National Park Service

U.S. Department of the Interior

Natural Resource Program Center

Assessment of Natural Resource Conditions

Isle Royale National Park

Natural Resource Report NPS/NRPC/WRD/NRR—2010/237
ON THE COVER

Left: Lichens on Rock at Davidson Island (Photograph by Dave Mechenich)

Top Right: Foggy Morning at Scoville Point (Photograph by Dave Mechenich)

Bottom Right: Sunrise on Davidson Island (Photograph by Steve Seiler)
Assessment of Natural Resource Conditions

Isle Royale National Park

Natural Resource Report NPS/NRPC/WRD/NRR—2010/237

George J. Kraft

David J. Mechenich

Christine Mechenich

Center for Watershed Science and Education

College of Natural Resources

University of Wisconsin-Stevens Point

Stevens Point, WI 54481

James E. Cook

Steven M. Seiler

College of Natural Resources

University of Wisconsin-Stevens Point

Stevens Point, WI 54481

This report was prepared with funding from the National Park Service under Task Agreement 

J2380085505 of the Great Lakes Northern Forest Cooperative Ecosystem Studies Unit under 

Cooperative Agreement CA H6000082000 between the National Park Service and the University 

of Minnesota.

September 2010

U.S. Department of the Interior

National Park Service

Natural Resource Program Center

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Program Center publishes a range of reports that 

address natural resource topics of interest and applicability to a broad audience in the National 

Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public. 

The Natural Resource Report Series is used to disseminate high-priority, current natural resource 

management information with managerial application. The series targets a general, diverse 

audience, and may contain NPS policy considerations or address sensitive issues of management 

applicability.

All manuscripts in the series receive the appropriate level of peer review to ensure that the 

information is scientifically credible, technically accurate, appropriately written for the intended 

audience, and designed and published in a professional manner. 

This report received informal peer review by subject-matter experts who were not directly 

involved in the collection, analysis, or reporting of the data. Data in this report were collected 

and analyzed using methods based on established, peer-reviewed protocols and were analyzed 

and interpreted within the guidelines of the protocols.

Views, statements, findings, conclusions, recommendations, and data in this report do not 

necessarily reflect views and policies of the National Park Service, U.S. Department of the 

Interior. Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use by the U.S. Government.

This report is available from the NPS Water Resources Division 

(http://www.nature.nps.gov/water/) and the Natural Resource Publications Management website 

(http://www.nature.nps.gov/publications/NRPM). 

Please cite this publication as:

Kraft, G. J., D. J. Mechenich, C. Mechenich, J. E. Cook, and S. M. Seiler. 2010. Assessment of 

natural resource conditions: Isle Royale National Park. Natural Resource Report

NPS/NRPC/WRD/NRR—2010/237. National Park Service, Fort Collins, Colorado.

NPS 139/105526, September 2010
iii

Contents

Page

Figures............................................................................................................................................ ix

Tables............................................................................................................................................ xii

Appendices................................................................................................................................... xiv

Commonly Used Abbreviations.................................................................................................... xv

Executive Summary.................................................................................................................... xvii

Acknowledgements..................................................................................................................... xxii

Introduction and Park Description.................................................................................................. 1

Island Communities and Regions............................................................................................ 3

Ecologic Groups Based on Vegetation Mapping..................................................................... 3

Lake Superior Communities and Regions............................................................................... 4

Climate..................................................................................................................................... 6

Historic and Current Uses........................................................................................................ 7

Soils and Geology.................................................................................................................... 9

Lake Superior................................................................................................................................ 13

Physical Characteristics......................................................................................................... 13

Coastal Geomorphic Zones and Processes............................................................................ 16

Coastal Wetlands and Nearshore Habitats............................................................................. 16

Lake Superior Shorelands...................................................................................................... 19

USEPA Shoreline Types.................................................................................................... 19

Great Lakes Rocky Shores (Ecologic Group 5)................................................................ 19

Shoreline Rock Pools........................................................................................................ 22

Biologic Resources................................................................................................................ 22

Aquatic and Shoreline Vegetation .................................................................................... 22
iv

Phytoplankton, Zooplankton, Aquatic Invertebrates, and Benthos .................................. 23

Lake Superior Fish Communities...................................................................................... 25

Fish Abundance and the Commercial and Sport Fishery................................................. 28

Ecosystem Condition............................................................................................................. 31

Offshore Water Quality ......................................................................................................... 33

Nutrients............................................................................................................................ 33

Dissolved Oxygen.............................................................................................................. 36

Alkalinity, Specific Conductance, and pH ........................................................................ 37

Major Cations and Anions................................................................................................ 37

Temperature...................................................................................................................... 37

Critical Pollutants and Substances of Emerging Concern ............................................... 39

Nearshore Water Quality ....................................................................................................... 40

Total and Fecal Coliform Bacteria................................................................................... 40

Contaminants in Fish and Other Organisms.......................................................................... 41

Inland Aquatic Resources............................................................................................................. 43

Physical Description .............................................................................................................. 43

Lakes................................................................................................................................. 43

Streams.............................................................................................................................. 48

Wetlands............................................................................................................................ 50

Northern Shrub/Graminoid Fens and Bogs (Ecologic Group 1) ..................................... 52

Wet Meadows and Marshes (Ecologic Group 3).............................................................. 56

Northern Conifer and Hardwood Forest and Shrub Swamps (Ecologic Group 4).......... 56

River-Associated Wetlands ............................................................................................... 57

Groundwater..................................................................................................................... 57

Biologic Resources................................................................................................................ 61
v

Fish Communities............................................................................................................. 61

Zooplankton, Phytoplankton, Macroinvertebrates, and Macrophytes ............................. 63

Herptiles............................................................................................................................ 67

Water Quality–Lakes............................................................................................................. 68

Water Clarity .................................................................................................................... 70

Temperature...................................................................................................................... 70

Specific Conductance........................................................................................................ 71

Dissolved Oxygen.............................................................................................................. 71

pH...................................................................................................................................... 71

Major Ions......................................................................................................................... 71

Dissolved Silica................................................................................................................. 73

Alkalinity........................................................................................................................... 73

Dissolved Organic Carbon ............................................................................................... 74

Chlorophyll-a and Trophic State Indices.......................................................................... 74

Total Phosphorus and Total Nitrogen .............................................................................. 75

Water Quality–Streams.......................................................................................................... 76

Terrestrial Resources .................................................................................................................... 78

Historic Vegetation................................................................................................................ 79

Current Vegetation................................................................................................................. 80

Boreal Associations, Uplands (Ecologic Groups 8-11, 13).............................................. 81

Northern Hardwood Forest & Woodland Group, Ecologic Group 12............................. 84

Upland Shrub and Herbaceous Associations, Ecologic Groups 6, 7, 13, 14 ................... 85

Avian Community ................................................................................................................. 86

Mammalian Community........................................................................................................ 87

Moose-Wolf Interaction and Population Changes ........................................................... 88
vi

Role of Moose in the Ecology of the Boreal System ......................................................... 89

Effect of Moose on Ecosystem Processes.......................................................................... 89

Effect of Moose on Aquatic Communities......................................................................... 91

Beaver Population Dynamics and Landscape Influence .................................................. 91

Indicators of Natural Resource Conditions................................................................................... 93

Vital Signs ............................................................................................................................. 93

Designations and Protections................................................................................................. 93

Presence of Endangered, Threatened, or Special Concern Species....................................... 93

Violations of Water Quality Standards.................................................................................. 94

Impairments, 303(d) Reports, and Fish Consumption Advisories ........................................ 95

Stressors........................................................................................................................................ 96

ISRO Air Quality................................................................................................................... 96

Air Monitoring Stations Near ISRO.................................................................................. 96

Local and Regional Air Emissions.................................................................................... 97

Long-Range Atmospheric Deposition............................................................................. 101

Acid and Nutrient Deposition ......................................................................................... 102

Mercury........................................................................................................................... 110

Great Lakes Shipping .......................................................................................................... 113

Shipping Lanes and Shipwrecks...................................................................................... 113

Cargo .............................................................................................................................. 115

Fuel and Engine Types.................................................................................................... 115

Bilge Water ..................................................................................................................... 117

Ballast Water .................................................................................................................. 117

Ferry Service................................................................................................................... 118

Recreational Boating ........................................................................................................... 119
vii

Water Use and Wastewater Treatment ................................................................................ 120

Natural and Altered Terrestrial Disturbance Regimes......................................................... 121

Boreal Forest .................................................................................................................. 121

Northern Hardwood Forest ............................................................................................ 123

Other Upland Conifer Forests........................................................................................ 124

Lowland Forests.............................................................................................................. 125

Human Effects on Terrestrial Resources, 1840–1940 ......................................................... 125

Mining............................................................................................................................. 125

Logging ........................................................................................................................... 125

Fragmentation................................................................................................................. 128

Recreational Effects and Visitor Use................................................................................... 128

Fuel Storage and Discharges at ISRO ................................................................................. 130

Aquatic Invasive Species..................................................................................................... 131

AIS Known in ISRO......................................................................................................... 131

AIS Believed to Be Encroaching on ISRO ...................................................................... 133

Other AIS Found in Lake Superior................................................................................. 135

Introduction Pathways and Control Strategies for Aquatic Invasive Species................ 135

Terrestrial Invasive Species................................................................................................. 136

Gypsy Moth ..................................................................................................................... 137

Emerald Ash Borer ......................................................................................................... 138

White Pine Blister Rust ................................................................................................... 138

Larch Sawfly ................................................................................................................... 139

Earthworms..................................................................................................................... 139

Climate Change ................................................................................................................... 140

Lake Superior Water Level Changes .............................................................................. 141
viii

Other Surface Water Impacts.......................................................................................... 141

Coastal Wetland Impacts................................................................................................ 142

Projected Impacts on Plants........................................................................................... 142

Projected Impacts on Animal Communities.................................................................... 145

Overall Impacts at ISRO................................................................................................. 145

Conclusions and Recommendations........................................................................................... 147

Lake Superior....................................................................................................................... 147

Inland Lakes, Rivers, and Wetlands.................................................................................... 148

Terrestrial Resources........................................................................................................... 149

Literature Cited ........................................................................................................................... 165

Appendices.................................................................................................................................. 213
ix

Figures

Page

Figure 1. Location of Isle Royale National Park in the upper Great Lakes region of the 

United States................................................................................................................................... 2

Figure 2. Occurrences of endangered, threatened, and special concern species and highquality natural communities by section, Isle Royale National Park ............................................... 5

Figure 3. Benthic natural regions and seascapes for Lake Superior.............................................. 6

Figure 4. (a) Monthly mean and (b) monthly mean maximum temperatures for summer 

months, Mott Island, Isle Royale National Park, 1940–2004......................................................... 8

Figure 5. Number of visitors per year to Isle Royale National Park, 1940–2008........................ 10

Figure 6. Surficial bedrock geology of Isle Royale National Park .............................................. 11

Figure 7. Lake Superior bathymetry and soundings.................................................................... 14

Figure 8. Major surface currents, downward water movements, and upwellings for Lake 

Superior......................................................................................................................................... 15

Figure 9. Shoreline sensitivity classifications for Isle Royale National Park.............................. 20

Figure 10. Rocky shores (Ecologic Group 5) in Isle Royale National Park ................................ 21

Figure 11. Lean lake trout, siscowet, and lake whitefish harvests from Michigan, 

Minnesota, and Wisconsin waters of Lake Superior, 1971–2006 ................................................ 30

Figure 12. Chub, rainbow smelt, and lake herring harvest from Michigan, Minnesota, 

and Wisconsin waters of Lake Superior, 1971–2006 ................................................................... 32

Figure 13. Locations of USEPA water sampling sites in Lake Superior in the vicinity of 

Isle Royale National Park ............................................................................................................. 33

Figure 14. Total phosphorus (unfiltered) for summer epilimnion composites, Lake 

Superior offshore sites around Isle Royale National Park, 1996–2006........................................ 35

Figure 15. Nitrate and nitrite-nitrogen (filtered) for summer epilimnion composites, Lake 

Superior offshore sites around Isle Royale National Park, 1996–2006........................................ 35

Figure 16. Dissolved silica (filtered) for summer epilimnion composites, Lake Superior 

offshore sites around Isle Royale National Park, 1996–2006....................................................... 36

Figure 17. Chlorophyll-a levels for summer epilimnion composites, Lake Superior 

offshore sites around Isle Royale National Park, 1996–2008....................................................... 36
x

Figure 18. Dissolved oxygen (n=1,108) values for all depths, Lake Superior offshore 

sampling sites SU-11–SU-16 near Isle Royale National Park, 1996–2008.................................. 37

Figure 19. Alkalinity (n=671), specific conductance (n=1,566), chloride (n=934), and pH 

(n=653) values for all depths, Lake Superior offshore sampling sites SU-11–SU-16 near 

Isle Royale National Park, 1996–2008 ......................................................................................... 38

Figure 20. Water temperature (o

C) for 1–5 m depths, Lake Superior offshore sampling 

sites SU-11–SU-16 near Isle Royale National Park, 1996–2008 ................................................. 39

Figure 21. Water features and watersheds of the western section of Isle Royale National 

Park, including the Washington Creek gaging station.................................................................. 44

Figure 22. Water features and watersheds of the central section of Isle Royale National 

Park ............................................................................................................................................... 45

Figure 23. Water features and watersheds of the eastern section of Isle Royale National 

Park ............................................................................................................................................... 46

Figure 24. Lake types of Isle Royale National Park by canonical correspondence analysis....... 49

Figure 25. Mappable wetland types for the western section of Isle Royale National Park ......... 53

Figure 26. Mappable wetland types for the central section of Isle Royale National Park........... 54

Figure 27. Mappable wetland types for the eastern section of Isle Royale National Park .......... 55

Figure 28. River-associated wetlands in the Big Siskiwit River valley, Isle Royale 

National Park, by various delineation methods. ........................................................................... 60

Figure 29. Comparison of values for selected water quality parameters between 1995–

1997 and 2007–2008..................................................................................................................... 70

Figure 30. Comparison of calcium and magnesium values for three lakes sampled in 

1980–1981, 1995–1997, and 2007–2008, Isle Royale National Park........................................... 72

Figure 31. Comparison of sulfate and chloride values for three lakes sampled in 1980–

1981, 1995–1997, and 2007–2008, Isle Royale National Park..................................................... 73

Figure 32. Upland ecologic groups for Isle Royale National Park .............................................. 82

Figure 33. Air quality monitoring sites in the vicinity of Isle Royale National Park. ................. 97

Figure 34. Regulated facilities that emit criteria air pollutants within 250 km of Isle 

Royale National Park .................................................................................................................... 99

Figure 35. Emissions of carbon monoxide from regulated facilities within 250 km of Isle 

Royale National Park .................................................................................................................. 100
xi

Figure 36. Emissions of particulate matter less than 10 microns from regulated facilities 

within 250 km of Isle Royale National Park............................................................................... 100

Figure 37. Emissions of volatile organic compounds from regulated facilities within 250 

km of Isle Royale National Park................................................................................................. 101

Figure 38. Emissions of sulfur dioxide from regulated facilities within 250 km of Isle 

Royale National Park .................................................................................................................. 103

Figure 39. Emissions of nitrous oxides from regulated facilities within 250 km of Isle 

Royale National Park .................................................................................................................. 103

Figure 40. Emissions of ammonia from regulated facilities within 250 km of Isle Royale 

National Park .............................................................................................................................. 104

Figure 41. Summer wet deposition of inorganic N (NH4-N plus NO3-N) for NADP 

stations at Isle Royale National Park (1985–2006), Hovland, MN (1997–2008), and 

Chassell, MI (1983–2008) .......................................................................................................... 105

Figure 42. Relationship between summer inorganic N wet deposition (kg ha-1

) at Isle 

Royale National Park and Hovland, MN, 1997–2006 ................................................................ 105

Figure 43. Base cations in summer wet deposition for Isle Royale National Park (1985–

2006) and Hovland (1997–2008)................................................................................................ 106

Figure 44. Summer field pH and laboratory pH for precipitation, NADP station at Isle 

Royale National Park, 1985–2006 .............................................................................................. 106

Figure 45. Calcium, magnesium, sodium, and potassium trendlines and values (kg ha-1) 

for annual wet deposition for Hovland, MN (squares), 1997–2008, and summer wet 

deposition for Isle Royale National Park (diamonds), 1985–2006............................................. 107

Figure 46. Lake Superior shipping lanes (NOAA 2007 a, b, c, d)............................................. 114

Figure 47. Location of mines operated 1843–1920, Isle Royale National Park ........................ 126
xii

Tables

Page

Table 1. Natural communities of Isle Royale National Park.......................................................... 4

Table 2. Physical processes that affect nearshore and coastal margin zones............................... 17

Table 3. Categories of Great Lakes coastal wetlands................................................................... 18

Table 4. Palustrine coastal wetlands of Isle Royale National Park.............................................. 18

Table 5. Lake Superior shoreline types, lengths, and USEPA shoreline sensitivity 

classification for Isle Royale National Park.................................................................................. 19

Table 6. Ecologic roles of important Lake Superior fish species, including nonindigenous 

species........................................................................................................................................... 26

Table 7. Commercial harvest of Lake Superior fish from 1867–2000 and in 2006..................... 29

Table 8. Charter boat excursions and catch for 1999, 2001, and 2005–2007 in the vicinity 

of Isle Royale National Park......................................................................................................... 33

Table 9. Water quality data (averages and ranges) for Lake Superior and for offshore 

sites around Isle Royale National Park, 2001–2007 ..................................................................... 34

Table 10. Fish consumption advisories for species of Lake Superior fish................................... 41

Table 11. Morphometric characteristics of 43 named lakes in Isle Royale National Park. ......... 47

Table 12. Lengths and watershed areas of named streams, Isle Royale National Park ............... 50

Table 13. Wetland types and sizes in Isle Royale National Park................................................. 51

Table 14. Stream lengths in Isle Royale National Park and their proximity to wetlands by 

type................................................................................................................................................ 59

Table 15. Wetland types in Isle Royale National Park and their proximity to streams............... 59

Table 16. Inland fish species found in lakes, Isle Royale National Park ..................................... 62

Table 17. Presence of unionid species in inland waters of Isle Royale National Park, 

2000–2001..................................................................................................................................... 66

Table 18. Comparison of water quality data for selected parameters for three lakes 

sampled in 1980–1981, 1995–1997, and 2007–2008, Isle Royale National Park ........................ 72
xiii

Table 19. Comparison of chlorophyll-a values for nine lakes sampled in 1995–1997 and 

2008, Isle Royale National Park ................................................................................................... 74

Table 20. Trophic state indices (TSIs) for inland lakes, Isle Royale National Park .................... 75

Table 21. Names and sizes of upland forest Ecologic Groups, Isle Royale National Park.......... 83

Table 22. Comparison of 1999 and 2009 state status for state-listed species found at Isle 

Royale National Park .................................................................................................................... 94

Table 23. Exceedences of freshwater and drinking water criteria for pH and metals for 

Washington Creek at Windigo, Isle Royale National Park, 1962–1993....................................... 95

Table 24. Water bodies on Michigan's 303(d) list in Isle Royale National Park ......................... 95

Table 25. Criteria pollutant emissions for regulated facilities and some ports within 250 

km of Isle Royale National Park................................................................................................... 98

Table 26. Commercial vessel trips to and from the port of Duluth-Superior, 2002–2006......... 116

Table 27. Results of monitoring for chemical and biologic parameters in 2008 and 2009 

at the Rock Harbor wastewater treatment plant, Isle Royale National Park............................... 120

Table 28. Locations of fuel storage tanks at Isle Royale National Park .................................... 130

Table 29. Part 201 hazardous material discharge (ERD) sites in the vicinity of Isle 

Royale National Park .................................................................................................................. 130

Table 30. Human-initiated mechanisms for transfer of aquatic invasive species in Lake 

Superior....................................................................................................................................... 135

Table 31. Condition summary for general resources, Isle Royale National Park. ..................... 150

Table 32. Condition summary for air quality, Isle Royale National Park.................................. 151

Table 33. Condition summary for Lake Superior, Isle Royale National Park. .......................... 152

Table 34. Condition summary for inland lakes, rivers, and wetlands, Isle Royale National 

Park. ............................................................................................................................................ 156

Table 35. Condition summary for forest resources, Isle Royale National Park......................... 160

Table 36. Impact of stressors on aquatic and upland resources in Isle Royale National 

Park. ............................................................................................................................................ 163
xiv

Appendices 

Page

Appendix A. Sources of data for base map and notes on map content development. ............... 213

Appendix B. Description of GIS layers, sources, and metadata for maps used in the 

preparation of this report............................................................................................................. 216
xv

Commonly Used Abbreviations

AIS aquatic invasive species

BP before present

BTEX benzene, toluene, ethylbenzene, and xylene

C Celsius

CAA and CAAA Clean Air Act and Clean Air Act Amendments

CASTNet Clean Air Status and Trends Network

cm centimeter

DO dissolved oxygen

DOC dissolved organic carbon

FIA Forest Inventory and Analysis National Program (USDA–Forest Service)

FPOM fine particulate organic matter

FRI fire return interval

GCM general circulation model

GLKN Great Lakes Inventory and Monitoring Network 

ha hectare

HACCP Hazard Analysis and Critical Control Point 

HCB hexachlorobenzene

HFO heavy fuel oil

HUC Hydrologic Unit Code

IADN United States-Canada Integrated Atmospheric Deposition Network

IJC International Joint Commission

IMPROVE Interagency Monitoring of Protected Visual Environments

IPCC International Panel on Climate Change

kg kilogram

km kilometer

L liter

LaMP lakewide management plan

LUST leaking underground storage tank

m meter

m3

day-1 cubic meters per day

m3sec-1 cubic meters per second

m3

year-1 cubic meters per year

MDCH Michigan Department of Community Health

MDEQ Michigan Department of Environmental Quality

MDNR Michigan Department of Natural Resources 

mg L-1 milligram per liter (part per million in water)

MI Michigan

MN DNR Minnesota Department of Natural Resources

MNFI Michigan Natural Features Inventory

MT metric ton

MMT million metric tons

MTBE methyl tertiary butyl ether

MN Minnesota

N nitrogen
xvi

NADP National Atmospheric Deposition Program

NADP NTN National Atmospheric Deposition Program National Trends Network

NCDC National Climatic Data Center

NHD National Hydrography Dataset

NOAA National Oceanic and Atmospheric Administration

NOx nitrous oxides

NPS National Park Service

NWI National Wetlands Inventory

OSRW outstanding state resource water

PAH polyaromatic hydrocarbon

PCB polychlorinated biphenyl

PM particulate matter

ppm parts per million

PWC personal watercraft

SLSMC St. Lawrence Seaway Management Corporation

SOLEC State of the Lakes Ecosystem Conference

TMDL total maximum daily loading

TN total nitrogen

TP total phosphorus

TSI Trophic State Index

μg L-1 microgram per liter (part per billion in water)

μS cm-1 microSiemens per centimeter (units of specific conductance)

USACE United States Army Corps of Engineers

USDA United States Department of Agriculture

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service

USGAO United States General Accounting Office

USGS United States Geological Survey

VHS viral hemorrhagic septicemia 

VOC volatile organic compound

WDNR Wisconsin Department of Natural Resources

WI Wisconsin

WRD NPS Water Resources Division
xvii

Executive Summary

This report is an assessment of the condition of the natural resources of Isle Royale National 

Park (ISRO) and an evaluation of the threats and stressors that act on these resources. This 

assessment focuses on three broad resource groups: Lake Superior, inland waters, and terrestrial 

resources. It is based entirely on an in-depth review of scientific literature and agency reports, 

and on compilations, syntheses, and new analyses of existing data; no new field studies were 

conducted. It broadly describes ISRO and its natural resources, identifies stressors and threats to 

those resources, examines existing data about natural resource conditions, and makes 

recommendations for further study and management priorities where appropriate. 

ISRO consists of a group of islands in northwestern Lake Superior, the surrounding Lake 

Superior waters up to 4.5 miles (7.2 kilometers [km]) offshore, and a small portion of the 

mainland. The main island, 45 miles (72 km) long and 9 miles (14 km) wide, is surrounded by 

approximately 400 much smaller islands. The park protects 572,000 acres (231,400 hectares

[ha]) of land and water (NPS ca. 2003). Although ISRO is generally perceived as isolated, it is 

only about 15 miles (24 km) from points on the Canadian and Minnesota shoreline.

Lake Superior has the greatest surface area of any freshwater lake in the world and includes 10% 

of the world’s fresh surface water. ISRO encompasses over 400,000 acres (165,000 ha) of Great 

Lakes waters (Lafrancois and Glase 2005). With its many inlets and islands, ISRO includes 337 

miles (543 km) of Lake Superior shoreline (Crane et al. 2006). Rock pools on the Lake Superior 

shoreline provide a unique habitat for frogs and other amphibians as well as arctic and alpine 

plant and insect species.

ISRO’s topography is generally rugged and determined by ridges and valleys in the volcanic and 

sedimentary bedrock. The resulting “washboard-like” pattern affects animal and plant 

distributions, migration patterns, microclimates, wetland distribution, and human uses 

(Thornberry-Ehrlich 2008). Soils are derived from bedrock and range from thin and sandy or 

loamy in northern uplands (Woodruff et al. 2003) to deeper, better-developed, and more 

calcareous in the south (NPS 2005, Schlesinger et al. 2009). Holocene soils are mainly alluvium 

in the form of lake and stream deposits on beaches and in swamps, bogs, and ponds made by 

beaver (Castor canadensis) (Thornberry-Ehrlich 2008).

ISRO has 278 lakes and ponds (USGS 2008), ranging in size from Siskiwit Lake at 1,635 ha and 

over 45 m deep to numerous shallow ponds. It has 43 named inland lakes, more than any other 

Great Lakes area national park, six named perennial streams, and many kilometers of unnamed 

perennial and intermittent streams. Most streams, lakes, and wetlands are oriented southwest to 

northeast as determined by the bedrock topography. Beaver activity has also enhanced wetland 

formation (Lafrancois and Glase 2005, Crane et al. 2006). 

ISRO is densely forested, with northern boreal spruce-fir forest in the northeast part of the island 

and near the cool, moist shoreline of Lake Superior and northern hardwood forests in the 

warmer, drier interior, especially in the southwest (NPS ca. 2003). The ridges and interior 

portion of the main island support many open, non-arboreal plant communities. ISRO has 52 
xviii

plant community types, two of which (the white cedar–yellow birch forest and the boreal 

calcareous seepage fen) are globally rare. 

The plant composition of ISRO is highly diverse. In 2008, ISRO had 55 plant species that are 

currently state-endangered, threatened, or of special concern (NPS 2008b, MNFI 2009b). The 

greatest botanic value of the park lies in its disjunct species, those that are most commonly found 

in arctic or alpine habitats or in the western U.S. Most of these occur along the Lake Superior 

shoreline (Judziewicz 1995, 1997, 2004) and on Passage Island. The range of community types, 

large number of species of concern, and minimal incidence of exotics, coupled with minimal 

human impact during the settlement era, make ISRO a suitable reference condition for other 

protected areas in the region (Schlesinger et al. 2009). Fire exclusion has not occurred long 

enough on ISRO to cause major changes in plant species composition.

Critical animal resources in ISRO include moose (Alces alces, a species of special concern in 

Michigan) and the federal-endangered and state-threatened gray wolf (Canus lupus), whose 

interrelationships have been intensively studied. ISRO has the only naturally reproducing coaster 

brook trout (Salvelinus fontinalis) populations in the United States; the most genetically diverse 

lake trout (S. namaycush) population in Lake Superior; the largest remaining population of statethreatened common loon (Gavia immer) in Michigan (MI), and increasing nesting populations of 

bald eagles (Haliaeetus leucocephalus) and osprey (Pandion haliaetus) (NPS ca. 2003). Two 

state-endangered birds, the short-eared owl (Asio flammeus), and peregrine falcon (Falco

peregrinus) are occasional visitors to ISRO, and the park is home to other animals that are

threatened or of special concern in MI. 

Bird and mammal assemblages present contrasting situations at ISRO. Mammalian composition 

(both additions and losses) has fluctuated significantly over the past approximately 115 years. 

There are currently 15 mammals confirmed present on ISRO (NPS 2003b), and some 

conspicuous species that are common on the mainland are absent (Hansen et al. 1973). The bird 

community, though not static, has been more stable and is more comparable to that of mainland 

areas. The important difference is primarily dispersal capacity, and this fundamental difference 

suggests the mammalian community will be more susceptible to future stressors.

ISRO is also rich in human history. Native Americans likely inhabited ISRO throughout the 

Holocene (the past 11,000 years) and may have mined pure native copper on Isle Royale as long 

as 4,500 years ago (Schlesinger et al. 2009). The North Shore Ojibwe people had a long history 

with ISRO and regularly used it for subsistence activities such as making maple sugar, 

harvesting plants, snaring rabbits, netting passenger pigeons, and gathering gull eggs. ISRO was 

also “the good place,” which still has spiritual significance to them (Cochrane 2009). 

ISRO experienced three distinct periods of copper mining activity in the 1800s, and 22 mine sites 

from this era are known (Karamanski et al. 1988). ISRO was not extensively commercially 

logged, although a great deal of lumber was needed to operate the mines and establish the 

associated settlements. An extensive forest fire in 1936 followed a large pulpwood logging 

operation in the spruce and balsam swamp near Siskiwit Bay, just before ISRO was dedicated as 

a national park (Karamanski et al. 1988, Schlesinger et al. 2009).
xix

The first commercial fishing operation in Michigan was run on ISRO by the American Fur 

Company from the 1830s–1842. The largest human population related to fishing on ISRO 

occurred in the 1920s, but commercial fishing was virtually eliminated by 1960 (Karamanski et 

al. 1988). Four hotels existed on ISRO by 1910, and a golf course was built at Belle Island. 

Resorts were located in Washington Harbor, Chippewa Harbor, and Rock Harbor, and on Belle 

Island, Barnum Island, and Davidson Island (Karamanski et al. 1988). Ten shipwrecks are 

documented around ISRO. The Emperor, which sank off Canoe Rocks on the northeast end of 

ISRO in 1947, was the last major wreck at ISRO (Karamanski et al. 1988).

ISRO was authorized as the 21st national park by Congress in 1931 “to conserve a prime example 

of North Woods Wilderness,” and the private holdings on the island were bought up from the 

late 1930s to 1940. ISRO was further designated part of the National Wilderness Preservation 

System in 1976. Over 99% of ISRO’s land area is designated as wilderness (Crane et al. 2006). 

In 1980, the United Nations Man and the Biosphere Programme named ISRO an International 

Biosphere Reserve, giving it global scientific and educational significance.

ISRO has no roads and is accessible by boat or plane. The National Park Service maintains a 

ferry service from Houghton, MI, to ISRO; commercial ferries travel from Copper Harbor, MI,

and Grand Portage, MN. The National Park Service also operates a seasonal headquarters on 

Mott Island, visitor centers at Rock Harbor and Windigo, and a dormitory for visiting researchers 

on Davidson Island. A concessionaire operates lodging at Rock Harbor, with 60 lodge rooms and 

20 cottages. The National Park Service makes available 113 tent sites, 88 shelters, and 43 group 

tent sites for camping (Isle Royale and Keweenaw Parks Association 2009). Visitation to ISRO 

increased from 2,962 in 1940 to a high of 31,760 in 1987; the mean was 16,350 yr-1 from 2004–

2008 (NPS 2009).

Although ISRO is isolated from the mainland, it is by no means isolated from stressors and 

pollution sources. Lake Superior waters contain measurable levels of mercury and other toxic 

metals; pesticides such as chlordane, aldrin, dieldrin, and DDT; and other organic compounds 

such as polychlorinated biphenyls (PCBs), dioxin, and polycyclic aromatic hydrocarbons, to 

name just a few (LSBP 2008). Atmospheric deposition is the major source of mercury and 

persistent organic pollutants to Lake Superior (Swackhamer and Hornbuckle 2004). Some 

contaminants originate in the southern U.S., such as chlordane (Hafner and Hites 2003) and 

toxaphene (Ma et al. 2005). DDT originates both from Midwestern soils and from Mexico and 

Central America (Bidleman et al. 2006, LSBP 2006a). The Chicago area is the major source of 

PCBs to the region (Hafner and Hites 2003). Regulated facilities in the U.S. and Canada within 

155 miles (250 km) of ISRO produce 167,000 tons (151,138 metric tons) yr-1 of criteria air 

pollutants (carbon monoxide, nitrous oxides, sulfur dioxide, particulate matter, volatile organic 

compounds, and ammonia) that are linked to smog and acid rain. ISRO waters are not 

particularly sensitive to the acidifying effects of acid rain. Acid deposition has not yet caused 

notable alteration of terrestrial ecosystem function, but ISRO is experiencing additions of some 

nutrients and losses of others that could affect its ecosystems, especially the boreal forest, over 

time.

Great Lakes shipping also presents risks including accidental releases of fuel and the 

introduction of aquatic invasive species. Approximately 1,000 vessels use the channel between 
xx

Blake Point and Passage Island each year en route from the locks at Sault St. Marie to the port of 

Thunder Bay, Ontario. Rayburn et al. (2004) simulated a spill of 26,000 gallons (100 m3) of 

Intermediate Fuel Oil in this channel and concluded that “a spill of this magnitude to Isle Royale 

will be a major event with regional, national and international importance.” In addition to using 

the channel, vessels may use ISRO for shelter during harsh weather while traveling between the 

locks and ports at the head of the lake such as Taconite Harbor, Silver Bay, Two Harbors, 

Duluth, Superior, and Ashland.

Ballast water is the source of 29 invasive aquatic animal and protist species introduced and 

established in the Great Lakes since 1959 (Grigorovich et al. 2003a). In addition to deliberately 

introduced fish species such as rainbow trout (Oncorhynchus mykiss), brook trout (Salmo trutta),

and Pacific salmon (Oncorhynchus spp.), known aquatic invasive species at ISRO are the sea 

lamprey (Petromyzon marinus), threespine stickleback (Gasterosteus aculeatus), spiny waterflea 

(Bythotrephes longimanus), and the plants Typha spp. (cattails) and Phragmites australis

(common reed). In addition, either zebra mussels (Dreissena polymorpha) or quagga mussels (D. 

bugensis) were found in Washington Harbor in September 2009 (Flesher 2009b, Myers 2009).

Climate change is also a threat to ISRO resources. Statistically significant increases in monthly 

mean and monthly mean maximum temperatures occurred at Mott Island from 1940 to 2004. 

This observation agrees with the published report of Austin and Coleman (2007) for the Lake 

Superior region. Tree species now at ISRO that would lose >90% of their range in the U.S. under 

current climate change scenarios include quaking aspen (Populus tremuloides), sugar maple 

(Acer saccharum), northern white cedar (Thuja occidentalis), balsam fir (Abies balsamea), and 

paper birch (Betula papyrifera) (Hansen et al. 2001). Although Lake Superior may buffer ISRO 

from temperature changes compared to mainland sites (Davis et al. 2000), current climate change 

scenarios will likely result in changes in plant species ranges, species abundance, community 

composition, and many ecosystem properties. 

ISRO’s wilderness status does protect it from local anthropogenic contamination sources, 

however. For example, ISRO inland lakes are free from many human impacts present in 

mainland lakes, and the water quality of ISRO lakes is good, although in some cases outside the 

boundaries of the ecoregion reference criteria. There has been minimal introduction of terrestrial 

exotic plant species. No truly problematic terrestrial exotic species are present at levels of 

concern, although the larch sawfly (Pristiphora erichsonil) greatly reduced the population of 

tamaracks on the island in the past. However, recreation is a possible dispersal mechanism, and 

thus careful regular monitoring is important.

Major recommendations for future study on ISRO include bathymetric assessments, habitat 

mapping, water quality monitoring, and biological inventories of Lake Superior nearshore waters

and shoreline splash pools. Water quality sampling of inland lakes should continue. We endorse 

continued or expanded monitoring for both aquatic and terrestrial invasive species, including 

earthworms. Inland and nearshore fish surveys should be regularly conducted, and the status of 

coaster brook trout should be carefully monitored. Wetland biota and chemistry need further 

study. Atmospheric deposition impacts on aquatic and terrestrial ecosystems need continued 

study. More information is needed about the status of the boreal forest relative to its historic 

range and variability. Finally, given ISRO’s status as a refuge for arctic and disjunct species, and 
xxi

the limited dispersal potential of its mammalian population, monitoring should be done to 

identify and assess potential effects of climate change.
xxii

Acknowledgements

We would like to thank the many people who assisted us in the preparation of this report. At 

ISRO, Alex Egan helped us with our accommodations at Davidson Island during our site visit. 

Betsy Rossini and Mark Romanski met with us to help define the report’s scope, and Mark gave 

us a tour of the island and acted as the park liaison, helping us find data and reports throughout 

the project. Mark Flora and Jeff Cross of the NPS Water Resources Division accompanied us on 

our site visit and provided guidance throughout the project. Jay Glase and Brenda Moraska 

Lafrancois of WRD and Joan Elias of GLKN gave valuable advice, and Joan provided a detailed 

and thoughtful review of our draft document. Other anonymous reviewers also provided helpful 

comments.

Special thanks also go to Emmet Judziewicz of UWSP for providing resources on ISRO 

vegetation surveys, Robert Stottlemyer of USGS for finding some old reports for us and 

providing us with an extensive bibliography of his research, Scott Pugh in assisting with data 

extraction from the FIA website, and Ulf Gafvert of GLKN for sharing numerous useful GIS 

layers.
1

Introduction and Park Description

Congress, in its FY 2003 Appropriations Act, instructed and funded the National Park Service 

(NPS) through the Natural Resource Challenge to assess environmental conditions in coastal 

watersheds where national park units are located, including Great Lakes coastal parks and 

lakeshores. This report for Isle Royale National Park (ISRO) is one such assessment. Its purpose

is to use the many existing published reports, unpublished research findings, and agency reports 

to briefly describe the natural resources of ISRO, assess the degree to which they are affected by 

natural and anthropogenic stressors, identify information gaps, and make recommendations for 

future study and management where appropriate. 

ISRO consists of a group of islands in northwestern Lake Superior, the surrounding Lake 

Superior waters up to 7.2 kilometers (km) offshore, and a small portion of the mainland. The

main island, 72 km long and 14 km wide, is surrounded by approximately 400 much smaller 

islands. The park protects 231,400 hectares (ha) of land and water (Figure 1) (NPS ca. 2003). 

Although ISRO is generally perceived as isolated, it is located only about 24 km from points on 

the Canadian and Minnesota (MN) shoreline. Ninety-nine percent of the land area of ISRO is 

managed as wilderness. 

ISRO is densely forested, with northern boreal spruce-fir forest near the cool, moist shore of 

Lake Superior, and northern hardwoods in the warmer, drier interior (NPS ca. 2003). ISRO has 

278 lakes and ponds, more named inland lakes than any other Great Lakes area managed by the 

National Park Service, six named perennial streams (Washington, Grace, and Tobin creeks and 

Big Siskiwit, Little Siskiwit, and Siskiwit rivers), and many kilometers of unnamed perennial 

and intermittent streams. Numerous inland wetlands are associated with lake littoral zones and 

the pronounced ridge-valley topography; beaver activity has also enhanced wetland formation 

(Lafrancois and Glase 2005, Crane et al. 2006).

A scoping report by the NPS Great Lakes Inventory and Monitoring Network (GLKN) lists 

“critical resources” for ISRO, including the moose, a species of special concern in Michigan 

(MI), and the federal-endangered and state-threatened gray wolf, whose interrelationships have 

been intensively studied. ISRO also has the only naturally reproducing coaster brook trout

population in the United States, the most genetically diverse lake trout population in Lake

Superior, the largest MI population of the state-threatened common loon, and increasing nesting 

populations of bald eagles and osprey (NPS ca. 2003). Two state-endangered birds, the shorteared owl and peregrine falcon, are occasional visitors to ISRO (NPS 2003b), and the park is 

home to other animals that are threatened or of special concern in MI (MNFI 2009a, b).

ISRO also includes a park headquarters, visitor center, parking area, and dock on the Portage 

Lake waterfront on the east side of Houghton, MI (SENW and SWNE, S 36, T55N, R34W). This 

small area is not managed for its natural resource value and will not be discussed further in this 

report. 
2

Figure 1. Location of Isle Royale National Park in the upper Great Lakes region of the United States (see Appendix A for sources).
3

Island Communities and Regions

Although ISRO is legally part of Keweenaw County in MI’s Upper Peninsula, it is physically 

closer to, and shares greater biogeographic affinity with, its northern neighbors of MN and 

Ontario. It is located in an ecotone (zone of transition) between two major North American 

ecosystems or biomes—the boreal forest and the northern hardwood forest. On ISRO, boreal 

forest vegetation dominates the NE part of the island and nearshore terrain, while northern 

hardwoods are more prevalent to the SW (Schlesinger et al. 2009).

ISRO is entirely contained within the USGS Lake Superior Hydrologic Unit (HUC 04020300) 

(Seaber et al. 1987). The United States Environmental Protection Agency (USEPA) includes 

ISRO in its ecoregion VII, level III ecoregion 50, Northern Lakes and Forests (USEPA 2000) for 

purposes of assessing nutrient levels in streams and lakes (USEPA 2000, 2001).

The ISRO terrestrial ecosystem has been categorized as coastal rock barrens (S4b) (USEPA and 

Environment Canada 2008c). On the Canadian Shield, this ecosystem includes both the basalt 

bedrock systems found on ISRO and gneissic or granitic barrens. The basalt bedrock systems are 

characterized by thin soils and exposed areas of bedrock and a plant community composed of 

scattered trees, shrub thickets, and a partial layer of graminoids, mosses, and lichens. Throughout 

the Great Lakes basin, the coastal rock barrens ecosystem is considered to be in good or

improving condition, with the main threats being shoreline development and recreational uses 

such as campsites and boat launches (USEPA and Environment Canada 2008a). In the Regional 

Landscapes Ecosystem classification, Isle Royale is given its own sub-subsection (IX.7.3) of 

Section IX, Northern Continental Michigan, Wisconsin, and Minnesota. The Isle Royale subsubsection is described in brief as “island of volcanic bedrock ridges and wetlands; hardwoodconifer-dominated upland and wetland vegetation” (Albert 1995). It is distinguished from other 

sub-subsections of the Keweenaw subsection (IX.7) by the even-stronger influence of Lake 

Superior on its climate. Its bedrock balds and bedrock beaches support a diverse flora of boreal 

and disjunct northwestern montane species (Albert 1995).

The Michigan Natural Features Inventory (MNFI) lists 18 distinct natural communities for ISRO

(Table 1) (Kost et al. 2007). Two (northern balds and volcanic lakeshore cliffs) are ranked S1 

(critically imperiled in MI) and two others (volcanic cliffs and volcanic bedrock glades) are 

ranked S2 (imperiled). Most occurrences of threatened, endangered, and special concern species 

and high-quality natural communities are in the NE one-third of the island (Figure 2).

Ecologic Groups Based on Vegetation Mapping

A vegetation mapping project conducted for ISRO in cooperation with the United States 

Geological Survey (USGS) and the Nature Conservancy (TNC) identified 52 plant associations, 

which they combined into 14 “ecological groups” (hereafter, ecologic groups) as follows: 1)

northern shrub/graminoid fens and bogs, 2) rooted/floating aquatic marshes, 3) wet 

meadows/marshes, 4) northern conifer and hardwood forest and shrub swamps, 5) Great Lakes 

rocky shores, 6) rock barrens, 7) cliffs and talus, 8) northern dry conifer (hardwood) forests and 

woodlands, 9) northern mesic conifer (hardwood) forests, 10) northern spruce-fir (hardwood) 

forests, 11) boreal hardwood forests and woodlands, 12) northern hardwood forests and 

woodlands, 13) northern shrublands, and 14) semi-natural meadows (TNC 1999, USGS 2000a). 

This classification system will be used through the remainder of the report. Ecologic group 5 is 
4

discussed in the Lake Superior section (page 19), groups 1–4 in the inland aquatic resources 

section (page 56), and groups 8–14 in the terrestrial resources section (page 80). 

Table 1. Natural communities of Isle Royale National Park (Kost et al. 2007).

Natural Community State Rank Global Rank

Northern bald S1 GU

Volcanic lakeshore cliff S1 GU

Volcanic cliff S2 G4G5

Volcanic bedrock glade S2 GU

Intermittent wetland S3 G2

Northern fen S3 G3

Poor fen S3 G3

Dry northern forest S3 G3?

Sand and gravel beach S3 G3?

Dry-mesic northern forest S3 G4

Hardwood-conifer swamp S3 G4

Mesic northern forest S3 G4

Volcanic bedrock lakeshore S3 G4G5

Boreal forest S3 GU

Bog S4 G3G5

Poor conifer swamp S4 G4

Northern wet meadow S4 G4G5

Northern shrub thicket S5 G4

State Ranks (S1-S5)

S1 = critically imperiled; S2 = imperiled; S3 = vulnerable; S4 = uncommon but not rare; S5 = common 

and widespread in the state.

Global Ranks (G1-G5)

G2 = imperiled; G3 = vulnerable; G4 = apparently secure: uncommon but not rare; G5 = secure: 

common; widespread; GU = currently unrankable due to lack of information or substantially conflicting 

information about status or trends.

Lake Superior Communities and Regions

Great Lakes Natural Regions and Seascapes, equivalent to terrestrial ecoprovinces and 

ecodistricts, were developed for Lake Superior in the late 1990s (World Wildlife Fund 1997,

World Wildlife Fund Canada 1999). Natural regions are delineated on the basis of light 

penetration and macrotopography. Lake Superior consists of 11 natural regions. Four benthic 

natural regions (Figure 3) are overlain by seven pelagic natural regions (not pictured). Three of 

the benthic regions (#2 – #4) each have two different pelagic zones; a euphotic zone of <20 m 

depth, and a deeper dysphotic-aphotic zone where light does not penetrate. In the zone where 

light penetrates to the bottom (#1), there is no dysphotic-aphotic pelagic zone.

The Photic Zone (Natural Region #1) is the entire benthic euphotic zone of Lake Superior,

including significant offshore shoals. The West Slope (Natural Region #2) lies on the windward 

side of the lake and is characterized by low relief at depth of about 150 m. The Central Basin 

(Natural Region #3) is a deep basin (up to 400 m) with upwelling zones. The Southeastern Rise 

(Natural Region #4) is characterized by very irregular bottom topography and depths from 100 to 
5

300 m. The north side and part of the south side of ISRO lie in Natural Region #2, while the 

eastern and western ends of the island lie in Natural Region #1.

Figure 2. Occurrences of endangered, threatened, and special concern species and high-quality natural 

communities by section, Isle Royale National Park (from MNFI 2004).

Lake Superior can be further divided into 20 seascapes, 13 benthic and seven pelagic (LSBP 

2006a). The pelagic seascapes are identical to the pelagic natural regions. The benthic seascapes 

within the nearshore euphotic zone (#1) are defined by exposure to wave energy. Benthic 

seascapes in the offshore natural regions (#2 – #4) are delineated by water mixing (upwelling 

and stratification) and bottom substrate type (particle size).

The benthic seascapes are labeled on Figure 3 as 1a–1b, 2a–2d, 3a–3b, and 4a–4e. Unfortunately, 

we were unable to discover the meaning of the letter labels, since the LSBP (2006a) used the 

map without including a complete key. We can surmise, however, that the eastern and western 

ends of ISRO share similarities with the near south shore areas of Lake Superior. The north side 
6

of ISRO is similar to the open lake area to the west of it, while the south side of ISRO is a unique 

seascape (ecodistrict).

Figure 3. Benthic natural regions and seascapes for Lake Superior (from LSBP 2006a).

Climate

The climate of ISRO is dominated by the influence of Lake Superior. Short, cool summers and 

long, cold winters are normal. Winters are somewhat warmer and summers cooler than on nearby 

inland sections of the mainland. The mean annual frost-free period is 120 to 140 days yr-1

(USEPA and Government of Canada 1995). Fog is frequent near the lakeshore, especially in the 

spring (NPS 2004a) and from mid-July to late summer (Crane et al. 2006). The strongest winds 

come in October and November, when waves can reach 8 m in height (Shelton 1997).

Precipitation falls year-round, mostly as rainfall, averaging approximately 75 centimeters (cm)

yr-1. Snow typically accumulates from mid-November through April (NPS 2005). On average, 

from 1973 to 2002, Lake Superior on the north side of ISRO had 90% ice cover 60–75 days yr-1

and the south side had 90% ice cover only 30–60 days yr-1 during the period January –March

(Assel 2003). However, Lake Superior ice cover is declining; at the current rate of decline, the 

lake will be ice-free in a typical winter in about three decades (Austin and Colman 2007).

Thirteen weather stations are located in ISRO, with varying periods of record; five were still 

active in 2007 (Davey et al. 2007). One of these stations on Mott Island, part of the National 

Climatic Data Center (NCDC) network, has precipitation and temperature data, mainly for 

summer months, going back to 1940 and available at www.ncdc.noaa.gov/oa/climate/

stationlocator.html. Local climate data for ISRO is also available through the National Data 

Buoy Center (NDBC), part of the National Oceanic and Atmospheric Administration (NOAA), 

which maintains automated stations at Passage Island Lighthouse, NE of the main island, and 

Rock of Ages Lighthouse off the SW end of the main island (NDBC 2009a, b). Standard 
7

meteorologic data and continuous wind data are available for a 12-month period. Historic

meteorologic data are available from 1984 to present and wind data from 1996 to present. 

Climate summary tables are also available for wind speed, air temperature, sea level pressure, 

and wind gusts at www.ndbc.noaa.gov. 

We plotted monthly mean (mean of the mean of each day’s high and low temperature) and mean 

maximum temperatures (mean of each day’s maximum temperature) for the Mott Island station 

from 1940 to 2004 (Figure 4). Observations were available for a minimum of 42 years (mean 

September temperature) and a maximum of 55 years (mean maximum July temperature). A 

statistically significant upward trend was observed for each of the months (p <0.02). We 

increased the size of the data set by including all months with 27 or more observations, 

increasing the minimum number of years to 55 (mean September temperature). The upward trend 

for all months was then significant at p <0.01. Similarly, Austin and Colman (2007) reported that

stations within a 500-km radius of the center of Lake Superior had an increasing summer (July–

September) temperature trend of 0.059 ± 0.018oC yr-1 from 1979 to 2005.

Historic and Current Uses

Native Americans likely inhabited ISRO throughout the Holocene. The island was first visited 

and claimed by the French in 1671 and became a possession of the United States in 1783 

(Schlesinger et al. 2009). 

Native Americans likely mined pure native copper on Isle Royale 4,500 years ago (Schlesinger 

et al. 2009). Prehistoric mining sites are found at Scoville Point, Mott Island, Hill Island, 

McCargoe Cove, the Siskiwit Mine, and the Island Mine (Karamanski et al. 1988). Archeologists 

estimate that 280–375 tons of copper were removed from ISRO (Rennicke 1989) using oblong 

beach stones as tools (Karamanski et al. 1988).

The North Shore Ojibwe people had a long history with ISRO and regularly used it for 

subsistence activities such as making maple sugar, harvesting plants, snaring rabbits, netting 

passenger pigeons, and gathering gull eggs. It was also “the good place,” which had spiritual 

significance to them (Cochrane 2009). Their relationship to the island was greatly changed in the

latter third of the 19th century after the island was ceded to the United States in the 1842 Treaty 

of La Pointe (Karamanski et al. 1988, Cochrane 2009). The Grand Portage Ojibwe, who claimed 

ISRO, were not party to the treaty, which was made with other Ojibwe (Cochrane 2009). Today, 

the Grand Portage Ojibwe are working with NPS to reclaim their ancestral connections to ISRO.

Ten shipwrecks are documented around ISRO. The oldest known shipwreck in ISRO is the 

Cumberland, which lies near the Rock of Ages Lighthouse. The two largest wrecks in ISRO 

waters are the Congdon and the Emperor. The Congdon sank in 1918 in Congdon Shoals on the

NE end of ISRO; it involved the largest loss of life and cargo in Lake Superior up to that time. 

The Emperor, which sank off Canoe Rocks on the NE end of ISRO in 1947, was the last major 

wreck at ISRO (Karamanski et al. 1988).

ISRO experienced three distinct periods of copper mining activity in the 1800s; a “speculative” 

wave from 1843–1855; a period of exploitation of archaeologic copper mining sites from 1873 to 

1881, which also saw the development of year-round settlements on ISRO; and a “scientifically-
8

a.

b.

Figure 4. (a) Monthly mean and (b) monthly mean maximum temperatures for summer months, Mott 

Island, Isle Royale National Park, 1940–2004.
9

based, well-capitalized” effort from 1889 to1893 (Karamanski et al. 1988). Twenty-two sites 

from this era are known on ISRO.

The first commercial fishing operation in MI was run on ISRO by the American Fur Company 

from the 1830s to 1842. Because of whitefish population declines, stocking began in the Great 

Lakes by the 1870s and near ISRO in 1893. The largest human population related to fishing on 

ISRO occurred in the 1920s (Karamanski et al. 1988). Scandinavian immigrants “surged” into 

the ISRO region, especially from 1880 to 1900; they had great success in fishing for lake trout 

and herring (Cochrane 2009), but commercial fishing was virtually eliminated by 1960 

(Karamanski et al. 1988). 

ISRO was not extensively logged; Karamanski et al. (1988) reported that “By 1920 there had 

been no significant logging on the Isle.” A logging effort in the 1890s near Washington Harbor 

may have included a dam across Washington Creek; a storm pushed most of the logs into Lake 

Superior, and most of those were lost. An extensive forest fire in 1936 followed a large 

pulpwood logging operation in the spruce and balsam swamp near Siskiwit Bay (Karamanski et 

al. 1988, Schlesinger et al. 2009). More details on the effects of human uses on ISRO’s terrestrial 

resources are included in the Stressor section below.

Four hotels existed on ISRO by 1910, and a golf course was built at Belle Island. Resorts were 

located in Washington Harbor, Chippewa Harbor, and Rock Harbor, and on Belle Island, 

Barnum Island, and Davidson Island (Karamanski et al. 1988). ISRO was authorized as a 

national park by Congress in 1931 “to conserve a prime example of North Woods Wilderness”;

the private holdings on the island were bought up from the late 1930s to 1940. ISRO was further 

designated part of the National Wilderness Preservation System in 1976; over 99% of ISRO’s 

land area is designated as wilderness (Crane et al. 2006). In 1980, the United Nations Man and 

the Biosphere Programme named ISRO an International Biosphere Reserve, giving it global 

scientific and educational significance.

ISRO has no roads and is accessible by boat or plane. The National Park Service maintains a 

ferry service from Houghton, MI, to ISRO; commercial ferries travel from Copper Harbor, MI,

and Grand Portage, MN. The National Park Service also operates a seasonal headquarters on 

Mott Island, visitor centers at Rock Harbor and Windigo, and a dormitory for visiting researchers 

on Davidson Island. A concessionaire operates lodging at Rock Harbor, with 60 lodge rooms and 

20 cottages. The National Park Service makes available 113 tent sites, 88 shelters, and 43 group 

tent sites for camping (Isle Royale and Keweenaw Parks Association 2009). Visitation to ISRO 

has generally increased since 2,962 people visited in 1940 (Figure 5); the high was 31,760 in 

1987, and the mean was 16,350 yr-1 from 2004 to 2008 (NPS 2009).

Soils and Geology

The bedrock units exposed at ISRO are of the Proterozoic Eon of Precambrian time 

(approximately 2.5 billion to 542 million years ago). They consist of thick lava flows 

interlayered with sedimentary rocks (together, the Portage Lake Volcanics) overlain in some 

places by the Copper Harbor Conglomerate (Figure 6) (NPS 2004c). The lava flows document a 

period in Earth history when a mid-continental rift extended across what is now the center of 

Lake Superior, possibly as far south as the Gulf of Mexico (Huber 1975). Lava flows also 

contain rare minerals, including the Michigan state mineral chlorastrolite. This stone is 
10

commonly called Isle Royale greenstone, although it is not technically a greenstone (ThornberryEhrlich 2008). The Copper Harbor conglomerate reflects the presence of a sedimentary basin and 

the cessation of rifting. It is an alluvial fan deposit that spread over the Portage Lake Volcanics 

from a highland area to the west (Huber 1975).

Figure 5. Number of visitors per year to Isle Royale National Park, 1940–2008 (NPS 2009).

The Portage Lake volcanics are generally tilted SE toward the long axis of the Lake Superior 

basin; erosion has exposed the upturned edges of the individual layers. The island’s topography

is dominated by a series of long parallel ridges and valleys, with the SE-facing slopes being 

gentler than the NW-facing ones. Ridges are frequently interrupted by crosscutting ravines or 

depressions (Huber 1975). The sedimentary rocks interbedded in the lava flows are not generally 

exposed; they are more easily eroded than the volcanic rocks and usually lie buried beneath 

surficial materials in depressions between the ridges of more resistant volcanic rock (Huber 

1975). Thus, the bands of alluvium in Figure 6 are likely underlain by sedimentary rock, 

although a bedrock geology map was not available for verification. 

The age gap between the bedrock and the overlying unconsolidated surficial deposits is more 

than 570 million years. Approximately 10,000 years ago, thick ice sheets covered the Great 

Lakes area; glacial features on ISRO are the result of the most recent Marquette readvance. 

Glacial plucking and scouring helped form the parallel ridges on ISRO; their alignment and the 

islands’ shape and orientation indicate that the most recent glaciers covering the area flowed 

from NE to SW over the northern part of the island and E to W in the southern part (ThornberryEhrlich 2008). The resulting “washboard-like” pattern affects animal and plant distributions, 

migration patterns, microclimates, wetland distribution, and human uses (Thornberry-Ehrlich 

2008). Glacial features, including layers of till, ice margin deposits, drumlins, and moraines, are 

concentrated on the SW part of the island (Huber 1973). ISRO also exhibits several 

paleoshorelines that correlate with Lake Agassiz levels that were low for their times but were 

still much higher than Lake Superior levels today. These include features such as beaches, 

terraces, and wave-cut benches (Thornberry-Ehrlich 2008).
11

Figure 6. Surficial bedrock geology of Isle Royale National Park (NPS 2004c). 
12

Most soils on ISRO are derived from materials left by retreating glaciers and meltwater (NPS 

2005). Shetron and Stottlemeyer (1991) mapped 15 soil series and 14 distinct soil associations at 

ISRO. Soils on uplands in the northern part of ISRO developed directly on bedrock or on thin 

glacial cover; they are typically thin and sandy or loamy, and boulders are common (Woodruff et 

al. 2003). In the northeast, the thin soils are highly organic and are a major influence in the 

dominance of boreal forest vegetation (NPS 2005). In the southern part of ISRO, soils are 

deeper, better-developed, and less organic (NPS 2005) and more calcareous (Schlesinger et al. 

2009), favoring northern hardwoods. Holocene soils are mainly alluvium in the form of lake and 

stream deposits on beaches and in swamps, bogs, and beaver ponds (Thornberry-Ehrlich 2008). 

A detailed soil survey is currently being prepared for ISRO but was not available in time for this 

report.
13

Lake Superior

Physical Characteristics

ISRO is located in Lake Superior, which has the greatest surface area of any freshwater lake in 

the world. The lake is 563 km long and 257 km wide at its longest and widest points, 

respectively, and its shoreline length is 4,800 km, including islands. With its many inlets and 

islands, ISRO includes 543 km of Lake Superior shoreline (Crane et al. 2006). Since ISRO 

includes the waters of Lake Superior out to 7.2 km from the shoreline, it encompasses over 

165,000 ha of Great Lakes area (Lafrancois and Glase 2005).

The volume of Lake Superior is 12,100 km3, 10% of the world’s fresh surface water (USEPA 

and Government of Canada 1995). Lake Superior’s mean depth is 147 m, and its maximum 

depth (near Pictured Rocks National Lakeshore, PIRO) is 406 m (LSBP 2006a). Within the 

ISRO boundaries, depths are over 230 m N of Five Finger Bay and over 250 m S of Siskiwit Bay 

(Figure 7).

The modern-day water level of Lake Superior (approximately 183 m above mean sea level) was 

naturally established approximately 2,000 years ago when uplift of the St. Marys River sill 

isolated the Superior basin (LSBP 2006a). The level of Lake Superior has been regulated since 

1914 by structures on the St. Marys River (Wilcox et al. 2007); the average difference between 

summer (August–September) high and late winter (March–April) low levels was about 30 cm 

from 1918–1999 (Trebitz et al. 2002). In the last 90 years, the lake level has varied from 182.72 

m in April 1926 to 183.91 m in October 1985 (USACE 2008). Since 1998, the lake has generally 

been below its long-term (since 1918) historic average (USACE 2009), with a record low for the 

month of September (183.02 m) set in 2007 (NOAA 2009a).

Bennett (1978a) proposed a water budget for Lake Superior with inputs of direct precipitation 

(69.6 cm, 51%) and land drainage (65.7 cm, 49%) and outputs of evaporation (47.0 cm, 35%) 

and outflow through the St. Marys River (88.3 cm, 65%). Similarly, Holtschlag and Nicholas 

(1998) estimated that approximately 56% of the lake’s water arrives as direct precipitation on the 

lake surface, 11% enters as runoff from adjacent land surfaces, and 33% arrives as indirect 

groundwater discharge, defined as the groundwater component of streamflow. Direct 

groundwater discharge to Lake Superior has not been measured, but it is estimated to be 

“insignificant” in the vicinity of ISRO, on the north shore of Lake Superior, because of the low 

permeability of the aquifers (Olcott et al. 1978). Similarly, Young and Skinner (1974) estimated 

that “underflow to Lake Superior averages 0.5 inches (1.3 cm) yr-1 from the Wisconsin Lake 

Superior shoreline.” Lake Superior has a residence time (volume related to inputs) of 113 years, 

and a flushing time (volume related to outflow) of 177 years, but mixing time within the lake is 

only a few years. Thus, persistent substances can remain in the lake for a long time, but become 

uniformly distributed in relatively short order (Matheson and Munawar 1978).

Lake Superior is strongly dimictic, with summer stratification beginning from late June to midJuly and ending in November, and weaker winter stratification from January to mid-April 

(Bennett 1978b). A strong relationship exists between vertical temperature structure and 

horizontal water currents. Both Lake Superior’s currents and circulation influence water 

temperatures, sediment transport, ice cover, distribution of nutrients and oxygen, and dispersal of 

planktonic organisms, and so are important to the aquatic community (LSBP 2006a). The lake 
14

Figure 7. Lake Superior bathymetry and soundings (NOAA 2007a, b, c, d).
15

has both epilimnetic and hypolimnetic currents, mainly longshore (LSBP 2006a). The summer 

circulation is generally counterclockwise (Beletsky et al. 1999), although in the relatively 

shallow western Lake Superior basin, the circulation is clockwise (Harrington 1895) (Figure 8). 

A small gyre also forms south of ISRO (LSBP 2006a). Overall, currents on the south side of the 

lake are strongest (Matheson and Munawar 1978). Current speeds are low and uniform with 

depth in the spring. As temperatures warm, currents accelerate in the epilimnion, reaching a 

maximum in early September, while currents in the hypolimnion decelerate, reaching a minimum 

in August (Bennett 1978b). Fall mixing again makes the current speeds homogeneous (Lam 

1978), and they decelerate from summer epilimnion levels and continue to flow through the 

winter (LSBP 2006a).

Figure 8. Major surface currents, downward water movements, and upwellings for Lake Superior (after 

LSBP 2006a).

Upwelling likely contributes to strong summer hypolimnetic currents on the south side of ISRO. 

Such upwelling may bring nutrients and organic matter from the lake bottom and hypolimnion 

into more biologically active surface waters and thus increase productivity (LSBP 2006a). In 

summer, upwelling tends to force surface water from the north side of the lake toward the south 

side. In August 1999, a band of warm water was observed stretching from the south side of ISRO 

toward the Keweenaw Peninsula, and chlorophyll levels were elevated in this band (Budd 2004). 

Other water movements on Lake Superior are related to weather systems, including storm surges 

(rising water levels), storm set-downs (water level drops), and seiches (tide-like periodic 

oscillations caused by rapid changes in wind direction or air pressure) (Keillor and White 2003).
16

Coastal Geomorphic Zones and Processes

The Lake Superior shoreline of ISRO can be divided into three general zones, each with its own 

geomorphic characteristics (Mackey 2005). The coastal margin, from the ordinary high water 

mark to the 3 m isobath, has a low-energy area of embayments, tributary mouths, and coastal 

wetlands and a high-energy area around open coasts and island fringes. The nearshore open 

water area from the 3 m–15 m isobaths can be further divided into two areas based on water 

depth: <10 m water depth (including shallow reef complexes) and >10 m water depth. The 

former is a low-energy area characterized by limited exposure, short fetch distances, and finegrained, soft substrates, while the latter has an open exposure, long fetch distances, and coarsegrained, hard substrates and bedrock.

Mackey (2005) has further described the natural physical processes that affect these zones and 

organized them according to their place of origin, the direction in which they operate, their 

variability, and their interconnectivity (Table 2). Evaluating the relative significance of these 

processes at ISRO is difficult because the groundwater flow system is not well understood 

(Thornberry-Ehrlich 2008) and the only long-term streamflow monitoring site is the gaging

station on Washington Creek near Windigo (currently not in operation) (Crane et al. 2006). 

Coastal Wetlands and Nearshore Habitats

Great Lakes coastal wetlands are important ecosystems that are generally biologically 

productive, store and cycle nutrients and organic materials carried in by rivers and streams, and 

provide habitats for a wide variety of Great Lakes species. Many fish species, for example, 

depend upon coastal wetlands for some portion of their life cycles (USEPA and Environment 

Canada 2008c). Coastal wetlands are a subset of Lake Superior nearshore habitat, and the term 

“nearshore” has been variously defined to begin at depth contours of 10 m (Bennett 1978b), 15 

m (Gorman and Moore 2006), and 80 m (LSBP 2000).

Although ISRO reportedly has 10.2 km of coastal wetland shoreline (USEPA Region 5 2000), 

details about these are generally lacking. The USGS–NPS Vegetation Mapping Program lists one 

vegetation community, the Great Lakes shoreline bulrush–cattail marsh, dominated by hardstem 

bulrush (Scirpus acutus) and also including arrowhead (Sagittaria latifolia), woolly-fruit sedge

(Carex lasiocarpa), and flat-leaf bladderwort (Utricularia intermedia) (TNC 1999). A 

photointerpretation signature was not established for this community, so it could not be mapped. 

Albert et al. (2005) have listed 10 geomorphic types of Great Lakes coastal wetlands in three 

hydrologic systems (Table 3), but the location and proportion of each type in ISRO are unknown. 

In a fourth category, Herdendorf et al. (1981) listed 29 palustrine coastal wetlands for ISRO 

totaling 971 ha (Table 4), but this list also includes some relatively isolated inland lakes (e.g.,

Patterson Lake). Rayburn (2003) also describes some ISRO bays and coastal wetlands.

Gorman and Moore (2006) conducted a nearshore fish population and community structures 

survey and reported four major nearshore habitat types in ISRO: low slope with fine substrates, 

low slope with coarse substrates, high slope with coarse substrates, and high slope with bedrock

substrate. The predominant nearshore habitat of ISRO is characterized by moderate to steep

slopes and coarse substrates, composed of cobble to boulder-sized sediments and the underlying 

basalt bedrock. Most shorelines were relatively unprotected and were exposed to wind and wave

action from the open lake. Embayments of varying lengths and widths provided protection from 
17

the open lake; at the heads of these embayments, nearshore habitats were characterized by fine to 

mixed substrates and low slopes (Gorman and Moore 2006, Gorman et al. 2008). 

Table 2. Physical processes that affect nearshore and coastal margin zones (after Mackey 2005).

Natural

Process Attributes Pathways/Area Connectivity

Fluvial

Processes

Channelized flow

Highly dynamic

Spatially and temporally

variable and episodic

Generally unidirectional

(down slope) flow

Acts within or along linear

stream corridors and/or 

drainage networks within

watersheds

Lateral hydraulic

connectivity with adjacent

floodplain and watershed

surface

Longitudinal hydraulic 

down-slope continuity and 

connectivity within stream

channels

Groundwater

Processes

Infiltration and

groundwater flow

Highly dynamic

Spatially and temporally

variable and episodic

Unidirectional and/or

bidirectional flows

Act across broad

landscape surfaces and/or

within stream channels or 

lakes

Hydraulic continuity

(groundwater-surface 

water connections) and 

recharge area

Potentiometric surface

(water table elevation) –

surficial geology and soils

(aquifers)

Coastal 

Margin

and Nearshore

Processes

Wave and storm-generated

currents and flows

Intermittent fluvial influence 

near river mouths

Highly dynamic

Spatially and temporally

variable and episodic

Oscillatory bidirectional

and/or unidirectional flows

Act within or along both

shore-parallel and shorenormal linear corridors, 

with seasonal onshoreoffshore

components

Water-depth dependent

Shore-parallel hydraulic

connectivity (littoral 

processes)

Shore-normal hydraulic 

connectivity (deltaic, 

estuarine, wetland, barrier 

connectivity)

Open Lake

Processes

Wave and storm-generated

currents and flows

Superimposed over broadscale hydraulic (riverine) or 

thermally-driven (seasonal) 

flows

Spatially and temporally

variable and episodic

Oscillatory bidirectional

and/or unidirectional flows

Broad-scale regional 

unidirectional flows

Act within and between 

lake sub-basins, major 

connecting and tributary 

channel inflows and 

outflows

Lateral hydraulic 

connectivity with adjacent 

water masses

Hydraulic connectivity with

major connecting and 

tributary channel inflows 

and outflows
18

Table 3. Categories of Great Lakes coastal wetlands (Albert et al. 2005).

Hydrologic 

system Geomorphic types

Lacustrine Open shore, open embayment, protected embayment, sand-spit embayment

Riverine Connecting channel, delta, drowned river-mouth (barred), drowned river-mouth (open)

Barrier-enclosed Barrier beach lagoon, swale complex (ridge and swale complex, sand-spit swale, 

tombolo)

Table 4. Palustrine coastal wetlands of Isle Royale National Park (Herdendorf et al. 1981, Meeker et al. 

2007).

Wetland Location Size (ha)

Streams Entering

Named Unnamed Intermittent

Grace Harbor 18 Grace Creek 0 0

Thomsonite Beach 12

Little Todd Harbor 79

Florence Bay-Pickett Bay 111 1

Pickett Bay Area 4 1

Beaver Lake-McDonald Lake Area 136 1

McCargoe Cove 71 2 1

Lake Eva 4 1

Lane Cove 2

Horner Area 2

Five Finger Bay Area 4

Patterson Lake 20

Duncan Bay Tributary 38 1

Duncan Bay 45

Hidden Lake 16

Tobin Harbor 10

Moose Lake 8 1

Tobin Creek 61 Tobin Creek

Raspberry Island 6

Siskiwit Mine Area 6 1

Moskey Bay Campground 28

Chippewa Harbor Area 2

Lake Richie Outlet 8 1

Malone Bay Area 30

Hay Bay Area 65 Little Siskiwit

Caribou Creek 65 Caribou Creek

Francis Point Area 4 1

Attwood Beach Area 72 1

Long Point Area 45 1

Brady Cove*

Pickerel Cove*

Robinson Bay*

Stockly Bay*

Unstarred wetlands listed in Herdendorf et al. (1981); starred wetlands added by Meeker et al. (2007).
19

Lake Superior Shorelands

USEPA Shoreline Types

ISRO includes 530–540 km of Lake Superior shoreline (USEPA Region 5 2000, Lafrancois and 

Glase 2005). In 1993, NOAA identified and mapped 14 shoreline types in ISRO as part of a 

USEPA assessment of shoreline vulnerability to oil spills (Table 5, Figure 9) (USEPA Region 5 

2000). The shoreline types in ISRO can be roughly described as sheltered scarps or vegetated 

low banks (40%); rocky cliffs or bedrock shores (36%); sand, sand and gravel, or gravel beaches, 

sometimes with shelving bedrock (22%); wetlands (2%); and human-made structures (<1%)

(USEPA Region 5 2000).

Table 5. Lake Superior shoreline types, lengths, and USEPA shoreline sensitivity classification for Isle 

Royale National Park (USEPA Region 5 2000).

Shoreline Type Length

 (km)

% of 

ISRO

NOAA ESI

Shoreline

Classification

USEPA Shoreline

Sensitivity

Classification

Exposed Rocky Cliffs 69.6 13.0 1A Low

Shelving Bedrock Shores 123.2 23.1 2 Low

Riprap Revetments, Groins, and Jetties 0.3 0.1 6B Low

Subtotal 193.2 36.2

Sand Beaches 1.4 0.3 4 Low-Medium

Exposed Flats/Shelving Bedrock Shores 0.3 0.1 7/2 Low-Medium

Mixed Sand and Gravel Beaches 27.0 5.1 5 Low-Medium

Mixed Sand and Gravel Beaches/Shelving 

Bedrock Shores

0.4 0.1 5/2 Low-Medium

Gravel Beaches 84.2 15.8 6A Low-Medium

Gravel Beaches/Shelving Bedrock Shores 1.5 0.3 6A/2 Low-Medium

Subtotal 114.8 21.5

Sheltered Scarps in Bedrock 184.7 34.6 8A Medium-High

Sheltered, Solid Man-made Structures 0.6 0.1 8B Medium-High

Sheltered, Vegetated Low Banks 30.3 5.7 9A Medium-High

Subtotal 215.6 40.4

Fringing Wetlands 8.7 1.6 10A High

Extensive Wetlands 1.5 0.3 10B High

Subtotal 10.2 1.9

Total 533.7 100.0

Great Lakes Rocky Shores (Ecologic Group 5)

The Great Lakes basalt/diabase cobble-gravel lakeshore as described by the USGS–NPS 

Vegetation Mapping Program is 2.6% of the ISRO shore, mainly occurring at the SW end in 

Lake Superior bays underlain by sandstone and conglomerate bedrock (Figure 10) (TNC 1999, 

USGS 2000a). Most of the shore has little or no vegetation because it is regularly disturbed by 

waves and winter ice movement. The most abundant herbs are grasses. A shrub zone usually 

occurs on the highest beach ridge with shrub cover of 20–60% (TNC 1999).
20

Figure 9. Shoreline sensitivity classifications for Isle Royale National Park (USEPA Region 5 2000).
21

Figure 10. Rocky shores (Ecologic Group 5) in Isle Royale National Park (USGS 2000a).
22

The Great Lakes basalt (conglomerate) bedrock lakeshore, another community of sparse 

vegetation, occupies 9.7% of the ISRO shore and occurs primarily along SE-facing shores 

(Figure 10) (TNC 1999, USGS 2000a). In general, this association is dominated by crustose and 

foliose lichens (average 25%–50% cover) and mosses; the most common herb is shrubby 

fivefingers (Sibbaldiopsis tridentata, average 2% cover). Rock pools are generally part of this 

community; around rock pools, perched meadows, dominated by tufted graminoids, can be found 

(TNC 1999). This community is the most common location in ISRO for arctic/alpine disjunct 

species, probably because of cold water upwelling offshore, protection from wind, and proximity 

of open water to the east in winter (Judziewicz 1995).

Shoreline Rock Pools

Rock pools are a feature of the Lake Superior shoreline found on gently sloping, exposed, and 

rocky shores at the NE end of ISRO (Crane et al. 2006), on Passage Island, on “unexplored 

portions of the main island shoreline,” and on many of ISRO’s south-facing barrier islands 

(Glase and Lafrancois 2007). They are created by wind and wave action and ice scour and are 

filled with rainwater and wave wash. 

The pools are biologically active and usually support a simple community of aquatic 

invertebrates, algae, and amphibians (Van Buskirk 1992a). They are one of the most southern 

locations for Aeshna juncea, a dragonfly typically found in arctic ponds and peat bogs (Van 

Buskirk 1992a, 1993), and the terrestrial habitats surrounding them include rare floral elements 

characteristic of arctic and alpine environments (Judziewicz 1995, 1999). Black crowberry

(Empetrum nigrum), dwarf false asphodel (Tofieldia pusilla), and small cranberry (Vaccinium 

oxycoccos), all listed as threatened in MI, occur in rock pool habitat at ISRO, as do butterwort 

(Pinguicula vulgaris) and English sundew (Drosera anglica), which are MI species of special 

concern (Judziewicz 2004). Boreal chorus frogs (Pseudacris maculata) on ISRO are thought to 

breed almost exclusively in these pools (Smith 1983). Adult green frogs (Lithobates clamitans

melanota), larval blue-spotted salamanders (Ambystoma laterale), eastern red-spotted newts

(Notophthalmus viridescens viridescens), and dace (Rhinichthys and/or Phoxinus sp.) have also 

been observed (Glase and Lafrancois 2007).

Crane et al. (2006) summarized past studies on rock pool ecology that focused on ecologic 

interactions between larval frogs, salamanders, and dragonflies, including Smith (1987), Van 

Buskirk and Smith (1991), Van Buskirk (1992a, b, 1993), and Smith and Van Buskirk (1995). 

Boreal chorus frogs are constrained mainly to pools of intermediate size and shoreline position; 

small pools and those near the shoreline do not persist long enough for metamorphosis, and large 

permanent pools near the forest edge contain predators such as dragonfly and salamander larvae 

(Smith 1983). A study of these pools is currently underway with Great Lakes Restoration 

Initiative funding.

Biologic Resources

Aquatic and Shoreline Vegetation

Lake Superior has been classified as an ultra-oligotrophic lake because of its low nutrient levels 

and cold temperatures (LSBP 2006a). When aquatic vegetation is present, it is generally 

confined to nearshore areas (Edsall and Charlton 1997). 
23

Meeker et al. (2007) collected aquatic plants and searched for exotic species in ten Lake Superior 

bays (Chippewa Harbor, Duncan Bay, Five Finger Bay, Lane Cove, McCargoe/Brady Coves, 

Moskey Basin, Pickerel Cove, Robinson Bay, Stockly Bay, and Tobin Harbor) from 2003 to 

2006. In ISRO, 402 wetland plant taxa were identified. The seven aquatic taxa that occurred in 

>50% of 40 Lake Superior cove and bay transects were quillwort (Isoetes spp., 85.0%), needle 

spikerush (Eleocharis acicularis, 82.5%), long-beak water-crowfoot (Ranunculus longirostris, 

75.0%), whorl-leaf water-milfoil (Myriophyllum verticillatum, 65.0%), Richardson pondweed 

(Potamogeton richardsonii, 65.0%), water sedge (Carex aquatilis, 60%), and grass-leaved 

pondweed (Potamogeton gramineus, 52.5%). Thirteen shoreline taxa occurred in >50% of 31 

shoreline segments: reed canary grass (Phalaris arundinacea, 87.1%), spotted joe-pye-weed 

(Eupatorium maculatum, 83.9%), winter bentgrass (Agrostis hyemalis, 80.6%), jewelweed 

(Impatiens capensis, 64.5%), narrow-panicle rush (Juncus brevicaudatus, 64.5%), purplestem 

aster (Aster puniceus, 61.3%), fireweed/willowherb (Epilobium spp., 61.3%), water sedge

(54.8%), bluejoint (Calamagrostis canadensis, 51.6%), bottlebrush sedge (Carex hystericina, 

51.6%), American bugleweed (Lycopus americanus, 51.6%), wild mint (Mentha arvensis, 

51.6%), and purple meadow-rue (Thalictrum dasycarpum, 51.6%). 

Meeker et al. (2007) also searched for seven aggressive plant taxa: broadleaf cattail (Typha 

latifolia), narrow-leaf cattail (Typha angustifolia), common reed, reed canary grass, curly-leaf 

pondweed (Potamogeton crispus), Eurasian water-milfoil (Myriophyllum spicatum), and purple 

loosestrife (Lythrum salicaria). Curly-leaf pondweed, Eurasian water-milfoil, and purple 

loosestrife were not found at any sampling sites in ISRO. Reed canary grass was widely 

distributed along bay shorelines, as indicated above. Broadleaf cattails were found in all bays 

except for Robinson Bay and Tobin Harbor, and were also found in Washington Harbor. 

Narrow-leaf cattails were found in Brady Cove and McCargoe Cove. Common reed occurred in 

Brady Cove and Duncan Bay. 

Phytoplankton, Zooplankton, Aquatic Invertebrates, and Benthos

Both the zooplankton and phytoplankton communities at ISRO are indicative of Lake Superior’s 

oligotrophic conditions. Approximately 300 phytoplankton species are present (LSBP 2006a). 

Lake Superior has been divided into six phytoplankton regions based on taxonomic and 

biophysical data. Lake Superior areas north and west of ISRO’s NE/SW axis are in the northern 

nearshore region, while those south and east are in the open lake region. The open lake region 

has the lowest phytoplankton biomass, and the northern nearshore region has a moderate 

biomass; however, species composition is broadly similar among regions. Phytoflagellates 

(including cryptomonads, chrysomonads, and dinoflagellates) comprise approximately 35 

percent of the species, while diatoms comprise 31 percent and green algae (Chlorophyta) 

comprise 22 percent (Munawar and Munawar 1978). 

In 1973, diatoms and phytoflagellates, especially cryptomonads and chrysomonads, contributed 

most of the lake-wide phytoplankton biomass, which is in general very low (0.1–0.2 g m-3

). No 

clear seasonal trends were observed, and there was little difference in biomass between inshore 

and offshore waters (Munawar and Munawar 1978). A 1998 study similarly found the spring 

lake biovolume dominated by cryptophytes (27%), diatoms (33%), and chrysophytes, and 

concluded that the results “suggest the lake has changed little in the past 20 years” (Barbiero and 

Tuchman 2001). However, unlike Munawar and Munawar (1978), Barbiero and Tuchman (2001)

did find a difference in species composition between spring and summer, with the cryptophyte 
24

Rhodomonas minuta and the filamentous centric diatom Aulacoseira islandica most common in 

spring and the diatom Cyclotella comta and the chrysophyte Dinobryon bavaricum most 

common in summer. 

In a published study of Lake Superior phytoplankton at ISRO, Taylor (1935) examined 

phytoplankton samples collected in July and August from McCargoe Cove, Rock Harbor, Tobin 

Harbor, and an open water site approximately 2.2 km off McCargoe Cove toward Hawk Island. 

Except for Rock Harbor, the sampled sites were dominated by Dinobryon and diatoms, with 

Botryococcus third in rank. In relatively shallow waters at Rock Harbor (0.6 and 3 m), the bluegreen alga Anabaena and the dinoflagellate Ceratium were also important (Taylor 1935).

Lake Superior has the lowest zooplankton density of all the Great Lakes, as well as the lowest 

number of taxa (Barbiero et al. 2001). In the open waters of Lake Superior, large calanoid 

copepods dominate the zooplankton community; four species of calanoids (Leptodiaptomus

sicilis, L. ashlandi, Limnocalanus macrurus, and Senecella calanoides) and one species of 

cyclopoid copepod (Diacyclops thomasi) are known to exist in the lake year-round and comprise 

99.9% of the spring zooplankton community. Cladoceran zooplankton, indicative of more 

eutrophic conditions, are uncommon. Little change was detected in this community from the 

early 1960s to 1998 (Barbiero et al. 2001). Nearshore trawls in four Lake Superior ecoregions 

(MN North Shore between Two Harbors and the Canadian border, Wisconsin (WI) Apostle 

Islands, MI eastern Keweenaw Bay between Sand Bay and Bete Grise, and MI Whitefish Bay) 

were also dominated by Leptodiaptomus sicilis and Limnocalanus macrurus, as well as the 

smaller cyclopoid Diacyclops thomasi (Barbiero et al. 2007).

Watson and Wilson (1978) divided Lake Superior into fifteen zones based on temperature 

variations for purposes of zooplankton analysis; the three surrounding ISRO were 11th, 12th, and 

13th in zooplankton concentration (numbers m-3

) and 10th, 12th, and 14th in zooplankton biomass 

(mg m-3), and are characterized by an early summer peak population. Two of the zones that touch 

on ISRO are open-water zones that encompass a large part of Lake Superior, and the third is a 

zone between the north side of ISRO and the north shore of the lake. In a lakewide sampling 

during summer 1998, Barbiero et al. (2001) found one of the highest zooplankton densities NW 

of ISRO; over half these zooplankton were immature calanoids, and cladocerans were not 

present in significant numbers. In general, however, zooplankton distribution and abundance are 

strongly associated with surface water temperature, and so highest concentrations are found 

inshore, especially in the major embayments of the southern and eastern shores (LSBP 2006a).

Two large-bodied zooplankters, Mysis relicta and Diporeia affinis, were major components of 

Lake Superior food web at the time of European settlement (GLFC 2001). Diporeia is an 

indicator of lake health because it was once the most abundant benthic organism in cold, offshore 

regions of all the Great Lakes and is food for many forage fish species (USEPA and 

Environment Canada 2008b). Diporeia are “in a state of dramatic decline” in parts of all the 

Great Lakes except Lake Superior, likely due to the rapid spread of zebra and quagga mussels 

(USEPA and Environment Canada 2008b). Diporeia numbers did not significantly decline from 

1994 to 2000 in western Lake Superior (Scharold et al. 2004) and are currently thought to be in 

“good” condition in Lake Superior, with an “unchanging” trend (USEPA and Environment 

Canada 2008b).
25

In addition to Diporeia, the offshore benthic community at depths 56–228 m also included 

oligochaetes, especially the Enchytraeidae and the lumbriculid worm Styoldrilus heringianus in 

1999 (Barbiero et al. 2007). Molluscs (primarily the sphaeriid pea clam Pisidium conventus) and 

insects (primarily the chironomid Heterotrissocladius oliveri) accounted for less than 10% of the 

total biomass (LSBP 2006a). A total of 10 taxa were found at the 11 sites sampled in 1999 

(Barbiero et al. 2007). The relatively simple benthic community of Lake Superior reflects the 

low diversity of habitat rather than impaired water quality (LSBP 2006a). 

Barton and Hynes (1978) described the macrobenthos in wave-swept nearshore zones of the 

north shore of Lake Superior as typically lotic. They also determined that the diversity and 

abundance of macrobenthos were directly related to the stability of substrate, with more stable 

substrates supporting higher diversity and abundance. Granitic boulders commonly hosted 

Ephemeroptera (mayflies), Trichoptera (caddisflies), Plecoptera (stoneflies), Orthocladiinae 

(midges), and Oligochaeta (worms). Granitic bedrock was home to chironomids, including 

Orthocladiinae and Tanytarsini, hydropsychids (caddisflies, including Lepidostoma), Antocha

(craneflies), Naididae (worms), Baetis (mayflies), and Acari (mites) (Barton and Hynes 1978). 

Nichols et al. (2001a) surveyed 30 m2 of McCargoe Cove and found five species of mussels; 

additional sampling was performed in inland lakes and is addressed in more detail in the Inland 

Waters section. The mussels found, although common, are at great risk in the Great Lakes basin 

because of invasive mussels, sprawl, and herbicide and pesticide use (Nichols et al. 2001a). The 

authors suggested that ISRO’s mussels may be among only a few remaining populations in MI in 

10–15 years (Nichols et al. 2001a). The authors also looked for sponges but did not find any in 

McCargoe Cove. Detailed information for other ISRO nearshore and offshore benthos was not 

found; the Water Resources Management Plan (Crane et al. 2006) identified this as a need. 

Lake Superior Fish Communities

At the time of European settlement, over 70 fish species occurred in Lake Superior and its

tributaries. Today, 96 fish species are listed for Lake Superior, 16 of those nonindigenous (Horns 

et al. 2003). The deliberate introduction of Pacific salmon and the invasion of exotic fish species 

have perhaps irreversibly altered the food web of the lake. However, Lake Superior’s native fish 

community has remained relatively intact, and unlike the other Great Lakes, “the past 30 years is 

highlighted by recovery rather than continued ecological disruption” (Bronte et al. 2003). 

The highest trophic level in Lake Superior is occupied by siscowet lake trout (Salvelinus 

namaycush siscowet) (Horns et al. 2003). They feed on coregonines and cottids (sculpins), which 

in turn feed on zooplankton and larger invertebrates (Table 6) (Harvey et al. 2007). Siscowet are 

closely followed by burbot (Lota lota) and lean lake trout (Salvelinus namaycush) on the trophic 

level pyramid (Harvey and Kitchell 2000). Burbot occupy both offshore and nearshore habitats, 

where they prey on a variety of benthivores, including sculpins, sticklebacks (primarily ninespine 

sticklebacks [Pungitus pungitus]), suckers (Catostomus spp. and Moxostoma spp.), and pygmy 

whitefish (Prosopium coulteri). Humper lake trout, a variety of S. namaycush found mainly on 

deep offshore underwater reefs around Isle Royale and in the eastern waters of the lake around 

Caribou Island (Horns et al. 2003), probably occupy a slightly lower trophic level since they eat 

the zooplankter Mysis relicta as well as sculpins (Sitar et al. 2007). Many piscivores, including 

brook trout (Salvelinus fontinalis), walleye (Sander vitreus), lake sturgeon (Acipenser 

fulvescens), yellow perch (Perca flavescens), and northern pike (Esox lucius), also occupy rivers, 

bays, and coastal waters (Horns et al. 2003). 
26

Table 6. Ecologic roles of important Lake Superior fish species, including nonindigenous species (Horns 

et al. 2003).

Common Name Scientific Name Adult Habitat

Planktivores (diet predominantly zooplankton or phytoplankton)

Lake herring Coregonus artedi Offshore, nearshore

Bloater Coregonus hoyi Offshore

Rainbow smelt* Osmerus mordax Nearshore

Benthivores (diet predominantly macroinvertebrates)

Kiyi Coregonus kiyi Offshore

Lake whitefish Coregonus clupeaformis Nearshore

Brook trout Salvelinus fontinalis Tributaries, bays, coastal waters

Ninespine stickleback Pungitus pungitus Nearshore

Pygmy whitefish Prosopium coulteri Nearshore

Slimy sculpin Cottus cognatus Nearshore

Lake sturgeon Acipenser fulvescens Nearshore, tributaries

Deepwater sculpin Myoxocephalus thompsoni Offshore, nearshore

Longnose sucker Catostomus catostomus Nearshore, tributaries

White sucker Catostomus commersoni Nearshore, tributaries

Piscivores (diet predominantly fish)

Coho salmon* Oncorhynchus kisutch Offshore, nearshore, tributaries

Chinook salmon* Oncorhynchus tshawytscha Offshore, nearshore, tributaries

Sea lamprey* Petromyzon marinus Offshore, tributaries

Pelagic lean lake trout Salvelinus namaycush Offshore, nearshore

Humper lake trout Salvelinus namaycush Offshore, nearshore

Siscowet lake trout Salvelinus namaycush siscowet Offshore, nearshore

Rainbow trout* Oncorhynchus mykiss Nearshore, tributaries

Brown trout* Salmo trutta Nearshore

Burbot Lota lota Offshore, nearshore, tributaries

Walleye Sander vitreus Tributaries, bays, coastal waters

Northern pike Esox lucius Tributaries, bays, coastal waters

Smallmouth bass Micropterus dolomieu Tributaries

Yellow perch Perca flavescens Tributaries, bays, coastal waters

*nonindigenous species

Approximately 77% of the surface area of Lake Superior is offshore habitat (>80 m deep) and

23% is nearshore habitat (Horns et al. 2003). The offshore zone contains nearly all the spawning 

and feeding habitat for siscowet lake trout, humper lake trout, deepwater ciscoes (Coregonus

spp.), and deepwater sculpin (Myoxocephalus thompsoni). Burbot, Pacific salmon, sea lamprey, 

and lake herring (Coregonus artedi) are also members of the offshore community. The nearshore 

zone contains most of the important and critical habitat for lean lake trout, lake herring, and lake 

whitefish (Coregonus clupeaformis). Other members of the nearshore fish community are

siscowet lake trout, humper lake trout, burbot, Pacific salmon, brown trout, round whitefish 

(Prosopium cylindraceum), rainbow smelt (Osmerus mordax), lake sturgeon, ninespine 

sticklebacks, pygmy whitefish, deepwater ciscoes (including the two commercially harvested 

“chubs” bloater [Coregonus hoyi] and kiyi [C. kiyi]), slimy sculpin (Cottus cognatus), deepwater 

sculpin, trout perch (Percopsis omiscomaycus), and longnose and white suckers (Catostomus

catostomus and C. commersoni) (Table 6). The major sport and commercial fisheries in Lake 

Superior utilize the nearshore zone (Horns et al. 2003).
27

Gorman and Moore (2006) characterized the ISRO fish community for the subset of the 

nearshore zone <15 m deep. Sampling with Windermere traps and fyke nets, they found a 

community dominated by common native species, including lake chub (Couesius plumbeus), 

ninespine stickleback, slimy sculpin, burbot, and trout-perch, in a habitat characterized by coarse 

and bedrock substrates with moderate to steep slopes. At the heads of bays, protected areas 

provided habitat for spottail shiner (Notropis hudsonius), blacknose dace (Rhinichthys atratulus), 

and white sucker. Mouths of bays were characterized by high slope, rocky substrates, and high 

structure and were home to simple assemblages dominated by lake chub. A similar nearshore 

fish community was found at Apostle Islands National Lakeshore (APIS), suggesting that 

nearshore fish communities in the two parks are drawn from a common source pool (Gorman et 

al. 2008).

One of the most studied fish species at ISRO is the coaster brook trout. Many brook trout are 

stream-resident forms that live their entire life in tributary streams feeding Lake Superior. 

However, some utilize nearshore habitat along broad sections of the coastline; these are 

collectively referred to as ‘coaster’ brook trout. Coaster brook trout can be broadly defined as 

brook trout that “have the potential to utilize lake habitats for an ecologically significant portion 

of their development and resource acquisition” (Huckins et al. 2008). There are two forms; the 

adfluvial form moves out of streams and into Lake Superior to forage for a time and returns to 

stream habitats to spawn, while the lacustrine form spends its entire life in Lake Superior and 

spawns on shoals. One noticeable result of using lake habitat is that coaster brook trout often 

attain large size, probably by exploiting more or higher quality food resources.

Brook trout were once the most common salmonid in tributary streams throughout Lake 

Superior, with portions of each population also utilizing nearshore habitat for foraging and 

spawning (Newman and Dubois 1997, Wilson et al. 2008). Presently, coaster brook trout 

populations are known only from the Lake Nipigon region in Canada, the Salmon Trout River in 

MI, and at Isle Royale, with adfluvial populations in Siskiwit River, Siskiwit Bay, and 

Washington Creek and a lacustrine population in Tobin Harbor (Huckins et al. 2008, Ridgway

2008). They may also persist in other areas of Lake Superior, including streams in PIRO and 

APIS; however, confirming migratory behavior in small populations of trout from remote 

streams is difficult. A creel survey from recreational fishing boats at Isle Royale conducted in 

1998 did not document coaster brook trout (Lockwood et al. 2001). The small coaster brook trout 

population (an estimated 150 fish) in Tobin Harbor (Gorman et al. 2008) and uncertain size of 

other ISRO populations highlight the need for protection and restoration efforts.

Habitat alteration by the mining and timber industries and ecologic factors such as competition 

and predation by nonnative fish species are considered primary reasons for the decline and 

collapse of brook trout populations that utilize lake habitats (Newman and Dubois 1997). 

Overharvest of coaster brook trout, due to their large size and nearshore distribution, is thought 

to be a key reason for their decline throughout Lake Superior (Newman and Dubois 1997). 

Coaster brook trout populations remain low despite control of sea lamprey populations, reduction 

in stocking of nonnative fishes, and other conservation efforts. As a result, multi-agency efforts 

that include state, federal, tribal, and provincial cooperation are being conducted, with the aim of 

preserving the remaining diversity within brook trout populations and planning recovery efforts 

throughout Lake Superior and tributary streams. Changes to fishing regulations to reduce bag 

limits and, more recently, toward catch and release fishing only, have been enacted by state and 
28

provincial managers to help coaster brook trout populations. Unfortunately, the stocking of 

nonnative salmonid species such as rainbow trout, brown trout, and coho salmon for recreational 

fishing may impact coaster populations, because these species probably require similar stream 

and nearshore habitats (Newman et al. 2003).

Protecting the genetic diversity of the remaining populations of coaster brook trout is a concern 

shared by researchers across Lake Superior (Schreiner 2008, Hewitt et al. 2008, Huckins et al. 

2008). Studies by Burnham-Curtis (2001), D’Amelio (2002), and Wilson et al. (2008) indicate 

that coaster brook trout are genetically more closely related to the resident brook trout in streams 

they utilize for spawning than to coaster brook trout populations elsewhere, suggesting that 

migration to lake habitats is a life-history strategy that was present in Lake Superior brook trout 

and may return if stream resident populations recover sufficiently. Alternatively, stocking stream 

resident populations with fish created using gametes from coaster brook trout populations may 

introduce migratory behavior back into stream populations. Coaster brook trout populations on 

ISRO play an important role in the range-wide recovery efforts for two key reasons. First, ISRO 

has important remnant populations of coaster brook trout that exhibit both life histories.

Collection of gametes from adfluvial fish at Siskiwit River and lacustrine fish at Tobin Harbor 

has created captive hatchery stocks that are used in restoration efforts at mainland streams. 

Second, stream and nearshore habitat at ISRO remains relatively pristine, and the threat of future 

development to this habitat is very low compared to coaster populations in mainland sites. In 

fact, the survey by Gorman et al. (2008) identified several embayments at ISRO that have similar 

habitat to Tobin Harbor and thus may provide good opportunities for creating new, selfsupporting populations. 

Fish Abundance and the Commercial and Sport Fishery

Commercial fishing began in Lake Superior in the 1830s (Horns et al. 2003). For larger species, 

such as lake trout, lake whitefish, and lake sturgeon, maximum commercial harvest occurred 

before 1904 (Table 7) (Baldwin et al. 2002). Numerous authors have documented the nearcollapse of the commercial fishing industry between 1940 and 1960 and its causes (LSBP 2000), 

which included overfishing, logging, dam building, discharge of paper mill wastes, toxic 

contaminants in water and air, mining, agriculture, urban development, and road and railroad 

construction (Horns et al. 2003). The introduction of non-indigenous species, some accidental 

(such as the sea lamprey and rainbow smelt) and others deliberate (including rainbow trout and 

Pacific salmon) also affected the natural food web and fish distribution within the lake. The 

1960s marked the period of maximum degradation of the lake and its fisheries (Horns et al. 

2003). However, with some notable exceptions in embayments and tributaries where there are 

Areas of Concern (AOCs), the status of fish habitat in the lake is generally good at this time 

(Horns et al. 2003).

Lean lake trout stocks declined in Lake Superior in the 1950s, but appeared to be “close to 

restoration” in the early 2000s (Bronte et al. 2003). As of 2001, lean lake trout stocking was no 

longer required in most areas of the lake to meet Great Lakes Fishery Commission (GLFC) fish 

community objectives, but sea lamprey predation continued to be a problem (Horns et al. 2003).
29

Table 7. Commercial harvest of Lake Superior fish from 1867 to 2000 and in 2006 (Baldwin et al. 2002, 

NOAA 2009b).

Species Maximum Harvest (kg) Year 2006 Harvest (kg)

Lake Herring 8,740,000 1941 327,000

Lake Trout 3,335,000 1903 72,000

Lake Whitefish 2,350,000 1885 638,000

Smelt 1,835,000 1976 9,800

Chubs 1,000,000 1965 20,000

Suckers 259,000 1988 3,800

Walleye 171,000 1966 1,000

Lake Sturgeon 102,000 1885 0

Round Whitefish 83,000 1995 600

Yellow Perch 63,000 1981 200

Sauger 56,000 1952 0

Northern Pike 52,000 1921 0

Burbot 36,000 1978 14

Pacific Salmon 13,000 1989 1,700

Rainbow Trout 500 1999 0

Carp 900 1998 0

Most lake trout harvested in Lake Superior in the 1990s came from the U.S., specifically from 

MI and WI (Figure 11), at a value of $151,258 in 2000 (Kinnunen 2003) and $46,284 in 2006 

(NOAA 2009b). Commercial lean lake trout harvest is prohibited in MN because the fishery is 

not yet considered fully recovered (Bronte et al. 2003). Commercial lean lake trout harvest was 

closed in 1962 in MI and is allowed only by tribal fishers and in limited assessment fisheries in 

management zones MI-1 (in which ISRO is located), MI-5, and MI-6 (Peck and Sitar 2000). 

Assessment fisheries are located in both Washington and Rock Harbors (Crane et al. 2006). In 

Washington Harbor, private commercial fishers are allowed up to 600 lean lake trout, 4,500 kg 

each of lake whitefish and lake herring, and 7,300 kg of chubs annually. In Rock Harbor, the 

Edison fishery is a demonstration fishery, and ISRO is the permittee. Allowable annual harvests 

are 400 lean lake trout, 450 kg of lake whitefish, and 450 kg of other coregonines.

Siscowet (a type of lake trout) increased in abundance from 1970 to 1999 and may be 

approaching an ancestral state of abundance (Bronte et al. 2003). Siscowet was a commercially 

important species in 2000 (Kinnunen 2003), The market for siscowet as an edible fish has 

declined (Figure 11) because of its high fat content, but there is currently interest in exploring its 

use for producing high-grade fish oil as a nutritional supplement.

Lake whitefish are abundant and considered “resistant to exploitation” (Horns et al. 2003). They 

have been the primary target of the commercial fishery in Lake Superior since the late 1980s 

(Bronte et al. 2003) and were the most important fish species commercially harvested in Lake 

Superior in the year 2006, with an estimated value of $1,000,000 (Figure 11) (NOAA 2009b). 

Throughout the 1990s, most lake whitefish were harvested from MI and WI waters (Kinnunen 

2003). However, from 1997 to 2004, gill-net fishing for lake whitefish was “minimal” (<1,000 

kg yr-1

) in the Lake Superior management unit around ISRO (Schneeberger 2006). 

Commercially harvested “chubs” in Lake Superior are two deep-water ciscoes: bloaters and kiyi. 

Peck (1977) determined that bloaters were the most abundant chub (51–87%) in commercial 

catches around the Keweenaw Peninsula from 1974 to 1976. Kiyi were 7–40% of the catch over 
30

Figure 11. Lean lake trout, siscowet, and lake whitefish harvests from Michigan, Minnesota, and 

Wisconsin waters of Lake Superior, 1971–2006 (NOAA 2009b).
31

the same time period. The commercial chub fishery has declined greatly since the 1970s (Figure 

12). 

Lake herring were historically the dominant prey fish in Lake Superior but declined drastically in 

the mid-1960s, likely because of overfishing and competition with and predation by introduced 

rainbow smelt (Horns et al. 2003 and citations therein). Biomass of lake herring was relatively 

high from the mid-1980s to the mid-1990s but has since declined and, in 2008, was <3% of peak 

biomass (Gorman and Bunnell 2008). Rainbow smelt were abundant during the 1930s, 1940s, 

and 1950s (Horns et al. 2003), but their numbers have been greatly reduced by lake trout 

predation (Bronte et al. 2003). Their biomass fluctuated but declined during 1978–2008 and in 

2008 was only 3% of peak levels (Gorman and Bunnell 2008). Commercial harvest of rainbow 

smelt has declined as well (Figure 12).

Populations of some nearshore fish, especially lake sturgeon, walleye, and brook trout, are still 

below historic levels, but state and tribal management agencies are attempting rehabilitation.

Harvest controls are being developed by state and tribal management agencies (Horns et al. 

2003). Fishing for coaster brook trout in the Lake Superior waters of ISRO is catch and release 

only (Schreiner 2008). 

In 2007, 359 charter boat excursions were conducted in the MI waters of Lake Superior, carrying 

1,630 anglers. This number of excursions is the lowest for the period of record 1990–2007; 791 

excursions occurred in 1990, and the number has been variable but generally declining since then 

(Wesander and Clapp 2008). The MI Department of Natural Resources (MDNR) also collects 

data periodically on charter fishing excursions in the ISRO vicinity (MDNR 2009); the number 

of excursions ranged from 100 in 1999 to 5 in 2006 (Table 8). Lake trout are the great majority 

of the fish harvested.

Table 8. Charter boat excursions and catch for 1999, 2001, and 2005–2007 in the vicinity of Isle Royale 

National Park (MDNR 2009).

Year Number of excursions Angler 

hours

Lake trout

harvested

Pacific salmon

harvested

Other fish 

harvested

1999 100 3,263 850 17 3

2001 59 1,758 502 1 2

2005 33 482 97 3 2

2006 5 52 8 0 0

2007 28 306 58 1 0

Ecosystem Condition

The USEPA and Environment Canada (2007) reported that the overall status of the Great Lakes 

ecosystem in 2006 was mixed, with some conditions good and others poor, and that ecosystem 

trends varied from improving to worsening. Assessment is made more difficult by the fact that 

“for many indicators, ecosystem objectives, endpoints, or benchmarks have not been established” 

(USEPA and Environment Canada 2007). Numerous authors are currently engaged in developing 

indices of biologic integrity that will allow resource managers to assess the condition of specific 

parts of the Great Lakes, especially in coastal waters. Indicators used in these indices include 

invertebrates (Uzarski et al. 2004); diatoms (Reavie et al. 2006); fish (Uzarski et al. 2005); and a 

community approach using rock bass (Ambloplites rupestris), woolly-fruit sedge, stephano-
32

Figure 12. Chub, rainbow smelt, and lake herring harvest from Michigan, Minnesota, and Wisconsin 

waters of Lake Superior, 1971–2006 (NOAA 2009b).
33

discoid diatoms, spring peepers (Pseudacris crucifer), and insectivorous birds (Brazner et al. 

2007).

Offshore Water Quality

The USEPA conducts offshore sampling on the Great Lakes during spring and summer each 

year. Lake Superior has 23 sampling sites. Sites SU-11 to SU-16 roughly surround ISRO, and 

SU-13 is within ISRO’s boundaries (Figure 13). Parameters measured at least once for sites SU11 to SU-16 include polychlorinated biphenyls (PCBs), alkalinity, ammonia nitrogen, beam 

attenuation, calcium (Ca2+), organic carbon, chloride (Cl-), chlorophyll-a, specific conductance 

(field and laboratory), fluorescence, chlordane, chlorthal-dimethyl, cis-nonachlor, lindane, total 

hardness, heptachlor epoxide, hexachlorobenzene (HCB), irradiance, magnesium (Mg2+), total 

kjeldahl nitrogen, nitrate+nitrite nitrogen (NO3+NO2-N), dissolved oxygen (DO), oxychlordane, 

pH, total phosphorus (TP) (filtrate and bulk), dissolved silica (Si), sodium (Na+

), total solids, 

temperature, dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE), 

horizontal transmittance, trans-nonachlor, turbidity, and volume (USEPA 2008a). Plankton and 

benthos samples are also collected.

Figure 13. Locations of USEPA water sampling sites in Lake Superior in the vicinity of Isle Royale 

National Park (USEPA 2006, 2008a). 

Nutrients

In an examination of nutrients in Great Lakes waters, Kelly (2008) focused on TP, NO3+NO2-N, 

dissolved silica (Si), and chlorophyll-a (Table 9). Lakewide, TP levels are below the upper limit 

of 5 μg L-1 set by the 1980 Phosphorus Management Strategies Task Force to maintain the lake’s 

oligotrophic state (USEPA and Environment Canada 2007). The lakewide TP average is similar 
34

to the average for the offshore sites around ISRO, with SU-11, SU-14, and SU-16 slightly lower 

and SU-12, SU-13, and SU-15 slightly higher (Table 9, Figure 14). In 2007, the status of Lake 

Superior offshore waters for TP was “good,” with an “undetermined” trend (USEPA and 

Environment Canada 2007). 

NO3+NO2-N levels lakewide occur within a narrow range of 0.29–0.36 mg L-1

, and values in the 

ISRO vicinity are similar (Table 9, Figure 15). This concentration of inorganic nitrogen, when it 

occurs in spring, is sufficient to support summer algal blooms in lakes (Shaw et al. 1996). 

However, nitrogen is not the limiting nutrient in Lake Superior. Nitrate concentrations in Lake 

Superior doubled every 34 years between 1906 and 1976, from 0.075 mg L-1 to 0.311 mg L-1

(Bennett 1986). Bennett thought this increase was caused almost entirely by atmospheric 

deposition, but more recent research indicates that atmospheric deposition represents only about 

27% of annual N loading to the lake (Sterner et al. 2007). In-lake nitrification is currently 

thought to be responsible for the increase in nitrate over time; Lake Superior is a net generator of 

nitrate because it is so strongly limited by phosphorus, organic carbon, and iron (Finlay et al. 

2007, Sterner et al. 2007, Kumar et al. 2008).

Table 9. Water quality data (averages and ranges) for Lake Superior and for offshore sites around Isle 

Royale National Park, 2001–2007 (Kelly 2008, USEPA 2008a).

Location

TP

(μg L-1)

NO2+NO3-N

(mg L-1)

SiO3+SiO4 as Si 

(mg L-1)

Chlorophyll a

(μg L-1)

Epilimnion composites, offshore waters, summer, 2001–2007

Lakewide 2.13 (0.89–3.77) 0.34 (0.29–0.36) 2.17 (1.62–2.79) 0.96 (0.11–2.07)

SU-11 2.04 (1.24–3.15) 0.32 (0.32–0.33) 1.01 (0.87–1.12) 1.08 (0.73–1.35)

SU-12 2.16 (1.25–3.26) 0.32 (0.29–0.35) 0.98 (0.84–1.08) 1.21 (0.42–1.64)

SU-13 2.19 (1.80–2.76) 0.30 (0.29–0.33) 0.95 (0.83–1.10) 1.56 (1.02–2.04)

SU-14 1.92 (0.99–2.86) 0.32 (0.31–0.33) 0.99 (0.77–1.10) 1.13 (0.62–1.65)

SU-15 2.32 (1.47–2.84) 0.32 (0.31–0.32) 1.00 (0.87–1.07) 1.19 (0.65–2.03)

SU-16 2.06 (1.42–2.57) 0.32 (0.31–0.34) 1.02 (0.95–1.06) 1.08 (0.47–1.73)

Nearshore waters, summer, 2002–2007

Lakewide 6.43 (1.90–19.21) 0.33 (0.14–0.50) 2.23 (1.75–4.40) 1.10 (0.27–15.3)

Dissolved reactive silica is high in Lake Superior relative to the other Great Lakes (LSBP 2000) 

and is considered to be available in sufficient quantities for diatom production. Si levels around 

ISRO generally ranged from 0.8 to 1.3 mg L-1 (Figure 16) and were uniformly lower than the 

lakewide average (Table 9). Conversely, mean chlorophyll-a levels around ISRO were higher 

than the lakewide average (Table 9, Figure 17), perhaps indicating that diatoms were producing 

chlorophyll and lowering silica levels.
35

Figure 14. Total phosphorus (unfiltered) for summer epilimnion composites, Lake Superior offshore sites 

around Isle Royale National Park, 1996–2006 (USEPA 2008a).

Figure 15. Nitrate and nitrite-nitrogen (filtered) for summer epilimnion composites, Lake Superior offshore 

sites around Isle Royale National Park, 1996–2006 (USEPA 2008a).

0

1

2

3

4

5

6

7

8

9

1994 1996 1998 2000 2002 2004 2006 2008

TP (ug L-1)

SU-11

SU-12

SU-13

SU-14

SU-15

SU-16

0.25

0.27

0.29

0.31

0.33

0.35

0.37

1994 1996 1998 2000 2002 2004 2006 2008

NO2+NO3-N (mg L-1)

SU-11

SU-12

SU-13

SU-14

SU-15

SU-16
36

Figure 16. Dissolved silica (filtered) for summer epilimnion composites, Lake Superior offshore sites 

around Isle Royale National Park, 1996–2006 (USEPA 2008a).

Figure 17. Chlorophyll-a levels for summer epilimnion composites, Lake Superior offshore sites around 

Isle Royale National Park, 1996–2008 (USEPA 2008a).

Dissolved Oxygen

All but one of 1,108 DO samples collected contained more than the 7 mg L-1 necessary for trout 

survival and optimal growth; no trends are apparent (Figure 18) (Shaw et al. 1996, USEPA 

2008a).

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1994 1996 1998 2000 2002 2004 2006 2008

SiO3-SiO4 as Si (mg L-1)

SU-11

SU-12

SU-13

SU-14

SU-15

SU-16

0

0.5

1

1.5

2

2.5

1994 1996 1998 2000 2002 2004 2006 2008

Chlorophyll-a (ug L-1)

SU-11

SU-12

SU-13

SU-14

SU-15

SU-16
37

Figure 18. Dissolved oxygen (n=1,108) values for all depths, Lake Superior offshore sampling sites SU11–SU-16 near Isle Royale National Park, 1996–2008 (USEPA 2008a).

Alkalinity, Specific Conductance, and pH

Alkalinity is a measure of water’s buffering capacity and ability to resist a change in pH (USEPA 

1986). Alkalinity values for sites around ISRO ranged from 39 to 47 mg L-1 as CaCO3 and 

showed a significant upward trend from 1996 to 2008 (Figure 19). All values were well above 25 

mg L-1

, the threshold below which lakes are considered susceptible to acid rain (Taylor 1984). 

Laboratory conductivity (specific conductance) values ranged from 96 to 104 μS cm-1

, agreeing 

well with calculated field values labeled “specific conductance” (21–104 μS cm-1). As expected 

(Shaw et al. 1996), the numeric values for specific conductance (in μS cm-1

) were approximately 

double the values for total hardness or alkalinity (in mg L-1 as CaCO3) (Figure 19). All pH values 

were within the acceptable range of 6.5 – 9.0 pH units (Figure 19).

Major Cations and Anions

Average concentrations for major cations were Ca2+

, 13.8 mg L-1; Mg2+, 2.8 mg L-1; and Na+, 1.4 

mg L-1 (all n=35) (USEPA 2008a). No recent data were found for potassium (K+

). For anions, Cllevels were low from 1996 to 2008 (<1–2 mg L-1

) (Figure 19) but are projected to increase over 

the next 500 years from anthropogenic sources (road salts and brines) (USEPA 2008a, b). No 

recent data were found for sulfate (SO4

2-

).

Temperature

Water temperatures ranged from 0 to 18.6o

C at depths of 1–5 m from 1996 to 2008, with April 

and May samples being much colder than those taken from August to October (Figure 20). A 

clear trend did not appear in this data set. However, three buoys installed in Lake Superior from 

1979 to 1981 and since operated continuously from April to November indicate that July–

September surface water temperatures increased 2.5o

C from 1979 to 2006, and that this increase 

was significantly in excess of regional atmospheric warming (Austin and Colman 2007). This 

trend was attributed to declining winter ice cover, which is causing the stratified season to start 

earlier at the rate of a half-day per year.

5

10

15

20

1995 2000 2005 2010

Dissolved Oxygen (mg L-1)
38

Figure 19. Alkalinity (n=671), specific conductance (n=1,566), chloride (n=934), and pH (n=653) values for all depths, Lake Superior offshore 

sampling sites SU-11–SU-16 near Isle Royale National Park, 1996–2008 (USEPA 2008a).

30

35

40

45

50

1995 2000 2005 2010

Alkalinity (mg L-1 CaCO3)

80

90

100

110

1995 2000 2005 2010

Specific Conductance (μS cm-1)

Conductivity

Specific 

Conductance 

(Seabird)

0.0

0.5

1.0

1.5

2.0

2.5

1995 2000 2005 2010

Chloride (mg L-1)

7.0

7.5

8.0

8.5

1995 2000 2005 2010

pH
39

Figure 20. Water temperature (oC) for 1–5 m depths, Lake Superior offshore sampling sites SU-11–SU16 near Isle Royale National Park, 1996–2008 (USEPA 2008a).

Critical Pollutants and Substances of Emerging Concern

The Lake Superior Binational Program (LSBP) has initiated a Zero Discharge Demonstration 

Program to end the use of nine critical pollutants in industrial processes and products and prevent 

their release in the Lake Superior basin by 2020. These pollutants are chlordane, DDT and its 

metabolites, aldrin/dieldrin, dioxin, HCB, mercury, octachlorostyrene, PCBs, and toxaphene 

(LSBP 2008). Although progress has been made, concentrations of PCBs, HCB, dieldrin, and 

toxaphene in Lake Superior water still remained above one or more “yardstick values” 

established by states or the province of Ontario as of 2005 (LSBP 2008). Another set of 

chemicals (polycyclic aromatic hydrocarbons [PAHs], alpha-hexachlorocyclohexane [α-HCH], 

cadmium, heptachlor and its breakdown product heptachlor epoxide, and another set of dioxins 

and furans) are on a “critical pollutant lakewide remediation” list, while a third set of chemicals 

(mostly heavy metals) is on a “local remediation” list (LSBP 2008).

Other substances of emerging concern for the Great Lakes include flame retardants, fluorinated 

surfactants, personal care products (including triclosan and benzalkonium chloride), 

pharmaceuticals (steroids, hormones, caffeine, and cotinine), detergents, plasticizers, pesticides, 

and short-chain chlorinated paraffins. Of these, the first two categories have been most 

intensively studied in Lake Superior. The flame retardants called polybrominated diphenyl ethers 

(PBDEs) are increasing in fish tissue and sediment in Lake Superior. Fluorinated surfactants, 

specifically perfluorinated alkyl acids, are now the predominant halogenated organic 

contaminants in Lake Superior waters (LSBP 2008).

In 2007, the status of Lake Superior for toxic chemical contaminants in offshore waters was fair, 

with an undetermined trend (USEPA and Environment Canada 2007). Thirteen of 21 

organochlorine pesticide compounds for which tests were conducted were detected in Lake 

Superior at very low concentrations. Mercury concentrations were very low offshore, but the 

highest concentrations occurred near Thunder Bay and Duluth. PAHs were found throughout 

Lake Superior, although at extremely low concentrations.
40

Nearshore Water Quality

There has been little systematic water quality sampling of the nearshore waters of Lake Superior, 

either lakewide (Kelly 2008) or in the ISRO vicinity. Crane et al. (2006) stated that three sites 

sampled near Amygdaloid Island between June and August 1974 (NPS 1995) exceeded the 10 m 

depth contour that defines the nearshore environment but are thought to give a general indication 

of Lake Superior conditions near ISRO. No USEPA data were found for nearshore sites near 

ISRO (USEPA, Mid-Continent Ecology Division, Anne Cotter, email, May 26, 2009). However, 

the 2008 draft State of the Lakes Ecosystem Conference (SOLEC) document titled “Nearshore 

Areas of the Great Lakes 2008” presented summary data for 207 samples collected in other Lake 

Superior nearshore areas from 2002 to 2007 (Table 9). For TP, the lakewide average was higher 

for nearshore samples than offshore samples (6.43 μg L-1

vs. 2.13 μg L-1), and the coefficient of 

variation was lower (48% vs. 69%). The 2007 status and trend for Lake Superior nearshore 

waters for TP were “undetermined” (USEPA and Environment Canada 2007). Lakewide 

averages for nearshore and offshore environments were similar for NO3-N (0.33 vs. 0.34 mg L-1), 

Si (2.23 vs. 2.17 mg L-1), and chlorophyll-a (1.10 vs. 0.96 mg L-1). Coefficients of variation were 

higher nearshore for Si (13% vs. 7%), much higher for chlorophyll-a (103% vs. 38%), and lower 

for NO3-N (14% vs. 31%) (Kelly 2008).

Total and Fecal Coliform Bacteria

Total and fecal coliform are groups of organisms used to assess the suitability of water for 

drinking or for body-contact recreation. Some bacteria in the total coliform group are naturally 

found in soil and thought to present negligible health risk, while fecal coliform are generally 

accepted to represent the presence of human or animal fecal material in water (Health Canada 

2006). Debate currently exists about the human health significance of animal fecal material in 

recreational waters; USEPA currently does not differentiate between human and animal fecal 

sources in its recreational waters criteria, citing “a lack of detailed and unequivocal information 

concerning the relative risks of human illness from various...(human or animal) sources of fecal 

contamination in recreational waters” (USEPA 2009e).

Little sampling for fecal or total coliform has been documented for ISRO. A 1995 report (NPS 

1995) covering the period 1965–1993 included sampling sites at Amygdaloid Island and at 

Washington Creek at Windigo and revealed some violations of the WRD screening limits for 

primary body-contact recreation for both total and fecal coliform. However, it is unclear how 

these results were interpreted, since current standards require examination of five or more 

samples taken over a 30-day period and the calculation of a geometric mean (Ledder 2005). A 

1984–1985 study (Meldrum 1987 in Crane et al. 2006) explored bacterial contamination in Isle 

Royale waters, especially in Lake Superior bays near heavy human-use areas. The ratio of fecal

coliform to fecal streptococcus bacteria (FC:FS) was used as an indicator of whether the bacteria 

were of human or animal origin, and ISRO samples normally were indicative of non-human 

sources. Higher bacteria levels were generally found at Rock Harbor, and FC:FS ratios indicative 

of human fecal sources were occasionally found at Chickenbone West, Moskey Basin, and 

McCargoe Cove. Follow-up sampling occurred in 1987 at Benson Creek and Daisy Farm, and 

the conclusion was that “there was no evidence of human waste from pit toilets” in Benson 

Creek or Lake Superior in the Daisy Farm vicinity (Crane et al. 2006).
41

Contaminants in Fish and Other Organisms 

In 2007, the MI Department of Environmental Quality (MDEQ) analyzed USEPA contaminant 

data on whole lake trout from Lake Superior from 1977 to 2000 and reported that overall, 

contaminant concentrations were less in Lake Superior fish than in fish from the other Great 

Lakes (MDEQ 2008a). Carlson and Swackhamer (2006) reported that in 1999 and 2000, 

contaminants in lake trout and salmon were generally lowest in Lake Superior and highest in

Lake Michigan by a factor of three. However, they reported that concentrations of toxaphene and 

α-HCH in water and fish flesh are greatest in Lake Superior. Lake Superior is losing toxaphene 

(and probably α-HCH) at a slower rate than the other Great Lakes because of the lake’s larger 

volume, lower productivity, and colder temperatures (Carlson and Swackhamer 2006).

In 2007, the status of Lake Superior for contaminants in whole fish was fair, with an improving 

trend (USEPA and Environment Canada 2007). Total PCB concentrations in fish tissue showed 

little change from the late 1970s to 2003 and were above the Great Lakes Water Quality 

Agreement (GLWQA) criteria of 0.1 parts per million (ppm) and the USEPA wildlife protection 

value of 0.16 ppm. Total DDT had fluctuating concentrations but was below the GLWQA 

criterion of 0.1 ppm. Mercury was below the GLWQA criterion of 0.5 ppm. Toxaphene 

concentrations were declining. Other contaminants, including PBDEs and 

perfluoroctanesulfonate (PFOS), have more recently been detected in Lake Superior fish

(USEPA and Environment Canada 2007).

The MI waters of Lake Superior have fish consumption advisories for chlordane, dioxin, 

mercury, and PCBs. The PCB advisory includes the greatest number of species (brown trout, 

Chinook and coho salmon, lake herring, lake trout, rainbow trout, siscowet, suckers, and 

whitefish). The mercury advisory includes lake trout and walleye. For the general population, 

these advisories pertain mainly to the largest fish; for women and children, most fish should be 

eaten only once a week or once a month (Table 10). Siscowet have an advisory for chlordane and 

dioxin as well as PCBs; the MI Department of Community Health (MDCH) advises no 

consumption of siscowet greater than 46 cm in length (MDCH 2009).

Table 10. Fish consumption advisories for species of Lake Superior fish (MDCH 2009).

Contaminant Species Consumption Advisory - 

Women and Children

Consumption AdvisoryGeneral Population

Mercury Burbot >56 cm, one meal/month >56 cm, one meal/week

Walleye >56 cm, one meal/month >56 cm, one meal/week

PCBs Brown trout >25 cm, one meal/week No restrictions

Chinook salmon >25 cm, one meal/month No restrictions

Coho salmon >25 cm, one meal/week No restrictions

Lake herring all, one meal/week >76 cm, one meal/week

Rainbow trout >66 cm, one meal/week No restrictions

Suckers all, one meal/week No restrictions

Whitefish all, one meal/week No restrictions

Chlordane, PCBs, 

Dioxins

Siscowet 36–46 cm, one meal/month;

>46 cm, do not eat

>46 cm, do not eat

Mercury, PCBs, 

Chlordane

Lake trout 36–66 cm, one meal/week; 

66–76 cm, one meal/month; 

>76 cm, do not eat

>76 cm, one meal/week
42

Toxic contaminants have also been found in the flesh of fish taken from ISRO interior lakes. 

Swain (1978) documented PCBs, DDT, α-HCH, and dieldrin in lake trout from Lake Superior 

near ISRO and from Siskiwit Lake; concentrations were higher in Siskiwit Lake. A later study 

(Swackhamer and Hites 1988) showed that organochlorine concentrations in lake trout from 

Siskiwit Lake and Lake Superior were similar, and that they generally decreased between 1975 

and 1983. More recently, Kannan et al. (2000) documented polychlorinated naphthalene (PCNs) 

and PCBs in fish from Siskiwit Lake. All inland lakes, reservoirs, and impoundments in 

Michigan have an advisory against eating most types of fish more than once a week because of 

mercury contamination, with additional restrictions for women of childbearing age and children 

under age 15 (MDCH 2009).

Monitoring of six organic contaminants (PCBs, DDE, HCB, heptachlor epoxide, mirex, and 

dieldrin) in herring gull (Larus argentatus) eggs has been conducted at 15 Great Lakes sites, 

including two sites in Lake Superior, since 1974 (Weseloh et al. 2006, USEPA and Environment 

Canada 2007). The current status of contaminants in colonial nesting waterbirds is considered 

good in Lake Superior, with an improving trend. Levels of these six contaminants have declined 

93.9–99.8% between 1974 and 2005 (USEPA and Environment Canada 2007). The closest of the 

15 sites to ISRO is at Granite Island, 60 km N. Granite Island was the 10th most contaminated 

overall, with a range of 3rd most contaminated by dieldrin to 10th most contaminated for PCBs. 

Statistically, Granite Island was not different from a site in the Niagara River that was within 

gull feeding distance of an Area of Concern. Eggs from Granite Island had significantly greater 

dieldrin concentrations than those from Chantry Island in Lake Huron and significantly greater 

heptachlor epoxide concentrations than all other sites except Gull and Big Sister islands in Lake 

Michigan and Agawa Rocks in Lake Superior (Weseloh et al. 2006). 

One exception to the declining contaminant concentrations in herring gull eggs is brominated 

diphenyl ethers (BDEs), used as fire retardants; these increased dramatically in gull eggs during 

1981–2000 at the same 15 Great Lakes sampling sites (Norstrom et al. 2002). Granite Island was 

the 6th most contaminated site for total BDEs. The most contaminated sites were in northern 

Lake Michigan and in Toronto Harbor on Lake Ontario; the authors suggested that some Lake 

Superior herring gulls travel to northern Lake Michigan during severe winters and may pick up 

contaminants there. In 2002, BDEs had the third highest concentrations among groups of 

organohalogen compounds, behind PCBs and DDE but ahead of chlordanes, chlorobenzenes, 

HCHs, and dieldrin (Norstrom et al. 2002).

The GLKN monitoring protocol for monitoring and assessing methylmercury and organic 

contaminants in aquatic food webs calls for testing yellow perch, northern pike, and dragonfly 

larvae at three-year intervals (Wiener et al. 2008); candidate sites include Angleworm (or Eva), 

Harvey, Richie, and Sargent lakes. William Bowerman of the Institute of Environmental 

Toxicology at Clemson University is reportedly tracking contaminants in herring gull eggs and 

in blood and feather samples from bald eagles in the Great Lakes region, including ISRO (Crane 

et al. 2006).
43

Inland Aquatic Resources

ISRO has perennial and intermittent streams, numerous inland lakes, and wetlands widely 

distributed across the island. Generally, streams are oriented along a SW to NE axis as controlled

by the underlying ridge and valley bedrock topography. The numerous inland lakes on ISRO are 

the result of glacial quarrying that accentuated the existing stream channels; thus, many lakes 

exhibit a long axis oriented to the ridge and valley topography. Lake Halloran and Feldtmann

Lake are unique in that they are basins originally connected to Lake Superior that were enclosed 

by beach bars (Crane et al. 2006). The many wetlands on ISRO are broadly associated with 

stream margins in the ridge and valley topography, the littoral zone in lakes, and beaver activity 

(Lafrancois and Glase 2005). 

Physical Description

Lakes

Wallace (1966) estimated that ISRO contains 202 lakes and ponds ranging in size from Siskiwit 

Lake at 1,635 ha and over 45 m deep to numerous shallow ponds. Based on the National 

Hydrography Dataset (NHD), ISRO has 278 lakes (USGS 2008); total surface area of these lakes 

is 3,618 ha. Only 43 ISRO lakes have been named, and these include larger lakes that receive 

recreational use or have been subject to investigation for biologic or chemical characteristics 

(Figure 21–Figure 23, Table 11).

Koelz (1929) provided one of the first physical descriptions of lakes on ISRO while surveying 

fish populations from 38 inland lakes. Lagler and Goldman (1959, 1982) gave brief descriptions 

of 32 lakes in a guide to recreational fishing. They roughly divided ISRO lakes into two types: 

large and deep lakes that contain whitefish (Coregonus sp.) and shallow and boggy lakes. 

Toczydlowski et al. (1978) conducted a broad survey of 13 lakes/ponds and eight stream sites to 

provide baseline data relevant to basic water chemistry and biologic characteristics that included 

plankton and macroinvertebrate diversity and aquatic vegetation mapping.

The most complete physical description of ISRO lakes was provided by Kallemeyn (2000), who 

surveyed 32 of the lakes originally studied by Koelz (1929) and collected morphometric, water 

chemistry, and fish community data. Aside from being the first comprehensive study of ISRO 

lakes in 70 years, a particular strength of this study was in establishing baseline data for fish 

communities and chemical parameters through standardized sampling methods. 

Siskiwit Lake has the largest watershed area of any ISRO lake, and its surface area is almost four 

times greater than the next largest lake, Lake Desor (430.0 ha) (Kallemeyn 2000). Excluding 

Siskiwit Lake, the mean surface area of the lakes surveyed by Koelz (1929) and Kallemeyn 

(2000) is 55.4 ha, and average maximum depth is 5.8 m. Only Lake Desor, Lake Richie, 

Feldtmann Lake, and Sargent Lake have watershed areas >100 ha. Of the 43 named lakes, 20

have surface areas that are <50 ha and 11 have a maximum depth ≤ 5 m (Table 11). The mean 

perimeter and surface area of the 235 unnamed lakes on ISRO is 383.5 m and 0.78 ha

respectively (USGS 2008).
44

Figure 21. Water features and watersheds of the western section of Isle Royale National Park, including the Washington Creek gaging station

(USGS 2008).
45

Figure 22. Water features and watersheds of the central section of Isle Royale National Park (USGS 2008).
4

6

Figure 23. Water features and watersheds of the eastern section of Isle Royale National Park (USGS 2008).
47

Table 11. Morphometric characteristics of 43 named lakes in Isle Royale National Park. Lake area and 

perimeter from the USGS (2008). Watershed area, maximum length, breadth, and depth data from 

Kallemeyn (2000).

Lake Map 

page

Area

(ha)

Perimeter 

(m)

Watershed 

area

(ha)

Maximum

length

(km)

Maximum

breadth

(km)

Maximum

depth

(m)

Ahmik 46 10.32 2,600.7 35.4 0.89 0.16 3.35

Amygdaloid 46 11.12 3,133.5 26.1 1.53 0.10 8.84

Angleworm 46 49.80 7,331.4 495.6 3.51 0.20 8.40

Beaver 45 20.35 3,110.1 258.3 1.09 0.31 5.18

Benson 46 23.75 3,209.1 83.0 1.38 0.33 3.80

Chickenbone 45 91.01 8,903.8 1,556.4 2.84 0.36 6.40

Desor 44-45 429.96 15,404.9 1,436.7 4.45 1.91 14.02

Dustin 45 4.31 1,257.0 497.8 0.49 0.14 6.10

Epidote 46 1.18 449.2 55.8 0.19 0.09 3.96

Eva 46 17.15 2,572.7 231.1 0.97 0.23 6.40

Feldtmann 44 186.04 6,524.0 886.6 2.66 1.02 2.74

Forbes 46 6.56 1,326.6 40.8 0.54 0.17 2.70

George 45 3.71 1,388.8 18.1 0.61 0.10 2.70

Halloran 44 78.93 4,395.7 230.7 1.82 0.42 2.70

Harvey 45 51.40 6,009.5 292.8 1.75 0.46 4.00

Hatchet 45 49.54 4,094.3 502.2 1.90 0.41 5.20

Hidden 46 1.54 573.7 - - - -

Intermediate 45 70.32 6,522.5 481.7 1.77 1.01 6.70

John 46 3.25 1,115.1 126.4 0.47 0.16 5.49

LeSage 45 44.83 5,845.9 933.0 1.66 0.48 6.40

Lily 44 6.72 981.0 - - - -

Linklater 46 17.42 3,506.0 99.4 1.56 0.17 6.00

Livermore 45 29.82 3,729.4 168.8 1.57 0.30 5.50

Mason 46 23.78 3,852.6 492.8 1.73 0.24 8.50

McDonald 45 15.06 2,346.4 104.9 0.93 0.31 4.00

Moose 46 1.99 914.2 - - - -

Mud 45 21.00 2,107.1 - - - -

Newt 46 5.58 1,776.6 - - - -

Ojibway 46 15.02 3,659.5 - - - -

Otter 45 20.34 2,858.6 96.3 1.19 0.28 4.27

Patterson 46 10.25 2,018.3 43.3 0.76 0.19 3.60

Richie 45 200.04 15,671.7 2,080.2 3.20 1.99 10.67

Sargent 46 142.41 16,661.6 1,089.3 4.37 0.86 13.72

Scholts 45 2.45 1,104.2 469.3 0.52 0.08 1.52

Shesheeb 46 10.69 2,547.2 155.1 0.88 0.35 5.49

Siskiwit 45 1,619.12 38,389.2 7,287.1 11.06 2.30 46.00

Stickleback 44 6.93 1,137.8 - - - -

Sumner 46 9.32 1,744.7 - - - -

Theresa 46 6.56 1,746.3 - - - -

Wagejo 46 6.04 1,264.7 58.2 0.49 0.22 2.19

Wallace 46 3.91 1,115.6 - - - -

Whittlesey 45 60.83 8,597.1 450.5 2.97 0.27 7.65

Wood 45 44.67 5,090.5 - - - -
48

Kallemeyn (2000) recognized three main ISRO lake types based on thermal regime: those that 

have stable stratification during summer (dimictic), those that are not stratified during the 

summer (continuous polymictic), and those that become stratified during short and irregular 

intervals during warm weather (discontinuous polymictic). Although continuous monitoring 

would be required to definitively describe thermal regime in ISRO lakes, Kallemeyn (2000) 

found 21 stratified and 11 unstratified lakes during single sampling events in summers of 1995–

1997. Generally, deeper lakes were stratified, and shallower lakes (maximum depths <5 m) were 

not. 

An extension of the analysis of the lake habitat data from Kallemeyn (2000) indicates that ISRO 

lakes can be classified into four categories: 1) small shallow lakes with high dissolved organic 

carbon (DOC), 2) large deep lakes with low DOC, 3) lakes with hard water and high algal 

biomass, and 4) soft water lakes with high phosphorus (Carlisle 2000). Although there does not 

seem to be a distinct spatial pattern of these lake types, there is a higher concentration of hard 

water lakes on the north-central to NW end of ISRO (Figure 24). These categories correlate with 

fish assemblages (Carlisle 2000) and are probably associated with other biologic characteristics. 

Because ISRO is remote, and park personnel have limited ability to perform regular monitoring 

of lakes, this classification framework with four lake types was recommended as a starting 

position in choosing index lakes for long-term water quality monitoring programs through 

agencies such as the GLKN (Crane et al. 2006, Elias et al. 2008).

Streams

The NHD recognizes eight named streams on ISRO: Benson Creek, Big Siskiwit River, Caribou 

Creek, Grace Creek, Little Siskiwit River, Siskiwit River (outlet from Siskiwit Lake), Tobin 

Creek, and Washington Creek (USGS 2008). Other streams have been referenced by name in 

various publications; these shorter stream segments are outlets from lakes and often take the 

name of the water body or basin they drain. Five prominent streams that fit this category are 

Wallace Creek (outlet from Wallace Lake), Moskey Basin Creek (draining an unnamed lake to 

the east of Moskey Basin), Lake Richie outlet, Chickenbone Lake outlet, and Feldtmann Lake 

outlet (Figure 21–Figure 23, Table 12). The combined length of these 13 streams is 71.57 km. 

Given the remoteness of ISRO and its topography, it is not surprising that many smaller streams 

remain unnamed. In total, 172.3 km of perennial streams exist on ISRO, with an additional 44.9 

km identified as intermittent (USGS 2008).

Washington Creek is 10.4 km long with a total watershed area of 3,616 ha. As part of the USGS 

National Hydrologic Network, a gage was operated on Washington Creek from 1964 to 2003. 

During that time, Washington Creek mean monthly discharge ranged from 0.016 m3

sec-1 in 

September 1976 to 4.66 m3

sec-1 in April 2001 (USGS 2010). Peak flow occurs during spring 

runoff, and a secondary increase in flow occurs in late fall due to lowered evapotranspiration and 

increased precipitation (Crane et al. 2006).

Wallace Creek has also been the subject of long-term biologic and chemical study; however, 

much of the island contains smaller perennial and intermittent streams that remain unstudied. 
49

Figure 24. Lake types of Isle Royale National Park by canonical correspondence analysis (Carlisle 2000).
50

Table 12. Lengths and watershed areas of named streams, Isle Royale National Park (USGS 2008). 

Watershed areas from Crane et al. (2006).

Stream Map page Total length 

(km) Notes Watershed Area

(ha)

Named in NHD

Benson Creek 46 2.52 1 216

Big Siskiwit River 44 12.95 2 5,075

Caribou Creek 44 1.09 3 -

Grace Creek 44 14.55 1,684

Little Siskiwit River 44-45 13.49 4 3,054

Siskiwit River 45 0.67 6,894

Tobin Creek 46 6.76 5 869

Washington Creek 44 10.43 3,616

Referenced in publications

Lake Richie outlet 45 2.16 2,768

Chickenbone Lake outlet 45 0.79 1,885

Feldtmann Creek 44 1.38 1,265

Wallace Creek 46 0.43 213

Moskey Basin Creek 46 4.35 193

Total Named 71.57

1. Includes 80 m connecting creek to Moskey Basin not indicated as perennial in the dataset.

2. Includes 518.4 m that appear as ponds or wetlands along stream path.

3. Includes 45 m that appear as ponds or wetlands along stream path.

4. Includes 113.9 m that appear as ponds or wetlands along stream path.

5. Includes 934.5 m that appear as ponds or wetlands along stream path.

Wetlands 

Wetland habitats on ISRO have been inventoried in the NHD, the National Wetland Inventory 

(NWI) (USFWS 2008) and the USGS–NPS Vegetation Mapping Program (TNC 1999, USGS 

2000a). Crane et al. (2006) have described some of the advantages and disadvantages of the NWI 

for ISRO, which lists 14,890 ha of wetlands (10,155 ha palustrine, 4,564 ha lacustrine, and 172 

ha other wetlands). Based on the NHD, ISRO has 7,030.3 ha classified as wetlands but not 

differentiated by type (USGS 2008). The USGS–NPS Vegetation Mapping Program (TNC 1999, 

USGS 2000a) lists 10,445.0 ha in Ecologic Groups 1–4 and is considered to be the best currently 

available description of ISRO wetlands; this is the classification we will discuss here.

Ecologic Groups 1–4 include communities that vary from sedge (Carex spp.)-dominated (sedge 

meadow complex) to shrub-dominated communities (especially alder and leatherleaf

[Chamaedaphne calyculata]), to a variety of tree-dominated associations. Group 1 and 2 

wetlands are too small or do not have a photointerpretation signature and so could not be 

mapped. We have grouped mapped wetlands in Ecologic Groups 3 and 4 into seven categories. 

White cedar–dominated communities are the most abundant of all ISRO wetlands 

(approximately 6,178 ha for both the closed and open phases, or 61.3%) (Table 13) (USGS 

2000a). Various forms of the (wet) sedge meadow association occupy nearly 1,500 ha (14.5%), 

making it the second most common wetland type. Speckled alder (Alnus incana), bluejoint 

eastern meadow, and black spruce (Picea mariana)–dwarf shrub swamp complex are the third 
51

Table 13. Wetland types and sizes in Isle Royale National Park (USGS 2000a).

% of 

total Hectares % of group

Name 

(Photointerpretation- NPS)

Map Name

(Figure 25–Figure 27) and 

Ecologic Group

Not mapped but 

related

258.0 76.9 Black ash-mixed hardwood 

swamp complex

61.8 18.4 Black ash (cedar)-mixed 

hardwood swamp complex

15.7 4.7 Red maple-ash-birch swamp 

forest

-- <1 White cedar-black ash 

swamp

-- <1 Black ash-mixed hardwood 

swamp 

3.2 335.5 100.0 Mixed Hardwood Swamp–

Ecologic Group 4

230.0 3.6 Northern tamarack rich 

swamp

White cedar-sweet 

gale scrub fen– Ecologic Group 1 4,652.7 72.6

White cedar-(mixed 

conifer)/alder swamp (closed 

phase)

1,525.1 23.8

White cedar-(mixed 

conifer)/alder swamp (open 

phase)

61.3 6,407.8 100.0 White Cedar/Alder 

Swamp–Ecologic Group 4

-- <1 Black spruce/Labrador tea 

poor swamp

4.6 479.6 100.0 Black spruce/dwarf-shrub 

swamp complex

Black Spruce/Dwarf 

Shrub Swamp–Ecologic

Group 4

1.0 108.2 100.0 Dwarf shrub fen complex Dwarf Shrub Fen–

Ecologic Group 4

Leatherleaf-sweet 

gale shore fen, 

Leatherleaf bog, 

white cedar-sweet 

gale scrub fen–

Ecologic Group 1

9.3 974.4 100.0 Speckled alder swamp Speckled Alder Swamp–

Ecologic Group 4

42.9 2.8 Sedge/sphagnum meadow 

complex

Northern poor fen– Ecologic Group 1

1,476.2 97.2 Sedge meadow complex

Boreal calcareous 

seepage fen– Ecologic Group 1

Northern sedge wet 

meadow, twig rush 

wet meadow– Ecologic Group 3

14.5 1,519.1 100.0 Sedge Meadow–

Ecologic Group 3

5.9 620.4 100.0 Bluejoint eastern meadow

Bluejoint Eastern 

Meadow–Ecologic Group 

3

100.0 10,445.0 All wetlands
52

Table 13. Wetland types and sizes in Isle Royale National Park (USGS 2000a) (continued). 

Other unmapped wetlands

Ecologic Group 2:

Midwest pondweed submerged aquatic vegetation (not discernable on early spring photography). 

Related to Water mapping unit.

Northern water lily aquatic wetland (not discernable on early spring photography, noted as uncommon). 

Related to Water mapping unit.

Ecologic Group 3:

Midwest mixed emergent deep marsh (generally below minimum mapping unit size, noted as 

uncommon)

Water horsetail-spikerush marsh (generally below minimum mapping unit size, noted as an uncommon 

and extremely narrow type)

Ecologic Group 4:

Black spruce/alder rich swamp (noted as rare on the island)

Ecologic Group 11:

Aspen-balsam poplar lowland forest (below minimum mapping unit, several individual balsam poplar 

trees observed near Caribou Creek west of Siskiwit Bay)

through fifth most common associations or groups, followed by mixed hardwood swamp and 

dwarf shrub fen. 

Physiography, soil characteristics, groundwater and surface water movement, and the chemical 

makeup of parent material collectively determine where wetlands occur and which species or 

group of species dominate the association. The first four factors interact to determine how much 

moisture there is on a site, for how long the soils stay saturated, the magnitude of annual water 

fluctuation, and the amount and type of nutrient input (Richardson 2000, Weber et al. 2007). 

These hydrologic characteristics determine, at a community level, which species are suited for a 

site. At a smaller scale, the hydrologic conditions are modified by microtopography and 

windthrow.

In ISRO, inland wetlands are associated with lakes, stream valleys, and upland areas and 

generally occur along a SW to NE axis following the underlying geology (Figure 25–Figure 27). 

The largest concentration of wetlands is found in the SW, associated with the Big Siskiwit River 

and its tributaries where alluvial soils are more developed (Figure 6).

Northern Shrub/Graminoid Fens and Bogs (Ecologic Group 1)

Fen-type associations stand out from the other wetland types. These communities occur on 

uncommon soil and/or parent materials (e.g., calcareous) that result in higher soil pHs, and often 

have high levels of dissolved salts in soil solution. These chemical differences may have 

important impacts on nutrient and mercury input to lakes or creeks.

Bogs are another physiographic feature that support a conifer-dominated community. They 

typically have no drainage outlets and thus have standing water for much of the year. The soil is 
53

Figure 25. Mappable wetland types for the western section of Isle Royale National Park (TNC 1999, USGS 2000a).
54

Figure 26. Mappable wetland types for the central section of Isle Royale National Park (TNC 1999, USGS 2000a).
55

Figure 27. Mappable wetland types for the eastern section of Isle Royale National Park (TNC 1999, 2000a). 
56

acid to very acid. They occur on peat soils in a narrow elevational band (183–213 m). Black 

spruce–speckled alder–sphagnum moss (Sphagnum spp.) is the community type found in bogs at 

ISRO. This is an uncommon type and is scattered. These communities have a sparse tree layer 

(< 20% cover) which occasionally includes white spruce. The tall shrub layer is denser than in 

the rich swamps (TNC 1999).

The leatherleaf–Labrador tea (Ledum groenlandicum)–laurel (Kalmia polifolia) dwarf shrub 

community is a type that shares many characteristics and species with the spruce–alder–

sphagnum moss type. It is uncommon and found at elevations from 183 to 232 m on saturated, 

fibric peat soil. It is very acidic (pH < 4.3) and isolated from groundwater. The community often 

has a few scattered trees and stunted trees in the tall shrub layer (approximately 5% cover). The 

short shrub layer for which the community is named is extensive (40–70% cover) and includes 

some combination of the three dwarf shrubs. A sedge (Carex oligosperma) is the most common 

herbaceous plant (TNC 1999).

Wet Meadows and Marshes (Ecologic Group 3) 

The ISRO wetlands in Ecologic Group 3 are sedge meadow and bluejoint eastern meadow. 

Sedge meadow is concentrated along stream channels on the western side of ISRO (Table 13,

Figure 25) and along stream channels and bays/coves of several lakes in central and eastern 

ISRO (Figure 26–Figure 27). Two distinct areas of sedge meadow that are not directly associated 

with stream valleys include a strip to the west of Feldtmann Lake along a beach bar (Figure 25)

and a section to the north of Siskiwit Lake. The sedge meadow category includes four groups

from the Vegetation Mapping Program (TNC 1999): northern sedge wet meadow, northern poor 

fen, boreal calcareous seepage fen, and twig rush wet meadow. All of these categories are 

characterized by a high percent coverage of sedge and smooth sawgrass (Cladium mariscoides) 

and a lower percent coverage of sweetgale (Myrica gale) or leatherleaf. Sphagnum moss may be 

common in the groundlayer in drier soils (i.e., all groups except northern sedge wet meadow).

Bluejoint eastern meadow (Table 13, Figure 25–Figure 27) is commonly found in close 

association with sedge meadow. Bluejoint eastern meadow is primarily composed of bluejoint 

(43%), bulrush (Scirpus cyperinus, 25%), and beaked sedge (Carex rostrata, 15%). Other 

species commonly found but at less than 10% coverage include woolly-fruit sedge, speckled 

alder, and sphagnum moss (TNC 1999).

Northern Conifer and Hardwood Forest and Shrub Swamps (Ecologic Group 4)

As noted above, the common forest type in this group is the cedar-speckled alder swamp. Cedar 

swamps are most commonly found at elevations between 183 and 305 m in wet depressions on 

level to gently sloping terrain. The soil is peat or muck and is saturated most of the year. The 

shrub layer of this type typically includes speckled alder and alder-leaf buckthorn (Rhamnus 

alnifolius). There may be scattered black spruce or balsam fir (TNC 1999).

The tamarack–alder community type is rare, covering only 230 ha in ISRO. It is a ‘rich swamp’ 

(i.e., minerotrophic due to consistent groundwater input) and has soils similar to the cedar–alder 

type, but is found in the SW part of the island only on conglomerate or sandstone parent 

material. The tall shrub layer may include stunted forms of cedar and birch, whereas leatherleaf 

and bog Labrador tea are the most common short shrubs (TNC 1999).
57

Mixed hardwood swamps are dominated by the black ash (Fraxinus nigra)–mixed hardwood 

swamp complex (258 ha, Table 13). Soils are muck, and black ash averages 37% cover, with 

speckled alder averaging 62% cover. Red maple (Acer rubrum) and birch are found in other 

minor variants of the mixed hardwood swamp type. 

Other life forms and water quality of wetlands remain relatively unstudied on ISRO; a recent 

assessment of vegetation in wetland habitat of lakes by Meeker et al. (2007) had a goal to serve 

as a baseline for future studies and is described in the Macrophytes section below.

River-Associated Wetlands

As noted by Crane et al. (2006), riverine wetland habitats in ISRO have not been quantified by 

previous studies. The NWI classification scheme (Cowardin et al. 1979) defines riverine 

wetlands as those “contained within a channel” and excludes “wetland dominated by trees, 

shrubs, persistent emergents, emergent mosses, or lichens.” By this definition, few, if any, 

riverine wetlands exist on ISRO because of the lack of large river channels. However, since 

information about wetlands along ISRO rivers has been described as a need, we performed the

following analysis to provide estimates of wetland coverage in river corridors. We will refer to 

these wetlands as ‘river-associated’ rather than ‘riverine’ wetlands.

We overlaid stream vectors from the NHD (USGS 2008) onto vegetation types from the 

Vegetation Mapping Program (TNC 1999, USGS 2000a) to estimate river-associated wetlands 

on ISRO. Because this estimate is based solely on proximity to streams, the specific amounts and 

types of river-associated wetlands on ISRO vary with the definition of the stream corridor. We 

compared four corridors: 1) a simple quantification of stream lengths adjacent to wetlands, in 

essence a ‘zero-width’ corridor; 2) a variable-width corridor defined by the size of the wetland 

polygons touching the stream; 3) a 100 m buffer zone along each side of a stream or a 200 m 

wide corridor; and 4) a 10 m buffer zone along each side of a stream or a 20 m wide corridor 

(Table 14–Table 15). 

Most ISRO streams (73.5%) are associated with wetland areas (Table 14). Wetlands within 10 m 

of a stream tend to be of the sedge meadow (34.2%) or white cedar/alder swamp (32.7%) types 

but account for only 3.9% of all ISRO wetlands. The larger the corridor or buffer width selected, 

the more closely the distribution of wetland types mirrors the overall distribution of those types 

within ISRO. The adjacent wetland polygon method (2) estimates nearly twice the total riverassociated wetland area as the 100 m buffer method (3) (4,381 ha and 2,223 ha, respectively). 

This reflects the large wetland areas touching streams but also extending considerable distances 

from the stream vectors, such as in the Big Siskiwit River valley dominated by white cedar/alder 

swamp areas (Table 15, Figure 28). 

Groundwater

The groundwater of ISRO is generally poorly understood; there are no hydrologic models or 

maps of recharge zones or fracture zones for the park (Thornberry-Ehrlich 2008). However, its 

ecologic significance has been noted by some authors. Schlesinger et al. (2009) noted that newly

identified areas of deeper soils in ISRO have influence on groundwater storage and discharge, 

and that ISRO’s groundwater-fed seepage lakes will likely respond differently to climate change 
58

than its drainage lakes. Some groundwater-fed mineral springs are important sources of minerals 

for ISRO’s moose (Thornberry-Ehrlich 2008). 

Most of the limited study of groundwater in ISRO has related to the potential for development of 

drinking water supplies. Groundwater at ISRO is most likely to be found in fractured and jointed 

zones associated with faulting in bedrock, or in glacial sand and gravel deposits. In 1981, three 

test wells installed near Windigo revealed that the basaltic lava at that location did not yield

sufficient water at depths less than 50 m (Grannemann and Twenter 1982). Water at that depth or 

below might be salty, based on yields from similar rocks in the Keweenaw Peninsula. The 

authors recommended that further water supply exploration at Windigo occur in glacial deposits.

Static water levels were reported for two of the three wells; they were 15 m and 37 m above the 

level of Lake Superior. However, given the complexity of the geology, the significance of this 

finding is undetermined.

Shallow soils and a high water table at ISRO may make its groundwater vulnerable to 

contamination from human wastes, oil spills, and other spills or past disposal of toxic substances 

(Thornberry-Ehrlich 2008). 
59

Table 14. Stream lengths in Isle Royale National Park and their proximity to wetlands by type (TNC 1999, USGS 2000a, 2008).

Wetland Type (1) Stream Lengths Adjacent to Wetland Type

Meters Percent

White Cedar/Alder Swamp 66,076 32.3%

Sedge Meadow 70,398 34.4%

Speckled Alder Swamp 37,086 18.1%

Bluejoint Eastern Meadow 21,471 10.5%

Black Spruce-Dwarf Shrub Swamp 4,149 2.0%

Mixed Hardwood Swamp 4,666 2.3%

Dwarf Shrub Fen 521 0.3%

Total stream lengths adjacent to wetlands 204,365

Total of all stream lengths 277,981

Percent of all stream segments adjacent to wetlands 73.5%

Table 15. Wetland types in Isle Royale National Park and their proximity to streams (TNC 1999, USGS 2000a, 2008).

Wetland Type All Wetlands

(2)

Variable-width 

Corridor

(3)

200 Meter Stream 

Corridor

(4)

20 Meter Stream 

Corridor

Hectares Percent Hectares Percent Hectares Percent Hectares Percent

White Cedar/Alder Swamp 6,408 61.3% 2,840 64.8% 1,026 46.1% 132 32.7%

Sedge Meadow 1,519 14.5% 759 17.3% 604 27.2% 138 34.2%

Speckled Alder Swamp 974 9.3% 343 7.8% 288 12.9% 73 18.0%

Bluejoint Eastern Meadow 620 5.9% 219 5.0% 188 8.5% 42 10.5%

Black Spruce-Dwarf Shrub Swamp 480 4.6% 138 3.1% 62 2.8% 8 2.1%

Mixed Hardwood Swamp 336 3.2% 49 1.1% 41 1.8% 9 2.3%

Dwarf Shrub Fen 108 1.0% 34 0.8% 14 0.6% 1 0.3%

Total wetland hectares adjacent to 

streams 10,445 4,381 2,223 404

Percent of wetlands adjacent to streams 41.9% 21.3% 3.9%
60

Figure 28. River-associated wetlands in the Big Siskiwit River valley, Isle Royale National Park, by various delineation methods.
61

Biologic Resources

Fish Communities

Although early biologic surveys on ISRO documented fish communities (Ruthven 1909), the 

first larger scale survey of fishes was not until Koelz (1929), who sampled 38 lakes across the 

island. This survey documented lake depths and gave descriptive summaries of the inlet and 

outlet streams to many lakes. Despite additional studies documenting fish species on ISRO 

(Hubbs and Lagler 1949, Lagler and Goldman 1959, Sharp and Nord 1960), a study comparable 

in scale to the Koelz survey did not take place until 1995–1997 (Kallemeyn 2000). Because 

Kallemeyn (2000) is the most comprehensive and current study of inland fishes on ISRO, we use 

it as the primary source to report on fish resources. 

The main goals of Kallemeyn (2000) were to document changes or stasis in aquatic communities 

since 1929 and establish a standardized sampling protocol for future monitoring. Kallemeyn 

(2000) used minnow traps, seines, and gill nets to survey fish from 32 lakes and found 26 of 28 

fish species that were originally reported by Koelz (1929) and Hubbs and Lagler (1949) (Table 

16). Despite numerous nonnative fish species being present in Lake Superior, including invasive 

species such as the round goby (Neogobius melanostomus) and ruffe (Gymnocephalus cernuus), 

no new fish species, either native or nonnative to the Great Lakes, were found by Kallemeyn 

(2000). 

Northern pike and yellow perch are the most prevalent species in ISRO lakes, found in all but 

four of the 32 surveyed lakes. Northern pike are absent from Lake Desor, Forbes Lake, Harvey 

Lake, and Hatchet Lake; yellow perch are absent from Lake Desor, Hatchet Lake, Mud Lake, 

and Lake Wagejo. Blacknose shiner was the most common prey fish, found in 20 lakes. Lake 

trout were present only in Siskiwit Lake, probably due to its connectivity and conditions similar 

to Lake Superior. In general, larger lakes on ISRO have more fish species than smaller lakes.

Two species noted by Koelz (1929) but not collected by Kallemeyn in any lake during 1995–

1997 were brook trout and mottled sculpin (Cottus bairdi). Kallemeyn (2000) concluded that 

these species are still present in ISRO lakes because both have been collected during other recent 

studies on ISRO and from inlets and bays on Lake Superior near ISRO. Absence of these in 

Kallemeyn was thought to be due to sampling method.

A main component of Kallemeyn (2000) was documenting the loss or gain of fish species in 

lakes compared to earlier surveys. Numerous lakes gained species through apparent natural 

dispersal of fish upstream or downstream from other lakes or through upstream movement from 

Lake Superior. Failure to detect species in lakes where they were reported earlier was attributed 

to either sampling inefficiency for smaller species (i.e., stickleback, sculpin, and logperch are not

easily captured using beach seines or gillnets) or possible species loss for larger species. Two 

species that exemplify the latter situation were brook trout absent from Lake Desor and Hatchet 

Lake and northern pike from John Lake. Kallemeyn (2000) concluded that water temperature 

and/or dissolved oxygen levels were marginal for brook trout in Lake Desor and Hatchet Lake 

but stated that “there is no apparent explanation for the disappearance of northern pike from John 

Lake” while noting that a former beaver dam on its outlet stream is no longer present allowing 

more accessibility to Lake Superior. A potential ecologic explanation is that that the small size of 

John Lake (at 3.3 ha, only two ISRO lakes are smaller) and corresponding smaller population 
62

size of fishes relative to larger lakes may cause these population to be more susceptible to 

extinction MacArthur and Wilson 1967).

Table 16. Inland fish species found in lakes, Isle Royale National Park (from Kallemeyn 2000).

Scientific name Common name

Coregonus artedi Cisco

Coregonus clupeaformis Lake whitefish

Salvelinus fontinalis Brook trout *

Salvelinus namaycush Lake trout

Esox lucius Northern pike

Couesius plumbeus Lake chub

Margariscus margarita Pearl dace

Notemigonus crysoleucas Golden shiner

Notropis atherinoides Emerald shiner

Notropis heterolepis Blacknose shiner

Notropis hudsonius Spottail shiner

Notropis volucellus Mimic shiner

Phoxinus neogaeus Finescale dace

Pimephales promelas Fathead minnow

Semotilus atromaculatus Creek chub

Catostomus commersoni White sucker

Percopsis omiscomaycus Trout-perch

Lota lota Burbot

Culaea inconstans Brook stickleback

Pungitius pungitius Ninespine stickleback

Lepomis gibbosus Pumpkinseed

Etheostoma exile Iowa darter

Perca flavescens Yellow perch

Percina caprodes Logperch

Sander vitreus Walleye

Cottus bairdi Mottled sculpin*

Cottus cognatus Slimy sculpin

Cottus ricei Spoonhead sculpin

*Brook trout and mottled sculpin were identified by Koelz (1929), but not 

collected in samples from Kallemeyn (2000); these species are 

considered present on ISRO.

A fish that is listed as threatened in MI is the Siskiwit Lake cisco (Coregonus bartlettii) (MNFI 

2009a). Some confusion exists with taxonomic classification of this population and Great Lakes 

ciscoes in general. In the 2004 edition of Fishes of the Great Lakes, Hubbs and Lagler (2004) 

describe cisco from Siskiwit Lake as a subspecies of the shortjaw cisco (C. zenithicus), and 

MDNR has referred to these fish as a subspecies of lake herring (MDNR 2005). The American 

Fisheries Society (AFS) recognizes ciscoes from Siskiwit Lake as C. artedi (Nelson et al. 2004)

based on the genetic analyses from Turgeon and Bernatchez (2003). The common name ‘cisco’ 

is more often used than ‘lake herring;’ thus, the latter has been dropped from use by AFS 

(Nelson et al. 2004).
63

As noted earlier, riverine habitat in general on ISRO is understudied (also see Crane 2006), and 

fish communities in ISRO streams have received relatively little attention. Notable exceptions 

include investigations by Slade and Olson (1994) to report fish communities from several 

tributaries draining to Lake Superior and studies aimed at identifying coaster brook trout 

populations (Slade 1994, Quinlan et al. 1999). Gametes were collected from coaster brook trout 

from Big Siskiwit River and Little Siskiwit River in 1995 and 1999 to establish and maintain 

populations in hatcheries for reintroduction efforts (Newman et al. 2003). 

Kallemeyn (2000) commented that perennial and intermittent streams and rivers serve as 

corridors for fish dispersal between lakes and from Lake Superior. Perennial streams and rivers 

probably also serve as important spawning and rearing locations for many species. As also noted 

by Kallemeyn (2000), fish communities on ISRO exemplify the unique opportunities to study 

ecologic and evolutionary questions about fish dispersal and speciation in a relatively pristine 

setting. Management practices to protect inland lakes and streams should continue. A Fisheries 

Management Plan is currently in progress for ISRO.

Zooplankton, Phytoplankton, Macroinvertebrates, and Macrophytes

Surveys of invertebrate aquatic communities in ISRO lakes, streams, and wetlands have often 

taken place in conjunction with studies of water quality or fish communities. Toczydlowski et al. 

(1978) initiated one of the first baseline studies for water quality and aquatic invertebrates and 

plants from lakes and streams primarily on the southern portion of ISRO, including the Wallace 

Lake watershed. More recently, a study by Whitman et al. (2000) used systematic and 

standardized sampling techniques to document phytoplankton and zooplankton from Sargent 

Lake and Siskiwit Lake. Larson et al. (2000) analyzed zooplankton samples from 36 lakes, 32 of 

which were also the focus of the fish community and water quality survey by Kallemeyn (2000). 

We will use these studies as the primary sources for ISRO invertebrate communities.

Zooplankton: During 1995 and 1996, Larson et al. (2000) analyzed 55 plankton samples 

collected by Kallemeyn using a 63 μm mesh net at the deepest point of each lake. Single samples 

were taken from the majority of the sites; however, four samples were taken from Lake Ahmik, 

Angleworm Lake, Lake Desor, Sargent Lake, and Siskiwit Lake, and three samples were taken 

from Feldtmann Lake and Mud Lake. These samples were taken at different times during the 

summer of either 1995 or 1996.

Across all samples, species richness ranged from 3.00 to 15.00 with species diversity ranging 

between 0.6 and 2.39. Five species were found in >75% of the samples: the cladoceran 

crustacean Bosmina longirostris (46/55) and the rotifers Keratella cochlearis (54/55 samples), 

Conochilus unicornis (47/55), Ploesoma hudsoni (44/55), and Polyarthra dolichoptera (42/55). 

Across all samples, K. cochlearis and C. unicornis had relative abundances of 39.0% and 30.8%, 

respectively, illustrating the prevalence of these species in ISRO lakes. B. longirostris comprised 

<10% of the individuals in 46 samples. Density of rotifers or crustaceans, species richness, and 

species diversity were not correlated with any water quality variables or environmental 

characteristics from the lakes (Larson et al. 2000).

In concluding their report, Larson et al. (2000) noted that zooplankton assemblages across ISRO 

lakes are similar to each other and nearby mainland lakes. Zooplankton communities from ISRO 

lakes were distinct from zooplankton communities in Lake Superior, which are dominated by 
64

three copepod species not found in ISRO lakes. The authors also cautioned that further sampling 

is needed to assess interannual variation in zooplankton composition and recommended a subset 

of lakes based on water quality and spatial distribution to serve as a proxy for long-term 

monitoring activity.

Whitman et al. 2000) provided additional detail about the zooplankton and phytoplankton 

communities in Sargent Lake and Siskiwit Lake using samples collected during 1997 and 1998.

Zooplankton were collected from limnetic sites (deeper water) and littoral sites using an 80 μm 

or a 63 μm mesh net and preserved. The authors reported on the density and species composition 

calculated from triplicate samples taken from limnetic and littoral zones at multiple time periods 

between May and October between 1997 and 1999 in order to draw conclusions about temporal 

trends. 

Sargent Lake had similar total zooplankton density within the limnetic zone between 1997 and 

1998, with averages over the summer of 82 ± 10 individuals L-1 and 104 ± 20 individuals L-1 for 

1997 and 1998, respectively. Pronounced peaks occurred in early summer and late summer, with 

lowest density in mid-summer (Whitman et al. 2000). Zooplankton density in the littoral zone 

was lower than in the limnetic zone and showed a consistent decline in abundance in midsummer 

with a rebound in late summer (Whitman et al. 2000). The community consisted of 39 species,

dominated by rotifers and cladocerans, including abundant species such as C. unicornis and 

Keratella spp. also found by Larson et al. (2000). Whitman et al. (2000) concluded that the 

zooplankton community in Sargent Lake was typical of large, cold lakes from northern latitudes.

The zooplankton in Siskiwit Lake showed many contrasts to Sargent Lake during the concurrent 

sampling between 1997 and 1999. In particular, zooplankton density in the limnetic zone was 

lower in Siskiwit Lake, 22 ± 4 individuals L-1 and 17 ± 3 individuals L-1 in 1997 and 1998, 

respectively, probably due to lower primary productivity (Whitman et al. 2000). Additionally, 

zooplankton abundance in Siskiwit Lake showed just a single peak in late June to early July.

Thirty zooplankton taxa were found; the composition was evenly distributed, with no dominance 

by particular rotifer or cladoceran species. Because total density of zooplankton was low and 

variable between years and sampling locations, the authors cautioned about making 

interpretations from these data and recommended increased sampling efforts on Siskiwit Lake to 

confirm the true community composition.

W. Charles Kerfoot of MTU conducted zooplankton surveys of ISRO inland lakes in 2008 and 

2009; these data were not received in time for inclusion in this report.

Phytoplankton: Whitman et al. (2000) summarized phytoplankton communities sampled from 

limnetic and littoral zones of Sargent Lake and Siskiwit Lake during 1997, 1998, and 1999. They 

identified 55 and 57 taxa for Sargent Lake in 1997 and 1998, respectively, with abundant species 

including Cyclotella sp., Sphaerocystis sp., Chlorochromonas sp., and Synedra sp. In general, 

community composition was even between yellow-green algae, diatoms, and green algae, with 

some seasonal variation. In July 1997, diatoms reached a high of 48% of the total density in the 

littoral zone, while in May 1998, yellow-green algae were the dominant species (62%) in the 

limnetic zone (Whitman et al. 2000). 
65

Forty and 49 phytoplankton taxa were collected from Siskiwit Lake in 1997 and 1998, 

respectively. This community was considerably different from that of Sargent Lake. Diatoms in 

limnetic samples ranged from 60–80% of the total density and increased from 54% of the littoral 

samples in June to 87% of the total density by August. Cyclotella sp. and Dinobryon sp. were 

very abundant, while green algae, yellow-green algae, and other groups were never recorded 

higher than 20% of the community (Whitman et al. 2000).

Macroinvertebrates: Scientific descriptions of macroinvertebrate communities on ISRO are 

limited to notes from a few reports, a pair of master’s theses, and the aquatic inventory by 

Toczydlowski et al. (1978). Nichols et al. (2001a) reported that Bulimnea megasoma, a large 

snail, was collected nearshore in Siskiwit Lake and Lake Superior, and Johnson (1980) and 

Bowden (1981) summarized trends in invertebrates from stream habitats. We use Whitman et al. 

(2000) as the main description of macroinvertebrate communities because it is recent, the authors 

used standardized methods, and their intent was to continue sampling to build a long-term 

dataset. 

Whitman et al. (2000) collected benthic macroinvertebrates from limnetic and littoral zones of 

Sargent and Siskiwit lakes using an Ekman dredge sampler. Total invertebrate density in Sargent 

Lake was “about 3,000 m-2 in both the littoral and limnetic zones” during 1997. Chironomidae 

were the dominant group in the littoral zone. However, two measures of community diversity 

(Margalef’s and Shannon-Weiner) were always higher in the littoral zone because of a greater 

number of invertebrate species relative to the limnetic zone (Whitman et al. 2000). 

In 1997, the total invertebrate density in Siskiwit Lake was “about 4–5 times lower” in the 

littoral zone than the limnetic zone, with the amphipod Diporeia predominant in the benthic 

community of the limnetic zone and various insects dominating the littoral zone community 

(Whitman et al. 2000). Higher total abundance in the littoral zone did not persist in 1998, when 

density between the zones was similar. Similar to Sargent Lake, both measures of species 

diversity were higher in the littoral zone during 1997, but the Shannon-Weiner index was higher 

in the limnetic zone than the littoral zone in 1998 (Whitman et al. 2000). 

Mussels: Whitman et al. (2000) reported finding some sphaeriid clams (Pisidium sp.) in their 

benthic samples from Sargent and Siskiwit lakes, but the most comprehensive survey of ISRO 

mussels is by Nichols et al. (2001a), who visually inspected ISRO lakes and streams for unionid 

mussels, followed by systematic sampling from 11 lakes. No mussels were found in streams, 

most likely due to unsuitable substrate and heavy ice formation during winter. Across all lake 

sampling sites on ISRO, four species from two genera were found: Lampsilis luteola, L. radiata, 

Pyganodon cataracta, and P. grandis.

Three lakes had all four mussel species present, as well as individuals that were identified as 

hybrids between P. cataracta and P. grandis (Table 17). At least one mussel species was found 

in five of the eight remaining lakes. Feldtmann Lake, Hatchet Lake, and the smaller lake along 

the Minong Ridge Trail that the authors named “Leech” Lake did not have any mussels, despite 

having suitable substrate and biotic and environmental factors similar to ISRO lakes that support 

mussels (Nichols et al. 2001a). The authors could only speculate that the concentration of copper 

or other untested factors may prevent mussels from occupying these sites.
66

Mussel distribution within ISRO lakes appeared related to depth. Most individuals were found at 

depths <9.1 m; the authors attributed the lack of individuals at greater depths to lower 

temperature below the thermocline. Because mussels are filter feeders and can bioaccumulate 

contamination, analysis of tissue was undertaken in some individuals, but the few contaminants 

detected were “well below any concentration of concern” (Nichols et al. 2001a). Exotic mussel 

species such as zebra and quagga mussels were not found in this survey. The native unionid 

mussel populations were healthy and considered valuable because many species in streams and 

lakes from nearby mainland locations are imperiled or extinct. 

Table 17. Presence of unionid species in inland waters of Isle Royale National Park, 2000–2001. X = 

present, O = absent. (Nichols et al. 2001a).

Lake Unionid Species

Lampsilis 

luteola

L. 

radiata

Pyganodon 

cataracta

P. 

grandis

Pyganodon 

hybrids

Chickenbone X X X X X

Desor O O X O O

Feldtmann O O O O O

Hatchet O O O O O

Intermediate X X X X X

“Leech” O O O O O

Livermore O O X O O

LeSage O O X O O

Richie O X X X X

Siskiwit X X X X X

Whittlesey O O X X X

Freshwater Sponges: During their survey of unionid mussels, Nichols et al. (2001a) 

documented unique freshwater sponge colonies in four of 11 lakes visually surveyed on ISRO. 

Although sponges are common in water bodies, Nichols et al. (2001a) observed “tall sponges”

forming large colonies that are considered rare in freshwater systems. Further research was 

suggested to better understand the role sponges may have in primary production, contaminant 

cycling, and ecologic interactions (i.e., competition) with other species (Nichols et al. 2001a).

Further details about the distribution and identification of sponge species on ISRO comes from 

Meeker et al. (2007), who documented the presence of three sponges (Spongilla lacustris, 

Corvomeyenia everetti [classification marked as questionable], and Ephydatia mulleri) while 

surveying aquatic vegetation from lakes. At least one sponge species was found in Ahmik Lake, 

Amygdaloid Lake, Lake Eva, Forbes Lake, Intermediate Lake, Lake LeSage, Lake Richie, and 

Wood Lake. S. lacustris was the species most frequently encountered. 

Macrophytes: Whitman et al. (2000) estimated macrophyte coverage and community 

composition from multiple transects on Sargent Lake and Siskiwit Lake during August 2000. 

They reported 20 taxa and estimated 30% macrophyte coverage in the littoral zone for Sargent 

Lake. Although their specific definition of littoral zone was not given, it is assumed that their 

surveys progressed from the shoreline to the maximum depth where light was suitable for rooted 

vegetation. One notable species was alternate-leaved water-milfoil (Myriophyllum 

alterniflorum), a species of special concern in Michigan. In Siskiwit Lake, only eight taxa were 

found and were estimated to cover <1% percent of the littoral zone, probably due to rocky 

substrate and steep slope prevalent in this lake (Whitman et al. 2000). Given the high clarity of 
67

Siskiwit Lake, the authors left open the possibility that additional species may be present in 

unsampled locations away from the shoreline at depths difficult to survey.

Between 2003 and 2006, Meeker et al. (2007) collected aquatic plants and searched for exotic 

species in 36 ISRO lakes. The lakes were chosen primarily to overlap with the fish and water 

quality survey from Kallemeyn (2000), but additional lakes were included. An effort was made 

to compare plant communities from small lakes (<20 ha) to large lakes (>20 ha), which were 

thought to have communities similar to Lake Superior bays and coves.

In all, 402 wetland plant species were encountered. The nine species that were found in >50% of 

84 transects from large lakes were muskgrass (Chara spp., 72.6%), spikerush (Eleocharis 

palustris, 63.1%), water horsetail (Equisetum fluviatile, 79.8%), quillwort (78.6%), slender naiad 

(Najas flexilis, 76.2%), bullhead pondlily (Nuphar variegata, 54.8%), big-leaved pondweed 

(Potamogeton amplifolius, 57.1%), grass-leaved pondweed (95.2%), and Richardson pondweed 

(70.2%). The 16 species that were found in 50% or more of the 44 transects from small lakes 

were Beck’s water-marigold (Bidens beckii, 61.4%), woolly-fruit sedge (63.6%), muskgrass 

(50.0%), threeway sedge (Dulichium arundinaceum, 63.6%), needle spikerush (50.0%), 

spikerush (59.1%), water horsetail (81.8%), northern mannagrass (Glyceria borealis, 54.5%), 

quillwort (59.1%), bullhead pondlily (97.7%), big-leaved pondweed (65.9%), grass-leaved 

pondweed (90.9%), broad-leaved arrowhead (63.6%), hemlock water-parsnip (Sium suave, 

56.8%), floating-leaved bur-reed (Sparganium fluctuans, 59.1%), and common bladderwort 

(Utricularia vulgaris, 77.3%). The project also added 13 new taxa to the flora of ISRO. These 

included the aquatic lake cress (Armoracia lacustris) and Farwell’s water milfoil (Myriophyllum 

farwellii), both ranked as threatened in MI. The authors noted “a hint of separation” between 

large and small lakes in their ordination analysis and speculated that reasons might include 

differences in wave energy, water temperature, substrate, and nutrient availability (Meeker et al. 

2007).

The aggressive wetland invaders cattails and common reed were detected in several inland lakes. 

Specifically, individual plants or larger beds of cattails were found in 30 lakes (83.3%), and 

common reed was found in 11 lakes (30.6%) (Meeker et al. 2007).

Herptiles

Six species of anurans, three species of salamanders, one species of turtle, and two species of 

snakes are currently known within ISRO (Casper 2008). The anurans include one toad (eastern 

American toad, Anaxyrus americanus americanus) and five frogs (spring peeper, boreal chorus 

frog, northern green frog, mink frog [Lithobates septentrionalis], and wood frog [L. sylvaticus]). 

Spring peepers are considered to be in high abundance, chorus frogs in low abundance, and the 

other three of intermediate abundance (Egan 2005). Egan (2005) reported on annual calling 

surveys for frogs and toads at 42 points on the main island of ISRO (seven vernal pond sites, 

three wet meadow sites, one bog, 12 marsh sites, 15 wooded swamp sites, and four pond sites). 

Wet meadows, ponds, and marshes were preferred frog habitats; vernal ponds and wooded 

swamps were rarely used (Egan 2005). Beaver play a role in providing the ponds preferred by 

frogs, but their numbers in ISRO are declining; the effect of this ecologic change on frog 

populations is uncertain (Egan 2005). 
68

The three salamanders present are the blue-spotted salamander, central newt (Notophthalmus

viridescens louisianensis), and common mudpuppy (Necturus maculosus maculosus), although 

Casper (2008) expresses some uncertainty about the latter. Eastern red-spotted newts were also 

reported by Glase and Lafrancois (2007). Casper (2008) indicated that differentiation between 

eastern red-spotted newts and central newts is problematic in the region. The reptiles present are 

the northern red-bellied snake (Storeria occipitomaculata occipitomaculata), common garter 

snake (Thamnophis sirtalis), and western painted turtle (Chrysemys picta bellii) (Casper 2008). 

With the exception of the boreal chorus frog and the common mudpuppy, which were not found 

in Casper’s (2008) survey, resident species probably have park-wide distributions in appropriate 

habitats (Casper 2008).

Water Quality–Lakes

Despite the long history of ecologic research on ISRO, water quality monitoring efforts at ISRO 

have been few, with data collected from a limited number of lakes or streams for specific 

research programs. An aquatic baseline survey sampled six lakes in the late 1970s 

(Toczydlowski et al. 1978). Stottlemyer et al. (1998) surveyed 18 lakes in the early 1980s. The 

most complete characterization of ISRO inland lakes was done in Kallemeyn’s (2000) survey of

32 lakes in 1995–1997. Whitman et al. (2000) studied two of those lakes (Sargent and Siskiwit) 

in 1997 and 1998. Crane et al. (2006) provided detailed analysis of water quality studies 

conducted to that date and reproduced many of the reports’ summary tables; that work will not 

be repeated here. The most recent work is the sampling of nine lakes by Elias and VanderMeulen 

(2008) and Elias (2009) in 2007 and 2008, respectively; this work is intended to be 

representative of all ISRO lakes and is expected to be ongoing. A protocol has been developed 

for inland lake monitoring to standardize and guide future sampling efforts (Elias et al. 2008).

Toczydlowski et al. (1978) provided one of the earliest attempts to document biotic and abiotic 

conditions of water bodies on ISRO. As part of this effort, they sampled six inland lakes 

(Feldtmann, Intermediate, Richie, Siskiwit, Whittlesey, and Wood). They reported a mean pH of 

5.70 (range 5.25–6.50) and low buffering capacity, measured as alkalinity, and concluded that 

aquatic habitats on ISRO may be susceptible to acidification through atmospheric transport of 

ions in precipitation. A detailed analysis of the Wallace Lake watershed also laid the groundwork 

for long-term analysis of geochemical processing of precipitation (Stottlemyer and Toczydlowski 

1999b) discussed in the Air Quality section of this report. 

Stottlemyer et al. (1998) reported pH and other parameters from 18 lakes sampled in 1980 and 

1981. The mean pH was 7.2 ± 0.5 (mean ± standard deviation). Only one lake had a pH value

below 6.5, (Chickenbone Lake, 6.3) and 13 had pH values ≥ 7.0. These values, along with 

moderate to low values for NH4

+ (undetected in 15 lakes) and NO3- (10 lakes below detection 

limits), suggest that acidic precipitation is moderated by soil processes before reaching surface 

waters.

Whitman et al. (2000) surveyed Sargent Lake and Siskiwit Lake during 1997 and 1998 as part of 

an NPS program to monitor trends in lakes within national parks in the Great Lakes region. They 

provided a narrative description of the watershed conditions, shoreline habitat and development, 

presence of inlet and outlet streams, occurrence and size of islands, unique features about bay 

habitats, and use of the lakes by humans and wildlife, and reported lake morphometrics, water 

temperature from multiple sampling events, and water chemistry information. Sargent Lake is 
69

slightly alkaline. Mean littoral zone alkalinity was 38.64 ± 0.93 mg L-1 (mean ± standard error 

for all ranges in this paragraph). Mean pH was 7.97 ± 0.05. Mean specific conductance for 15 

sampling events from the littoral zone was 86.5 ± 2.64 μS cm-1

. Nitrate, nitrite, and ammonia 

were mostly below detection limits, and TP was low, suggesting that Sargent Lake is 

oligotrophic to slightly mesotrophic. Siskiwit Lake was also slightly alkaline (mean littoral zone

alkalinity 29.20 ± 0.34 mg L-1

). The mean pH was 8.13 ± 0.05. All measurements of specific 

conductance from the littoral zone were <90 μS cm-1, with a mean of 66.76 ± 2.02 μS cm-1 for 17 

sampling events. TP, nitrate, nitrite, and ammonia were mostly below detection. Siskiwit Lake is 

considered a hardwater lake and was classified by Whitman et al. (2000) as oligotrophic or 

slightly mesotrophic. In both Sargent and Siskiwit lakes, there were no significant differences 

between samples collected in the littoral zone and the limnetic epilimnion.

Kallemeyn (2000) conducted a comprehensive study of water quality on ISRO during 1996 and 

1997 by surveying a suite of 17 chemical parameters from 32 lakes known to contain fish. This 

survey covered a broad range of chemical parameters from the largest number of ISRO lakes 

ever sampled and used modern, standardized methodology. Angleworm, Sargent, and Siskiwit 

lakes exhibited notably high clarity, with Secchi disk depths >4.0 m. More details of 

Kallemeyn’s (2000) study are discussed in the individual parameter descriptions below. 

Qualitatively comparing the surveys from Toczydlowski et al. (1978) and Kallemeyn (2000), the 

water quality of ISRO lakes did not change during the nearly 20 years between sampling events.

To meet the goal of long-term monitoring of lakes in the Great Lakes region, Elias and 

VanderMeulen (2008) and Elias (2009) sampled water quality in nine index lakes on ISRO 

(Ahmik, Beaver, Desor, Feldtmann, George, Harvey, Richie, Sargent, and Siskiwit) as part of a 

larger monitoring effort developed by the NPS GLKN (Route and Elias 2006, Elias et al 2008). 

Multiple sampling events were conducted during 2007, 2008, and 2009, and will continue into 

the future, for lake water levels, a core water quality suite (clarity, temperature, specific 

conductance, DO, and pH), an estimate of primary productivity based on chlorophyll-a, relative 

concentrations of nutrients (phosphorus and nitrogen species), and an advanced water quality 

suite of nine additional parameters. Diatom communities were sampled as part of a separate 

project in 2007 but will be incorporated into the monitoring plan in the future.

Water quality can be evaluated in reference to narrative and numeric criteria intended to protect 

aquatic life and human health. In the case of ISRO, these criteria are determined by the State of 

Michigan but cannot be less stringent than USEPA standards (see Ledder 2005 for a discussion 

of these water quality standards for ISRO). They are included in MI Administrative Code (State 

of Michigan 2006b). Water quality can also be evaluated in terms of USEPA ecoregion nutrient 

reference criteria (USEPA 2000, 2001). The intent of these criteria is to “represent conditions of 

surface waters that are minimally impacted by human activities and thus protect against the 

adverse effects of nutrient overenrichment from cultural eutrophication” (USEPA 2000). They 

are based upon the 25th percentile of all sampled lakes in a USEPA region. Thus, water quality 

standards might be thought of as “what is harmful for some intended use,” while ecoregion 

nutrient reference criteria include a smaller set of parameters and might be thought of as “what is 

natural or normal in a geographic region.”

Water quality can also be evaluated in terms of changes over time. However, the limited data for 

ISRO inland lakes requires proceeding with caution. We have chosen to use the largest set of 
70

ISRO inland water data (Kallemeyn 2000) and the two most recent, but smaller, sets (Elias and 

VanderMeulen 2008, Elias 2009). In order to aggregate the data as much as possible, we 

averaged the Elias data for the two years (n=6) and compared the data for each lake for each 

parameter to the Kallemeyn data (n=1 or 2). We have plotted the results as a ratio (Figure 29), 

where values >1 (above the dashed black line) indicate an increase in the value between the time 

periods, and values <1 indicate a decrease. These comparisons must be interpreted with the 

understanding that equipment, methods, and personnel have changed over time, and metadata for 

past results are not always available.

Figure 29. Comparison of values for selected water quality parameters between 1995–1997 and 2007–

2008 (Kallemeyn 2000, Elias and VanderMeulen 2008, Elias 2009).

Water Clarity

The photic depth of 32 ISRO lakes in 1995–1997, as determined by Secchi disk readings, was 

1.3–9.0 m, with a mean of 2.9 m (Kallemeyn 2000). Similarly, photic depths for the nine index 

lakes were 1.4–7.8 m in 2007 and 2.2–7.2 m in 2008 (Elias and VanderMeulen 2008, Elias 

2009). In 2008, the Secchi disk was visible at the bottom of three lakes. Five lakes had Secchi 

disk depths less than the USEPA reference criterion of 4.2 m. Elias (2009) attributed this finding 

to tannin-stained waters and algae.

Temperature

Mean summer epilimnetic temperatures, or water column temperatures in unstratified lakes, 

ranged from 16.7 to 23.9o

C in 32 lakes in 1995–1997 (Kallemeyn 2000). Similarly, temperatures 

at 1.0 m depth ranged from 17.6 to 22.0oC in nine lakes in 2008 (Elias 2009). 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

TP

TN

Ca

Mg

Na

K

SO4

SiO2

Cl

Cond

DOC

Ratio of 2007-08 average to 

1995-1997 average 

Ahmik

Beaver

Desor

Feldtmann

George

Harvey

Richie

Sargent

Siskiwit
71

Specific Conductance

Specific conductance values ranged from 50.7 to 99.5 μS cm-1 in 32 lakes in 1995–1997 

(Kallemeyn 2000) and from 69 to 120 μS cm-1 in nine lakes in 2007 (Elias and VanderMeulen 

2008). Specific conductance values for nine lakes were higher by ratios of 1.0–1.3 from 1995–

1997 to 2007–2009 (Figure 29).

Dissolved Oxygen

Mean epilimnetic/water column DO levels were not included in Kallemeyn (2000); in the nine 

index lakes, they ranged from 7.7 to 9.5 in 2007 and 7.6 to 9.7 in 2008 (Elias and VanderMeulen 

2008, Elias 2009). However, DO levels in the hypolimnion of all stratified lakes except Siskiwit 

Lake dropped below 4 mg L-1

, the USEPA criterion for freshwater aquatic life, in 1995–1997 

and 2007 (Kallemeyn 2000, Elias and VanderMeulen 2008). In 2007, Lake Richie became 

anoxic at depths below 5 m; the likely reason is the dieoff of a large cyanobacteria bloom (Elias 

and VanderMeulen 2008).

pH

The pH values for 32 lakes ranged from 7.3 to 8.9 in 1995–1997, with only Lake Harvey 

exceeding 8.0 (Kallemeyn 2000). In 2007, mean near-surface pH ranged from 7.6 in Lake Ahmik 

to 8.5 in Lake Richie, with one value greater than the USEPA criterion of 9.0 for freshwater 

aquatic life. This exceedence likely related to the cyanobacteria bloom that also likely affected 

DO levels at depth (Elias and VanderMeulen 2008). Three lake means were 8.0, and three were 

>8.0. In 2008, mean near-surface pH values ranged from 7.5 in Lake Ahmik to 8.4 in both Lake 

Harvey and Lake George. One lake mean was 8.0, and four were >8.0. Elias (2009) suggests that 

pH levels may be increasing over time. A very small data set (three lakes that were sampled in 

1980–1981, 1995–1997, and 2007–2008) also suggests this (Table 18); future sampling should 

be able to shed further light on this possible trend. 

Major Ions

The ionic composition of ISRO inland lakes is characteristic of lakes in the temperate zone 

(Kallemeyn 2000). Among cations, proportions of Ca2+ and Mg2+ are higher in lakes associated 

with the Copper Harbor conglomerate and sandstone and conglomerate outcrops (Kallemeyn 

2000). Ca2+ values in 32 ISRO lakes ranged from 5.8 mg L-1 in Angleworm and Sargent Lakes to 

14.0 in Patterson Lake in 1995–1996 (Kallemeyn 2000). Ca

2+ and Mg2+ appear to have increased 

between 1995–1996 and 2007–2008; ratios for nine lakes were 1.0–1.7 (Figure 29). Values for 

Lakes Desor, George, and Richie also generally increased from 1980–1981 to 2007–2008 

(Figure 30) The Ca2+ increase, if verified in future sampling, is of concern because the minimum 

Ca2+ threshold for zebra mussel settlement and growth is 8–12 mg L-1, with peak mussel 

densities at concentrations ≥ 20 mg L-1 (Jokela and Ricciardi 2008 and citations within). Ratios 

of Na+ also increased, but ratios of K+ decreased for nine lakes between 1995–1996 and 2007–

2008 (Figure 29). 
72

Table 18. Comparison of water quality data for selected parameters for three lakes sampled in 1980–

1981, 1995–1997, and 2007–2008, Isle Royale National Park (Stottlemyer et al. 1998, Kallemeyn 2000, 

Elias and VanderMeulen 2008, Elias 2009).

Lake pH (pH units) Specific conductance (μS cm-1) Ca (mg L-1)

1980-81 1995-96 2007-08 1980-81 1995-96 2007-08 1980-81 1995-96 2007-08

Desor 7.9 7.9 8.25 88 88 103.0 7.4 11.7 12.65

George 7.0 7.9 8.55 94 92 118.5 10.1 17.5 20.65

Richie 7.5 7.5 8.20 77 68 77.5 6.3 9.8 9.60

Mg (mg L-1) Na (mg L-1) K (mg L-1)

1980-81 1995-96 2007-08 1980-81 1995-96 2007-08 1980-81 1995-96 2007-08

Desor 5.49 3.47 4.10 1.84 1.83 1.80 0.51 0.72 0.5

George 1.48 1.56 1.95 0.46 0.96 1.05 0.04 0.15 0.1

Richie 2.60 2.90 2.95 1.45 1.49 1.60 0.23 ND 0.3

NH4-N (μg L-1) NO3-N (μg L-1) SO4 (mg L-1)

1980-81 1995-96 2007-08 1980-81 1995-96 2007-08 1980-81 1995-96 2007-08

Desor ND 19 5.0 ND 13 2.5 4.32 2.55 3.45

George ND <10 4.0 154 <5 1.5 3.70 2.29 2.55

Richie ND <10 8.5 ND <5 2.0 5.62 3.24 3.90

Cl (mg L-1)

1980-81 1995-96 2007-08

Desor 0.32 0.87 0.90

George 0.28 0.29 0.90

Richie 0.64 1.03 1.25

Figure 30. Comparison of calcium and magnesium values for three lakes sampled in 1980–1981, 1995–

1997, and 2007–2008, Isle Royale National Park (Stottlemyer et al. 1998, Kallemeyn 2000, Elias and 

VanderMeulen 2008, Elias 2009).

0

5

10

15

20

25

1980-81 1995-97 2007-08

mg L-1

Desor Ca

George Ca

Richie Ca

Desor Mg

George Mg

Richie Mg
73

Among major anions, SO4

2- appeared to have decreased between 1980–1981 and 1995–1996 

(Figure 31). Crane et al. (2006) suggested that the decrease may have been caused by more 

stringent air quality regulations. However, SO4

2- in nine index lakes increased slightly from 

1995–1996 to 2007–2008 (Figure 29). Cl- in nine index lakes apparently increased from 1995–

1996 to 2007–2008, with ratios from 1.0–4.0, and had an upward trend from 1980–1981 to 

2007–2008 (Figure 29, Figure 31). 

Figure 31. Comparison of sulfate and chloride values for three lakes sampled in 1980–1981, 1995–1997,

and 2007–2008, Isle Royale National Park (Stottlemyer et al. 1998, Kallemeyn 2000, Elias and 

VanderMeulen 2008, Elias 2009).

Dissolved Silica

Silica is an important nutrient for freshwater sponges and diatom algae. Some of the nine lakes 

sampled by Elias and VanderMeulen (2008) showed great variability throughout the summer 

season, reflecting uptake and release by organisms. Thus, comparisons between years become 

even more difficult, but ratios between 1995–1997 and 2007–2008 were generally <1, with a 

range of 0.3 in Lake George to 1.7 in Lake Ahmik (Figure 29). The September 2007 silica values 

for seven sampled lakes were 1.0–12.0 mg L-1 SiO2, within the range considered sufficient for 

diatom production (Elias and VanderMeulen 2008).

Alkalinity

Alkalinity ranged from 20.8–53.5 mg L-1 in 32 ISRO lakes from 1995–1997; 19 were soft-water 

lakes (20–39 mg L-1 alkalinity) while the other 13 had medium alkalinity (Kallemeyn 2000). 

From 2007 to 2008, the range of alkalinity values was 22–58 mg L-1, and the only lake with 

mean alkalinity below the acid rain susceptibility threshold of 25 mg L-1 (Taylor 1984) was 

Feldtmann Lake in 2008. Alkalinity for nine lakes appeared unchanged between 1995–1997 and 

2007–2008, with ratios ranging from 1.0 to 1.1 (Kallemeyn 2000, Elias and VanderMeulen 2008,

Elias 2009) (Figure 29). 

0

1

2

3

4

5

6

1980-81 1995-97 2007-08

mg L-1

Desor SO4

George SO4

Richie SO4

Desor Cl

George Cl

Richie Cl
74

Dissolved Organic Carbon

Dissolved organic carbon (DOC) values in 32 ISRO lakes from 1995 to 1997 ranged from 5.0 in 

Siskiwit Lake to 15.3 in Epidote Lake (Kallemeyn 2000). DOC for nine lakes appeared mostly 

unchanged to slightly higher between 1995–1997 and 2007–2008, with ratios ranging from 1.0–

1.1 (Figure 29). Elias and VanderMeulen (2008) reported that DOC sources in these nine ISRO 

lakes were both autochthonous and allochthonous, and high enough to attenuate light and reduce 

photosynthesis.

Chlorophyll-a and Trophic State Indices

Chlorophyll-a values in 32 ISRO lakes from 1995 to 1997 ranged from 0 mg m-3 in Scholts Lake 

to 7.68 mg m-3 in Lake Eva (Kallemeyn 2000). As with dissolved silica, chlorophyll-a values 

vary considerably at one site throughout a sampling season, and so comparisons between sample 

sets are difficult. However, for nine ISRO lakes sampled both in 1995–1997 and 2008, only four 

of the earlier samples fell within the range of the more recent samples (Table 19); for four lakes, 

recent samples had higher chlorophyll-a ranges, and only one (Lake Desor) had a lower range. 

The significance of this disparity is unknown and may be determined by future annual sampling. 

Table 19. Comparison of chlorophyll-a values for nine lakes sampled in 1995–1997 and 2008, Isle Royale 

National Park (Kallemeyn 2000, Elias 2009).

Lake 1995–1997 2008 mean 2008 range

Ahmik 1.27 1.9 1.71–2.20

Beaver 0.53 2.6 2.38–2.79

Desor 3.80 2.6 2.23–2.84

Feldtmann 0.27 4.7 2.89–7.48

George 1.00 1.6 0.46–2.96

Harvey 2.32 2.4 1.97–2.84

Richie 2.86 6.0 5.03–8.42

Sargent 0.07 2.5 1.66–3.34

Siskiwit 1.07 1.0 0.75–1.45

The trophic state of a lake is based on the total weight of its living biologic material at a specific 

location and time (Carlson and Simpson 1996). Carlson’s trophic state indices (TSIs) use algal 

biomass as the basis for trophic state classification. Three variables (chlorophyll pigments, 

Secchi depth, and TP) independently estimate algal biomass, with chlorophyll being the best 

predictor (Carlson 1977). Carlson TSIs were calculated for 32 ISRO lakes by Kallemeyn (2000), 

for Sargent and Siskiwit Lakes by Whitman et al. (2000), and for nine ISRO lakes by Elias and 

VanderMeulen (2008) and Elias (2009) (Table 20). Since Kallemeyn (2000) provided only 

summary data, comparisons for individual lakes between 1995–1996 and 2007–2008 could not 

be made. 

Using chlorophyll–a values, Kallemeyn (2000) found 47% of the 32 sampled lakes to be 

oligotrophic, 50% to be mesotrophic, and 3% to be eutrophic in 1995–1997. In 2008, Elias 

(2009) found only Siskiwit Lake to be oligotrophic by this standard, with the other eight lakes 

being mesotrophic. However, Kallemeyn (2000) and Elias (2009) did not use the same 

breakpoint for dividing oligotrophic lakes from eutrophic ones (35 vs. 30, respectively). If 

Kallemeyn’s breakpoint was applied to Elias’s data, Lake George, with a chlorophyll-a TSI of 

32, would also be categorized as oligotrophic. 
75

Kallemeyn (2000) found that the Secchi TSI gave the greatest number of mesotrophic (88%) and 

eutrophic (9%) lakes. He attributed this to the negative relationship between transparency and 

both color and DOC. Elias (2009) found that Siskiwit Lake was mesotrophic by its Secchi TSI, 

although the difference in values (29 for chlorophyll-a TSI and 32 for Secchi TSI) was slight. On 

the other end of the scale, Elias and VanderMeulen (2008) found Lake Richie to be eutrophic in 

2007 (TP and Secchi TSIs of 55). In 2008, Lake Richie was at the upper end of the scale for 

mesotrophic (TSI ≥ 50) lakes, with chlorophyll-a and TP TSIs of 50 and a Secchi TSI of 47 

(Elias 2009).

Table 20. Trophic state indices (TSIs) for inland lakes, Isle Royale National Park (Kallemeyn 2000, Elias 

and VanderMeulen 2008, Elias 2009).

Year Assessment 

Method N Trophic State

Oligotrophic Mesotrophic Eutrophic

1995–1997 TP TSI 32 8 (25%) 24 (75%) 0

Secchi TSI 32 1 (3%) 28 (88%) 3 (9%)

Chl-a TSI 32 15 (47%) 16 (50%) 1 (3%)

2007 TP TSI 9 1 (11%) 7 (78%) 1 (11%)

Secchi TSI 8 1 (13%) 7 (88%) 0

Chl-a TSI - - -

2008 TP TSI 9 1 (11%) 8 (89%) 0

Secchi TSI 9 0 9 (100%) 0

Chl-a TSI 9 1 (11%) 8 (89%) 0

Total Phosphorus and Total Nitrogen

Mean summer TP for nine ISRO index lakes from 2007 to 2008 ranged from 4 μg L-1 in Siskiwit 

Lake to 25–34 μg L-1 in Lake Richie (Elias and VanderMeulen 2008, Elias 2009). The USEPA 

reference criterion for TP for lakes in the ISRO ecoregion is 9.69 μg L-1 (USEPA 2000). Eight 

and seven of the index lakes exceeded this criterion in 2007 and 2008, respectively. In 

Kallemeyn’s (2000) study of 32 ISRO lakes from 1995 to 1997, TP ranged from 5–18 μg L-1

. 

The ratios of current to past TP between 1995–1997 and 2007–2008 for the nine current index 

lakes ranged from 0.3 for Siskiwit Lake to 3.0 for Lake Richie (Figure 29). 

Mean summer TN values for nine ISRO index lakes ranged from 0.241 mg L-1 in Siskiwit Lake 

to 0.664 mg L-1 in Lake Richie in 2007 (Elias and VanderMeulen 2008) and from 0.220 in 

Siskiwit Lake to 0.766 mg L-1 in Lake Ahmik in 2008 (Elias 2009). The USEPA reference 

criterion for TN for lakes in the ISRO ecoregion is 0.4 mg L-1 (USEPA 2000). Six and seven of 

the index lakes exceeded this criterion in 2007 and 2008, respectively. In Kallemeyn’s (2000) 

study of 32 ISRO lakes from 1995 to 1997, TN ranged from 0.25 to 0.65 mg L-1. The ratios of 

current to past TN between 1995–1997 and 2007–2008 for the nine current index lakes ranged 

from 0.3 in Lake Desor to 1.3 in Feldtmann Lake, Lake Harvey, and Lake Richie (Figure 29). 

Thus, TN levels appear less variable than TP levels in the index lakes. Elias (2009) noted that 
76

these lakes do not receive direct anthropogenic inputs, so sources of TP and TN are likely 

resuspension within the lakes or atmospheric deposition.

Water Quality–Streams 

Two stream monitoring programs provide long-term datasets allowing temporal trends to be 

analyzed. A USGS gaging station on Washington Creek (Figure 21) provides approximately 30 

years of data ending in 2003 as part of the Hydrologic Benchmark Network, and the NPS 

Watershed Research Program monitored acidic deposition, climate change, and other large-scale 

stressors in the Wallace Creek watershed from 1982 to 1996 (summarized by Stottlemyer et al. 

1998). GLKN will begin pilot monitoring work on Washington and Benson Creeks in 2010.

Washington Creek is the longest flowing water body on ISRO, draining much of the northwest 

part of the island. Mast and Turk (1999) summarized station data for the years 1967–1995. The 

number of samples was 141–145, with exceptions noted below. The median field pH was 7.5, 

median alkalinity was 61 mg L-1 as CaCO3, and median specific conductance was 130 μS cm-1. 

Median values for major cations were Ca2+,18.0 mg L-1; Mg2+, 5.1 mg L-1; Na+, 3.0 mg L-1; and 

K+

, 0.5 mg L-1. Among anions, median SO4

2- was 5.8 mg L-1 and median Cl- was 3.0 mg L-1

. 

Median NO3+NO2-N was 0.44 mg L-1 (n=102) and median ammonium was 0.04 mg L-1 (n=61)

(Mast and Turk 1999). Washington Creek did have a few exceedences for metals and pH, which 

are discussed in the section on Indicators.

The authors concluded that Washington Creek was well buffered, and base cation, silica, and Clconcentrations were related mainly to geologic sources in the basin, while SO4

2- was derived 

primarily from atmospheric sources. The report also noted that observed elevated SO4

2-

concentrations in the late 1980s may have been related to the analysis method used between 

1986 and 1989. However, decreases in Ca2+

, Mg2+, and Clwere likely caused by environmental 

change; a statistically significant decrease in annual mean discharge at the gaging station 

occurred between 1965 and 1980, and National Atmospheric Deposition Program (NADP) air 

monitoring stations also noted declines in these ions in precipitation between 1980 and 1992 

(Mast and Turk 1999).

Water quality monitoring in the Wallace Creek watershed, draining into the western end of 

Moskey Basin, was initiated in 1982 as part of the NPS Watershed Research Program. The main 

focus of this program was to measure ecosystem structure and function in response to 

atmospheric deposition and climate change in study sites in four national parks (ISRO, Olympic, 

Rocky Mountain, and Sequoia-Kings Canyon). Stottlemyer et al. (1998) summarized data 

collected from 1982 to 1996 that included surveys of several streams and lakes on ISRO and 

concluded that surface waters are well buffered and parameters indicative of acidic deposition 

(i.e., SO2) declined after passage of the Clean Air Act. 

In planning for initiation of the Watershed Research Program on ISRO, numerous sites were 

sampled once from 1980 to 81, including 26 stream sites. As reported by Stottlemyer et al. 

(1998), most streams had moderate values for chemical parameters, including pH (range 6.2–7.8) 

and conductivity (range 55–162 μS cm-1). Ranges for major cations were Ca2+, 1.5–15.8 mg L-1; 

Mg2+, 1.3–17.0 mg L-1; Na+, 0.5–5.4 mg L-1; and K+, less than detection to 1.3 mg L-1. Among 

anions, the range for SO4

2- was 1.4–21.9 mg L-1

, and the range for Cl- was less than detection to 

1.9 mg L-1

. The ranges for nitrate and ammonium were less than detection to 0.99 mg L-1 and 1.3
77

mg L-1

, respectively. The survey revealed that ISRO surface waters were not susceptible to acid 

precipitation, and lower specific conductance and pH waters were dominated by high 

concentrations of dissolved organics (Stottlemyer et al. 1998). Because precipitation is processed 

by snowpack or soils before reaching surface water, more recent studies from the Wallace Creek 

watershed focus on possible changes in biogeochemistry, surface water quality, and nutrient 

cycling given potential climate change scenarios (Herrmann et al. 2000, Stottlemyer et al. 2002).
78

Terrestrial Resources

The terrestrial communities of ISRO have been viewed and studied at both coarse and fine 

scales. At the coarse scale, the vegetation is often placed into three broad community types 

consisting of shoreline vegetation and two types of forest vegetation: boreal forest and northern 

hardwoods. Many ecologic studies (e.g., Risenhoover and Maass 1987, Pastor et al. 1988) have 

not distinguished among the many variants of the boreal forest or the deciduous forest types. 

At a fine scale, detailed botanic and classification efforts have enumerated up to 52 associations 

(TNC 1999), including various shoreline communities, meadows, shrublands, woodlands, and 

deciduous and/or evergreen forests. At least six new community types were identified in this 

effort (white cedar-sweet gale [Myrica gale] scrub fen, Canada yew [Taxus canadensis] mixed 

shrubland, yellow birch [Betula alleghaniensis]-spruce forest, white spruce [Picea glauca] rocky 

woodland, Great Lakes boreal talus woodland, and thimbleberry [Rubus parviflorus] shrubland). 

They also identified at least three unusual community types—the twig rush wet meadow, boreal 

calcareous seepage fen, and the sweet gale shrub fen. At least two from the ‘new and unusual 

group’ (the white cedar–yellow birch forest and the boreal calcareous seepage fen) are globally 

rare. 

The plant composition of ISRO is quite valuable for its diversity, and various estimates have 

been made over time of the number of rare or special plants found there. Judziewicz (1995) 

reported 102 “species of concern” in ISRO. Judziewicz (1997) quoted a MDNR report stating 

that ISRO contains over 70 plant “species of concern.” A GLKN report on Great Lakes national 

parks (NPS ca. 2003) listed “over 80 species of state-listed rare” plants. A recent NPS 

environmental impact statement (NPS 2008b, MNFI 2009b) listed 55 species that are currently 

state-endangered, threatened, or of special concern. In general, these changes are the result of 

differences in definitions between authors and not an indication that plant species are widely 

disappearing from ISRO.

The greatest botanic value of the park lies in its disjunct populations, most of which are found 

along the Lake Superior shoreline (Judziewicz 1995, 1997, 2004) and on Passage Island. This 

group contains 21 arctic and alpine species and 12 species whose ranges are centered in the 

western U.S. (Judziewicz 1995). The majority of these plants are found on S–SE-facing slopes at 

the NE end of the island (Judziewicz 1995), but two other areas (“nodes”) have secondary 

concentrations of these species. These disjunct populations and other regionally uncommon 

species were part of the 102 “species of concern” Judziewicz (1995) listed for the park. 

Judziewicz (1997) documented 12 plant communities on Passage Island alone, five of which are 

dominated by woody species. Many of the species of concern at the state level (34) are on 

Passage Island (Judziewicz 1997). 

The detailed surveys conducted by Judziewicz (1995, 1997) are invaluable in their contribution 

to our understanding of the flora of ISRO. His surveys updated and refined previous reports of 

occurrence, distribution, and abundance of many ‘uncommon–to–rare’ species, and he found that 

many of these are in fact more abundant and found in more places than previously reported. 

Judziewicz (1995) also reported a species—dwarf mountain cranberry (Vaccinium vitis-idaea)—

that had not been documented anywhere in Michigan since 1868. On the other hand, at least 

seven species previously reported were not found by Judziewicz (1995, 1997).
79

A detailed and useful study by Hansen et al. (1973), which focused on forests, listed at least 16 

forest types; they also described minor variants of several of these. Though these authors 

sampled the understory, only the overstory was used in their classification. Their criterion for 

naming a ‘type’ was the species that comprised 50% or more of the overstory. Thus, their effort 

is relatively fine scale, but essentially ignored the subordinate layers in defining a community 

type. The forest types were mapped using 1957 aerial photographs, and a cover type had to be 

relatively homogenous and distinguishable from adjacent forests based on composition, age 

(size), or “developmental differences.” They tabulated the acreage by cover type and also 

estimated the amount of shrubs, lakes, rock outcrops, and beaver ponds. This mid-20th century 

assessment found that upland boreal forest types collectively covered almost 72% of the land 

surface of the island, lowland boreal types (black spruce, tamarack [Larix laricina], and northern 

white cedar) occupied 9.3%, and the northern hardwood type occupied 7.3%.

Due to the relative isolation of the island, the upland plant and animal communities are relatively 

simple; that is, they contain only a subset of the species typically associated with these plant 

communities in the nearby continental areas of MN, WI, MI, and Ontario. ISRO as a whole, and 

the communities in general, also have a much lower exotic species presence, both in terms of 

number of species (approximately 15% of the flora) (NPS 2005) and the abundance of those 

species. 

Historic Vegetation 

One useful perspective for assessing the current status and condition of ISRO terrestrial 

ecosystems is to look at the changes in plant community composition and distribution since the 

last glacial retreat; another is the landscape conditions just prior to extensive European 

settlement. Pre-European settlement condition(s) should not be viewed as ‘the benchmark’

because they are simply a set of conditions at one point in time, and these conditions fluctuate 

naturally (Swetnam et al. 1999). In the eastern U.S., the pre-settlement landscape has been 

frequently characterized by use of the General Land Office survey notes (Manies and Mladenoff 

2000).

Flakne (2003) studied sediment cores from two lakes—Lake Ojibwa in the NE end surrounded 

by boreal forest and Lily Lake in the SW end surrounded by northern hardwoods—to describe 

changes in vegetation since approximately 10,000 years before present (BP). Flakne concluded 

that the overarching trends matched those noted in the region. The strongest patterns for woody 

species were dominance by spruce early in the Holocene due to a cooler climate and an increase 

in pine dominance in the mid-Holocene due to drier conditions. In the late Holocene, the two 

sites diverged as precipitation increased. A typical boreal mix established around Lake Ojibway, 

whereas birch dominated in the Lily Lake watershed. Throughout the past 9,000 years, pine and 

birch have strongly dominated the pollen profile. There was a shift from pine to birch domination 

approximately 4,000 years BP, as the dry period of the mid-Holocene waned.

Janke et al. (1978) utilized General Land Office records (survey conducted 1847–1848) to 

compare the “upland boreal forests” of ISRO to the forests of 1974, restricting their sampling to 

areas less than 244 m above mean sea level. The 1974 data were split between areas burned by 

1936 fires and those not burned. They found massive shifts in some species, including large 

reductions in the relative density of balsam fir and northern white cedar, a large increase in paper 

birch, and a modest increase in quaking aspen. Tamarack was uncommon (2% relative density) 
80

in the 1840s but not found at all in 1974. The burned area had much less balsam fir, less aspen,

and less spruce, but considerably more paper birch than the unburned areas. A highly significant 

shift in the shrub layer was also noted. Canada yew was the most common shrub noted by the 

surveyor in 1847–1848, and thimbleberry was not noted at all. By 1974, yew was completely 

absent from the main island, whereas thimbleberry was found at 51% of the locations sampled.

Current Vegetation

In 2008, the USDA–Forest Service inventoried 51 locations on ISRO as part of their annual 

Forest Inventory and Analysis (FIA) nationwide long-term, permanent, plot-based monitoring 

program. This equates to one sample per 1,012 ha, and thus the precision of estimates for 

uncommon forest types is low; however, the estimates are adequate for the common forests and 

for all forested areas combined. Due to differences in forest type classification, it was not always 

possible to align these estimates with those of Hansen et al. (1973). However, it was generally 

possible to match the forest types, and thus make valid comparisons over time. Therefore, the 

primary values of these data are to illustrate broad trends. Forty-seven of the ISRO sample 

locations were classified as forestland (USDA–Forest Service Northern Research Station, 

Houghton, MI, Scott Pugh, Research Scientist, pers. comm.) and are the basis for the following 

characterization of current forest conditions. The data summaries specific to ISRO were 

extracted from the FIA website with the program ‘Evalidator’ with the assistance of Scott Pugh.

These data suggest some very significant changes in forest community type abundance since the 

late 1960s (based on the extensive survey of Hansen et al. 1973). Total forest land increased 

approximately 2,429 ha, and the northern hardwood forest type(s) exhibited an increase from 

approximately 10% to almost 23%. The upland boreal forest types have exhibited a concurrent 

decrease from 71.5% to approximately 52.6%. Among the lowland forest types, Hansen et al. 

(1973) reported ‘black spruce–northern white cedar’ as the most abundant (4,089 ha). The FIA 

data reveal that 10,628 ha are dominated by northern white cedar today, and an additional 445 ha 

is a mixed black spruce-balsam fir-northern white cedar forest type. Though a small, but 

unknown, portion of this is uplands, the data clearly document that a large area has succeeded 

from black spruce to northern white cedar. 

Overstory age data were also extracted from the FIA website. To simplify reporting, we have 

grouped the age data into 10-year age classes from 46 to 96 years, and into a young forest 

ranging from 16 to 45 years. The two most common age classes are > 100 years and 86–96 years, 

and both are dominated by northern white cedar and northern hardwood forest types. These data 

corroborate the successional changes noted in the paragraph above. The third most common age 

class is 46–56 years, and paper birch is the most common type in this group. However, this 

group, which partly originates from the 1936 fires, is not the most abundant for birch; there is 

about 60% more birch acreage in the 76–86 years age class, indicating that a large portion of 

paper birch forests originated in the 1920s. The dominant age class for other common forest 

types is balsam fir, 46–56 and 66–76 years (roughly tied), and aspen, 76–86 years. 

Approximately 4% of the landscape is occupied by forest <46 years old. Collectively, these data 

indicate the park is dominated by mature, but not old-growth, forest, and that there has been very 

little severe disturbance for approximately 50 years.

Most of the associations identified in the USGS–NPS Vegetation Mapping Program have not 

been studied in detail, although GLKN will begin terrestrial vegetation monitoring in 2010. For a 
81

strong majority, the only descriptions of entire communities are the ones produced as part of this 

mapping and classification effort (TNC 1999). The 52 associations were placed in 14 Ecologic 

Groups, which will serve as the structure for more detailed descriptions when available. Groups 

2, 3, and 5 are primarily aquatic and are covered in other sections of the report. The ecologic and 

botanic investigations that have taken place at ISRO either pre-dated the Classification work, or 

the investigators were unaware of it; thus, the vegetation descriptions in these studies cannot 

always be linked to a particular association, but we can place them in an Ecologic Group.

Boreal Associations, Uplands (Ecologic Groups 8-11, 13)

These communities include all those dominated by woody vegetation and found on upland sites; 

i.e., the soil is not saturated for much of the growing season. It is important to note that several 

species (e.g., northern white cedar and paper birch) also occur in lowland forest types, and 

several of the woody species (paper birch, aspen, balsam fir, and white spruce) occur as minor 

elements in the Northern Hardwood Forest & Woodland Group (Ecologic Group 12).

Boreal associations are the dominant group of plant communities at ISRO, and one or more of 

these occupy the vast majority of the near-shore habitat, most slopes and ridge tops on the NE

two-thirds of the island, and other places where the soil is shallow (Figure 32, Table 21) (Pastor 

et al. 1988, Stottlemyer and Toczydlowski 1999a). Ecologic Group 10, the Northern Spruce-Fir 

(Hardwood) Forests, is the most abundant group in this association, covering just over 20,000 ha

(TNC 1999). The tree species that commonly define this group include balsam fir and white 

spruce, with lesser amounts of paper birch, quaking aspen, or balsam poplar (Populus balsamea). 

Ecologic Group 9, Northern Mesic Conifer (Hardwood) Forests, covers 1,627 ha in ISRO. In this 

group, white cedar is the most abundant canopy species, and balsam fir is typically a codominant. The white cedar–yellow birch forest type is a variant in this group that is rather 

unique. Occasionally, black spruce, yellow birch, jack pine (Pinus banksiana), and white pine 

(P. strobus) are found in the overstory. Ecologic Group 8, Northern Dry Conifer (Hardwood) 

Forests and Woodlands, almost always contains one species of pine as a dominant and is found 

predominantly along the south shore, with smaller amounts on ridges and drier slopes in the 

interior; it makes up 765 ha in ISRO (Figure 32, Table 21) (TNC 1999, USGS 2000a).

Aspen and/or paper birch are the species that largely define the Boreal Hardwood Forests and 

Woodlands group, Ecologic Group 11. They can form pure stands or occur in almost any 

proportional mixture. This forest type is largely restricted to elevations below 300 m (Albert 

1995) and covers 13,450 ha in ISRO (TNC 1999, USGS 2000a). The aspen-birch type often 

functions as a classic pioneer community. Balsam fir and white spruce commonly establish in the 

understory of this type and gradually replace aspen and birch. In forests of this type ranging in 

age from 60 to 120 years, tree basal areas ranged from 6.9 to 57.4 m2 ha-1 (mean = 25.7) and tree 

density averaged 741 stems ha-1. The upper canopy exceeded 24.4 m in height, and tree 

diameters ranged from 2.5 to 58.4 cm (Hansen et al. 1973). Albert (1995) reported that fir and 

thimbleberry often dominate the “short shrub” layer in the aspen-birch (fir, spruce) forest type. 

Hansen et al. (1973) found at least 19 species in the shrub layer (across all stands), the most 

speciose by far of the cover types they reported. Seven taxa averaged more than 240 stems ha-1

(see Hansen’s Table 6 for composition and exact numbers). Reproduction of trees taller than 0.3 

m in this type was dominated by balsam fir, mountain ash (Sorbus decora), and aspen (Hansen et 

al. 1973). Hansen and co-workers sampled about 30 stands in the ‘birch-aspen-fir-spruce’ cover 

type, and these stands were scattered the full length of the main island, on both the south and 
82

Figure 32. Upland ecologic groups for Isle Royale National Park (TNC 1999, USGS 2000a)
83

Table 21. Names and sizes of upland forest Ecologic Groups, Isle Royale National Park (TNC 1999, 

USGS 2000a).

Ecologic Group Forest Type Area (ha)

8-Northern Dry Conifer-(Hardwood) Forests and Woodlands Boreal pine rocky woodland 198

Jack pine-black spruce/feathermoss forest (forest phase) 286

Jack pine-black spruce/feathermoss forest (woodland phase) 132

White pine-aspen-birch forest 149

Total Ecologic Group 8 765

9-Northern Mesic Conifer-

(Hardwood) Forests White cedar-boreal conifer mesic forest 1,004

White cedar-yellow birch forest (cedar-birch phase) 116

White cedar-yellow birch forest (mixed phase) 507

Total Ecologic Group 9 1,627

10-Northern Spruce-Fir-

(Hardwood) Forests Balsam fir/Canada yew-devil’s club 53

Balsam fir woodland 5

Balsam fir-aspen-paper birch forest 6,177

White spruce-balsam fir-aspen forest 1,570

Spruce-fir-aspen open forest 269

Balsam fir/paper birch forest 576

Spruce-fir/feathermoss forest 6,377

Spruce-fir and sugar maple-yellow birch mosaic 1,956

White spruce woodland alliance 3,020

Total Ecologic Group 10 20,003

11-Boreal Hardwood Forests 

and Woodlands Aspen-red maple forest 194

Aspen-red maple rocky woodland 594

Aspen-birch/boreal conifer forest (sparse canopy phase) 616

Aspen-birch/boreal conifer forest (aspen phase) 790

Aspen-birch/boreal conifer forest (mixed aspen-birch phase) 6,816

Aspen-birch/boreal conifer forest (woodland phase) 1,722

Aspen-birch/sugar maple-mixed hardwoods forest (aspen phase) 309

Aspen-birch/sugar maple-mixed hardwoods forest (paper birch 

phase) 787

Aspen-birch/sugar maple-mixed hardwoods forest (mixed phase) 771

Paper birch/bush honeysuckle-fir forest 851

Total Ecologic Group 11 13,450

12-Northern Hardwood Forests 

and Woodlands Maple-yellow birch-northern hardwoods forest (yellow birch phase) 359

Maple-yellow birch-northern hardwoods forest (mixed phase) 456

Maple-yellow birch-northern hardwoods forest (sugar maple phase) 2,426

Red oak-sugar maple forest 31

Yellow birch-(spruce) forest 1,917

Total Ecologic Group 12 5,189

Total Ecologic Groups 8-12 41,034
84

north sides, and a few on the smaller islands. Thus, this type is the most completely characterized 

of any forest type.

The understory layer of Ecologic Groups 10 and 11 is the most diverse of all cover types. Hansen 

et al. (1973) list a total of 62 vascular species for this broad community type, but do not indicate 

how many they found, on average, per community. They list the average cover of each species, 

but not constancy, so only a general indication of abundance is provided.

A version of this type, without much balsam fir, occupies much of the area burned by the large 

1936 wildfire. Paper birch was a strong dominant 32 years after the fire, with white spruce and 

aspen as minor components of the overstory (Hansen et al. 1973). The overstory averaged around 

12.2 m tall and 17.8 cm in diameter by this time. Stem density was very high, 7,360 stems ha-1, 

and basal area was moderate at 20 m2 ha-1

. Paper birch also was the most common species (3,952 

stems ha-1) in the seedling size class (greater than 0.3 m tall). Sugar maple was present in modest 

amounts (874 stems ha-1). The understory is almost as diverse as that of the group discussed 

above and has a high degree of compositional similarity. Thus, the understory had largely 

recovered from the fires by 1972.

Hansen et al. (1973) documented 21 shrub species in ISRO, with the boreal forest types being the 

most diverse.

Northern Hardwood Forest & Woodland Group, Ecologic Group 12

There are four specific community types in this group, each with distinct overstory dominants: 1) 

sugar maple–yellow birch, 2) mountain ash–mountain maple (Acer spicatum)–spinulose wood 

fern (Dryopteris carthusiana), 3) northern red oak (Quercus rubra)–sugar maple, and 4) yellow 

birch–spruce. The forest types in this group are strongly concentrated in the SW one-third of the 

island (Figure 32).

Unlike the others, the mountain ash–mountain maple–spinulose wood fern community (called a 

“scrub” in the Vegetation Mapping Program report) is rare and restricted to a few other islands at 

the NE tip of the park. The canopy cover varies from 40 to 90%; uncommon tree species include 

fir, white spruce, and paper birch. The shrub layer may be sparse or abundant (10–70% cover) 

and may include the disjunct species devil’s-club (Oplopanax horridus) (TNC 1999).

The sugar maple–yellow birch community type is the ISRO variant of the traditional ‘Northern 

Hardwood forest’ that is common in northern MN, northern WI, the upper peninsula of MI, and 

parts of Ontario (TNC 1999). Canopy cover ranges from 60 to 80%, and co-dominant canopy 

species include white pine, northern white cedar, and northern red oak. This type is found at 

elevations from 208 to 385 m on moderately to well-drained, loamy soils.

The northern red oak–sugar maple type is closely related to the sugar maple–yellow birch 

community type, but is more rare and restricted to somewhat steep, very well-drained sites above 

367 m. Co-dominant canopy species (< 10% cover) include white pine, northern white cedar, red 

maple, white spruce, and mountain ash (TNC 1999). This forest type has greater shrub cover (in 

both the ‘tall’ and ‘short’ layers) than the sugar maple–yellow birch community type and 

different dominant species. Common juniper (Juniperus communis) and serviceberry 

(Amelanchier spp.) dominate in the northern red oak–sugar maple forest, whereas beaked 
85

hazelnut (Corylus cornuta) is most common in the related forest type. Hansen et al. (1973) 

inventoried three stands with very complex age structures that had a mixed yellow birch–maple 

overstory; the co-dominant species suggest these stands are examples of community type 1 in 

this Group. The basal area and canopy height ranges were 23–37 m2 ha-1 and approximately 

18.3–23.2 m, respectively. The larger birch and maple were 71 cm and 63.5 cm in diameter, 

respectively. The tree reproduction of these three stands was strongly dominated by sugar maple 

(59,500 stems ha-1

) with red maple a distant second (2,400 stems ha-1) and yellow birch 

uncommon (123 stems ha-1

). 

Unlike Janke et al. (1978), Hansen et al. (1973) found Canada yew in two variants of the boreal 

hardwood types on the main island.

The compositions of the understory assemblages in this group are largely unknown. Dominant 

species, and the ranges of understory cover, are presented in TNC (1999). This publication lists 

vast differences in cover among the three forest types described; cover ranges from 40 to 80% in 

the yellow birch–spruce type to 0–5% in the sugar maple–yellow birch type. These data suggest 

large differences in richness. Hansen et al. (1973) provide abundance information on the 

common shrubs, forbs, and ferns in the various upland forest types (see Hansen’s tables 6 and 7). 

The ground layers of the northern hardwood types are extremely depauperate according to their 

data (Hansen et al. 1973), with only 18 species listed for three communities. 

The understory of northern hardwood forest can be quite diverse and includes species with 

different phenologies; the two most speciose groups are spring ephemerals and summer 

deciduous (Rogers 1982). In one year of sampling vegetation less than 0.5 m tall, Kern et al. 

(2006) found 94 species (spring and summer combined) in a sugar maple-dominated northern

hardwood forest in NE WI. Other studies of the northern hardwood type in the region generally 

found similar levels of richness (e.g., Cain 1935, Rogers 1982, Scheller and Mladenoff 2002). 

Though the richness of the understory is probably lower on ISRO, the level documented by 

Hansen et al. (1973) is certainly non-representative. Detailed studies are needed to assess the

differences among forest types and their conservation value.

Upland Shrub and Herbaceous Associations, Ecologic Groups 6, 7, 13, 14

Twenty-eight associations have no or few arboreal species in them. Three of these twenty-eight 

are in Ecologic Group 5, Great Lakes Rocky Shores (with an areal extent of approximately 141 

ha); these are covered in the Lake Superior section of this report. Similarly, two are clearly more 

aquatic than terrestrial (Ecologic Group 2), and three are considered marshes (part of Ecologic

Group 3). Among the remaining non-arboreal associations, there are very striking compositional, 

life form, and structural differences. From a biodiversity standpoint, these associations are quite 

important because many species found in one or two of these are not found elsewhere in the 

park, and these communities contain the majority of the species of concern (Judziewicz 1995).

An example is the ‘bedrock glades’ (sensu Judziewicz 1995) that resemble meadows comprised 

of alpine species, prairie species, and western disjunct species. The TNC classification effort 

greatly increased the number of distinct associations at ISRO; as of 2007, the MNFI listed only 

18 distinct natural communities for ISRO (Kost et al. 2007), 12 of which are non-arboreal.

A challenge with monitoring and management of these associations and the species they contain 

is their extent. At least five of the 20 terrestrial groups were not mapped because they occurred at 
86

a spatial scale below the minimum mapping unit (0.5 ha). Another, Canada yew shrubland, is 

found only on Passage Island and is the only mappable member of Ecologic Group 13. 

Exceptions to this pattern are the communities that occur on rock outcroppings. Hansen et al. 

(1973) estimated this type of feature to cover 2,023 ha, or 3.7% of the island. In contrast, ‘upland 

shrubs’ were found on only 23.5 ha (0.04%). The mapping effort of TNC (1999) for types that 

fall in the Upland Shrub and Herbaceous Association category totals approximately 1,813 ha, 

and the Rock Barrens group contributes 98% of that acreage. Thus, this broad group has been 

relatively stable in extent over the past 50 or more years.

The Rock Barrens (Ecologic Group 6) in ISRO includes one forested community (the spruce–fir 

basalt bedrock glade), 1,202 ha in three shrubland communities (rocky boreal shrubland and 

common juniper rocky krummholz with its white cedar–balsam fir/leatherleaf/black crowberry 

krummholz phase), and 580 ha in herbaceous vegetation (poverty grass [Danthonia spicata] 

barrens) (TNC 1999, USGS 2000a). Spruce–fir basalt bedrock glades occur on well-drained, 

rocky ridges where usually 5–30% of the ground surface is exposed bedrock. White spruce is the 

most abundant tree (20–50% cover); balsam fir, paper birch, mountain ash, and white cedar are 

also found. Boreal rocky shrublands are also found high on ridges. Shrub cover is 25–80% and 

consists mainly of beaked hazelnut, hawthorn (Crataegus douglasii), serviceberry, or saplings 

and browsed scrub of pin cherry (Prunus pensylvanica), white spruce, or mountain ash. Also on 

well-drained rocky ridges are poverty grass barrens, where poverty grass averages 46% cover.

Common juniper rocky krummholz is found on low, often steep, S- or SE-facing rocky ridges 

near the Lake Superior shore. The most abundant shrubs are common juniper (average 33% 

cover) and creeping juniper (J. horizontalis, average 21% cover); lichens and feathermoss are 

also common. On Passage Island, a rare phase of this community is dominated by stunted, scrub 

forms of white cedar and balsam fir in the 2–5 m height range. Leatherleaf and black crowberry 

are the most abundant shrubs <1 m tall (TNC 1999).

The Great Lakes basalt/diabase cliff (Ecologic Group 7) is an uncommon community at ISRO, 

found mostly on ridges near the NW shore. It is sparsely vegetated; crustose and foliose lichens 

average 40% cover, and mosses average 30% (TNC 1999). Also found on steep NW–facing talus 

slopes or cliffs on the NE end of the island are the Great Lakes boreal cliff forest and Great 

Lakes boreal talus woodland. Mountain maple dominates the cliff forest and is abundant in the 

talus woodland. Both include white spruce, paper birch, and Canada yew, but the most common 

herbs vary. In the talus woodland, mosses such as Pleurozium schreberi are common in the 

groundlayer. 

Avian Community

The composition of the avian community on ISRO has been documented since the early 1900s, 

with two reports in 1909 (Egan 2009). Periodically, reports of new species (e.g., Wood 1937) 

have come in, and by the mid-1960s, 197 species had been reported on the island (Krefting et al. 

1966 in Hansen et al. 1973). New sightings and confirmations continued through the 1980s (e.g., 

Martin 1989). In 1985, Van Buskirk presented a record of breeding birds on 36 small islands 

within 1.5 km of the main island and assessed the relationship between island size and bird 

richness. He found a tight relationship between island size and number of breeding pairs, and the 

study indicated that pairs on these islands need less area than the same species on the mainland. 

Recent efforts to locate all breeding species on the island have led to two atlas surveys (Egan 
87

2009). The NPS species list, dated April 2003 (NPS 2003b) for ISRO includes 238 bird species 

(confirmed reports only). This includes 88 breeding species, 69 migrants, 54 residents, and 27 

vagrants. The most recent atlas, based on field work from 2002 to 2008, noted 144 species, with 

79 confirmed as breeding on the island. Unlike the mammalian community, the avian community 

on ISRO is essentially the same as the community in adjacent Canada (Van Buskirk 1985).

The park has a number of recent or ongoing surveys of various breadth and focus. These include 

a bald eagle and osprey survey in the 1960s, 1980s, and 1990s. Surveys for all raptors were 

carried out in 1996, 1997, and 2001. Common loon surveys have been conducted since 1990. 

Since the 1980s, inventories for herring gull, ring-billed gull (L. delawarensis), great blue heron 

(Ardea herodias), and double-crested cormorant (Phalacrocorax auritus) have been done. In 

1994, a ‘formal’ breeding bird survey with a focus on neo-tropical migrants was established. In 

1996, each sample point was tagged so that each year the surveys were done from the exact same 

point utilizing standard ‘point count methods’ (Ralph et al. 1995). The trends from 1996 to 2008 

were reported in Egan (2009) and provide an evaluation of changes in composition and 

abundance. Based on the 130 points surveyed, 57 species were detected annually, with an 

accumulated total richness of 85 species over the 13-year period. Significant increases were 

noted for 10 species, and declines for eight. The population trends were compared to adjacent 

study areas (MI, MN, and Ontario) and most were similar (Egan 2009). This analysis confirms 

that the avian species on ISRO are functionally a part of a larger population, and that they have 

not suffered more declines than has been observed regionally in northern North America.

Mammalian Community

Due to its isolation (Belant and Van Stappen 2002), the mammalian community of ISRO 

changes frequently when viewed from an ecologically relevant time frame. The basic principles 

of island biogeography theory (MacArthur and Wilson 1967, Belant and Van Stappen 2002) are 

quite evident in the recent history of the composition and density of the mammalian assemblage.

The key processes of immigration, emigration, and local extirpation continue to shape this 

assemblage (and others). Accordingly, the mammalian community of ISRO is less species-rich 

than the nearby mainland areas in MN and Canada.

The most common mammals on the island today include red squirrel (Tamiasciurus hudsonicus 

regalis), red fox (Vulpes vulpes), beaver, moose, deer mouse (Peromyscus maniculatus), and 

hare (Lepus americanus) (Mech 1966). A number of common and conspicuous mammals found 

at this latitude were not reported at ISRO in 1973: black bear, fisher, gray fox, eastern chipmunk, 

gray squirrel, and porcupine (Hansen et al. 1973). The community is currently comprised of 27 

species (15 “present in park,” three “historic,” five “probably present,” and four “unconfirmed”),

seven of which are bats (four “present in park” and three “probably present”) (NPS 2003b). In 

1905, there were 14 species, including three bats. The early-20th-century estimate is probably a 

conservative one due to limitations of access. The history of mammalian presence since 

approximately 1900 is fairly well established in the survey by Adams (1909). Some very 

conspicuous mammals apparently did not exist on the island in the late 19th century but showed 

up in the 20th century (e.g., moose, coyote [Canis latrans], and wolf), and others (caribou

[Rangifer tarandus] and lynx [Lynx canadensis]) were still present in 1905 but disappeared 

shortly thereafter (Johnson and Shelton 1960, Mech 1966). This assemblage continues to be 

dynamic as populations fluctuate due to weather shifts, biotic interactions, genetic bottlenecks,

and, in a few cases, disease. The species with small home ranges and high capacity for 
88

reproduction will probably always be part of the mammalian assemblage at ISRO; however, 

significant fluctuation in composition and density of the other non-volant mammals (those 

without wings) is to be expected. The extremely low amount of genetic variation within the wolf 

population probably makes it particularly susceptible to extirpation from agents such as disease 

(Peterson 1999). The lack of success of intentional introduction of white-tailed deer by the State 

of Michigan in 1906 is testament to the vagaries of population establishment in this habitat 

island. It is probable that currently unrepresented species (e.g., coyote) will appear, as they have 

the capacity to disperse to the island, and conditions seem suitable. Humans have probably had a 

small hand in this compositional dynamic since the mid-1800s, but their precise impact is 

unknown.

There are detailed, long-term population density estimates and predator-prey pairs that have been 

studied intensely. These include red fox-hare, wolf-moose, and beaver. 

Moose-Wolf Interaction and Population Changes

These long-studied species form a predator-prey system in that the moose is the primary food 

item for wolves (Peterson and Vucetich 2001). However, the moose population exhibited very 

large swings prior to arrival of the wolf. The species probably arrived shortly after the turn of the 

century and grew in population very rapidly after that. It reached very high densities by the

1920s and early 1930s, and then the population crashed. Wolves did not come on the scene until 

the late 1940s (Pastor et al. 1988). Wolves have been aerially censused since the late 1950s; 

between 1988 and 1997, 15 were live-captured, had blood drawn, and were radio-collared. 

Moose were also counted by air beginning in 1983 (Peterson 1999). The density from 1982 back 

to 1959 was “reconstructed” by Fryxell et al. (1988), and Mech (1966) compiled various 

accounts to document the major trends in moose density from 1915 to 1957.

Recent analyses of these data have generated a range of conclusions, some of which are 

contradictory. During the 1960s and 1970s, both wolf and moose increased in density. Wolf 

numbers then declined from 1980 to 1996, due in part to an introduced disease. The moose 

population began to increase in 1984–1985 and continued to climb until 1996. It then crashed, 

with 80% mortality (Peterson 1999). This suggests limited density-dependent regulation within 

the moose population and a rather loose coupling of the two species. Post et al. (2002) reported a 

non-linear time series analysis of densities from 1958 to 1999. This mathematic analysis 

suggested a distinct phase-dependent system with significant changes in the degree of density 

dependence, and delayed density dependence in moose. A concurrent analysis of the same data,

but focused on kill-rate, found that a) predator density outperformed prey density as a predictor, 

b) a ratio model outperformed a prey-based model, and c) the maximum explanatory power of 

any model was 37% (Vucetich et al. 2002) These results support the characterization of a ‘loose’ 

connection between species. A very recent analysis of the situation has uncovered an important 

weather signal in the relationship of the two species (Peckarsky et al. 2008). In particular, the 

North American Oscillation, which exerts a large influence on snowfall totals, impacts wolf 

predation rates due to the concentration of its prey during high snowfall years or its dispersion 

during low snow years. Thus, this more-or-less cyclic weather pattern is an important driver of 

predation rates (kill rates), and thus has some influence on the densities of both species.
89

Role of Moose in the Ecology of the Boreal System

The conclusions regarding the impacts of this large herbivore are based on exclosures set up in 

the 1940s or on patterns noted across gradients of moose density that occur naturally. The moose 

is closely associated with the boreal forests. The overall pattern of abundance has been described 

as “.... southwestern end where densities are greatest” (Peterson 1977 in Pastor et al. 1988). 

Likewise, the study by Brandner et al. (1990) had two of three intermediate density and high 

density study sites at the SW end. This generally confirms the pattern noted by Peterson (1977), 

but it is clear that moose density varies spatially over smaller areas. In addition, moose density 

has fluctuated dramatically over time. The general pattern has been from 4 to 10 animals km-2 in 

the 1930s, to a low point in the late 1950s of about 1 animal km-2, increasing to approximately 3 

animals km-2 in 1973–74, followed by an approximate 10-year decline, a rapid increase for 10 

years, and a precipitous decrease from the mid-1990s to 1998 to only 1 animal km-2 once again 

(Peterson 1999). Thus, the magnitude (intensity, spatial extent, etc.) of moose herbivory is quite 

variable in space and time. The population densities on Isle Royale are much higher than 

populations in Canada and Alaska (Peterson 1999). This, coupled with their need to consume 

approximately 15 kg of food per day (Pastor et al. 1988), indicates they have the potential to 

significantly affect the vegetation. The diet of moose includes herbaceous upland plants, aquatic 

plants, deciduous trees, and, when food is scarcer, conifer seedlings and saplings (Pastor et al. 

1988).

By the 1930s, Canada yew was practically eliminated from the main island, and this is 

consistently attributed to moose browsing (Brown 1935 in Brandner et al. 1990, Slavik and Janke 

1987). Red-osier dogwood (Cornus stolonifera) and mountain ash have declined precipitously in 

some areas, as has balsam fir. However, there are a suite of other influences (or lack of in some 

cases) that should be noted to fully understand the impacts of moose. Total tree seedling density 

typically shows no increase with moose exclusion and is not lower in high moose-density areas 

(Janke 1979, Risenhoover and Maass 1987). Where balsam fir sapling densities are low, moose 

suppress the trees and limit their height growth (Brandner et al. 1990). A similar effect was noted 

for sugar maple in ‘transitional’ and boreal forests (Sell and Jordan, ca. 2006). However, where 

sapling densities are high, moose serve to release the residual balsam fir saplings, resulting in 

increased height growth and recruitment to larger size classes. For patches of low balsam fir

density, the longer-term effect is to reduce its abundance in the canopy and thereby favor white 

spruce (Brandner et al. 1990). In two valleys on the NE end of the island with moose density of 

3.7 km-2

, Pastor et al. (1998) noted elimination of aspen and birch stems less than 10–15 cm as 

annual browse consumption exceeded 4 g m-2; neither balsam fir nor white spruce showed this 

effect. A wide range of impacts on the shrub layer has been noted. Janke (1979) noted reduced 

heights, an increase in biomass was reported by McInnes et al. (1992), and Snyder and Janke 

(1976) found no effect on tall shrubs. As moose density increases, herb-layer diversity and 

biomass typically increase (McInnes et al. 1992). Low levels of browsing permit greater numbers 

of stems (and perhaps species) to recruit to the canopy, which in turn suppresses the shrub and 

herb layers.

Effect of Moose on Ecosystem Processes

The documented effects of moose browsing on ecosystem processes are rather limited, and the 

vast majority are restricted to areas of high (above average) moose density and have taken more 

than four decades to manifest (e.g., Pastor et al. 1993). Within ISRO, the number of locations 

(not samples) where these linkages have been assessed is small, and thus most conclusions from 
90

these studies should not be viewed as established fact for the park in general. The most 

consistent effects have been seen in productivity, nitrogen availability and cycling, and cation 

concentrations (McInnes et al. 1992, Pastor et al. 1993, 1998). In particular, tree and litter 

production were greater in areas protected from moose browsing; herbaceous litter was lower, 

but shrub production was unaffected (McInnes et al. 1992). Standing biomass also differed 

between exclosures and control (browsed) areas for all three strata; tree biomass was greater

while shrub and herb biomass was lower in the exclosures. 

The first ISRO study to report on below-ground processes found 10 of 24 monitored parameters 

differed between exclosures and controls. At the Windigo site, which had much higher moose 

density than the other three sites, six parameters (soil carbon, soil N, cation exchange capacity

[CEC], field N mineralization, potentially mineralizable N, and microbial respiration) were 

higher in the exclosure (Pastor et al. 1988, Table 1). In a follow-up study at the same exclosures, 

annual N mineralization, potential N mineralization, CEC, and the concentrations of Na+, K+, 

and Mg2+ were higher at the Windigo site (Pastor et al. 1993). The only significant difference at 

the Siskiwit Camp site, which had intermediate moose density, was annual N mineralization. 

Total N and total carbon in the soils differed at only one site for one of three months tested. 

These results are 40 years after the exclosures were erected; during this time period the 

vegetation changed markedly. After 33 years, total woody stem density was almost twice as high 

in the control area (excluding Rubus, which probably was not included in the original count), and 

the relative abundance of many species changed (Risenhoover and Maass 1987). The relative 

abundance of balsam fir, paper birch, mountain maple, and mountain ash declined while that of 

yew went up in the exclosures. In the browsed plots, both balsam fir and white spruce increased 

dramatically (3X), but fir was six times more common and was tied with mountain ash as the 

dominant arboreal species by 1982. Paper birch was the third most common arboreal species in 

the control plots, which had a small tree/shrub layer dominated by mountain maple, serviceberry, 

and bush honeysuckle. Between 1949 and 1982, aspen disappeared from both browsed and 

control plots (Risenhoover and Maass 1987). 

Thus, the community in the exclosure at Windigo had less vertical structure and a tighter canopy, 

but its composition did not differ from the browsed plots. In areas, or time periods, of modest-tolow herbivory, forest structural changes may contribute to a ‘browsing effect’ on below-ground 

processes by enhanced warming of the litter layer and waste deposition that enhance nutrient

cycling (Pastor et al. 1993). The study by Pastor et al. (1998) noted above extended the scope of 

the relationship between moose browsing, arboreal vegetation composition, and nitrogen 

availability. They found a relationship between high levels of browsing (approximately 5 g 

m-2

), N-availability, and conifer basal area at the patch and small-valley scale (250–500 m wide).

This body of work suggests that most areas used by moose will not have had any pronounced 

alteration of ecosystem processes, either because the level of browsing is below the threshold 

level, or the intensity of browsing varies over time such that the arboreal component of the 

community has time to recover during low browsing periods. Variation in intensity of browsing 

can arise due to weather patterns altering moose behavior, their large (500–1000 ha) home range, 

the variety of habitats used, or changes in moose density (see Population Changes, above; Pastor 

et al. 1988). Though it is clear that moose browsing can affect vegetation, which in turn affects 

nutrient cycling and availability, these effects are probably not the norm for ISRO but vary 

spatially and temporally. Pastor et al. (1988) noted that there are significant differences in the 
91

microbial communities between locations that create effects as large as those induced by 

browsing. Thus, moose browsing is only one of several important factors that determine 

ecosystem function in this landscape.

Effect of Moose on Aquatic Communities

Moose were recognized as utilizing aquatic vegetation from ISRO lakes as early as the survey by 

Koelz (1929). As cited in Lafrancois and Glase (2005), later studies by Jordan and Aho (1978) 

and Aho and Jordan (1979) found that moose probably alter the aquatic community on ISRO 

through direct consumption of aquatic vegetation and by disturbing sediment while foraging, 

increasing turbidity. Most recently, Meeker et al. (2007) compared photographs of their sample 

sites from the early 1900s, before moose arrived on ISRO, to conditions present during 2003–

2006 to illustrate that aquatic vegetation in several ISRO lakes has been reduced or eradicated. 

The presence of remnant underwater stems and moose prints in lake sediments suggest that 

moose have a strong impact on aquatic plants (Meeker et al. 2007). Both consumption of 

vegetation and increases in turbidity may negatively affect fish and sponge communities. 

However, no studies have been conducted to specifically test these hypotheses.

Beaver Population Dynamics and Landscape Influence

Beaver appear to have occupied ISRO in the early 1800s but then disappeared toward the end of 

the 19th century (Mech 1966, Hansen et al. 1973). This pattern is consistent with the findings of 

Belant and Van Stappen (2002) in the Apostle Islands, which indicate limited colonization 

potential but high local extirpation rates for non-volant vertebrates. Adams (1909) did not note 

any sign of beaver, but by 1920 the species was “common along the south shore.” The 

population has exhibited large fluctuations since then, peaking in the late 1940s (Hansen et al. 

1973). A population decline from the late 1940s to approximately 1960 was attributed to a 

combination of depleted food resources, coyote predation, and a tularemia-like disease (Hansen 

et al. 1973). Krefting (1963) and Shelton (1966) documented dozens of active colonies, perhaps 

as many as 140 in 1960. Peterson and Romanski (2008) reported their beaver sightings and 

population estimates for 2006–2008, as well as presenting an annual estimate back to 1960. 

There was a sharp increase in number of beaver from approximately 1960 to 1970, up to more 

than 300 active colonies, followed by a rapid decline. By the early 21st century the numbers were 

down to less than 75 colonies. From 2006 to 2008, beaver density was relatively stable (125–135 

active colonies). The species is concentrated on the eastern end of the island due to the steeper 

and more dissected topography (Peterson and Romanski 2008).

Food resource level and predation will continue to affect the dynamics of the species. The wolf is 

the primary predator now that the coyote is gone. Shelton (2004) reported that wolves heavily 

preyed upon the beaver population, whereas Mech (1966) (in Hansen et al. 1973) found that 

between 7 and 19% of wolf scat contained evidence of beaver. Fluctuating food resources are to 

be expected due to beavers’ preference and ability to deplete the local resource. Fryxell (2001) 

reported an association between colony size and local food availability in Algonquin Provincial 

Park. The current and potential effect of disease is unknown. Fryxell (2001) concluded that local 

interactions were more important than broad-scale influences, such as weather, in determining 

the fate of local populations. 

The beaver has been characterized as an ecosystem engineer and keystone species (Naiman et al. 

1986) due to its impacts on key processes such as hydrology and, in some cases, channel 
92

geomorphology. At ISRO, more than 80% of the active colonies are on streams (Shelton 2004),

primarily 3rd and 4th order streams (Naiman et al. 1986). The dams erected by a colony, which 

typically include primary and secondary dams, have a multitude of influences. They temporarily 

create new shallow, flooded wetland habitat in and adjacent to the stream channel. The dam(s) 

catch sediment (up to 6,500 m3 per dam), moderate some floods, alter hydrology, change channel 

morphology, and alter biogeochemical pathways such as denitrification (Naiman et al. 1986). 

Due to their ability to fell relatively large, sometimes mature trees, beaver have profound effects 

on riparian community structure and composition (Johnston and Naiman 1990). These effects 

fall into two distinct classes when viewed from the standpoint of temporal persistence. All 

effects directly or indirectly associated with dams are typically short lived (< 10 years) because 

most colony sites are not used consistently for extended periods of time (Fryxell 2001, Peterson 

and Romanski 2008). In contrast, effects related to the utilization of trees can last for many 

decades and even exceed 100 years.

Utilization of woody plants by beaver is concentrated in a small area; for streams, the beaver do 

not commonly forage more than 50–70 m from the water’s edge. Within this zone, tree basal area 

can be reduced up to 43% over a six-year period. Beaver show strong preference for deciduous 

species, especially aspen, willow, and birch, and avoid conifers and alder (Johnston and Naiman 

1990). In one study, about two-thirds of all stems cut were <5 cm, but the average size of aspen 

used was 12 cm, and the largest was 43.5 cm (Johnston and Naiman 1990). This selective 

foraging shifts the woody plant composition toward conifers, non-palatable hardwoods, and 

shrubs. Thus, over decades, the long-term effect of beaver activity is to make the habitat 

decidedly sub-optimal for the species.
93

Indicators of Natural Resource Conditions

Vital Signs

The GLKN has developed conceptual ecosystem models for long-term ecological monitoring 

(Gucciardo et al. 2004); models pertinent to ISRO are those for Great Lakes nearshore and 

coastal wetland areas, inland lakes, wetlands, and northern forests. A detailed discussion of 

natural resource conditions in ISRO based on these models and their associated vital signs is 

found in the Conclusions section beginning on page 147. A discussion of other indicators 

requested as part of the task agreement for this report follows.

Designations and Protections

ISRO was designated as the 21st national park in 1931. It was further designated part of the 

National Wilderness Preservation System in 1976; over 99% of ISRO’s land area is managed as 

wilderness (Crane et al. 2006). In 1980, the United Nations Man and the Biosphere Programme 

named ISRO an International Biosphere Reserve, giving it global scientific and educational 

significance.

All waters within the designated boundaries of ISRO (including Lake Superior and inland lakes 

and streams) are designated as “Outstanding State Resource Waters (OSRW)” by the State of 

Michigan. These waters are protected by applying controls on pollution sources so that existing 

uses are maintained and water quality is not reduced in the OSRW (State of Michigan 2006a). In 

addition, Desor, Ritchie, Sargent, and Siskiwit lakes are designated as “cisco lakes” where the 

state-threatened cisco, or lake herring, is found (MDEQ 2008b).

Presence of Endangered, Threatened, or Special Concern Species

A list of federal- and state-listed species appears as an appendix in two recent ISRO management 

plans (NPS 2003a, 2008b). We have updated the status of species on this list (which was current 

as of 1999) using data from the 2009 MNFI (MNFI 2009a, b).

ISRO has one federal-endangered species: the gray wolf, which had been delisted but was 

relisted in September 2009 (USFWS 2009). No ISRO species are currently listed as federalthreatened.

ISRO is occasionally visited by two state-endangered birds, the short-eared owl and peregrine 

falcon. ISRO has six state-endangered plants: round-leaved orchid (Amerorchis rotundifolia); 

rosy pussytoes (Antennaria rosea), listed as “historic” in the ISRO species list; smooth whitlowgrass (Draba glabella); Canbyi’s bluegrass (Poa canbyi); awlwort (Subularia aquatica); and 

mountain cranberry. One ISRO plant species, blue lettuce (Lactuca pulchella) is now considered 

extirpated (MNFI 2009b). In addition, ISRO has the state-threatened gray wolf, seven statethreatened birds, four state-threatened fish, and 36 state-threatened plants. Among species of 

concern, ISRO has the moose, 10 birds, the boreal chorus frog (Pseudacris triseriata maculata),

two fish, and 13 plants (MNFI 2009a, b). From 1999 to 2009, five ISRO species have improved 

in state status, while two have declined (Table 22).
94

Table 22. Comparison of 1999 and 2009 state status for state-listed species found at Isle Royale National 

Park (NPS 2008b, MNFI 2009a, b) (+ indicates improved status from 1999–2009, - indicates a decline in 

status).

Common name Scientific name 1999 MI status 2009 MI status +/-

Gray wolf Canis lupus Endangered Threatened +

Siskiwit Lake cisco Coregonus bartlettii Special concern Threatened -

Bald eagle Haliaeetus leucocephalus Threatened Special concern +

Osprey Pandion haliaetus Threatened Special concern +

Rosy pussytoes Antennaria rosea Threatened Endangered -

American rock brake Cryptogramma 

acrostichoides

Endangered Threatened +

Blue lettuce Lactuca pulchella Threatened Extirpated -

Mountain cranberry Vaccinium vitis-idaea Extirpated Endangered +

ISRO does not have a comprehensive inventory of its insects, snails, or mussels (NPS 2008b). 

The MNFI (2009c) lists state-endangered, threatened, and special concern lichens, snails, insects, 

and other organisms for Keweenaw County, but their presence or absence in ISRO is 

undocumented. State-endangered and threatened natural communities are listed in discussed in

the Lake Superior section (page 21), groups 1–4 in the inland aquatic resources section (page 

58), and groups 8–14 in the terrestrial resources section (page 82). 

Table 1. 

Violations of Water Quality Standards

During 1993 an NPS contractor reviewed water quality data for ISRO Lake Superior waters and 

inland lakes and streams using USEPA’s national water quality databases. The summary report 

(‘Horizon’ report) covered the period 1962–1993 (NPS 1995). Data included 26 monitoring 

stations, 15 of which were within ISRO, and 9,248 water quality observations representing 366 

water quality variables. Only two stations (Washington Creek at Windigo and an offshore site 5 

km S) collected long-term data; the Washington Creek station accounted for 81% of all ISRO 

data (NPS 1995). 

The report revealed six parameters (pH, total coliform, cadmium, copper, lead, and zinc) that 

exceeded screening criteria at least once (NPS 1995). At the Washington Creek at Windigo 

station, isolated violations for pH, cadmium, copper, lead, and zinc occurred between 1965 and 

1974 (Table 23). In all cases, numerous subsequent samples failed to show further violations, so 

these violations appeared to be of a temporary or transient nature.

The Washington Creek at Windigo site also recorded ten violations of the NPS Water Resources 

Division (WRD) total coliform criterion for bathing waters (1,000 colony-forming units 

[CFU]/most probable number [MPN]/100 mL) from 1967 to 1980, and ten violations of the fecal 

coliform criterion of 200 CFU/MPN/100 mL from 1971 to 1993. 
95

Table 23. Exceedences of freshwater and drinking water criteria for pH and metals for Washington Creek 

at Windigo, Isle Royale National Park, 1962–1993 (NPS 1995).

Criterion Exceeded or 

Equaled Value Month/year Later Sampling Dates that Met 

Criterion

pH

freshwater life 6.5–9.0 pH 

units

6.3 pH 

units 5/1965 179 samples from 7/1965 to 2/1993;

range of values 6.6–8.1 pH units

Cadmium

freshwater life 3.9 μg L-1

;

drinking water 5.0 μg L-1

10 μg L-1 10/1969 60 samples from 5/1970 to 5/1982;

range of values 0–3 μg L-1

Copper

freshwater life 18 μg L-1 20 μg L-1 5/1968 22 samples from 10/1968 to 5/1982;

range of values 0–11 μg L-1

Lead 

drinking water 15 μg L-1

*

33 μg L-1

22 μg L-1

10/1970

5/1974

17 samples from 10/1974 to 5/1982;

range of values 0–14 μg L-1

Zinc

freshwater life 120 μg L-1 200 μg L-1 5/1974 55 samples from 10/1974 to 8/1991;

range of values 0–59 μg L-1

*more violations were reported in NPS 1995 because lead criterion was mistakenly reported as 5 

μg L-1

Impairments, 303(d) Reports, and Fish Consumption Advisories

The federal Water Pollution Control Act (PL92-500, Clean Water Act) requires each state to 

prepare a biennial report on the quality of its water resources, often called a Section 305(b) 

report after the pertinent subsection of the act. Michigan’s 2008 report includes Lake Superior 

and Siskiwit Lake in its list of impaired water bodies (often called a Section 303(d) list, again 

after the pertinent subsection of the act). These water bodies must have total maximum daily 

loads of pollution (TMDLs) established for them (Table 24) (MDEQ 2008b). Lake Desor and 

Lake Richie are included on the 303(d) list as being “not assessed” or having “insufficient 

information” for the development of TMDLs (MDEQ 2008b). In addition to these impairments, 

all inland lakes, reservoirs, and impoundments in MI have an advisory against eating most types 

of fish more than once a week because of mercury contamination, with additional restrictions for 

women of childbearing age and children under age 15 (MDCH 2009).

Table 24. Water bodies on Michigan's 303(d) list in Isle Royale National Park (MDEQ 2008b).

Water Body Impairment TMDL Date

Lake Superior Chlordane

Dioxin (including 2,3,7,8-TCDD)

Mercury in fish tissue

PCB in fish tissue

2012

2012

2012

2012

Siskiwit Lake PCB in fish tissue

Mercury in fish tissue 

2010

2011
96

Stressors

ISRO Air Quality

Air pollution is a broad term that includes all compounds, particles, aerosols, gases, and metals 

in the atmosphere. Relevant substances are those entering at rates that clearly exceed the 

background rates and having the potential to affect ecosystem structure, function, or 

composition. They may originate locally or travel long distances from their sources. Air 

pollution may affect ISRO resources through atmospheric deposition of contaminants, nutrient 

enrichment, or vegetation damage, and may affect human uses of the park by limiting visibility 

and harming human health.

ISRO is designated as a Class I air quality area, which provides it with the highest degree of 

protection against air pollution under the USEPA Clean Air Act (CAA). In 2006, ISRO met the 

NPS goal of having stable or improving air quality, as defined by meeting the national ambient 

air quality standards for ozone, particulate matter less than 2.5 microns in size (PM2.5), and sulfur 

dioxide (SO2) (NPS 2007). Nitrogen and sulfur deposition were rated as being of “significant 

concern” and “caution,” respectively. Ammonia and sulfur concentrations in precipitation 

increased during 1996–2005, although the increases were not statistically significant.

No trend was found during 1996–2005 for the haze index (related to visibility) at ISRO on either 

the clearest or dirtiest days; its condition was rated as “caution.” Ozone data were insufficient to 

establish a condition or trend (NPS 2007). An analysis of air pollution data and plant species 

type and relative abundance ranked Isle Royale as the least susceptible to vegetative damage 

from ozone, as well as sulfur oxides, among 22 midwestern parks (Crane et al. 2006).

Air Monitoring Stations Near ISRO

Currently, no international, federal, or state air quality monitoring stations are operated on the 

island. However, Eagle Harbor, MI, 64 km SE, is the site of an Interagency Monitoring of 

Protected Visual Environments (IMPROVE) monitoring site where fine aerosols, particulate 

matter less than 10 microns in size (PM10), and light extinction and scattering are measured

(IMPROVE Network 2004). The site also features a camera for qualitative observation. Also at 

Eagle Harbor, an Integrated Atmospheric Deposition Network (IADN) station operated by the 

USEPA and Environment Canada monitors PCBs, organochlorine pesticides, and PAHs (IADN 

2002). The Midwest Regional Planning Organization operates a HazeCam at the Grand Portage 

Indian Reservation in MN that looks out at ISRO, 32 km SE, and provides particulate monitoring 

and meteorologic data (www.mwhazecam.net). 

A NADP National Trends Network (NTN) site that monitored wet deposition was operated at 

ISRO from 1980 to 1984 and 1985 to 2006. Now, the closest NADP NTN sites are at Hovland, 

MN (41 km W), and Chassell, MI (83 km SSE) (http://nadp.sws.uiuc.edu/). A seasonal ozone 

monitoring site was operated on ISRO from 2002 to 2004 (Crane et al. 2006). A passive ozone 

monitoring site is reportedly part of the IMPROVE site on the mainland (Maniero and Pohlman 

2003), although no ozone data were found for this site. The nearest dry deposition site operated 

by the Clean Air Status and Trends Network (CASTNet) is at Voyageurs National Park 

(VOYA), 180 km W of ISRO (Figure 33).
97

Figure 33. Air quality monitoring sites in the vicinity of Isle Royale National Park.

Local and Regional Air Emissions

Within ISRO, park vehicles, recreational marine engines, and campfires are potential sources of 

several major air pollutants: nitrous oxides (NOx), particulate matter (PM), carbon monoxide 

(CO), volatile organic compounds (VOCs), and PAHs (Swackhamer and Hornbuckle 2004). 

Although quantification is difficult, long-range sources are generally thought to be of greater 

concern for these pollutants than in-park sources (Swackhamer and Hornbuckle 2004). 

Waterborne commerce is also a local source of air emissions. Corbett and Fischbeck (2000) 

estimated that cargo movement on the Great Lakes produced NOx emissions of 5–10 metric tons 

(MT) km-1

. The USEPA (2002b) estimated that the four U.S. Lake Superior ports nearest ISRO 

(Duluth-Superior, Taconite Harbor, Two Harbors, and Silver Bay) produced combined emissions 

of 19 MT yr-1 hydrocarbons, 81 MT yr-1 CO, 540 MT yr-1 NOx, 34 MT yr-1 PM, and 235 MT yr-1

SO2 (Table 25). The USEPA has made rule changes in recent years to reduce emissions from 

diesel boats and ships: allowable levels of sulfur in fuel used in marine vessels were reduced by 

99% in 2007, which also resulted in a decrease in PM emissions (USEPA 2009a). In March 

2008, the USEPA also finalized a three-part program to reduce emissions from category 1 and 2 

marine diesel engines. PM emissions from some ships that exclusively sail the Great Lakes

would have been reduced as much as 90% and NOx emissions as much as 80%, when these rules 

were fully implemented (USEPA 2009a). However, a deal reached with congressional 

negotiators in October 2009 exempted 13 ships from these regulations and allowed others to 

apply for exemptions (Flesher 2009a).

Within 50 km of ISRO, the Thunder Bay area has several regulated facilities that produce one or 

more of the criteria air pollutants (CO, NOx, SO2, PM10, VOC, and ammonia [NH3])
98

(Environment Canada 2009). A 100-km radius includes the Keweenaw Peninsula. We mapped a 

250 km range (Figure 34) to be consistent with the report of Swackhamer and Hornbuckle 

(2004); this includes the western half of MI’s Upper Peninsula, part of northern WI, and the Iron 

Range of MN.

Regulated facilities in the U.S. and Canada within 250 km of ISRO produce 151,138 MT yr-1 of 

criteria air pollutants (Canadian data from 2007 and U.S. data from 2002) (Table 25)

(Environment Canada 2009, USEPA 2009c). The largest sources of CO in the ISRO vicinity are 

at Thunder Bay and Terrace Bay, Canada (Figure 35). The largest sources of PM10 are on the 

Iron Range (Figure 36), while large VOC source areas include Thunder Bay and Terrace Bay, 

Canada, and the Rhinelander and Phillips areas in northern WI (Figure 37). Compared to 

Swackhamer and Hornbuckle’s (2004) report, CO emissions in the U.S. within 250 km of ISRO 

decreased 23% from 1996 to 2002; PM10 emissions decreased 64%, and VOC emissions 

increased 114% (from 578 to 1,239 MT yr-1) during the same time period. SO2, NOx, and NH3

are discussed in the section on acid and nutrient deposition.

During 2007–2008, the prevailing wind directions at ISRO’s Passage Island were N to E, 23%; E 

to S, 18%; S to W, 26%; and W to N, 33%. At Rock of Ages, they were 29%, 15%, 29%, and 

27%, respectively (Figure 34) (NBDC 2009a, b). Thus, wind directions are relatively evenly 

distributed, with E–SE–S winds slightly less likely at ISRO, making it unlikely that any one 

source of pollutants is the predominant influence on ISRO’s air quality. 

Table 25. Criteria pollutant emissions for regulated facilities and some ports within 250 km of Isle Royale 

National Park (Environment Canada 2009, USEPA 2009c).

Regulated facilities locations Pollutant emissions (metric tons yr-1)

NOx NH3 SO2 PM10 CO VOC

Terrace Bay, Canada <91 185 <91 <91 3,096 271

Thunder Bay, Canada area 2,563 11 3,703 333 5,057 1,098

Iron Range, MN 25,916 <91 7,326 9,227 <91 159

Duluth-Superior, MN/WI area 1,548 11 2,624 1,156 2,820 521

Rhinelander, WI area <91 <91 <91 <91 <91 661

Phillips, WI area <91 <91 <91 <91 <91 232

Iron Mountain, MI/WI area <91 <91 <91 <91 1,694 <91

Hubbell, MI area <91 161 <91 <91 <91 <91

Marquette, MI area 17,796 <91 17,812 1,266 <91 242

Other (including those <91 MT yr-1) 15,977 185 16,668 3,088 6,579 1,152

Total regulated facilities 63,800 553 48,133 15,070 19,246 4,336

Ports of Duluth-Superior, Taconite Harbor, 

Two Harbors, and Silver Bay

540 no 

data

235 34* 81 19**

Total regulated facilities and ports 64,340 553 48,368 15,104 19,327 4,355

*all PM, not just PM10; **hydrocarbons
99

Figure 34. Regulated facilities that emit criteria air pollutants within 250 km of Isle Royale National Park (Environment Canada 2009, USEPA 

2009c).
100

Figure 35. Emissions of carbon monoxide from regulated facilities within 250 km of Isle Royale National 

Park (Environment Canada 2009, USEPA 2009c).

Figure 36. Emissions of particulate matter less than 10 microns from regulated facilities within 250 km of 

Isle Royale National Park (Environment Canada 2009, USEPA 2009c).
101

Figure 37. Emissions of volatile organic compounds from regulated facilities within 250 km of Isle Royale 

National Park (Environment Canada 2009, USEPA 2009c).

Long-Range Atmospheric Deposition

The effects of atmospheric deposition have been extensively studied at ISRO because of its 

wilderness status and lack of local air pollution sources. Swackhamer and Hornbuckle (2004) 

conducted an extensive review of past studies and monitoring efforts on ISRO and concluded 

that long-range atmospheric transport was the major source of mercury and persistent organic 

pollutants (POPs) including dioxins, PCBs, chlorinated compounds (DDT and metabolites, 

transnonachlor, cis- and trans-chlordane, hexachlorobenzene, octachlorostyrene,

pentachloroanisole, decachlorodiphenyl ether, and mirex), fluorinated compounds, and 

brominated flame retardants.

Volatilization of the pesticide chlordane from soils in the southern U.S. is the predominant 

source of chlordane to the Great Lakes (Hafner and Hites 2003), even though chlordane has been 

banned in the U.S. since 1988. Similarly, soils in the cotton-growing region of the SE U.S. 

account for 59% of the toxaphene deposited in Lake Superior, even though it was banned in 

1982 with residual use allowed until 1986 (Ma et al. 2005). Midwestern agricultural soils and 

urban areas continue to emit significant quantities of DDT (Bidleman et al. 2006), although 

continuing use in Mexico and Central America is another potential DDT source. An LSBP 

committee (LSBP 2006b) reported that Lake Superior is moving toward a steady state for some 

banned contaminants, such as PCBs and α-HCH. At steady state, atmospheric inputs to the lake 

will equal outputs from the lake.

Hafner and Hites (2003) reported that the major source of PCBs to the IADN monitoring site at 

Eagle Harbor is the Chicago area. Fluorene, one of the PAHs (products of incomplete 
102

combustion of fossil fuels), arrives at Eagle Harbor mainly from a SW source region reaching 

from MI through Iowa and North Dakota (Hafner and Hites 2003). 

Thurman and Cromwell (2000) found that trace concentrations of triazine herbicides also arrive 

at ISRO via atmospheric transport. Atrazine, deethylatrazine, deisopropylatrazine, and cyanazine 

were detected in ISRO rainfall and inland lakes during their study period from 1992 to 1994. The 

authors suggested that residence time for these compounds is longer (up to 10 years) in deeper 

ISRO lakes than in shallower ones.

Within the Lake Superior basin, emissions of pollutants (to both air and water) were reduced by 

the following percentages between 1990 and 2005: mercury, 71%; dioxin, 76–79%; and HCB, 

85% (HCB reduction on the Canadian side only). PCB reductions cannot be estimated because 

the inventory is incomplete (LSBP 2006b). 

Acid and Nutrient Deposition

Acid deposition is a subset of air pollution that includes all reactive forms of nitrogen and sulfur 

that form or can form acids when in contact with water. It specifically includes gases, particles, 

rain, snow, clouds, and fog that are composed of sulfuric acid, nitric acid, and ammonium, 

derived from SO2, NOx, and NH3, respectively. These compounds are emitted primarily by the 

burning of fossil fuels, but also by agricultural activities (Driscoll et al. 2001). The potential 

effects of acid precipitation include acidification of ecosystems and addition of sulfur and 

nutrients, especially nitrogen that can lead to eutrophication.

Regional Emissions: Emissions of SO2 from regulated facilities in the U.S. and Canada within 

250 km of ISRO are 48,133 MT yr-1 (Canadian data from 2007 and U.S. data from 2002) (Table 

25) (Environment Canada 2009, USEPA 2009c). The largest source of SO2 is a power plant at 

Marquette, MI (Figure 38). Despite these seemingly large sources, atmospheric SO4

2- deposition 

at ISRO exhibited a downward trend from 1985–2005 (Drevnick et al. 2007). Similarly, in New 

England, the region with the longest deposition record in North America, a decline in SO4

2- input 

has been documented since the 1970s (Hedin et al. 1994, Likens et al. 1996). This decline 

extended as far west as MN. Driscoll et al. (2001) reported a decrease in SO4

2- wet deposition in 

northern MI as a result of the Clean Air Act Amendments (CAAA) of 1990.

However, in the 1990s, nitrate and ammonia emissions, which had not yet been fully addressed 

by the CAAA, continued to increase in northern MI (Driscoll et al. 2001). Emissions from 

regulated facilities in the U.S. and Canada within 250 km of ISRO include 63,800 MT yr-1 of 

NOx and 553 MT yr-1 NH3 (Canadian data from 2007 and U.S. data from 2002) (Table 25) 

(Environment Canada 2009, USEPA 2009c). The largest sources of NOx in the ISRO vicinity are 

iron ore–related industries in MN’s Iron Range (Figure 39), while large NH3 sources are located 

at Terrace Bay, Canada, and Hubbell, MI (Figure 40). Compared to Swackhamer and 

Hornbuckle’s (2004) report, NOx and SO2 emissions in the U.S. within 250 km of ISRO 

decreased 6% and 8%, respectively, from 1996 to 2002. Comparative data for NH3 were not 

available.
103

Figure 38. Emissions of sulfur dioxide from regulated facilities within 250 km of Isle Royale National Park

(Environment Canada 2009, USEPA 2009c).

Figure 39. Emissions of nitrous oxides from regulated facilities within 250 km of Isle Royale National Park

(Environment Canada 2009, USEPA 2009c).
104

Figure 40. Emissions of ammonia from regulated facilities within 250 km of Isle Royale National Park

(Environment Canada 2009, USEPA 2009c).

Local Deposition Rates: Estimating the amount of inorganic nitrogen deposition at ISRO is 

difficult both because the NADP station was discontinued in 2006, and because prior to that, 

only summer deposition levels were monitored. Deposition rates ranged from 0.52–1.42 kg ha-1

inorganic N-1 summer during 1985–2006, with a mean of 0.86 kg ha-1 and no apparent trend 

(Figure 41). The nearest NADP station monitoring inorganic N deposition year-round is at 

Hovland, MN, and summer deposition rates at ISRO had a statistically significant relationship 

(p ≤ 0.02) to deposition rates at Hovland (Figure 42). Summer inorganic N deposition at Hovland 

averaged 25.0% of annual inorganic N deposition (S.D. 8.5%, range 10.2–38.5%). By 

extrapolation, ISRO would be estimated to have received an average of 3.5 kg ha-1 inorganic N 

yr-1 during 1985–2006, with a range of 2.2–8.5 kg ha-1, compared to the average of 4.0 kg ha-1

yr-1 for Hovland during 1997–2008. Similarly, Stottlemyer et al. (1998) found a bulk 

precipitation nitrogen input of 3.5 kg ha-1 from 1982 to 1996 in the Wallace Creek watershed, 

and Stottlemyer and Toczydlowski (1999b) measured an average precipitation N input of 3 kg 

ha-1yr-1 in year-round sampling from 1992 to 1997.

The form in which nitrogen is deposited may be significant and depends in part on whether the 

deposition is wet or dry. Wet deposition may include HNO3, NO3

-

, and NH4

+

. Dry deposition 

includes HNO3, particulate NO3

-

, particulate NH4

+

, and NH3 (NAPAP 2005). Of total nitrogen 

deposition at VOYA from 2005 to 2007, 83.5% was wet deposition, while the remaining 16.5%

was dry deposition (USEPA 2009b); similar estimates have not been made for ISRO.
105

Figure 41. Summer wet deposition of inorganic N (NH4-N plus NO3-N) for NADP stations at Isle Royale 

National Park (1985–2006), Hovland, MN (1997–2008), and Chassell, MI (1983–2008) (NADP 2009a, b, 

c). 

Figure 42. Relationship between summer inorganic N wet deposition (kg ha-1

) at Isle Royale National 

Park and Hovland, MN, 1997–2006 (NADP 2009 a, c).

The emission and atmospheric deposition of base cations (Ca2+

, Mg2+, K+, and Na+), which help 

counteract acid deposition, have declined significantly since the early 1960s with the enactment 

of particulate matter pollution controls (Driscoll et al. 2001). A decline in base cation input has 

been documented for New England since the 1970s (Hedin et al. 1994, Likens et al. 1996), and a 

concentration trend of -1.2 μeq/L yr-1 was observed for 12 stations in the Midwest (including 

three in MI) from 1979 to 1990 (Hedin et al. 1994). The average summer wet deposition of base 

cations at ISRO during 1985–2006 was 13.1 μeq/L, with a weak upward trend (p ≤ 0.1). At 

Hovland, the average summer base cation deposition during 1997–2008 was 12.9 μeq/L with no 

0

0.5

1

1.5

2

1980 1985 1990 1995 2000 2005 2010

Inorganic N (kg ha-1)

Summer

ISRO

Hovland

Chassell

R2 = 0.736

0.3

0.8

1.3

0.3 0.8 1.3

Hovland Inorganic N 

(kg ha-1

)

ISRO Inorganic N (kg ha-1)
106

trend (Figure 43). For individual cations, Ca2+ deposition (in kg ha-1

) appeared to increase at 

ISRO from 1985 to 2006 (Figure 45), Mg2+ appeared unchanged, and Na+ and K+ appeared to 

decrease, but the changes were not significant.

Figure 43. Base cations in summer wet deposition for Isle Royale National Park (1985–2006) and 

Hovland (1997–2008) (NADP 2009a, c).

A basic measurement of acid deposition is rainfall pH. The mean pH of rain at the NADP 

monitoring station on ISRO has varied from 4.35 in 1992 to 5.38 in 2006, with a general upward 

trend, but with notably lower values in 2004 and 2005 (Figure 44).

Figure 44. Summer field pH and laboratory pH for precipitation, NADP station at Isle Royale National 

Park, 1985–2006 (NADP 2009a).

0

5

10

15

20

25

1980 1985 1990 1995 2000 2005 2010

Base Cations (μeq L-1)

Summer

ISRO

Hovland
107

Figure 45. Calcium, magnesium, sodium, and potassium trendlines and values (kg ha-1) for annual wet deposition for Hovland, MN (squares), 

1997–2008, and summer wet deposition for Isle Royale National Park (diamonds), 1985–2006 (NADP 2009a).

0

0.5

1

1.5

2

1980 1990 2000 2010

kg ha-1

Calcium

0

0.1

0.2

0.3

1980 1990 2000 2010

kg ha-1

Magnesium

0

0.1

0.2

0.3

0.4

1980 1990 2000 2010

kg ha-1

Potassium

0

0.1

0.2

0.3

1980 1990 2000 2010

kg ha-1

Sodium
108

Ecosystem Effects: The effect of acid precipitation on aquatic ecosystems is determined largely 

by the ability of the water and watershed soil to neutralize the acid deposition they receive. 

Generally, small watersheds with shallow soils and few alkaline minerals are most sensitive to 

acidification. Watersheds that contain alkaline minerals such as limestone, or those with welldeveloped riparian zones, generally have a greater capacity to neutralize acids. Low pH levels 

and higher aluminum levels that result from acidification hinder fish reproduction and decrease 

fish sizes and population densities (NAPAP 2005). Lake Superior and ISRO inland waters, with 

alkalinities over the threshold value of 25 mg L-1 as CaCO3, are not considered particularly 

vulnerable to acid precipitation (Sheffy 1984, Shaw et al. 1996).

The effects of acid precipitation on upland and forest ecosystems include direct and indirect 

impacts on plants, changes in forest floor and/or soil chemistry, and altered rates of mineral and 

nutrient accumulation and loss (Ohman and Grigal 1990, Aber et al. 1998, 2003). The possible 

direct effects on plants (e.g., reducing the integrity of the epidermis) are well-known 

(McLaughlin 1985) and are all negative, with the possible exception of a fertilization effect. The 

indirect effects on plants derive largely from changes in chemistry of the system and include 

nutritional, toxic, and altered symbiosis effects (Hedin et al. 1994, Aber et al. 1998, Friedland 

and Miller 1999, Zaccherio and Finzi 2007). 

Buffering capacity in forest soils is largely a function of four factors: a) surface horizon texture 

and depth, b) B-horizon texture and depth, c) total CEC and base saturation, and d) abundance of 

fungi and bacteria in the upper soil profile (Johnson et al. 1983, Aber et al. 1998). Generally, 

buffering capacity is low in systems with coarse, acid soils; soils low in organic matter (OM); 

and soils that are shallow. Since ISRO soils are generally shallow, acidic, and moderately coarse, 

their buffering capacity is generally low. This is partially offset in some locations in the NE end 

of the island by greater OM content (NPS 2005), a combination of forest floor depth and OM in 

the upper soil profile. The Wallace Lake watershed in the NE has been studied for more than 20 

years by Robert Stottlemyer and colleagues. In this watershed, the soil pH under spruce was 4.4–

4.5 and slightly higher (4.6–5.0) in the deciduous forest (Stottlemyer and Toczydlowski 1999a).

Eutrophication can also be a consequence of nutrient deposition. A compilation and analysis by 

Aber et al. (2003) indicates that some effects on terrestrial and aquatic systems are likely to 

occur if the N-deposition rate exceeds approximately 8 kg ha-1

yr-1 for an extended period of time. 

At this deposition rate, N saturation generally occurs (Aber et al. 1998); nitrogen cycling 

processes such as mineralization, immobilization, and retention efficiency are affected; leaching 

increases; and increased N is detected in surface waters. Since the deposition monitoring stations 

around ISRO indicate a deposition rate of approximately 3 kg N ha-1

yr-1, nitrogen saturation is 

unlikely. 

However, in susceptible systems, N saturation can occur at low deposition rates if the input is 

elevated over a long enough period of time (Aber et al. 2003). In the Engelmann spruce forest 

type of central Colorado, litter quality (assessed by many indicators) and potential net 

mineralization were affected at deposition rates of 3–5 kg N ha-1

yr-1 (Rueth and Baron 2002). A

large-scale, longitudinal study of 161 spruce-fir forests across the NE U.S. suggested that effects 

will show up at a deposition rate of 6–8 kg N ha-1

yr-1, and that many nutrient cycling processes 

respond to increasing levels of deposition (McNulty et al. 1991). A study in Alaska with white 
109

spruce found many of the same effects from approximately 30 years of increased deposition 

(Lilleskov et al. 2001). One very striking result from the Alaska study was the responsiveness of 

the ectomycorrhizal fungal community, which was ten times richer at the upper end of the 

deposition gradient. Other sensitive organisms (e.g., lichens, phytoplankton) may show a 

negative effect at deposition rates of 3–8 kg N ha-1

yr-1 (Fenn et al. 2003). Because streams and 

rivers integrate the deposition on land and deposition directly to the aquatic system, the N

concentration in water has been suggested as a suitable sentinel of N-deposition problems 

(Williamson et al. 2008). 

Old-growth coniferous forests in Colorado have exhibited different responses to low levels of 

fertilization. A site with small N pools and high carbon-to-nitrogen (C/N) ratios, which has 

received 1.1–1.7 kg N ha-1yr-1, had no soil processes affected, but foliar N levels and the amount 

of N in the organic horizon increased (Rueth et al. 2003). The site with higher N pools and a 

lower C/N ratio (deposition rate of 3.2–5.5 kg N ha-1

yr-1) showed an increase in mineralization 

and an increase of N in the soil fraction. These results suggest how initial N-deposition effects 

will likely manifest in the boreal forests of ISRO, well before any N increase is noted in the 

streams or rivers.

The slow decomposition rate and demand for N demonstrated by the high level of nitrate and 

ammonium immobilization by soil profile decomposers in the Wallace Lake watershed 

(Stottlemyer and Toczydlowski 1999a) suggests that N is the prime limiting nutrient in the boreal 

forest types at ISRO, as it is elsewhere (Bonan and Shugart 1989). In boreal forests in Sweden, a 

fertilization effect on productivity has been noted with increased N deposition (Zackrisson et al. 

2004). The additional N can cause plants to grow later in the season, but then the newer tissue is 

killed by the first frost. This effect has been noted in high elevation spruce-fir of New England

and could happen at ISRO, given the climatic regime.

The boreal system may have low resilience to chemical stressors. Stottlemyer and Hanson (1989) 

determined that the concentrations of SO4

2-

, Ca2+, and Mg2+ were higher in soil solution than in 

precipitation at ISRO sites, and SO4

2- had a flux 2–3 times that of other nutrients under conifers. 

These findings demonstrate how acid deposition could affect a terrestrial system by setting the 

stage for accelerated loss of cations. The hydrogen ions associated with sulfate anions replace 

other cations on the soil exchange sites (Tomlinson 2003), and then the cations are leached if 

water moves down through the soil profile. The cations being lost are important macronutrients, 

needed by plants and decomposers in fairly large amounts, and have the potential to become 

limiting resources. An imbalance in Mg2+ was suggested as a possible cause of forest decline in 

spruce-fir forests in the NE U.S. (McNulty et al. 1991), though at higher sulfate deposition rates 

than are occurring at ISRO. Here, K+ appears most likely to become a limiting resource due to 

reduced input since 1990.

Nutrient deficiency is particularly likely for any upland ecosystem that has low base saturation, 

which is common on acidic sites. However, cation loss occurs even on soils with high buffering 

capacity. The effect is cumulative and continues even after acid deposition is mitigated. In New 

England, large quantities of Ca2+ and Mg2+ have been lost from the soil (Likens et al. 1996, 

Friedland and Miller 1999) even after nitrate and sulfate inputs were reduced and the pH of 

precipitation increased (Likens et al. 1996). 
110

A second undesirable effect that might manifest from N deposition is simplification of 

composition. That is, a subset of species is favored under the changed nutrient conditions and is 

able to outcompete other species. Simplification has not been documented in a boreal forest, but 

has been demonstrated in some forest fertilization trials (Rainey et al. 1999). Shifts in relative 

abundance of common understory species could also occur. Canada mayflower (Maianthemum 

canadense) and starflower (Trientalis borealis) moved in opposite directions in response to 

increasing nitrogen in a red pine forest, and one fern (Dennstaedtia punctilobula) appeared to be 

at a sharp competitive disadvantage as nitrogen was added (Rainey et al. 1999).

In 2004, Swackhamer and Hornbuckle concluded there is “... little indication of this problem 

(acid rain) ... at ISRO.” Factors supporting the Swackhamer and Hornbuckle (2004) conclusion 

include relatively low nitrogen deposition rates, an upward trend in precipitation pH from 1985

to 2006, an overall low sulfate deposition rate with a downward trend from 1985 to 2006, and the

magnitude of conservation within the forest floor and soil of potassium and nitrate-N 

(Stottlemyer and Hanson 1989, NADP 2009a). However, N deposition cannot be completely 

dismissed as a potential stressor for the boreal system, which is N limited (Bonan and Shugart 

1989, Zackrisson et al. 2004). The boreal system may have low resilience to chemical stressors

and be susceptible to cation losses due to low buffering capacity and inherently low soil pH 

values (Stottlemyer and Hanson 1989, Stottlemyer and Toczydlowski 1999b). Further, N 

saturation can occur at low deposition rates if the input is elevated over a long enough period of 

time and the system is susceptible (Aber et al. 2003).

Mercury

Mercury is a persistent, bioaccumulative toxic pollutant with harmful health consequences for 

both humans and animals. Although it is naturally occurring, human activities have facilitated its 

spread throughout the environment. Mercury emissions to the atmosphere are the result of 

industrial processes and incineration, but the major source is coal-fired power plants. In 1999 and 

2000, respectively, 56.7% of the mercury emissions in Michigan and 43.5% of those in 

Minnesota were related to the generation of electricity (MDEQ et al. 2003). Approximately 

3,700 kg yr-1 of mercury were released to the atmosphere in MI, MN, and WI in that time frame 

(MDEQ et al. 2003).

The presence and concentration of mercury have been studied in a number of lakes at Isle 

Royale, and the concentration is quite variable across the landscape. In some lakes, it has reached 

levels in fish that are a concern. At present, Lake Superior and Siskiwit Lake are on Michigan’s 

303(d) list because of the presence of mercury in fish tissue (MDEQ 2008b), and of 32 ISRO 

inland lakes sampled in 1995 and 1996, six (Angleworm, Eva, Intermediate, Sargent, Shesheeb, 

and Wagejo) had fish with mercury levels that exceeded fish consumption advisory levels 

(Kallemeyn 2000, Drevnick et al. 2007). At first, bedrock was suspected of contributing mercury 

to soils and surface water. Further studies showed that mercury resulted mainly from

atmospheric deposition, although some minerals associated with native copper minerals had trace 

amounts (Cannon and Woodruff 1999, 2000, Woodruff et al. 2003, Thornberry-Ehrlich 2008). 

Studies have also shown that precipitation at ISRO (Hall et al. 2005) and soils in a broad zone 

including ISRO (Nater and Grigal 1992) have mercury concentrations at or above the regional 

averages.
111

Crane et al. (2006) reviewed ISRO aquatic mercury studies to date, including Kelly et al. (1975), 

which compared mercury levels in fish in a 1971 sample to fish from museum collections (ca. 

1929). Mercury levels were elevated, but there was no indication of a change over time. In 1987–

1989 and 1992–1993, the MDNR sampled lake trout from Siskiwit Lake and nearshore waters of 

Lake Superior. They found no change over time, and fish from Siskiwit Lake met health 

guidelines for mercury, but some from Lake Superior did not (Crane et al. 2006). In mussels, the 

highest mercury concentrations have been found in Lake Richie; at 0.221 mg kg-1

, they were 

slightly above the threshold effects concentration of 0.200 mg kg -1 (Nichols et al. 2001a). 

Kaplan and Tischler (2000) described ISRO adult common loons as having “moderate to low” 

blood mercury levels compared to loons in other parts of the Great Lakes and North America. 

Male loons had significantly higher blood and feather mercury levels than female loons (Evers et 

al. 1998, Kaplan and Tischler 2000). Ten percent of adult loons at ISRO had feather mercury 

concentrations at or above the suggested threshold level of 20 μg g-1 (Kaplan and Tischler 2000),

and mercury concentrations were approximately ten times greater in adults than in juveniles 

(Evers et al. 1998). Kaplan and Tischler (2000) noted that their study results suggested a link 

between elevated mercury levels in fish and reproductive failure of loons on ISRO inland lakes.

Mercury occurs in three forms in the atmosphere: 1) gas-phase elemental form (Hg[0]), 2) 

gaseous inorganic form (Hg[II]) formed in photochemical reactions, and 3) particulate form 

(Hg[P]). Ninety-five percent of the total in the atmosphere is in the elemental form (Grigal 

2002), but the inorganic form is more soluble and is the dominant form in precipitation. In 

aquatic ecosystems, particularly in anaerobic environments such as wetlands and lake sediments, 

microbes transform deposited inorganic mercury into methylmercury (MeHg), which 

biomagnifies in food webs, resulting in high concentrations in fish (Drevnick et al. 2007 and 

citations therein). In Lake Superior, a small amount (< 6%) of the total mercury deposited is 

MeHg; this occurs mainly during low-volume rain events where it is “washed out” of the 

atmosphere. Sources of this MeHg may include lake-effect cloud and fog, nearby wetlands, or 

upwelling of deep waters from the lake (Hall et al. 2005). 

Although mercury has been studied extensively in ISRO’s aquatic systems, little study has been 

done on terrestrial systems. Such study is warranted both because mercury can bioaccumulate in 

the methylmercury form and because of the intimate process connection between terrestrial and 

aquatic systems. Because most of the ISRO landscape is terrestrial and largely forested, the 

majority of the total mercury load for the island enters via forest ecosystems. Studies have shown 

that between 5% and 25% of deposited mercury will reach associated lakes (Grigal 2002). Thus, 

the land is an important contributor to the mercury status of lakes, and a strong majority of the 

incoming mercury stays in the terrestrial system for some period of time. This suggests that 

bioaccumulation needs to be examined, as well as direct effects on organisms in the soil.

The roots of plants act as a natural barrier to mercury, and an adsorption site, and thus there is 

limited uptake (Grigal 2003). The review of inputs and outputs by Grigal (2002) concluded that 

less than 10% of the mercury in plants is from the soil. The gas-phase elemental form adsorbs to 

leaf surfaces and enters the plant through open stomates. It binds to mesophyll tissues readily and

is easily oxidized, and thus ‘captured,’ in the leaves. Consequently, litterfall is the dominant flux 

between the atmosphere and the terrestrial system, and is the primary pathway by which mercury 
112

gets to the soil sub-system. This fact explains why characteristics of the surface are an important 

part of the movement of mercury; the length of the growing season, the longevity of leaves, and 

the amount of leaf surface area all play a critical role in determining how much mercury is 

deposited on an annual basis. Though Hg(0) is the most abundant form, approximately 1.5% of 

the mercury in litterfall is MeHg.

The fate of mercury in the terrestrial system is not well understood. It is subject to volatilization 

at ambient temperatures and readily adheres to most forms of organic matter. For this reason, the 

concentration of mercury in the organic horizon on the forest floor is six times that of the mineral 

soil, though the total mass in the mineral soil is five times higher (Nater and Grigal 1992). At 

ISRO, soils burned in the 1936 forest fire have low carbon and mercury content compared to 

unburned areas (Cannon and Woodruff 2000).

Hg(0) and Hg(II) are the more common forms in the soil (MeHg is about 0.6% of the total), and 

both forms go into solution and adhere to soil adsorption sites (Grigal 2003). Thus, mercury 

decreases with depth in the soil profile. Under certain conditions, it is converted to the MeHg 

form. 

Published values indicate that the concentration of mercury in “plants” is: herbs < trees + shrubs

< aquatic macrophytes < sphagnum moss < mosses < lichens < fungi (Moore et al. 1995). In 

Ontario, the lowest concentrations of total mercury and MeHg were found in the leaves of trees 

and shrubs. Thus, herbivores that feed on forbs or upland woody plants get a very low dose of 

mercury. Though top predators often have higher concentrations than herbivores, there appears 

to be little biomagnification in terrestrial food chains (Grigal 2002). In a study of deer mice on 

ISRO, mercury concentrations were “not remarkably high compared to heavily polluted sites,” 

but the authors expressed concern about both biomagnification and the (then) unknown source of 

the mercury (Vucetich et al. 2001).

Sulfate-reducing bacteria are the organisms responsible for the methylation of mercury (Grigal 

2003, Drevnick et al. 2007). These microbes are most abundant under anoxic conditions and in 

places where carbon accumulates. This explains why the wetland area around a lake is a critical 

determinant of mercury concentration in lakes, and why beaver ponds have higher levels of 

mercury than lake sediments (Grigal 2003). Sulfate availability influences mercury methylation. 

Recent research indicates that for the last century, mercury accumulation in ISRO fish has been 

controlled by the deposition and cycling of sulfur. Thus, acid rain reduction programs have had 

the unexpected benefit of reducing methylmercury contamination of fish at ISRO and in other 

sulfur-limited environments; mercury levels in northern pike had “substantially declined” in the 

past decade at ISRO and dropped below the fish consumption advisory level at Sargent Lake, 

after a lag time caused desorption from soil of sulfate deposited in earlier years (Drevnick et al. 

2007). The authors warned that a significant increase in atmospheric sulfur loading (such as that 

proposed by some to slow climate change) could reverse this positive effect (Drevnick et al. 

2007). However, Drevnick et al. (2008) showed that even at the reduced levels of mercury 

contamination found in ISRO fish, fish health, as suggested by condition factor, is inversely 

related to total mercury levels in liver tissue; mercury toxicity is still a concern. 
113

Great Lakes Shipping

Lake Superior is an important water highway for the transfer of goods and materials. The largest 

port on the lake, Duluth, handles 40 million metric tons (MMT) of cargo annually and is ranked 

first among Great Lakes ports and 18th in the nation in total cargo volume. About 1,100 vessels 

visit the port of Duluth each year (Duluth Seaway Port Authority 2009a), and approximately 400 

vessels visit the port of Thunder Bay (Thunder Bay Port Authority 2009). 

Cargo ships may affect aquatic ecosystems in numerous ways, including the introduction and 

transfer of aquatic exotic species; emissions of air pollutants such as oxides of sulfur and 

nitrogen; accidents that spill cargo or fuel; normal losses of fuel during engine operation; transfer 

of substances to water from biocides and antifouling paints; noise and vibration; prop wash, 

surge, and wake; groundings and anchoring; wildlife encounters; and discharges of garbage, 

cargo sweepings, human sewage, dunnage (material placed between cargo during shipping), 

ballast water, and bilge water (Lewey et al. 2001, Transport Canada et al. 2007). Ballast water

and bilge water are described in more detail below.

Many regulations are in place to attempt to prevent water pollution from both recreational 

boating and commercial shipping activities. The International Convention for the Prevention of 

Pollution from Ships (MARPOL 73/78) and its amendments is an international treaty that 

addresses pollution from oil, noxious substances, harmful substances in packaged form, sewage, 

garbage, and air pollution (International Maritime Organization 1978). The Refuse Act of 1899 

prohibits the throwing of any refuse into the waters of the United States (Code of Federal 

Regulations 1899). The Federal Water Pollution Control Act prohibits the discharge of oil or 

hazardous substances into U.S. navigable waters (Code of Federal Regulations 1987). All vessels 

with propulsion capability must have capacity to retain oily materials on board. Coast Guard 

regulations make it illegal to dump plastics, dunnage, lining and packaging materials, and 

garbage (except dishwater, greywater, and fresh fish parts) anywhere in the Great Lakes. The 

discharge of raw sewage from boats is also prohibited in the Great Lakes, and no discharge of 

treated sewage from marine sanitation devices is permitted in Lake Superior in MI (USEPA 

2005). Ballast water rules are discussed in the Ballast Water section below.

Shipping Lanes and Shipwrecks

The risk of a shipwreck or accident on Lake Superior that results in a spill of fuel or cargo is not 

insignificant. Lake Superior’s cliffs and reefs and unpredictable weather have contributed to 350

shipwrecks in the past (Minnesota Sea Grant 2005), including at least 13 within the present 

boundary of ISRO (Rayburn et al. 2004). The most recent shipwreck on Lake Superior occurred 

in November 1975 NW of Whitefish Point; the Edmund Fitzgerald was the largest ship ever to 

sink on the Great Lakes (NOAA 2000). 

Approximately 1,000 large commercial vessels use the channel between Blake Point and Passage 

Island at ISRO each year en route from the Locks at Sault Ste. Marie to the port of Thunder Bay, 

Ontario (Figure 46) (Rayburn et al. 2004). In addition, at the discretion of ships’ masters, vessels 

may use ISRO for protection during harsh weather while traveling between the locks and ports at 

the head of the lake (Taconite Harbor, Silver Bay, Two Harbors, Duluth, Superior, or Ashland). 

Typically, they seek refuge off the north shore of ISRO because of strong southeasterly or 

southwesterly winds or off the south shore when winds are northwesterly. Such 
114

Figure 46. Lake Superior shipping lanes (NOAA 2007 a, b, c, d).
115

rerouting usually occurs only a few times a season, and the vessels approach no closer than a 

kilometer from shore (Rayburn et al. 2004). However, since accidents are more likely in bad 

weather conditions, the location of the designated shipping lanes around ISRO does not fully 

describe the degree of risk. The Edmund Fitzgerald had passed the south side of ISRO on her 

final voyage (NOAA 2000). In 1990, the M/V Kinsman Independent ran aground on a reef at the 

entrance to Siskiwit Bay because of a navigational error, but was later pulled free and proceeded 

to Thunder Bay (NOAA 1990).

Cargo

In 2008, the port of Thunder Bay handled 5.7 MMT grain (70% of cargo), 1.7 MMT coal (20%), 

0.3 MMT potash (4%), and 0.4 MMT liquid bulk, dry bulk, and general cargo. It also announced 

a “breakthrough” in reaching an agreement with CN Rail to provide a “gateway” to move 

supplies and heavy equipment to the oil sands region of Alberta. Its first major shipment was five 

reactors that arrived from Japan after traveling through the Panama Canal and the St. Lawrence 

Seaway (Thunder Bay Port Authority 2008). Also in 2008, the port of Duluth-Superior handled 

20 MMT coal and coke (48% of cargo), 17 MMT iron ore and concentrates (40%), and 3.5 MMT 

limestone, grain and byproducts, bulk, and general cargoes (Duluth Seaway Port Authority 

2009b). Other smaller ports from which ships may pass ISRO are Two Harbors, MN, which 

ships iron ore; Taconite Harbor, MN, and Ashland, WI, which receive coal; and Silver Bay, MN, 

which ships iron ore and receives coal (Lake Carriers Association 2009).

The Great Lakes–St. Lawrence Seaway System is considered “underutilized” (Transport Canada 

et al. 2007), and the “Hwy H2O” program has been established to promote marine transportation 

and attract new shippers. As a result, the St. Lawrence Seaway Management Corporation 

(SLSMC) reported in 2006 that new cargoes attracted to the system had doubled since the 

previous year (SLSMC 2006).

Fuel and Engine Types

Both oceangoing ships (“salties”) and ships confined to the Great Lakes (“lakers”) carry cargo on 

Lake Superior. In the late 1990s, 90% of the commercial vessel trips to the port of DuluthSuperior were reportedly made by lakers, and 10% were made by salties (USEPA 1999a). In 

2008, 6% of the vessels using the port of Duluth-Superior were salties (Duluth Seaway Port 

Authority 2009c). Also in 2008, 346 domestic (Canadian) vessels, 5 American vessels, and 64 

(15%) foreign vessels used the port of Thunder Bay (Thunder Bay Port Authority 2009).

Between 2002 and 2006, between 2,075 and 2,569 trips were made into and out of DuluthSuperior by commercial vessels; 56–66% were by domestic vessels and 34–44% were by 

foreign-flagged vessels (Table 26) (USACE 2002, 2003, 2004, 2005, 2006). However, since 

Canadian vessels are foreign-flagged in this listing, these data are not useful in separating salties 

from lakers.

Cargo ships are very large vessels that carry large volumes of fuel. For example, a typical 300 m 

ship carries 689 m3 of primarily #6 fuel oil (a heavy fuel oil [HFO] also known as residual fuel 

or bunker C fuel), 167 m3of #2 fuel oil (a lighter diesel fuel), and 72 m3 of lube and waste oil 

(U.S. Coast Guard, Greg Schultz, pers. comm. 2005). The type of fuel burned by lakers may 

differ from the fuel burned by salties, depending on the speed and type of the engine. 
116

Table 26. Commercial vessel trips to and from the port of Duluth-Superior, 2002–2006 (USACE 2002, 

2003, 2004, 2005, 2006).

Year Domestic vessel trips % Foreign vessel trips % Total

2002 1,378 56 1,079 44 2,457

2003 1,227 57 924 43 2,151

2004 1,387 61 882 39 2,269

2005 1,363 66 712 34 2,075

2006 1,564 61 1,005 39 2,569

Marine diesel fuels are categorized as residual, intermediate, or distillate fuels depending on their 

viscosity. Residual fuels (HFO) are those that do not boil during the distillation process; they are 

thicker and more tar-like than distillate fuels. Intermediate fuels can be formed during the 

distillation process or created by blending residual and distillate fuels (USEPA 1999b).

A 2003 study of oceangoing transport ships showed that 91% of the bulk carriers and tankers, 

and 100% of large container vessels, were operated with two-stroke engines, and 95% of lowspeed two-stroke engines burn HFO. Seventy percent of four-stroke, medium-speed engines also 

burn HFO, while the remaining 30% burn intermediate weight marine distillate oil or lightweight 

marine gas oil. Thus, the vast majority of salties burn HFO (Corbett and Koehler 2003). These 

heavier fuels are harder to clean up in a spill, and the two-stroke engines in which they are used 

operate less efficiently and generate more emissions than four-stroke engines. Lakers tend to 

have USEPA Category 2 engines (USEPA 2002a), which have a smaller displacement per 

cylinder (and are therefore less powerful) than the Category 3 engines in most oceangoing ships 

(USEPA 2004). Most Category 2 ships burn distillate diesel fuel similar to non-road diesel fuel 

(ICF Consulting 2005). 

The potential harm from an oil spill resulting from a bulk cargo vessel running aground was 

evaluated for ISRO in Lake Superior in a simulation assuming a spill of approximately 100 m3 of 

Intermediate Fuel Oil (Rayburn et al. 2004) from a ship running aground on the SW side of 

Passage Island in late April. The scenario’s primary impact was to the NE tip of ISRO, heavily 

oiling Duncan Bay, Merritt Lane, Tobin Harbor, and Rock Harbor. It was approximated that the 

oil would reach Blake Point in seven hours and Tobin Harbor in 18–19 hours (Rayburn et al. 

2004).The researchers concluded that shoreline cleaning methods for freshwaters are not well 

documented and that floating platforms would be needed in the nearshore environment for 

cleanup operations. The greatest risks occurred under the “natural recovery” scenario and 

included catastrophic losses to coastal wetland macroinvertebrates; shoreline vegetation, 

herptiles, and birds; and nearshore fish. Critical losses were also anticipated for birds and fish in 

coastal wetlands, wolves, and shoreline mammals. Because of the number of populations in 

ISRO that are highly rare, genetically distinct, or otherwise unique, “a spill of this magnitude to 

Isle Royale will be a major event with regional, national and international importance” (Rayburn 

et al. 2004).

The Western Lake Superior Area Committee has an Area Contingency Plan that “describes the 

strategy for a coordinated federal, state and local response to a discharge or substantial threat of 

discharge of oil, and or a release of a hazardous substance within the boundaries of the coastal 
117

and inland area of Western Lake Superior.” In 2006, it determined that the “worst case 

discharges” for a vessel in western Lake Superior are the grounding of a tanker passing on the 

north side of ISRO on its way to Thunder Bay, potentially spilling 9,500 m3 cargo and 750 m3

bunker fuel, or a freight vessel grounding and discharging 600 m3 of fuel in the form of a light to 

intermediate grade oil (Western Lake Superior Area Committee 2006).

In 1993, NOAA identified and mapped 14 shoreline types in ISRO as part of a USEPA 

assessment of shoreline vulnerability to oil spills (USEPA Region 5 2000). Areas of low 

sensitivity included 193 km of exposed rocky cliffs, shelving bedrock shores, and riprap 

revetments, groins, and jetties. Low-medium sensitivity areas were 115 km of sand beaches, 

exposed flats/shelving bedrock shores, mixed sand and gravel beaches, and gravel beaches. 

Medium-high sensitivity areas were 216 km of sheltered scarps in bedrock, sheltered solid 

(hu)man-made structures, and sheltered vegetated low banks. High sensitivity areas were 10.2 

km of wetlands (Table 5, Figure 9).

Bilge Water

Bilge water is the water that collects at the bottom of the hull of a ship or boat. It is often 

contaminated with fuel as well as oily materials used to lubricate moving parts. Bilge water may 

also carry solid wastes, and often has a high oxygen demand (Copeland 2005). 

Although MARPOL 73/78 specifically forbids the discharge of bilge water that produces a sheen 

or has an oil content of more than 15 mg L-1 (International Maritime Organization 1978), illegal 

bilge discharges do occur. Specific data for the Great Lakes were not found, but data on ships’ 

practices in the ocean may provide some insight into possible risks to Lake Superior. Currently, 

50% of the oil entering the sea from shipping activities comes from bilge and fuel oil sludges, 

mainly due to the lack of onshore reception facilities, according to the Ocean Conservancy 

(2001). A study of foreign-flag cruise ships found 72 cases in which they had discharged oil or 

oil-based products into U.S. waters between 1993 and 1998 (USGAO 2000).

In 2002, the World Wildlife Fund of Canada reported that 300,000 birds are killed each year on 

Canada’s ocean coast because of illegal bilge discharges (Wiese 2002). Bird mortality rates in 

the U.S. were significantly lower. Fines up to 1,000 times higher in the U.S. were thought to 

dissuade more ships from discharging in U.S. waters.

Ballast Water

Ballast water is water carried in special holding tanks on a ship to allow for trimming and more 

efficient and safe sailing. Ballast water is usually taken on board when cargo is unloaded and 

discharged when cargo is loaded. Concerns with ballast water discharges center around the 

possible introduction of exotic invasive species. Ballast water contains organisms ranging from 

bacteria and algae to worms and fish. Grigorovich et al. (2003a) identified 67% of the 43 

invasive aquatic animal and protist species introduced and established in the Great Lakes since 

1959 as having originated in ballast water from commercial vessels.

All oceangoing ships are required to exchange their ballast water in the open ocean before 

traveling into the Great Lakes. However, 90% of ships that enter the Great Lakes are reported as 

“no ballast on board” (NOBOB) because they are filled with cargo (Grigorovich et al. 2003a).
118

Because the ballast tanks of NOBOB ships are not completely empty, some organisms survive in 

sediments or the small remaining amount of water in the tanks. As the ships unload cargo, they 

take on additional ballast water from other Great Lakes ports. From 1981 to 2000, 70% of 

NOBOB ships made their final stop at Lake Superior, where they discharged their mixed ballast 

water as new cargo was loaded. Lake Superior also received about 75% of the ballast water 

discharged by transoceanic ships that enter the Great Lakes with ballast on board (Grigorovich et 

al. 2003b). Thus, Lake Superior appears to be at high risk for the introduction of exotic species. 

However, Lake Superior’s oligotrophic nutrient state, limited primary productivity, and high 

ratio of profundal-limnetic to littoral zones may be mitigating factors that limit aquatic invasive 

species (Grigorovich et al. 2003b).

The State of Michigan has established a general permit system for ballast water reporting on the 

Great Lakes. Permit holders must demonstrate that they do not discharge ballast water into state 

waters or that they have treated the water with hypochlorite, chlorine dioxide, deoxygenation, or 

ultraviolet light preceded by suspended solids removal . The permit system does not apply to 

lakers that move only within the Great Lakes (MDEQ 2006). The MDEQ maintains a list of

oceangoing ships that report compliance with the “Code of Best Management Practices for 

Ballast Water Management” provided by the Shipping Federation of Canada and of nonoceangoing vessels that report compliance with the “Voluntary Management Practices to Reduce 

the Transfer of Aquatic Nuisance Species within the Great Lakes by United States and Canadian 

Domestic Shipping” provided by the Lake Carriers Association and the Canadian Shipowners’ 

Association to the MDEQ. The MDEQ listed 244 ships as of April 6, 2009; 62 were from the 

U.S., 76 from Canada, and the remainder from 14 foreign nations (MDEQ 2009a).

In April 2005, a U.S. District Judge ordered the USEPA to repeal regulations exempting ship 

owners from obtaining pollution discharge permits for ballast water, and in September 2006, a 

federal court ordered the USEPA to develop new ballast water regulations under the Clean Water 

Act by September 2008 (Ocean Conservancy 2006). In 2008, the U.S. House of Representatives 

passed a ballast water control measure, but it was never signed into law, and the USEPA issued a 

general permit for ballast water discharges. As of May 15, 2009, the Department of Homeland 

Security (which contains the U.S. Coast Guard) had submitted a Ballast Water Discharge 

Standard Notice of Proposed Rulemaking package to the Office of Management and Budget 

(USCG 2009).

Ferry Service

ISRO is served by the Ranger III, a 50 m ship that is the largest vessel operated by the NPS 

(NPS 2008a). It operates from Houghton to Mott Island, Rock Harbor, and occasionally to 

Windigo, and can carry 128 passengers and 590 MT of cargo, including refrigerated and frozen 

goods, dry goods, and 28,000 L of #2 fuel oil (LeLievre 2006, NPS 2008a). In an average year, it 

transports 300 recreational and NPS work boats to and from the island. It has a strengthened bow 

and is capable of breaking ice in the spring (NPS 2008a). The Ranger III’s ballast water 

currently undergoes treatment to destroy aquatic invasive species.

Commercial ferry service is provided by two carriers. The Isle Royale Line operates the 30 m 

Isle Royale Queen IV from Copper Harbor to Rock Harbor. The Grand Portage–Isle Royale 

Transportation Lines operates the 18 m Voyageur II from Grand Portage to Windigo, McCargoe 
119

Cove, Belle Isle, Rock Harbor, Chippewa Harbor, and Malone Bay and the 19 m Wenonah from 

Grand Portage to Windigo. Seaplane service is also available from Houghton (Isle Royale and 

Keweenaw Parks Association 2009). Risks associated with these forms of transportation are 

similar to those for cargo ships, most notably accidental transfer of aquatic invasive species and 

fuel releases.

Recreational Boating

All ISRO waters are closed to water skiing and personal watercraft (PWC). No-wake zones are 

established in all or parts of Todd Harbor, Johns Island, Barnum and Washington Islands, Hay 

Bay, Wright Island, Malone Bay, Chippewa Harbor, Conglomerate Bay, Moskey Basin, Lorelei 

Lane, Tobin Harbor, Merritt Lane, Passage Island, Duncan Bay, Five Finger Bay, Stockly Bay, 

Lane Cove, the Robinson Bay/Pickerel Cove/Belle Harbor Area, Crystal Cove, and McCargoe 

and Brady coves. Inland lakes can be explored only by portaging in and paddling (NPS 2004b). 

In general, the major impacts of motorized watercraft on aquatic ecosystems may include 

sediment resuspension, water pollution, disturbance of fish and wildlife, destruction of aquatic 

plants, and shoreline erosion. The mechanisms by which these impacts occur include propeller 

contact with plants and animals, turbulence caused by the propulsion system, wakes, noises, and 

movement that disturbs wildlife (Asplund 2000). Recreational boating may also help to transfer 

invasive species; this effect is discussed in the Introduction Pathways and Control Strategies 

subsection of the Exotic Species-Aquatic section.

Conventional two-stroke outboard engines contribute to both air and water pollution because 

they burn gasoline inefficiently and discharge as much as 30% of their fuel to the environment. 

Direct-injection two-stroke engines are cleaner than conventional engines, but still not as cleanburning as four-stroke engines. For example, when 90-horsepower gasoline-powered outboard 

motors are compared, a conventional two-stroke engine creates 164 g of smog-forming pollution 

per kilowatt-hour, while a direct-injection two-stroke engine creates 45 g and a four-stroke 

engine creates 11 g (California Environmental Protection Agency Air Resources Board 1999).

The primary water and sediment pollutants of concern from marine engines include MTBE 

(methyl tertiary butyl ether); PAHs; BTEX (benzene, toluene, ethylbenzene, and xylene); and

heavy metals such as copper (NPS 2002). In 2003 and 2004, Clements and Cox (2006) sampled 

12 locations in ISRO for 39 PAH compounds. Background sites were dominated by petrogenic 

PAH compounds (of natural origin); marina sites were influenced by pyrogenic PAH 

compounds, which are produced by the burning of fossil fuels, industrial processes, and 

emissions from combustion engines. Highest concentrations were found at Rock Harbor marina. 

The amphipod Diporeia spp. was consistently more abundant at reference sites than at paired 

marina sites, although results in 2004 were statistically significant at only one site. The survival 

of another amphipod, Hyalella azteca, was negatively correlated with PAH concentrations 

normalized to total organic carbon concentrations in toxicity tests. However, the only statistically 

significant difference (p ≤ 0.05) was between Rock Harbor marina and its reference location. The 

authors considered this finding “not surprising” because Rock Harbor marina is the only ISRO 

location to exceed the threshold effect concentration for PAHs (Clements and Cox 2006).
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Water Use and Wastewater Treatment

The ISRO Water Resources Management Plan (Crane et al. 2006) cites a 2001 ISRO Business 

Plan to document the presence of nine electric generators, seven water treatment facilities, one 

wastewater treatment plant, 115 privies (including 90 pit toilets at 36 campgrounds), eight 

residential septic systems, and five remote ranger and research stations with individual solar 

electric and water treatment systems as part of ISRO’s utility infrastructure.

ISRO has three federal-regulated transient non-community public water supplies (supplies that 

serve at least 25 people at least 60 days of the year, but do not serve the same people over six 

months of the year) (USEPA 2009f). Mott Island serves 75 people day-1, while Windigo serves 

115 and Rock Harbor, 335 (USEPA 2009f). No violations of water quality standards have been 

noted for these three facilities in the past ten years. 

With water shortages becoming more prevalent nationwide, concerns have been raised about the 

possibility that Great Lakes water will be sold or diverted to other parts of the nation or world. 

The Great Lakes–St. Lawrence River Basin Water Resources Compact of 2005 would prevent 

new or increased diversions of water from the Great Lakes except under limited circumstances, 

mainly for public water supplies for counties that “straddle” the Great Lakes basin (Council of 

Great Lakes Governors 2005). The compact was approved by the U.S. Senate and House of 

Representatives and was signed into law by President George W. Bush in October 2008.

ISRO now has two wastewater treatment systems with National Pollution Discharge Elimination 

Permits. The Mott Island facility has a very small flow (2.6 m3 day-1

, or 700 gallons day-1) and 

participates in a self-monitoring annual certification program. The larger Rock Island facility 

discharged 56 m3 day-1 (14,700 gallons day-1) in 2008 and 35 m3 day-1 (9,400 gallons day-1) in 

2009 (USEPA 2009f). The discharge is monitored for various chemical parameters (Table 27).

Table 27. Results of monitoring for chemical and biologic parameters in 2008 and 2009 at the Rock 

Harbor wastewater treatment plant, Isle Royale National Park (USEPA 2009f).

Parameter 2008 2009

DO (minimum) (mg L-1) 4.57 6.93

pH 6.62–7.47 7.22–7.36 

Total Suspended Solids (average) (mg L-1

) 2.24 (92.8% removal) 1.98 (98.1% removal)

TP (mg L-1) 0.492 0.503

Chlorine 0 0

Fecal bacteria (MPN/100 mL) 1.4 0

Biological oxygen demand (average) 

(mg L-1)

1.22 (97.8% removal) 1.50 (98.6% removal)

No violations of discharge requirements were reported. The plant won a National Wastewater 

Management Excellence Award in 2001.
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Natural and Altered Terrestrial Disturbance Regimes

All terrestrial ecosystems in the temperate and boreal regions have, throughout their evolutionary 

history, been subjected to a suite of disturbances (White 1979, Bonan and Shugart 1989). Thus, 

disturbance is the factor most integral to the short- and long-term dynamics of a plant 

community. The disturbance history of ISRO is poorly known due to very limited study, but the 

historic disturbance regime for communities at ISRO must be described to the extent possible to 

help understand the current vegetation patterns and how the vegetation is likely to change in the 

future. 

A complete disturbance regime is described by these components: frequency, intensity (a 

measure of the force of the phenomenon), timing and season, extent, duration (in some cases), 

variation in frequency, and variation in intensity for each type of disturbance (White 1979, Sousa 

1984).

Disturbances with severe impacts have significant and immediate effects on vegetation and 

abiotic conditions as well as important indirect effects (Halpern and Franklin 1990). These 

indirect effects often stress a significantly larger number of organisms and create an opportunity 

for invasion and establishment of novel species. In some cases, disturbance is necessary for the 

maintenance of specific communities or landscape patterns (Sousa 1984, Turner et al. 1997, 

Barnes et al. 1998). 

A potentially important factor whose precise influence at ISRO is unknown is the heterogeneous 

physiography of the area. Work elsewhere has conclusively demonstrated that topography exerts 

a strong influence on some disturbance components. Slope, elevation, and aspect result in 

changes in radiational load and soil water, which in turn influence the vegetation. Thus, fire 

intensity and spread can change due to fuel combustibility (moisture differences) and fuel 

complex (community) structure (Graham et al. 2004). Wind damage often varies by slope, 

species, and canopy position (Foster 1988, Canham et al. 2001).

Boreal Forest

The fire regime for boreal forests in ISRO has not been fully described, although the fire regimes 

of boreal forests in general have been well-described in northern MN (Heinselman 1973, Frelich 

and Reich 1995, Frelich 2002); parts of Canada (Bergeron 1991, Arseneault and Sirois 2004); 

and Alaska (Viereck 1983). However, the fire return interval (FRI) is variable across this broad 

region, with a range of 65–200 years, and reports from other sites may not apply well to ISRO

(NPS 2004a). The study by Bergeron (1991) in Quebec was the only study found to compare fire 

regimes on islands and an adjacent mainland in the boreal region. The islands experienced more 

fires than the lakeshore, and fire years were uncorrelated. Bergeron (1991) also documented a 

greater range of fire sizes on the islands. In both landscapes, fire frequency had declined over the 

past approximately 120 years (i.e., from 1870 to 1990). The FRI on the islands was 74 years 

prior to 1870 and 112 years thereafter. Thus, it would be incorrect to assume that fire was less 

common or consistently smaller on ISRO than on the mainland.

The Isle Royale Fire Management Plan (FMP) (NPS 2004a) cites a compilation (Martin 1988) of 

documents that describe fire occurrence since 1848, but expresses concern about the accuracy of 

extrapolation based on this time period. The concern is warranted; this period is too short, given 
122

the probable fire cycle, to describe the regime well. It does provide a complete picture of fire 

frequency and extent since approximately 1900 but understates fire occurrence during the 

‘Mining Era.’ A careful reading of Karamanski et al. (1988) adds to the characterization of the 

regime pre-1900. 

The FMP also draws on sediment cores taken by Cole et al. (1995) to characterize fire 

occurrence over the past 4,500–5,000 years. Unfortunately, the information in Cole et al. (1995) 

is qualitative and incomplete. The statement that the SW end of the island has “... seen little fire 

over the past 4,500 years” may be true but is based on very limited data. Extrapolating from a 

few cores with very limited spatial coverage is tenuous. The SW end of the island is not a 

homogenous landscape; there are notable changes in topography, and there is a significant 

amount of boreal forest near the lakeshore. The FMP concludes, based primarily on Cole et al.

(1995), that “... fire was more frequent and/or severe prior to settlement” on the NE half of the 

island. This statement may be accurate, but it is a coarse characterization of the fire regime 

without sufficient data to warrant a solid conclusion. The information presented by Janke (1975), 

based on work by graduate student Randal Raymond, provides a useful extension of probable 

fire history. This student determined the charcoal influx curve for four lakes (Angleworm, 

Chickenbone, Siskiwit, and Wallace). These data (Figure 1, Janke 1975) reflect, broadly, fire 

occurrence and intensity in the surrounding watershed over a 1,000-year period. The four curves 

suggest a) that fire was constant at an interval of approximately 50 years at all four sites; b) there 

were more severe fires or periods of greater fire activity at one or more points in time; and c) the 

Wallace Lake watershed experienced more fire than the other three (Janke 1975).

Though the fires since the 1930s are well documented (NPS 2004a), information is sketchy about 

the role of fire across the island. More importantly, little is known about the historic range of 

variation in the fire regime, other than the two limited studies cited above. Extensive work in 

Canada has documented notable shifts in the fire cycle within the past 500 years or less 

(reviewed in Johnson et al. 2001) and over longer time scales in a black spruce–jack pine forest 

(Arseneault and Sirois 2004). 

In addition to the above, there are several lines of evidence to suggest that the boreal forest fire 

regime is different than presented in the FMP. This evidence includes a) lightning-caused fires 

noted in the FMP are equally common in the SW and NE parts of the island; b) since the boreal 

forest type is more flammable than pure birch-aspen, or any of the northern hardwood types, then 

the significant amount of boreal forest in the SW half should tend to make the regimes on the 

two ends more similar; and c) pine is abundant in the pollen record (Flakne 2003), which 

suggests frequent fire occurrence (Arseneault and Sirois 2004).

We can be confident that the historic (pre-1840s) disturbance regime of ISRO included fire 

(unknown frequency, probably long-interval high-severity fire); frequent, small-scale canopy 

gaps; beaver activity; and spruce budworm outbreaks (unknown frequency, sometimes of high 

severity). A budworm outbreak in the 1930s killed a large number of trees, mostly balsam fir. 

Herbivory by the budworm during outbreaks has frequently impacted large areas across eastern 

North America (Peltonen et al. 2002) since at least the 1920s. However, it is not known how 

many other outbreaks also occurred on ISRO. Different types of disturbance can readily interact, 
123

as was noted for the 1936 fire; fire in an area impacted by the budworm was more severe than in 

the non-impacted area. The same is true for widespread windthrow. 

Since 1840, the disturbance regime has changed in several ways: a) more human-caused 

ignitions occurred between 1843 and approximately 1940 or perhaps a little later; b) a major 

herbivore (moose) became part of the regime; 3) widely scattered, but locally important removal 

of overstory trees occurred during the mining era; and 4) fire suppression occurred after 

approximately 1940. The net effect on the regime is unclear, because humans increased fire 

frequency (at the scale of the island) during one period and reduced it in another. Furthermore, 

the scientific consensus is that 20th-century fire suppression has not yet altered the fuel load, fuel 

structure, or fire regime in boreal forests in any significant way (Johnson et al. 2001). Therefore, 

we cannot conclude that the fire regime has been altered substantially by humans since 1840. We 

can be confident that a portion of the island, concentrated within a band along the shore, had 

elevated canopy disturbance and non-fire mortality rates from approximately 1845 through 1940.

Thus, we have an incomplete picture of the historic disturbance regime for the boreal forests in 

ISRO. This is especially important for the two more severe types of disturbance—fire and spruce 

budworm outbreaks—because they determine, to a large degree, landscape structure. Of equal 

importance is the lack of information about the historic range of variation in the regime (Landres 

et al. 1999).

Northern Hardwood Forest

The diverse nature of the overstory in the northern hardwood type (Allen 1988) usually results in 

less impact from outbreak-type insects or pathogens. Though the northern hardwood forests on 

ISRO are less diverse than their mainland counterparts, the tree composition is variable enough

so that this general characterization probably applies. Consequently, the long-term dynamics of 

the northern hardwood forest type are driven by low-to-moderate intensity disturbances, 

primarily abiotic, and the life history traits of the constituent species. Based on data from MI’s 

Upper Peninsula, a typical forest would have 5.7–6.9% of its canopy die or be killed every 

decade (Frelich and Lorimer 1991). This translates into a canopy residence time of less than 175 

years. In contrast, severe disturbances reoccur on very long intervals (>800 years) (Whitney 

1986, 1987, Frelich and Lorimer 1991). The FRIs for all sites, pre-suppression period, were 566 

years for surface fires and 2,797 years for canopy-killing fires (Frelich and Lorimer 1991). Thus, 

fires of any type were very infrequent in this forest type pre-settlement; return intervals for 

spreading surface fires range from 300 to 900 years depending on the site and assumptions of the 

calculation. Note that this is more frequent than implied by Cole et al. (1995). Though we have 

no direct estimates of gap-formation rates for ISRO, it is likely that the northern hardwood forest 

type rate is similar to that on the mainland because the agents of damage (ice, wind, pathogens, 

and secondary insects) are common there also. Because this forest type occurs at higher 

elevations on the island, we would expect higher rates of wind-caused disturbance than on the 

mainland, other factors being roughly equal.

The recent (post-settlement) and future (next 25–50 year) disturbance regime has not been and 

will not be significantly different than the pre-settlement disturbance regime. This is due to the 

highly infrequent and limited extent of fires (Frelich and Lorimer 1991) and the dominance of 

the regime by localized, small-scale abiotic (wind and ice) and biotic (endemic insects and 
124

pathogens) events; these small scale and generally low-severity events have largely been 

unaffected by anthropogenic activities in the 19th and 20th centuries. As in the boreal forest, the 

period of anthropogenic fire exclusion is too short to have made a difference from the natural 

regime (Johnson et al. 2001). Since this forest type is found further inland and is not readily 

accessible, it was largely spared from harvesting and local use during the mining and resort eras.

Other Upland Conifer Forests

Fire is one of the most important types of disturbance for all pine forests in the Great Lakes 

region (Heinselman 1973, Whitney 1986). ISRO includes forest types dominated by white, red 

(Pinus resinosa), and jack pines (TNC 1999). A strong majority of the jack pine at ISRO occurs 

in three community types: boreal pine rocky woodland, jack pine–black spruce/feathermoss 

forest, or jack pine–black spruce/feathermoss woodland phase. The latter two types have more 

moisture than typical jack pine forests across the Great Lakes. In the boreal pine rocky 

woodland, the white pine present is most commonly found mixed in with broadleaf species 

(aspen and birch), the trees are small, and the vegetation is patchy. These conditions, plus the 

patchy, small-scale nature of these forest types at ISRO and the climatic conditions, all suggest 

that fire occurrence would be less frequent in these forest types on the island than in their 

mainland counterparts.

Though there is a considerable body of work on fire from the region, there are no published 

studies from ISRO. As a starting point, Whitney (1986) estimated that FRIs for high-intensity 

fires in MI’s Lower Peninsula were 80–167 years (generally <100) for jack pine and 120–260 

years for mixed pine forests. Heinselman (1973, 1981) reported FRIs of 50 years for jack pine 

and 180 years for mixed pine for the Boundary Waters Canoe Area of northern MN. Frissell 

(1973) reported a similar value (150 years) for a mixed pine forest in central MN. Cwynar (1977) 

examined an 18,600 ha preserve in Ontario dominated by white pine and aspen and found a FRI 

(for a fire anywhere in the park) of 14 years, a FRI for ‘major fires’ of 45 years, and a rotation of 

70 years.

Thus, there is general consistency among studies of high-intensity fires, with a shorter FRI for 

jack pine than the other pine types. The fuel characteristics and weather at ISRO probably mean 

that the FRI is at the upper end of the range noted elsewhere, and that there are fewer, highintensity fires, making the fire regime in jack pine areas roughly equivalent to that of the boreal 

forest. Other components of the disturbance regime for upland conifer forests undoubtedly 

included small-scale canopy damage and mortality, as noted for the types above. The current

disturbance regimes in upland conifer forest types at ISRO are probably quite similar to those of 

the boreal forest, with two exceptions: less frequent windthrow for those sites that are drier and 

have modest soil depth and the potential inclusion of blister rust for white pine (described in 

more detail in the Terrestrial Invasive Species section). The regime has changed in several ways 

since European settlement, mostly in line with the impacts noted on the boreal forest types: 1) 

more human-caused ignitions between 1843 and 1940, 2) widely scattered but locally important 

removal of white pine overstory trees during the Mining Era, 3) fire suppression after 

approximately 1934, and 4) potential white pine blister rust mortality.
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Lowland Forests

Physiography, soil characteristics, water movement, and tree characteristics collectively 

determine the primary form of disturbance—windthrow—in these community types. Shallow 

roots and growth on soils that are commonly saturated and have high levels of organic matter 

make trees susceptible to windthrow. When a tree is windthrown, microtopographic 

heterogeneity in the form of pit-and-mound topography is created. The mound part provides a 

microsite that is considerably drier than the area in general. The bole of the downed tree also 

provides surface heterogeneity that is important for the regeneration of some plant species (e.g.,

white cedar [Rooney et al. 2002] and conifers in general [St. Hilaire and Leopold 1995]). As a 

result, plant diversity is greater because the microsites provide places for species that are not 

quite so tolerant of saturated soils to survive. 

As one might expect, the return interval for high-severity fire is quite long in lowland forests of 

MI’s Lower Peninsula (1,400 years in the hemlock–white pine–northern hardwoods type and 

3,000 years in the swamp conifer type) (Whitney 1986), and probably also at ISRO. Since 

dominant species, especially white cedar, have natural resistance to pests, insect and diseaserelated disturbance had a minimal influence historically. One exception is tamarack (larch); its 

occurrence has been greatly reduced by the larch sawfly (described in more detail in the 

Terrestrial Invasive Species section).

Human Effects on Terrestrial Resources, 1840–1940

Mining

Activity associated with copper mining between approximately 1843 and 1920 added several 

new anthropogenic disturbances to the landscape and had pronounced effects on part of the 

island. Though the mine sites were strongly concentrated near the lakeshore (Figure 47), their 

impacts extended inland. Mining-related impacts included the cutting of trails and roads from 

docking points and the use of fire. Karamanski et al. (1988) state that prospectors commonly 

used fires in their searches for areas to mine. Two such fires are evidence of the extent to which 

mining has impacted the park. The Island Fire in 1875 burned for three days before it went out, 

and in 1892, a fire that was started near Todds Harbor spread for three weeks before rains put it 

out. 

Though most mines and mining camps were small, and hence had a small impact area, each 

required some clearing and one or more small roads for access. A few of the mining camps grew 

to considerable size. The Island Mine north of Siskiwit Bay (1874–1875) had its own sawmill. 

The Minong Mine site (1875–1891) had at least 150 people and may have swelled to 300 for a 

short period. The Island Mine site had the largest number of occupants (approximately 600) but 

was active for a shorter period of time than the Minong site (Karamanski et al. 1988). These 

mines were farther inland than most, so sizable roads were pushed through the vegetation to 

bring in wagons with supplies.

Logging

Mining operations preferentially used tamarack, white pine, and white cedar trees (Karamanski 

et al. 1988). Relatively large quantities of wood were necessary to support even a mid-sized 

mine, and near the larger mines, wood utilization reached a high level. Karamanski et al. (1988) 
126

Figure 47. Location of mines operated between 1843–1920, Isle Royale National Park (after Karamanski et al. 1988, NPS 2004d).
127

stated “The mines consumed great quantities of wood ..... many areas were effectively cut as if 

there had been commercial lumbering.” Utilization by families (e.g., home construction) and 

personal use (heating, cooking) would have involved other species. These disturbances were 

concentrated near the mines and largely within 2–3 km of the shoreline. With the exception of 

the forest immediately adjacent to the village/mine site, harvesting would have been somewhat 

selective by size and/or species of tree. 

The isolation of the islands and the rather mediocre value of the timber resource greatly reduced 

the level of commercial logging at ISRO, compared to adjacent areas in MN, WI, and MI. 

Meager commercial logging began at ISRO in the 1890s. In 1894–1895, extensive logging took 

place in forests near Washington Harbor, and the paper mills in Duluth began purchasing spruce, 

but only a small amount was actually cut and transported from the island. Practically speaking, 

there was no significant commercial logging prior to 1920. In 1922, a precursor of the Mead 

Corporation bought 26,900 ha near Siskiwit Bay. Though a camp with approximately 200 men 

was set up on the SW shore of Siskiwit Bay, much of this acreage was never cut. The Minnesota 

and Ontario Paper Company harvested some timber in the mid-1930s, also near Siskiwit Bay; 

these two efforts were the last commercial operations on the island (Karamanski et al. 1988). 

Timber utilization was much heavier in the vicinity of the Island Mine; however, it was shortlived and concentrated near Lake Superior.

The direct and indirect impacts of logging on the understory are an important and valid concern 

(Gilliam and Roberts 2003). This is true because the vast majority of plant species are found in 

this layer, and there is potential to substantially change the composition by harvesting (Craig and 

Macdonald 2009). The abundance and composition of the ground layer also can play an 

important role in nutrient retention, as documented in Appalachian spruce-fir (Moore et al. 2007)

and boreal forests in Sweden (Nilsson and Wardle 2005). The more intensive the tree utilization, 

the greater is the potential for a reduction in diversity (Craig and Macdonald 2009) and/or the 

initiation of a novel successional pathway (Roberts 2004). However, many understory species 

survive a harvest, even a clearcut (Crowell and Freedman 1994), and thus the understory can be 

more diverse after a harvest than before (Crowell and Freedman 1994, Gilliam and Roberts 

2003). This net increase involves the loss of a few late-successional species and the invasion of 

many pioneer species. Whether or not logging has decreased the vascular plant richness on ISRO 

is unknown due to the lack of pre-logging data or recent, detailed studies. Climate, growth rates, 

and dispersal capacity of many species affect recovery time from severe disturbance. In southern 

mixedwood boreal forests of Saskatchewan, understory richness was still declining 200 years 

after stand-replacing fires (Chipman and Johnson 2002). 

Given the history and distribution of timber utilization, the boreal forest and the forests

containing northern white cedar are the two broad community types likely to have been 

impacted, but only in scattered locations around the island, and especially in the vicinity of 

Siskiwit Bay. Studies in different types of boreal forest have noted that disturbance of the forest 

floor is as important as, or more important than, the magnitude of overstory reduction (Fleming 

and Baldwin 2008, Craig and Macdonald 2009). This means that season of harvest (Wolf et al. 

2008) would have played a role, as well as the method of extraction (machine vs. horse, etc.). 

Given that all commercial logging occurred prior to 1936, the method of extraction should have 

minimally disturbed the forest floor and soil, unless the soil was wet at the time.
128

We can only hypothesize, due to lack of data from the island, but it seems unlikely that logging 

reduced native plant diversity. However, it is probable that some areas near the shore and in the 

vicinity of Siskiwit Bay are still recovering from the harvesting that occurred between the mid1800s and the mid-1930s. 

Fragmentation

All roads, the few railroad tracks installed by the miners, and even trails create a narrow break in 

the canopy and thus have some edge effects. In addition to breaking up extensive areas of 

vegetation, these human-created breaks and corridors can serve as ‘conduits’ for exotic plants 

(Gelbard and Belnap 2003, Watkins et al. 2003). In a northeastern WI landscape dominated by 

hardwood forests, exotic species were most prevalent within 15 m of roads; however, native 

richness and diversity were equal to interior conditions within 5 m of the roads (Watkins et al. 

2003). Tyser and Worley (1992) studied alien species along three transportation corridors in 

grasslands of Glacier National Park: primary roads, secondary roads, and backcountry trails. 

Surprisingly, they found equal abundance of alien species 2, 25, and 100 m from the trails. Thus, 

the potential for exotic invasion at ISRO may be much higher than the level of human impact 

and utilization in the interior would suggest. Invasiveness can differ significantly among 

community types, and thus we do not know if 15 m is about the limit, or if exotics might show 

up 100 m away from a trail. See the section below on Exotic Plants for discussion of the possible 

impacts by exotic species. 

Recreational Effects and Visitor Use

Beginning in the late 1800s, a number of resorts were established on Isle Royale. They utilized 

wood for construction and heating purposes, and also cut trails toward the center of the island for 

their guests. As with the mining effort, very few resorts lasted long, and all were located very 

close to the lake’s shore. Thus, the impact of this activity was also quite localized. The negative 

impacts of the past resort industry on terrestrial systems could include soil compaction, 

fragmentation of the vegetation, reduction or elimination of native species, and introduction of 

exotics. Soil compaction would be highly concentrated, if present, and is most likely to have 

occurred in areas that are currently devoted to non-wilderness objectives. 

As noted in the introduction, ISRO had an average of 16,350 visitors yr-1 from 2004–2008 (NPS 

2009). A wilderness and backcountry environmental impact statement prepared in 2005 (NPS 

2005) documented potential visitor impacts. The effects of campground development and use 

may include increased light intensity when sites are cleared, increased runoff, littering, water 

pollution, track formation, soil compaction and loss, and an increase in fire frequency (Sun and 

Walsh 1998, NPS 2005). These changes create damage to and loss of vegetation, changes in 

plant composition, and ideal conditions for the establishment of weeds and exotic plants. Foot 

trampling by campers and hikers reduces plant cover, biomass, and species richness (Cole 2004). 

In a study conducted in canoe-accessible campsites in low-elevation riparian forests in the 

eastern U.S., most vegetation had been eliminated, and a shift in the remaining vegetation from 

forbs to graminoids was observed (Marion and Cole 1996). 

Trail use can cause erosion, especially when hikers widen trails to avoid wet and muddy patches 

(NPS 2005). Hiking trails may get enough use to cause soil compaction. Even backountry 

recreation can have negative impacts. In a study of six midwestern forest sites at three nature 
129

preserves, Adkison and Jackson (1996) found that areas along the trails had reduced litter cover 

at five of six study sites, and significant soil compaction at all six, compared to sites 10 m away 

from the trails. In hiking and camping areas, an array of damages may show up; tree damage is a 

common form and can be rather pervasive (Reid and Marion 2005). This, however, is highly 

localized and probably does not cause long-term harm. The possibility of local extirpation of an 

uncommon or rare species is relatively high because the vast majority of the species of concern 

occur near the shoreline (see Upland Resources section) where recreation, logging, and mining 

were concentrated. The lack of a species list from the 1800s precludes any rigorous assessment 

of the extent of this possible impact to date. Nonetheless, this threat merits careful consideration 

as it relates to recreational use of different areas of the park.

Many visitors to NPS and USDA–Forest Service campgrounds perceive campfires to be an 

important aspect of their camping experience, but numerous aesthetic and ecologic impacts have 

been attributed to campfires (Reid and Marion 2005). In an extensive literature review, Reid and 

Marion (2005) report that the resource damage attributable to campfires includes “fire site 

proliferation; overbuilt fire sites and associated seating arrangements; fuel wood depletion; 

sterilized soils; charred rocks and tree roots; ash and charcoal buildup; semimelted plastic, glass, 

and metal trash; chemical contamination of soils; unburned food, which attracts wildlife; tree 

damage and felling; and vegetation trampling associated with firewood collection.” Studies 

conducted at ISRO and two other national parks (Great Smoky Mountains and Shenandoah) 

showed that the total number of damaged trees at campsites where fires were allowed ranged 

from 190 to 1,128; ISRO had 281 (Reid and Marion 2005). Firewood collecting affects the 

availability of woody material and density of saplings around campsites (Cole 2004). Trampling 

in search of firewood causes soil compaction and changes the composition of the understory. The 

gathering of downed wood for fires may also reduce site productivity, especially on droughty or 

infertile soils, and habitat for spiders, arthropods, birds, and small mammals (Cole and DalleMolle 1982). Burning garbage in campfires produces toxic metals that remain in the ash and may 

be washed into surface waters during high water or storms. Plastic cup lids, chip bags, and 

plastic forks and spoons contribute lead to ash; colored cardboard boxes contribute cadmium; 

and cigarette and candy wrappers contribute mercury (Davies 2004). 

Detailed research on noise levels and their effects on the natural environment has not been done 

at ISRO. However, the draft wilderness and backcountry management plan for ISRO (NPS 2005) 

included an inventory of human-made sources of noise and light within the park. These included 

human voices; motorboats operated by visitors and park personnel; seaplanes; aircraft; 

emergency medical helicopters; generators at Windigo, Rock Harbor, and Mott Island; 

chainsaws and other power tools used by park personnel; and foghorns at Passage Island and 

Rock of Ages. Light pollution within ISRO originates from residential areas within the park and 

Thunder Bay to the north (NPS 2005). 

ISRO participates in a Leave No Trace project, in which a booklet is available for visitors 

describing how to minimize human impacts by traveling and camping on durable surfaces, 

properly disposing of wastes, leaving natural features undisturbed, eliminating introduction of 

non-native species, minimizing campfire impacts, respecting wildlife, and being considerate of 

other visitors (Leave No Trace Center for Outdoor Ethics 2004). The 2005 wilderness and 

backcountry environmental impact statement (NPS 2005) also called for a monitoring plan and a 
130

report at five-year intervals, including such topics as campsite crowding, rates of trail encounters, 

annual visitation and its temporal and spatial distribution, density of boats in anchorage areas, 

biophysical conditions and recreational impacts at campgrounds and off-trail, wolf-human 

encounters, loon success, and conditions of archaeologic sites and cultural landscapes.

Fuel Storage and Discharges at ISRO

ISRO has five oil storage facilities that are regulated under the Oil Pollution Act of 1990 as 

“significant and substantial harm facilities.” Tanks are located at Rock Harbor, Mott Island,

Amygdaloid Island, Windigo, and Malone Bay (Table 28) (USEPA Region 5 2000). ISRO

maintains trained personnel and some equipment to respond to the accidental release of oil from 

one of their tanks (Rayburn et al. 2004).

Table 28. Locations of fuel storage tanks at Isle Royale National Park (USEPA Region 5 2000).

Location Products stored Volume (L) Number of tanks

Rock Harbor Gasoline, diesel

 

 189,000 3

Malone Bay Gasoline 7,600 1

Mott Island Gasoline, diesel 210,000 4

Windigo Gasoline, aviation fuel, diesel 197,000 5

Amygdaloid Island Gasoline 7,600 1

The MDEQ keeps records of discharges of hazardous materials (ERD sites) and of leaking 

underground storage tanks (LUST sites) under Parts 201 and 213, respectively, of MI’s Natural 

Resources and Environmental Protection Act 451 of 1994 (State of Michigan 1996). Keweenaw

County has 10 active Part 201 sites, four of which are within ISRO (Table 29). One active Part 

213 site is located on Amygdaloid Island (MDEQ 2009b, c). 

The risk scores in Table 29 are determined by an MDEQ Site Assessment Model and range from 

zero to 48, with 48 indicating the highest degree of risk (MDEQ 2009d). Up to 20 points are 

awarded for environmental threats associated with the contaminants, up to five points are 

awarded for the mobility of the contaminants, and up to three points are given for sensitive 

environmental resources at the site. Up to 15 points are awarded for the types and quantities of 

the released chemicals, and the final five points are given for the size of the individual and

institutional human populations around the sites. 

Table 29. Part 201 hazardous material discharge (ERD) sites in the vicinity of Isle Royale National Park

(MDEQ 2009b).

Name Substances and Source Risk Score

and Date Status

Rock Harbor Lodge benzo(a)pyrene, 

naphthalene; Petroleum and 

coal products

33/48;

12/12/2003

interim response in 

progress

Windigo Generator 

Shed

naphthalene;

n/a

32/48;

2/13/2004

inactive; no actions 

taken to address 

contamination
131

Windigo Tank Farm phenanthrene; 

Petroleum products

42/48;

2/18/2004

evaluation in 

progress

Passage Island 

Lighthouse

benzene, lead;

National security

30/48;

1/19/2006

evaluation in 

progress

Aquatic Invasive Species

Invasive species are those organisms not native to an area whose introduction harms or is likely 

to harm the economy, environment, or human health (USEPA 2008c). They may be either 

terrestrial or aquatic. Aquatic invasive species (AIS) may threaten the diversity or abundance of 

native species or the ecologic stability of the waters into which they are introduced, or impair the 

water for some human use (MDEQ 2002). At least 182 invasive species are found in the Great 

Lakes basin, and a new invader is discovered every 28 weeks (Ricciardi 2006). The introduction 

of aquatic invasives may be the most serious threat to the ecologic health of the Great Lakes 

today (Jude et al. 2002). 

Crane et al. (2006) described AIS as a particular threat to ISRO because of the high quality, 

uniqueness, and fragility of its aquatic ecosystems, especially its inland lakes. The prevention 

and control of AIS was identified as the top priority at an April 2002 water resources 

management plan scoping workshop (Crane et al. 2006).

Known AIS at ISRO are deliberately introduced non-native fish (i.e., rainbow and brown trout 

and Chinook and coho salmon) and accidental introductions such as sea lamprey, threespine 

stickleback, spiny waterflea, and the plants cattails and common reed. In addition, either zebra or 

quagga mussels were found in Washington Harbor in September 2009 (Flesher 2009b, Myers 

2009). AIS believed to be encroaching on ISRO are invertebrates (fishhook waterflea 

[Cercopagis pengoi], Asian clam [Corbicula fluminea], rusty crayfish [Orconectes rusticus], and 

Chinese mitten crab [Eriocheir sinensis]); fish (ruffe, white perch [Morone americana], round 

goby, and tubenose goby [Proterorhinus marmoratus]); a virus (viral hemorrhagic septicemia 

[VHSv]); and plants (purple loosestrife and Eurasian water-milfoil) (Crane et al. 2006, Meeker et 

al. 2007, Quinlan et al. 2007, NPS and Grand Portage Band of Lake Superior Chippewa 2008,

Benson and Fuller 2009, Schlesinger et al. 2009, USEPA 2009d). These species are further 

described below. The USFWS has identified five of these species (ruffe, white perch, rusty 

crayfish, zebra mussels, and quagga mussels) as priority species for monitoring at ISRO 

(Quinlan et al. 2007); however, mitten crabs and VHSv were not included in their analysis. 

AIS Known in ISRO

Introduced Non-Native Fish Species: Of Lake Superior’s seven top predator fish, only three 

are native species (lake trout, burbot, and walleye) while the other four are introduced species 

(coho salmon, Chinook salmon, rainbow trout, and brown trout) (GLFC 2001). These non-native 

fish consume prey fish, eat native fish eggs, and take over optimal habitat for native fish (Crane 

et al. 2006). Environmental changes, including overfishing and logging in the late 19th century, 

as well as the introduction of these non-native species, mean that natural, pre-European 

settlement fish communities may never return to Lake Superior. However, a recent review 

reported that the introduction of non-native fish species appears to have little effect on native 

aquatic species in Lake Superior with the notable exception of coaster brook trout (Schlesinger et 

al. 2009). Rainbow trout and salmon compete with juvenile coaster brook trout for food and 
132

rearing areas in stream and nearshore Lake Superior habitats. Non-native salmonids also 

compete with adult coaster brook trout and lake trout in nearshore and reef areas (Schlesinger et 

al. 2009).

Sea Lamprey: Probably the best-known exotic species in Lake Superior is the sea lamprey. This 

species, native to the Atlantic Ocean, entered Lake Superior via the St. Lawrence Seaway in the 

early 1940s (Smith et al. 1974) and quickly depleted lake trout populations in eastern Lake 

Superior (Crane et al. 2006). Adult lampreys spawn on gravel beds in tributary streams, and 

immature lampreys grow from three to seven years before migrating into the lake. Adults 

parasitize fish, extracting blood and body fluids with their suctorial mouths. Each sea lamprey 

may kill as much as 18 kg of fish during the 12–20 months of its adult life (GLFC 2000). Sea 

lamprey numbers in Lake Superior declined slowly from 1962 to 2000 as a result of chemical 

treatments and barriers, but the GLFC’s target of <5% lake trout mortality attributable to sea 

lamprey has not yet been met (Fodale and Cuddy 2007). 

Threespine Stickleback: The threespine stickleback has been known in Lake Superior since at 

least 1994. Threespine stickleback feed on a variety of fauna, including zooplankton, oligochaete 

worms, macroinvertebrates (insect larvae), small fish, fish eggs, crustaceans, adult aquatic 

insects, and drowned aerial insects (Quinlan et al. 2007). The species was introduced to the Great 

Lakes in ballast water and had not resulted in any documented environmental damage as of 2002 

(Jude et al. 2002). However, it is a very aggressive fish (Zhuikov 1997) and may outcompete 

native sticklebacks for food and space (Quinlan et al. 2007). It was reported present in ISRO by 

Quinlan et al. (2007), but not in a nearshore survey by Gorman and Moore (2006).

Spiny Water Flea: Spiny water flea is a large cladoceran (zooplankter) with a long spine, native 

to freshwater, oligotrophic lakes of Eurasia. Its spine makes it unattractive as prey for small fish 

(Lehman and Caceres 1993). It competes for common zooplankton resources with native pelagic 

fish (Jude et al. 2002), but it may be a food source for larger fish (Minnesota Sea Grant 2006b). 

Live bait fish can disperse the spiny water flea because its resting eggs can survive passage 

through the digestive tract of fish (Garton and Berg 1990). It is easily introduced into new lakes 

through fishing and anchor lines, bilge water, and live fish bait. Therefore, lakes that are popular 

fishing spots are the most susceptible to new invasions of the spiny water flea (Jarnigan 1998). If 

introduced into ISRO inland waters, it might adversely affect native fish, mussels, and sponges. 

It was first found in Lake Superior in 1987 (Cullis and Johnson 1988), and it is currently found 

in Tobin Harbor and the Lake Superior waters of ISRO (Crane et al. 2006). It was not found in a 

survey of eight inland lakes in ISRO during July 2005 (Crane et al. 2006).

Reeds, Cattails, and Other Invasive Aquatic Plants: Common reed and two species of cattails 

were found in ISRO in a survey published in 2007 (Meeker et al. 2007). These aggressive plants 

form clones that crowd out nearly all other wetland plants. The authors suggested that although 

cattails would continue to spread in ISRO, they would not reach “extreme abundance”; currently, 

1.2% of the interior lake and Lake Superior bay shoreline are occupied by these species. This 

same survey looked for, but did not find, the invasives curly-leaf pondweed, Eurasian watermilfoil, or purple loosestrife on ISRO (Meeker et al. 2007). 
133

Zebra Mussels and Quagga Mussels: Invasions of zebra mussels and quagga mussels are a 

major concern in the Great Lakes because of the resulting catastrophic decline of native mussels. 

These two species have expanded their ranges at an “alarming rate” because of their wide 

environmental tolerances and high reproductive rate (Nichols 1993). They are very mobile and 

colonize most hard surfaces, including the shells of native mussels (Nichols et al. 2001b). They 

are omnivores as adults and will feed on algae, zooplankton, their own young, and detritus. 

Quagga mussels can live in colder water (Snyder et al. 1997) and live at greater depths and on 

softer substrates than zebra mussels (Dermott and Kerec 1997). 

Zebra mussels probably entered the Great Lakes in 1985 or 1986 in ballast water in Lake St. 

Clair (Minnesota Sea Grant 2006a). They have difficulty establishing populations in Lake 

Superior because they need calcium for proper shell development (Crane et al. 2006). As 

previously noted, the minimum Ca2+ threshold for zebra mussel settlement and growth is 8–12 

mg L-1, with peak mussel densities at concentrations ≥ 20 mg L-1 (Jokela and Ricciardi 2008 

and citations within), and concentrations in Lake Superior currently average 14 mg L-1 (USEPA 

2008a). Zebra mussels have been detected in Duluth and Thunder Bay, and areas around ISRO 

are considered moderately susceptible to invasion (USEPA 2008d). In September 2009, news 

reports stated that either zebra or quagga mussels were found in Washington Harbor on the pier 

at Windigo (Flesher 2009b, Myers 2009). Quagga mussels were first found in Lake St. Clair in 

1988 (Minnesota Sea Grant 2006b). They have been found in Duluth Harbor and near the tip of 

the Keweenaw Peninsula (USEPA 2008d). 

AIS Believed to Be Encroaching on ISRO

Fishhook Water Flea: The fishhook water flea is an exotic species from the Caspian Sea. It is 

similar to the spiny water flea in its size, life history, and habits, although it may eat smaller prey 

(Jude et al. 2002); however, it does not have a straight caudal spine but rather a spine that is 

curved at the end. It may compete with larval fish and fish planktivores for small zooplankton 

(Jude et al. 2005). A single specimen of this species was found in Lake Superior in 2003, but it is 

not believed to be established there (Benson et al. 2009). 

Asian Clam: The Asian clam is considered “one of the world’s most invasive species” because 

of its rapid dispersal, high fecundity and growth, and early maturity (Jude et al. 2002). It, like the 

zebra and quagga mussels, colonizes and fouls hard surfaces (USEPA 2008d). Asian clams were 

found throughout the Great Lakes as early as 1984 (White et al. 1984), and have been found in 

the Portage Canal at Houghton, MI, in effluent water from Upper Peninsula Power Company 

(Ward and Hodgson 1997). They are considered “established” in Lake Superior (USEPA 2008d), 

but specific locations were not reported.

Rusty Crayfish: Rusty crayfish are native to the Ohio River basin, but are considered a threat to 

MI’s native crayfish populations (MDNR 2007). They have been invading northern lakes and 

streams, including 31 lakes and streams in 11 counties in WI (Gunderson 2008) and five North 

Shore counties in MN (USGS 2009), but are not yet found in the Great Lakes (USEPA 2008d).

They are easily transported as live fish bait, in bait bucket water, and in live wells, although it is 

illegal to take, possess, or sell them in MI. They inhabit lakes, ponds, and streams (including 

pools and riffles), and prefer areas that have rocks and/or logs as cover (Gunderson 2008). They 

are aggressive toward other crayfish (Capelli 1982) and destructive of aquatic macrophytes 
134

(Lodge and Lorman 1987). They consume twice the food of the similar sized Orconectes virilis, 

a native crayfish (Momot 1992). 

Chinese Mitten Crabs: A single Chinese mitten crab was found on a water intake screen in 

Lake Superior at Thunder Bay (Herborg et al. 2007). However, this species’ swimming 

planktonic larvae require saline water, so it is uncertain that they pose a serious threat to the 

Great Lakes.

Eurasian Ruffe: Ruffe are a small but aggressive type of exotic percid native to Eurasia. They 

are highly fecund, feed on a wide assortment of prey, and are able to forage efficiently under 

reduced light conditions such as in turbid water or at night (Gunderson et al. 1998). They were 

introduced to the Great Lakes in ballast water at the St. Louis River near Duluth in the early to 

mid-1980s, and were found in Thunder Bay harbor in 1991 (Keppner et al. 1997). Based on 

bottom trawl samples, ruffe are approximately 80% of fish in the SW regions of Lake Superior 

(Leigh 1998). Ruffe may harm more desirable Lake Superior species, such as yellow perch, 

whitefish, or walleye, by feeding on the young of these species or by competing for food (Crane 

et al. 2006, Fuller and Jacobs 2009). At ISRO, its most significant threat is to the nearshore 

native fish communities from ecologic and sportfishing standpoints (Crane et al. 2006).

White Perch: The white perch, not a perch at all, is a species of the temperate bass genus. It was 

first found in Lake Superior in 1986 in Duluth Harbor and appears to continue to be restricted to 

that location, perhaps because the harbor is warmer than the rest of the lake. It eats the eggs of 

walleye and white bass, and could contribute to a decline in the populations of those two species 

(Wisconsin Sea Grant 2002).

Round and Tubenose Gobies: The round goby, originally from the Black and Caspian seas of 

Eastern Europe, is a small, aggressive, bottom-dwelling fish that exhibits prolific spawning and 

voracious eating behaviors. It was first introduced to Duluth Harbor in 1986 via ballast water. In 

some areas where it has become well-established, it appears to be the only fish species present 

(USGS 2000b). The tubenose goby, with similar aggressive tendencies, was discovered in 

Duluth Harbor in September 2003 (Crane et al. 2006). 

A concern about the potential invasion of gobies at ISRO is that they compete with native 

benthic fish such as sculpin, trout-perch, and darters (Etheostoma spp.) for food and habitat. 

Because they can deeply penetrate interstitial spaces in cobble substrates, they might become 

effective predators on lake trout eggs, setting back lake trout rehabilitation (Crane et al. 2006). 

VHSv: Viral hemorrhagic septicemia rhabdovirus (VHSv) kills fish by causing both internal and 

external hemorrhages (Whelan 2009). Twenty-eight vulnerable fish species have been identified 

in Lake Superior (NPS and Grand Portage Band of Lake Superior Chippewa 2008). Preliminary 

positive results for VHSv were found at four locations in Lake Superior (Paradise/Whitefish 

Point and Skanee/Huron Bay in MI and St. Louis Bay and Superior Bay near Duluth, MN) in 

January 2010 (Cornell University 2010, WDNR 2010). Ballast water was the most likely 

mechanism by which it entered the Great Lakes, while anglers and recreational boaters are the 

most likely mechanism for transfer into inland waters (NPS and Grand Portage Band of Lake 

Superior Chippewa 2008). 
135

Other AIS Found in Lake Superior

Alewife: The alewife is a planktivorous marine member of the herring family, first found in Lake 

Superior in 1954. Alewives are considered beneficial as prey for salmonines, but are detrimental 

to zooplankton and the pelagic larvae of native fish species (Jude et al. 2002). 

New Zealand Mud Snail: The New Zealand mud snail is a tiny snail first discovered in the 

Duluth-Superior harbor in fall 2005, probably introduced via ballast water from ocean-going 

ships. It reproduces asexually. The mud snail outcompetes important forage species for native 

trout and other fishes, but provides little nutrition to these predators (MN DNR 2007). 

Didymosphenia geminata (Didymo): Didymo is a freshwater diatom that produces dense 

benthic algal blooms. These can block sunlight and disrupt ecologic processes, causing a decline 

in native plant and animal life (USDA 2009). Although it has become an AIS in some locations, 

it is native to Lake Superior, and has been known on the North Shore for over fifty years 

(USEPA Mid-Continent Ecology Division, Jo Thompson, Biologist, email September 15, 2009). 

Stoermer (1980) characterized it as a sensitive, boreal species that on the Lake Superior shoreline 

preferred oligotrophic conditions. Therefore, recent concerns about its presence (Spaulding et al. 

2008, USEPA 2009d) appear to be unwarranted. 

Introduction Pathways and Control Strategies for Aquatic Invasive Species

Numerous pathways, both natural and human-made, exist to transfer aquatic species from one 

location to another. Ludwig and Leitch (1996) list connections between basins at times of high 

water, animal transport, and extraordinary meteorologic events as natural mechanisms for 

species transfer. Bossenbroek (2006) also notes the importance of stream connections. These 

natural events and conditions may be difficult to predict or manage. However, human-initiated 

mechanisms, including escapes from aquaculture facilities, aquarium release, stocking activities, 

ballast release, and angler escape or release are more amenable to control through management 

and public education. Eberhardt (2008) provided a comprehensive list of human-initiated 

mechanisms (Table 30). 

Table 30. Human-initiated mechanisms for transfer of aquatic invasive species in Lake Superior

(Eberhardt 2008).

Category Subcategories

Maritime Commerce ballast water, hull/anchor fouling 

Water Recreation boating equipment, live wells, fishing equipment, bait

Organisms in Trade pets/aquariums, aquatic plants, shoreline restoration, bait, live food fish, 

on-line sales

Commercial Fishing fishing equipment/vessels, bait, fish aquaculture

Canals and Diversions locks, power canals, compensating works, diversions

Agency Activities stocking/hatcheries, assessment, harbor maintenance, navigation, homeland 

security, research

Illegal Activities plants, fish stocking, on-line sales

Tourism charter fishing, ecotours, float planes, diving
136

The three most apparent pathways for the introduction of AIS at ISRO are ballast water from 

commercial ships, recreational boating in Lake Superior and its harbors, and commercial touring 

vessels (Crane et al. 2006). ISRO’s inland lakes and streams are accessible only by kayak or 

canoe and only at a limited number of established portages. The use of natural fishing bait is 

prohibited in inland waters. ISRO also has a spiny water flea awareness program that asks 

visitors to change their reel line before moving from Lake Superior to inland waters to fish (NPS 

and Grand Portage Band of Lake Superior Chippewa 2008).

Terrestrial Invasive Species

The introduction of alien species probably began with the arrival of European settlers (DiTomaso 

2000). It was not unusual for immigrants to bring useful plants or seeds with them from their 

native lands. Collectively, exotic plants represent an important ecologic threat (Ehrenfeld 2003, 

Heneghan et al. 2006). In the recent past, eastern North America has experienced a rapidly 

increasing number of exotic plant populations. Effects have been widespread and have included, 

at a minimum, alteration of community structure (Heneghan et al. 2006); reduction of native 

richness (Rooney et al. 2004); alteration of ecosystem process such as decomposition, 

mineralization, and primary productivity (Ehrenfeld 2003, Heneghan et al. 2006); and altered fire 

regimes (Brooks et al. 2004). However, most exotics do not have any appreciable ecologic 

effects, and among those that do, some have minor impacts.

Many, although not all, of the problem exotic species are especially adept at invading recently 

disturbed areas. Spotted knapweed (Centaurea spp.) is such a species and is rapidly expanding 

its range in the Lake States. Even in largely unfragmented landscapes and mature forests, more 

subtle human manipulation of the landscape and accidental introduction can lead to steady 

increases in the number and dominance of exotics in the flora (Martin et al. 2009); this was 

recently documented for a 50-year period in upland forests of northern WI (Rooney et al. 2004). 

The increase by exotics led to an 18.5% decrease in native species density at a 20 m2 scale. Even 

the establishment of a park by no means guards land against further exotic invasion. A recent 

study of a small (19 km2) newly established national park in Quebec found that the proportion of 

exotics increased from 16 to 25% in just 21 years (1984–2005) (Lavoie and Saint-Louis 2008).

For forests in general, exotic taxa of serious concern are garlic mustard (Alliaria petiolata), the 

alien buckthorns (Rhamnus sp.), Oriental bittersweet (Celastrus orbiculatus), Japanese knotweed

(Fallopia japonica), Norway maple (Acer platanoides), and the honeysuckles (Lonicera spp.)

(Nuzzo 1991, Woods 1993, Czarapata 2005, Martin et al. 2009). These species can invade intact 

communities and reduce the number and/or diversity of native species. The buckthorns can thrive 

in richer soils and thus could invade birch, aspen, or northern hardwood forests.

Careful, regular, and extensive monitoring is the key to prevention of an exotic problem. At 

ISRO, the areas in which exotic plants are most likely to come into the island are around the 

docks and developed areas and along the popular trails. The staff at ISRO regularly monitor near 

developed areas and along trails and respond quickly to any new findings (NPS, Mark Romanski, 

pers. comm., 2009). These efforts must be continued on a frequent basis to prevent the invasion 

and spread of problematic exotics. 
137

Gypsy Moth

Two gypsy moths (Lymantria dispar) have been found on the island, but both were males (NPS, 

Mark Romanski, pers. comm., 2009); a reproducing population is not thought to be present. It 

should be noted that the female gypsy moth cannot fly. Nonetheless, this discovery has raised 

questions about whether this exotic pest is likely to get established on ISRO and what its 

probable impact would be. The egg masses are laid on the underside of limbs and bark, but also 

on campers and boats (Edmonds et al. 2000). Hence, the species could readily reach the island by 

human transportation, and a preliminary assessment of its potential impacts is warranted.

Gypsy moth populations were well distributed in the lower peninsula of MI by the mid-1980s 

(Liebhold et al. 1997) and in WI by the late 1990s (Tobin 2005). Thus, possible source 

populations for ISRO have existed for over 25 years. The fact that a population has not become 

established on ISRO to date is encouraging.

The gypsy moth is considered the “worst defoliation threat to deciduous trees in northeastern 

North America” (Doane and McManus 1981 in Edmonds et al. 2000) and is highly polyphagous 

(will feed on and survive on a wide variety of species). Over 300 trees and shrubs have been 

utilized in North America (McManus et al. 1992, Liebhold et al. 2000), though it shows a 

preference for oak. According to Liebhold et al. (2000), Populus is one of the more common 

hosts, and McManus et al. (1992) listed alder, white birch, and poplar as preferred species. 

Climatic regime has been commonly suggested as limiting the northern spread of the species 

(Tobin 2005). For example, gypsy moth egg masses cannot withstand temperatures below –29o

C 

for more than 48 hours (McManus et al. 1992). Furthermore, alternating freeze-thaw cycles in 

late winter and early spring are believed to prevent eggs from hatching. However, the rate of 

spread in MI has recently been inversely related to temperature (Tobin 2005) suggesting that the 

relationship between growth/dispersal and weather is not as straightforward as previously 

thought. This does not, of course, negate the importance of weather to the population dynamics 

of the species; recent analyses have determined that weather is an important factor contributing 

to the large scale synchrony of outbreaks (Liebhold et al. 2000). Given the presence of several 

preferred tree species on ISRO, the continued spread of gypsy moth in WI, and the possibility of 

minimal temperature limitation, it may be easier for a population to become established on ISRO 

than appears on the surface.

If a population gets a foothold on ISRO, it most likely will be in an aspen, paper birch, or mixed 

aspen-birch forest. Gypsy moths avoid the conifers that dominate the upland boreal forest types 

(balsam fir, white spruce, and occasionally northern white cedar) (McManus et al. 1992). Larval 

development is strongly influenced by both plant host and temperature (Knapp and Casey 1986, 

Rossiter 1987); utilization of non-preferred hosts and temperatures < 25 o

C substantially retard 

larval development. Gypsy moth larvae typically emerge in mid-May (Knapp and Casey 1986);

thus, cold temperatures could realistically serve to minimize population growth. Given these 

factors, it is unlikely that many of the common forest types on ISRO, including those classified 

as northern hardwood (Liebhold et al. 1994), would support more than endemic-level 

populations of gypsy moth. 

Most vigorous broadleaf trees can endure up to 50% defoliation by gypsy moths with minimal 

growth loss (McManus et al. 1992), and some can experience a second year of defoliation at the
138

same level and still recover. However, repeated defoliation often results in a major increase in 

mortality, at least among oak species. Only one growth and mortality study of gypsy moth

defoliation involved species common on ISRO. In Massachusetts, New York, and New Jersey, 

the previous year’s level of defoliation had little or no effect on the growth of aspen (Muzika and 

Liebhold 1999). Thus, it is likely that aspen-dominated forests could sustain a low-density 

population of gypsy moths with no substantial changes in structure or composition. If the 

population were to reach epidemic levels and stay there for a few years, extensive aspen growth 

loss and die-back would be expected [based on its response to tent caterpillar (Hahn et al. 2000)], 

but mortality would be uncommon. This level of impact would encourage understory and/or 

midstory growth, and thus alter forest structure. It could also facilitate recruitment of new species 

into the forest. Safford et al. (1990) list gypsy moth as a common defoliator of paper birch, but 

state that defoliation alone (by any insect) seldom results in mortality of a healthy tree, though it 

does result in growth loss. Thus, it appears that the resiliency of birch is almost as high as that of 

aspen.

Our current state of knowledge suggests that the only extensive susceptible forest types on ISRO 

are those with paper birch and/or aspen as dominants (e.g., the 1936 burned area). Given the 

location of these forest types and the probable weather limitations, a population of gypsy moths

would not build to epidemic proportions on the island. Should an endemic-level population 

become established, the resiliency of birch and aspen, plus the low utilization of later 

successional species (white spuce, balsam fir, or sugar maple in some areas) suggest that the 

outcome would be minor shifts in forest type abundance.

Emerald Ash Borer

Another exotic herbivore that is moving through the Midwestern U.S. and causing extensive tree 

mortality is the emerald ash borer (Agrilus planipennis) (Poland and McCullough 2006). Black

ash is the susceptible species at ISRO, occurring on approximately 300 ha, but almost always in 

mixed deciduous forests or with northern white cedar. If human introduction (e.g., firewood) is 

prevented, it is very unlikely that this insect will reach ISRO. Should it find its way to the island, 

the impact on community structure would be minimal and short-lived as other species would fill 

in the gaps. The possible concern is any species, such as invertebrates, fungi, or others, that are 

specialists on black ash; if these exist, there could be a loss of biodiversity due to the lethality of 

the ash borer.

White Pine Blister Rust

White pine has an important biotic disturbance agent, white pine blister rust (Cronartium

ribicola), an exotic fungal pathogen that was brought into the country in the late 1800s

(Edmonds et al. 2000). This pathogen killed many white pine in the 20th century and was 

prevalent throughout the white pine–growing area of Minnesota by the mid-1950s (Stewart 

1957). We found no documentation of the disease on ISRO, though it could be or could have 

been present but overlooked. The impact of this fungus was likely never great, and the potential 

is lower today due to the restricted distribution of white pine. White pine was not even 

mentioned by Hansen et al. (1973), indicating how rare the species was on ISRO in the mid-20th

century. The USGS-NPS Vegetation Mapping Program (TNC 1999) identified only one 

community type that contained white pine (white pine–quaking aspen/beaked hazelnut forest) 

and described it as “uncommon.”
139

Larch Sawfly

The larch sawfly is a foliage-feeding insect introduced from Europe in 1880 (USDA–Forest 

Service 2001). It apparently arrived in the Great Lakes region by approximately 1900, and the 

population reached epidemic levels in MN in the early 1900s (Brown 1935 in Janke et al. 1978). 

It is thought that this herbivore reached ISRO later in the 20th century and greatly reduced the 

abundance of larch (tamarack) (Janke et al. 1978). The witness trees noted in the original land 

survey were 2% larch, but in their 1974 inventory of the same area, Janke et al. (1978) found 

none.

Earthworms

The scientific consensus is that there are no native earthworms in the forests of the western Great 

Lakes Region because they have not migrated back since the retreat of the Wisconsin glacier 

(Hendrix and Bohlen 2002). However, due to human migration and commerce (e.g., use of 

worms as fish bait and for composting) at least 45 exotic species have been introduced to North 

America. Most exotic earthworms are from Europe. They have spread substantially over the past 

few decades (Bohlen et al. 2004) and are found on ISRO. Regionally, the most numerous are 

members of the family Lumbricidae (Hendrix and Bohlen 2002). As early as the 1960s, it was 

noted that these species had significant impact on soil properties in areas devoid of native 

earthworm species (Hendrix and Bohlen 2002). More recently, some far-reaching implications 

for the composition and function of northern hardwood forests, aspen forests, and pinedominated forests in the northern parts of the Great Lakes region and Canada have been 

identified (Hale et al. 2005, Frelich et al. 2006). 

When earthworms invade a site, there is typically a succession of species, similar to the changes 

of plant species during succession (Hale et al. 2005, Suárez et al. 2006). The first group to invade 

typically are smaller, stay in the litter (Oi) layer, have minimal impact on the lower layers of the 

forest floor, and have almost no impact on soil properties or nutrient cycling (Frelich et al. 2006). 

The second and third waves include larger species and ones that move between the litter/duff 

layer and mineral soil. The species Lumbricus rubellus (Hale et al. 2005) and L. terrestris

(Suárez et al. 2006) seem to be of particular influence. These later-successional species reduce 

the depth of the litter layer and move substantial amounts of carbon into the soil to depths of 25–

30 cm (Bohlen et al. 2004, Frelich et al. 2006). In a northern hardwood forest, the presence of 

earthworms increased the rate of litter breakdown by 1.5–3.0 times under field conditions 

(Suárez et al. 2006). Subsequent alterations occur in the dynamics of carbon and nitrogen in the 

soil, soil structure (e.g., bulk density) and the composition of the understory (Bohlen et al. 2004, 

Hale et al. 2005, 2006). Exotic earthworms have consistently increased the total N in the system 

(Groffman et al. 2004, Wironen and Moore 2006), but the effects on its availability and 

movement have been variable—ranging from no change (Groffman et al. 2004) to increased 

availability and increased leaching (Bohlen et al. 2004). After invasion, the understory in the 

northern hardwood forest will typically have reduced species richness, reduced recruitment of 

sugar maple saplings, and increasing amounts of Pennsylvania sedge (Carex pensylvanica) (Hale 

et al. 2006). It has also been noted that at least one plant species, little goblin moonwort 

(Botrychium mormo), is negatively correlated with the abundance of L. rubellus (Gundale 2002). 

Although this plant is not reported from ISRO, other species of Botrychium are, and this finding 

adds to the threat exotic earthworms may represent.
140

Most of the earthworm work in North America has been in northern hardwood forests. However, 

studies from Europe indicate significant differences in invasion potential among the various 

forests at ISRO. A strong majority of earthworm species are sensitive to litter quality, dry 

conditions, and soil pH. Thus, forest ecosystems such as the spruce-fir or pine-spruce boreal 

types are not likely to be invaded because of their acidic conditions and low-quality (high lignin 

and low nitrogen) litter (Frelich et al. 2006). These forest types have not been invaded in 

northern Scandinavia despite the presence of earthworms for thousands of years. However, a 

mixed deciduous–conifer forest (e.g., aspen-spruce) has a substantially higher risk of invasion 

due to the moderating effects of the deciduous species.

Climate Change 

Global air temperatures increased 0.74 ± 0.18o

C from 1906 to 2005, mostly attributable to 

human activities (IPCC 2007). In addition to creating this general warming, climate change also 

likely contributes to rises in sea level; changes in wind patterns and extra-tropical storm tracks; 

increased temperatures on extreme hot nights, cold nights, and cold days; increased risk of heat 

waves; increased area affected by drought; and greater frequency of heavy precipitation events 

(IPCC 2007). Signs that climate change is already occurring in the Great Lakes region include 

increases in average annual temperatures, more frequent severe rainstorms, shorter winters, and 

decreases in the duration of lake ice cover. By the end of the 21st century, winter temperatures in 

MI and MN may increase 3oC –6oC, and summer temperatures may increase 4oC –7oC and 4oC –

9 oC, respectively. The growing season might increase by 8–10 weeks in MI and 3–6 weeks in 

MN. Annual average precipitation may not change much, but may increase in winter and 

decrease in summer to the point where soil moisture declines and more droughts occur. The 

frequency of heavy rainstorms could increase 50–100% in both states (Kling et al. 2003a, b). 

Significant uncertainty accompanies most predictions related to global climate change, not only 

those related to the magnitude of changes in physical parameters, but also in their ecologic 

implications. The uncertainty, though, is not in the general trend, but rather in how large the 

changes will be, the rate at which they occur, and the net effect of all of the indirect and 

interactive effects. A wide variety of ecologic processes (Aber et al. 2001) and species-specific 

responses (Walther et al. 2002; McKenney et al. 2007) have been, or will be, affected. An 

additional source of uncertainty is that average climate changes may not be key. The fluctuation 

in temperature among seasons, the extremes that occur, the timing of certain phenomena, and the 

duration of a condition could all have more of an impact than the average condition (Morris et al. 

2008). 

All predictions of future climate are based on General Circulation Models (GCM), of which 

there are several, and they vary in their predictions for the 21st century. Predictions of the 

ecologic impacts of climate change are achieved by taking the predictions of a GCM and 

plugging them into one or more other models (see Hansen et al. [2001] and Aber et al. [2001] for 

the common models used in this way). These, as well as the GCM models, are simplifications of 

reality and are based on a set of assumptions, creating further uncertainty in the predictions. 

Furthermore, there is not a single model that can even begin to predict the full range of 

phenomena that are likely to be affected, their interactions, and the net outcome. Thus, all 

models focus on a few of the changes and ignore the others. For example, we have limited 

capacities to predict what biotic disturbances are likely to influence a community if the average 
141

temperature increases by 3o

C or 4oC, or where ice storms are going to be most frequent (Dale et 

al. 2001). The predictions of models apply to a finite scale, and the majority of ecologic models 

project for a smaller spatial scale than the GCMs. To make these mesh, either the GCM 

predictions have to be interpolated or the ecologic model extrapolated, creating yet another 

source of uncertainty.

Lake Superior Water Level Changes

Climate change is already affecting chemical, biologic, and physical aspects of the Great Lakes

(Boyer et al. 2006). The Great Lakes are forecast to have a reduced ice cover season, declining 

lake levels, and reduced inputs related to lowered groundwater levels and stream baseflows, but 

increased inputs related to higher runoff during extreme precipitation events (IJC 2003). When 

two GCMs (called CGCM1 and HadCM2) were run for the Great Lakes region, air temperature 

differences were 5.4o

C and 2.9oC, respectively, by 2090. Changes in mean annual runoff varied 

between the models from -13% to +4%, respectively, by 2090, and mean annual evaporation 

varied from +39% to +19%. As a result, Lake Superior levels varied from -0.42 m to +0.11 m by 

2090 (Lofgren et al. 2002). Of 12 scenarios run with 10 models, only one showed a net water 

gain.

Changes in Lake Superior water levels have been limited since 1914 by a control structure at the 

lake’s mouth. In the 55 years of preregulation data, water levels had a range of 1.10 m, from 

182.76 m in February 1866 to 183.86 m in August 1876. As regulated, the mean annual 

variability is 0.30 m, with a 1.19 m range from 182.72 m in April 1926 to 183.91 m in October 

1985 (Wilcox et al. 2007, USACE 2009). However, Lake Superior set a new record low for 

September of 183.02 m in 2007, and as of January 2009 was 0.22 m below the average for the 

last 90 years (NOAA 2009a). In Lake Michigan, which is unregulated, water levels are currently 

0.38 m below average (NOAA 2009a) and have been described as “worrisome” because they 

appear consistent with several climate change projections (Sellinger et al. 2008). 

Lake Superior would be a terminal lake (a lake without an outlet) if precipitation dropped 60% or 

more from the present, or if air temperature increased 13oC above the present, or some 

combination of the two (Croley and Lewis 2006). One such combination would be a 25% 

precipitation decrease combined with a 5oC mean temperature increase (Lewis et al. 2008). 

Lewis et al. (2008) demonstrated that the Great Lakes experienced such a low period during 

which they lacked connecting channels during the early Holocene dry period (approximately 

8,770 years BP).

Other Surface Water Impacts

In the future, surface waters will likely be warmer. DO may decline, and extended periods of 

thermal stratification may increase the decline’s effects. Lower oxygen levels and warmer 

temperatures in inland waters may promote phosphorus release and increase mercury release and 

uptake by biota (Kling et al. 2003c). Warming of the Great Lakes would cause greater 

volatilization of semi-volatile compounds from the water column, which will cause contaminants 

currently sequestered in sediment reservoirs to desorb and re-enter water and air (Boyer et al. 

2006). Nonpoint pollution may also increase with higher intensity precipitation events.
142

Biologic productivity of aquatic ecosystems will likely increase with temperature, because of 

longer growing seasons and increased metabolic rates, but existing natural communities may be 

greatly changed (IJC 2003). However, Lake Superior’s already-low productivity may further 

decrease because of a longer summer stratification period that prevents the recycling of nutrients 

and redistribution of oxygen (Kling et al. 2003c). Populations of coldwater fish may decline. 

Whitefish reproduction may be harmed by loss of winter ice cover (Kling et al. 2003a). Some 

habitats may be reduced, especially wetlands and their vegetation communities. Invasive species 

may be more successful (Kling et al. 2003c).

Coastal Wetland Impacts

Models for Great Lakes coastal wetlands in the Canadian Great Lakes (Erie, Ontario, and St. 

Clair) were examined for their responses to climate change and lake-level changes as projected 

by climate models. Results indicated that “the lower water levels projected under most climate 

change scenarios will have an impact on the distribution and abundance of wetland vegetation, 

bird, and fish communities; major shifts in all taxonomic groups are likely with long-term water 

level declines, beginning with vegetation responses” (Mortsch et al. 2006). Wetland communities 

within lacustrine embayments were the most capable of naturally adapting to lower water levels, 

while drowned river-mouth wetlands showed the greatest potential for change. Invasive plant 

species such as purple loosestrife and common reed were less vulnerable to change than native 

species, and the spread of invasives may be facilitated by cumulative stresses on natural 

ecosystems. Birds that need prolonged, relatively stable water levels during the breeding season, 

such as terns, grebes, rails, and bitterns, were considered vulnerable, as were fish that spawn in 

shallow water in spring and have a preference for vegetated habitat in all life stages (Mortsch et 

al. 2006). Loons are also vulnerable to fluctuating water levels.

Water level fluctuations are essential to the diversity of wetland plant communities and the 

habitats they provide for fish and wildlife. Lake level regulation has already created problems for 

Lake Superior wetlands (Wilcox et al. 2007). Periodic high lake levels are needed to kill trees, 

shrubs, and canopy-dominating emergent plants in Great Lakes wetlands. Subsequent low water 

levels are needed to promote seed germination and growth of numerous species (Wilcox et al. 

2007). 

Projected Impacts on Plants

Plants and plant communities may be affected by climate change in myriad ways that involve a 

large number of interacting conditions and biotic interactions, as constrained by the local site 

conditions and genetic variation of each species. These effects will include very basic, cellular 

level processes; whole plant processes; interactions between plants (e.g., competition), between 

plants and their mutualists, and among plants, insects, and pathogens; the frequency and severity 

of disturbances; and community-wide processes and characteristics. In the earlier stages of CO2-

induced warming, the photosynthetic rate and water use efficiency is expected to increase, and 

thus plant growth may increase (Aber et al. 2001). This will probably not be a universal 

response; species near the southern end of their range and those closely adapted to mesic site 

conditions will most likely be stressed by the increased temperatures (Davis et al. 2000). In all 

likelihood the increase in productivity will be short-lived as temperatures continue to rise, and 

drought becomes more common or severe (Dale et al. 2001). 
143

Another well-established response to climate change is phenology. An increase in temperature 

over the past 100 years (primarily 1910–1945 and 1976 to date) has altered the timing of 

important life history stages of many species (reviewed in Walther et al. 2002). For example, a 

broad-scale assessment of initiation of spring growth in North America found that it has occurred 

1.2–2.0 days earlier per decade for the past 35–63 years (Walther et al. 2002). Following warm, 

wet winters, nine of 13 European species bloomed earlier by 13–26 days, and one-third bloomed 

13–19 days longer (Post and Stenseth 1999); however, woody plants were less sensitive than 

herbaceous species to climatic variability. A greater impact on spring stages of life history has 

been noted as opposed to late summer or fall (Walther et al. 2002). Shifts of this magnitude, 

which will probably continue through the 21st century, could profoundly affect other taxa that 

key in on a particular stage of the life cycle of plants. Obvious examples include nectar-gathering 

insects and folivores that feed on new leaves and shoots. These are examples of cascading, or 

indirect, effects of climate change. Physiologic and phenologic adjustments will continue until 

climate change exceeds the tolerance of the species and its capacity to adapt (Davis et al. 2005). 

Alternatively, the species may migrate to an area with a more favorable climate (Davis et al. 

2005).

At the community scale, it is highly probable that at least a few community types as we currently 

know them will ‘disassemble’ and reform in different combinations, or into a similar and

recognizable community. Others will disappear from the landscape, and species that currently do 

not commonly associate will do so in the future (Hansen et al. 2001, Williams et al. 2007). This 

will result in communities that are novel (sensu Williams et al. 2007), without a current or prior 

analog. It is highly unlikely that communities will migrate as a unit because of differences 

among species (in reality, populations) in genotypic variation, generation time, dispersal mode 

and capacity, and phenotypic plasticity; subtle differences in physiologic tolerances; impacts of 

novel insect and fungal pests; and differences among species in the need for mutualists. Hence, it 

is quite likely that in a matter of decades there will be groups of species occurring together that 

have not done so in the recent past (several hundred years). Management efforts will then be 

dealing with novel entities or assemblages with unknown levels of temporal stability.

Predicted responses for common tree species (below) highlight the probable magnitude of the 

impact, as well as what is likely to happen for some other life forms and species. However, it 

would be dangerous to extrapolate from one or a few species in an assemblage to all of the 

species; the dendro-chronologic and pollen records clearly show that co-occurring species can 

respond in very different ways to decade- and century-long climatic change (Villalba et al. 1994,

Villalba and Veblen 1998, Black and Abrams 2005). Two key components to the response by a 

species (or population) are how quickly it can adapt, if at all, and how rapidly it can disperse 

(Davis et al. 2005, McKenney et al. 2007). The capacity to adapt increases with greater 

population-level genetic variation and effective population size, a mating system that is partially 

or entirely out-crossing but does not rely on a specialized pollinator, and a larger range size. It is 

anticipated that adaptation will vary tremendously among life forms and significantly among 

species within a life form (Dale et al. 2001, Davis et al. 2005). Herbaceous species should adapt 

more quickly than trees and insects more quickly than most plants; this is primarily a function of 

life cycle length. However, annual plants and short-lived species are more sensitive than longerlived species to temperature fluctuation (Morris et al. 2008). The second component is migration. 

Based on the pollen record, we know that species, even within a life form, migrate at very 
144

different rates (e.g., Graumlich and Davis 1993) at the scale of millennia. The primary question 

is whether a species will be able to disperse rapidly enough to match the rates of change in 

temperature and precipitation regimes (Williams et al. 2007). 

Hansen et al. (2001) predicted the impacts of climate change on forest types and major tree 

species in the conterminous U.S. The future distribution of trees and forest types was based on 

changes in hydrology, light, nutrients, and plant response to increased CO2. Relevant predictions 

for ISRO include that suitable habitat for both spruce-fir and aspen-birch will decrease by >90%; 

species now at ISRO that would lose 90% of their range within the U.S. include quaking aspen, 

sugar maple, northern white cedar, balsam fir, and paper birch; and potential suitable 

environments for alpine communities will “all but disappear.” It should be noted that these 

predictions cannot be applied directly to ISRO because they are for mainland areas only and do 

not account for the moderating effects of Lake Superior. Currie (2001) predicted the long-term 

change in richness (number of species within a community) of trees under a scenario of doubling 

of CO2 and found that short-term changes are likely to be negative, but tree richness will increase 

in cooler climates and mountainous areas. 

A more recent assessment using a similar approach found a smaller magnitude of changes. 

McKenney et al. (2007) examined the predicted range response of 130 tree species in the 

conterminous U.S. They used the concept of climate envelope, which simply means that the 

climatic boundaries of a species today probably indicate the conditions it can endure in the 

future. Using this approach (which ignores many possible interactions that may manifest and 

influence where a species thrives in the future) they determined that 72 species would show a 

decrease in the size of their range within the conterminous U.S. Many of the more northerly 

distributed species will increase dramatically in Canada (McKenney et al. 2007), and this is the 

general expectation for the boreal forest type in the U.S. The authors ranked species based on the 

magnitudes of the reduction in the size of the climate envelope assuming no dispersal and the 

northward shift in the climate envelope latitude. No ISRO species were in the top 20% of the 

first category, but five species (sugar maple, yellow birch, northern red oak, eastern white pine, 

and mountain maple) were in the top 20% of the second (range shift). The extent of the northern 

range shift varies depending on which GCM model is used and the migration rate of a species. 

For example, sugar maple could have its range move northward as little as 3.3 degrees of latitude 

or as much as 8.9 degrees. Classic boreal species (paper birch, white spruce, balsam fir) were not 

predicted to change as much in this assessment.

Winter soil temperatures decreased as air temperatures warmed from 1951 to 2000 in the Great 

Lakes region (Isard et al. 2007). This is probably a function of warmer winter air temperatures 

leading to less and more variable snow pack and is another example of the interactions that will 

manifest in the future. A decrease in soil temperature would work to delay the onset of plant 

growth in the spring and thus minimize the phenologic changes noted earlier. In turn, this could 

mean a shorter growing season, which could offset the increased productivity related to higher 

CO2. Conversely, a decrease in ice cover on Lake Superior could lead to more lake-effect snow 

in ISRO (Davis et al. 2000), which could result in warmer wintertime soil temperatures (Isard 

and Schaetzl 1995, Isard et al. 2007). 
145

Projected Impacts on Animal Communities

The richness of birds and mammals is tied closely to temperature but only weakly to 

precipitation (Hansen et al. 2001), and thus in North America the greatest levels of vertebrate 

richness is in moderately warm areas. Therefore, if animals can disperse to ISRO, the richness of 

these two groups may increase by a magnitude similar to the prediction (11–100%) for the upper 

montane areas of the U.S. (Currie 2001). It should be noted that these predictions are based 

solely on temperature and precipitation by season, and thus do not account for all of the indirect 

influences (see below for moose) that could come into play. Nonetheless, they establish a 

benchmark from which to work.

As noted for plants, phenologic shifts have been noted for other life forms. Earlier arrival of 

migrant birds and butterflies and early nesting has been noted in many species (Walther et al. 

2002). In addition, climate change may not affect all currently linked processes at the same rate, 

leading to asynchrony between the time of flowering and pollinator activity, or the arrival of 

migratory birds and the availability of their prey (Kling et al. 2003c).

Post and Stenseth (1999) examined long-term trends in fecundity, body mass, and population 

size of 16 populations of six ungulate species and related these characteristics to the North 

Atlantic Oscillation (NAO). The NAO is a large-scale alternation in atmospheric pressure 

between Iceland and the Azores and has direct and strong impacts on climatic variation and 

temperature over the span of years and decades. Hence, it functions similarly to the El Nino 

Southern Oscillation in the Pacific. Some important demographic responses (body mass, 

fecundity) varied between mainland and maritime populations. Moose density on ISRO declined 

two years after warm, wet winters, and moose populations in Scandinavia exhibited significant 

changes in calf, yearling, and adult female mass with changes in winter characteristics. The 

population in Norway, which has a more maritime climate, had heavier yearling moose 

following a warmer-than-average winter. Though these two outcomes work in opposite 

directions, the prevailing indication is that warmer winters lead to reduced moose density.

LaSorte and Thompson (2007) estimated the poleward movement of 254 winter avifauna of 

North America from 1975 to 2004. The center of occurrence shifted 0.45 km yr-1

, and the 

northern boundary changed 1.48 km yr-1

. Thus, many bird species would likely disappear from 

ISRO, but many more southern species would migrate to the islands.

Overall Impacts at ISRO

Davis et al. (2000) noted that “the Western Great Lakes parks...” (including ISRO) “...are 

important reservoirs of biologic diversity in a landscape that has been altered by logging, mineral 

extraction, agriculture, and urbanization.” The accumulated pollen record over the Holocene 

suggests that ISRO’s location on Lake Superior may buffer it from temperature changes, at least 

temporarily, and allow it to serve as a refuge for plants and animals that cannot survive farther 

inland. However, that same location may jeopardize plants and animals because it is more 

subject to precipitation extremes than inland sites (Davis et al. 2000). 

Given current climate change scenarios, biologically significant changes will likely occur in 

plant species ranges, species abundance, community composition, and many ecosystem 

properties. Novel assemblages may form, creating many challenges because we will not know 
146

the outcome of interactions like competition, nor will we know the successional pathways some 

communities will take. ISRO’s isolation may magnify some effects on species by increasing 

extinction and limiting new arrivals. Species’ capacity for and method of dispersal will take on 

an even more important role than on the mainland. Under current climate change projections, it 

is almost certain that some species that are disjunct populations with an alpine affiliation, or are

near the southern limit of their range, will disappear. During roughly the same time period, an 

unknown (probably smaller) number of novel plant species will expand northward and appear at 

ISRO. Species that are scattered and uncommon (not limited to threatened or endangered

species), have limited genetic variation (e.g., wolves), or rely on specialized pollinators will be 

more vulnerable to local extinction. It is likely that mammalian richness will decrease, but avian 

richness will not. It is unknown how important groups like the arthropods, amphibians, and fungi 

will respond, but clearly there will be important ecologic changes if and when the climatic 

regime, and the plant composition and abundance, change.
147

Conclusions and Recommendations

NPS has developed conceptual ecosystem models for long-term ecologic monitoring in Great 

Lakes nearshore and coastal wetland areas, inland lakes, wetlands, and northern forests 

(Gucciardo et al. 2004). Each ecosystem has a set of vital signs, defined as “...attributes that are 

determined to be the best indicators of ecologic condition, or respond to natural or anthropogenic 

stresses in a predictable or hypothesized manner, or have high value to the park or the public...” 

(Route and Elias 2006). We have used those vital signs to evaluate the condition of ISRO 

ecosystems; unless a source is listed under “Condition,” the rankings are our own. We also added 

indicators using our professional judgment (Table 31–Table 35). The current and potential 

impacts of major stressors have also been identified (Table 36). 

In addition to specific recommendations below, we recommend a review of the three recent 

reports by Schlesinger et al. (2009), Crane et al. (2006), and Lafrancois and Glase (2005), which 

make detailed monitoring and management recommendations for ISRO. 

Lake Superior

Although Lake Superior has the greatest surface area of any freshwater lake in the world and is 

an ultra-oligotrophic lake (LSBP 2006a), it is still susceptible to anthropogenic stress. 

Atmospheric deposition of contaminants and their resulting trophic bioaccumulation is an area of 

significant concern for Lake Superior (Table 32, Table 33). Deposition of chlordane, dioxin, 

mercury, and PCBs is reflected in fish consumption advisories for many species, especially for 

larger fish. Aquatic invasive species are also of significant concern; sea lamprey, threespine 

stickleback, spiny water flea, and dreissenid mussels have been found at ISRO.

Vital signs with a ranking of “caution” include Lake Superior water levels, which have been 

below long-term averages, and a trend toward increasing water temperature and nitrate 

concentration. Exotic cattails and reeds were found in a recent survey of coastal wetlands. The 

aquatic pathogen VHSv has recently been detected in the lake. Coaster brook trout populations 

remain low, and the fish community is strongly (and perhaps irrevocably) influenced by 

introduced species.

Nearshore water quality data were not found for ISRO. Major data gaps exist for the vital signs 

of sediment analysis, toxic concentrations in sediments, and benthic invertebrates. Metrics were 

unavailable for the vital signs of algae, nutrient dynamics and biogeochemistry, geomorphology, 

primary productivity, zooplankton, and indices of biological integrity.

Major existing stressors for Lake Superior are atmospheric deposition and exotic species (Table 

36). Other potential problems are Great Lakes shipping and recreational boating, which could be 

sources of fuel spills or discharges of human wastes and other contaminants. Wastewater 

disposal and soil and groundwater contamination are small-scale sources that appear to be 

adequately addressed as they are discovered. Climate change may affect all ISRO resources in 

ways not yet understood. For Lake Superior, effects could include changes in water levels, water

chemistry, and biotic communities. 
148

Along with Lafrancois and Glase (2005), we recommend bathymetric assessments, habitat 

mapping, and biological inventories (including nearshore fish surveys) of Lake Superior 

nearshore waters, and we add a recommendation for baseline core and advanced water quality 

testing. We endorse the recommendation of Kallemeyn (2000) to frequently monitor nearshore 

waters and bays for invasive species, especially dreissenid mussels. Given the importance of the 

remnant coaster brook trout populations at ISRO, we recommend continued study and evaluation 

of any threats to this population. Further genetics investigations of lake trout are necessary to 

determine if there are different stocks around the island and if potential over-exploitation could 

be possible due to low numbers of some stocks (Lafrancois and Glase 2005). 

We acknowledge the challenge of addressing threats to park resources that originate far beyond 

park boundaries; perhaps a mechanism should be set up in NPS to address this challenge, if one 

does not already exist.

Inland Lakes, Rivers, and Wetlands

No vital signs were ranked as significant concerns for ISRO inland waters (Table 34). However, 

many vital signs received a rank of “caution,” often because data were limited in geographic 

scope and collected some time ago. Very limited data suggest changes in the water chemistry of 

some lakes, including increases in major ions, specific conductance, pH, and chlorophyll–a. 

Some lakes exceed nutrient criteria for their ecoregion; this finding seems unusual for lakes in a 

wilderness setting, but does not by itself indicate a problem. In general, ISRO inland waters 

appear to be of good quality and free of local anthropogenic influences. Because ISRO is isolated 

from mainland impacts and mostly protected as wilderness, water quality monitoring activities 

can serve as valuable datasets to assess long-term effects of atmospheric deposition or global 

warming. Thus, it is important that the monitoring programs already in place be continued.

Aggressive exotic plants were found in a recent survey of inland lakes and wetlands. Fish in 

some inland lakes have consumption advisories for mercury. Little is known about certain groups 

of organisms such as benthic invertebrates, algae, zooplankton, or freshwater sponges. Little is 

known about water levels on inland water bodies, and the only long-term gaging station on 

ISRO, located on Washington Creek, was recently deactivated.

Atmospheric deposition is considered an existing problem for inland waters because of the fish 

consumption advisories (Table 36). To date, exotic animals have not been detected, but have the 

potential to be introduced through visitor use. Climate change is a potential threat to inland water 

levels, water chemistry, and biotic communities.

ISRO’s wetlands inventory is incomplete (Crane et al. 2006), and inventories for wetland biota 

other than plants are generally lacking. We recommend a more thorough look at ISRO wetlands, 

using the 1999 Vegetation Mapping Program (TNC 1999) and Meeker et al. (2007) as starting 

points. Inland lake fish assessments should be conducted on a regular basis, especially because 

some inland coregonid populations (such as those in Lake Desor) may be vulnerable to the 

effects of climate change (Lafrancois and Glase 2005). 
149

Terrestrial Resources

The plant composition of ISRO is quite valuable for its diversity. At least two plant communities 

(the white cedar–yellow birch forest and the boreal calcareous seepage fen) are globally rare 

(TNC 1999). The greatest botanic value of the park lies in its disjunct populations, most of which 

are found along the Lake Superior shoreline (Judziewicz 1995, 1997, 2004) and on Passage 

Island. This group contains 21 arctic and alpine species and 12 species whose ranges are centered 

in the western U.S. (Judziewicz 1995). The range of community types, large number of species 

of concern, and minimal incidence of exotics, coupled with minimal human impact during the 

settlement era, make ISRO a suitable reference condition for other protected areas in the region 

(Schlesinger et al. 2009).

No vital signs were ranked as significant concerns for ISRO forests (Table 35). Some woody

species (white pine, tamarack, and Canada yew) have declined since approximately 1860, largely 

due to human activities. Nutrient deposition could affect nutrient cycling, decomposition, 

nitrogen availability, and the availability and leaching of cations in the future. Concerns exist 

about fluctuating moose and wolf populations and lack of genetic diversity among wolves, but 

bird communities appear to be in good condition and are similar to mainland bird communities. 

Priority should be given to monitoring and evaluating the mammalian community, since it has 

limited dispersal capacity and so is vulnerable to stressors such as climate change.

Metrics have not been defined for the vital signs of special habitats; biotic diversity; trophic 

relations; health, growth, and reproductive success; lichens and fungi; or primary productivity. 

We recommend continuation, and expansion if necessary, of monitoring for exotic plants along 

trails and in other human use areas. Schlesinger et al. (2009) further encouraged the analysis and 

integration of current monitoring of changes in vegetation. They suggested that synthesizing

several large datasets could allow insight into the role of moose, climate, and soils in controlling 

the composition and dynamics of vegetation and providing a baseline for understanding the role 

of moose and/or climate change in future vegetation changes. In addition, detailed studies of the 

understory are needed to assess the differences between forest types and their conservation value.

More information is needed on the status of the ISRO boreal forest and the abundance of each 

successional stage relative to its historic range and variability. Further monitoring and mapping 

of the possible presence and abundance of exotic earthworms in the various forest types should 

be considered.

We endorse the recommendations of Schlesinger et al. (2009) to monitor atmospheric deposition, 

especially for nitrogen, and to assess impacts on aquatic and terrestrial components of the ISRO

ecosystem. Similarly, Swackhamer and Hornbuckle (2004) recommended research to evaluate 

the relative impact of local versus regional or global sources of atmospheric contaminants at 

ISRO. Lafrancois and Glase (2005) supported the continuation of Stottlemyer’s work in 

additional scattered ISRO watersheds with particular attention to how climate warming may 

affect the cycling of nutrients and organic carbon in ISRO watersheds.
150

Table 31. Condition summary for general resources, Isle Royale National Park.

Vital Sign Metric Condition Data Summaries or References Quality of Data

Light pollution Not defined UNRANKED Originates from residential areas within ISRO and 

Thunder Bay to the north (page 129).

Good

Soundscapes Not defined UNRANKED Inventory completed for Wilderness and 

Backcountry Management Plan (NPS 2005) (page 

129).

Fair

Land use/land 

cover coarse scale

Conversion rate of 

non-developed 

land to developed 

and of nonforest to 

forest.

GOOD Lowest conversion rate of non-developed land to 

developed and highest conversion rate of nonforest 

to forest of all Great Lakes from 1992 to 2001 

(USEPA and Environment Canada 2007).

Good

Land use/land 

cover fine scale

Area and percent 

land cover change 

per year

Types and 

frequency of 

disturbance

Patterns of 

connectivity and 

fragmentation

Changes in road 

and building 

density

GOOD 99% of ISRO is managed as wilderness. Good

Phenology Dates that 

flowering and 

growth are 

initiated

CAUTION Regional changes are occurring (Walther et al. 

2002), but not documented for ISRO (page 143).

Poor

Weather/

meteorologic data

Not defined CAUTION Summer temperatures are trending upward (page 7). Good
151

Table 32. Condition summary for air quality, Isle Royale National Park.

Metric Condition Data Summaries or References Quality of data

Air quality for Class I 

area

GOOD Met NPS goal of stable or improving air quality for ozone, PM2.5, 

and SO2 (NPS 2006).

Good

Ozone UNRANKED Insufficient data (NPS 2006). Poor

Visibility–clear days CAUTION

(NPS rank)

No trend, 1996–2005 (NPS 2006). Good

Visibility–hazy days CAUTION

(NPS rank)

No trend, 1996–2005 (NPS 2006). Good

Sulfate in precipitation CAUTION

(NPS rank)

Degrading trend, but not statistically significant, 1996–2005 

(NPS 2006).

Emissions of SO2 within 250 km of ISRO decreased 8% from 

1996–2002 (page 102).

Good

Nitrate in precipitation SIGNIFICANT 

CONCERN

(NPS rank)

No trend, 1996–2005 (NPS 2006).

Inorganic N deposition was 0.52–1.42 kg/ha/summer from 

1985–2006; estimated to be 3.5 kg ha-1yr-1 by extrapolation 

from station at Hovland, MN (page 104).

Good

Ammonium in 

precipitation

SIGNIFICANT 

CONCERN

(NPS rank)

Degrading trend, but not statistically significant, 1996–2005 

(NPS 2006).

Good

pH of precipitation CAUTION Mean pH has varied from 4.35 in 1992 to 5.38 in 2006, with 

notably lower values in 2004 and 2005 (page 106).

Good

Mercury and persistent 

organic pollutants

CAUTION Long-range atmospheric transport continues to be the main 

source of these compounds at ISRO; emissions within the basin 

are decreasing (page 101).

Good
152

Table 33. Condition summary for Lake Superior, Isle Royale National Park.

Vital Sign Metric Condition Data Summaries or References Quality of Data

Plant exotics Presence/abundance CAUTION Cattails and reeds found on 1.2% of shoreline 

(page 23).

Good

Animal exotics Presence/abundance SIGNIFICANT 

CONCERN

Sea lamprey, threespine stickleback, spiny 

water flea, and invasive mussels present (page 

132).

Good

Core water quality 

suite

Water clarity

Temperature

Specific conductance

Dissolved oxygen

pH

GOOD

CAUTION

GOOD

GOOD

GOOD

Good and unchanged, 1992–2002 (USEPA 

2006).

Trend toward increasing temperatures, 1979–

2006 (page 37).

No apparent trend, 1996–2008 (page 37).

All but one of 1,108 samples met standard 

(page 36).

All of 653 samples met standard (page 37).

Fair

Fair

Fair

Fair

Fair

Threatened and 

endangered species

Presence/abundance GOOD ISRO has unique habitats and is home to many 

species threatened elsewhere in their ranges.

Fair

Water level

fluctuations 

Measurement of 

water levels over 

time

CAUTION Lake Superior water levels are controlled, but 

have been below long-term average since 1998.

Good
153

Table 33. Condition summary for Lake Superior, Isle Royale National Park (continued).

Vital Sign Metric Condition Data Summaries or References Quality of Data

Advanced water 

quality suite 

Major ions

Dissolved silica

Alkalinity

Dissolved organic carbon

Chlorophyll-a

Nutrients

GOOD

GOOD

GOOD

UNRANKED

GOOD

CAUTION

Values low, but some parameters are missing 

and proportions cannot be calculated (page

37).

Considered sufficient for diatom production 

(page 34).

Sufficient to buffer acid rain (page 37).

Lake Superior is limited by organic carbon 

(page 34).

In oligotrophic range (page 34).

TP is below the upper limit of 5 μg L-1; 

NO3-N is increasing (page 33).

Poor

Fair

Fair

Poor

Fair

Fair

Aquatic and wetland 

plant communities 

Not defined CAUTION Inventory recently completed; some AIS 

found (page 23).

Good

Fish communities Not defined CAUTION Inventory recently completed; coaster brook 

trout populations remain low; fish 

community is strongly influenced by the 

presence of introduced species (page 25).

Good
154

Table 33. Condition summary for Lake Superior, Isle Royale National Park (continued).

Vital Sign Metric Condition Data References or Summaries Quality of Data

Trophic 

bioaccumulation 

Monitoring and assessing 

methylmercury and 

organic contaminants in 

yellow perch, northern 

pike, and dragonfly larvae 

at three year intervals

SIGNIFICANT 

CONCERN

The Michigan waters of Lake Superior 

have fish consumption advisories for 

chlordane, dioxin, mercury, and PCBs

(page 41).

Good

Mussels and snails Not defined GOOD Healthy mussel population found in very 

limited sampling in McCargoe Cove 

(Nichols et al. 2001a).

Fair

Sediment analysis Not defined UNRANKED No data found. Poor

Toxic concentrations 

in sediments

Presence of toxics at 

levels exceeding standards

UNRANKED No data found. Poor

Toxic concentrations 

in water

Presence of toxics at 

levels exceeding standards

FAIR 

(SOLEC 

ranking)

Low levels of numerous toxics have been 

found in Lake Superior waters (page 39).

Fair

Benthic invertebrates Not defined UNRANKED No data found. Poor

Aquatic pathogens Presence/absence CAUTION VHSv recently found in Lake Superior, and 

28 fish species are vulnerable (page 134).

Fair
155

Table 33. Condition summary for Lake Superior, Isle Royale National Park (continued).

Vital Sign Metric Condition Data References or Summaries Quality of Data

Algae Not defined UNRANKED USEPA annual surveys (page 33). Fair

Nutrient dynamics/

biogeochemistry

Not defined UNRANKED USEPA annual surveys (page 33). Fair

Aeolian, lacustrine 

geomorphology

Not defined UNRANKED No data found on condition. Poor

Primary productivity Not defined UNRANKED USEPA annual surveys (page 33). Fair

Index of biological 

integrity (IBI)

Numerous indices in 

development (see page 

31Error! Bookmark not 

defined.).

UNRANKED No indices have been applied to ISRO to 

date.

Poor

Zooplankton Not defined UNRANKED USEPA annual surveys (page 33). Fair
156

Table 34. Condition summary for inland lakes, rivers, and wetlands, Isle Royale National Park.

Vital Sign Metric Condition Data Summaries or References Quality of Data

Plant exotics Presence/abundance CAUTION Aggressive exotic species detected in broad 

survey of inland lakes and wetlands 

(Meeker et al. 2007).

Good

Animal exotics Presence/abundance GOOD No nonnative fish species detected in lakes 

during most recent survey (Kallemeyn 

2000).

Good

Core water quality suite Water clarity GOOD Recent comparison of several lakes 

suggests normal variation in clarity 

(Kallemeyn 2000).

Fair

Temperature GOOD No long-term change in lake temperature 

detected (Kallemeyn 2000, Elias 2009).

Fair

Specific conductance CAUTION Comparison from lakes suggests slight 

increase in conductance (Figure 29).

Fair

Dissolved oxygen CAUTION Hypolimnion of stratified lakes was below 

USEPA criterion on some dates; Lake 

Richie became anoxic below 5 m (page 

71).

Fair

pH CAUTION Limited long-term sampling, but one pH 

reading exceeded USEPA criterion (page 

71).

Fair

Bird communities Not defined GOOD Trends of ISRO bird populations are 

similar to mainland bird communities 

(page 86).

Good
157

Table 34. Condition summary for inland lakes, rivers, and wetlands, Isle Royale National Park (continued).

Vital Sign Metric Condition Data Summaries or References Quality of Data

Threatened and 

endangered species

Presence/abundance CAUTION Desor, Ritchie, Sargent, and Siskiwit Lakes 

are designated as “cisco lakes” (page 93).

ISRO supports at least two populations of 

threatened coaster brook trout (page 27).

Communities of freshwater sponges and 

mussels are present but relatively unstudied 

in many lakes (Nichols et al. 2002, Meeker 

et al. 2007).

Good

Good

Poor

Water level fluctuations Measurement of 

water levels over 

time.

CAUTION Limited data exist for water level on inland 

water bodies (GLKN now measures index 

lakes three times per year); a long-term 

gaging station on Washington Creek was 

recently deactivated (Crane et al. 2006).

Fair

Advanced water quality 

suite

Major ions CAUTION Increases in some major ions noted by 

comparing samples from 1995–1996 to 

2007–2008 (Figure 29 and page 71).

Fair

Dissolved silica CAUTION Limited data suggests that silica is variable 

but within range necessary for aquatic 

organisms (page 73).

Fair

Alkalinity GOOD Alkalinity in lakes is within acceptable 

range and unchanged between recent 

surveys (Figure 29).

Fair

Dissolved organic 

carbon

GOOD DOC is within acceptable range and 

unchanged between recent surveys (Figure 

29).

Fair
158

Table 34. Condition summary for inland lakes, rivers, and wetlands, Isle Royale National Park (continued).

Vital Sign Metric Condition Data Summaries or References Quality of Data

Advanced water quality 

suite (continued)

Chlorophyll-a CAUTION Chlorophyll-a concentration can be 

variable, but many lakes show increase 

between recent surveys (page 74).

Fair

Nutrients CAUTION Several lakes exceeded USEPA reference 

criteria for the ecoregion during recent 

survey (page 75).

Fair

Aquatic and wetland plant 

communities

Not defined GOOD Native communities appear stable despite 

some exotic, aggressive species; Native 

species previously undocumented were 

found by Meeker et al. (2007).

Good

Amphibians and reptiles Presence/distribution GOOD Apparent broad distribution of native 

salamanders, snakes, and turtle (page 67).

Fair

Fish communities Change in native 

communities over 

time

GOOD Few changes in the species composition of 

ISRO lakes from early 1900s to 1990s 

(Kallemeyn 2000).

Good

Trophic bioaccumulation Concentration in 

organisms exceeding 

recommended 

levels/benchmarks

CAUTION Mercury concentration in fish is above 

recommended levels in several lakes (page

110).

Fair

GOOD Organic compound and heavy metals were 

detected in mussels at ‘levels well below 

any concentration of concern’ (Nichols et 

al. 2001a).

Fair
159

Table 34. Condition summary for inland lakes, rivers, and wetlands, Isle Royale National Park (continued).

Vital Sign Metric Condition Data Summaries or References Quality of Data

Toxic concentration in 

sediments

Presence of toxics at 

levels exceeding 

standards

UNRANKED No data found. Poor

Toxic concentrations in 

water

Presence of toxics at 

levels exceeding 

standards.

GOOD Some data exceeded USEPA criteria in 

Washington Creek between 1965 and 

1974, but subsequent readings were normal 

(Table 23).

Good

Health, growth and 

reproductive success

Not defined GOOD Eagle and osprey population increasing 

(NPS ca. 2003) and populations of aquatic 

organisms apparently stable.

Good

Benthic invertebrates Not defined CAUTION Limited sampling of invertebrate 

communities from Siskiwit and Sargent 

Lake did not raise concern (Whitman et al. 

2000).

Fair

Aquatic pathogens Presence CAUTION VHS has not been detected in inland 

waterways on ISRO, but has been found in

Lake Superior (page 134).

Fair

Algae/Phytoplankton Not defined CAUTION Samples from Siskiwit and Sargent Lake 

between 1997 and 1999 did not report 

unusual community composition (Whitman 

et al. 2000).

Fair

Nutrient 

dynamics/biogeochemistry

Not defined GOOD Early concerns regarding acidic 

precipitation indicate that acidity is 

buffered and has not significantly altered 

aquatic systems (page 110).

Fair

Zooplankton Not defined GOOD Zooplankton communities from ISRO 

lakes are similar to nearby mainland lakes,

but regular monitoring efforts have been 

recommended (Whitman et al. 2000).

Fair
160

Table 35. Condition summary for forest resources, Isle Royale National Park.

Vital Sign Metric Condition Data Summaries or References Quality of Data

Plant exotics Distribution/abundance GOOD Judziewicz 1997. Fair

Animal exotics Distribution/abundance GOOD No data found to support the 

presence of animal exotics.

Fair

Terrestrial plants Abundance, number of 

populations

UNRANKED Judziewicz 1997. Fair

Bird communities Not defined GOOD Trends of ISRO bird populations 

are similar to mainland bird 

communities (page 86).

Good

Problem species (whitetailed deer)Presence/abundance GOOD White tailed deer are not present 

on ISRO.

Good

Problem species (exotic 

earthworms)

Presence/abundance of 

key taxa (e.g.,

Lumbricus terrestris)

UNKNOWN

(GOOD?)

Significant differences in 

invasion potential in ISRO 

forests (page 140).

Poor

Threatened and 

endangered species

Number and 

distribution of 

populations

CAUTION Judziewicz 2004 listed many 

plant species of concern, 

especially disjunct species, 

mainly along the Lake Superior 

shoreline (page 78).

Good

Mammal communities Number of species; 

population density of 

wolf

CAUTION NPS records and Peterson 1999. Good

Uncommon inland 

community types

TNC Community 

types 1, 16, 22, 31, 37, 

44, and 48

CAUTION Judziewicz 1997, TNC 1999. Good
161

Table 35. Condition summary for forest resources, Isle Royale National Park (continued).

Vital Sign Metric Condition Data Summaries or References Quality of Data

Plant species that have 

declined since 

approximately 1860

Decline in population 

from historic levels

CAUTION Eastern white pine, larch, and 

Canada yew populations have 

declined, in part due to past 

harvesting (Janke et al. 1978).

Fair

Special habitats Not defined UNRANKED Unknown

Harvested species Not defined GOOD No species are harvested in 

ISRO.

Good

Mercury concentration Concentration in soil 

solution or associated 

with organic matter

UNRANKED Cannon and Woodruff 2000, 

Grigal 2003.

Poor

Terrestrial pests and 

pathogens

Presence, damage GOOD None are known to be a major 

issue (page 137).

Fair

Succession Abundance of each 

boreal forest 

successional stage 

relative to historic 

range and variability 

CAUTION Hansen et al. 1973, FIA data 

(page 80).

Fair to Poor

Biotic diversity Not defined; may be 

covered by other 

metrics

UNRANKED Unknown

Trophic relations Not defined UNRANKED Unknown
162

Table 35. Condition summary for forest resources, Isle Royale National Park (continued).

Vital Sign Metric Condition Data Summaries or References Quality of Data

Soils, soil organic matter Carbon/nitrogen ratio, 

concentration of 

nitrogen

CAUTION Deposition rates suggest that 

nitrogen levels in soil could be 

rising (page 110).

Poor

Health, growth and 

reproductive success

Not defined UNRANKED These types of metrics tend to be 

ambiguous and require longterm intensive monitoring to 

have much potential as 

indicators.

Unknown

Lichens and fungi Not defined UNRANKED Unknown

Nutrient 

dynamics/biogeochemistry

Concentration of 

sulfate and potassium 

ions in soil solution, 

ammonium 

immobilization rate

CAUTION Stottlemyer and Hanson 1989, 

Stottlemyer and Toczydlowski 

1999a.

Poor

Primary productivity Not defined UNRANKED Unknown
163

Table 36. Impact of stressors on aquatic and upland resources in Isle Royale National Park.

Stressor/Resource Lake Superior

and coastal 

wetlands

Inland 

lakes

Streams Interior

wetlands

Upland 

resources 

Lowland 

forests

Atmospheric Deposition

Nutrient Enrichment

Altered Disturbance Regime - Fire Exclusion -- -- -- --

Soil and Groundwater Contamination

Wastewater Disposal

Great Lakes Shipping -- --

Commercial And Recreational Fishing -- -- --

Recreational Boating -- -- --

Visitor Use

Climate Change

Exotic Species

=existing problem; =potential problem; =not a known problem; =insufficient information

165

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Appendices

Appendix A. Sources of data for base map and notes on map content development.

All maps and associated geoprocessing were done with the ArcGIS 9.3 software by 

Environmental Systems Research Institute, Inc., Redlands, CA (2009). Maps are shown in the 

NAD 1983 UTM Zone 16N coordinate system. Spatial data obtained in other datums or 

coordinate systems were re-projected using ArcGIS.

Park boundaries (lines and areas), hydrography (streams, lakes, shorelines), and terrain (DEM 

elevation grids and hillshading) were typical base map features used on many of the report maps. 

The overall park boundary and area defined as the 4.5 mile extension onto Lake Superior is the 

Isle Royale NP Park Boundary (parkbnd) layer (MTU 1993). The boundary and areas for the 

main and included islands are based on the shoreline features (FCode 56600 L. Superior 

Coastline) from the National Hydrography Dataset (NHD) - High Resolution (USGS 2008) 

obtained from Ulf Gafert, NPS Ashland, WI Center on 06/19/2008. The NHD was also the 

source for the ISRO stream/river flowline features (FTypes 33400-Connectors, 46003-

Intermittent, 46006-Perennial, and 55800-Artificial Path) and lake/pond waterbody features 

(FTypes 39004-Perennial and 39009-Perennial with stage; also included Big Siskiwit River 

outlet FType 46006). Elevation data was obtained from NPS-Ashland, WI (Ulf Gafert, 

06/24/2008), as 2 m DEMs from bare earth LIDAR data. North and south DEMs were combined, 

irregularities fixed, and fitted to the island boundaries noted above. The hillshade layer was 

created with the standard ArcGIS hillshading tool applied to the final 2 m DEM.

Regional scale maps included layers for state and county (province and upper tier municipal unit 

for Ontario), that were created by merging detailed layers from Michigan (MI Center for 

Geographic Information, 2008, Michigan Geographic Framework ver 8a; 

http://www.mcgi.state.mi.us/mgdl accessed 2/5/2009), Wisconsin (WDNR, 1992, Wisconsin 

County Boundaries, Madison, WI), Minnesota (MNDNR, 2003, Minnesota County Boundaries; 

http://deli.dnr.state.mn.us accessed 7/7/2008), Ontario (ESRI Canada, 2004, Ontario Base Map 

Delivery Website, Upper Tier Municipal; 

http://www.geographynetwork.ca/website/obm/viewer.htm accessed 6/30/2008), and the park 

boundary noted above. Edge problems were fixed and closure lines added as needed.

Sources for other content on individual maps are noted in the figure caption. Digital versions 

(GIS-ready) of the source data were used when possible. When GIS layers were not available, 

new layers were developed from available spatial information (see below). Layer symbolization 

represents our interpretation or application of the data. Figures that are direct copies from other 

reports (not our GIS product) are noted as “from” (Figure 2 and Figure 3), and figures that are 

GIS reproductions of the original report figure are noted as “after” (Figure 8 and Figure 47).

Figure 7, Lake Superior bathymetry and soundings, is based on water depth information 

(sounding points, shoreline, and shallow depth contours) from NOAA electronic navigation 

charts (ENCs), primarily chart 14961 for Lake Superior and chart 14976 for Isle Royale. 

Additional sounding point data was also obtained as needed from charts 14962–14969 and 

14973–14974. A 50 m depth grid for the ISRO area and a 200 m grid for Lake Superior were 
214

developed from the ENC data using ArcGIS and Golden Software’s Surfer interpolation tools 

along with manual contouring and detailing. The bathymetry shading layer was made with the 

ArcGIS hillshading tool. A masking layer to cover landward extents of the bathymetry 

interpolation was also developed by utilizing the general Lake Superior coastline from ENC 

14961 and the ISRO coastline from ENC 14976.

Figure 8, Lake Superior currents, was created by on-screen digitization of Figure 7 in the Lake 

Superior Lakewide Management Plan (LSBP 2006a). 

Figure 13 (USEPA open water sampling sites), Figure 33 (air quality monitoring sites), and 

Figure 34–Figure 40 (regulated facilities and emissions for criteria air pollutants), were made 

using published lat/long coordinates from the noted sources. The air direction roses for the air 

emission maps were based on 2007-2008 averages for Rock of Ages and Passage Island sites 

(NBDC 2009a,b). Figure 34, regulated facilities, also displays a distance overlay from ISRO, 

created by buffering the base map park boundary (water extent). 

Watershed delineations shown on Figure 21–Figure 23 were made using the ArcGIS watershed 

tool and the 2 m DEM discussed above. Some manual fine adjustments were made to smooth the 

junction of watersheds and to best represent outlet areas.

Figure 24, Lake types by canonical correspondence analysis, utilized a subset of the base map 

waterbody layer. The canonical correspondence grid position for each target lake was obtained 

from the referenced source and the lake symbolized based on a continuous gradient of colors 

developed for the analysis grid.

The wetland figures (Figure 25–Figure 27) utilized a subset of the vegetation layer (TNC 1999, 

USGS 2000a). As described in the report in the Inland Aquatic Resources section, the wetland 

communities in Ecologic Groups 3 and 4 were grouped into seven types, an attribute field was 

added to the veg layer for this classification, and the maps symbolized on this field. Figure 28, 

river-associated wetlands, also uses this wetland subset of the vegetation layer. In this case, the 

contiguous polygons with the same wetland grouping were dissolved and unioned with the 

stream layer in order to quantify wetland areas adjacent to streams. This river-associated 

wetlands analysis also utilized 10 and 100 m buffers of the base map stream layer and a subset of 

the stream layer representing the intersection of the stream and veg based wetland layer.

Figure 46, Lake Superior shipping lanes, is based mostly on the Lake Superior ENC chart 14961 

for the Lake Superior coastline and the recommended ship routes. The ENC’s navigation line 

feature was symbolized by type and direction, and a point direction (arrowhead) layer was 

created from the navigation line orientation field. Some additional ferry route segments were 

obtained from ENC charts 14964, 14968, and 14976.

Figure 47, location of mines, reproduces the original report map in a new GIS format. In addition 

to the original report figure as a general guide, mine site locations were obtained from the Mine 

and Mine Related Point Features of Isle Royale National Park (ISROMIN) layer (NPS 2004d), 

and mine sites noted on the DRG available for ISRO as noted below.
215

Although not used directly on any maps, digital version of the USGS topographic maps (DRGs) 

and airphotos (DOQs) were used to verify other data, serve as a base for digitization, and as a 

general reference for locating features. A composite of 1:24k DRG quads and a 2005 NAIP color 

photo mosaic, both in .sid format, were obtained from the NPS Ashland Center on 06/24/2008.

A complete list of GIS layers, sources, and available metadata is included as Appendix B.
216

Appendix B. Description of GIS layers, sources, and metadata for maps used in the preparation of this report.

Layer Type Source Description Metadata File

Air_Canada2007 point Environment 

Canada 2009

facilities on the Canadian national pollutant 

release inventory

Air_Canada2007.xls

Air_Monitoring_Sites point various-see text air quality monitoring stations pertinent to the 

ISRO area

ISROAirSites.xls

Air_US2002 point USEPA 2009c facilities on the USEPA AIRS/AFS air release list 

for the MN, WI, and MI area

Air_US2002.xls

APIS polygon Apostle Islands National Lakeshore area from 

previous Coastal Assessment report

Bathymetry_mask polygon NOAA 2007a,d land area polygon mask to cover landward extent 

of the bathymetry grids

NOAA_ENC_download.txt

CCA_Axes line new (legend) the central axes for the CCA_Grid layer

CCA_Grid polygon new (legend) a canonical correspondence grid to match values 

in CCA_Lakes

CCA_Lakes polygon USGS 2008, 

Carlisle 2000

a subset of the Hydro_Lakes layer for lakes with 

canonical correspondence analysis available

see Carlisle 2000

DEM2I grid Ulf Gafert, NPS, 

06/24/2008

2 m DEM (integer centimeter) for ISRO

DEM50I grid see DEM2I 50 m DEM (integer centimeter) resampled from 

DEM2I

EPA_Sensitivity line USEPA Region 5 

2000

shoreline type and sensitivity classification 

extracted for ISRO shorelines

Inland_Sensitivity_Atlas.HTM, 

UPMESI.txt, UPMESI.pdf

Geology polygon NPS 2004c geologic units of ISRO; a geologic group attibute 

field was added for mapping

isroglg.shp.xml

Hillshade2 grid derived Ground surface elevation hillshade created in 

ArcGIS using the DEM2I layer

Hillshade50 grid derived Ground surface elevation hillshade created in 

ArcGIS using the DEM50I layer

Hydro_Coast line USGS 2008 NHD feature type 566 (Lake Superior coastline) National Hydrography Dataset (NHD) -

High-resolution.htm

Shading indicates modification, attribute editing, or significant geoprocessing of source GIS data
217

Appendix B. Description of GIS layers, sources, and metadata for maps used in the preparation of this report (continued).

Layer Type Source Description Metadata File

Hydro_Flow line USGS 2008 NHD feature types 334 (connectors), 460 

(intermittent and perennial streams), and 558 

(artificial paths)

National Hydrography Dataset (NHD) -

High-resolution.htm

Hydro_Flow_200Corridor polygon derived a 100 m buffer around the Hydro_Flow layer

Hydro_Flow_Wetlands line USGS 2008 subset of ISRO rivers and streams (Hydro_Flow) 

that intersect wetland vegetation

Hydro_Lakes polygon USGS 2008 NHD feature type 390 (perennial waterbodies) National Hydrography Dataset (NHD) -

High-resolution.htm

Hydro_Marsh polygon USGS 2008 NHD feature type 466 (undifferentiated 

swamp/marsh)

National Hydrography Dataset (NHD) -

High-resolution.htm

Hydro_Named_Lakes polygon USGS 2008 subset of Hydro_Lakes for named lakes National Hydrography Dataset (NHD) -

High-resolution.htm

ISRO_Bath_Hillshade grid derived 50 m Lake Superior depth hillshade for the ISRO 

vicinity created in ArcGIS using the 

ISRO_Bathymetry grid 

ISRO_Bath_HS_comb grid derived 50 m hillshade combination of 

ISRO_Bath_Hillshade (L Superior) and 

Hillshade50 (ISRO land area)

ISRO_Bathymetry grid NOAA 

2007a,b,c,d

50 m integer grid of Lake Superior water depth in 

the vicinity of ISRO

NOAA_ENC_download.txt

ISRO_veg polygon USGS 2000a, 

TNC 1999

vegetation mapping used for upland and wetland 

analysis; wetland group added to attributes

USGS_ISRO_Spatial_Veg_Data_Metad

ata.txt, 

NatureConservancyVegClass.pdf, 

PhotoInterpretationReport.pdf

ISRO_veg_area polygon USGS 2000a, 

TNC 1999

the extent of the ISRO_veg layer

ISRO_veg_wetlands_7grps polygon USGS 2000a, 

TNC 1999

subset of the ISRO_veg layer for wetland types; 

dissolved on seven major wetland groups

ISRO_veg_wetlands_20corridor polygon USGS 2000a, 

TNC 1999

subset of ISRO_veg for wetlands within a 20 m

corridor along rivers and streams

ISRO_veg_wetlands_200corridor polygon USGS 2000a, 

TNC 1999

subset of ISRO_veg for wetlands within a 200 m

corridor along rivers and streams

Shading indicates modification, attribute editing, or significant geoprocessing of source GIS data
218

Appendix B. Description of GIS layers, sources, and metadata for maps used in the preparation of this report (continued)

.

Layer Type Source Description Metadata File

L_Superior polygon see 

Region_Counties

Lake Superior boundary created from 

Region_Counties

L_Superior_ENC polygon NOAA 2007a Lake Superior area from NOAA ENC 14961 

depth area features

NOAA_ENC_download.txt

L_Superior_ENC_arc line NOAA 2007a Lake Superior boundary from NOAA ENC 14961 

depth line features for coastlines

NOAA_ENC_download.txt

L_Superior_Surface_Current_Dir point LSBP 2006a digitized Lake Superior surface current vector 

direction indicators

see LSBP 2006a

L_Superior_Surface_Currents line LSBP 2006a digitized Lake Superior surface current vectors see LSBP 2006a

L_Superior_Vertical_Currents polygon LSBP 2006a digitized Lake Superior areas of upwelling and 

downward water movement

see LSBP 2006a

LS_Bath_Hillshade grid derived 200 m Lake Superior depth hillshade created in 

ArcGIS using the LS_Bathymetry grid 

LS_Bathymetry grid NOAA 

2007a,b,c,d

200 m integer grid of Lake Superior water depth NOAA_ENC_download.txt

LS_sample_sites point USEPA 2006, 

USEPA 2008a

Lake Superior water quality sampling sites in the 

ISRO area

GLENDA WQ Data.xls

LS_Soundings point NOAA 

2007a,b,c,d

compilation of sounding point features from 

available NOAA ENCs

NOAA_ENC_download.txt

Mines point NPS 2004d, 

DRGs

location of historic mines on ISRO isromin.shp.xml

Karamanski et 

al. 1988

Park_arc line see Park_poly ISRO land and water boundaries created from 

Park_poly

park_buffers polygon derived Five buffer zones, 50 km each, extending from 

the ISRO water park boundary (Park_poly layer)

Park_poly polygon MTU 1993, 

USGS 2008

ISRO park areas created from the NPS park 

boundary feature and the Hydro_Coast line 

features

parkbnd.xml, National Hydrography 

Dataset (NHD) - High-resolution.htm

Shading indicates modification, attribute editing, or significant geoprocessing of source GIS data
219

Appendix B. Description of GIS layers, sources, and metadata for maps used in the preparation of this report (continued).

Layer Type Source Description Metadata File

PIRO polygon Pictured Rocks National Lakeshore area from 

previous Coastal Assessment report

Region_Counties polygon MNDNR 2003 regional county level map created from Mn, WI, 

MI, and Ontario layers

MN_county_boundaries.htm

WDNR 1992 WI_county_boundaries.htm

MCGI 2008 MI_Geographic_Framework.html

ESRI Canada 

2004

Ontario Base Map Data Delivery 

Website.htm

Region_State_Land_Boundaries line see 

Region_States

regional state land boundary map created from 

Region_States

Region_States polygon see 

Region_Counties

regional state level map created from 

Region_Counties

Shipping_Lanes line NOAA 

2007a,b,c,d

navigation line features from four NOAA ENC 

charts 14961, 14964, 14968, 14976

NOAA_ENC_download.txt

Shipping_Lanes_Direction point derived direction of recommended track lines based on 

description and orientation in the 

Shipping_Lanes layer

SLBE polygon Sleeping Bear Dunes National Lakeshore area 

from previous Coastal Assessment report

Watershed_arc line derived arc version of the Watershed_poly layer

Watershed_poly polygon derived the ISRO main island subdivided into watersheds 

for principal streams, drainages, and coastal 

areas, based on DEM2I layer

Shading indicates modification, attribute editing, or significant geoprocessing of source GIS data

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and 

other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and 

affiliated Island Communities.

NPS 139/105526, September 2010
National Park Service

U.S. Department of the Interior

Natural Resource Program Center

1201 Oakridge Drive, Suite 150

Fort Collins, CO 80525

www.nature.nps.gov

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