BOREAL SHIELD WATERSHEDS Lake Trout Ecosystems in a Changing Environment ppt

France Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment Edited by J.M.. Government works International Standard Book Number 1-56670-646-7 Library of Congress Car

BOREAL SHIELD

WATERSHEDS

Lake Trout Ecosystems

Handbook of Water Sensitive Planning and Design

Edited by Robert L France

Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

Edited by J.M Gunn, R.J Steedman, and R.A Ryder

Integrative Studies in Water Management and Land Development

Series Editor

Robert L France

Published Titles

Forests at the Wildland-Urban Interface: Conservation and Management

Edited by Mary Duryea

Restoration of Boreal and Temperate Forests

Edited by John A Stanturf

Stormwater Management for Low Impact Development

Edited by Lawrence Coffman

The Economics of Groundwater Remediation and Protection

Paul E Hardisty, Ece Ozdemiroglu, and Jonathan Smith

Forthcoming Titles

LEWIS PUBLISHER S

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Library of Congress Cataloging-in-Publication Data

Boreal shield watersheds : lake trout ecosystems in a changing environment / edited by J.M Gunn, R.J Steedman, and R.A Ryder.

p cm — (Integrative studies in water management and land development) Includes bibliographical references and index.

ISBN 1-56670-646-7 (alk paper)

1 Lake trout—Ecology 2 Lake ecology—North America I Gunn, J.M (John Maxwell),

II Steedman, Robert John, 1958- III Ryder, R.A (Richard Alan) IV Series.

QL638.S2B57 2003

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Series statement:

Integrative studies in water

management and land

development

Ecological issues and environmental problems have become exceedingly complex Today,

it is hubris to suppose that any single discipline can provide all the solutions for protectingand restoring ecological integrity We have entered an age where professional humility isthe only operational means for approaching environmental understanding and prediction

As a result, socially acceptable and sustainable solutions must be both imaginative andintegrative in scope; in other words, garnered through combining insights gleaned fromvarious specialized disciplines, expressed and examined together

The purpose of the CRC Press series Integrative Studies in Water Management andLand Development is to produce a set of books that transcends the disciplines of scienceand engineering alone Instead, these efforts will be truly integrative in their incorporation

of additional elements from landscape architecture, land-use planning, economics, cation, environmental management, history, and art The emphasis of the series will be

edu-on the breadth of study approach coupled with depth of intellectual vigor required forthe investigations undertaken

Robert L France

Series Editor Integrative Studies in Water Management

and Land Development Associate Professor of Landscape Ecology Science Director of the Center for Technology and Environment,

Harvard University Principle, W.D.N.R.G Limnetics Founder, Green Frigate Books

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Foreword by series editor

This volume, edited by John Gunn, Rob Steedman, and Dick Ryder, pulls together anincredibly broad mix of people and topics under a single cover As such, it is a worthyaddition to the new series from CRC Press — Integrative Studies in Water Managementand Land Development — that was initiated in 2002 with publication of my own editedvolume, Handbook of Water Sensitive Planning and Design Books like these are rare, but theyshouldn’t be Complex environmental problems can only be identified, understood, andrectified through the collective actions of a diversity of approaches from a variety ofdisciplines Gunn, Steedman, and Ryder well recognize this as witness to the fact thattheir contributors to this volume come from many different provincial, state, and federalagencies, universities, and private consulting or research organizations Likewise, thetopics covered in these pages are truly catholic in scope: natural and cultural history,stocking and management, rehabilitation, commercial fisheries, land-use modifications,reservoir creation, nutrient inputs and transformations, lake chemistry and morphometryinfluences, atmospheric deposition, trace contaminant cycling, species introductions, andclimatic alterations All directed toward a single sentinel species — the lake trout of theBoreal Shield — a wonderful fish I know well as a research subject (and also as a culinaryobject!), and in an area of the continent of incredible sublime beauty in which I have spentmuch time in both recreational and scholarly pursuits

Until some future author writes a popular account of the anthropological history ofthe lake trout — along the lines of, for example, John McPhee’s The Founding Fish (aboutthe shad), Mark Kurlonsky’s Cod: A Biography of the Fish that Changed the World, or RichardScheid’s Consider the Eel — the present book, with its emphasis on the management of,and environmental influences on, this particular species of fish, should become widelyread What all of these works share is their demonstration that the true distribution forcertain species of fish encompasses sociological space just as much as it does Euclidianspace Lake trout, then, are a truly integrated cultural and biological symbol of the BorealShield ecoregion

Another important message that one takes away from the present book — one alluded

to several times but not formally enunciated — is of a compelling challenge to our myth

of “pristine nature” or “wilderness” free from human influences When looking at a map

of human inhabitation in North America (or the photo of illuminated cities shown in thefirst chapter), one could erroneously assume that somehow the great Boreal forest is “thetrue north, strong and free” from human manipulation What we learn from this book isthat the Boreal Shield ecosystem is really just as much a designed landscape as any onthe planet So, in addition to the well-known artificiality of the forests due to wildfiresuppression, we now realize that since soon after glaciation, the resident relict populations

of lake trout have been repeatedly poked at and prodded by us While in the past (andeven in the recent past), this has been mostly through direct tinkering such as fisheriesL1646_C00.fm Page vii Thursday, November 6, 2003 8:44 AM

viii Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

and restocking programs, today it seems that these fish populations function as barometers

of changes in both the landscape and the airscape We would be wise to learn the lessonsthat these aquatic canaries might be able to tell us, and for this we should be indebted tothe authors of this timely and important volume

Robert L France

Harvard University

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Foreword: An ideal icon

The lake trout, a coldwater denizen of Boreal lakes, makes an ideal icon The spectacularfish is a memory of its past and a vision for a desired future, an icon to stir human action

on behalf of valued and relatively unspoiled Boreal lakes These lakes are increasinglyexposed to new and more intense human pressures An icon can help foster the protection,management, and restoration of these treasured systems Can lake trout be such an icon?

Is this fish the only icon needed to stir the human passions to behave ethically for asustainable future? In the Pacific Northwest, anadromous salmon, Douglas fir, marinemammals, and other components combine into a more general set of icons worth preserv-ing because they are valued by different groups Is the lake trout part of such a set ofeffective icons for the Boreal lake systems? My answer would be a hearty “yes.”

This noble animal depends on the maintenance of a suite of aquatic, terrestrial, andaerial environments; thus it is an indicator not only of the deep, cold, oxygenated waters,but also of land at a landscape scale and of air at regional and global scales Thus, thespecies integrates anthropogenic pressures on the environment giving further credibility

to Barry Commoner’s first law of ecology: “Everything is related to everything else.” Does

it seem inconsistent that the icon is also the indicator? I think not This is often the case.This interlocking of the vision and the practice brings together excitement and technique,purpose and strength Is the lake trout a sufficient indicator through which to judge status,function, and dynamics of Boreal lake ecosystems? I doubt it The inshore fish communitywould be a great indicator, but not as good an icon The spruce and the aspen, the mooseand the wolf, and other components inform us about other facets of our influence thatcould influence the lakes, and mechanisms are equally or more important as indicators.Challenges are many: overfishing and extraction, exotics and toxins, human popula-tion growth and expansion, energy use, and climate change Some of these influences can

be dealt with or fixed at the local, lake, or perhaps watershed level Others are moreprovincial and linked to regional economic development that may undervalue ecosystemsustainability Some of the pressures are continental with transboundary movement amongnations of people, dollars, toxins, water, and exotics Others are truly global, such as thegeneration of greenhouse gases or development of carbon storage

As I read the chapters, it became increasingly clear that some of these Boreal lakesare more sensitive to different pressures, and that they are not all equally sensitive to thesame pressure For example, a lake sensitive to overfishing because the trout are key tothe local economy or because an urban, recreational fishing population is only a shortdrive away may not be the same lake that is most vulnerable to climate warming or aeriallyborne toxics or acids Of this the writers are well aware

More daunting was the realization that some lakes we can protect, some we canmanage to some degree, some we can restore, but others we cannot help, at least in theshort term or through local action Changes will occur, and one needs to decide how toL1646_C00.fm Page ix Thursday, November 6, 2003 8:44 AM

x Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

respond to those changes As in the medical analogy, triage should be part of any strategy.Behaviors in respect to short-term, faster-acting pressures may differ depending on theexpected response of Boreal lakes to the long-term drivers Sorting such things out amongthe various kinds of lakes is important to establishing short- and long-term strategies

So from my point of view, the lake trout is certainly an icon and a tool that can help

us realize the more desirable future The species is perhaps uniquely suited to help achieve

a sustainable future for Boreal lake ecosystems and the humans who love them It cannot

Preface: Boreal Shield ecosystems

Deep, clear Boreal Shield lakes carved from Precambrian bedrock have long defined thenorthern wilderness and are the ancestral home and interglacial refuge of the lake trout,

Salvelinus namaycush The lakes, streams, and wetlands of this ecozone are tightly linked

to the austere watersheds of the north woods and are sustained by them This land ofwhite pine, black spruce, moose, wolf, beaver, and woodland caribou poses dauntingenvironmental management challenges at the beginning of the 21st century New sciencegleaned from these ecosystems may provide a powerful general model for those concernedabout freshwater fisheries, water quality, and watershed ecosystems worldwide

Humans have long been part of the Boreal Shield world A few adaptive and ful aboriginal peoples followed fish, game, young forests, and receding glaciers northward

resource-5000 to 10,000 years ago The number of people living in the Boreal forest is still smallrelative to those in more hospitable regions, but humans continue to move northward andexert ever-increasing demands on the Boreal landscape Now, 200 years after the area’srich fur, fish, timber, and mineral resources first attracted the interest of Europeans, forestryand mining still form the backbone of the region’s economy The unspoiled landscape andwaters have become easily accessible and support a huge tourism and recreation industry.The new wave of industry and technology in distant cities now plays a dominant role inthe health of Boreal Shield ecosystems through market-driven extraction and consumption

of resources, through long-range atmospheric transportation of contaminants, and throughchanging global climate

This book brings together a uniquely qualified group of scientists to extend andinterpret the scientific legacy of the Boreal watersheds For the last 50 years, pristine BorealShield waters have served as crucibles for world-class research into impacts of waterpollution, acid rain, climate change, fisheries, and watershed disturbance This book builds

on that research foundation and explores the ability to manage human interactions withthese unique ecosystems at local, regional, and global scales Our ability to sustain healthyBoreal Shield waters constitutes a crucial test of ecosystem management concepts, tech-niques, and commitment

RAR & Associates

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Acknowledgments

We would like to thank all the authors for their time and effort in producing these chapters

It was a long struggle from start to finish, and we really appreciate their patience andcontinued support Special thanks to Carissa Brown and Christine Brereton, our very ableeditorial assistants This project could not have been completed without them

Many of the authors participated as peer reviewers on associated chapters We werealso fortunate to have the assistance of the following external reviewers: Chris Brousseau,Randy Eshenroder, David Evans, John Fitzsimons, Chris Goddard, John Havel, Bill Keller,Terry Marshall, Norman Mercado-Silva, Greg Mierle, George Morgan, Henk Rietveld,Helen Sarakinos, Wolfgang Schieder, Ed Snucins, Vincent St Louis, and James Wiener.Michael Malette, Seija Mallory, Leila Tuhkasaari, and Amanda O’Neil (CooperativeFreshwater Ecology Unit, Laurentian University, Sudbury, Ontario) compiled the lake troutdata set with assistance from Rob Korver, Rod Sein, and Wayne Selinger (Ontario Ministry

of Natural Resources), Michel Legault (Société de la faune et des parcs du Québec), GarySiesennop and Mark Ebbers (Minnesota Department of Natural Resources), and WalterKretser, Richard Costanza, Bill Gordon, and Richard Preall (Adirondack Lake SurveyCorporation) Paul Morgan established the Canadian Shield Trout Scholarship Program

at Laurentian University to support associated research projects Michel Legault (Société

de la faune et des parcs du Québec) and Judi Orendorff (Ontario Ministry of NaturalResources) participated in the original steering committee for this project Ed Snucins andVic Liimatainen provided many of the photographs

We gratefully acknowledge the Canadian National Atmospheric Chemistry(NatChem) Database and its data-contributing agencies and organizations for the provi-sion of the wet deposition data used to produce the 1980–1989 and 1990–1999 averageannual deposition figures (Plate 6) The agencies and organizations responsible for datacontributions to the NatChem Database include Environment Canada; the provinces ofOntario, Quebec, New Brunswick, Nova Scotia, and Newfoundland; the U.S Environ-mental Protection Agency; and the U.S National Atmospheric Deposition Pro-gram/National Trends Network

Information and maps for the long-term monitoring sites were provided by JohnShearer (Experimental Lakes Area), Jim Rusak (North-Temperate Lakes — Trout LakeStation), Martyn Futter (Dorset), Mark Ridgway, Trevor Midell (Harkness/Lake Opeongo),Dean Jeffries (Turkey Lakes Watershed), Bill Keller (Sudbury Lakes), Christine Brereton(Sudbury Lakes and Killarney Park), and John Gunn (Killarney Park)

Financial and logistic support for the project was provided by the Ontario Ministry

of Natural Resources, Laurentian University (Cooperative Freshwater Ecology Unit), andthe Sustainable Forest Management Network

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About the Editors

John M Gunn is a senior research scientist for the Ontario Ministry of Natural Resourcesand heads the Cooperative Freshwater Ecology Unit at Laurentian University During thepast 25 years much of his research has focused on restoration ecology of acid-damagedecosystems in northeastern Ontario, with particular emphasis on the recovery of stressedlake trout ecosystems He was the recipient of several awards, including the 2000 Presi-dent’s Award for Conservation from the American Fisheries Society

Robert J Steedman is a research scientist with the Ontario Ministry of Natural Resources

in Thunder Bay, where he has led long-term, interdisciplinary studies of watershed system response to forest management and provided science-based policy advice to theProvince of Ontario He is presently on assignment with the National Energy Board inCalgary, Alberta, as Professional Leader, Environment

eco-Richard A Ryder is a semiretired fisheries research scientist after a 44-year career withthe Ontario Ministry of Natural Resources and its predecessor, the Ontario Department

of Lands and Forests He is the recipient of numerous awards and honors, including mostrecently an election into the National Fisheries Hall of Excellence (1999) and the Merito-rious Service Award (2001) He has served as president of the American Fisheries Society(1980–1981) and the Canadian Conference for Fisheries Research (1987–1988)

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University of North Carolina at Charlotte

Charlotte, North Carolina

Great Lakes Science Center

Ann Arbor, Michigan

Syracuse, New York

xviii Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

Christopher Eagar

Northeast Forest Experiment Station

USDA Forest Service

Durham, New Hampshire

Mark P Ebener

Great Lakes Fishery Commission

Sault Saint Marie, Michigan

Mike Fruetel (deceased)

Quetico Mille Lacs Fisheries Assessment

Unit

Ministry of Natural Resources

Thunder Bay, Ontario

John M Gunn

Cooperative Freshwater Ecology Unit

Ontario Ministry of Natural Resources

Great Lakes Fishery Commission

Ann Arbor, Michigan

Robert S Kushneriuk

Ontario Ministry of Natural Resources

Centre for Northern Forest Ecosystem

Michel Legault

Direction de la recherche sur la fauneSociété de la faune et des parcs

du QuébecQuébec, Québec

Charles H Olver

Ontario Ministry of Natural Resources (retired)

Hunstville, OntarioL1646_C00.fm Page xviii Thursday, November 6, 2003 8:44 AM

RAR & Associates

Thunder Bay, Ontario

Ontario Ministry of Natural Resources

Centre for Northern Forest Ecosystem

Corvallis, Oregon

M Jake Vander Zanden

Center for LimnologyUniversity of Wisconsin, MadisonMadison, Wisconsin

Norman D Yan

Biology DepartmentYork UniversityToronto, OntarioL1646_C00.fm Page xix Thursday, November 6, 2003 8:44 AM

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Preface: Boreal Shield ecosystems xi

John M Gunn, Robert J Steedman, and Richard A Ryder

Section I: Introduction

Chapter 1 Lake trout, the Boreal Shield, and the factors that shape

lake trout ecosystems 3

John M Gunn and Roger Pitblado

Chapter 2 History and evolution of lake trout in Shield lakes:

past and future challenges 21

Chris C Wilson and Nicholas E Mandrak

Chapter 3 Rehabilitation of lake trout in the Great Lakes: past lessons

and future challenges 37

Charles C Krueger and Mark Ebener

Section II: Environmental factors that affect Boreal Shield ecosystems

Chapter 4 Land, water, and human activity on Boreal watersheds 59

Robert J Steedman, Craig J Allan, Robert L France, and Robert S Kushneriuk

Chapter 5 Impact of new reservoirs 87

Michel Legault, Jean Benoît, and Roger Bérubé

Chapter 6 Lake trout (Salvelinus namaycush) habitat volumes and boundaries

in Canadian Shield lakes 111L1646_C00.fm Page xxi Thursday, November 6, 2003 8:44 AM

xxii Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

Bev J Clark, Peter J Dillon, and Lewis A Molot

Chapter 7 The effects of phosphorus and nitrogen on lake trout

(Salvelinus namaycush) production and habitat 119

Peter J Dillon, Bev J Clark, and Hayla E Evans

Chapter 8 Dissolved organic carbon as a controlling variable in lake trout

and other Boreal Shield lakes 133

David W Schindler and John M Gunn

Chapter 9 Mercury contamination of lake trout ecosystems 147

R.A (Drew) Bodaly and Karen A Kidd

Chapter 10 Acidic deposition in the northeastern United States: Sources

and inputs, ecosystem effects, and management strategies 159

Charles T Driscoll, Gregory B Lawrence, Arthur J Bulger, Thomas J Butler,

Christopher S Cronan, Christopher Eagar, Kathleen F Lambert, Gene E Likens,

John L Stoddard, and Kathleen C Weathers

Section III: Biological effects and management reactions

Chapter 11 The control of harvest in lake trout sport fisheries on

Precambrian Shield lakes 193

Charles H Olver, Daniel Nadeau, and Henri Fournier

Chapter 12 Lake trout stocking in small lakes: factors affecting success 219

Michael J Powell and Leon M Carl

Chapter 13 Species introductions and their impacts in North American

Shield lakes 239

M Jake Vander Zanden, Karen A Wilson, John M Casselman, and Norman D Yan

Chapter 14 Effects of forestry roads on reproductive habitat and exploitation

of lake trout 265

John M Gunn and Rod Sein

Section IV: Models and issues associated with ecosystem management

Chapter 15 Climate change and sustainable lake trout exploitation: predictions

from a regional life history model 281

Brian J Shuter and Nigel P Lester

Chapter 16 Monitoring the state of the lake trout resource: a landscape approach 293

Nigel P Lester and Warren I Dunlop

Appendix 16.1 Calculation of criteria based on lake area and TDS 323

Appendix 16.2 The effect of recruitment variability on estimating survival rates 325

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Contents xxiii

Section V: Synthesis

Chapter 17 Boreal Shield waters: models and management challenges 331

Robert J Steedman, John M Gunn, and Richard A Ryder

Section VI

Appendix 1 Long-term monitoring sites on the Boreal Shield 349

Appendix 2 Lake trout lakes of the Boreal Shield ecozone of North America 361

Appendix 3 Common and scientific names for fish species in selected

Boreal Shield lake trout lakes 481

Appendix 4 Conversion factors 483

Index 487L1646_C00.fm Page xxiii Thursday, November 6, 2003 8:44 AM

• Lake trout drawing by B.E Harding, Game Fish and Fishing in Algonquin Park,

Government of Ontario, Department of Lands and Forests, Parks Branch, Toronto,1955; revised 1958, 1965

Section Breaks

• Section I: Vic Liimatainen

• Section II: Ed Snucins

• Section III: Vic Liimatainen

• Section IV: Ed Snucins

• Section V: Carissa Brown

• Section VI: Steve Elliott/Mark Johnston

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section I

Introduction

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L1646_C01.fm Page 2 Saturday, July 12, 2003 4:10 PM

The lake trout Salvelinus namaycush (also known as lake charr) is a northern species welladapted to austere conditions in the Arctic and Boreal regions of North America(Figure 1.1) For much of the last 2.5 million years, the land of the lake trout experiencedvarious ice ages, and S namaycush made its living in cold unproductive waters, lakes, andrivers near the ever-shifting margins of the continental glaciers (Winograd et al., 1997;Power, 2002; Wilson and Mandrak, Chapter 2, this volume) A winter scene on the DogRiver, a Lake Superior tributary that once supported a spawning run of lake trout (Loftus,1958), is perhaps reminiscent of some of the habitat occupied by lake trout during much

of its evolutionary history (Figure 1.2)

The lake trout is well equipped to survive in such demanding and dynamic ments It is a large and long-lived fish that produces large, well-provisioned eggs; it has

environ-a metenviron-abolism thenviron-at environ-allows movement environ-and growth environ-at low temperenviron-atures; it cenviron-an withstenviron-andlong periods of food deprivation and will eat almost any available prey item; it is a strong

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4 Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

long-distance swimmer and is able to use thermal refugia (lake hypolimion, groundwatersprings; Figure 1.3) to survive weather and climate extremes (Martin and Olver, 1980;Power, 2002; Snucins and Gunn, 1995) Although extremely hardy in northern conditions,

Salvelinus namaycush performs best in the absence of competitors and predators and isoften most productive in small lakes that contain only simple fish communities (Evansand Olver, 1995; Shuter et al., 1998; Vander Zanden et al., 1999)

Ironically, this hardy northern species appears to be rather poorly adapted to dealwith many “southern” phenomena associated with modern human activity Like other

Chapter one: Factors that shape lake trout ecosystems 5

Arctic animals that live in unproductive ecosystems, the lake trout has evolved a lifehistory strategy that invests in a few, long-lived, late maturing, large-bodied individuals.This makes the lake trout highly vulnerable to a suite of modern threats These includeintroductions of warm water and cool water competitors; stocking of domesticated trout;increasing access, exploitation, and habitat disruption by humans; climate warming; inputs

of nutrients and toxic contaminants; and hydroelectric development (Ryder and Johnson,1972; Schindler, 1998; also see later chapters in this volume)

In North America, lake trout lakes can be found throughout the Precambrian Shieldbut are heavily concentrated in a great sweeping arc that extends along the Shield’ssouthern edge (Figure 1.4) That same arc pattern coincides with or parallels other envi-ronmental phenomena (isotherms, vegetation communities, human activity, etc.) that

(C)

(D)

(D) Emergent alevins in May (photo by Rod Sein).

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6 Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

Figure 1.2 Denison Falls on Dog River, just above a historic spawning site for lake trout (photo by Vic Liimatainen).

Figure 1.3 Behavioral thermoregulation in lake trout The graph shows the core body temperature

of a lake trout in a deep, cold lake (Michaud) where it maintains its preferred temperature by staying

in the hypolimnion or moving up and down in the water column In an extremely warm lake (Gullrock), the lake trout make use of a cold water seepage site during midsummer, when water temperature approaches 20°C Note the fluctuations in the fish’s body temperature in August as it moves in and out of the seepage area From Gunn (2002).

0 5 10 15 20 25

05-May 30-May 24-Jun 19-Jul 13-Aug 07-Sep 02-Oct 27-Oct

Chapter one: Factors that shape lake trout ecosystems 7

shape the distribution and dynamics of lake trout populations and their managementchallenges These lakes exhibit a rather narrow range of physical and chemical character-istics (Table 1.1) They are usually rather cold, clear, deep, and dilute lakes (Martin andOlver, 1976) and have been aptly described as “swimming pools carved out of granite”(Ryder and Johnson, 1992) This book focuses on a group of about 3000 small lake troutlakes (75% of which are less than 500 ha in surface area) in forested catchments at thesouthern edge of the lake trout distribution range in the ecozone referred to as the BorealShield (Ecological Stratification Working Group, 1995) Some examples of these ecosystemsare illustrated in Figure 1.5

The Shield

In the terminology of plate tectonics, the process of plate collisions has left behind stablegeological cores, which are generally located within the interiors of the continent Theseshield areas are comprised of rocks that were initially formed during periods of thebuilding of ancient mountain systems In North America, this continental core is referred

to as the Precambrian Shield, the Canadian Shield, in some places the Laurentide Plateau,

or simply the Shield Like many exposed shield areas throughout the world, it is oftencharacterized by broadly convex surface profiles The Shield is exposed at the surface as

a vast horseshoe-shaped geologic region (about 7,000,000 square kilometers) that coverscentral and eastern Canada and small parts of the northern United States (Figure 1.6).Within the United States, the continental core or shield is extensive (roughly 75% of thesurface area of the country), but most of it is overlain by post-Precambrian earth materials.The Shield landscape in the United States reveals itself only in the Adirondack Mountains,the Boundary Waters Area of Minnesota, and along the Great Lakes Basin

The Precambrian Shield consists mostly of Archean rocks that are at least 2.5 billionyears old This is particularly the case in the northern two-thirds of the exposed Shieldwhere granite, granitic gneiss, and Archean metamorphosed sedimentary and volcanicrocks are dominant Archean rocks are also present along the southern Shield, but in theseareas (for example, at the western end of Lake Superior, just north of the St LawrenceRiver basin, and throughout the Adirondack Mountains) there is a greater predominance

of Proterozoic or late Precambrian volcanic and sedimentary rocks in various degrees of

Figure 1.4 Boreal Shield lake trout lakes.

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8 Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

Chapter one: Factors that shape lake trout ecosystems 9

10 Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

metamorphosis Most Shield rocks are low in cations such as calcium and magnesium.This limits the productivity of the region’s soils and provides surface waters with limitedacid-neutralizing capability Consequently, many of the lakes in these areas that are inhab-ited by lake trout are highly sensitive to acidic precipitation

During the latter parts of the Precambrian, the last 500 to 600 million years, the Shieldwas reduced to an almost featureless surface Then, it was gradually submerged beneathshallow seas beginning in the early Paleozoic The sedimentary limestones, sandstones,and shales that formed beneath those seas can still be seen in areas surrounding thepresently exposed Shield and in isolated pockets within the Shield itself Later erosionstripped away these Paleozoic sedimentary rocks leaving what is today, for the most part,

a tectonically stable area of rolling or undulating topography However, as illustrated inFigure 1.7 (produced using a digital elevation model), the contemporary Shield is not flat

It has hills and mountains that in places reach elevations of between 1200 and 1700 mabove sea level Some of these areas, notably the Adirondack Mountains, were uplifted

by tectonic activity that began during the Tertiary period and continues to this day Manymillions of years of precipitation and stream erosion significantly modified all of theselandscapes, even before they were scraped and scoured by the last continental glaciations(Figure 1.8)

Figure 1.5 Examples of lake trout ecosystems (A) Ultraclear lakes in Killarney Park, Ontario (photo

by Ed Snucins) (B) Lake 233 at the Experimental Lakes Area in northwestern Ontario (photo by John Shearer) (C) Close-up of southern part of McCulloch Lake (47°20 ¢ N, 80°42 ¢ W) near the height of land for Ontario Lake shown again in Landsat image (Figure 1.7) (photo by Vic Liimatainen) (D) Trout Lake, Wisconsin (photo by Carl Bowser).

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Chapter one: Factors that shape lake trout ecosystems 11

Figure 1.6 Outline map of the Precambrian Shield The southern shaded portion of the Shield (in black) is the ecozone referred to as the Boreal Shield and is the focus of this book Boreal or northern

forest refers to the mainly coniferous forest that covers most of the northern portion of the ecozone.

Shield refers to the exposed Precambrian Shield bedrock that extends across the entire ecozone (Ecological Stratification Working Group, 1995).

Figure 1.7 A digital elevation model highlighting the general topographic features of parts of eastern North America, following the methods of Pitblado (1992).

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12 Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

Continental glaciation

It has long been held that the Pleistocene epoch consisted of four continental-scale glacialstages In North America these stages were named (from earliest to latest) Nebraskan,Kansan, Illinoian, and Wisconsinan, with the names usually representing the most south-erly extent of ice movement from north to south However, it is now recognized that theremay have been as many as 10 major glacial periods during the last 1.6 million years and

40 or more minor episodes (Douglas, 1970; Winograd et al., 1997) Still, it was the advancesand retreats of the Laurentide ice sheet during the most recent Wisconsinan glaciation thatshaped today’s lake trout waters The three main legacies of the Wisconsin glaciers weredeeply scoured lake basins, creation of complex temporary drainage systems that acted

as dispersal routes and refugia for aquatic biota, and the deposition of glacial tills andlacustrine deposits, the parent materials of present-day soils

As the 1- to 2-km-thick Laurentide ice sheet advanced southward from multiple domes

in northern Canada, it stripped away the existing soils and most of the underlying ered bedrock Over ice-scoured plains and undulating terrain the advancing glaciersdeepened existing depressions and created numerous others These have now filled withwater to form the myriad of lakes and ponds that are so characteristic of the Shield Thenumber of lakes that the Pleistocene glaciers left behind is not known However, there areapproximately 500,000 lakes (>1 ha) in Ontario alone (Cox, 1978), and the PrecambrianShield is thought to have close to half of the fresh water lake surface area of the world.Elsewhere, numerous glacial lakes have given rise to nicknames such as “The Land of10,000 Lakes” for Minnesota Figure 1.9 shows a portion of a satellite image that illustrates

weath-a Shield lweath-andscweath-ape dotted by lweath-akes thweath-at were creweath-ated by the scouring weath-and dredging ofPleistocene glaciers

As the continental ice sheets retreated, proglacial lakes of various sizes and longevitywere formed The earliest of these were probably Lake Maumee, which developed some14,000 years ago in the western Erie Basin, and Lake Chicago, only a few hundred yearslater in the most southerly basin of what is now Lake Michigan These early proglaciallakes in the Laurentian Great Lakes area initially drained southward through theMississippi River system As the glacier retreated further northward, removal of the

Figure 1.8 Bedrock polished by the glaciers (photo by David Pearson).

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Chapter one: Factors that shape lake trout ecosystems 13

great masses of ice allowed underlying land to rise (isostatic rebound) Drainage patternswere altered, first adding the eastward outlets of the Mohawk–Hudson River valleys;elimination of the southward flow through the Mississippi; opening of the North Bayspillway through the Mattawa and Ottawa rivers; and then finally drainage of the GreatLakes through the St Lawrence River

Further west and north, the largest of the glacial lakes existed, taking on many shapesand sizes from about 12,000 to 8,000 years ago Lake Agassiz was impounded betweenthe retreating ice margins and the Manitoba Escarpment — the present-day remnantsincluding Lakes Manitoba, Winnipeg, Dauphin, and Winnipegosis In addition to theseManitoban areas, at various stages of its life Lake Agassiz also extended well into Ontarioand Saskatchewan in Canada and the northern parts of the states of North Dakota andMinnesota in United States Additional proglacial lakes also appeared and disappearednorth and west of Lake Agassiz as the Laurentide ice sheet retreated from its earliercoalescence with the Cordilleran ice sheet

These lakes, and the rivers that either fed them or emanated from them, were likelyideal pathways for the movement of lake trout throughout this glacial and postglacialperiod (see Wilson and Mandrak, Chapter 2, this volume)

Climate, soils, and vegetation

The climate of the North American Precambrian Shield can generally be described as

“continental,” with long cold winters and short warm summers However, the principalecoregions (Bailey et al., 1985; Ecological Stratification Working Group, 1995; Bailey, 1996)

of the southern portion of the Shield (Figure 1.10) are buffeted by alternating cold anddry polar air masses from the north and warmer moist maritime air masses, generally

Figure 1.9 Landsat satellite image of a lake-strewn Shield landscape north of Sudbury, Canada Electrical transmitting corridors (A), forestry roads (B), clearcut areas (C), and the location of one

of the lakes in Figure 1.5 (D) are indicated.

14 Boreal Shield Watersheds: Lake Trout Ecosystems in a Changing Environment

from the south Annual precipitation increases from west to east in the region, and meanannual temperatures increase from north to south However, there are large seasonal andspatial variations throughout the region, as illustrated in Table 1.2

Advances of the Laurentide ice sheet removed most, if not all, of the soils that haddeveloped in previous interglacial periods It left behind vast areas of Archean and Prot-erozoic bedrock that were completely bare or plastered with a relatively thin (2 to 8 m)till of poorly sorted, coarse-grained, noncalcareous rock debris In more localized areasthe Laurentide ice sheet deposited unsorted morainic debris or sorted glaciofluvial

Figure 1.10 Principal ecoregions of the southern portions of Shield (see Table 1.2 for the mapping keys to these ecoregions).

Table 1.2 Temperature and Precipitation within Selected Ecoregions of the Boreal Shield

Total Annual Precipitation (mm)

Mean Temperatures (°C)

Source: Ecological Stratification Working Group, 1995.

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Chapter one: Factors that shape lake trout ecosystems 15

sediments The latter include a wide variety of ice-contact landforms (kames, eskers) andproglacial features Proglacial features range from the moderately sorted sand and graveldeposits of streams emanating from the ice terminus to the highly sorted silts and claysdeposited in proglacial lakes

Broadly speaking, then, with the retreat of the Laurentide ice sheet dated at only 8,000

to 10,000 years ago, relatively little time has passed for the development of mature mineralsoils, especially over the exposed bedrock areas Thus, thin well-drained stony soils pre-dominate, interspersed with pockets of poorly drained but deeper silt/clay and organicsoils The dominant soil-forming process is podzolization, a process whereby organic acidsform in the surface horizons, leach basic elements (calcium, magnesium), iron, and alu-minum from the upper layers, and then deposit these in soil horizons immediately below.Under forest cover, brunisolic soils may form with relatively poor horizonation and onlyslight illuviation They are characterized by a subsoil horizon that is only slightly altered

by hydrolysis, oxidation, or solution Elsewhere, but still under forest cover, light-coloredluvisols develop, distinguished from the previous two soil orders by a subsoil horizoncontaining clay that has been translocated from upper mineral horizons Scatteredthroughout the study area are soils developed under waterlogged or very poor drainageconditions (gleysols and mesisols) Large, contiguous areas of gleysols are most oftenassociated with extensive areas of silt and clay deposited in glacial lakes

The vegetation of these areas characterize the southern portion of the circumpolarboreal forest (Figure 1.11), dominated by conifers, and the transition zone of mixed conif-erous–deciduous woodlands of the Great Lakes–St Lawrence forest region Black spruce(Picea mariana) is the climax tree species of the more northerly ecoregions, but as onemoves southward it is replaced by other conifers such as white spruce (Picea glauca),balsam fir (Abies balsamea), and eastern white pine (Pinus strobes) Throughout the area,warmer and drier sites are dominated by jack pine (Pinus banksiana) and red pine (Pinus resinosa); poorly drained sites are characterized by black and white spruce, balsam fir,tamarack (Larix laracina), eastern red cedar (Juniperus virginiana), and willow (Salix sp.)

As one moves closer to the Great Lakes, the dominant vegetation is mixedwood forest ofsugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), eastern hemlock (Tsuga canadensis), and eastern white pine, with beech (Fagus sp.) appearing on warmer sites Drysites are dominated by red and eastern white pine and red oak (Quercus rubra) Wetter

Figure 1.11 Circumpolar boreal forest Data source: Olson et al (2001).

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