be largely through the cloud base. In the
convective cloud both the ice-capture mechanism of the cold cloud and the
condensation, coalescence growth of the warm cloud are effective in removing
sulfate from the atmosphere. The removal potential exceeds that of either
the individual warm or cold clouds primarily because those droplets that grow
into collector particles have grown by coalescence in the lower portions of
the cloud where the cloud water contains high concentrations of sulfate.
Showery, summertime precipitation in Minnesota should exhibit removal
characteristics of the convective cloud; that is, extremely high concen-
trations of sulfate should be associated with convective showers affecting a
small (approximately 1-10% of the total area) area at any one time.
* Hydrometeors refer to ice or water particles large enough to fall from the
cloud to the land surface
23
-------
These qualitative results can be expressed explicitly in terms of a
washout ratio, E, defined as the ratio of sulfate concentration in the
precipitation water (gsulfate/8water) C° the sulfate concentration
in air below the cloud base (ggulfate^air^ ' Fi§ure 3 (from Scott
and Laulainen 1979) illustrates the predicted variation in washout ratio as a
function of precipitation rate, J, for the cold cloud (curve 3), the warm
cloud (curve 2), and the convective cloud (curve 1). For a fixed concen-
tration of airborne sulfate and for a given precipitation rate, Figure 3
predicts the lowest sulfate concentrations in precipitation originating as
snow. Factor 2 and 3 increases are predicted when precipitation develops by
warm phase mechanisms in stratiform clouds. The greatest sulfate concen-
trations are predicted to occur in precipitation from convective clouds. The
convective and warm cloud mechanisms would be most prevalent during the
summer months whereas the ice-growth mechanism would naturally occur during
the winter.
If the precipitation is in the form of snow or originated as snow in the
upper portions of the clouds (curve 3), then the surface sulfate concen-
tration in precipitation is roughly proportional to J".3 over the
interval from J = 0.2 to 2.0 mm h~^. If the precipitation-sized drops
develop independently of an ice stage, then the surface sulfate concentration
becomes more strongly dependent upon rainfall rate and upon the airborne
sulfate concentration at the inflow levels of the storm. If the precip-
itation forms without the benefit of an initial ice-growth stage, then for
light precipitation rates (j-0.2 mm h~^) the sulfate concentrations in
precipitation water can increase by a factor of 70 or more over the ice-
dependent predictions. At more moderate precipitation rates (J<1 mm h~l)
the precipitation originating as snow is predicted to have about one-third to
one-half the sulfate concentration of that originating on water droplets. At
heavy precipitation rates (j>7 mm h~^), the sulfate concentration is
nearly independent of the precipitation-formation mechanisms.
The curve of Figure 4 provides a clue that might help to explain natural
seasonal variations in sulfate concentration detected in the northeast United
States. Figure 4 illustrates the variability observed in the Multistate
Atmospheric Power Production Pollution Study (MAP3S 1977) precipitation
chemistry network. Although the scatter is considerable in these
precipitation-chemistry data, there seems to be a definite decline in winter
concentrations of sulfate followed by an increase during the warmer seasons.
High concentrations in the summer may be related to removal by convective
storms, whereas winter-time removal of sulfate is probably associated with
cold rain and snowstorms. Similar seasonal variations in sulfate removal are
also expected in northern Minnesota.
In summary, both experimental and theoretical data are beginning to
accumulate that suggest that sulfate deposition is seasonally dependent and
related to such features as storm type, precipitation rate, and concentration
of pollutant being drawn into the storms. Of the three storm situations
discussed above, the sulfate concentration in the precipitation falling on
the BWCA should be best predicted by using the cold cloud model, except for
situations when the precipitation is clearly from convective clouds.
24
-------
CL
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25
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03 rH
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26
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The BWCA faces an additional impact due to the washout of S02> which
once in the surface waters is likely to convert to SO^. This conversion of
S02 in surface waters may or may not present problems for the environment,
depending upon its concentration and acidity.
DESCRIPTION OF THE THREE-DIMENSIONAL DISPERSION MODEL
The model may be characterized as a grid-type model of atmospheric
dispersion which numerically integrates the species continuity equation.
Chemical reaction between two species, horizontal advection, vertical
diffusion, and wet and dry deposition processes are simulated. The model
computes temporal and three-dimensional spatial concentration distributions
due to single or multiple point and area sources. A fully implicit finite
difference scheme is utilized so that numerical errors are minimal. A single
station is used to characterize the meteorological conditions throughout the
grid. Three-h, 24-h, and annual average concentrations and deposition fluxes are
computed.
The model formulation, the numerical solution procedure, and the
meteorological data used are described in the remainder of this section.
The modeling scheme and treatment of meterological parameters follows that
reported by Ragland (1973), and Ragland and Dennis (1975).
Model Formulation
Consider first a two-component mixture undergoing a first-order chemical
reaction. The pollutant species are affected by advection of the wind,
diffusion in the lateral and vertical direction, and removal by dry and wet
deposition. The wind speed and diffusivity vary with height, surface
roughness, and net heat flux (Figure 5). The plume is trapped by an elevated
inversion layer.
If we align the x-axes with the wind vector and use the fact that the
diffusion term in the x-direction is small compared to transport by the wind,
then the set of equations to be solved for two species C and S is:
— + u — - K —- - — (K |-C) * -kC - W + Q (1)
>\ 4- ^-v NT ^-\rZ % v v % v r r*
o L o-*t y o y o z & o£ *- *—
— + u — - K -^ - — (K ~) - kC ms - W + Q (2)
at u 3x y ayz 3z ^ z 3z' w~ s xs
at z = 0 ^ |C = (3)
z 3z DC
v -§Ji - v r
K ^ - ~vnc,i>
z 3z DS
k
for the reaction ^ •> S. (5)
The upper boundary condition is zero species flux into the inversion layer at
z=zm. For example, C represents the concentration of sulfur dioxide and S
represents the concentration of sulfate aerosol. If, for example, mercury is
to be simulated, C represents mercury and S is zero. Equation (5) defines
27
-------
Heat Flux
V
Inversion Layer
Diffusity
Chemical Rxn.
so;
T Wet T
Deposition
Surface Roughness
Dry Deposition
Figure 5. Schematic diagram of the parameters
used in the grid model.
28
-------
the rate constant, k. The letter W is the wet deposition removal rate per
unit volume, Q is the mass flow rate of emissions, Vp is the dry deposition
velocity, and m is the molecular weight.
The wind speed (u) and vertical eddy diffusivity (Kz) are calculated
as a function of height (z) within the surface layer which extends up to
ZSL and from the top of the surface layer to the inversion layer zm.
According to the scheme outlined in Table 3 the parameter L is defined as
-u pel
0.16 u
and .. £
- 1.8
It should be noted that the geostrophic wind (Vfe)> the net heat flux
(H), and the surface roughness (ZQ) are required inputs. Since only the
surface wind at 10 m is available hourly, the program internally computes the
geostrophic wind.
The net heat flux is obtained from data for cloud cover and cloud ceiling
height by first computing a radiation index according to the scheme used for
STAR data (Turner 1964). The radiation index is then converted by the
following procedure:
Radiation Index 43210 -1 -2
- min) 0.24 0.18 0.12 0.06 0 -0.03 -0.06
The lateral diffusivity is an important parameter that is not well-
known for the time and distance scales of this study. The available data
have led us to the assumption that Ky = 100 KZ . This accounts for gusts
that veer and back and also accounts for a certain amount of wind vector shift
with height due to the Coriolis force.
Changes in the wind direction from hour to hour are handled by a
coordinate rotation transformation. In this way any arbitrary wind direction
can be simulated.
The deposition velocities (Vp) that appear in Eq. (3) and (4) depend
on an aerodynamic resistance (ra). and a surface resistance (rg),
V = - 1 -- (8)
D
ra + rs
The aerodynamic resistance is represented by
ra = "(1) . (9)
29
-------
TABLE 3. WIND AND DIFFUSIVITY PROFILES
i Surface Laver
•H
4-
•H
13
H
OJ
Surface La1
0
,£>
Vertical Wind speed
Stability distance u
Uj, Z+Z_
Neutral 0
-------
and hence may change hourly. The surface resistance depends on the
particular pollutant and surface such as snow, water, vegetation, etc.
The reaction rate constant (k) can also vary hourly and is a function of
the solar radiation index and other pollutants present in the plume. In very
clean air, such as is typical of the BWCA, the conversion rate constant is
smaller than in urban air. Following the work of Husar et al. (1978) we have
used 2% per hour during the day time and 0.5% at night.
The wet deposition removal rate is calculated according to the
procedures outlined in Appendix A. By using Eq. (A-22) we have
Wc(rain) = 0.96 3 C J0'9, (10)
Wc(snow) = 0.48 B C J0-9 (l-exp(-2m)),
and Ws(rain or snow) = 0.44 S J0'625. (12)
The symbols C and S are the average sulfur dioxide and sulfate
concentrations (pg/m-5) and J is the rate of precipitation (water equivalent) in
millimeters per hour. From Eq. (A-15) m is given by
m = 1.56 + 0.44 In J. (13)
The parameter 3 depends on the pH of the rain according to Figure A-2, which
for this study has been simplified to the following equation:
Iog10 B = -2 + 0.75 (pH-3.9) (14)
for pH less than 5.1; otherwise 3 = 0.067.
As explained in Appendix A,
pH = -log 10(2,000 Sw/96), (15)
where Sy is the sulfate concentration in the cloud drops from Eq. (A-10):
Sw = 0.45 S J~°-27. (16)
The wet deposition fluxes are determined by multiplying Eqs. (10), (11), and
(12) by the height of the layer being scavenged, which is given by Eq. (A-9).
For this study we have used a height of 2,000 m as an approximation to Eq.
(A-9).
Numerical Solution of the Plume Model
The solution of the diffusion equation with the various terms as
described above can only be accomplished by numerical techniques. Equation
(1) with boundary and initial conditions is solved numerically by means of a
first-order fully implicit finite difference technique. This method is
numerically stable for any step size. Consider a volume of fluid with sides
Ax> Ay» AZ located at a point i+1, j, k. Properties at the point i, j, k at
31
-------
the time t are known, but in the i+1 plane at time t and the i plane at the
time t + At are unknown. Conservation of mass for a particular species in
an element of fluid not adjacent to a boundary may be written as:
ukc'i+i,j,k(dydz)
(Ky)k(C'i+1J)k-C'i+ljj_1)k)(dxdZ/dy)
= c (dxdydz/dt) + UkC'. (dydz) + Qc (17)
11-1 jj » K i > J > K
Here C' denotes the unknown concentration at time t + At, and C denotes
the known concentration at time t. At a boundary one or more terms on the
left hand side is zero. A similar equation is written for each cell of fluid
in the i+1 plane, and the set of equations is solved simultaneously stepping
forward along x and then stepping through t. A similar equation is written
for species S from Eq. (2) and solved along with Eq. (1). The source
emission rate Qc is added in only one cell at the point of effective
release .
For an individual step it is seen that Eq. (17) can be written as
[A] [C] x + AXj t or x> t + At = u [C] Xjt>
where [A] is determined as a dispersion matrix (NUMY'NUMZ)^
large containing only known meteorological parameters and
step size, and
[C] is the concentration vector NUMY times NUMZ long. The right-
hand side contains only known terms, and NUMY and NUMZ are
the number of cells in the cross-wind and vertical directions,
respectively.
The set of equations (18) is solved by factoring A such that A = LL ,
where L is a lower triangular matrix and L" is the transpose of L. This
may be readily done since A is a positive-definite, symmetric band matrix.
The solution of the system of linear equations is determined by lettering Y
L™C and computing Y by back substitution in the equations LY = D. When Y =
is known, C may be determined by back substitution in L^C = Y.
Changes in wind direction were handled by means of a rotation of the
coordinate axes. Hence two grid systems are used: a rotating grid in which
32
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the computations are done and a fixed system in which the results are stored.
The x and y coordinates of a grid point are transformed as follows:
XF = Xr cos (6) - Yr sin
YF = Xr sin (6) + Yr cos (9)
where 0 is the wind direction.
A major difficulty in the procedure is that the grid rectangles don't
overlap in a uniform way, so the question arises of how to apportion the
concentrations for one grid to the grids for the other system. This difficulty
was overcome by subdividing a grid into a number of smaller grids and assigning
to each small grid the concentration of the larger divided by the number of
subgrids. The subdivision can be as fine as desired, but more subgrids means
greater computing time and cost. In this model there are nine subgrids. The
final concentration is the sum of all the smaller grids of the rotation system
which overlap it. The concentrations originally calculated in the rotating
system have now been stored in the fixed system, so we can rotate the grid to
the new wind direction. Then we simply reverse the process and subdivide the
grids in the fixed system, use the above f ixed-to-rotating equations to
transform the coordinates, arrive at the "already present" concentrations in
each larger grid in the rotating system, and begin the model's numerical
calculations for the next hour. This procedure of going back and forth between
the rotating and fixed grid systems for wind-direction changes continues for as
long as there is a continuous set of meteorological data. The errors created
by the coordinate transformation are generally less than 5%.
For the model runs reported here a box system of 13 x 17 x 6 high was
used with AX, AY = 9,655 m (6 mi) and AZ = 50 m for the lower three boxes and
AZ = (ZM-150)/3 for the upper three boxes, where ZM is the height of the
inversion layer. The time step used in the model's numerical scheme was 10
min. The meteorological input, as previously noted, varies every hour. The
model can therefore simulate on a continuous basis and is limited only by
computer core space and time.
The required computer core space for a single non-reacting species was
28 K and for the S02/S0^ reacting species was 40 K. The computing time
per hour of simulated time was approximately 9.7 s for a single species and
20.1 s for S02/S04. The computer used was a UNIVAC 1110, and the code for
the model is on file at the Madison Academic Computing Center.
The parameters in the model, which are dependent on the type of pollutant
to be simulated, are summarized in Table 4, and the values that we have used
are shown.
Meteorological Data Used in the Model
International Falls, Minn., was selected as the site for the meteoro-
logical data. It is reasonably close to the BWCA and is the nearest site with
a consistent set of surface and upper air data. International Falls is
considered to be representative of the BWCA.
33
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TABLE 4. MODEL PARAMETERS THAT ARE SPECIES DEPENDENT
Parameter
S02
Fly ash
Hg
Chemical reaction
rate (%/h)
Dry deposition
surface resistance
(summer s/cm
(winter s/cm)
Wet deposition
coefficient
(%/h)
0.5 (nighttime)
2.0 (daytime)
0.5
3.0
5.0
5.0
5.0
5.0
36
a
a
0.5
a For Hg a dry deposition velocity of 0.001 m/s was used rather than
specifying the surface resistance, which is not known.
k The washout of S02 and SO^ was handled in a more complex manner than
the fly ash and mercury. See text for a detailed description of the
precipitation washout formulation.
34
-------
The year 1964 was chosen for the model runs because this was the last
year when hourly surface data were recorded. After 1964 the surface data are
available only every 3 h. The total precipitation was about 10% greater than
average during 1964. Upper air data, which are taken twice daily, are used to
obtain the height of the inversion layer. Hourly values of the inversion
height were obtained from a National Climatic Center data tape. All other
necessary data are generated from the surface observation data tape.
The cloud cover, cloud ceiling height, day of the year, and time of day
are used to calculate a radiation index, which is used to define the net heat
flux, H, as indicated earlier. The wind speed at the inversion height, Ug,
is calculated from the wind speed at 10 m. In summary, the following
meteorological data are needed as input to the model:
1) Surface wind speed
2) Surface wind direction
3) Net heat flux
4) Surface air temperature
5) Height of the inversion
6) Precipitation type and amount
The Atikokan generating station subtends an arc of about 90° across the
BWCA. The model was run for those periods when the wind persisted from the
NW to NE direction for at least 6 h. A duration of 6 h or more implies that
the plume will be over the BWCA for 3 h or more. Forty-nine different
periods covering 901 h, or 10.3% of the year 1964, met this criterion and
hence were used. Only winds from the NW to NE were considered to reduce the
amount of computing time without seriously influencing the results in the
BWCA.
The total precipitation during the year was 68 cm (26.63 in.) of water,
and with winds from NE-NW sector the total precipitation was 4.9 cm (1.92
in.) or 7.2%. The total rain for the region was 55.8 cm (21.96 in.) of
water, and the total snow was 11.9 cm (4.67 in.) of water. With the winds out
of the NE-NW sector, total rain was 3.1 cm (1.22 in.) of water or 5.5%, and
the total snow was 2.0 cm (0.77 in.) of water or 16.4%.
Although the model is run from hourly data, it is instructive to consider
some seasonal and annual average meterological data from International Falls
(Table 5). The wind is northerly 20% of the time, the annual mean wind
through the mixed layer is 7.2 m/s, the annual nighttime inversion height is
400 m, and the annual daytime inversion height is 1,300 m. Frequently at
night and also sometimes during the day in winter the plume rise from a tall
stack such as Atikokan is in or above the inversion layer and hence isolated
from the ground.
PLUME MODEL RESULTS FOR ATIKOKAN
The model was run for every hour in the year when the wind was from the
NW to NE sector causing the Atikokan plume to flow over the BWCA. Three
separate runs were made: one for sulfur dioxide and sulfates, one for
particulate matter, and one for mercury. Ambient air concentrations, dry
deposition fluxes, and wet deposition fluxes for each cell in the region and
for each hour were computed and stored on tape. Annual, seasonal, 24-h, and
35
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3-h average ground-level concentrations were obtained, and frequency
distributions of 1-h, 3-h, and 24-h averages were tabulated by means of a
separate tape-processor program. The seasonal and annual wet and dry
deposition fluxes were obtained. The total mass of the particular pollutant
that is transported out of the region by the wind during the year was also
computed.
The ambient air concentrations and deposition fluxes were computed for
each grid point indicated in Figure 1. Since only winds from the NW to NE
were used, it is appropriate to consider a traverse across the region in the
N-S direction starting with the grid containing the source at Atikokan.
Figures 6-10 present the model output as a function of distance due south of
Atikokan for sulfur dioxide, sulfates, fly ash, and mercury.
The annual arithmetic average ambient ground-level concentrations due to
the Atikokan generating station are presented in Figure 6. In the BWCA the
levels were computed to be 0.25 yg/m3 for S02> 0.025 yg/m3 for SO^,
0.01 yg/m3 for fly ash, and 4xlO~" yg/m3 for mercury. The 24-h average
worst-case concentrations, which is a composite of the worst-case days for each
grid point, is shown in Figure 7. The worst-case day occurred on February 23
along the N-S line. In the BWCA the highest 24-h concentrations were computed
to be 10 yg/m3 S02, 0.75 yg/m3 804, 0.4 yg/m3 fly ash, and 0.0015
yg/m3 Hg. The 3-h worst-case concentrations, which also occurred in the BWCA
on February 23, are shown in Figure 8. In the BWCA the levels were 30-35
yg/m3 S02, 1.8 yg/m3 804, 1 yg/m3 fly ash, and 0.0004 yg/m3 Hg.
The frequency of occurrence of 1-h, 3-h, and 24-h average SC>2
concentrations at a grid point due south of Atikokan just across the U.S.
border in the BWCA is presented in Table 6. The results for the non-snow season
from April 15 to November 15, defined here as "summer," are also shown. The
summer season experiences significantly lower concentrations than the winter
(snow) season because the inversion height is generally higher in the summer,
and the thermal turbulence that disperses the plume is greater.
The computed levels for sulfur dioxide and particulate matter may be
compared to the U.S. standards for wilderness areas. According to the Clean
Air Act Amendments of 1977 for any class I area, the maximum allowable increase
in concentrations of sulfur dioxide and particulate matter over the baseline
concentration of such pollutants shall not exceed the following amounts:
Particulate matter
Annual geometric mean 5 yg/m3
24-h maximum 10
Sulfur dioxide
Annual arithmetic mean 2 yg/m3
24-h maximum 5
3-h maximum 25
The modeling results show that the 24-h and the 3-h SC>2 standards would
be exceeded a few times during the year during the snow season. The annual
average SC>2 standard would not be exceeded. The particulate matter standards
may be addressed by adding the fly ash and the sulfate concentration levels.
The results indicate that the particulate matter standards would not be
exceeded. ~
-------
1.4
1.0
0.6
0.2
0
Annual S02
z 0.06
O
I- 0.03
UJ
O
0.05
8 0.025
20
10
Annual SOJ (/ig/m3)
I I I I
Annual Fly Ash (/ig/m3)
Annual Hg (/z/ng/m3)
BWCA^
20 40 60 80 100 120
DISTANCE SOUTH FROM SOURCE, km
Figure 6. Computed annual average concentrations
due south of Atikokan for S02> SCT, fly ash,
and mercury.
38
-------
20
16
12
8
4
0
1.25
1.0
Z
O
f= 0.5
<
Q:
t 0
24-hr S02 (/ig/m3) _
U.S. Class I Std.
LU
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0.4
24-hr Fly Ash
i i i i
j I
0.3
0.2
O.I
24-hr Hg (ng/m^)
-BWCAH
20 40 60 80 100 120
DISTANCE SOUTH FROM SOURCE, km
Figure 7. Computed 24-h worst-case concentrations
due south of Atikokan for SO , SOT1, fly ash,
and mercury.
39
-------
U.S. Class IStd.
UJ
o
z
o
o
0
0.8
0.4
0
3-hr Fly Ash (/ig/m3)
3-hr Hg (ng/m3)
BWCA-]
20 40 60 80 100 120
DISTANCE SOUTH FROM SOURCE , km
Figure 8. Computed 3-h worst-case concentrations
due south of Atikokan for SO , S07, fly ash,
and mercury.
40
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The deposition fluxes from the model runs are shown in Figures 9 and 10.
These annual and seasonal values were obtained by summing the hourly values.
The deposition fluxes due to the Atikokan generating station may be summarized
as follows for a location due south of the source in the BWCA:
S02
Winter
Summer
Annual
804
Winter
Summer
Annual
Fly ash
Winter
Summer
Annual
Mercury
Winter
Summer
Annual
Dry
deposition
0.3
0.25
0.55
Dry
deposition
0.010
0.005
0.015
Dry
deposition
4
2
6
Dry
deposition
1
0.5
1.5
Wet
deposition
0.01 kg/ha
0.02
0.03
Wet
deposition
0.01 kg/ha
0.01
0.02
Wet
deposition
6 g/ha
6
12
Wet
deposition
0.05 mg/ha
0.05
0.10
The dry and wet deposition may be added to obtain the total deposition.
If we assume that the SC>2 deposition is converted to sulfate at the surface
(multiply by 1.5 for additional 02), then the total sulfate deposition at
this location in the BWCA is 0.9 kg/ha-yr. The fly ash total deposition is 18
g/ha-yr, and the mercury deposition is 0.0016 g/ha-yr. These deposition
values are, of course, an addition to the regional background deposition
fluxes of 11 kg/ha-yr for sulfates (see Table 1), indicating an absolute
increase of about 10 percent in sulfate loadings over present background at
the BWCA.
Two other comparisons are also worth making. Earlier (Section III) it
was noted that the sulfate in the precipitation of the Quetico-BWCA area is
about two-thirds neutralized (7.6 kg/ha-yr) by other atmospheric constituents,
while 3.1 kg/ha-yr of sulfate (and a contribution of nitrate) are producing
the net depression in pH. The projected addition of 0.9 kg/ha-yr of sulfate
42
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0.5
0
2.5
I
0
S02 Dry Deposition
(kg/hectare)
$04 Dry Deposition
(g/hectare)
Summer
Fly Ash Dry Deposition
(g/ hectare)
Hg Dry Deposition
(mg/hectare)
BWCAHl
20 40 60 80 100 120
DISTANCE SOUTH FROM SOURCE ,km
Figure 9. Computed annual and seasonal dry deposition
flux due south of Atikokan for S0?, S0=, fly ash,
and mercury. There are only two seasons: summer
and winter. Summer is defined as the time when the
snow is not on the ground.
43
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0.4
0.2
O.I
0
S02 Wet Deposition
(kg/hectare)
Deposition
g/hectare)
Fly Ash Wet Deposition
( g/hectare)
Hg Wet Deposition
* (mg/hectare)
X,
BWCAH
20 40 60 80 100 120
DISTANCE SOUTH FROM SOURCE,km
Figure 10. Computed annual and seasonal wet deposition
flux due south of Atikokan for S0?, S0=, fly ash,
and mercury. There are two seasons: summer is
rain, and winter is snow.
44
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(and nitrogenous compounds) from operation of the Atikokan generating station
at full capacity thus represents a potential increase of 25 percent in the
unbuffered atmospheric acidity.
These estimates of total acid deposition also can be evaluated from the
viewpoint of mitigative needs. The present Steep Rock iron mine operations,
which release 15 to 30,000 tons of SC>2 annually, may be terminated before
the Atikokan power facility is completed. Thus, the present deposition rates
for sulfate could be expected to decrease somewhat at that time. The Steep
Rock emissions are about 40 percent of those expected from the 800-MW
generating station, but the reduction in sulfate deposition in the BWCA would
be less than half of this proportion of the projected power plant increase
because doubling the stack height of the power plant effectively transmits
twice the amount of S02 to the BWCA compared to the shorter stack height of
the iron sintering operations. These data, however, allow the contribution
of the Atikokan generating facility to be judged as a percent addition to the
background acid deposition levels after the proposed closing of iron ore
operations. Taking half of the 40 percent of the generating station transport
to the BWCA as the improvement from closing of the iron mines gives a net
decrease of 0.2 kg/ha-yr in total sulfate deposition and unbuffered acidity.
These considerations indicate little change in the projected 10 percent total
increase in sulfate loadings and 30 percent increase in unbuffered acidity (0.9
kg deposition in relation to 2.9 kg/ha-yr of unbuffered acidity) following the
closing of the iron mine. Even if the mine closed, and only one-half of the
Atikokan plant was constructed (400-MW), the unbuffered acid sulfate
contributed by the new source represents a 15 percent deterioration in
precipitation quality. Thus, the absolute levels of acid loadings in the
region will significantly increase by operating the Atikokan facility at
400-MW, even assuming the iron ore facility closes.
Atmospheric Loadings in the Quetico Area
As indicated in Figures 9 and 10, the deposition loadings are much higher in
the northern Quetico than in the BWCA for the 10.3% of the time the winds are
from the NE to NW for a duration of more than 6 h. The watersheds of the
Maligne River and other rivers in the Quetico south of Atikokan drain to
international waters along the BWCA boundary. Hence deposition from the
Atikokan plume within these watersheds must be considered in the total
BWCA-VNP impacts evaluation. Model estimates of deposition 35 km south of
Atikokan in the area of Sturgeon Lake are as follows:
Annual sulfate deposition 3.4 kg/ha-yr
Annual fly-ash deposition 88 g/ha-yr
Annual mercury deposition 4 mg/ha-yr
These results for the proposed Atikokan source are for only the long duration
windfield; three to five times these values will be the probable minimum
total deposition at the Sturgeon Lake location. These estimates represent a
100% or more increase over the current sulfate deposition in this area, and a
much larger increase over the expected background deposition following
closing of the Steep Rock Iron mine operations.
45
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VALIDATION OF THE MODEL
In a brief study such as this it is not possible to complete direct
validation of the model in the field. A number of approaches can be used,
however, to determine the present level of confidence appropriate for the
model.
First of all, a version of this model which does not include deposition
or chemical transformation has been used successfully in a seven-county region
in southeastern Wisconsin. A detailed emission inventory was developed by
State and local agencies. Computed annual average particulate concentrations
were compared with 25 high-volume particulate monitors, and a correlation
coefficient of 0.87 was obtained. Computed annual average sulfur dioxide
concentrations were validated with six monitoring stations, and a correlation
coefficient of 0.78 was obtained (Southeastern Wisconsin Regional Planning
Commission 1978). The modeling work is being used to develop the Wisconsin
Implementation Plan as required by the U.S. Clean Air Act.
The validity of the model depends in part on the value of the parameters
selected for the execution of the model. The key parameters which are
dependent on the particular pollutant species to be modeled were summarized in
Table 4. These values were selected from experimental values in the
literature and are felt to be known within a factor of 2 except for the values
for mercury, which are probably known only to a factor of 10. In addition, the
surface roughness and the horizontal eddy diffusivity are important parameters.
One surface roughness must be selected for the entire region, and the selected
value of 1 m represents typically wooded terrain. The horizontal eddy
diffusivity is not well known for this scale model, and more research is needed
on this parameter (see Liu and Durran 1977). The model used a value of 100
times the vertical diffusivity.
A sensitivity analysis was performed on the key parameters in the model.
A worst-case day was selected, and the model was run for 24 h. The sensitivity
of the ground-level concentration of S02 to a factor of 2 change in each of
the key parameters was determined as shown in Figure 11. The most sensitive
parameter was the height of the inversion. This parameter was measured at
International Falls and hence is well known. The horizontal eddy
diffusivity was the next most sensitive parameter: a doubling decreased the
S02 concentration by 10-15%. The other three parameters —the chemical
reaction rate, the surface resistance, and the surface roughness— when
doubled, changed the concentration by less than 10%.
The accuracy of the input data is another factor that influences the
validity of the results. Assumptions have been made on the type of coal used
and the reliability of the electrostatic precipitator. The meteorological
data— the wind speed, wind direction, solar intensity, inversion height, and
precipitation amount and type —will all influence the resultant output.
Nevertheless, it is felt that the input data are rather well known.
When any complex model is used, the results should be compared with those
from other models, and especially from less complex models. Examination
46
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ro
E
\
o>
o
!5
LU
O
O
o
27
25
23
21
19
17
15
LU 13
LU
O
CC
CVJ
OJ
O
V)
Slack Height
2RS
2ZR
Base Case
2RR
2EDDY
EDDY = Horizontal Eddy Diffusivity
- RR = Chemical Reaction Rate
- RS = Surface Resistance
ZM = Height of Inversion Layer
I I- ZR = Surface Roughness
i i i i
j i
-BW.CA-
10 30 50 70 90 110 130
DISTANCE DUE SOUTH OF ATIKOKAN ,km
Figure 11. Results of. the sensitivity tests of the grid
model showing the influence on SO concentration for
a worst-case day.
47
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of the similarities and differences between different modeling results can
yield confidence in the final results. Modeling results from a simple box
model approach, from Gaussian plume concepts, and from the EPA CRSTER model
are summarized in Appendix B. These results lend support to the findings of
the numerical grid model.
SUMMARY DISCUSSION OF THE ATIKOKAN MODELING RESULTS
A time-dependent plume model that includes transport, diffusion coupled
chemical transformation, and wet and dry deposition has been developed and
applied to Atikokan. A grid was set up that included Atikokan, Quetico
Provincial Park, and the Boundary Waters Canoe Area. The model was run hour
by hour for an entire year for those hours when the wind was from the NW to
NE. Separate model runs were made for sulfur dioxide and sulfates, fly ash,
and mercury. The sensitivity of key model parameters was analyzed, and the
validity of the results was examined.
The following conclusions are drawn from the modeling effort with respect
to the Atikokan plume on the BWCA:
1. The 3-h and 24-h worst-case sulfur dioxide concentrations exceed
the U.S. allowable incremental standards of 25 and 5 yg/rn^,
respectively, for protection of a Class I wilderness area. The
frequency with which these values are exceeded is low, however. The
annual average S02 concentration was 0.25 yg/nH, which is eight
times less than the U.S. standard.
2. The increase in particulate matter is not expected to approach the
U.S. allowable incremental standards for a Class I wilderness area.
The annual particulate (fly ash plus sulfate) concentration was 0.03
yg/m-% and the worst-case 24-h concentration was 1.1 yg/nH.
The particulate matter contains twice as much sulfate as fly ash.
3. The total potential sulfate deposition was 0.9-1.4 kg/ha-yr in the
BWCA, which is significant compared to the existing regional
background deposition of 11 kg/ha-yr.
4. The total deposition of fly ash was 0.018 kg/ha-yr for the BWCA.
5. Annual mercury ambient air concentrations were 4 x 10~^ g/m »
and the total deposition flux was 1.6 x 10~^ g/ha-yr for the
BWCA.
48
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SECTION 4
POTENTIAL EFFECTS OF COAL-COMBUSTION EMISSIONS
ON THE TERRESTRIAL BIOTA OF THE BWCA
INTRODUCTION AND GOALS
The expanse of relatively pristine terrestrial ecosystems in Minnesota's
Boundary Waters Canoe Area Wilderness is a major reason for its recognition as
a unique recreational resource in the United States. The flora and fauna
growing in the BWCA have not previously been subjected to elevated
concentrations of toxic air emissions or the deposition of chemically
transformed products of these emissions (Section 3). However, the emissions
inventory presented earlier indicates a gradual increase in toxicant
concentrations and deposition over previous very low levels (Section 3). A
careful assessment of the consequences of continued increases for terrestrial
species in these ecosystems now seems warranted.
In this section we will:
1) Characterize the components of terrestrial ecosystems in the BWCA
that could be affected by elevated concentrations or increased
deposition, as a consequence of coal-burning emissions;
2) summarize the research results available for evaluating the
responses of sensitive species to changes in air, water, and soil
characteristics, and the overall sensitivity of the ecosystems to
these changes; and
3) define potential effects on plants, animals, and ecosystems where
sufficient information is available to cause concern, but is
insufficient to quantify the magnitude or timing of responses.
Sensitivities of the regional biota to the emissions and deposition
products from coal-fired generating facilities have been reviewed in several
previous forms (N. R. Glass 1978). Because of measurable differences in
terrain, meteorology, vegetation density, rainfall, and soil moisture from one
location to the next within the BWCA, absolute comparisons are not possible for
short- or long-term biological responses at specific sites. Thus, responses to
air pollutants and dry fall that hold for several locations already studied
must be used to evaluate potential impacts on other, locations, such as the
BWCA.
Under relatively extreme emission loads, many effects on ecosystems such
as the BWCA are well documented. Some responses are evident on a short-term
(less than a decade) time scale, and others are apparent on a long-term
(decades) time scale. Studies of other influences on the vegetation of the
49
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BWCA, particularly the effects of intermittent fire in the past, require the
use of time scales of hundreds of years. Although the studies presented here
focus on relatively immediate, often subtle impacts on species, it is
apparent that these impacts also should be viewed in a time frame of 100 or
200 yr if their ultimate effect upon the entire ecosystem is to be assessed
fully.
BIOLOGICAL AND TEMPORAL CHARACTERISTICS OF THE BOUNDARY WATERS CANOE AREA
Approximately 70,000 ha (172,000 acres) of the total 439,000 ha
(1,085,000 acres) of the BWCA are taken up by lakes and streams over 4 ha (10
acres) in size. Some 215,000 ha (532,000 acres) support remnants of the
natural ecosystems of Minnesota's Laurentian shield country, virgin areas
with the flora and fauna nearly intact. These virgin areas are those which
have never been directly altered by human activities such as logging,
clearing, tree planting, farming, mining, road building, etc. Almost all
these areas, however, have been burned in the past 400 yr, and many virgin
forests are postfire successional communities less than 110 yr old
(Heinselman 1973) . It is these virgin areas of natural vegetation patterns
upon which this discussion will focus.
Part of the Superior Upland Physiographic Region, the BWCA's landscape
has a generally slight but locally rugged relief left by preglacial erosion.
Elevations above sea level range from 341 m (1,119 ft) at Crane Lake to 680 m
(2,232 ft) in the Misquah Hills (Ohmann and Ream 1971); local differences in
elevation range from 30 to 150 m (Heinselman 1973). Most of the relief of
this area, glaciated repeatedly during the Pleistocene and deglaciated some
16,000 yr ago, is related to the contours of its exclusively pre-Cambrian
bedrock: metamorphosed sedimentary rock leading to quartzite, metagraywacke,
and slate. In contiguous Quetico Provincial Park (Ontario) the bedrock types
are principally associated with a granite batholith exposed as part of the
Laurentian Shield.
A network of more than 1,000 interconnected lakes and streams occupies
the bedrock troughs and basins of the BWCA, some lying in granite (Saganaga
Lake and Lac La Croix) and some in ancient greenstones and slates (Knife
Lake). The landforms are determined by the configurations of the bedrock:
slates typically form long, narrow, steep ridges, and granites the low,
irregular round-topped hills (Ohmann and Ream 1971).
Deposition was offset by glacial scouring, which left bedrock exposed on
many ridgetops, cliffs, and lakeshores, and a thin covering of till, outwash,
and lacustrine deposits varying considerably within short distances. Glacial
boulders are common within the soils derived from this sandy and gravelly
loam glacial deposition.
Plant Community Type_s
The plant communities of the virgin upland forests have been quantita-
tively described by Ohmann and Ream (1971). Even after 60 yr of fire control
the jack pine (Pinus banksiana) communities remain the most common of the
virgin upland forest, followed closely by the broadleaf group, which is
50
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largely dominated by aspen (Populus tremuloides) and paper birch (jetula
papyrifera) (Table 7). White pine (Pinus strobus) and red pine (J\ resinosa)
communities made up 10% of the 106 virgin stands randomly sampled by Ohmann
and Ream (1971). The distribution of the vegetation types in the BWCA area
is shown in Figure 12.
Transitional between the Great Lakes-St. Lawrence and boreal forest
regions, biotic communities in the area have an abundance of boreal trees:
jack pine, black and white spruce (Picea mariana, J^. glauca), balsam fir
(Abies balsamea), tamarack (Larix laricina),northern white cedar (Thuja
occidentalis),and paper birch. The two pines characteristic of the Great
Lakes forest, eastern white pine and red pine, are also plentiful (Heinselman
1973). Citing Dean's preliminary 1971 study of the area wetland communities,
Heinselman (1973) indicates that they are closely related to the glacial Lake
Agassiz peatland communities, a region some 160 km (100 miles) to the west.
Of the 12 community types described by Ohmann and Ream (1971), only the
lichen community type is nonforest. Characterized by the lack of many woody
plants and by the importance of lichens and mosses, this type comprises
slightly less than 5.7% of the stands in their random sample of 106 sites.
Ohmann and Ream grouped lichens other than the reindeer mosses, and mosses
other than the feather mosses, Dicranum, and the hairycap moss. Together
they make up 40% of the ground cover within the community. Another 30% of
the ground surface is bare rock. The reindeer mosses (actually lichens) are
also important in this essentially two-layered community.
Lichens and mosses are also an important component of the ground cover
in four other communities designated by Ohmann and Ream: jack pine (fir),
19% of the ground cover; red pine, 26%; black spruce-jack pine, 59%; and
budworm-disturbed balsam fir, 46%, including herbs. As computed by Ohmann
and Ream, these communities make up 32% of the upland virgin vegetation area
in the BWCA. They view the lichen community as an early stage of succession
after some major disturbance, such as fire, as primary succession on rock
outcrop.
In the BWCA today tree lichens are found largely on the lower limbs of
old fir and spruce and on dead balsam fir killed by the spruce budworm.
Ground lichens are most abundant on open bedrock ridges and upper slopes,
which become well covered by lichens 60-100 yr after fire (Heinselman 1973).
Stands including the white and red pine community types are slightly
older than those in most of the other communities and make up 9.5% of total
stands sampled by Ohmann and Ream in 1971 (5.7% white pine; 3.8% red pine).
As described by these researchers the white pine community is really a two-
layer forest: an upper canopy of large, old white pines with scattered red
pines, and a lower layer of balsam fir trees and saplings. The attractive-
ness of the red pine community stems from the presence of open stands of old,
majestic red and white pines that survived fires along the lakeshore and are
prominent along the ridgetops forming the skyline. The understory is short
on saplings and seedlings, and shrubs and lichens characteristic of dry
conditions are dominant.
51
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TABLE 7. VIRGIN UPLAND COMMUNITIES IN THE BWCA AND THE IMPORTANCE OF
STANDS, TYPES, SPECIES, AND FAMILIES3
Stands
Community
type
Lichen
Jack pine (oak)
Jack pine (fir)
Jack pine-black spruce
Black spruce-jack pine
Aspen-birch
Maple-aspen-birch
White pine
Red pine
Budworm-disturbed balsam fir
Fir-birch
White cedar
Numb er
6
11
7
7
10
13
15
6
4
10
8
9
Percentage
of total
5.7
10.4
6.6
6.6
9.4
12.3
14.2
5.7
3.8
9.4
7.5
8.5
Number of
species
32
81
95
83
75
112
104
80
67
102
86
85
Number of
families
19
25
30
26
23 -
30
34
23
25
31
30
28
aAdapted from Ohmann, L. F., and R. R. Ream (1971).
52
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53
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The mammals and birds of the area are also representative of a transi-
tion between the Great Lakes and boreal forest ecotones. The moose (Alces
alces), Canada lynx (Lynx canadensis), fisher (Martes pennati), pine marten
(Martes americana), snowshoe hare (Lypus americana),spruce grouse
(Canachites canadensis), Canada jay (Perisoneus canadensis), and (formerly)
the woodland caribou (Rangifer caribou)are all species with boreal
affinities. The northern white-tailed deer (Odocoileus virginianus) and
bobcat (Lynx rufus) are species more typical of the Great Lakes forests. The
eastern timber wolf (Canis lupus), red squirrel (Tamiasciurus hudsonicus),
red fox (Vulpes fulvaT^beaver (Castor canadensisT]otter (Lutra canadensis),
mink (Mustella vison), black bear (Ursus americanus), ruffed grouse (Bonasa
umbellus),bald eagle (Haliaeetus leucocephalus), etc., are all species more
typical of the Great Lakes forests. Most of the native animals and birds
also have habitat requirements that correspond with niches in various post-
fire successional stages (Heinselman 1973).
Long-Term Stability of the BWCA Landscape
Ohmann and Ream (1971) conclude from their studies that the structure
and composition of each stand in today's virgin forests are more closely
related to the length of time since the last fire, and probably to the
character of the fire and the age of composition of the former stand, than to
all of the other environmental factors studied, such as soils, aspect, slope,
or elevation.
The stand origin and fire year maps developed by Heinselman (1973)
indicate that from 1595 to 1973 nearly all of the one-million-acre virgin
forest study area burned at least once, 1910 being the last year of major
burns. At least 44% of the million-acre virgin study area was involved in
the drought year burns of 1893 and 1894. Many even-aged stands also date
from a similar drought-fire sequence 220 yr ago in 1755-59. Those large
upland ridges and ridge complexes distant from or west of natural firebreaks
were the areas most frequently or intensely burned. Such areas are today often
dominated by jack pine, black spruce, birch, and other sprout hardwoods. White
pine, red pine, white spruce, northern white cedar, black ash, elm, and fir are
relatively more abundant on those sites burned least frequently or intensely:
swamps, valleys, ravines, the lower slopes of high ridges, islands, and the
east, north, northwest, or southeast sides of large lakes or streams. Very
fire-sensitive northern white cedar has retreated to the lakeshores where it
forms a typical narrow fringe (Heinselman 1973).
Heinselman (1973) cites Ayres' 1899 observation that by 1855, because of
its long history of fire, only 20% of the region supported the mature pines
desired for lumber. Thus, Heinselman indicates, just a small fraction of the
BWCA was affected by the early logging, and the young stands, recent burns,
and scattered areas of older forest that covered three-fourths of the region
were little touched. As of 1973, he notes, the net land area undisturbed by
cutting exceeded 167,950 ha (415,000 acres), most within the lands set aside
for national forest between 1902 and 1913. The Anderson bill, recently
passed by the U.S. Congress, eliminates logging as a management alternative
from the entire BWCA.
54
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As indicated by H. E. Wright Jr. (1974), the same 370 years covered by
Heinselman1s tree-ring/fire studies in the BWCA represent only a portion of
the total lifespan of the forest. Although humans may have modified the
natural frequency of fire during those years, pollen curves and charcoal
profiles from the sediment of Lake of the Clouds (in the heart of the BWCA)
show that major fires occurred about every 80 yr for the last 1,000 yr.
What H. E. Wright Jr. (1974) has called the "time factor in landscape
evolution" must be applied to environmental influences other than fire
control. If we look ahead 50, 100, or 200 yr to how succession in the
absence of a natural constituent, fire, may significantly change the BWCA
forest communities, then it is equally appropriate to consider a similar time
frame for assessing what effects rising levels of pollutant deposition may
eventually have on these same communities. Such a long-range view provides
an important perspective on the possible significance of relatively
immediate, if subtle, effects now manifested in individual indicator species
in other ecosystems, where effects of exposure to increased doses of S(>2,
NOX, TSP, H2SC>4, HF, and Hg are already known.
The vegetation resource that presently covers the BWCA was initiated 300
to 100 yr ago. Today's land managers and policy decision-makers are stewards
of whatever the landscape of this area is to be 200 years from now.
BIOTIC RESPONSES TO COAL-FIRED POWER-PLANT EMISSIONS
The following considerations have been summarized from various current
research projects on the impact of coal-fired generating stations and from
the literature on the BWCA ecosystem components and their response to known
levels and durations of exposure to point-source pollutants from coal-fired
power plants.
Various types of terrestrial ecological effects may be anticipated from
exposure to generating station emissions and associated deposition (Figure
13). Direct effects may be anticipated from both dry and wet deposition of
air pollutants on ecosystem components (see Section III). In addition to
direct effects, a number of indirect effects may be manifested through
changes in ecosystem processes, such as bioaccumulation of toxic compounds,
alterations in mineralization or rates of nutrient flow, and changes in
host-parasite relationships.
The discussion that follows considers such major emission products
(residuals) from the viewpoint of the plant, animal, and soil components of
the terrestrial ecosystem on which they could have important potential
effects. The material presented reflects data or information already
available. New data needs are identified by the inadequacy or lack of
results from long-term, low-level exposures. The emission residuals
considered are those for which sufficient information is available to
anticipate some effect on an ecosystem component at some concentration, and
for which the air-quality modeling work has provided estimated concentrations
and loadings in the BWCA.
55
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Residuals of Concern
so2—
Sulfur dioxide and the effects of exposure to it have been studied more
than any other pollutant (Benedict et al. 1971, Guderian 1977, Rennie and
Halstead 1977). A wide variety of organisms are sensitive to damage from
exposure to elevated S02 concentrations (Tibbitts et al. 1977, Electric
Power Research Institute 1976, Van Haut and Stratman 1970). Many organisms
also exhibit synergistic reactions to combinations of S02 with other
coal-fired power plant emissions such as 03 or NOX (Dochinger et al.
1970, Kress and Skelly 1977, Houston 1974).
Numerous extensive reviews of SC>2 and its effects are available
(Braunstein et al. 1977, N. R. Glass 1978). A reading of these and other
references in relation to the principal vegetation types reviewed supports
focusing on responses of pines, lichens, and soils in the BWCA.
NOX N02—
Forest soil and insects are generally less sensitive to N02 than
to other major pollutants (National Academy of Sciences 1977). Although
organisms are more sensitive to N02 than to the other nitrous oxides,
the usual measurement combines the forms as NOX, and levels necessary to
affect susceptible members of the terrestrial ecosystem (vegetation) are much
greater than for sulfur dioxide and photochemical oxidants (MacLean 1975).
Estimates of the economic impact of air pollutants on vegetation have not
included NOX by itself; rather it has been combined with ozone and
peroxyacetyl nitrate (PAN). However, emissions of NOX have been increasing
substantially throughout the United States and Canada, and the synergistic
effects on plants from low concentrations of N02 and sulfur dioxide
(found in experimental exposures) and of NOX in the production of
photochemical smog and acid precipitation pose the greatest threat (N. R.
Glass 1978) .
Ozone—
Photochemical oxidants, ozone (03), and, to a lesser extent, peroxy-
acetyl nitrates are the most damaging air pollutants affecting agriculture
and forestry in the United States (Jacobson 1977). Peroxyacetyl nitrate is
more phytotoxic than 03, but the ambient concentration of PAN is much lower
than 63 in most areas of the United States (Taylor 1969). In the northern
Minnesota area it may be almost negligible. Formation of ozone in the
atmosphere has a complex dependence on the amounts of precursors (nitrogen
dioxide and hydrocarbons), meteorological conditions, and time of day
(National Academy of Sciences 1977), but moderately high levels are being
observed in northern Minnesota given the area's relative isolation from the
usual ozone sources (Table 1). Photochemical oxidants, including ozone, have
been problems in southern California for more than 30 years. The severity of
losses to agricultural crops, exclusive of forests and ornamental plantings,
had reached more than $55 million by the 1970's (Millecan 1976).
57
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Trace elements—
Trace elements have been defined as those elements present in the crust
of the earth at less than 0.1% or 100,000 ppm. More than 63 of them are
found in coal. Some are more concentrated than others in coal, and there is
considerable variation in trace-element concentration from different coal
sources. Most trace elements (including arsenic, beryllium, chromium,
copper, lead, selenium) appear to occur at mean concentrations less than
7,000 ppm, notable exceptions being boron, zinc, and titanium (Ruch et al.
1974, Zubovic 1975). These trace components, however, are concentrated on
the surface of the fly ash particles and are highly reactive (G. E. Glass 1978)
Of the macro elements in coal (e.g., aluminum, calcium, iron, silicon,
sulfur, and sometimes titanium) only sulfur is the element of concern here.
Sulfur oxides represent the major pollutants of gaseous emissions and are
mentioned here because of the known ability of some metallic trace elements
to catalyze the further oxidation of sulfur oxides into more toxic substances
capable of greater respiratory damage than sulfur dioxide alone (Amdur and
Underbill 1970) or to interact and form metallic sulfates. Excessive
deposition of trace elements upon a balanced ecosystem can cause problems
because of the high toxicity of many trace elements and the potential for
bioaccumulation.
Acidic fallout (acid rain)—
Although acidic fallout has long been studied by European researchers
(Oden 1968), the phenomenon received only cursory attention by Canadian and
United States scientists until the early 1970"s. Since the beginning of the
decade, however, scientists of both these North American countries have
expanded their interest in the long-term effects of acidic precipitation and
the precursors of this phenomenpn. Canadian scientists have shown that
acidic precipitation is a serious problem in both terrestrial and aquatic
ecosystems of eastern Canada (Summers and Whelpdale 1976, Beamish 1976,
Stokes and Hutchinson 1976).
In the United States a report to the Secretary of the Department of
Health, Education, and Welfare by a special scientific advisory committee
considered the long-term consequences of the United States National Energy
Plan (NEP). This committee concluded that one of the most serious
environmental consequences of the expanded use of coal-fired power plants
will be increased acidic precipitation throughout the areas where the power
plants are located (U.S. Federal Register 1978). Although this advisory
committee supported the conversion from oil to a coal-based energy economy
(NEP), they concluded that all converted and new facilities should install
the best available abatement technology to reduce to a minimum the precursors
of acidic precipitation.
Contributors reviewing the literature and current research for this
report reached the consensus that, for the BWCA, the principal ecosystem
components or organisms to be emphasized regarding the effects of acid rain
were pines, lichens, insects, and amphibians (direct effects) and soils
(indirect effects).
58
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Conifers (Pines) and Aspen
Effects of SC>2 on pines —
The effect of the gaseous emissions of large coal-fired power plants
initially becomes evident in the responses of the most sensitive of the
species in any ecosystem. In the BWCA these sensitive species are lichens,
conifers of the genus Pinus, and trembling aspen. The three dominant species
of Pinus in the BWCA are P_. strobus, j>. resinosa, and jP. banksiana. Of these
three species eastern white pine is the most sensitive to S(>2. Red pine
and jack pine are considered about equally sensitive to SC^j but not as
sensitive as eastern white pine. Trembling aspen is a dominant species over
20% of the BWCA (Table 7, Figure 12) and is recognized by Driesinger and
McGovern (1970) as a very sensitive species.
The major manifestations of pollution damage in these three species of
pine are foliar tip necrosis, mottling chlorosis, basal necrosis of the
needle tissues beneath the fascicular sheaths, and premature needle casting.
The premature loss of needles from the second-, third-, and fourth-year
internodes causes a reduction in annual growth as well as the loss of normal
health and vigor, which in turn predisposes these species to more severe
effects of other abiotic (drought, frost, nutrient deficiencies) and biotic
(insect infestations, root-attaching fungi) causal agents (Carlson 1978).
Several studies document the development of visible injury symptoms on
eastern white pine by low level chamber fumigations. Costonis (1970)
reported tissue damage on new needles of eastern white pine after a single
1-h treatment with 5 pphm SC>2 • Houston (1974) observed necrosis in
elongating needles of eastern white pine after 6 h of fumigation with 2.5
pphm S02• In a field study in the Sudbury, Ontario, region Linzon (1971a)
observed damage to eastern white pine at a 7-yr fumigation average of 0.8
pphm, a level of S02 commensurate with the background levels already being
recorded in areas of Ontario near Atikokan (Table 1).
After field observations Costonis (1972) reported that 6 pphm of S02
caused acute injury to the new needles of eastern white pine after A h of
exposure. Ozone measurements in the field did not exceed 4 pphm.
Preliminary laboratory tests conducted before these field studies indicated
that sensitive white pines developed necrotic lesions after S02 exposure of
3 pphm for 1 h; if fumigation was continued for 3 h, severe necrosis on
current needles occurred. Laboratory tests also revealed that 03
fumigations of 15 pphm for 4 h produced equivalent injuries.
Houston and Dochinger (1977) reported a decrease both in the number of
seeds produced per cone and in the percentage of pollen germination in white
pines in a low level S02~polluted area. Effects on red pines included
decreases in cone length, seed weight, percentage seed germination,
percentage pollen germination, and pollen tube length. None of the trees
displayed foliar injury patterns, indicating that low levels of air
pollutants may be affecting the reproductive tissues of pines at
concentrations lower than those required to produce visible injury. In the
vicinity of a copper smelter at White Pine, Mich., low level S02 exposure
59
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has caused no plainly visible vegetation damage, but ring widths of balsam
fir and white spruce suggest that growth has been substantially reduced in
trees downwind from the smelter (Kotar 1978) .
Driesinger and McGovern (1970) found trembling aspen to be the most
sensitive forest species to air pollution in the Sudbury, Ontario, area.
Visual injury to foliage was caused by S02 concentrations of 26 pphm for
4 h. Pollen-tube elongation is inhibited at S02 concentrations greater
than 30 pphm for 4 h (Karnosky and Stairs 1974).
The U.S. Environmental Protection Agency (Davis and Wilhour 1976)
attempted to classify the susceptibility of various woody plants to SC>2 and
photochemical oxidants based on foliar injury, growth loss, etc. They
observed that eastern white pine near the Sudbury, Ontario, region (S02
source) has a poorer regenerative capacity to repeated S02 exposures than
various hardwoods (aspen, birch). They also documented that red pine was
very sensitive to S02 emissions.
Effects of NOX on pines—
Skelly et al. (1972) carried out field observations of eastern white
pines exposed to S02 and NOX. The most severely affected trees were in
areas where the highest readings were 8.5 pphm NOX (l-h average) and 69
pphm S02 (2-h average). They also found that oxides of nitrogen at
moderate concentrations acting alone or in combination with low S02
concentrations caused acute to chronic damage in eastern white pine. Young
seedlings were extremely susceptible to NOX fumigations. Van Haut and
Strattman (1967) observed damage to plants exposed to 250 pphm NOX for 4-8
h.
Effects of ozone on pines and aspen—
In chamber studies conducted by the EPA, eastern white pine was
classified in the intermediate sensitivity range to 0-j and red pine in the
tolerant range. Davis and Wood (1972) used chamber experiments to determine
the relative susceptibility of 18 conifers to ozone. They found jack pine to
be the most susceptible, damaged by 4 h of 25 pphm 0^• Eastern white pine
was also very sensitive, damaged by 8 h of 25 pphm 0-j, but red pine was
resistant (no injury manifestation) at these fumigation levels.
In a field study in West Virginia, Berry and Ripperton (1963) observed
damage to eastern white pines 48 h after a l-h fumigation of 5 pphm 03.
The damage observed was considered a "light attack" of emergence tipburn, but
severe symptoms were noticed following ambient 03 exposures of 6.5 pphm for
a total of 4 h during a 48-h period. Using chamber experiments, they
determined 03 was the causal agent of the injury observed in the field.
(The damaged area was remote from any major sources of air pollutants.)
Ozone levels higher than these have already been observed in the BWCA (Table
1).
Botkin et al. (1971) observed that fumigations of 03 (50 pphm for 4 h
and 80 pphm for 3 h) suppressed photosynthesis of eastern white pines.
60
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Further studies carried out by Botkin et al. in 1972 determined that
photosynthetic depression occurs before visible 63 damage becomes apparent.
In a chamber experiment on 5-yr-old eastern white pine they determined that
50 pphm fumigations of 63 for 4 h was the threshold level for photo-
synthetic suppression (Botkin et al. 1972).
Treshow and Stewart (1973) found visible injury to trembling aspen at 15
pphm 03 for 2 h. Since this was the lowest concentration tested, it does
not establish the injury threshold, but does indicate that trembling aspen is
among the most sensitive species tested.
Effects of SC>2 and 63 in combination on pines—
Eastern white pine is generally considered to be more susceptible than
other pines to a pollutant mix. Several studies support the finding that
greater than additive responses occur when eastern white pine is exposed to
both S02 and 03 (jaeger and Banfield 1970, Berry 1971, Banfield 1972,
Costonis 1973, Houston and Stairs 1973, Houston 1974) (Table 8). Menser and
Heggestad (1966) support the findings that "tolerable levels of a single
pollutant can damage plants (in general) when in association with another at
an equally low level." These studies, however, are mainly chamber studies
and deal only with SC>2 and 63. They do not account for other pollutants
and environmental stresses that occur in the field.
Berry (1971) conducted chamber studies to determine the relative sensi-
tivities of red pine, jack pine, and eastern white pine seedlings to 03 and
SC>2 fumigations. The 3-, 5-, and 7-wk-old seedlings were exposed to 2-h
fumigations of 25 pphm 03, 50 pphm 63, 25 pphm 862, or 50 pphm SC>2.
Jack pine was the most sensitive to both SC>2 and 63, but there was no
significant difference in the sensitivities of the age groups of any of the
trees. At 50 pphm 03 red pine was less tolerant than eastern white pine.
Fumigations with SC>2 at 25 pphm, however, were more injurious to eastern
white pine than to red pine. Red pine injury was detected at 25 pphm 03
for 2 h, but at 50 pphm 63, 87% of the 468 seedlings observed were injured
(banding, flecking, tip necrosis). Injury symptoms were detected from 24 to
48 h after fumigation.
Jaeger and Banfield (1970) studied responses of eastern white pine to
prolonged exposures to 63, SC^j and a mixture of both pollutants. When
eastern white pine was exposed to 50 pphm of 03 and 50 pphm SC>2 for 10
days, profuse necrotic spotting occurred on new and 1-yr-old needles. The
most significant finding was that at the above fumigation levels, with
increasingly humid environments, severe necrotic spotting occurred after 3
days. That is, the synergistic effect was much more severe with high
humidity. Banfield (1972) observed necrotic spotting and tipburn of eastern
white pine when exposed to 10 pphm 03 and 0.5 pphm SC>2 for 1-12 days in a
chamber fumigation study.
Dochinger et al. (1970) observed injury to eastern white pines when they
were exposed to 10 pphm 03 for 10-20 days and 10 pphm SC>2 for 10-20 days.
When exposed to 10 pphm of both 03 and SC>2 for the same time intervals,
injury to the pines quadrupled.
61
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62
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Effects of trace elements on pines—
Accurate assessment of trace-element impact cannot be known without a
thorough characterization of endogenous levels of soil trace elements and the
processes ongoing within soil. Trace element input from weathering differs
from that of fossil fuel combustion and, in some cases, may exceed that from
fossil fuels. Trace-element input is attentuated by distance from the
pollutant point source and by filtering action of the surrounding canopy.
Since more than 80% of the BWCA is forested (about 75% of this in coniferous
stands), most trace-element emissions may affect the tree canopy directly.
Very little is known concerning the effects of most trace elements applied
directly to foliage.
Fluoride is known to be directly phytotoxic, but very little work has
been done on the susceptibility of either eastern white pine or red pine to
ambient concentrations of fluoride pollutants. In 1970 the EPA carried out
field studies on fluoride-affected vegetation in Glacier National Park,
Montana, the closest boundary of which is 15 miles northeast of a large
aluminum reduction facility (U.S. EPA 1973). They observed that tip necrosis
due to fluorides was clearly visible on older needles of sensitive western
white pine growing in areas deep within the interior of Glacier National
Park. Western white pine (Pinus monticola) was classified by EPA in 1976 as
being "less sensitive" to airborne pollutants than eastern white pine (Pinus
strobus). In another report (Gordon 1974), the EPA observed tissue necrosis
on western white pine occurring at fluoride levels only two or three times
higher than background fluoride levels in healthy trees.
Linzon (1971b) carried out studies during the 1969 growing season in the
Cornwall area of Ontario near three fluoride-emitting industries. Early in
the growing season the current 1969 needles on eastern white pine had not
emerged, but the 1968 foliage displayed severe brown terminal necrosis and
many needles were prematurely lacking. Later the 1969 needles displayed
severe orange-red terminal necrosis. Studies carried out in the summer of
1977 in the same area of Ontario by the University of Montana documented
severe visible injury to both eastern white pine and red pine despite
considerably lower fluoride concentrations in the needles than determined by
Linzon in 1971 (Miles 1978).
Solberg and Adams (1956) state that, in general, fumigation of
vegetation with HF or S02 may produce temporary decreases in photosynthesis
in the absence of visible injury. They found that histological responses to
S02 and HF were indistinguishable in ponderosa pine and apricot leaves.
Impacts of acidic precipitation on coniferous forests—
Effects on growth of fully mature coniferous species have been difficult
to document with methods currently available. Several studies have failed to
identify significant effects (Abrahamsen et al. 1977, Tamm et al. 1977),
whereas other studies provide suggestive circumstantial evidence that acidic
precipitation has adversely affected growth of trees in coniferous forests
(Jonsson and Sundberg 1972, Jonsson 1977). Long-term growth effects are
exceedingly difficult to demonstrate because their cause may be confounded by
interaction with numerous variables. In addition, even if the long-term
63
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effects on growth are very significant, significant changes in growth do not
usually occur within the timespan of typical research projects.
The quickest and most severe impact of acidic precipitation on soils is
likely to occur in the 1-2-cm horizon. Deeply rooted plants (e.g., trees)
are not likely to be directly affected very much by changes in this horizon,
but plants rooting in this zone (understory vegetation and germinating plants
of all types) may be affected considerably (Mayer and Ulrich 1977). Effects
on understory vegetation may be very important because at certain stages of
succession a greater weight of chemical elements circulates through the
understory than through the trees. This relationship has been demonstrated
in old spruce and pine forests in the U.S.S.R. (Ovington 1962).
Perpetuation of a coniferous forest depends upon the continued
reproductive success of the conifers. Spruce (Picea abies) germination has a
broad optimum around pH 4.8 and is adversely affected at soil pH of 4.0 or
lower. Spruce seedling establishment has a narrow optimum at pH 4.9 and is
quite sensitive to pH levels lower than this (Abrahamsen et al. 1977). In a
20-wk study of the effects of acid rain on growth of white pine (Pinus
strobus) seedlings, best growth was found in seedlings exposed to rain of the
lowest pH (pH 2.3) (Wood and Bormann 1977). This increased growth was
presumed to be caused by the increased nitrogen impact from the acid rain.
Apparently, once seedlings are established, they are relatively tolerant of
acidic soil. Considerable mineral leaching occurred throughout the 20-wk
experiment. Availability of basic cations would probably have become limiting
to growth had the experiment been carried out over an extended period.
Impacts of acidic precipitation were also reported at the First
International Symposium on Acid Precipitation and the Forest Ecosystem
(Dochinger and Seliga 1976) when European, Canadian, and United States
scientists presented the data obtained on both continents during the last 20
yr.
Summary of effects on pines—
Based on the above literature evidence and the projected ambient air
levels of total suspended particulates (TSP), SC^, NOX, and trace elements,
it is possible but unlikely that short-term, visible damage will be incurred by
the pines in the BWCA. Acid rain damage to plant tissues seems possible in
view of results suggesting that the pH of rain under worst conditions may
become as low as 3.5-4.3, although the projected frequency of these rains is
not immediately available (Section 3). Literature reports indicate that this
range of pH could alter growth and reproductive success of conifers.
The long-term implications of small, subinjurious effects on processes
such as photosynthesis rates, radial growth, nutrient uptake, germination
success, and lifespan could be substantial. Whether the effect would be
strong enough to affect community structure or the rate of secondary
succession is open to debate. In view of recent data which indicate that
impacts may occur at residual levels lower than previously reported (Gordon
et al. 1978, Kotar 1978), the possibility of long-term effects must be
seriously considered. Signficant new research programs focused on the most
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sensitive species and on subinjurious effects must be carried out if these
problems are to be resolved.
Lichens and Bryophytes (Sphagnum)
Effects of SC>2 on lichens—
The adverse effects of gaseous SC>2 °n lichens are well documented in
field and laboratory observations. The laboratory observations have
generally been made at S02 levels of above 50 pphm and will not be
elaborated on here. The field observations have tended to concentrate on
mapping lichen communities around pollution sources, documenting the
disappearance of lichen species as one approaches the pollution source
(LeBlanc and Rao 1975). This approach seems to be accurate in determining
zones of air quality in urban and industrial areas where there has been a
pollution source for a long period of time (e.g., Sudbury, Ontario; LeBlanc
et al. 1972), where environmental conditions are such that no interruptions
in adequate indicator lichen cover would be expected. The approach is also
useful where one is close enough to the source that short-term acute effects
can be easily observed (Clay Boswell plant, Cohasset, Minn.; Coffin 1978).
LeBlanc and Rao (1973) indicate that lichens in the Sudbury, Ontario,
area were not injured if ambient S02 concentration for the 6-month growing
season was less than 0.2 pphm; growing season average concentrations of 0.6-3
pphm were adequate to produce chronic injury. Average growing season
concentrations above 3 pphm produced acute injury. Background levels in the
BWCA have reached 10 pg/m3, or 0.37 pphm (Table 1).
Significant decreases in respiration rates of lichen samples occurred in
100-200 days at median S02 concentrations of 1.8 pphm in southeastern
Montana (Eversman 1978), a level that could be approached in the BWCA given
projected effects from Atikokan (Section 3). Thalli of yellow-green lichens
(Parmelia chlorochroa, Usnea hirta) bleached to a yellower color within 100
days, and the percentage of normally plasmolyzed-^ cells increased from a
baseline of 5-8% to 25-30% in 30 days (Eversman 1978). Usnea hirta is an
epiphyte on trunks and branches of ponderosa pine in southeastern Montana.
It also grows in the BWCA (Hale 1969). This type of lichen (fruticose) is
particularly sensitive to air pollutants. Parmelia chlorochroa lives on bare
soil between grass clumps and shrubs in the grasslands. This foliose lichen
intergrades with western forms of P. taractica, and is found on exposed rocks
in the BWCA (Hale 1969). ~
At median S02 values above 2 pphm in southeastern Montana, bleaching
and plasmolysis occurred faster, and P. chlorochroa and U. hirta exhibited
symptoms of acute damage. Within 33 days of S02 exposure at median concen-
trations greater than 3.3 pphm, plasmolysis of algal cells approached 100%,
and the respiration rate of these lichens dropped significantly below that of
controls (Eversman 1978). Selected indicator species in Minnesota, such as
•^Plasmolysis is the shrinking of the cytoplasm away from the wall of a
living cell due to water loss by exosmosis.
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E-' caPerat:a and U_- subfloridana, could be expected to show effects of SC>2
at median concentrations of less than 2 pphm.
Recent studies of lichens in the vicinity of the Columbia generating
station in Wisconsin (S. Wolf, personal communication, 1979) have shown more
subtle responses. Here, maximum 1-h SC>2 exposures at only 3-5 pphm occur
once or twice a month. Two of four species studied (Parmelia caperata and P.
bolliana) showed significant increases in the number of plasmolysed cells at
the "high" impact sites (1-h exposures at 3-5 pphm once or twice a month)
compared with samples from more remote sites. In another part of the study,
these results have been related to small changes in the abundance of these
and other lichen species during a 4-yr field study of lichen species
composition in a zone around the power plant impacted by the 1-h exposures at
3-5 pphm. A number of secondary effects, including nitrogen fixation (see
later section) are influenced by the composition of lichens in conifer
forests, and species changes over a period of a decade or more could be
significant for forest growth.
Effects of 03 on lichens—
The very few studies that have been made on the effects of Og on
lichens indicate that at concentrations of about 25 pphm and below, 03 has
stimulatory effects. A study by Anderson (1963) cited in Rosentreter and
Ahmadjian (1977) concluded that 0^ may have induced production of young
reproductive structures in Cladonia coniocraea, a common ground species.
They also cited a study by Sernander-du-Rietz (1957), that suggested
lightning storms stimulate fruiting of lichens.
Rosentreter and Ahmadjian (1977) found that 63 concentrations of 10,
30, 50, and 80 pphm for 1 wk did not appreciably change the chlorophyll a_
content of the algae, the thallus color, or morphology of the reproductive
structures of C. arbuscula. Chlorophylls a and b_ increased slightly at 10
pphm. Rosentreter and Ahmadjian (1977) agreed with Anderson and Sernander-
du-Rietz that 03 may induce lichen fruiting. Lichens may thus respond
physiologically to levels of 63 already reached on occasion in the BWCA
(Section 3, Table 1). Nash and Sigal (1979), however, documented significant
reduction in gross photosynthesis in Parmelia sulcata and Hypogymnia
enteromorpha when these lichens were fumigated with 0.5 and 0.8 ppm ozone.
Unpublished field data (Sigal, personal communication, 1978) from the
San Bernadino Mountains in California show a marked reduction in percentage
cover of Letharia vulpina and Nypogymnia enteromorpha on conifers in areas
subjected to oxidants (03 and PAN), compared with those on control sites.
Effects of trace elements on lichens—
Work involving lichens has not usually dealt with any potential or
possible effects of trace elements. One Michigan study conducted near Lake
Superior established an inverse relationship between lichen cover on tree
bark and the presence of chloride precipitate found in snow (Brown 1977).
Lichen cover varied from 85% at 0.001 g/cm H20 of chloride precipitate to
0% at 0.012 g/cm 1^0 chloride. Among the lichens eliminated at the higher
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concentrations of chloride precipitate were P. caperata, J>. exasperatula, and
Physcia millegrana, all present in the BWCA flora (Hale 1969, Wetmore,
personal communication, 1978) .
Effects of total suspended particulates on lichens—
Relatively little information is currently available regarding
potential or possible effects of TSP on lichens. In his study of snow as an
accumulator of air pollutants, Brown (1977) recorded an inverse relationship
between lichen cover on tree bark and the amount of total particulate matter
present in the snow. At 0.045 g/cm t^O of total solid particulate, lichen
cover was 85%; at 0.23 g/cm 1^0 it was 0%. He did not determine, however,
if this decrease was due to the levels of TSP or to those of SC>2 and
chloride also measured.
Impacts of acidic precipitation on lichens—
Lichens are sensitive first to the ambient SC>2 concentration, then to
the pH of stem-flow water (Robitaille et al. 1977). The gaseous SC>2 and
particulate SO^ are adsorbed onto moist bark surfaces, as well as onto
lichen surfaces, a process that decreases pH.
Lotschert and Kohm (1977) compared ambient S(>2 concentrations with
bark sulfur content and pH of deciduous trees (which have a higher natural pH
than conifers) in Frankfurt. Where the SC>2 concentration was less than 2.8
pphm (0.09 rng/m^), the bark pH was greater than 3.5 and the "greatest
number" of lichens occurred. As SC>2 concentration increased to 3.9 pphm
(0.10-0.11 mg/m-'), bark pH dropped to 3.1-3.2, and the lichens disappeared.
The buffering capacities of both bark and lichens decrease with acidic
precipitation according to Robitaille et al. (1977). From this 1977 study
these researchers concluded that stem-flow pH determined bark pH, thus the
proportions of sulfurous acid (^SOg) and the very toxic HSO-j,
which in turn determine the presence or absence of sensitive lichen species.
Of the derivatives S02 forms with water, HSO^ is the most toxic to
lichens (Puckett et al. 1973, Robitaille et al. 1977). In addition, when the
HS05 dissociates to H+ and S03=, the ratio of S03= to HSO^
(which is 1:1 at pH 7) increases by a factor of 10 for each decrease of one
unit in pH (i.e., 10:1 at pH 6, 100:1 at pH 4) (Turk and Wirth 1975).
The mapping studies of Gilbert (1970) showed that bark pH and lichen
cover decrease as SC>2 increases and that lichens only survive on highly
buffered substrates (e.g., limestone and calcareous soil). Conifer trees,
the habitat of many epiphytic lichens in northern Minnesota, probably have
bark pH of less than 5.00 (Gough 1975). Thus lichens on conifer trees have
very little pH "maneuvering space" and could be expected to be adversely
affected by increasing ambient SC>2 and resulting acid precipitation
conditions before lichens on deciduous trees and calcareous substrates.
Denison et al. (1977) reported less nitrogen fixation by Lobaria
pulmonaria at pH 2 than at pH 4, 6, or 8. As acid rain increases in Pacific
67
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northwest forests, they expect the nitrogen-fixing activities on L.
pulmonaria and similar _L. oregana to decrease.
Impacts of acidic precipitation on Sphagnum—
Although much is known of the distribution of swamp and bog organisms in
relation to natural pH gradients, there is currently no complete study of the
effects of acid deposition upon wetland ecosystems (Gorham 1978).
Gorham (1978) has observed completely "dead" peat bogs in the vicinity
of Sudbury, Ontario, where both acid and heavy metal pollution are extreme.
Apparently, a progressive decline in both biotic diversity and productivity
occurs with increasing saturation of the peat exchange complexes by hydrogen
ions. Direct and secondary effects upon invertebrate and vertebrate animals
may be anticipated, but are essentially unknown as are effects upon bacteria
and fungi—which must be presumed vital to the breakdown of organic detritus
and the recycling of limiting nutrient elements such as nitrogen, phosphorus,
etc. (Gorham 1978) .
Ferguson et al. (1978) state that the disappearance of Sphagnum species
from the bog vegetation of the southern Pennines in Great Britain is
correlated with the Industrial Revolution of the past 200 yr. Peat profiles
of the southern Pennines show that Sphagnum species were once a much larger
component of the blanket bog vegetation than they are now.
The laboratory studies (artificial acid rain, immersion, fumigation)
reported by Ferguson et al. (1978) suggest that the growth of a number of
Sphagnum species is sensitive to sulfur pollutants (HSO^, SO^,
802) within the range of concentrations found in Great Britain today. The
species differ in their response to the pollutants; 0.5 mM HSC>3
eventually proved lethal to the most sensitive species, but reduced the
growth rate of the most resistant, S. recurvum, by only 35%.
Ferguson et al. (1978) also note that in 1973 Tallis determined _S_.
recurvum to be a recent dominant in the mire communities of north Cheshire.
The only Sphagnum to exist in considerable quantities in the southern
Pennines today, it is confined to flush areas. The ability of j^. recurvum to
withstand relatively high concentrations of the sulfur pollutants may
contribute to its ability to survive and achieve dominance.
Summary of effects on lichens and Sphagnum—
Lichens are among the most sensitive organisms to air pollution. Though
response thresholds for SC>2 exposure have not been established for most
species, available information suggests that effects are not to be expected
at median S02 concentrations below 0.2 pphm. Lichens appear to be tolerant
of short-term exposure to relatively high ozone concentrations (up to 80
pphm). Lichens on the trunks of conifers are probably those most susceptible
to direct effects of acid rain and SC^ because their substatum may have an
inherently low pH and be poorly buffered.
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Sphagnum has been shown to be sensitive to lowered pH due to acidic
rainfall near industrial areas. Thresholds for effects have not been
established.
Concentrations of those toxic emissions from Atikokan known to affect
lichens and Sphagnum are not expected to affect lichen populations in any
substantial manner quantitatively or qualitatively. Some worst-case rainfall
events in the BWCA may have low enough pH to have some effect on some
species. Effects (if they occur) will be subtle and insidious.
Arthropods (insects)
Effects of SC>2 °n insects—
The effects of air pollutants on insects and plants are complex. The
effects of environmental contaminants on insect-plant interfaces may be
reciprocal, acting on the insect through the plant or on the plant through
the insect. Air pollutants reported to have significant effects on
entomological systems include sulfur and nitrous oxides, ozone, hydrocarbons,
fluorocarbons, smog, dusts, acid mists, major and trace elements, and
radionuclides.
Air contaminants accumulate in the tissues of insects by ingestion,
respiration, or penetration through the cuticle. These substances may act
directly on an insect, be passed through food webs to the insect, or
indirectly affect the insect through alterations in food and habitat
resources. Toxic substances may be transferred through food chains to higher
trophic levels and accumulate in the insect predators and parasites. Pollin-
ators, particularly social insects such as bees, appear to be especially
susceptible to poisoning from the zootoxins they accumulate during their
foraging activities.
Known effects of air pollutants on insects include death of sensitive
species, proliferation of pest insects in forests and croplands, loss of
parasitic and predacious insects, loss of saprophagous insects, and loss of
pollinators. Other effects include temporary or permanent changes in
behavior, reduced hatchability and fecundity, teratologies, and genetic
alterations such as chromosome disjunction. No one has attempted to
establish the thresholds of dose responses. Reported relationships between
pollutant concentrations and changes in insect systems represent, for the
most part, historical incidents and not a reliable threshold of response.
The response threshold probably occurs at lower concentrations than reported.
Investigations of S02 effects by Bromenshenk (1979, 1978b) and
Bromenshenk and Gordon (1978) at the EPA Zonal Air Pollution Delivery System
(ZAPS) in southeastern Montana have demonstrated significant reductions in
decomposer beetles, particularly Canthon laevis, on the fumigated plots of ZAPS
sites I and II. Data from 15 cm, the lowest fumigation level measured,
indicated that the levels at which these beetles first responded did not exceed
2.1-2.6 pphm average for 30 days. Because S0£ concentrations decreased
closer to the ground, this level probably was higher than that to which the
beetles were responding. The decreased abundance (sometimes termed
69
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activity abundance) occurred on the lowest SC>2 treatment plots at both ZAPS
I and II during 1976 and 1977. Beetle captures demonstrated a significant
inverse linear regression with increasing SC>2 expressed as the reciprocal of
the sulfation concentrations.
Similarly, Leetham et al. (1979) noted population reductions with
increasing S(>2 concentrations for the coleopteran families Curculionidae
and Carabidae (predators), the lepidopteran family Pyralidae (larvae), and
adult grasshoppers (Acrididae). Also population reductions were observed in
the high-treatment plots at both the ZAPS areas for tardigrades and rotifers
in the soil.
Hillmann (1972) studied insect populations near a 615-MW coal-burning
power-generating station in Clearfield County, Pennsylvania, which emitted
172 metric tons (190 tons) of S02/day. (Atikokan emissions are projected
to range from 83 to 192 metric tons (92-212 tons) of S02/day.) One site
was located 1,219 m (4,000 ft) from the power plant, the other 23.5 km (14.7
miles) from the power plant. Significantly greater numbers of Aphididae and
significantly lower numbers of parasitic Hymenoptera (wasps) and social
Apidae (bees) were captured at the site nearest to the power plant. Since
aphid numbers in the area exposed to greater amounts of S(>2 increased
concurrently with parasitic wasp decline, Hillmann concluded that SC>2 may
have induced host-parasite imbalance.
Freitag et al. (1973) conducted a field investigation on ground beetle
populations near a Kraft paper mill in Ontario, Canada, and found that a
drastic reduction in the number of carabid fauna paralleled increasing
fallout of sodium sulfate (^2804) .
Effects of 03 on insects—
The work on the effects of 03 on insect systems that has been done to
date has been carried out under 03 levels higher than would be encountered
in the BWCA-Quetico area.
Effects of NOX on insects—
As with 03, very little seems to be known about the effects of oxides
of nitrogen on insect systems. The work that has been done has involved
higher levels than would 1 experienced in the BWCA-Quetico area.
Effects of trace elements on insects—
Studies have shown that a large number of trace elements can move
through insect systems, often accumulating in insects at the higher trophic
levels. Many of these elements are toxic to insects at relatively low
concentrations, and many are toxic to insects at levels lower than those that
affect mammals.
The most extensive trace-element work has been carried out on substances
harmful to honeybees. This work has been reviewed by Lillie (1972),
Debackere (1972), Toshkov et al. (1974), and Steche (1975). Because of their
70
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extensive foraging activities, bees contact, gather, and consume these
materials. Bees also are magnifiers of noxious substances in their environs.
Pesticide studies indicate that pollinators smaller than honeybees may be
more susceptible to toxicosis because they receive a proportionally larger
dose relative to body size (Johansen 1972).
A few studies have particular relevance to problems associated with
emissions from coal-fired power plants. Svoboda (1962) found that about 500
bee colonies were destroyed within a 6-km radius of a power plant that
released arsenic into the air.
Hillmann (1972) found that social pollinators and parasites (which are
similar in terms of trophic relations to predators) were most severely
affected by power-plant emissions. He recorded a significant decrease in
social insects such as bumblebees and predatory wasps near a 615-MW power
plant in Pennsylvania when compared with populations at a site 23.5 km (14.7
miles) away. Hillman correlated declines in insect abundance with 863
levels, but did not analyze for trace elements. Many trace elements are more
toxic to bees than sulfur dioxide (see review by Debackere (1972)).
Dewey (1972) found relatively high fluoride levels in the 1,005 preda-
tory insects collected near an aluminum smelter which reportedly emitted
between 1,134 and 2,837 kg/day (2,500 and 7,600 Ib/day) of fluoride. Four
major groups of insects were collected within a half mile of the plant:
tissues of pollinators contained 5,800-58,500 pphm fluoride; predators
610-17,000 pphm; foliage feeders 2,130-25,500 pphm; cambial feeders 850-5,250
pphm. Levels in the control groups, taken at least 80 km (50 miles) away,
ranged from 350 to 1,650 pphm.
Bromenshenk (1976, 1978a, b, 1979) reported that preoperational and
postoperational studies of honeybees taken from commercial apiaries near two
350-MW power plants in southeastern Montana showed significant increases in
the levels of fluorides in or on the tissues of adult worker honeybees.
After 1 yr of operation, during which neither plant had been in continuous
operation and both had operated at one-third to one-half capacity, fluorides
increased by as much as twofold in bees taken from apiaries downwind and as
far as 15 km away from the plants. There were no increases in fluoride
levels in bee tissues upwind from the power plant.
Other elements from coal combustion also affect insect populations.
Before to the development of synthetic organic insecticides, several
inorganic chemicals were widely used for insect control. These included
compounds of arsenic, fluoride, mercury selenium, antimony, boron, and
thallium (O'Brien 1967). The first six, and possibly all seven, are released
by combustion of coal in electric power generating stations. The mercury
content of the coal, emission rates of Hg, deposition fluxes, and background
levels in fish from lakes of the BWCA have been characterized elsewhere in
this report (Table 2, Figures 7, 8, 9, 10). Based on concentrations in
Saskatchewan lignite coal (Appendix C), the ratios of some other toxic
elements to mercury in coal are 268-430 for fluoride, 21-34 for arsenic,
0.59-3.0 for cadmium, and 2.5-4.0 for selenium. Taking into account the
concentration in precipitator fly ash, and assuming that these materials are
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emitted in ways similar to mercury, estimated emissions as a ratio to mercury
are 233-399 for fluoride, 14-28 for arsenic, 0.42-2.4 for cadmium, and
1.3-3.2 for selenium.
Fluoride and arsenic are likely to be released in quantities much
greater than mercury, and they are of particular concern with regard to
long-term, low-level exposures, since many compounds of fluoride and arsenic
act most effecively through slow release by weathering and rapid release in
the gut (O'Brien 1967). In addition, honeybees and presumably other
pollinators are magnifiers of arsenic and fluoride in their environs
(Bromenshenk 1979). According to Debackere (1972) danger to bees from
arsenic poisoning is greatest when: (1) the wind has blown in the same
direction for extended periods, (2) precipitation has been low or infrequent,
(3) in spring when blossoms are few and foraging is intense, and (4) after a
heavy dew, fog, or mist. Whereas arsenic poisoning often causes sudden
die-off for a few days, fluoride poisoning usually occurs as death over a
long period (Lillie 1972, Debackere 1972). Both fluoride and arsenic
compounds may be stored in food supplies resulting in even longer exposure
periods (Bromenshenk 1978a), and severe bee kills near industrial sources of
arsenic and fluoride are well documented (Lillie 1972, Debackere 1972).
In a later section on aquatic ecosystems (Section 5) concern is
expressed that: (1) mercury has been found to occur in fish at levels in
excess of FDA standards, (2) the sources of mercury are unknown, and (3)
emissions from the Atikokan power plant may increase these levels. Whatever
the source, where mercury is found, elevated levels of other injurious trace
elements are also likely to be found. In view of the high toxicity of
arsenic and fluoride to insects, and because large quantities of these
materials (in comparison to mercury) are to be emitted by the Atikokan power
plant, more information is needed about the background levels of these
substances in the BWCA and in the insects, vegetation, and soil of the
region. With these background data the significance for entomological
systems of the worst-case concentrations and depositions could be evaluated.
Summary of effects on insects—
Although responses to threshold exposures to pollutants have not been
established, a number of insect groups with strong sensory systems,
particularly saphrophagous and predacious beetles, social bees (pollinators),
and parasitic wasps, have been shown to be reduced in abundance at very low
concentrations of air pollutants, apparently because of pollutant avoidance
or disorientation, or both. Several plant-feeding insect groups increase
rapidly when the activity of parasite or predator-control insects is reduced,
or the vigor of host-plant species is reduced, both of which have been shown
to occur from gaseous air emissions. If physiological stress is demonstrated
by the host coniferous trees in the BWCA, concurrent alterations in
entomological systems will occur. The available literature suggests that
disturbances in the population dynamics of phytophagous forest insects may
occur at levels below those manifesting visible injury to pines. Direct
injury to the vegetation of the BWCA by exposures to pollutants from the
Atikokan power plant, and from other regional sources if incurred, could be
intensified by insect interactions.
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Amphibians
In the United States 50% of the frog and toad species breed in temporary
pools formed annually by accumulated rain and melted snow. One-third of the
species of salamanders in the United States that are aquatic before
metamorphosing into terrestrial adults also breed in temporary ponds. Such
ponds are more fragile than lakes or streams because their acidic
precipitation input has little contact with soil buffer systems and is not
diluted by mixing with standing water (Pough 1976).
A study of embryonic mortality of spotted salamanders (Ambystoma
maculatum) (Pough 1976) showed less than 1% egg mortality in pools near
neutrality, but more than 60% in low pH (less than 6) ponds, with an abrupt
transition in mortality below pH 6. Furthermore, field results were
reproducible in the laboratory, where effects of both predation and
temperature were eliminated.
Other studies of anurans include one in which the breeding sites of most
anurans in or near the New Jersey Pine Barrens were limited to grassy ponds
and gravel pits resulting from the normally lower pH (3.6-5.2) of sphagnous
pools (Gosner and Black 1957). Prestt et al. (1974) postulate that
acidification of anuran breeding sites may be contributing to the recent
decline in British frog populations. Pough (1976) reiterates the earlier
observations of several authors that the significance of any widespread failure
of salamander reproduction will have far-reaching consequences. Salamanders in
temporary ponds are an important predator on dipteran larvae (flies) and an
important energy source for higher trophic levels in an ecosystem (as are other
anurans such as frogs). Pough also notes that these ponds are major breeding
sites for many invertebrates as well. Changes in these ponds could therefore
limit the breeding of numerous species, while allowing pest species to
flourish.
Some changes in the acidity of standing pools in the BWCA may occur
because of acidic snowmelt and acidic precipitation. If this change occurs
in the spring, salamander reproduction may be affected.
Soils
The configuration of granites, slates, and argilites and ultrabasic
bedrocks in the BWCA have determined the local patterns of soils and
land forms. Glacial scouring also has exposed the bedrock on many ridges and
left only a shallow varying cover of till on the slopes and ravines.
Although locally some soils are deep, large areas of thin rocky soils are
derived from sandy glacial deposits. These soils are among the most
sensitive in the Superior National Forest area (Heinselman 1977).
Bedrock geology—
Bedrock in the Voyageur's National Park and the Boundary Waters Canoe
Area shows a wide variation in rock types. All bedrock found in the two
parks is part of the Precambrian (>600 m.y.) Canadian Shield and is covered
by varying depths of glacial till, outwash, and lacustrine material deposited
during the Wisconsin stage of glaciation. Bedrock in the VNP is part of a
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high grade metamorphic terrain, with schists, gneisses, migmatites, and
granites as major rock types; minor feldspathic quartzite and metaconglom-
erate are also present. Metamorphic grade increases to the south and east.
Rock types present in the VNP include 50% (of park area) metagraywacke and
biotite schist, 20% schist-rich migmatite with 25-75% paleosome (a migmatite
is a rock that has been raised to temperatures and pressures high enough to
cause partial melting; paleosome is that portion of rock which does not
melt), 12% granite, 10% granite-rich migmatite, 4% mixed metavolcanic rocks,
2% leucogranite, 1% feldspathic quartzite/metaconglomerate, 1% quartz-
feldspar gneiss.
The BWCA contains rocks generally representative of a much lower
metamorphic grade terrain than that seen in the VNP as well as a much wider
variety of rock types. The western portion of the BWCA, that occurring west
of R8W-R9W (91°25'W) boundary and north of Highway 18 (47°58'N) consists
dominantly of rocks of the Vermilion Massif, a series of granitic intrusives
ranging from diorite to granite. Related rocks include granite-rich
migmatite, amphibolite-migmatite and biotite schists. The migmatites found
in the VNP represent the northern contact zone of the Vermilion Massif with
surrounding country rock (Southwick 1972). On the eastern edge of this
portion are rocks of the Newton Lake Formation, a series of mafic to
intermediate metavolcanic flows and tuffaceous sediments (Sims 1972), rocks
of the Knife Lake Group, which include slate-graywacke, conglomerate,
arkose-graywacke, agglomerate, and andesite porphyry (McLimans 1972), and
rocks of the Ely Greenstone, a series of dominantly basaltic and diabasic
metavolcanic flows (Sims and Viswanathan 1972).
The central portion of the BWCA, that area between R8W to R11W (91°25'W
to 91°40'W) and R1W (90°31'W), below the Gunflint Trail, contains a wide
variety of rock types. This area is dominated by rocks of the Duluth Gabbro
Complex, a series of mafic intrusions ranging from gabbroic to troctolitic to
anorthositic. Within, and surrounded by, the Duluth Complex are rocks of the
North Shore volcanic group, a series of lava flows dominantly basaltic but
with appreciable amounts of felsic and intermediate flows.
The remainder of the area, that north of the Duluth Gabbro Complex
contact, is underlain by a variety of rock types. The majority of the Knife
Lake Group occurs in the western half as do minor amounts of Ely Greenstone
and rocks of the Giants Range Batholith, a series of tonalitic (quartz
diorite) to granitic intrusions (Sims and Viswanathan 1972). The Saganaga
Batholith, dominantly tonalitic in composition, is present east of the Knife
Lake Group. Minor amounts of metabasalt, metaandesite and metadiabase
(minor) are also present to the south and southwest of the Saganaga
Batholith. Part of the Gunflint Iron Formation occurs along the Duluth
Gabbro Complex Contact. In addition to the forementioned rock formations,
small granitic to andesitic intrusives are present, and are generally
associated with the Knife Lake Group.
The eastern portion of the BWCA, that between R2W (91°31'W), above the
Gunflint Trail (47°54'N), and R2E (90°15'W), is dominated by the Rove Formation
(graywackes and argillites) and the Logan Sills, a series of diabasic dikes and
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sills which intrude the Rove Formation. To the south a lesser amount of Duluth
Gabbro is present. By visual estimate, the area covered by each rock type (for
the entire BWCA) is:
Duluth Complex 40
Vermilion Massif 30
Knife Lake Group 8
Saganaga Batholith 5
Granite-rich magmatite 5
Logan Sills 3
Rove Format ion 2
North Shore Volcanic Group 2
Newton Lake Formation 2
Giants Range Batholith 2
Ely Greenstone 1
Distribution of poorly buffered soils—
A number of soil surveys have been carried out on parts of the BWCA, but
the survey by Prettyman (1978) of the Kawishiwi area of Minnesota covered an
area central to the BWCA and included the soil-type boundaries on printed
aerial photographs. Lakes and streams associated with the deeper soils in
the BWCA seem less likely to show effects from acid rainfall within the
immediate future.
The report by Prettyman describes 22 soil-mapping units in the Kawishiwi
area. These units are grouped into roughly 12 soil types, half loosely
defined (e.g., "peat and muck" and "poorly drained loamy soils"). The
principal soil types covering a large acreage are the following:
Barto Gravelly coarse sandy loam
Conic Gravelly sandy loam
Insula Gravelly sandy loam
Mesaba Gravelly sandy loam
Quetico Rock Complex Loam
Of these five types the Mesaba and Conic soils are described as usually
deep soils, 51-102 cm (20-40 in.) to bedrock, whereas the Barto and Insula
soils are 13-51 cm (5-20 in.) deep. The Quetico Rock Complex has soils that
range from 10 to 20 cm (4 to 8 in.) deep, and although its texture is given
as "loam," this texture refers to the portion of the soil that is not coarse
fragments and small rocks. Thus, if the capacity of the soil to withstand
additions of hydrogen ions can be measured by a combination of soil texture
and total soil depth (within the specified mineralogy of the Canadian Shield
bedrock types), then we can define a soil grouping within the Kawishiwi area
by combining the three shallow soils, Barto, Insula, and Quetico, despite the
fact that some differences in texture and geological origin can be
recognized.
Chemical data on these shallow soils are quite limited. Results of a
number of analyses for the Barto soils have been provided, however, by
personal communication from Dr. Prettyman. These results indicate the
following cation exchange capacity (CEC) and percentage base saturation:
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CEC
Soil (meg/lOOg) Base
series Horizon pH average saturation (%)
Barto B 21 4.8 24.21 18.63
B 22 5.2 21.95 16.58
B 3 5.7 13.78 10.39
The data here contrast with similar analyses for Mesaba soils. The latter have
37% base saturation in the parent material horizon (compared with 10% for Barto
soils). The higher base saturation in the upper horizons of Barto soils (18%)
probably reflects the increased organic matter and clay content and the
different type of exchange sites present there.
Effects of Acidic Precipitation on Soils —
The absence of a large soil volume for geological weathering greatly
influences the potential for small watersheds to withstand changes in the
rate of addition of hydrogen and sulfate ions from the atmosphere. These
pollutants are likely to enter the soil environment primarily through
precipitation, stem flow (precipitation draining along the trunks and stems
of vegetation), and throughfall (precipitation filtering through the forest
canopy). Pollutants transported long range will probably enter forest
systems primarily through precipitation. Effluents from local sources may
also contribute to this regional precipitation loading. In addition,
quantities of local pollution will be dry deposited on vegetation. The
fraction of this material which is not biologically assimilated will be
subject to leaching by precipitation and will enter the soil as stem flow or
throughfall. Stem flow and throughfall may be considerably enriched in
pollutants compared to precipitation carrying only the regional atmospheric
load (Abrahamsen et al. 1977).
The most significant soil-mediated effects may result from the fact that
rainfall bearing pollutant loads initiated as 862 or NOX has depressed
pH.
Effects of Acid Precipitation on Geochemical Weathering—
Since the pH of water in contact with minerals has a. marked effect on
weathering products that result during the breakdown of mineral, changes in
the pH of precipitation also have effects on the products and rate of
weathering. Through hydrolysis specific cations can be removed from the
mineral, allowing a more rapid change of crystal structure. Jenny (1950)
showed H+ replacing Na+, K+, or Csr+ in the crystal structure or
bonding with an 0 to form an OH" group. The H+ ion is very important
because its size allows easy penetration into the mineral, and its high
charge-to-radius ratio has a marked disrupting influence on the crystal's
charge balance (Loughnan 1969).
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Birkeland (1974) determined a series of mobilities for various ions and
found:
Ca2+ > Na1 + > Mg2+ > K1+ > Si4+ > Fe3+ > A13+.
Under the normal pH produced by background levels of carbonic acid (112003),
values for Fe and A13+ are generally so low as to be negligible.
Situations do occur, however, where the pH of soil solutions is such as to
allow Al to become soluble. In well-drained northern soils containing
abundant organic matter a pH of < 4 is possible. The compound A^C^ may
become mobile and migrate to a less acidic area and be precipitated (Loughnan
1969).
Where precipitation exceeds evaporation and soils are very permeable,
several pH dependent responses are observed:
1) Most of the Na+, K+, Ca2+, and Mg2+ is leached.
2) A10 and Si0 are released.
a. If soils are neutral to alkaline with low Csr+ and Mg ,
SiC>2 may leave in solution as does Na+ and K+.
b. If moderately acidic (4.5-6.5), Si02 and Al2C>3 are
immobile with the development of clay or a fine-grained mixture
of gibbsite (AHOH^) and quartz (Si02).
c. If highly acidic and rich in humic or other organic material,
Al2C>3 and Fe2C>3 may be removed in solution (Moore and
Maynard 1929) (Figure 14).
Since background levels of H+ in these major soils are traceable to
the carbonic acid in water, as well as the humic reactions, additions of
H+ from nitric and sulfuric acid in precipitation can dominate the
inorganic reactions. The separation of A13+ and Fe3+ may also be
seen in soils that show some evidence of podzolization, a process where Fe ,
Al, and organic material are leached from an eluvial (exit) horizon to an
elovial (into) horizon below. Recent work suggests that Fe and Al are
carried as part of a metallo-organic chelating complex, of which fulvic acids
are thought to be the common chelating compounds for a number of soils.
Fulvic acids are produced in the A or 0 horizons and chelate with A13+
and Fe3+ ions or with A13+ and Fe3+ hydroxy ions. Because these
compounds are water soluble they can be carried downward with percolating
water. At some depth in soils the complexes are destroyed and the metals
deposited, but if the percolating water reaches a soil or bedrock channel,
the metals can be carried with the organics to a stream or lake. Van
Schuylenborgh (1965) suggested that the organic portion of the molecule may
be destroyed by microbial action, with release of the cation.
Work by Schnitzer (1971) clarified the fulvic acid-metal complex
transfer. Under constant pH the complexes became more insoluble as metal
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ions were added to the fulvic acid solution; 1:1 molar Fe^+-Al^+-
fulvic acid complexes were completely soluble while 6:1 complexes were water
insoluble. Even 2:1 complexes showed decreasing solubility.
Thus transfer of Al^+ and Fe^+ could be envisioned as follows.
Fulvic acid is formed in the A or 0 horizon and, being water soluble, is
transported downward by percolating waters, constantly picking up Fe-*
and Al . As more metallic ions are picked up, the complex becomes
insoluble and can be precipitated in the B horizon if it has not reached a
bedrock surface or stream channel. Schnitzer (1971) showed that up to 56 g
of iron or 27 g of aluminum can be dissolved and kept in a solution by 670 g
of fulvic acid. These values are equivalent to 84 mg of iron or 40 mg of
aluminum per gram of fulvic acid.
Recent experiments indicate that increased acidity of precipitation,
through additions of dilute nitric and sulfuric acid, also can affect these
and other reactions in the soils. Availability of nitrogen, decreased soil
respiration and increased leaching of nutrient ions from the soil have been
reported (Abrahamsen et al. 1977). Since acid rainfall adversely affects
many other components of the soil-plant-water relationship, it has not yet
been possible to demonstrate clearly the nature of causal relationships in
the field. It is possible that acid damage to shallow, poorly buffered soils
might initially be partly offset by the nutritional benefits gained from
nitrogen compounds commonly occurring in the acid rain. Changes detected to
date in soil processes are too small to affect plant growth, but the studies
have been in areas of deeper soils than in the BWCA. In addition, the
enhanced acidification of soils produces a continuous loss of essential
cations and eventually the addition of nitrogen is of no advantage if other
nutrients are not available.
The H+ additions associated with the projected increase in SO^
deposition of 0.9-1.4 kg/ha-yr over the apparent presettlement depositon of
4-5 kg/ha-yr (Section 3) appear to be an increase of consequence for element
transformation and mobilization on the poorly buffered soils in this region.
Elements mobilized in this fashion may be taken up by plants, may reach
streams via the shallow groundwater, but most often will be carried to
deep, slow-moving groundwater surfaces. Here, these elements may remain in
their more toxic forms for extended periods and, in this sense an
irreversible effect is produced.
Nutrient Cycling
Soil-mediated effects of acidity on vegetation—
Although the relationships between soil acidity and vegetation growth,
metabolism, and reproduction are receiving increasing attention, many areas
of uncertainty remain. The following discussion will focus on available
information concerning soil-mediated effects on: (1) decomposition of
organic matter; (2) effects of cation losses and mobilized toxic elements on
growth of coniferous species; and (3) reproduction of coniferous species.
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Any potential reduction in a soil's cation exchange capacity and
essential nutrients, such as discussed in the previous section, will affect
the growth of the trees it supports. In general, forest plants obtain the
nutrients necessary for metabolism and growth primarily from soil.
Atmospheric sources are either indirect (mediated by soil) or secondary in
importance. Therefore, the potential for reduced availability of these
nutrients in forest soils is of concern.
In an unmanaged forest near its climax successional state important
macro- and micronutrients tend to be conserved in the soil-plant system.
Most remain within the cycle of organic production, decomposition, and
mineralization followed by reincorporation into living material. Leaching
losses in ground water are minimal (Frink and Voigt 1977) . Nutrient cycles
are not closed, however. Precipitation and nitrogen fixation are important
sources of nutrients to the forest (Ovington 1962), and additional supplies
of nutrients are made available by weathering of soil particles. These
inputs are countered by some ground-water leaching. Potential effects on
plant-soil interactions may result from effects on inputs and outputs to
nutrient cycles as well as soil-mediated changes in rate within the cycles.
Since Al^ is highly toxic to plants, the mobilization of this element by
additions of H+ to the soil medium can have important detrimental effects on
nutrient utilization and growth. Although Al^+ toxicity is well known for crop
plants, it is only now being investigated for the common tree species (McCormick
and Steiner 1978) .
Sulfur and nitrogen cycles—
The capacity of a forest to utilize additional sulfur is often closely
related to the nitrogen cycle. The two nutrients usually are utilized in a
fixed ratio. If nitrogen is abundant, the system may be sulfur limited and
have a considerable capacity to absorb anthropogenic sulfate. Such inputs of
sulfates might well stimulate increased growth. In such cases ttjSO^ in
rainfall might not increase soil acidity or degrade the nutrient pool.
However, mature timber stands are more likely to be nitrogen limited than
sulfur limited. If the capacity of these systems to utilize anthropogenic
sulfur inputs is exceeded, deleterious effects of I^SO^ on the
ecosystem's nutrient pool are possible.
As in the sulfur cycle, overall production and consumption of H+ ions
in the nitrogen cycle are balanced. Loss of soil bases and acidification are
still possible, however. When mineralization occurs followed by oxidation of
ammonium ion to nitrate, H+ ions formed will replace basic cations. These
basic cations are then subject to leaching in association with nitrate ions
as water passes through the soil profile if conditions allow any buildup of
nitrate ion (e.g., if the system is other than nitrate limited) (Reuss
1977).
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Most natural ecosystems tend to maintain low nitrate levels because
nitrates formed are rapidly taken up by the vegetation. In nitrogen-limited
forests anthropogenic' nitrates may stimulate plant growth. This would
prevent increased soil acidity due to processes within the nitrogen cycle and
also accelerate sulfate uptake reducing the potential for acidification due
to processes in the sulfur cycle.
Acid rain is postulated to decrease decomposition rates through adverse
effects on microbial activity (Oden 1976, N. R. Glass 1978). Apparently soil
pH values below 3.5 are required before effects on decomposition of pine
needles can be seen (Abrahamsen et al. 1977). Negative effects of soil
acidification in pine forests on microbial activity have been shown, but the
effect on decomposition was unclear (Tamm et al. 1977).
The direct effects of pollutants on ground beetles cited earlier can
have a marked effect on rates within the nutrient cycle. Benefits of
decomposer beetles include the return of nitrogen and inorganic phosphate,
the reduction of surface runoff, burial and mechanical breakdown of organic
materials, decreasing wastage of organic materials, increased surface storage
of nutrients, reduced loss of nutrients in runoff, and increased infiltration
and storage of moisture in the soil. In addition, these arthropods serve as
food for other insects and higher animals, aid in the dispersal of soil
microflora and microfauna, and may compete with less desirable (from a human
viewpoint) insects such as hornflies for organic material resources (Ritcher
1958, Macqueen 1975, McKinney and Morley 1975). In forest systems as much as
90% of the net primary production does not pass through herbivore food chains
but is deposited on the soil as litter and is acted on by complexes of
animals, fungi, and bacteria (Kurcheva 1960, Edwards and Heath 1963, Cross ley
1970, Whittaker 1975, and others). Examples of resource partitioning by
saprophagous arthropods are numerous, and their role in resource partitioning
and their use as indicators of environmental quality has been reviewed by
Cornaby (1975, 1978). He comments that they may have an exploitable role in
the deactivation of noxious materials and decomposition of slowly degrading
materials. Also, he points out that they may be very important as regulators
of the rate of release of nutrients and as detectors of subcritical levels of
pollutants in soils.
Specialists in the field of soil-litter arthropods seem to agree that
these insects are susceptible to harm from pollutants and that they may
affect important functional components of ecosystems. From a theoretical
study Harte and Levy (1975) and Dudzek et al. (1975) concluded that damage to
decomposers or nutrient pools is a potential source of instability to the
entire ecosystem.
Influence of affected lichens on nitrogen inputs in forests—
The potential reduction in nitrogen-fixing lichens or in their rate of
nitrogen fixation would have most effect in highly nitrogen-deficient soils,
such as those in the BWCA.
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Although most lichens contain only green algae, several genera contain
only nitrogen-fixing blue-green algae or blue-green algae in addition to
their green algae. Lpbaria pulmonaria (on Thuja occidentalis and sandy rocks
in northern Minnesota), many Peltigera and Nephroma species (on soils, duff,
and moss), and Sterocaulon paschale (on soil) contain blue-green and green
algae. Leptogium and Collema species (on soil and rock) contain only blue-
green algae. The percentage of cover of these lichens and their contri-
butions to the nitrogen regime of Minnesota forests is not presently known.
Forman and Dowden (1977) manipulated laboratory figures (Scott 1956,
Millbank and Kershaw 1969, Henriksson and Simu 1971) for amounts of fixed
nitrogen and determined that three Peltigera species (P. canina, P.
rufescens, and _P_. praetextata) would fix a total of 0/05-0.6 g N Tm2 lichen
cover)" day"-*- in a spruce-fir forest in Colorado.
Denison et al. (1977) investigated the current status of ^ fixation
in western Washington forests and the potential effects of acid rain on this
process. It is thought that even the low concentrations of S02 now found
in this area have a deleterious effect on N2 fixation by restricting the
distribution of the ephiphytic ^-fixing lichen, Lobaria pulmonaria. This
species, also present in the BWCA, is found in the Pacific Northwest forests
only where the mean annual SC>2 concentration is less than 5 yg/m^ (0.175
pphm), a figure lower than some background levels already recorded in the
BWCA (Section 3, Table 1). Lobaria pulmonaria fixes 100 times more nitrogen
than does litter and 10,000 times more nitrogen than soil organisms in these
acid forests. The sensitivities of Peltigera species are not known.
The rate of fixation of L. pulmonaria is about three times that of L.
oregana (Denison et al. 1977), the major N£ fixer of old growth and
coniferous forests in the Pacific Northwest. After exposure to l^SO^ of
pH 4 or less, L. oregana fixes less N2 •
Kallio and Varheenmaa (1974) exposed Stereocaulon paschale and Nephroma
articum to the air of Turku. Finland, where maximum SC>2 values in 1969 were
5.36 pphm S02 (153 yg SO^/m^) with NO^ and sulfates. Nitrogen
fixation decreased to 10-20% of controls. They suggest that the SC>2
combined with water on the lichen structures containing the blue-green algae
decreases the pH of the medium sufficiently to interfere with the metabolism
of the blue-green algae.
Influence of Affected Trees on Insect Populations
Three authors have reviewed interactions among air pollutants, plants,
and insects (Heagle 1973, Hay 1975, Ciesla 1975). Heagle notes "a common
finding is that trees injured and weakened by pollutants are more likely to
be atacked by insects that normally require weakened trees for successful
reproduction." Ciesla (1975) concludes that photochemical oxidant injury to
ponderosa pines in the San Bernardino Mountains predisposed the trees to bark
beetle attack. The understanding of the physiological mechanisms involved
needs to be determined for other combinations of pollutants, trees, and
insects.
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Pest insects do not always proliferate in areas subjected to air-pollu-
tion stress. In some instances declines in pest-insect populations have been
observed. The difference in response appears to be a result of interactions
of many variables. One variable seems to be feeding habit. Several lines of
evidence indicate that stress from pollutants such as S0£ and natural
occurrences such as drought may reduce the tannin content of leaves (Feeny
and Bostock 1968, oak leaves) and needles, which results in more free or
unbound protein foliage. Thus the foliage becomes more nutritious and a
"better" diet for foliage-feeding insects (G. Orians, University of
Washington, personal communication, 1978).
Our understanding of the effects of air pollutants on tree-insect
relations depends almost entirely on geographical historical surveys of trees
severely damaged by pollutants, insects, or combinations of the two. No
attempts have been made to determine dose-response thresholds. In most
cases patterns of insect outbreak relative to a pollution source, deviations
from normal outbreak patterns, or the appearance of insects in outbreaks that
rarely reach epidemic levels have been described (Ciesla 1975). Carlson et
al. (1974a) used stepwise multiple regression analyses and demonstrated that
foliar fluoride content was significantly related to damage caused by
complexes of foliage-feeding insects. Some of the observed insect-tree
pollution interactions are summarized in Table 9.
In an attempt to identify research problems considered critical for an
acceptable understanding of the interactions of air pollution and wood
vegetation, Bromenshenk and Carlson (1975) concluded, "There can be no doubt
that air contaminants are harmful to insect pollinators, although the exact
processes are not understood. Many forest trees and shrubs would not produce
seeds or reproduce themselves without insect pollinators...". Changes in the
population dynamics of forest pest insects may result from a predispositon of
the host to insect attack, as described earlier.
Bioaccumulation
Many trace elements are accumulated and concentrated through food-chain
processes. Organisms at higher trophic levels often have higher tissue
concentrations than do their prey. Potentially toxic compounds from the
Atikokan generating facility may become accessible and toxic to various
organisms through this process of biological magnification. The processes by
which this could occur are discussed below.
Trace-element availability from soils and plant uptake—
Factors affecting trace-element availability include pH, organic matter
content, soil drainage, soil-microorganism content, cation exchange capacity
(CEC), and anion content. Plant-root components may also affect nutrient
uptake by releasing organic compounds into the surrounding soil, modifying
the soil environment, and thereby modifying trace-element uptake (Tiffin
1977).
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Soils already high in various trace elements may be more vulnerable to
additional trace-element load, although in depleted or nutrient-poor soils
various trace elements (e.g., Mo, B, Zn) may improve the nutrient composi-
tion. In recent studies of the environmental impact of trace elements added
to soils as a result of coal combustion (Vaughan et al. 1975, Dvorak et al.
1977, Dvorak and Pentecost 1977), predictions of particulate deposition for
areas proximate to the power-plant model amounted to less than 10% of the
total endogenous content of trace elements. Each affected site must be
examined individually, however, since these models assumed worldwide soil
concentrations of trace elements and the variability factor among various
soils may be as much as several hundred.
The rates and processes involving trace elements are complex, and
factors controlling trace-element uptake in plants are not yet very well
understood. Once absorbed into the root system, however, trace elements may
be translocated to shoots which herbivorous animals may consume. Plants as
well as animals vary in their sensitivity to trace-element accumulation, and
different plant and animal organs respond differently with respect to trace-
element uptake. Obviously, the elements that are taken up in large
quantities and stored in organs preferred by certain wildlife forms
constitute a hazard to each trophic level in which this occurs. Furthermore,
the rate of vegetation turnover from grazing wildlife will modify the rate at
which material stored in shoots is recycled to the soil.
The bioaccumulation potential in various food chains requires much more
study in terrestrial animals. Food habits change seasonally, and seasonal
movements may take animals out of the path of the area of particulate
fallout, unless winds mix the pollutant path over a large area. This fallout
may be exacerbated by secondary pollutant sources from outlying areas, such
as is expected for the BWCA from the industrial north as well as areas on
either side of the Mississippi River, extending down to the Gulf of Mexico.
Incremental deposition of trace elements from the Atikokan facility onto
the BWCA is estimated to be comparatively small. The increase in deposition
of Hg predicted in Section 3 is being further investigated.
Impact of trace elements on terrestrial vertebrates—
The penetration of trace elements into animal systems largely occurs by
inhalation and ingestion (in food or water). Cutaneous absorption becomes
more critical in aquatic vertebrates, especially amphibians (such as
salamanders and frogs) and fish (which can absorb certain elements through
their gills). Virtually no information is available on the long-term effect
of low-dosage intake of various trace elements upon wildlife species,
information essential to an understanding of the long-term or cumulative
effects, or both, of trace-element accumulation.
Dewey's (1972) investigations show that fluorides may build up in
insects of the higher trophic levels, and he expressed concern that fluoride
accumulated by insects could affect insectivores up the food chain. Gordon
et al. (1978) are attempting to determine that portion of the diet of deer
88
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mice which constitutes a fluoride source for mice with excessive fluoride in
their femurs. Their data indicate that insects represent a considerable
percentage of the diet.
Kovacevic and Da'non (1952, 1959) analyzed stomachs of 136 species (34
families) of birds in Yugoslavia and found beetles representing 31 species
(17 families). Numerous other studies both in Europe and the United States
attest to the importance of insects as a food resource to birds. Thiele
(1977) provides a review of the predators of a specific family of insects
—the carabids. He lists hedgehogs, shrews, moles, bats, rodents, mice, and
birds (including owls and other birds of prey).
The population of timber wolves (Canis lupus) in northern Minnesota is
the largest of the continental 48 states. Because of their size wolves do
not appear to be immediately vulnerable to trace-element discharge, unless it
exceeds processing limits of soils and plant systems. The prey animals that
are herbivores will constitute the interface between trace elements in plants
and in wolves.
The eastern pine marten (Martes americana americana) is a fur-bearing
carnivore of considerable economic value in past years. Since the principal
regular food item for the marten is the small mammal (such as the red-backed
vole Clethrionomys gapperi in the BWCA), the greatest impact of trace
elements upon marten populations is likely to be exerted through small-mammal
populations. Voles may be affected by selected roots with high storage
levels of trace elements or through water supply (this may be obtained in
food).
The bald eagle (Haliaeetus leucocephalus) and osprey (Pandion haliaetus
cardinensis) rely upon fish for food items although other vertebrates appear
to be eaten as well. Ospreys have been known to take several species of
small mammals, other birds, reptiles, and frogs, as well as occasional
crustaceans, sea snails, and beetles. The bald eagle diet in north-central
Minnesota consists of 90% fish, 8% birds, and 2% mammals and invertebrates
(Dunstan and Harper 1975) . Obviously, trace-element effects on raptors are
best considered in view of their fish diet. Scientists have determined that
Hg levels in fish are already high in some lakes in northeastern Minnesota
(see Sections 5 and Appendix D).
Many other changes in major or key ecosystem processes, other than those
discussed, probably occur. Because of the lack of information on the effect
of pollutants on insect populations, food chains, and on the composition of
the ecosystems of the BWCA, it is premature to predict the potential economic
or ecological damage, or both.
Too many unknown factors make reliable statements impossible concerning
the effects of the Atikokan facility on trace-element fluxes through food
chains. Lakes already high in Hg may experience additional loads if acid
rain causes the release of existing sediment-bound Hg. Top carnivores and
fish consumers, such as raptors and aquatic mammals, are likely to accumulate
additional Hg, but the pace of bioaccumulation may vary considerably within
The BWCA. The low rates of trace-element deposition within the BWCA from
89
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Atikokan imply negligible short-term effects, but possible long-term
consequences.
APPLICATION OF RESEARCH FINDINGS TO THE BOUNDARY WATERS CANOE AREA
The impacts of air pollutants on terrestrial ecosystems and their compo-
nents can be grouped into four major categories: 1) acute direct effects on
ecosystem components; 2) acute indirect effects on components and complete
ecosystems; 3) chronic direct effects on ecosystem components; and 4)
chronic indirect effects on components and ecosystems. Each of these types
of impacts may have significance to the continued functioning of a given
ecosystem. To date the majority of data collected relate only to the acute
direct effects. In some cases, however, acute indirect and chronic effects
may be more important to the overall ecosystem than the acute direct effects
because the former relate to factors such as forest productivity, community
diversity, and ecosystem stability.
The severe limitations on data applicable to acute indirect and chronic
effects indicate a limit in the "state of the art" rather than an absence of
effects. These limitations have several causes: lack of long-term baseline
studies; lack of instruments that can measure very low levels of air
pollutants; and, perhaps most important, limitations in techniques that can
first measure the subtle changes occurring in ecosystems due to low levels of
pollution and then relate these changes to those levels of pollution.
Although data on direct and indirect effects from chronic low-level air
pollution are limited, basic ecological principles indicate the potential for
significant effects on the terrestrial ecosystems. These effects must be
extrapolated from studies of short-term effects, and the limits and the
sensitivity of such extrapolations must be taken into account. Through their
influence on the generation of oxidants, acid particulates, and acid
precipitation, the indirect effects of emissions contribute to regional
loading and are likely to be the most serious effects for the Quetico-BWCA
area.
In air-pollution impact studies a few characteristics remain fairly
consistent regardless of the differences between two or more physical and
biological areas:
1) Coniferous and lichen species within a polluted area are almost
invariably the first plants to manifest symptoms of injury, usually
because of toxic gases; and
2) Plant species growing along ridge tops or on any moderately elevated
area will accumulate greater effects from the phytotoxic gases than
the same species growing in the valleys, or riparian areas.
The following statements of projected significance of air^pollutants for
the terrestrial ecosystems of the BWCA are a synthesis of the research and
literature previously cited and, when possible, anticipate explicit responses
from applicable findings.
90
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Significance for Pines
The most sensitive native higher plant species for which information is
available is the eastern white pine, a prominent canopy tree. This species
is known to have been lost entirely from large areas subjected to frequent
exposures of high SC>2 levels. It can persist for many years, however, with
moderate levels of damage each year. In this situation growth is slowed, the
trees are less resistant to insect outbreak, and longevity is reduced.
Red pine and jack pine, the other two most dominant pine species in the
BWCA, may be less sensitive to SC>2 than eastern white pine. As such, at
increased SC>2 levels, these species would be expected to exhibit a lesser
degree of both visible and nonvisible effects than eastern white pine.
In general, most acid rain damage to plant tissues will occur over a
long period of time (many growing seasons) and, therefore, will be difficult
to evaluate. The earliest manifestation of acid damage in conifer needle
tissues will probably be the cessation of meristem activity in the basal
areas, causing the needles to be dwarfed and, in later stages, to abort and
be cast prematurely from the branch (Northern Cheyenne Tribe 1976). Although
slightly acidic rain in an area may not cause dwarfing during early needle
development, damage of the basal tissues may occur 1-3 yr later.
If the ambient concentrations of total solid part iculates, SC>2, 63,
and trace elements attributable to Atikokan are no higher than projected, it
is unlikely that short-term, visible damage will occur. Several recent
studies suggest, however, that growth and reproductive rates may be affected
at lower ambient pollution levels than those necessary to cause visible
injury, levels commensurate with S(>2 background levels already being
recorded near Atikokan (Section 3, Table 1). The usual time for planning and
developing the forest cover of a State forest, private property, or
recreational area is seldom less than 50-100 yr. More often it is as much as
200 years. White pine ordinarily live 350-400 yr. Plant scientists and
recreational area managers have, therefore, had to take a long-term view of
their resource and look at its development over tens of decades. Over these
periods, even small effects on the growth rates or lifespan of the dominant
species can have major consequences for the regional vegetation.
Significance for Lichens
Direct, visible effects on lichens are not anticipated in the BWCA
within 5 yr after the projected pollution levels attributable to the Atikokan
facility occur. The thresholds arid time-requirement for subtle effects on
species composition are not well established, but effects could be
significant in a decade or two. As more pollution sources begin operation
near the BWCA a complex interaction of potential lichen species
substitutions, changes in nitrogen balances, and other effects may begin.
Since the nitrogen-fixing species (Lobaria pulmonaria, many Peltigera spp.,
Nephroma, Collema, Leptogium, and Stereocaulon paschale) are present in the
Minnesota coniferous forests, detrimental effects on these components of the
forest ecosystem
91
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could lead to a significant loss to the nitrogen balance. Although the
ultimate consequences are not expected to be great, their degree cannot be
reliably predicted at this time.
Significance for Insects
The thresholds for air-pollution impacts on plant-insect relationships
are unknown. Effects at the concentrations for the BWCA have not been
documented. If effects occur they will probably be manifested as:
1) Injury to pollination systems dependent upon or benefited by insect
pollination (primarily by native pollinators). Compiled lists of
plants benefited by or dependent upon insect pollination for seed
production, or utilized by insects as food resources are lengthy;
2) Changes in the pest-insect populations of conifer and hardwood
forests;
3) Alteration in litter-soil subsystems resulting from harm to
saprophagous and predacious insects;
4) Mobilization of zootoxins through insect food chains to small
mammals and birds; and
5) Changes in key ecosystem processes or components that cannot be
identified in advance because of lack of information on the
functioning of insect populations in the BWCA.
Potential for the Bioaccumulation of Toxic Materials
The high density of forest vegetation in the BWCA potentially could
absorb and render unavailable much of the toxic material deposited from
aerial fallout. Trace elements could be expected to increase slightly in the
trees themselves (needles, seeds, bark, etc.) from direct dry deposition or
from secondary storage. Under the impact of acid rain the forest soils would
have lower cation exchange and organic matter content. Hence, the effect of
trace elements would be amplified by making the elements more available
(because of low pH) and by accumulating in small herbivores and fish.
Several fish species (e.g., bullhead, suckers, pike) form much of the
diet of osprey and eagle. Experimental work is needed to determine element
sensitivity and rates of bioaccumulation in these top carnivores of the
terrestrial system. Scientists have determined that mercury levels in fish
are already high in some lakes of northeastern Minnesota. Input from the
Atikokan plant itself may help shift the balance further toward harmful
levels of ingestion by raptors.
The BWCA also lies within the upper Mississippi flyway for migrating
birds. Incremental pollution damage to the BWCA ecosystem may harm not only
indigenous biota, but also affect migrants that pass through the area to
92
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feed. Many waterfowl are sediment filter-feeders, taking both invertebrates
and algae. These detrital materials may contain moderate levels of trace
elements in low pH systems, injurious to various birds.
Significance for Nutrient Cycles
Generalizations about the potential effects of acid rain on soils and
soil-plant interactions must be interpreted carefully because the BWCA is a
mosaic of diverse environments. Soils in the BWCA are already acid (pH 4 to
pH 5.7 at various depths). In many areas there is a 5-10-cm (2-4-in.) humus
layer with pH about 4, low cation exchange capacity (10-30 meq/100 g), and
high buffering capacity. For even sensitive soils, however, further
acidification by air pollutants whenever they are 15 cm (6 in.) or more deep
will be a slow process. Probably considerable time will elapse before growth
effects can be recognized. Sulfur and nitrogen entering the system in
precipitation could be a small nutrient source for the system.
Effects will be first noticeable on shallow soils or bare bedrock
systems. U.S. Forest Service studies have indicated that because thin, rocky
soils are widespread,the BWCA lands are the least productive and most
sensitive in the Superior National Forest (Heinselman 1977). Even small
additions of acidity to these systems could have relatively short-term,
irreversible effects.
Lake and Watershed Chemistry in Relation to BWCA Soils
By using the over-printed, six-photo maps provided in the Kawishiwi Area
Soil Report described earlier (Prettyman 1978), mapping of an area central to
the BWCA was carried out on all portions in which the potentially sensitive
soil types (shallow coarse soils overylying igneous bedrock) predominate.
This mapping is summarized on an index sheet (Figure 15). An example of the
pattern among the soils and the distribution of lakes is shown in a copy of
mapsheet number 1 (Figure 16).
Potentially sensitive headwater lakes—
Within the areas of shallow soils it is possible to recognize additional
criteria to define individual lakes most likely to show changes in lake
chemistry due to changes in rainfall chemistry. These criteria would include
the following:
1) No stream or spring inlets (i.e., headwater lakes);
2) Hard rock basins permitting no leakage except to the lake;
3) Shallow, coarse, or negligible soils throughout the watershed;
4) The absence of any significant adjacent wetland or peat; and
5) The watershed in which the adjacent land area is of about the same
or less than twice the area of the lake.
In the course of mapping Kawishiwi area soils into a "sensitive" group,
16 small lakes were identified within the mapping area, each apparently
93
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and evidence of drainage channels and wetlands from the aerial photographs.
Field inspection of these and 200-300 other small lakes in this area may
reveal that some of the 16 lakes identified as "susceptible" may fail to meet
the above criteria fully, and that other small sensitive lakes have been
missed. These 16 lakes, however, appear to be among the most likely
candidates for chemical and biological change if such changes are to be found
in the BWCA. It is urgent that observations of chemical characteristics be
made on these lakes at the earliest possible date. The lake locations and
characteristics are summarized in Table 10.
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SECTION 5
IMPACTS OF ACIDIFICATION ON AQUATIC ECOSYSTEMS OF THE BOUNDARY WATERS
CANOE AREA (BWCA) AND VOYAGEURS NATIONAL PARK (VNP)
INTRODUCTION
Deposition of acid from the atmosphere, with consequent severe effects
upon aquatic ecosystems, is by now a well-known phenomenon (Braekke 1976,
Dochinger and Seliga 1976). Both sulfuric and nitric acids are involved, and
hydrochloric acid may be a much more local source (Gorham 1976) . Many other
toxins are deposited in addition to acids, including heavy metals, a variety
of hydrocarbons, and nutrients such as nitrogen, potassium, calcium, and
probably phosphorus (Gorham 1976, 1978, Lunde et al. 1976, Wright and
Hendriksen 1978).
These pollutants may exert a wide range of effects upon organisms and
ecosystems, particularly oligotrophic (or nutrient-poor) ecosystems. Both
synergistic and antagonistic interactions are very likely. Although these
have had little investigation it is known that metal toxicity may increase
with increasing acidity. The acid may also have indirect effects upon the
toxicity of other ecosystem components (e.g., soil-derived metals, such as
aluminum and several trace metals) and upon the availability of nutrients
through weathering and biological activity (e.g., N, P, K, Ca, etc.) (Glass
1977).
The impact of increased acid loading and nutrients is determined by the
vulnerability of aquatic ecosystems. Geologic, physical, and chemical
characteristics of the aquatic environment are important variables in
determining the level of vulnerability. Biotic effects range from acute
toxicity and impairment or failure of reproduction within species to lowered
production and biotic diversity.
This section is a discussion of the impact of acidification on aquatic
ecosystems of temperate North America and Europe and the application of these
findings to the BWCA-VNP receptors. Comprehensive data on all aquatic organ-
isms present in the BWCA-VNP are lacking, but the information discussed can
be related to the BWCA-VNP by utilizing data collected in similar adjacent
areas. The Minnesota Copper-Nickel Study Area (MCNSA) (a 5,515-km^ area of
northeastern Minnesota south of the BWCA, including Ely, Minn.) and the
Experimental Lakes Area (ELA) of Ontario are located adjacent to and 150 km
from, respectively, the BWCA-VNP. Because of the similar terrestrial and
geological character of the areas, species present in both of these study
areas can be considered to be generally representative of the species present
in the BWCA-VNP. Therefore, lists of aquatic organisms found in the MCNSA
are included in Appendix D (Gerhart et al. 1978, Johnson et al. 1978, Piragis
et al. 1978). Specific information about the aquatic organisms in the ELA
98
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can be found in Hamilton (1971), Patalas (1971), Sakamoto (1971), Schindler
and Holmgren (1971), Schindler and Noven (1971), Stockner (1971) and Stockner
and Armstrong (1971). Information on the chemistry and fishes of 109 ELA
lakes can be found in Armstrong and Schindler (1971), Beamish et al. (1976),
Brunskill et al. (1971), Cleugh and Hauser (1971) and Schindler (1971).
CHARACTERISTICS OF LAKES VULNERABLE TO ACIDIFICATION
Lakes in eastern Canada and the northeastern United States are generally
very sensitive to acidification. Calcareous bedrock, overburden, and soil
are scarce in these regions, so that surface waters are poorly buffered
(Figure 17). Lakes of this type in the Adirondack Mountains of New York
state and Scandinavia have been severely damaged by anthropogenic S02
sources several hundred kilometers away (Johannessen et al. 1977, Hendrey et
al. 1976, Overrein 1977). Similar sources exist within a few hundred
kilometers of lakes in the southern Precambrian Shield areas of North
America, and it is likely that the most vulnerable waters are already
affected. It therefore seems important to identify physical and chemical
characteristics of these most sensitive waters so that they can be closely
examined and monitored for symptoms of increasing acidity or other changes.
Physical Factors in the Characterization of Vulnerable Lakes
For any given geological substrate, lakes with the smallest ratio of
drainage area to lake volume may have the poorest buffering because of the
small area of substrate available for neutralization by weathering. Lakes at
higher elevations are often affected first because more precipitation usually
falls in such areas, resulting in greater deposition. Such lakes also are
likely to be headwaters, or at least high in the order of lakes in a chain,
and likely to have less calcareous material in their drainages. Greater
volume (depth) allows greater capacity for diluting acid inputs. Few exact
studies of the efficiency of acidification exist because of the difficulty of
quantifying acid inputs and outputs in affected areas.
The location of Atikokan is of special significance since a large
portion of the area, within a 100-km radius, is in the Rainy Lake watershed
(Figure 18). The rivers within the 38,100-km^ watershed flow toward the
U.S./Canadian border lakes. Streams and lakes east of the Laurentian Divide
flow toward Lake Superior. Lakes to the west of the divide drain into the
western edge of Rainy Lake where the water flows at an annual average rate of
280,000 1/s through the dam at International Falls, Minn, before it starts a
northwest course through Lake of the Woods, Lake Winnipeg, and into Hudson
Bay.
The entire Quetico Provincial Park and Voyageurs National Park are
within the Rainy Lake basin. Most of the BWCA is included, except for the
eastern section, which is part of the Lake Superior watershed (Figure 19,
Figure 20). Of a park total of 88,800 ha, several thousand of the 34,700
ha of recreational water in the VNP were created by dams, leaving 54,080 ha
of land. The park has 31 named lakes and 422 unnamed swampy ponds larger
than 2 ha. The BWCA has a surface area of 439,093 ha patterned by 1,493
lakes greater than 2 ha, and over 480 km of major fishing and boating rivers
in addition to numerous streams and creeks.
99
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600
Miles
Rainy Lake
Basin
Figure 17. Regions of North America containing
lakes that are sensitive to acidification by
acid precipitation, based on bedrock geology.
Calcareous overburden will modify this picture
somewhat. (From Galloway and Cowling 1978).
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Chemical Characteristics and Responses of Vulnerable Lakes
Alkalinity, or the capacity of a solution to neutralize acid, is the
characteristic that reflects the sensitivity of lake water to pH change
resulting from strong acid input.
Any ion that enters into chemical reaction with strong acid, signifi-
cantly above the endpoint pH, can contribute to titrated alkalinity.
Alkalinity = [Cations] - [Anions] ~
Alkalinity = 2[Ca2+] + 2[Mg2+] + [Na+] + [K+] - 2[S0~] - [N03-] - [Cl~]. (19)
For the most part, alkalinity is produced by anions or molecular species of
weak acids that are not fully dissociated above a pH of 4.5. In most
natural water the alkalinity is practically all produced by dissolved
carbonate and bicarbonate ions. A definition expressing alkalinity in terms
of the "changeable" ions present is given in Eq. (20) (Deffeyes 1965):
Alkalinity = [HC03~] +
x ~
with [x] giving the sum of the equivalents of noncarbonate weak acid species
(e.g., organic acids, silicate, ammonia) where applicable. In humic lakes
of low total alkalinity, organic acid anions (carboxylates) may make up the
major fraction of the alkalinity (Beck et al . 1974). Equilibrium pH levels
in these brown-water lakes will be lower than in purely bicarbonate-buffered
waters because of the lower pKa values (4-5) of the carboxylic acids,
compared to carbonic acid (pKa 6.3). This also means that for comparable
levels of total alkalinity, a given level of strong acid input will produce a
lower pH in humic water than in pure bicarbonate water. The change in
hydrogen ion concentration per unit change in alkalinity (A[H+]/A
Alkalinity) is thus determined by the total concentrations and species of
weak acid present.
Under any system of reporting titrated alkalinity now in use the effect
of all the anions that may react when a strong acid is added are lumped
together and reported as an equivalent amount or a single substance or in
terms of postulated ions (e.g., CaCC>3 mg/liter or HC03~ eq/liter).
Irrespective of differences in the content of weak acids and their
influence on relative pH change, the distinguishing feature of all lakes
potentially sensitive to acidification is low total alkalinity. For lakes
situtated in regions of hard bedrock resistant to weathering, low alkalinity
is imparted by low concentrations of base-forming cations. Throughout large
areas of the Precambrian Shield, carbonates are undetectably low in lake
watersheds. In other areas calcareous drift deposited by receding glaciers,
lacustrine clays (for example, in the Lake Agassiz basin), or marine
sediments help to buffer lakes, rendering them less vulnerable to
acidification. The most vulnerable lakes in granite (noncalcareous) regions
have conductivities as low as 10-20 ymhos cm and alkalinities of 10-20
yeq/liter. Some BWCA-VNP lakes are as low as this in neutralizing capacity,
and many approach these levels. The percentage distribution of 85 BWCA-VNP
lakes based on the water alkalinity observed in November 1978 is shown in
Figure 21 (Glass et al., unpublished data, 1979; see also Appendix D) .
104
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Atmospheric Acidification of BWCA-VNP Lakes
Several lines of evidence suggest that some lakes in the BWCA are at or
near the threshold of serious acidification, severe enough to initiate
species depletion and lowered productivity.
1) The mean annual pH of precipitation in several areas on the
Laurentian Shield of eastern North America, both adjacent to and far from the
BWCA, is often at or below 4.8 (Table 11). This value is the minimum mean
annual pH level observed to be without major biotic consequences (so far) in
southern Scandinavia (Wright and Gjessing 1976). The pH of precipitation in
these Laurentian Shield areas seems likely to have declined since the
mid-19501 s, when it may well have been above 5.6 (cf. Likens 1976). At the
present time it is frequently observed to fall (in separate precipitation
events) below pH 4.5. A mean annual precipitation pH of less than 4.5 (only
twice the hydrogen ion concentration at pH 4.8) is associated with severe
damage to the aquatic biota in both southern Scandinavia (Wright and Gjessing
1976) and the Adirondack Mountains of New York (Schofield 1976a) and has led
lake pH in many instances to fall well below 5 from initial levels well above
6.
2) Many lakes in the BWCA-VNP are somewhat acid (pH 6.1-6.3) and low in
alkalinity «100 y equiv/liter) (Figure 22). They also exhibit calcite
saturation indices (CSl) (Conroy et al. 1974, Kramer 1976) high enough to
suggest great susceptibility to damage by acid loading (Table 12). Moreover,
these are not the most acid lakes in the BWCA. R. F. Wright (1974) has
reported one lake with a mean pH of 5.7, and it is likely that other lakes of
the more than 2,000 have even lower values.
3) Sulfate loadings to northern Minnesota from historic background and
distant urban-industrial sources now amount to an average of about 11
kg/ha-yr ranging from 4 to 14 kg/ha-yr (Table 1). Such loadings appear to
have reached a level that is extremely critical for lake acidification.
Dickson (1978) has shown that, in southern Sweden, sulfate loadings of as
little as 5 kg/ha-yr appear to lower the pH of some lakes below their initial
levels of about 6.5 (sensitive lakes with low neutralization capacity in
their surroundings) or 7.0 (less sensitive lakes with greater neutralization
capacity). In the more sensitive lakes, as sulfate loading enters the range
of 10-20 kg/ha-yr, pH declines very sharply from above 6 to nearly 5 (Figure
23). Further sulfate loading produces a much slower decline in lake pH,
about 60 kg/ha-yr being required to lower it to slightly above 4.
Any additional sulfate loading from the Atikokan power plant, e.g.,
0.9-1.4 kg/ha-yr to some BWCA lakes and 3.4-5.1 kg/ha-yr to some Quetico
lakes, is likely to tip the balance further toward the point of severe
acidification effects upon aquatic ecosystems, such as have been observed in
southern Scandinavia, the La Cloche Mountains of northwest Ontario, and the
Adirondack Mountains of New York. In these locations, however, the most
severe acidification — to levels of pH near 4 — has required loadings of
about 60 kg/ha-yr. It may be noted that the strong acid loadings observed in
southern Scandinavia, the La Cloche Mountains, and the Adirondacks have
resulted in very rapid declines of lake pH. The rate of acidification has
106
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TABLE 12. CALCITE SATURATION INDICES (CSl) FOR 85
BWCA-VNP LAKES3
Percentage
of lakes
10.6
18.8
34.1
29.4
7.1
CSI
index"
<1
1-2
2-3
3-4
4-5
CSI
classification
Terrain is most stable and
not susceptible to change
Possibly susceptible to change
Probably susceptible to change
Susceptible to change
Highly susceptible to change
aCalculated according to Conroy et al. (1974) and
Kramer (1976).
bCSI = p(Ca2+) + p(Alk) - p(H+) + pk, where p(x) =
-log^Q (x), pk = +2, (Ca2+) is given as mol/liter ,
and (Alk) and (H+) are given as eq/liter.
109
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ranged between -0.02 and -0.06 pH units/yr in southern Scandinavia, where
original lake pH values ranged from 6.2 to 7.3, and between -0.05 and -0.10
units/yr in eastern North America, where the original lake pH ranged from 5.0
to 6.7 (Wright and Gjessing 1976). Such rapid declines are not expected in
the BWCA unless acid loadings increase considerably above present levels.
Slower declines in lake pH may be occurring even with present loadings,
however, and cannot be viewed with equanimity.
An experimental example illustrates the great sensitivity of lakes with
low alkalinity. In 1976 and 1977 a total of 1.14 eq/liter of H+ were added
to the surface of an ELA lake (#223) as H2SC>4 (Schindler et al. 1979).
The bicarbonate content of the lake was reduced from an original value of 86
eq/liter to 10 eq/liter. Since the original pH of precipitation was 4.95,
this acidification regime is equivalent to changing the pH of precipitation
to 4.2 for a period of 10 years (Schindler, personal communication, 1978).
Lake 223 is not one of the most vulnerable lakes in the region. Its
bicarbonate value is slightly above the mean. Other lakes in the area have
alkalinities as low as 8% of that of lake 223. Depending on pH levels, such
lakes may be seriously affected by precipitation that has been acidified to
even a few tenths of a pH unit more acid than normal. The effect of acid
addition on the pH of water from selected BWCA-VNP lakes and the influence of
the alkalinity and CSI of the water are shown in Figure 24. Note the large
differences in acid required to reach pH 5, a value critical for most fish
reproduction.
In addition to the shifts in major ion composition that constitute
acidification, significant changes in certain trace metals and organic
fractions of acidified lakes have been observed. Increased concentrations of
aluminum, manganese, zinc, copper, and nickel have been reported in lake
water from acidified regions (Dickson 1975, Schofield 1976b, Wright and
Gjessing 1976, Dillon et al. 1977). These increased metal concentrations may
be due in part to increased atmospheric loading (Ni, Cu) associated with
specific pollutant sources, and to increased leaching from soils or lake
sediment (Al, Mn, Zn). Schofield (1977) determined that 0.25-1.0 ppm
aluminum leached from soil by snowmelt water at pH 4.4-5.9 was a major factor
in causing severe gill damage and death among larval brook trout, a fish
species found in the BWCA as well as the Adirondacks. Mobility of these
metals is also enhanced at low pH levels. Increased transparency reported in
some acidified lakes (Dickson 1975, Schofield 1976a) may be due to
precipitation of humic and fulvic acids at low pH and high aluminum
concentrations (Dickson 1977).
Marked temporal and spatial variations in strong acid and metal
concentrations have been observed' in lakes and streams as a result of snow-
melt (Johannessen et al. 1977, Schofield 1977, Siegel 1979). During the
initial phase of melting, acids stored in the snowpack are leached out by
water percolating down through the snowpack. Strong acids are thus concen-
trated in the early fractions of meltwater leaving the snowpack. Passage of
this acid meltwater through ice-covered lakes, at low levels of discharge,
results in the temporary formation of a shallow (usually <1 m) , but highly
acid layer of surface water under the ice. This phenomenon has even been
observed in moderately well-buffered lakes in the Adirondack region
111
-------
4.0r
4.9
"Alkalinity as ppm CaCQj
*LoKe number
eCalcl«* Saturation Index
900
KJOO 1900 XXX) 2900 3000 3900 4000
Mteroequivotonts [rf] added per liter of lake water
4500
9000
4.0 r
4.9
Alkalinity as ppm CoCOj
*Lokt number
cCalcltt Saturation Index
900
1000 1500 2000 2500 3000 3900 4000
Microequivalents [H*l added per liter of lake water
4900
5300
Figure 24. Effect of acid addition on the PH of water from selected
BWCA-VNP lakes.
112
-------
(Schofield 1976b) . Sensitivity of lakes to this short-term, but intense,
form of acidification is thus governed more by the physical process of acid
concentration from the snowpack and transport of meltwater under ice cover
than by alkalinity of the lake water alone. The degree and time of meltwater
in contact with soil's in the drainage system will also significantly affect
acid and metal levels in the runoff. Table 13 shows snow-meltwater quality
from samples collected in the BWCA-VNP in March 1978. First meltwater
contains concentrations of acids two to three times the mean values for the
samples. Measured snow loadings for 1977-78 are given in Appendix D.
The concentrations of most trace elements in the surface waters of the
BWCA-VNP are generally low (Poldoski and Glass 1975, Glass et al.,
unpublished data, 1979). Because of the low concentrations of most
components, increased concentrations will result in greater percentages of
toxic metals present in biologically active forms (Poldoski and Glass 1975,
Glass 1977).
Another concern related to acidification in northern Minnesota is the
recent (1976) discovery of elevated mercury residues in fish in several BWCA
lakes (Minnesota Department of Natural Resources 1978) . Mean Hg levels in
fish from two large lakes, Basswood and Sand Point, exceeded the 1978 FDA
action level of 0.5 ppm. Figure 25 and Tables 7-9 in Appendix D provide data
on the mercury levels in fish from lakes from the BWCA-VNP region. These
fish are from lakes that previously would not have been considered endangered
by acidification. No specific source for the mercury contamination has yet
been identified. Two hypothesized sources are fallout from regional
atmospheric concentrations of fossil-fuel combustion products or mobilization
of mercury from bedrock geological sources, or both.
Regardless of its source, the Hg problem in the BWCA is likely to be
aggravated in several ways by increased combustion-product deposition. The
direct addition of more mercury is one such way (see previous discussion).
Lower pH may increase the mobility of mercury from sediments and rocks.
Studying the relation of acidification to mercury accumulation in fish in
Sweden, Jernelov et al. (1976) and others (Brouzes et al. 1977) have found
that the formation of methylmercury, the form of mercury most rapidly
accumulated in tissues, is enhanced at pH levels below 6. In addition, fish
are thought to take up methylmercury more rapidly at low pH. The net effect
of reduced pH on accumulation is well illustrated by Figure 26 in which Hg
residues in brook trout from Adirondack lakes are compared (Schofield,
personal communication, 1978) . Trout from acid drainage lakes had mean
tissue concentrations that were three times higher than those of trout from
limed, seepage, and bog lakes.
IMPACTS UPON AQUATIC COMMUNITIES
The most obvious biological effects of acidification occur to fish
populations. Less conspicuous, but no less severe damage also occurs to
other organisms ranging from frogs to microbes. In fact, acidification
affects organisms at all trophic levels in fresh waters. The number of
species is reduced, biomass is altered, and major processes are interrupted.
113
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TABLE 13. SNOW-MELTWATER ENRICHMENT BY DISSOLVED COMPONENTS - CONCENTRATIONS
AND PERCENTAGE OF TOTAL MASS FOUND IN MELTED SNOW AS A FUNCTION OF THE
PERCENTAGE MELTED (AVERAGE OF THREE SITES IN BWCA-VNP)
Percentage [H+]
snow-melt pH %
10
20
30
40
50
60
70
80
90
100
4.26
4.25
4.30
4.46
4.63
4.71
4.76
4.80
4.82
4.86
(18)
(19)
(17)
(11)
(7)
(6)
(5)
(6)
(5)
(5)
[NH4 + ]
mg/1 %
0.15
0.19
0.16
0.11
0.08
0.08
0.07
0.07
0.07
0.07
(14)
(18)
(15)
(11)
(8)
(8)
(7)
(7)
(7)
(7)
[504]
mg/1 %
1.8
1.9
1.7
1.0
0.5
0.4
0.3
0.3
0.3
0.2
(21)
(23)
(21)
(12)
(6)
(4)
(4)
(4)
(3)
(2)
[NO^]
mg/1 %
2.3 (18)
2.4 (19)
2.3 (17)
1.5 (11)
l.Q (8)
0.8 (7)
0.8 (6)
0.6 (5)
0.7 (5)
0.6 (5)
[cr]
mg/1 %
0.15
0.16
0.15
0.11
0.11
0.08
0.09
0.08
0.09
0.07
(14)
(15)
(14)
(10)
(10)
(7)
(8)
(7)
(8)
(6)
[F-]
mg/1 %
0.02
0.02
0.02
0.02
0.01
0.01
0.01
0.01
0.01
0.01
(14)
(14)
(14)
(14)
(7)
(7)
(7)
(7)
(7)
(7)
114
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-left column, less than 15 inches
-right column, 15 inches and over
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Mercury Concentration (m g /1)
Northern Pike, 1977, Northern Minnesota
-left column, less than 21 inches
-right column, 21 inches and over
OO
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Mercury Concentration (m g /1)
Figure 25. Relationship between frequency and mercury concentrations
of walleye and northern pike taken from selected BWCA-VNP area lakes.
(Data from Minnesota Department of Natural Resources 1978.)
115
-------
1.00
0.50
E
Q.
Q.
;0. 10
O
k.
0>
0.05
Acid drainage lakes
O O °O O O
O
Limed, seepage 8 bog lakes
20
30
Length (cm)
40
Figure 26. Regressions of log mercury concentration
against total length for brook trout sampled from
acid drainage lakes and limed, seepage, and bog
lakes in the Adironacks. (©, adjusted mean
mercury concentrations from the two classes, for
convariance analysis). (After Schofield, personnal
communication, 1978).
116
-------
Although the literature concerning effects of acid mine drainage (AMD)
on freshwater ecosystems is extensive, it is not directly applicable to the
acid-precipitation problem. Often the uncontaminated waters of coal mining
areas have higher alkalinity and hardness than the very soft waters acidified
by acid precipitation. Acid mine drainage water usually has a heavy load of
iron and other heavy metals and frequently depresses the oxygen concentration
of receiving waters. High turbidity and the presence of chemical floe are
also common and greatly alter aquatic habitats. These factors make it very
difficult to extrapolate observations from AMD situations to those in the
Laurentian Shield, for example. The evidence used in this report is taken
primarily from literature pertaining to acid precipitation, although some
reference to AMD literature is made where relevant.
The variety of species of plants and invertebrate animals occurring in
fresh waters is enormous, and the kinds of organisms present differ markedly
from one locale to another even though water chemistry may be similar. It is
at best difficult and probably futile to try to interpret ecosystem damage at
lower trophic levels by comparing lists of species. On the other hand,
changes in major processes such as primary and secondary production and
decomposition can be broadly described and compared. Effects of stress on
the major functional guilds may be compared from place to place. Finally, a
few groups of organisms seem to be remarkably insensitive to strong mineral
acidity and are common to many acid environments, whereas some other groups
are clearly intolerant of pH levels below 6.0 to 5.5.
Effects on Microbiota
The production of fish and other animal life in a lake is ultimately
dependent upon the availability of organic food resources, primarily plant
materials. The sources of organic materials may be divided into two major
categories: autochthonous, originating by primary production in the lake,
and allochthonous, transported into the lake by inflowing water, airborne
litter, or dissolved in rain. The relative importance of each of these
sources varies greatly from lake to lake. One principal route for both
autochthonous and allochthonous organic matter into the trophic system of a
lake is via the detritus (organic particulate matter).
Bacterial consumption and mineralization of organic matter, both parti-
culate (POM) and dissolved (DOM), allows a cycling of carbon which dominates
the structure and the functioning of the system and provides what Wetzel
(1975) has called a fundamental stability to the system. In the deep, open
water of the pelagic zone, where phytoplankton production normally provides a
substantial portion of the nonrefractory organic matter, bacteria rapidly
assimilate dissolved labile organic substances (DOM) derived from photo-
synthesis and convert them into bacterial biomass (Hellebust 1974, Fogg
1977). Only a small portion of the DOM refractory material is likely to
survive longer than 24 h (Saunders and Storch 1971). The bacterial
mineralization rate of POM appears to be rather slow, a few percent per day
(Wiebe and Smith 1977, Cole and Likens 1979), so that this new biomass is
actually available to other trophic levels. Not only do the bacteria
conserve the energy stored in labile DOM, which otherwise would be lost from
the system, but they also convert (at a slower rate) some of the refractory
117
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DOM into a usable form. Fungal and bacterial communities render other POM
into forms that are useful for detritivores (Boling et al. 1975). The
significance of these activities to ecosystem energetics can be better
appreciated when one considered that on the order of 90% of the organic
carbon in the water column is DOM and that detrital POM is many times larger
than the total living carbon biomass.
There are other sources of detritus in the pelagic zone. In some lakes,
particularly small or shallow lakes, macrophytes and benthic algae are
important sources of autochthonous organic carbon. Material from these
plants may contribute significantly to detritus in the pelagic zone. In
deciduous forest lakes, leaf litter falling or blown onto the surface has
been found to be 200-500 g dry leaves per meter of wooded shore line (Jordan
and Likens 1975, Gasith and Hasler 1976). This forest litter plus that which
is added by stream inputs contributes to both DOM (after leaching) and POM.
Water-column detritus generated from all of these sources has three
possible fates. It can be transformed biologically, it can sink to the
sediments where it accumulates or is transformed biologically, or both, or it
is lost from the system by outflow. In the first two cases, microbial
activity plays a key role in removing detritus.
The inhibition of microbial decomposition can have profound effects
throughout an aquatic ecosystem. Detritus removal, conservation of energy,
nutrient recycling, primary production, detritivore production, and thus
production at higher trophic levels can all be affected by changes in
microbial activity.
Several investigations have indicated that microbial decomposition is
greatly inhibited in waters affected by acid precipitation. An abnormal
accumulation of coarse organic detritus has been observed on the bottoms of
six Swedish lakes where the pH decreased by 1.4-1.7 units in the past three
to four decades (Grahn et al. 1974). Bacterial activity apparently
decreased, and in some of the lakes the sediment surfaces over large areas
were made up of dense felts of fungus hyphae. In one of the lakes, Gardsjon,
85% of the bottom in the 0-2-m depth zone was covered with a thick felt of
fungus. Lime treatment caused a rapid decomposition of the organic litter as
well as great reductions of the fungal felt (Andersson et al. 1974),
indicating that an inhibition of bacterial activities had taken place at low
pH. Similar neutralizations of acidified lakes in Canada resulted in a
significant increase in aerobic heterotrophic bacteria in the water column
(Scheider et al. 1975). Results from field and laboratory experiments with
litterbags in Norway (Hendrey et al. 1976) also indicate reduced weight loss
of leaves in acidic waters. Dissolved organic carbon (DOC) in the inflowing
water was found to contribute ca. 50% of allochthonous inputs and 8% of all
organic carbon in Mirror Lake, while fine particulate organic carbon (FPOC)
was negligible (Jordan and Likens 1975). The extent to which this DOC input
is converted to bacterial biomass or otherwise enters into the energetics of
a lake is not known. Observations of abnormal accumulations of organic
debris have also been made in AMD waters in South Africa (Harrison 1958) and
West Virginia (DeCosta, personal communication, 1978).
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In laboratory experiments Bick and Drews (1973) found that the decompo-
sition rate of peptone by microbiota decreased with pH and that the oxidation
of ammonia ceased below pH 5. Bacterial cell counts and the species number
of ciliates also decreased. Numerous other studies indicate that the
microbial decomposition of organic materials is markedly reduced at pH levels
commonly encountered in lakes affected by acid precipitation (Hendrey et al.
1976).
Accumulations of organic debris and extensive mats of benthic algae, as
observed in the Swedish lakes (Grahn et al. 1974), both seal off the mineral
sediments from interactions with the overlying water and hold organically
bound nutrients that would otherwise have become available if normal
decomposition had occurred. The reduction in nutrient availability can be
expected to have a negative feedback effect on the organisms, further
inhibiting their activities. The reduction of nutrient supplies to the water
column from the sediments, because of the physical covering and from reduced
mineralization of organic materials in the water itself, will lead to reduced
phytoplankton productivity. These ideas have been formulated into the
hypothesis of "self-accelerating oligotrophication" by Grahn et al. (1974).
Qualitative observations support this hypothesis, but quantitative evaluation
is lacking.
Reduction of microdecomposer activities may have a direct effect upon
the invertebrates. Although certain benthic invertebrates appear to feed
directly on the allochthonous detritus material, it seems that "conditioned"
(colonized by microorganisms) material is preferred, and that the nutritional
value of the detritus is highly increased by conditioning (Boling et al.
1975). Bacteria may also be a food source to be removed by the filtering
apparatus of organisms such as the Calanoida. An inhibition of the
microbiota or a reduction in microbial decomposition processes would
therefore have a direct impact on the lakes' animal communities.
Because of the low temperature and lack of nutrients in the BWCA-VNP
waters for in-lake energy fixation, the terrestrial production of energy in
the form of plant detritus is very important for supplying energy to the food
chain as well as transferring nutrients to the aquatic production system.
When the decomposition and transformation of the detritus is reduced or
eliminated by acidification, then less energy is available for ultimate fish
production. Since the waters of the BWCA-VNP are generally infertile and
support relatively low concentrations of fish, the resultant decrease in the
fish crops would be expected to decrease to levels even lower than those at
the present time.
Effects on Benthic Plants
In waters affected by acid precipitation major changes occur within
plant communities. Most of the available data are qualitative and descrip-
tive although some experimentation has been done. Intact lake-sediment
cores, which included the rooted macrophyte Lobelia dortmanna, were incubated
at four pH levels (4.0, 4.5, 5.5, 6.0) at Tovdal in southern Norway. The
growth and productivity of the plant (C>2 production) were reduced by 75% at
pH 4 compared to the control (pH 4.3-5.5), and the period of flowering was
delayed 10 days at the low pH (Laake 1976).
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In five lakes of the Swedish west coast, a region severely affected by
acid precipitation, Grahn (1977) reports that in the past three to five
decades the macrophyte communities dominated by Sphagnum have expanded. In
the sheltered and shaded locality Lake Orvattnet, in the 0-2-m depth zone,
the bottom area covered by Sphagnum increased from 8% to 63% between 1967 and
1974. In the 4-6-m depth zone, the increase was from 4% to 30%. At the same
time, pH in Orvattnet decreased 0.8 units to approximately 4.8. Similar
growths of Sphagnum occur in other Swedish lakes, in Norwegian lakes, and in
AMD water as well (Harrison 1958, Harrison and Agnew 1962, Hagstrom 1977).
At the pH of these acid waters, essentially all of the available inorganic
carbon is in the form of C02 or 112^3. Conditions are more favorable
for Sphagnum, an acidophile which is not able to utilize HCO^j as do
many other aquatic plants. The moss appears to simply outgrow the flowering
plants under acid conditions.
In developing their hypothesis on oligotrophication, Grahn et al. (1974)
have stressed two biologically important consequences of this Sphagnum
expansion. First, Sphagnum has an ion-exchange capacity which results in the
withdrawal of base ions such as Ca from solution, thus reducing their avail-
ability to other organisms. Secondly, dense growths of Sphagnum form a
distinct biotype that is unsuitable for many members of the bottom fauna.
Under some acid conditions, unusual accumulations of both epiphytic and
epilithic algae may occur. In the Swedish lakes Grahn et al. (1974) report
that Mougeotia and Batrachospermum become important components of the
benthos. In Lake Oggevatn (pH 4.6), a clear-water lake in southern Norway,
not only is Sphagnum beginning to replace Lobelia dortmanna and Isoetes
lacustris, but these macrophytes have been observed to be festooned with
filamentous algae.
Heavy growths of filamentous algae and mosses occur not only in
acidified lakes, but have also been reported in streams in Norway affected by
acidification. In experiments in artificial stream channels using water and
the naturally seeded algae from an acidified brook (pH 4.3-5.5), increasing
the acidity to pH 4 by addition of sulfuric acid led to an increased
accumulation of algae compared to an unmodified control (Hendrey 1976). The
flora was dominated by Binuclearia tatrana, Mougeotia sp., Eunotia lunaris,
Tabellaria flocculosa, and Dinobryon sp., each accounting for at least 20% of
the flora at one time or another. The rate of radioactive carbon uptake per
unit of chlorophyll in the channels, measured on two occasions, was lower in
the acid channel by approximately 30%, suggesting greater algal biomass
accumulation at low pH despite lower productivity.
Several factors may contribute to these unusual accumulations of certain
algae. The intolerance of various species to low pH or consequent chemical
changes (Moss 1973) will allow just a few algal species to utilize the
nutrients available in these predominantly oligotrophic waters. Many species
of invertebrates are absent at low pH, and removal of algae by grazing is
probably diminished. Microbial decomposition is inhibited, as was previously
noted, which also reduces the removal of algal mass.
In the BWCA-VNP, reduction in growth and production of benthic plants
will probably not be important since the lakes most likely to be acidified
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are the same lakes that have few, if any, aquatic plants. If indeed the two
were to co-exist, then decreases in benthic plants could reduce juvenile fish
recruitment for those species which utilize macrophyte beds for nursery
areas. The biomass of benthic plants usually enters the detrital food chain
and reductions in this energy source could reduce fish standing crops. If
filamentous algae were to be established during acidification, the visual
aesthetics of pristine lake shorelines could be reduced.
Effects on Phytoplankton
There is no consistency among various investigations as to which
phytoplankton taxa are likely to be dominant under conditions of
acidification. The Pyrrophyta may be more common (e.g., species of
Peridinium and Gymnodinium) than others in lakes near pH 4.0. With
decreasing pH in the range 6.0-4.0, many species of the Chlorophyta are
eliminated, although a few tolerant forms are found in the acid range. In
their survey of 155 Swedish west coast lakes, Aimer et al. (1974) found that
blue-green algae became less important with decreasing pH, but Kwiatkowski
and Roff (1976) found the opposite to be true in lakes of the Sudbury,
Ontario, region.
Conspicuous decreases occur, however, in phytoplankton species number,
species diversity, biomass, and production per unit volume (mg/nH) with
decreasing pH. Lake clarity and the compensation depth increase with lake
acidification, so that primary production (mg/m2), although lower in acid
than non-acid lakes, is not as severely depressed as is production per unit
volume (Johnson et al. 1970, Aimer et al. 1974, Hendrey and Wright 1976,
Kwiatkowski and Roff 1976). The low phytoplankton biomass «1 mg/liter has
been correlated with the concentration of available phosphorus, which
generally decreases with lower lake pH (Aimer et al. 1974). Low availability
of inorganic carbon has also been suggested as a factor limiting primary
production in acidic lakes (King 1970, Johnson et al. 1970).
In the BWCA-VNP, if production is decreased, the energy available for
food-chain transfer is reduced, and an effect on total fish production would
be expected. If the grazing zooplankton are reduced before the phytoplankton
are affected, the fish population will respond to the zooplankton while the
algal populations will not be utilized, possibly removing nutrients from the
production system without being recycled.
Effects on Invertebrates
Zooplankton analyzed from net samples collected from 84 lakes in Sweden
showed that acidification caused the elimination of many species and led to
simplification of zooplankton communities (Aimer et al. 1974). Crustacean
zooplankton were sampled in 57 lakes during a Norwegian lake survey in 1974
(Hendrey and Wright 1976), and the number of species decreased with pH. The
distributions and associations of crustacean zooplankton in 47 lakes of a
region of Ontario affected by acid precipitation were strongly related to pH
and to the number of fish species present in the lakes. However, fish and
zooplankton were each correlated with the same limnological variables,
especially pH (Sprules 1975a, 1975b) . Zooplankton communities become less
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complex with fewer species present as acidity increases. Food supply,
feeding habits, and grazing of zooplankton will probably be altered following
acidification, as a consequence of decreased biomass and species composition
of planktonic algae and bacteria. Parsons (1968) reported that in streams
continuously polluted by AMD the number of zooplankton species was small
compared to the numbers of individuals; greater numbers were found in less
polluted conditions downstream.
Surveys at many sites receiving acid precipitation in Norway, Sweden,
and North America (Andersson et al. 1974, Conroy et al. 1975, Hendrey and
Wright 1976, Borgstr^m et al. 1976) have shown that waters affected by acid
precipitation have fewer species of benthic invertebrates than localities
that are less acid. In 832 lakes J. Okland (1969) found no snails at pH
values below 5.2; snails were rare in the pH range 5.2-5.8 and occurred less
frequently in the pH range 5.8-6.6 than in more neutral or alkaline waters.
The amphipod Gammarus lacustris, an important element in the diet of trout in
Norwegian lakes where it occurs, is not found in lakes with pH less than 6.0
(K. A. Okland 1969). Experimental investigations have shown that the adults
of this species cannot tolerate 24-48 h of exposure to pH 5.0 (Borgstr^m
and Hendrey 1976).
In the River Duddon in England, pH is the overriding factor that
prevents permanent colonization by a number of species of benthic inverte-
brates, primarily herbivores, of the upper acidified reaches of the river
(Sutcliffe and Carrick 1973). In the more acid tributaries (pH <5.7) the
fauna consisted of an impoverished plecopteran community. Ephemeroptera,
Trichoptera, Ancylus (Gastropoda), and Gammarus (Amphipoda) were absent. The
epiphytic algal flora was reduced (in contrast to increases noted in Norway),
and litter decomposition was retarded. The food supply of the herbivores was
apparently decreased, and this may have played a role in the simplification
of the benthic fauna. Quantitative data concerning the effects of low pH on
the benthic fauna are also available for some acid Norwegian lakes (Hendrey
et al. 1976), where notably low standing crops have been observed.
Many studies of invertebrate communities in streams receiving AMD have
been conducted. Comparisons are usually made between affected and unaffected
zones or tributaries, and experimental acidification has been performed
(Herricks and Cairns 1974). The numbers of species, species diversity, and
biomass are usually greatly reduced. Generally, in AMD waters Chironomidae
(midges) and Sialis (alderfly) are the most tolerant macroinvertebrates. The
order Trichoptera has more tolerant species than does Ephemeroptera (may-
flies) (Harrison 1958, Harrison and Agnew 1962, Dinsmore 1968, Parsons 1968,
1977, Dills and Rogers 1974, Wojcik and Butler 1977).
This order of tolerance is essentially the same as that in waters
acidified by acid precipitation. However, the Hemiptera, Notonectidae (back-
swimmer), Corixidae (waterboatman), and Gerridae (water strider) are often
abundant in acidified soft waters at pH as low as 4.0. This pattern of
distribution may, in part, be due to lack of fish predation, as well as the
partial adaptation of these invertebrates to terrestrial living.
Benthic plant communities in lakes may be greatly altered as a conse-
quence of lake or stream acidification (as discussed above). Under these
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conditions, benthic invertebrate populations may be affected by starvation,
evacuation, or extinction due to the loss of preferred habitat. Chironomids
(Oliver 1971) and other benthic invertebrates (Cummins 1973) present in many
of the poorly buffered northeastern lakes have diverse feeding habits
and habitats. These invertebrates, in many situations, will be affected by
altered decomposition cycles and variations in available foods caused by
increased acidification.
The tolerance of aquatic invertebrates to low pH varies over their life
cycles, and the emergence of adult insects seems to be a period particularly
sensitive to lower pH levels. Bell (1971) and Moss (1973), in similar
studies with Trichoptera and Ephemeroptera, found emergence patterns to be
affected at pH levels that were higher than the 30-day survival limits. Many
species of aquatic insects emerge early in the spring, even through cracks in
the ice and snow cover. Because of the contamination of spring meltwaters by
atmospheric pollutants, including heavy metals (Hagen and Langeland 1973,
Hultberg 1977, Johannessen et al. 1977, Henriksen and Wright 1976), the early
emergers must, in many cases, be exposed to the least desirable water
conditions .
Changes in invertebrate communities will influence other components of
the food chains. Benthic invertebrates assist with the essential function of
removing dead organic material. In litterbag experiments the effects of
invertebrates on leaf decomposition were much more evident at higher pH than
at low pH (Hendry et al. 1976). A reduction of grazing by benthic
invertebrates may also contribute to the accumulation of attached algae in
acidified lakes and streams.
A short reach of Norris Brook, a tributary to Hubbard Brook in New
Hampshire, was acidified to pH 4 in the spring and summer of 1977 to evaluate
the effects of acidification on a stream ecosystem. Excessive accumulations
of algae occurred, bacterial biomass and heterotrophic activity per unit of
organic matter were reduced, and both invertebrate diversity and biomass
decreased (Hall and Likens, unpublished data, 1979).
In unstressed lake ecosystems a continuous emergence of different insect
species tends to be available to predators from spring to autumn. In acid-
stressed ecosystems the variety of prey is reduced, and periods may be
expected to occur in which the amount of prey available to fish, waterfowl,
songbirds, and other predators is diminished.
In the BWCA-VNP the zooplankton and benthos are the algal grazers and
detritivores that transfer energy from vegetable to animal biomass. Factors
adversely affecting these organisms will adversely affect the transfer of
energy through the food chains and ultimately affect the fish product.
Effect on Vertebrates-Fish
The loss of fish species with increasing acidity has been well
documented in Scandinavia and in North America. In Sweden, Hultberg and
Stenson (1970) collected all of the fish in two lakes acidified by acid
precipitation. At a pH of 4.8 one lake contained a single yellow perch and
seven eels; the other lake at pH 4.6 contained 26 northern pike and 19 eels
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and had lost its former perch population. Jensen and Snekvik (1972) recorded
the elimination of salmon and trout populations from many rivers and lakes in
southern Norway. In Canada Beamish and Harvey (1972) described the loss of
eight species of fish from a lake as the pH fell from 6.8 to 4.4. Beamish et
al. (1975) recorded the loss of fish from another lake undergoing
acidification, and Harvey (1975) reviewed the effects of acidification on the
fish populations in a group of 68 lakes.
The tolerance of fishes to low pH has been studied under laboratory
conditions for half a century. This effort has been directed at recording
the death of fishes in relation to hydrogen ion concentration and duration of
exposure (Douderoff and Katz 1950, Lloyd and Jordan 1964, European Inland
Fisheries Advisory Commission 1969, Rooney 1973). The results of these works
are statements of criteria or pH tolerance of various fish species.
In the natural environment fishes may be exposed to adverse levels of
acidity throughout their life. Thus pH will act to control their survival or
well-being at the most critical stage or time in their life history.
Accumulation of acidic snow gives rise to spring runoff of acid water which
coincides with the time of spawning of many fish species. Headwater lakes
undergo more rapid acidification than those lower in the watershed, as a
function of flushing rate and buffering capacity of the drainage basin.
Thus, fish tend to be lost first from headwater lakes.
One of the effects commonly observed in populations of acid-stressed
fishes is a failure to reproduce successfully, often manifest by an absence
of young fish (Hultberg and Stenson 1970, Beamish and Harvey 1972, Ryan and
Harvey 1977). The cause of this reproductive failure varies from species to
species. In one population of white suckers, females failed to reach
spawning condition (Beamish and Harvey 1972); physiologically these fish did
not show the normal pattern in protein-bound serum calcium (Beamish et al.
1975). Lockhart and Lutz (1977) have also proposed disruption of Ca
metabolism as an explanation for losses of fish from acid lakes. Another
mechanism of action is the disruption of spawning behavior (Conroy et al.
1974).
In some species spawning is successful, but recruitment into year class
0 is lacking, indicating lesser tolerance of eggs and larvae (Milbrink and
Johansson 1975) or greater susceptibility of young or small fish such as
Robinson et al. (1976) found for brook trout. Two recent laboratory chronic
exposures (Menendez 1976, Smith 1977) have demonstrated a reduction in the
hatchability of brook trout embryos at pH 6.0 and lower. Both investigators
commented that continual exposure to pH values below 6.5 would be highly
detrimental. Trojnar (1977a) observed reduced hatchability of brook trout
embryos at pH 5.6. In a study of lake trout in the acidified lake number 223
of the ELA, L. Kennedy (personal communication, 1978) found that egg weights
were lower and survival was drastically reduced at a pH of 5.75. The
absence of a previous year class indicated that similar effects might have
occurred when the pH was 6.0. These data indicate that the lake trout, one
of the most sought after and valuable fish species in the BWCA-VNP, is highly
vulnerable to the effects of acidification.
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Other species found in the BWCA area are also very sensitive to low pH.
Mount (1973) observed a reduction in embryo production and hatchability at pH
5.9 in fathead minnows. A pH of 5.6 was marginal for vital life functions.
A reduction in the development of white suckers to the swim-up (early larval)
stage occurred at pH 5.3 and lower (Trojnar 1977b) . Embryo production,
embryo fertility, and fry growth were impaired at pH 6.0 and lower among
flagfish (Jordanella floridae), a species not found in the BWCA (Craig and
Baski 1977). Generally speaking, several fish species have been found to be
sensitive to pH levels around 6.0 or a little above.
Laboratory-determined effects appear to agree closely with field obser-
vations made in the LaCloche Mountain lakes area near Sudbury, Ontario. The
pH values at which various species disappeared from lakes are shown in Table
14 (Beamish 1976) .
Acute physiological effects of acid have also been investigated. It is
known that brook trout suffer malfunction of sodium regulation and lose
excessive amounts of this ion to the water (Packer and Dunson 1970). These
authors suggest (1972) that anoxia may be the primary cause of death in
fishes exposed to very low pH. Leivestad and Muniz (1976) also observed an
inability of acid-stressed fish to regulate plasma sodium and chloride
levels. Mudge et al. (1977) found evidence of an inhibition of RNA synthesis
and presumably of steroidogenesis in interrenal tissue.
Whatever the mechanism of action of the acid stress, serious changes in
the population structure can result. Beamish and Harvey (1972) noted the
complete absence of one age class (5-year-old fish) in a population of white
suckers, probably resulting from an acid pulse 5 yr earlier. In another
population of white suckers, older animals were lost in response to gradual
acidification, and maximum age declined from 16 yr to 7 yr (Beamish et al.
1975). Spinal deformity resulting from disintegration of several vertebrae
in adult fish was also observed.
The more common effect of acidification is to reduce the population to a
small number of older individuals. This change has been observed in
Scandinavia (Hultberg and Stenson 1970) and in a group of acid-stressed lakes
in Canada (Ryan and Harvey 1977). In some species the growth rate of
survivors increased, presumably in response to reduced competition for food.
These changes in the form of populations precedes their extinction.
There is a long and increasing list of water bodies from which some or all
fish populations have been lost because of low pH. Major rivers in southern
Norway have reduced populations of trout and salmon, and large kills have
been recorded in association with acid precipitation (Jensen and Snekvik
1972). Schofield (1975, 1976a) described the acidification and loss of
fishes from a large group of lakes in the Adirondack Mountains. Lakes at pH
4.5-5 yielded no fish in response to survey netting. In the LaCloche
Mountains of Ontario a study of 67 lakes yielded 28 that had lost the
majority of their fish; many of these lakes had supported good sport
fisheries until relatively recently (Beamish 1976). Many of the remaining
lakes showed reduced numbers of fishes, perhaps influenced by changes in
other populations of organisms (see section on effects on invertebrates).
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TABLE 14. APPROXIMATE pH AT WHICH FISH IN THE LACLOCHE
MOUNTAIN LAKES, ONTARIO, STOPPED REPRODUCTION3
pH
Species
Family
6.0+-5.5
5.5-5.2
5.2-4.7
4.7-4.5
Smallmouth bass
Micropterus dolomieui
Walleye
Stizostedion vitreum
Burbot
Lota lota
Lake trout
Salvelinus namaycush
Troutperch
Percopsis omiscomaycus
Brown bullhead
Ictalurus nebulosus
White sucker
Catostomus commersoni
Rock bass
Ambloplites rupestris
Lake herring
Coregonus artedii
Yellow perch
Perca flavescens
Lake chub
Couesius plumbeus
Centrarchidae
Percidae
Gadidae
Salmonidae
Percopsidae
Ictaluridae
Catostomidae
Centrarchidae
Salmonidae
Percidae
Cyprinidae
aAfter Beamish (1976).
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Most likely the early effects of acidification of BWCA-VNP lakes will be
a decrease in fish production, and very quickly 'direct effects on the fish
community will be apparent. Loss of production followed by loss of desirable
species and complete elimination of fish would be expected in the sensitive
lakes in the BWCA-VNP. Little or no effect is expected for nonsensitive
lakes and watersheds.
Effects on Other Vertebrates
Vertebrate animals other than fishes have received scant attention.
Birds and mammals that feed on fish are faced with a reduction or loss of
food supply. In the LaCloche Mountain lakes, for example, loons continued to
nest on and attempted to fish in lakes that had lost much or all of their
fish life.
Amphibians are especially prone to acidification of shallow surface
waters. Pough (1976) has described effects of acid precipitation on spotted
salamanders (Ambystoma jeffersonianum and A. maculatum), which breed in
temporary rain pools. Below pH 5 and 7, respectively, these species suffered
high mortality during hatching in laboratory tests. This mortality was
associated with distinctive embryonic malformations. The development of
salamander eggs in five ponds near Ithaca, New York, ranging from pH 4.5 to
7.0 was observed. An abrupt transition from low to high mortality occurred
below pH 6. Although a synergistic effect of several stresses may have been
possible, the studies suggested that pH was the critical variable. Pough
(1976) cites studies which indicate a decline in British frog populations.
Hagstrbm (1977) has investigated frog populations in Tranevatten, a lake
acidified by acid precipitation, near Gothenburg, Sweden. The lake pH has
declined to 4.0-4.5, and all fish have been eliminated. The frog species
Rana temporaria is being eliminated as well. Currently, only adults 8-10
years old are found. Many eggs were observed in 1974, but few were found in
1977. The few larva observed in 1977 subsequently died. A toad species,
Bufo bufo, is also being eliminated from this lake.
Frogs and salamanders are important predators on invertebrates in lakes
and puddles or pools, including mosquitoes and other pests. In turn, they
are themselves important prey for higher trophic levels in an ecosystem
(Pough 1976).
SUMMARY
Acid precipitation, by causing increased acidity in lakes, streams,
pools, and puddles, can cause slight to severe alteration in communities of
aquatic organisms. The effects are similar to those observed in waters
receiving acid mine drainage, but the toxicology and chemistry are not as
greatly complicated by the presence of high concentrations of heavy metals,
chemical floes, turbidity, etc. Bacterial decomposition is reduced, and
fungi dominate saprotrophic communities. Organic debris accumulates and
nutrient salts are taken up by plants tolerant of low pH (mosses, filamentous
algae) and by fungi. Thick mats of these organisms and organic debris may
develop which inhibit sediment-to-water nutrient exchange. Phytoplankton
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species diversity and production are reduced, although biomass accumulations
may be high due to reduced grazing. Zooplankton and benthic invertebrate
species diversity and biomass are reduced. Ultimately the remaining benthic
fauna consists of tubificids and Chironomus (midge) larvae in the sediments.
Some tolerant species of stoneflies and mayflies persist, as does the
alderfly. Air-breathing insects (water boatman, backswimmer, water strider)
may become abundant. Fish populations are reduced or eliminated; some of the
most sought-after species (brook trout, walleye, smallmouth bass) are the
most sensitive and therefore are among the first to be affected. Toxicity or
elevated tissue concentrations of metals may result either from direct
deposition or increased mobilization, or both. Amphibian species may be
eliminated. Finally, either the populations or the activities of terrestrial
vertebrates utilizing aquatic organisms for food (or recreation) are likely
to be altered.
Acidification of the BWCA-VNP will affect the fish communities in some
of the lakes, either by reducing populations, changing species composition,
or directly eliminating fish from the lakes. As the acid load increases or
continues, more lakes will fall in the affected category. Although the small
headwater lakes in poorly buffered watersheds are the most likely candidates
for impact, the importance of these lakes in the total recreational picture
is unknown. However, as more lakes are eventually affected, the general
objectives of wilderness management for the BWCA-VNP will be violated.
Operation of the Atikokan generating facility will add about 10% to the total
sulfate deposition on the area and increase the acid content by 25 to 30%.
These quantities should be judged in relation to the shortening of the time
period within the above effects are expected to be observed.
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REFERENCES
Abrahamsen, G., R. Horntvedt, and B. Tveite. 1977. Impacts of acid precipi-
tation on coniferous forest ecosystems. Water, Air Soil Pollut. 8:
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153
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APPENDIX A
WET REMOVAL RATES FOR S02 GAS AND 804 AEROSOL
In most models describing pollutant transport, transformation, and
removal one typically finds an equation of the form
c
-------
where w is the vertical wind speed and Vf (positive) is the fall speed of
precipitation particles. Application of Eq. (A-3) for the description of wet
removal implies that pollutant is carried to and from the volume of interest
only by the wind and falling precipitation. Assuming that boundary- layer flow
in the atmosphere is nondivergent and rearranging Eq. (A-3) in terms of a sub-
stantial derivative results in a form analogous to Eq. (A-l),
dn
dt
Integration over height, z, provides the desired expression for describing the
wet removal of pollutants from the atmosphere;
(yf>. - (yf >.„ (A.6)
dn = - >
dt
z -
where n represents the vertical average over a column extending from zo
to z. Therefore instead of finding that pollutant removal is directly
proportional to the pollutant concentration as in Eq. (A-l), we find that
removal is actually determined by the vertical flux divergence of pollutant in
the column under consideration. The rate of mass (concentration) removal is a
consequence of the mass flux of pollutant into the top of a volume minus the
mass flux of pollutant out the bottom.
For wet removal the mass flux of pollutant past a particular level can be
represented by the precipitation rate, j, multiplied by the pollutant
concentration of the precipitation water, C, where j has the units of a water
flux and C has units of mass of pollutant per mass of water. Thus, the flux
divergence can be represented by
(JC)Z - (JC)Z
dn o
dt
z ~ zo (A-7)
A major difficulty in describing the wet removal of pollutants is
determination of the vertical extent of the region being scavenged. Modelers
often wish to determine pollutant removal for a layer of fixed thickness and
generally apply Eq. (A-l) to a surface layer of air. However, unless the
surface layer encompasses the entire vertical extent of the region being
cleansed by precipitation, such an approach will produce only a crude
approximation to the true removal. As Eq. (A-7) illustrates, both the flux
into and out of the surface layer must be considered. Without the assistance
of detailed vertical profiles of precipitation rates and pollutant
concentration, the flux into the top of a surface layer will be indeterminate.
Currently detailed vertical profiles of precipitation and pollutant
concentration are unavailable. Thus we find our first restriction to apply Eq.
(A-7) or Eq, (A-l); the layer under consideration must extend to heights where
the wet, downward flux of pollutant is near zero.
155
-------
WET REMOVAL OF SULFATE AEROSOL
Figure A-l represents the simplest case for wet removal. Sulfate aerosol
removal is considered, and the removal model described by Scott (1978) is
employed. Briefly, the model assumes that in the portion of the figure above
cloud base, cloud droplets are nucleated on sulfate condensation nuclei. Large
collector particles (snowflakes) then enter the box from above and, as they
descend, grow to larger sizes primarily by accretion of the cloud droplets.
The process envisioned here is one of precipitation development in a cold cloud
by the Bergeron process. The sweeping out of a dirty layer of cloud water
above the cloud base by relatively pure collector particles is the major removal
mechanism. The region of the cloud where precipitation growth is primarily by
accretion of cloud droplets is designated as the rimtng zone. Since the snow-
flakes are assumed to be relatively sulfate free when they enter the riming
zone, the wet, downward pollutant flux at the top of riming zone is zero.
The thickness of the riming zone can be estimated from the fall speed of a
typical collector particle and from the time required for the particles to grow
to raindrop sizes. By utilizing the work of Kessler (1969), the fall speed of
the median volume drop can be expressed in terms of the precipitation rate as
vf = 3.89 jO.105 (m/s)f (A-8)
where here, J represents the precipitation rate in mm h~ . In continuous
rainfalls, precipitation rates generally average between 0.5 and 1.0 mm
h~l. For such rainfall rates the median volume drop diameter is roughly
between 0.7 and 1.0 mm. Millimeter-sized ice particles can be produced by
riming in 5-13 min in mixed phase clouds with water concentrations near 1 g
m~3 (Hindman and Johnson 1972, Scott 1976). Therefore, a time of 9 min is
felt to be an appropriate estimate for the time collector particles remain in
the riming zone while growing to precipitation sizes.
Taking the height of the riming zone to be defined by collector particle
velocity [Eq. (A-8)], and multiplying by the time of collector-particle growth
in the riming zone gives the riming zone thickness, Az, as
Az = 2100 J0.105 (m). (A-9)
Thus, the thickness of the riming zone is generally near 2,000 m and weakly
depends upon precipitation rate.
The distance from the ground to cloud base in a precipitating cloud is
typically small compared to 2,000 m. Therefore, Az can be considered to
represent the distance from the ground to the top of the riming zone. Since
Z-ZQ % Az, the flux divergence over the entire column extending from the
ground to the top of the riming zone can then be evaluated by computing only
the pollutant flux at the surface.
The concentration of sulfate in the precipitation water reaching the
surface can be described in terms of the sulfate concentration of the air being
drawn into the cloud base. Fitting curve 3 of Figure 2 in Scott (1978) with a
least square curve for 0.13
-------
CLOUD BASE
GROUND
RIMING ZONE
Figure A-l. The volume considered for sulfate removal. The
symbols represent: *, ice particles; 0, liquid drops; o,
cloud droplets; -»-, the direction of the sulfate flux at
the upper and lower boundaries of the volume.
157
-------
CT
io-2
10-3
3.0 3.5
4.0
4.5
5.0
5.5
6.0
6.5
PH
Figure A-2. Curves of C /xe as a function of pH. The labels
2& • / / -^ \
for the curves represent S02 air concentrations (yg/m ).
The units of C and x are grams of dissolved S02 per gram
of water and grams of air-borne SC>2 per cubic meter of air,
respectively.
158
-------
of sulfate (grams of sulfate per gram of water) as
C = 0.46 xg(SO^)j~°-27, (A-10)
where Xg(SO^) is the clear air concentration of sulfate (grams of sulfate
per m-* of air) being drawn into the cloud at cloud base. Generally, the
subcloud air is well mixed, and the sulfate concentration should be fairly
uniform between the ground and cloud base. Therefore we approximate xg with
the surface-air concentration of sulfate.
If we combine Eq. (A-7), (A-9), and (A-10), the wet removal rate for
sulfate can be expressed as
dx(SOp = _ o 92 x (S07)J°-625
- 0.22 xg^S04;j , (A-ll)
dt
where X(SO;jj) represents the average SO^ aerosol concentration (grams of
sulfate per m-* of air) in the layer extending from the ground to the top of
the riming zone.
REMOVAL OF S02 BY SNOW
Much of the preceding material can be used to describe the wet removal of
S02 • For the simplest case, that of S02 scavenging by snow, a direct
analogy follows. Here we assume that the bulk of S02 picked up by frozen
collector particles occurs as these particles capture cloud droplets in the
riming zone. The dissolved S02 in these cloud droplets is assumed to be in
equilibrium with the environment, which, if the S02 air concentration
decreases monotonically with height, implies that the droplets at the upper
portions of the riming zone will contain less S02 than those droplets near
cloud base. As the snowflakes collect cloud droplets, the droplets will freeze
rapidly and will have no opportunity to adjust to new equilibrium values as
they are carried to lower levels in the cloud.
Since the wet, downward flux of S02 through the upper boundary of the
riming zone is negligible, the S02 removal rate by snow is determined by
evaluating the pollutant flux at the ground. Written in terms of flux
divergence over the riming zone, the wet S02 removal rate is given by
dX(S02)
dt
= - JjC
snow 2
= 0.48 J°-9C, (A-12)
where C represents the dissolved S02 concentration in the snowflakes arriving
at the ground.
From Scott (1978) the final concentration of pollutant in a collector
particle passing through the riming zone is given by
C = C[l - exp(-2m)], (A-13)
159
-------
where C is the vertical average of the SC>2 water concentration in the
riming zone and m is the vertical average of the cloud water concentration.
Then, taking C to equal the arithmetic average of the equilibrium
concentration at the ground, Cg, and at the top of the riming zone, and
setting the upper level concentration equal to zero results in
dX(S02)
dt
snow
- 0.24 CeJ°-9(l-exp(-2m)).
(A-14)
Furthermore, Scott (1978) has presented an expression relating precipitation
rate to cloud water concentration:
m = 1.56 + 0.44 In J.
(A-15)
Equation (A-15) was intended to generalize all precipitation events. However,
no liquid water needs to be present in snow clouds. Caution should be
exercised when applying it to snowfalls, particularly when precipitation rates
are very light.
Values of Cg can be obtained from Figure A-2 which presents equlibrium
concentrations or SC>2 as a function of pH and SC>2 air concentration. The
curves of Figure A-2 result from the simultaneous solution of three equilibrium
equations describing the dissociation of SC>2 in water (e.g., see Appendix A,
Easter and Hobbs 1974).
REMOVAL OF S02 BY RAIN
To extend these concepts to S02 removal by rain scavenging, consider the
features illustrated in Figure A-3. Again the riming zone is represented by
the distance (Z-ZQ), and the freezing level height is designated by (zf
zo). For this model, snowflakes, as before, are assumed to accrete cloud
droplets containing dissolved S02 and then to melt to raindrops after falling
through the freezing level. In applying the flux divergence concept, the
vertical fluxes in and out of each of the two boxes in Figure A-3 must be
considered. In the upper box the only change in S02 concentration results
from a downward flux through the freezing level. As in the purely snow case,
the amount removed is
dX(S02)
dt
C(zf)
ice
(z-Zf )
(A-16)
where both the precipitation rate and the 862 concentration in the snow are
evaluated at the freezing level. Below the freezing level the removal due to
ran s
dX(S02)
dt
liquid
j(zf) C(zf) - j(z0) C(z0)
(zf-z0)
(A-17)
160
-------
FREEZING
LEVEL
GROUND
2km
1km
T
S02
Figure A-3. The volume considered for wet SO
removal by snow and rain. The ground is at
ZQ and the top of the riming zone is at z. The
freezing level is at Zf. The air concentration
of SO- is assumed to decrease with height.
161
-------
where j(zo) and C(ZQ) are ground values. Below the freezing level the SOo
concentration in the drops is assumed to be determined solely by establishing
an equilibrium concentration between the dissolved and airborne SOo.
To derive a removal rate that is analogous to the previous removal rates
and applied over the entire region being scavenged (the top of the riming
zone to the ground) a weighted average over both boxes is performed:
dX(S02)
dt
rain
(z-zf)
dX(S02)
dt
-f- (-7 -
' . (zf
ice
(z-z
dX(SOj
7 \ z ,
V dt
liquid .
0>
(18)
Substituting Eq. (A-16) and (A-17) into Eq. (A-18) results in the desired
expression for SC>2 removal by rain:
dX(S02)
dt
0.9r
= - 0.48 J cc
(A-19)
rain
Comparison between Eq. (A-14) and Eq. (A-19) illustrates that the rain
removal rate of S(>2 can exceed the snow removal rate by a factor of two or
more at equivalent precipitation rates. In particular, as the cloud water
concentration goes to zero, the wet removal of SC>2 by the snow riming
mechanism postulated above becomes negligible.
For both Eq. (A-14) and (A-19) the ground-level concentration of
dissolved SC>2 is related through the curves of Figure A-2 to the ground
level SC>2 air concentration, X(S02). That is,
Cg = 3 X(S02),
(A-20)
Thus, the expressions describing wet removal of S(>2 and 804 [Eq. (A-ll),
(A-14), and (A-19)] can be generalized to
dx
—= - K XeJa.
dt *
(A-21)
Notice that Eq. (A-21) is not an exact first-order expression, as was assumed
a priori in Eq. (A-l). The average wet removal of S02 and SO^ for a layer
depends not on the average pollutant concentration in the layer, but upon the
surface-level concentration in the layer. If the surface-level concentration,
Xg, can be expressed in terms of a layer average, then the first-order
relationship of Eq. (A-l) wij.1 result. For example, suppose the surface-level
concentrations of S02 and SO^ decrease linearly to zero at the top of the
riming zone. Then Xg = 2X and
162
-------
dX(S04) Q.625
^ _= - 0.44 X(S04)J
dt
dX(S02)
dt
-0.48 g X(S04)J°-9 (l-exp(-2m))
(A-22)
snow
dX(S02)
dt
-0.96 3 X(S02)J°'9%
rain
Another common situation is to assume a Gaussain profile for a plume. Then
Xg = X Az/ [1.25 az erf(Az/(1.41az))]s (A-23)
= YX .
Substitution of Eq. (A-23) into Eq. (A-ll), and (A-19) gives
BY = - 0.22 Y X(S04)J 0-625,
dt
dX(S02)
dt
snow
dX(S02)
dt
- 0.24 3Y X(S02) J°'9 (l-exp(2m)),
= - 0.48 BY X(S02) J°-9
(A-24)
rain
WET FLUX OF SULFUR AND PRECIPITATION pH
After procedures for computing removal rates of S02 and S04 by
precipitation have been developed, calculations to determine sulfur degostion
and rainwater acidity follow directly. In fact, the flux of S02 or S04 is
obtained by multiplying Eq. (A-21) by the region being scavenged, Az, which is
defined by Eq. (A-9). As for pH, the major portion of acidity found in
rainwater can be attributed to the incorporation of sulfate (Granat 1977).
Indeed, as Figure A-4 illustrates, a good approximation to rainwater pH results
from assuming two hydrogen ions for every sulfate ion (Dana 1978). The figure
presents precipitation chemistry data collected from the MAP3S precipitation
chemistry network and suggests that during the summer months when nitrate
concentrations in precipitation water are the lowest, the two hydrogen to one
sulfate ion is regularly observed. During the winter months when nitrates play
a greater role in determining rainfall acidity, there is an excess of hydrogen
ions; the molar ratio of hydrogen to sulfate is then_greater than 2. Still,
at pH values less than 4.3, the assumption of [H]/[S04] = 2 is quite good.
Thus, determination of the sulfate concentration in precipitation water should
provide accurate estimates of rainfall pH.
163
-------
1000
100
o>
o
E
10
I I I I I
10
100
pmoles/4
1000
Figure A-4(a). Observed relationships between the
ion concentrations of H and SOr for summer 1977.
The solid line represents two hydrogen moles for
every sulfate mole; the circles represent data
points.
164
-------
1000
g>
O
E
1000
Figure A-4(b). Observed relationships between the ion
concentrations of H and SOf for winter 1977-78. The
solid line represents two hydrogen moles for every
sulfate mole; the circles represent data points.
165
-------
REFERENCES
Dana, M. T. 1978. Seasonal trends of S(>2, SO^, Ntfy and NC>3 in
precipitation. MAP3S Precipitation Chemistry Network. Presented at the
MAP3S Precipitation Chemistry Network Meeting, May 11-12, 1978, Ithaca,
N.Y.
Easter, R. C., and P. V. Hobbs. 1974. The formation of sulfates and the
enhancement of cloud condensation nuclei in clouds. J. Atmos. Sci. 31:
1586-1594.
Granat, L. 1977. Sulfate in precipitation as observed by the European
Atmospheric Chemistry Network. Presented at the International Symposium
on Sulfur in the Atmosphere, September 7-14, 1977, Dubrovnik, Yugoslavia.
Hindman, E. E., II, and D. B. Johnson. 1972. Numerical simulation of ice
particle growth in a cloud of supercooled water droplets. J. Atmos. Sci.
29:1313-1321.
Kessler, E. 1969. On the distribution and continuity of water, substance in
atmospheric circulation. Meteor. Monogr. 10(32):1-84.
MAP3S Precipitation Chemistry Network. 1977. First periodic summary report.
Battelle, Pacific Northwest Laboratories, Richland, Wash. In press.
Scott, B. C. 1976. A theoretical study of the evolution of mixed phase
cumulus clouds. Ph.D. Thesis. Univ. Washington, Seattle, Wash. 209 p.
Scott, B. C. 1978. Parameterization of sulfate removal by precipitation. J.
Appl. Meteor. In press.
166
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APPENDIX B
SIMPLE MODEL CALCULATIONS OF EMISSIONS APPLIED TO ATIKOKAN
Annual averages, 3-h, and 24-h worst-case concentrations and deposition
fluxes may be estimated by using simplified models. These calculations
provide a comparison with the more complicated grid model.
ANNUAL AVERAGE CONCENTRATIONS
The single box model approach is used. Since all possible
meteorological conditions occur in a year we may consider that the plume is
uniformly mixed in a cylindrical box. Assume that the wind blows with equal
frequency in all directions. From conservation of mass,
or
Q = 2 TV x L U C
Q _ .
c =
2 IT x LU
Let C be the annual ambient air concentration (yg/m-*) at distance x (m)
from the source Q (g/s). Let U be the average annual wind speed (m/s)
through the average mixed layer of height L(m). Let us now divide this
result by 2 to account for the time when the plume is in stable air and
hence not dispersing to the ground. The equation to be evaluated ^'s then
C =
4ir x LU
Holtzworth (1972) gives the mean annual day time value of L at International
Falls as 1,300 m and the mean annual wind U as 7.2 m/s. We choose x = 80 km
as the distance from Atikokan to the center of the BWCA. For the indicated
emission rates
Species
, Q, the annual average concentrations, C, are as follows:
Q(f) c(£f) C(ppb)
S02
804
PM
Hg
NOX as N02
2,230
335a
328
0.0290
1,320
0.24
0.04
0.04
3 x 1(T6
0.14
0.09
0.01
0.001
0.005
a Assumed 2%/h conversion of S02 to 804 plus
2% conversion in the stack.
167
-------
The EPA CRSTER model, which runs a Gaussian plume calculation for every
hour of the year, gave an annual average S02 concentration at 80 km due south
of 0,25 Mg/ra (Goklany, personal communication, 1978).
THREE-HOUR WORST-CASE CONCENTRATIONS
Assume that the plume is fully trapped and calculate the plume centerline
concentration for neutral stability at 80 km downwind. The Gaussian plume
result is
C =
/2ira LU
y
Because of plume meandering an average concentration across the plume is more
appropriate than the centerline value. The width of the plume is taken as
4.3 a and the result is
0.4 Q .
/2rra y LU
For neutral stability Oy = 0.13 x 0.903, and assuming x = 80 km, u = 5 m/s,
and L = 500 m, we have
Q(g/s)
~ 106.5
In order for this to represent a 3-h average concentration the wind would
have to blow steadily in one direction for 7 h since the travel to the receptor
is about 4 h. Hence, this is an upper limit to the real situation. The
results of this 3-h calculation are as follows:
Species
S02
SO^
PM
Hg
NOX as N02
QV CV^j; C(ppb)
2,230
335
328
0.0290
1,320
21
3
3
0.0003
12
8
1
4 x
6
10-5
The EPA CRSTER model calculated the highest 3-h concentration of S02 at
80 km south-southeast as 20
TWENTY-FOUR-HOUR WORST-CASE CONCENTRATIONS
The 24-h case cannot be calculated without having actual meteorological
data because conditions do not persist in the atmosphere for 24 h. The EPA
CRSTER model calculated the highest 24-h S02 concentration 80 km south of
Atikokan as 5 ug/m^. Taking this in relation to the emissions we have the
following 24-h worst-case concentrations:
168
-------
Species Qxs' 1^3' u(ppb)
S02
SOr
PM
Hg
NOX as N02
2,230
335
328
0.0290
1,320
5
1
1
0.00006
3
2
0.2
7 x 10"
1.6
ANNUAL AVERAGE DRY DEPOSITION
The annual average dry deposition flux may be estimated by multiplying an
effective depositive velocity, Vp, by the annual average concentration:
or
FDRY = C VD (vg/™ per second),
F = 315 C VD (kg/ha-yr).
DRY
This assumes that the ambient air concentration is not significantly decreased
because of dry deposition upwind of the receptor point in question. Hence the
calculation is an upper limit. The annual average dry deposition fluxes are as
follows :
Species
S02
so?
PM
Hg
NOX as N02
VD(cm/s)
1
0.1
0.1
0.1
0.5
FDRY(kg//ha~yr)
0.75
0.014
0.014
1 x 10~6
0.22
WET DEPOSITION FLUXES
For typical rainfall rates of 1 mm/h continuous rainfalls, the procedure
outlined in Appendix A yields a concentration of 1.8 mg/liter for the sulfate
in precipitation if we assume an average sulfate concentration of 3 pg/m in
the air. By assuming two hydrogen moles for every sulfate mole, the sulfate
concentration converts to a rainfall pH of 4.4, and 3 = 0.0237. The removal
rate for 21 pg/m3 of S02 is
Wq0 = 0.24 (pg/m3 per hour),
and for 3 pg/m3 of SO^ is
WOA= = 1«0 (pg/m-5 per hour).
169
-------
If we use a height of 1,300 m for the mixed layer, the deposition rate due to
rain is
F
-------
Deposition
(kg/ha-yr)
Rain
Snow
Dry
S02
0.02
0.02
0.75
804
0.10
0.06
0.01
PM
0.01
0.01
0.01
Hg
3 x 10~8
3 x 10~8
1 x 10~6
,-6
Total 0.79 0.17 0.03 1 x 10
The deposition rates for SO^ are probably an upper limit because up-wind
removal between Atikokan and the BWCA due to wet and dry deposition would
decrease the concentrations used in the calculation. The wet deposition of
SC>2 might be increased since the pH of the rain would be less and therefore
the scavenging coefficient would be greater.
REFERENCES
Holtzworth, G. C, 1972. Mixing heights, wind speeds, and potential for
urban air pollution throughout the contiguous United States. U.S.
EPA, AP-1-1, January.
171
-------
APPENDIX C
REPRESENTATIVE ANALYSIS OF COAL AND FLY ASH FOR MAJOR AND TRACE COMPONENTS:
SOUTHERN SASKATCHEWAN LIGNITE3
Component
Aluminum (%)
Antimony (ppm)
Arsenic (ppm)
Ash (%)
Barium (%)
Beryllium (ppm)
Bismuth (ppm)
Boron (ppm)
Bromine (ppm)
Cadmium (ppm)
Calcium (%)
Cerium (ppm)
Cesium (ppm)
Chlorine (ppm)
Chromium (ppm)
Cobalt (ppm)
Copper (ppm)
Fluorine (ppm)
Gallium (ppm)
Gold (ppm)
Hafnium (ppm)
Heat content (BTU)
Holmium (ppm)
Iron (%)
Lead (ppm)
Coal
1.7
1.1
6.8
22
0.05
<0.14
9
37
2.7
<0.6
1.8
-
-
-
25
9
46
86
-
-
-
8,600
-
0.6
<29
Ash
9.4
2.1
19
-
0.50
3
-
400
2.0
1.8
8.1
112
3
460
60
9
43
94
1,090
0.005
12
-
6
2.2
30
Component
Lithium (ppm)
Magnesium (%)
Manganese (ppm)
Mercury (ppm)
Molybdenum (ppm)
Nickel (ppm)
Phosphorus (%)
Potassium (%)
Rubidium (ppm)
Silicon (%)
Selenium (ppm)
Silver (ppm)
Sodium (%)
Strontium (%)
Sulfur (%)
Tantalum (ppm)
Tellurium (ppm)
Tha 1 1 ium ( ppm)
Thorium (ppm)
Titanium (%)
Tungsten (ppm)
Uranium (ppm)
Vanadium (ppm)
Zinc (ppm)
Zirconium (ppm)
Coal
9
0.45
180
0.3
9
37
0.15
0.4
-
4
0.8
-
0.2
0.02
0.8
-
-
<0.5
-
0.05
-
8
20
40
80
Ash
-
2.5
400
-
20
39
-
-
40
-
<3
0.4
2
0.2
0.48
1.7
90
-
14
-
2.5
11
70
20
240
aG. E. Glass, unpublished data, 1979.
172
-------
APPENDIX D
DATA PERTINENT TO THE AQUATIC ECOSYSTEMS OF THE BOUNDARY WATERS CANOE AREA
Table D-l. Fishes Known to be Present in the BWCA and Border Lakes of
Minnesota
Table D-2. Lake Benthic Invertebrates Collected from Five Large Lakes in
Superior National Forest in 1976
Table D-3. Zooplankton Collected from Five Large Lakes in Superior National
Forest in 1976 and 1977
Table D-4. Phytoplankton Collected from Five Large Lakes in Superior
National Forest during the fall and summer of 1976 and 1977
Table D-5. BWCA-VNP Water Quality - November 1978: Field + Descriptive Data
(lakes within and near the BWCA and VNP sampled 11/6, 7, 8, 9,/78
and 11/15, 16/78)
Table D-6. Summary of Snow Data from the BWCA Region for the Period November
1977 - March 1978: Bulk Concentrations in Melted Snow and
Calculated Loadings
Table D-7. Mercury Concentrations in Fish from Selected Northern Minnesota
Lakes
Table D-8. Relative Sizes (inches) and Mercury Content (ppm) of Walleye from
12 Northern Minnesota Waters, 1977
Table D-9. Relative Sizes (inches) and Mercury Content (ppm) of Pike from 14
Northern Minnesota Waters, 1977
Figure D-l. Distribution of Lake Surface Areas for BWCA and VNP Fall 1978
sampling.
173
-------
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174
-------
TABLE D-2. LAKE BENTHIC INVERTEBRATES COLLECTED FROM FIVE LARGE LAKES3
IN SUPERIOR NATIONAL FOREST IN 1976b
PLECOPTERA
Capniidae
Acroneuria lycorias
Perlinella drymo
EPHEMEROPTERA
Isonychia sp.
Siphlonuridae
Siphlonurus sp.
Siphlonurus marshalli
Heptageniidae
Arthroplea bipunctata
Stenacron sp.
Stenacron candidum
Stenacron interpunctaturn
Stenacron minnetonka
Stenonema sp.
Stenonemn tripunctatum
Siphloplecton interlineatum
Bactidae
Callibactis sp.
Clocon sp.
Leptophlebiidae
Leptophlebia sp.
Ephemerella sp.
Ephemerella versimilis
Ephemerella temporalis
Caenis sp.
Ephemera simulans
Hexagenia sp.
Hexagenia limbata
ODONATA
Coenagrionidae
Enallagma sp.
Comphidae
Dromogomphus spinosus
Hagenius brevistylus
Acshnidae
Acshna sp.
Basiaeschna Janata
Boycria sp.
Boycria vinosa
Didymops transversa
Macromia sp.
(continued)
ODONTA (continued)
Macromia illinoiensis
Somatochlora williamsoni
Notonecta sp.
Ranatra sp.
Belostroma sp.
Lethocerus sp.
Corixidae
TRICHOPTERA
Nyctiophylax moestus
Polycentropus c^_nereuj[
Polycentropus interrupta
Hydroptillidae
Agraylea sp.
Hydroptila sp.
Ochrotrichia sp.
Agrypnia improba
Banksiola crotchi
Phrygabea cinerea
Ptilostomis sp.
Limnephilidae
Gramotaulis sp.
Nemotaulius hostilis
Pycnopsyche guttifer
Agarodes distinctum
Mo1anna sp.
Mo1anna blenda
Molanne tryphena
Helicopysche borealis
Ceraclea sp.
Ceraclea neffi
Ceraclea resurgens
Triaenodes injusta
Triaenodes tarda
MEGALOPTERA
Chauloideg rastricornis
Sialis sp.
COLEOPTERA
Haliplus sp.
Dytiscidae
Cyrinidae
Dineutus sp.
175
-------
Table D-2. (continued)
COLEOPTERA (continued)
Cyrinus sp.
Hydrophilidae
Ectopria nervosa
Dubiraphia sp.
Macronychus glabratus
Donacia sp.
DIPTERA
Tabenidae
Aedes sp.
Chironomidae
Clinotanypus sp.
Conchapelopia sp.
Dicrotendipes sp.
Endochironomus sp.
Eukiefferriella sp.
Glyptotendipes sp.
Larsia sp.
Palpomyia group
Polypedilum sp.
Procladius sp.
Stenochironomus sp.
Xenochironomus sp.
Chironomidae pupae
DECAPODA
CRUSTACEA
Crangonyx sp.
Hyalella azteca
NEMATODA
TURBELLARIA
HIRUDINEA
OLIGOCHAETA
GASTROPODA
of. Amnicola limosa
Carpeloma decisum
Ferrissia sp.
Cyraulus sp.
Hellsoma anceps
H. carpanulata
jl. corpulentum
ji. trivolvis
Helisomi sp.
Physa gyrina
Sphaerium strintinum
Stagnicola sp.
PELECYPODS
Sphaeriidae
OTHER
Lepidoptera
aBirch, Colby, Gabbro, Seven Beaver, and White Iron Lakes.
^Collections made by the Minnesota Copper-Nickel Study Group (MCNSG)
(Johnson et al.. 1978).
176
-------
TABLE D-3. ZOOPLANKTON COLLECTED FROM FIVE LARGE LAKES3 IN SUPERIOR
NATIONAL FOREST IN 1976 AND 1977b
ROTIFERA
Keratella cochlearis
Polyarthra vulgar Is
Synchaeta sp.
Conch ilus sp.
Kellicott La congispina
Tr ichocera cylindrica
Kell icott la bostoniens is
Collocheca sp.
Tr ichocera s im i1is
Fil inia long iseta
Keratella quadrata
Ploesoma truncatum
Pompholyx sulcata
Tr ichocera porcellus
Hexachra sp.
Ploesoma lent iculare
Lecane sp.
Trichocera mult icr inis
Asplanchna sp.
Lophochavis salpine
Trichocera weberi
Brachionus sp.
Lophocharis sp.
Tr ichocera clongata
Trichocera longiseta
Ascomorpha sp.
Enthlanis d ilatata
Hexarthra mira
Ploesoma hudsoni
Tescudinella patina
Trichocera sp.
Tr ichotria tetraet is
Ascomorpha oval is
^. saltans
Bdelloid sp.
Brach ionus quadr identatus
Cephalodella intuda
Euchlanxs sp.
Keritella h iemalIs
JK. paludosa
K. serrulata
1C. taurocephala
Kotholca acuminata
Notholca sp.
Rotaria peturia
Synchaeta stylata
CLADOCERA
Bos imina long irostris
Daphnia galeata mendotae
Holopedium gibberum
Daphnia retrocurva
D iaphanosoroa sp.
Chydorus sphaericus
Ceriodaphnia lacustr is
Daphnia pulex
Leptodora kindti i
Daphnia shodleri
Alona c trcumf irobr iata
Ceriodaphn ia quadrangula
Alona guttata
Cer iodaphnia sp.
Chydorus b icornutus
Daphnia catauba
Daphnia long iremis
13. parvula
V. sp.
COPEPODA
Tropocyclops pras inus
(Cyclopoida)
Cyclops b icuspidatus thomas i
(Cyclopoida)
Diaptomus oregonens is
(Calanoida)
Epischura lacustris
(Calanoida)
Cyclops vernal is
(Cyclopoida)
Mesocyclops edax
(Cyclopoida)
Diaptomus minutus
(Calanoida)
Ergas ilis chautaquaens is
(Cyclopoida)
Macrocyclops alb idus
(Cyclopoida)
Eucyclops agilis
(Cyclopoida)
Orthocyclops modestus
(Cyclopoida)
Diaptomus sic il is
(Calanoida)
aBirch, Colby, Gabbro, Seven Beaver, and White Iron Lakes.
^Collect ions made by the Minnesota Copper-Nickel Study Group (MCNSG)
(Piragis et al. 1978).
177
-------
TABLE D-4. PHYTOPLANKTON COLLECTED FROM FIVE LARGE LAKES3 IN SUPERIOR
NATIONAL FOREST DURING THE FALL AND SUMMER OF 1976 AND 1977b
BACILLARIOPHYTA
Asterionella formosa
Cyclotella bodanica
Fragilaria crotonensis
Melosira ambigua
Melosira distans
Nitzschia sp.
Tabellaria fenestrata
CHLOROPHYTA
Ankistrodesmus falcatus
including varieties
aricularis & mirabili^
Botryococcus Braunii
Oocystis sp.
CYANOPHYTA
Agmenellum quadruplicatum
(MerismopedJ^a glauca)_
Aphanocapsa delicatissima
Cpelosphaerium Kuetzingianum
CHRYSOPHYTA
Dinobryon bavaricum
_Dinqbrypn divergens
Dinobryon sertularia var.
protuberans
CRYPTOPHYTA
Cryptononas erosa
PYRRHOPHYTA
Ceratim hirundinella
aBirch, Colby, Gabbro, Seven Beaver, and White Iron Lakes.
^Collections made by the Minnesota Copper-Nickel Study Group (MCNSG)
(Gerhart et al. 1978).
178
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TABLE D-7. MERCURY CONCENTRATIONS IN FISH FROM SELECTED NORTHERN MINNESOTA LAKES3
Lake
Vermilion
Trout
Pelican
Basswood
Sand Point
Namakan
Kabetogama
Burntside
White Iron
Fall
Gunf lint
Colby
Greenwood
Gabbro
Pike River
Number
of
Species fish
Walleye
Northern pike
Walleye
Northern pike
Lake trout
Smallmouth bass
Walleye
Northern pike
Smallmouth bass
Walleye
Northern pike
Walleye
Northern pike
Walleye
Northern pike
Walleye
Northern pike
Walleye
Northern pike
Lake trout
Smallmouth bass
Walleye
Northern pike
White suckers
Yellow perch
Walleye
Northern pike
White suckers
Yellow perch
Walleye
Northern pike
Northern pike
White suckers
Yellow perch
Northern pike
White suckers
Yellow perch
Northern pike
White suckers
Yellow perch
Walleye
30
22
25
5
15
5
6
25
5
28
25
8
7
10
4
26
10
6
34
4
9
26
25
20
25
24
25
24
24
24
18
20
21
25
25
25
25
21
25
25
6
Range,
length
(inches)
12.4
17.6
14.0
20.0
15.0
11.3
9.5
10.8
13.1
12.5
15.5
11.8
19.2
11.5
15.5
9.4
15.8
11.2
19.5
21.0
9.0
11.0
15.2
12.8
5.2
9.3
14.0
8.8
5.2
10.0
14.0
6.7
13.1
5.3
14.9
8.5
5.4
17.6
8.8
5.7
14.2
- 23.0
- 33.0
- 21.4
- 30.0
- 24.8
- 14.8
- 25.9
- 28.2
- 15.4
- 29.0
- 25.5
- 21.0
- 24.5
- 17.5
- 23.3
- 21.3
- 30.5
- 24.0
- 32.0
- 28.0
- 18.0
- 21.5
- 23.7
- 20.0
- 10.6
- 18.8
- 40.7
- 22.1
- 11.3
- 26.0
- 28.0
- 21.0
- 19.6
- 8.6
- 27.7
- 18.8
- 10.9
- 34.5
- 22.0
- 9.6
- 29.0
Expected size
(inches) at the
Range, 0.5 ppm
ppm Hg threshold
0.09 -
0.10 -
0.20 -
0.25 -
0.11 -
0.28 -
0.10 -
0.13 -
0.13 -
0.24 -
0.23 -
0.25 -
0.21 -
0.13 -
0.09 -
0.03 -
0.09 -
0.18 -
0.19 -
0.37 -
0.27 -
0.26 -
0.21 -
0.03 -
0.10 -
0.21 -
0.15 -
0.04 -
0.09 -
0.21 -
0.12 -
0.09 -
0.09 -
0.15 -
0.31 -
0.07 -
0.08 -
0.22 -
0.03 -
0.08 -
0.46 -
0.73
0.47
0.95
0.98
0.50
0.42
0.87
0.69
0.36
1.95
0.86
2.67
0.83
0.58
0.28
0.40
0.24
0.95
1.01
0.76
0.65
0.78
0.58
0.27
0.68
0.53
1.29
0.35
0.50
1.23
0.56
0.80
0.62
0.53
0.75
0.56
0.68
0.95
0.20
0.88
1.50
25
N/Ab
18
24
20
30
15
21
13
22
>30
N/A
>30
17
28
15
24
25
23
16
29
18 (est.)
19 (est.)
22 (est.)
a Data from: Minnesota Department of Natural Resources. 1978. Mercury levels
in eleven northeastern lakes, 1977. Spec. Publ., Ecol. Serv. Sect, (mimeo). 34 p.
k N/A " not applicable.
183
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-80-044
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Impacts of Airborne Pollutants on Wilderness Areas
Along the Minaesota-Ontario Border
5. REPORT DATE
May 1980 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Gary E. Glass
Orie L. Loucks
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
SAME AS BELOW
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory - Duluth, MN
Office of Research and Development
U.S. Environmental Protection Agency
Duluth, Minnesota 55804
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The goal of this study was to examine previously unanswered questions concerning potential effects of the
proposed Atikokan, Ontario power plant on ecosystems in the Boundary Waters Canoe Area Wilderness (BWCA) and
Voyageurs National Park (VNF) of Minnesota by using the most relevant data and analytical methods. The principal
steps were to focus on: (1) the ultimate deposition of emissions from the plant (rather than only on pollutant
concentrations), (2) the use of a time-varying grid model with provision for atmospheric transformations, and (3) a
detailed review of all available data from the region on atmospheric deposition of pollutants, water quality, and
effects. The results are considered in relation to a review of responses by terrestrial and aquatic organisms to
changes in the chemistry of this environment.
The sensitive aquatic and terrestrial receptors in the BWCA-VNP region are described quantitatively, and this
information is assessed in terms of what is currently known about the Impacts of atmospheric pollutants. Specific
conclusions based on factual information, probable consequences, and possible impacts of the proposed coal-fired
power generating station at Atikokan are presented.
The study supports, in part, the conclusions reached previously concerning the predicted air concentrations of
sulfur dioxide, but differs significantly with the conclusions concerning the significance of future impacts. When
the total emissions from the proposed power plant are considered, the increased loadings of sulfuric and nitric
acids, fly ash, and mercury as an addition over and above other regional sources will, with high probability, have
significant consequences for the sensitive receptors in the BWCA-VNP region, especially for the future of sport
fisheries and other aquatic resources.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air pollution
Water pollution
Acid rain
Investigations
Documentation
Modeling
Wilderness areas
Park areas
Plumes
Power Plants
Northern Minnesota
BWCA,
Boundary Waters Canoe
Area Wilderness
Atikokan (Ontario)
Power Plant
1313 06F
06.T, 06P, 06S
08L08F
18. DISTRIBUTION STATEMEN1
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
199
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
187
(,US GOVERNMENT PRINTING OFFICE 1980-657-146/5663
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