State of Lake Superior

Edited by

M. Munawar and I.F. Munawar

Ecovision World Monograph Series

Foreword

Henry A. Regier* C.M.

Professor Emeritus, University of Toronto, Toronto, ON

It happens that some of Mohi Munawar’s favourite terms, as manifested in the title of this monograph and of the sponsoring society, are also among my favourite words. Here I reflect on some of my recent experiences with these terms.

First a comment about Lake Superior: It has not yet been degraded as badly as the other Laurentian Great Lakes, but some taxa of fish have been lost. Decades ago my colleague John Goodier (1981) searched old archives to identify various taxa or stocks of lake trout in this lake and how they organized their interactive community before human abuses became intense. The evolutionary complexity of the whole salmonid community reminded me of the diversity of the cichlid community that I had encountered briefly in Lake Victoria in 1970.

Over the past half century I’ve paid close attention to how the term ‘ecosystem’ is used by an author or speaker. I have inferred that people who use that term constructively are not likely to be hidebound reductionists. Nowadays empirical scientists who publish in leading journals use methods like those of the old reductionism responsibly; i.e. balanced with analyses of emergent ‘whole’ phenomena for which extreme reductionism is ineffective. Arthur Koestler (1969) termed such a balanced approach ‘holonic’ in which ‘hol’ refers to the whole integrated woolly phenomenon and ‘on’ to perceived less-woolly parts of that whole.

An ecosystem approach may now be cast as a kind of mindscape, with antecedents to be found in old writings of Kant, Kropotkin, Bergson, Teilhard, Vernadsky, etc., besides those of many more Non-Europeans. Starting about four decades ago, Magoroh Maruyama chose an empirical approach to identify, describe and analyze common mindscapes that he found in various cultures of the world. Among North Americans of European descent he found four common mindscapes each of which had a favoured scientific methodology. He termed one of these four ‘G’ and, in 1980, described it as follows: “Interactions generate more diversity, new combinations of mutually beneficial relations, new patterns, and a rising level of sophistication of biological, social, and some physical systems. The universe grows.”

My understanding of what we in the Laurentian Basin commonly call an ‘ecosystem approach’, is that it starts within Maruyama’s G mindscape, ontogenetically as well as epistemologically. One can perceive many complementary vistas within a generic G mindscape including ecologics, economics, ekistics, ecumenics, ecosophics and ecothealogics. These terms all start with a version of the Greek ‘oicos’ which refers to a household, or a home together (repeat, together) with its inhabitants, or a habitat with its inhabitants, to a text within its context, etc. It’s important to note that such a cross-level integrated phenomenon is taken to be an ‘elementary unit’ in ontogenetic reality and epistemological methods. In our Laurentian Basin ecosystem, in the widest sense of that ecosystem term, colleagues and I have found that the other three common mindscapes in our culture can be nested usefully and pragmatically as approximations for some ecosystem features. So we use all four Maruyaman mindscapes – H, I, S and G – in our work, but with the first three subservient to the fourth. The H mindscape is closest to obsolete fundamentalistic reductionism, which can nevertheless be useful in a tempered form.

An eco-phenomenon manifests features like self-organizing, holonic (as a more general kind of nesting than ‘hierarchic’ with its unfortunate etymological implications) and intentionally open to selected external influences (eustresses) but also intentionally closed to some unwanted influences (distresses). The term ‘integrity’ may refer to a complex dynamic phenomenon with sufficient autonomous propensities to sustain the identity of such an eco-phenomenon in trying circumstances and times (Rapport et al. 1985). Again, an emergent eco-phenomenon cannot be explicated fully through narrow reductionistic methods.

Recall the work in the 1980s by the World Commission on Environment and Development chaired by physician Gro Harlem Brundtland and titled “Our Common Future”. USSR Academician N. N. Moiseev submitted a recommendation at a WCED hearing in Moscow on 8 December 1986: “Some unique objects like Lake Baikal, …, the Great Lakes of Africa and North America, are parts of our global patrimony. They are some of the absolute values our planet possesses and their significance transcends any national boundaries. … What is needed today is the molding of a new ethos and new arrangements for building understanding among people, countries and regions.”

Some of us vibrate positively to Moiseev’s terms ‘absolute value’ and ‘ethos’. Compatible versions of a generic ecosystem approach to foster Lake Superior’s ‘health, integrity [and ethical] management’ are at hand. Those relevant to an ‘aquatic’ vista in our eco-mindscape, as in the present volume, are complemented by others relevant to the whole watershed and to social, economic and political vistas of the encompassing mindscape. Perhaps Anishinabek and Cree People could help any remaining reductionistic true believers to reform and appreciate sacred features of the Lake Superior ecosystem.

Recently the Editors of Nature (2009) have argued that the “economic downturn might be the best time to include ecosystem services in the real economy”. Further, they opine that “the ecosystem services approach clearly has great potential. Indeed, it is a natural extension of the market-based carbon tax or cap-and-trade approaches…” And then they call for more good science relevant to such valuation. Editor Mohi Munawar has been mobilizing such science for decades, as in the present volume.

References:

Goodier, J.L., 1981. Native lake trout (Salvelinus namaycush) stocks in the Canadian waters of Lake Superior prior to 1955. Canadian Journal of Fisheries and Aquatic Sciences 38, 1724-1737.

Koestler, A., and Smithies, J.R. (Eds.), 1969. Beyond Reductionism. Hutchinson, London, UK.

Maruyama, M. 1090. Mindscapes and science theories. Current Anthropology 21, 589-599.

Nature Editors. 2009. Natural value. Nature 457, 764.

Rapport, D.J., Regier, H.A., and Hutchinson, T.C., 1985. Ecosystem behavior under stress. American Naturalist 125(5), 617-640.

Word Commission on Environment and Development, Gro Harlem Brundtland, chair, 1987. Our Common Future. Oxford University Press, Oxford, UK

Preface

James F. Kitchell

Director, Center for Limnology Hasler Professor of Zoology

University of Wisconsin, Madison, Wisconsin, USA 53706

Lake Superior was saved from the extremes felt elsewhere because it is the top of the drainage landscape. Timber from the surrounding forests was sent to build large cities elsewhere. Local soils and the northerly climate did not invite agricultural development. Lessons learned in the downstream lakes evoked institutional responses. Those were successful in developing sea lamprey control in combination with reduction in fishery exploitation before Lake Superior was totally depleted. Fueled by the growing environmental movement, restoration and rehabilitation programs developed for each of the lakes. Superior offered the prospects of greatest success because it was, in general, least altered. Many decades later, Superior serves as the best example of success in recovering from environmental adversity. This is not to say that restoration is complete or that all ecological problems are resolved. The heavy hand of humanity continues to cause important concerns about the present and future state of Lake Superior.

This volume offers a polythetic view of current conditions in Lake Superior and some insightful suggestions about where and how improvements should continue. The chapters presented range from basic reviews of what we know as a consequence of effective research, to those that identify the little we know about challenging environmental issues for the future. Among those are the continuing concerns about contaminants, the burgeoning march of invasive species and the portent of global change. We find some encouragement in the resilience of this large lake ecosystem. In many respects, it is a success story emerged from the insights of research merged with the mindful attention of management agencies. There is credit and hope reflected in our abilities to guide both the continuing restoration and effective protection of Gitche Gummee, the world’s largest lake. Hiawatha would probably be pleased by the progress chronicled in the following pages.

Editorial

M. Munawar1 and I.F. Munawar2

1Fisheries and Oceans Canada, 867 Lakeshore Road, Burlington, ON.

2Phytoplankton Canada, 685 Inverary Road, Burlington, ON

The axe, the plough and the net that accompanied Europeans to North America wrought profound ecological changes in our Laurentian Great Lakes. Forests were harvested and prairies were ploughed. The offal appeared downstream and began the process of adverse environmental change in receiving waters. New canals circumvented the natural barrier at Niagara Falls and the first wave of invaders soon responded. Expansion of commercial fisheries created hundreds of fishing villages. Invasion of sea lampreys coupled with growing exploitation effects caused local extirpation of many native and endemic species. Agricultural expansion, new manufacturing centers and urban growth accelerated the nutrient loading expressed in declining water quality for Lakes Ontario, Erie, Huron and Michigan. Each suffered what must be deemed a severe decline of previous ecosystem goods and services. In combination, this series proceeded from easIt was in the spring of 1976, that a one day symposium on the Upper Great Lakes was organized at the 19th Great Lakes Research Conference held at the University of Guelph. This symposium was very successful in bringing together researchers working on the upper lakes, especially Lake Superior. Encouraged by its success, we initiated a working group called the Upper Lakes Multi-Disciplinary Group (ULM) at the Canada Centre for Inland Waters (CCIW). We met regularly in Burlington, Ontario to assess and review the current research being carried out. These meetings resulted in the development and publication of a special issue of the Journal of Great Lakes Research: “Limnology of Lake Superior” (IAGLR, 1978) which I edited. Following this special issue, not much was published about Lake Superior with the exception of a few papers (Munawar et al. 1987; Munawar and Munawar, 2000) which focussed mainly on phycology.

In order to fill in the long gap without information, a “State of Lake Superior” conference was organized by the Aquatic Ecosystem Health & Management Society (AEHMS) in the spring of 2002 at Houghton, Michigan. The conference was co-sponsored by Michigan Technological University, the Large Lakes Observatory of the University of Minnesota – Duluth and the U.S. Geological Survey. The meeting was instrumental in bringing together various investigators actively engaged in Lake Superior research. Some of the papers originating from the conference were published in a special issue of the society’s Journal, Aquatic Ecosystem Health & Management (AEHMS, 2004). A second group of papers were published in a special issue in the Journal of Great Lakes Research (IAGLR, 2004). The current book is being published by the AEHMS as part of its Ecovision World Monograph Series. The book contains papers which originated from the above conference, but in order to make the book as holistic as possible, additional papers on current topics and issues were solicited. This process was time consuming and onerous, but also necessary, especially considering that this is the first time that a comprehensive, peer-reviewed book on Lake Superior has been attempted.

It is an opportune time to highlight and emphasize here the historical background of the AEHMS’ role and impact in the propagation and coordination of large lakes research, via its journal (Aquatic Ecosystem Health and Management) and the monographs (Ecovision World Monograph Series). Initially, the society established a working group called “The Great Lakes of the World-GLOW” to bring together large lakes researchers for exchanging ideas, technology and interactions. Then GLOW embarked on organizing special symposia which resulted in several peer-reviewed books and special issues. In a short period of time of about 15 years, the AEHMS has published 10 peer-reviewed books (Table 1) and 11 special issues of its journal (Table 2).

Table 1. Books published under Ecovision World Monograph Series from 1995-2008.

Book title	Year
The Lake Huron Ecosystem: Ecology, Fisheries and the Management	1995
Phytoplankton Dynamics in the North American Great Lakes, Vol. 1: Lakes Ontario, Erie and St. Clair	1996
The State of Lake Erie Ecosystem (SOLE): Past Present and Future	1999
Phytoplankton Dynamics in the North American Great Lakes, Vol. 2.: Lakes Superior, Michigan, North Channel, Georgian Bay and Lake Huron	2000
The Great Lakes of the World (GLOW): Food-web, Health & Integrity	2001
Ecology, culture and conservation of a protected area: Fathom Five National Marine Park, Canada	2001
State of Lake Ontario(SOLO): Past, Present and Future	2003
State of Lake Michigan (SOLM): Ecology, Health and Management	2005
Checking the Pulse of Lake Erie	2008
State of Lake Superior	2008

Table 2. Special issues of the Aquatic Ecosystem Health and Management Journal 2000-2009.

Special Issue title	Volume	Year
Large Lakes of the World: Comparative Ecology	Vol 3 (1)	2000
Ecosystem Health of Lake Baikal, Russia	Vol 3 (2)	2000
Great Lakes of the World: Food Web, Fisheries, and Management	Vol 5 (3)	2002
Comparing Great Lakes of the World	Vol 6 (3)	2003
Coastal Wetlands of the Laurentian Great Lakes: Health, Integrity and Management	Vol 7 (2)	2004
Emerging Issues in Lake Superior Research	Vol 7 (4)	2004
Great Lake Victoria Fisheries: Changes, Sustainability, and Building Blocks for Management	Vol 10 (4)	2007
Changing Great Lakes of the World (GLOW IV)	Vol 11 (1)	2008
State of Lake Huron: Ecosystem Change, Habitat, and Management, Part I	Vol 11 (2)	2008
Checking the Pulse of Lake Ontario	Vol 11 (4)	2008
The State of Lake Huron: Ecosystem Change, Habitat and Management, Part II	Vol 12 (1)	2009

We take this opportunity to thank the following colleagues who assisted in various aspects of the development of this monograph:

Susan Blunt, Joanne Dziuba, Tom Edsall, Mark Fitzpatrick, Joe Leach, Jennifer Lorimer, Ed Mills, Nabila Munawar and Heather Niblock. Finally, we are grateful to Drs. Henry Regier and James Kitchell for providing valuable insights through their foreword and preface.

The “State of Lake Superior” monograph is a culmination of a dream to produce high quality, peer-reviewed books on each of the Laurentian Great Lakes. This book on Lake Superior completes the cycle. The popularity and success of these books has led to the initiation of special issues of AEHM dedicated to large lakes research which have also been well received by the large lakes community. We hope that the “State of Lake Superior” monograph will be a landmark publication useful for scientists, managers and students in their research and facilitate the conservation of this world resource.

References:

Aquatic Ecosystem Health & Management Society (AEHMS), 2004. Emerging issues in Lake Superior Research. Aquat. Ecosyst. Health Mgmt. 7(4), 435-528.

International Association for Great Lakes Research (IAGLR), 1978. Limnology of Lake Superior. J. Great Lakes Res. 4(3-4), 247-554.

International Association for Great Lakes Research (IAGLR), 2004. Lake Superior. J. Great Lakes Res. 30(Suppl. 1), 1-489.

Munawar, M., Munawar, I.F., 2000. Phytoplankton dynamics of the North American Great Lakes. Vol. 2. Backhuys Publishers, Leiden, Netherlands.

Munawar, M., Munawar, I.F., McCarthy, L., 1987. Phytoplankton ecology of large eutrophic and oligotrophic lakes of North America: Lakes Ontario and Superior. Arch. Hydrobiol. Bieh. Ergebn.Limnol. 25, 51-96.

Dedication

This book is dedicated to two extraordinary people whom I had the pleasure of being associated with in my research on the phytoplankton dynamics and ecology of the North American Great Lakes. The first is my mentor, Dr. Richard A. Vollenweider, Senior Scientist, whose genius and guidance had an enduring impact on my career. I was lucky that he chose me to be his first post-doctoral research fellow under the auspices of the National Research Council of Canada at Canada Centre for Inland Waters, Burlington, ON. The second is my colleague, Ms. Ginette Dupuis whose dedication and hard work could never be forgotten. She assisted in my research on Lake Superior which resulted in the Chandler-Misener Award from the International Association of Great Lakes Research. Ginette was one of the co-authors of the award winning paper. I hope this book will serve in some small way to keep their memories alive.

Richard A. Vollenweider

Dr. Richard A. Vollenweider passed away peacefully on January 20th, 2007, in Burlington, Ontario, after a long illness. He was born on the 27th of June, 1922, in Zurich, Switzerland, earned a Ph.D. in biology (Zurich, 1951) and quickly established himself as one of the world’s leading scholars on eutrophication. During his brief tenure with the OECD in Paris, he published an important report “Scientific fundamentals of the eutrophication of lakes and flowing waters with particular reference to Nitrogen and Phosphorus as factors in eutrophication” (OECD, 1971), which provided a new direction for controlling and treating water pollution. In 1968, at the invitation of Dr. J.R. Vallentyne of Fisheries Research Board of Canada he accepted a leading position to initiate biological research in the Laurentian Great Lakes. He was instrumental in launching multi-trophic, lake-wide and holistic biological surveys of the Great Lakes. I was fortunate that Dr. Vollenweider selected me to join his research team when he was initiating the unique, lake wide biological expeditions in the Great Lakes. I remember going on these long research cruises from Lake Ontario to Lake Superior collecting plankton and conducting primary productivity and bioassay experiments.

He was responsible for developing the phosphorus abatement model which served as the guiding document for the revision of the Great Lakes Water Quality Agreement. He published many landmark articles on the Great Lakes including the well known review paper “A comprehensive review of phytoplankton and primary production in the Laurentian Great Lakes” which quantified the relationship between phosphorous loadings, primary production and algal standing crop, and served as the scientific basis for phosphorous management plans as a means of controlling eutrophication. Dr. Vollenweider advocated water management on a global basis and was highly regarded for his research on phosphorus abatement. In recognition of his lifetime work, he was awarded the prestigious Tyler Environmental Prize in 1986, which he shared with Werner Stumm. He was also awarded the Naumann-Thienemann Medal of the International Association of Limnology (SIL) and many other awards. Even after his retirement Dr. Vollenweider was very active and visited my laboratory frequently. He strongly supported the establishment of the Aquatic Ecosystem Health & Management Society (AEHMS) when I approached him in the initial stages. Later he served enthusiastically on the advisory board of Aquatic Ecosystem Health & Management and the Ecovision World Monograph Series which he continued until he passed away. We greatly benefited by his continued support of the journal, advice and reviews of several manuscripts. He left a great legacy to the world of aquatic science in general and Great Lakes in particular. His research and guidance will serve the scientific community for a long time to come.

Ginette Dupuis Laliberte

Ginette Dupuis was born on August 13, 1951, in Montreal, Quebec. She earned a B.Sc. from the University of Toronto in 1973 after which she was employed by the Great Lakes Biolimnology Laboratory at the Canada Centre for Inland Waters Burlington, ON under my supervision. She participated actively in the first lakewide biological surveys of Lake Superior, 1973, working on phytoplankton dynamics and size fractionated primary productivity. This work resulted in the receipt of the Chandler-Misener Award in collaboration with me. She moved to the U.S. in 1975 and married Mr. Lawrence Laliberte. There she pursued a career in information technology and founded her own consulting firm. A fatal auto accident in July of 2000 brought an untimely end to a very promising career. Ginette will always be remembered not only in our laboratory but also as a family friend due to her friendly and warm disposition and lovely French accent.

Mohiuddin Munawar,

President, Aquatic Ecosystem Health & Management Society

Chief Editor, Aquatic Ecosystem Health & Management

Series Editor, Ecovision World Monograph Series

Physical and chemical regimes:

An Overview of the Characteristics of Lake Superior Meteorology, Hydrology and Physical Limnology

William M. Schertzer* and Yerubandi R. Rao

Water Science and Technology Directorate, Environment Canada, Canada Centre for Inland Waters, 867 Lakeshore Rd., Burlington, Ontario L7R 4A6

*Corresponding author: william.schertzer@ec.gc.ca

This paper provides an overview of historical and current knowledge regarding important characteristics of the surface meteorology, hydrology, thermal structure, energy fluxes and heat storage, water movements and hydrodynamic modelling in Lake Superior. Relevant descriptions of measurements and model simulations are also presented. The following provides a brief synopsis of the state of the research, and the effect of improvements in measurements and techniques on the current knowledge-base on selected physical components of the lake.

Advances and Required Improvements in Measurements

Historical analyses of the environmental climatology were largely based on shoreline meteorological observations. Current investigations have the benefit of in situ lake observations from NOAA and Canadian buoys. Combined observations from adjusted shore-based observations, limited lake buoys and use of satellite observations (e.g. AVHRR and QuikSCAT) have improved interpretations and analyses of dynamical processes. There are surveillance programs operational on the lake with meteorological buoys in ice-free periods, however, the spatial resolution of data is limiting for developing climatological time-series databases with high spatial resolution. Model simulations of nearshore dynamics such as upwelling and downwelling events and currents near the Keweenaw Peninsula have shown improved accuracy. Further improvements may be achieved through improvement in the coastal wind field possibly through coastal radar measurement systems or with mesoscale meteorological models. Modern observations and forecast systems for the Great Lakes over the past decades have allowed for greater advanced notice of storms with potentially extreme winds and waves which has increased the safety of ship transport on Lake Superior. Similarly, advancements in procedures to derive daily representations of water surface temperature using satellite as well as ice cover information as shown using GLSEA, will provide increased spatial information applicable to lakes research than traditional methods alone.

Advances in Hydrological Components and Evaporation Technique

An understanding of the magnitude and variation of lake hydrological components and response to climate is essential for lake management and for realistic regulation of the lake water levels and outflow. Early research (e.g. Bennett, 1978) established the baseline characteristics for water budget components. Over-lake evaporation on a lake the immense size of Lake Superior is a challenge to measure. Initial estimates of lake evaporation using constant transfer coefficients similar to the Lake Hefner studies resulted in very high levels of condensation (negative evaporation) during the months with very stable atmospheric conditions. Energy budget, water budget, and improved mass transfer formulations using variable transfer coefficients and recently including corrections for static stability and wind shear have shown a convergence of monthly mean evaporation values. Application of advanced techniques such as fast response eddy covariance methods will provide improved estimates of the lakewide evaporation as well as an understanding of the dynamic responses of the evaporative process to atmospheric forcing.

Improved Knowledge of Surface Heat Exchange and Heat Content

Knowledge of the surface heat exchange is an important boundary condition input to thermal and hydrodynamic models. Schertzer (1978) provided baseline values of the radiative and turbulent exchange components largely based on shoreline meteorological data. Bennett (1978) used water temperature profiles based on long-term lake surveys to approximate the lake heat storage for Lake Superior. Intensive observations conducted in 2005 from shoreline meteorological sites, lake meteorological buoys and in situ lake temperature profiles, offer a possibility to re-evaluate the magnitude and seasonal variation of both the heat flux components and lake heat storage.

Requirement for Improved Long-term Current Observation

As indicated previously, advancements in simulation of the lakewide circulation and dynamics of the water movements in the nearshore, requires improved resolution of boundary conditions such as the wind field. Current investigations have focused on generalization of the summer, winter and annual circulation based on historical data (e.g. Beletsky, 1999a: 1999b). Observations have shown that the summer circulation is mostly cyclonic and the Keweenaw current is a persistent feature of summer circulation in Lake Superior. In general, there is insufficient observational data to discern the large-scale winter circulation in Lake Superior.

Advances in Keweenaw Circulation Modelling and Role of Eddies

Recent research has seen the application of hydrodynamic models in the lakewide case and nearshore to simulate currents in the complex zone of the Keweenaw Peninsula. Mid-lake eddy fields have been observed in Lake Superior throughout the water column and throughout the lake during all seasons. Findings of Ralph (2002) raise several questions regarding the mechanisms of formation, propagation and dissipation as well as the complex 3-D structure. Eddies are postulated to have implications on how nutrients, sediments and contaminants are transported within large lakes and as well as the patchiness of phytoplankton and zooplankton.

Important Role for Remote Sensing

AVHRR imagery, supplemented by higher resolution SPOT-HRV, LANDSAT TM, or RADARSAT scenes, can provide high spatial coverage and real-time detail necessary to monitor dynamic changes associated with many meso-scale lake phenomena (Budd et al., 1999). Application of AVHRR and SeaWiFS instrumentation may provide further remotely sensed data to investigate dynamic temperature and circulation processes.

Requirement for Research on Climate Change and Development of Improved Scenarios

Modelling techniques for the simulation of climate change effects on lake hydrodynamics are available, however, data input to such models do not always exist (Lam and Schertzer, 1999). In the case of Lake Superior, Austin and Coleman (2007) indicated that while there have been theoretical and modelling studies on the lake, there is a paucity of direct observations from which to understand the actual responses. Annually averaged air temperatures from 1979 to 2005 have shown a positive trend, influencing a decreasing trend in ice extent in Lake Superior. Wind speeds from over-lake meteorological buoys show a tendency to higher average winds. These changes have an effect on the lake thermal response. July to September water temperatures have increased ~ 2.5 oC over the period 1979 – 2006 which is significantly in excess of regional atmospheric warming and has had the effect of lengthened the ice-free season resulting in earlier temperature stratification. Changes of this magnitude may have implications on other physical responses of the lake including aquatic ecosystem components.

Climate scenarios have been applied to Lake Superior largely focused on hydrological responses and ice extent. In general, these simulations have shown a potential toward reduced runoff, higher lake evaporation and a decrease in lake water level and decrease in ice extent. The magnitude of change can be quite different using scenarios from different GCM models. Simulation of potential climate impacts on water movements in Lake Superior requires improved climate scenarios and advances which may include lake-atmospheric coupling. Our understanding of physical limnological processes has increased greatly over the last three decades. Lake-wide models have been developed and the influence of meteorological and hydrological events is much more defined. However, further development in models at higher resolution in the nearshore will require an increase in spatial distribution of meteorological observations. Furthermore, these models have to be validated with hydro and thermodynamic variables in the lake. Analysis of trends in lake temperatures, water levels and ice cover strongly suggest that we are already experiencing warming in Lake Superior. Although future climate scenarios are uncertain, potential effects of climate change needs to be assessed using the deterministic lake models.

Keywords: climatology, energy budget, thermal regime, mesoscale wind forcing, coastal dynamics, circulation, eddies, climate impacts

Contemporary Lake Superior Ice Cover Climatology

Raymond A. Assel

NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd.,Ann Arbor, MI. 48105, U.S.A, Phone: 734 741 2268, Fax: 734 741 2055

*Corresponding author: Ray.Assel@noaa.gov

A thirty-winter (1973-2002) Great Lakes ice atlas and related publications are used for an analysis of Lake Superior ice cover. Dates of first ice, last ice, ice duration, and ice cover spatial averages and spatial patterns are analyzed within the context of lake bathymetric ranges. Results are summarized in a table, line graphs, and ice charts. Severe (mild) winters are identified based on the number of days each winter that the lake-averaged ice cover was above (below) the third (first) quartile of the 30-winter smoothed daily lake-average. Ice charts portray the spatial distribution patterns of ice cover concentrations for early, mid, and late winter and early spring for mild, typical, and severe winters. A study of the impact of global warming on the Great Lakes indicates that typical ice cover near the end of this century may be similar to mild winters described here. Such a change in the ice cover regime would impact the lake aquatic system and the regional economy.

Keywords: lake ice, Great Lakes, cryosphere, climate, physical Limnology

The effects of isostatic rebound and lake level on Lake Superior revealed through GIS: visualizing landscape evolution

Kevin P. Norton

School of Science, Penn State Erie – The Behrend College, Erie, Pennsylvania 16563

*Corresponding author: k.norton@mineralogie.uni-hannover.de

Paleolandscape reconstructions are an important step in understanding the climate and environment of the Holocene. The paleotopography for the Lake Superior basin was generated at 500 year intervals from 9500 yrs BP to the present. Two functions, a polynomial and an exponential, were used to model glacioisostatic uplift across the basin. A Geographic Information System (GIS) was used to remove the effects of isostatic rebound and fluctuating lake level. A single step method was used in which an iteratively weighted isobase surface was subtracted from the modern topography to create paleo-elevation datasets. The depth, surface area, volume, and shoreline locations of the lakes were calculated from the paleotopography. These data paint a picture of a rapidly changing post-glacial landscape that has become more subdued in the recent past.

Keywords: Holocene Epoch, paleotopography, glacioisostatic rebound

Nutrient Cycling in Lake Superior: A Retrospective and Update

N.R. Urban

Dept. Civil & Environmental Engineering Michigan Technological University Houghton, MI 49931

*Corresponding author: nurban@mtu.edu

Lake Superior, because of its large size and remote location, is perceived to be pristine and not susceptible to rapid changes. Nevertheless, Lake Superior has experienced large changes in concentrations of both nitrogen and phosphorus. Since the 1950s, concentrations of total phosphorus have declined nearly fourfold. This decrease in phosphorus concentrations is contemporaneous with the amelioration of cultural eutrophication in the lower Great Lakes, and it is probably a response to measures implemented on all of the Laurentian Great Lakes to reduce phosphorus inputs. Large seasonal swings in inventories of total phosphorus in the lake point to large fluxes associated with resuspension. However, much of the phosphorus resuspended into the lake in fall storms is not captured by the biota but sinks out of the lake prior to spring. Phosphorus entrained into the biological cycle is efficiently recycled into the lake and requires several years to be removed.

Nitrogen concentrations increased fourfold in the lake between 1900 and 1980 in response to emissions of NOx and subsequent acid deposition in North America. It is documented here for the first time that the historical increase in nitrate concentrations in the lake ended about 1980. The rapid response of nitrate concentrations in the lake to changes in atmospheric loading, points to a larger biological pump for nitrogen than previously recognized. Previous models of nitrogen cycling in the lake underestimated nitrogen burial by a factor of five. The magnitude of annual nitrate depletion in the lake suggests that primary production has been underestimated.

Keywords: phosphorous, nitrogen, historical trends

Carbon Cycling in Lake Superior: A Regional and Ecosystem Perspective

N.R. Urban

Dept. Civil & Environmental Engineering Michigan Technological University Houghton, MI 49931

*Corresponding author: nurban@mtu.edu

Carbon budgets are useful for tracing material and energy flows through ecosystems, for understanding linkages between adjacent systems, and for understanding trophic interactions. This paper highlights the dearth of data for Lake Superior, key gaps in data, and interesting hypotheses suggested by existing data. This paper does not address all aspects of carbon cycling but focuses on three questions: 1) What are the relative importance of the benthic and pelagic food webs? 2) What are the sources and pathways of carbon flow in near- and offshore areas of the lake? And 3) What is the regional significance of the CO2 flux across the lake surface? To answer these questions, the literature on production and biomass of each trophic level is briefly summarized, extant data on stable isotope ratios (d13C, d15N) in food web compartments are compiled, measurements by the U.S. EPA relating to pCO2 in the lake are utilized to estimate gas emissions, and CO2 measurements from a tall tower are examined to evaluate the regional effect of the lake. Existing data do not provide final answers to the questions above, but are adequate to pose the following hypotheses. The data suggest that only about 15% of net primary production is funneled into the benthic food web. The microbial loop reduces fish production in the lake by shunting carbon through longer food chains. Two distinct food webs are discernible with reported stable isotope ratios; additional measurements will be needed to determine the contribution of temporal and spatial variability to the observed patterns. The putative nearshore food web is more enriched in 13C, but existing data suggest that benthic algae are not the source of the heavy carbon. The carbon source for the putative offshore food web is not as clear, but it may be autotrophs living in the deep chlorophyll maximum or intermediate nepheloid layer (INL). Organic carbon in the benthic nepheloid layer (BNL) appears to be derived from the INL in offshore waters. Seasonal measurements indicate that the lake is highly supersaturated with respect to atmospheric CO2 in spring and less supersaturated in summer. Emissions from the lake cause elevated CO2 concentrations in a broad region, and may be a significant component of the regional carbon budget.

Keywords: foodweb, stable isotopes, CO2 emissions

Lake Superior Mining and the Proposed Mercury Zero-discharge Region

W. Charles Kerfoot1*, Jaebong Jeong2, John A. Robbins3

1Lake Superior Ecosystem Research Center, Department of Biological Sciences and

2Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, Michigan 49931

3NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105

*Corresponding author: wkerfoot@mtu.edu

Metal mining around Lake Superior has been extensive, concentrating on greenstone belts and a continental rift system. The amounts of ore processed (iron, copper, zinc, gold, and silver; more recently palladium, platinum, and nickel) are large, and yet long-term environmental impacts are poorly researched, especially regarding establishment of a Zero-discharge Region for mercury. Mining signatures are found in many places, ranging from Silver Bay (taconite tailings) to Sault Ste. Marie (copper, iron, zinc). We include a brief historical review of mining and then examine a particular example, copper mining on the Keweenaw Peninsula, where the EPA has adopted remediation strategies and yet faces long-term problems with shoreline tailing migration. Around the turn-of-the 20th-century (1855-1968), copper stamp mills sluiced 360 million metric tonnes (Mt) of copper-rich tailings into rivers and waterways, including 64 Mt directly into Lake Superior. The amount of copper released was massive, 4-10X greater than the existing copper inventory found down to 20 cm depth in Lake Superior sediments. Whereas Superfund activities have concentrated on remediation of stamp sands in low-energy interior sites, coastal piles have spread kilometers along high-energy shorelines. The coastal discharges have created a major copper “halo” around the Peninsula, producing a copper maximum, now buried, in sediments. Copper from the pulse appears to have spread out into Lake Superior via sediment focusing and sediment-water interactions. During investigations, we uncovered a high correlation between copper and mercury, related to parent ore composition. Mercury occurs in many regional metal (copper, silver, gold) ores and in accessory minerals (e.g. zinc mineral sphalerite). Anthropogenic mining inputs and erosion of natural ore deposits contribute to the 5-8 fold greater copper and mercury inventories in Lake Superior sediments beyond regional atmospheric deposition. The association of mercury with mining also poses a dilemma, as voluntary reporting is simply not working.

Keywords: Keweenaw Peninsula, anthropogenic, probable effect levels, tailings, surveys

Nutrient variability in Lake Superior coastal wetlands: the role of land use and hydrology.

John A. Morrice*, Anett S. Trebitz, John R. Kelly, Anne M. Cotter, and Mike L. Knuth

U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division 6201 Congdon Blvd., Duluth, Minnesota 55804

*Corresponding author: morrice.john@epamail.epa.gov

As part of a continuing study of linkages between hydrology, biogeochemistry and biota in Lake Superior’s coastal wetlands, we conducted samplings to identify factors that influence concentrations and spatial variability of nutrients within and among wetlands. We evaluated spatial and temporal variability in nutrient concentrations in relation to hydrology (tributary discharge, seiche strengths and the balance between these), nutrient retention and transformation (as differences in concentrations between main and off-channel zones), and landscape scale measures of anthropogenic activity for a set of coastal wetlands on Lake Superior’s Wisconsin shore. Differences in mean nutrient concentrations among coastal wetlands were significantly related to differences in land use. Variability in nutrient concentrations within wetlands was related to the hydrologic interaction between watershed (tributary discharge) and lake (seiche inputs). Retention of dissolved inorganic nitrogen was higher in backwater zones than along major flow paths, suggesting that internal cycling further contributed to spatial variability in nutrients.

Keywords: hydrologic interactions, seiche, nitrogen, phosphorus

Modeling contaminant behavior in Lake Superior: A comparison of PCBs, PBDEs, and mercury

M.D. Rowe, J.A. Perlinger*, and N.R. Urban

Department of Civil and Environmental Engineering Michigan Technological University,1400 Townsend Dr., Houghton, MI 49931

*Corresponding author: jperl@mtu.edu

A mass-balance model for Lake Superior was applied to polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and mercury to determine the major routes of entry and the major mechanisms of loss from this ecosystem as well as the time required for each contaminant class to approach steady state. A two-box model (water column, surface sediments) incorporating seasonally adjusted environmental parameters was used. Both numerical (forward Euler) and analytical solutions were employed and compared. For validation, the model was compared with current and historical concentrations and fluxes in the lake and sediments. Results for PCBs were similar to prior work showing that air-water exchange is the most rapid input and loss process. The model indicates that mercury behaves similarly to a moderately-chlorinated PCB, with air-water exchange being a relatively rapid input and loss process. Modeled accumulation fluxes of PBDEs in sediments agreed with measured values reported in the literature. Wet deposition rates were about three times greater than dry particulate deposition rates for PBDEs. Gas deposition was an important process for tri- and tetra-BDEs (BDEs 28 and 47), but not for higher-brominated BDEs. Sediment burial was the dominant loss mechanism for most of the PBDE congeners while volatilization was still significant for tri- and tetra-BDEs. Because volatilization is a relatively rapid loss process for both mercury and the most abundant PCBs (tri- through penta-), the model predicts that similar times (from 2 – 10 yr) are required for the compounds to approach steady state in the lake. The model predicts that if inputs of Hg(II) to the lake decrease in the future then concentrations of mercury in the lake will decrease at a rate similar to the historical decline in PCB concentrations following the ban on production and most uses in the U.S. In contrast, PBDEs are likely to respond more slowly if atmospheric concentrations are reduced in the future because loss by volatilization is a much slower process for PBDEs, leading to lesser overall loss rates for PBDEs in comparison to PCBs and mercury. Uncertainties in the chemical degradation rates and partitioning constants of PBDEs are the largest source of uncertainty in the modeled times to steady-state for this class of chemicals. The modeled organic PBT loading rates are sensitive to uncertainties in scavenging efficiencies by rain and snow, dry deposition velocity, watershed runoff concentrations, and uncertainties in air-water exchange such as the effect of atmospheric stability.

Keywords: persistent bioaccumulative toxicant, PBT, Hg, mass balance, model

Food web dynamics:

The base of the food web at the top of the Great Lakes: structure and function of the microbial food web of Lake Superior

M. Munawar1*, I.F. Munawar2, M. Fitzpatrick1, H. Niblock1, J. Lorimer1

1Fisheries & Oceans Canada, 867 Lakeshore Road, Burlington, Ontario, Canada, L7R 4A6

2Plankton Canada, Burlington, Ontario, Canada

*Corresponding author: mohi.munawar@dfo-mpo.gc.ca

We undertook a comprehensive analysis of the microbial food web of Lake Superior, including bacteria, autotrophic picoplankton, phytoplankton, heterotrophic nanoflagellates and ciliates, during the spring and summer of 2001. Total microbial loop biomass increased from 215 mg m-3 (spring) to 320 mg m-3 (summer). Bacteria did not show any change from spring to summer, while autotrophic picoplankton, heterotrophic nanoflagellates and ciliates all showed small but significant increases. Phytoplankton biomass did not change significantly from spring (˜950 mg m-3) to summer (˜1070 mg m-3). The composition of the phytoplankton community did change, however, with an increase in the biomass and relative composition of Diatomeae observed during summer. This was supported by a rise in net plankton (> 20 µm) biomass. Primary productivity was extremely low in both seasons (< 1 mg C m-3 h-1) but greatly exceeded bacterial productivity (< 0.02 mg C m-3). The microbial food web, when expressed as organic carbon, was overwhelmingly autotrophic (˜ 90%) in spring and summer. Carbon turnover rates (or P/B) were highest for picoplankton in both seasons (˜ 0.5 d-1) and dominated by a single species, Chroococcus dispersus var. minor. Carbon turnover rates of heterotrophic bacteria (0.06 d-1) were higher in the summer than autotrophic net plankton (0.05 d-1) and nanoplankton (0.04 d-1) but were still an order of magnitude less than picoplankton. Our 2001 survey of Lake Superior demonstrated that Lake Superior remains a cold stenothermic and ultra-oligotrophic ecosystem. While we observed that energy transfer was predominantly autotrophic, the significance and importance of heterotrophs in the physiological ecology of oligotrophic lakes deserves more attention. Research should be focussed on exploring sources of energy (autochthonous vs. allocthonous) and ultimately the linkages between lower and higher trophic levels.

Keywords: organic carbon, lower trophic levels, autochthonous carbon, community respiration

Phytoplankton communities of Lake Superior, 2001: Changing species composition and biodiversity of a pristine ecosystem

I.F. Munawar1, M. Munawar2*

1Plankton Canada, Burlington, ON, Canada L7L 2L8

2Fisheries and Oceans Canada, Canada Centre for Inland Waters, 867 Lakeshore Road, Burlington, ON, Canada L7R 4A6

*Corresponding author: mohi.munawar@dfo-mpo.gc.ca

Spring and summer surveys of Lake Superior were conducted by Fisheries and Oceans Canada and Environment Canada aboard the research vessel CCGS Limnos. During 2001, the mean concentration of phytoplankton biomass was low in the spring (0.9 g m-3) and summer (1.0 g m-3) seasons. Spring was dominated by Diatomeae, Chrysophyceae, Chlorophyta and Dinophyceae. The phytoflagellates together contributed significantly in both seasons. Diatomeae were more prevalent in the summer compared to the spring. Very high species diversity across the lake was observed in both seasons. Most of the species identified were rare individually contributing less than 1% of the total biomass but collectively contributed 23 to 26% in spring and summer. Similarly, less common species (≥1 and <5% of total biomass) comprised 50-54%. Only a limited number of species belonged to the common category (≥ 5% of total biomass). The species composition and high biodiversity reflect a characteristic ultra-oligotrophic environment. The size composition of the phytoplankton in both seasons showed an overall dominance of nanoplankton. The size fractionated primary productivity also support nanoplankton dominance with high rates of production comprising a mixture of phytoflagellates and diatoms. Minute picoplankton, though contributing little to the total biomass, was found to possess high rates of photosynthesis (31 – 55% of the total primary productivity) resulting in high P/B quotients. The picoplankton fraction was composed mainly of Chroococcus dispersus var. minor. A comparison of ecosystemic changes in Lake Superior between the summers of 1973, 1983 and 2001 was carried out at comparable stations. Surface temperature showed a dramatic rise of 5oC during the period of 1973 to 1983. The comparison further indicated that phytoplankton and its community structure changed considerably from 1973 to 2001 with a ten-fold increase in the mean biomass. The average size of algae increased from 9.9 µm in 1973 to 13.6 µm in 2001. The experimental data also shows important alterations in the physiological ecology of Lake Superior phytoplankton. Primary productivity in 2001 was ½ of its rate in 1973 with a corresponding decline in net and nanoplankton production rates. Cumulatively, P/B quotients showed a severe drop from 25.7 in 1973 to 1.2 in 2001. This is supported by an alarming drop in chlorophyll a to biomass ratios which are considered to be a barometer of algal health suggesting that the phytoplankton community is under stress. The structural and functional results indicate that Lake Superior phytoplankton reflect pristine oligotrophic conditions, in which the lower trophic levels are undergoing extensive changes. It is suggested that these alterations may be related to climate change and the observed warming of the lake from 13 – 18oC.

Keywords: oligotrophic, water quality, algae, nutrients, primary productivity, climate change, taxonomy

Metacommunity Perspective On Zooplanktonic Communities In Lake Superior

W. Charles Kerfoot1*, Judith W. Budd1, James H. Churchill2 and Changsheng Chen3

1Lake Superior Ecosystem Research Center, Michigan Technological University, Houghton, Michigan 49931

2Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543

3School of Marine Science and Technology, University of Massachusetts- Dartmouth, New Bedford, Massachusetts 02742

*Corresponding author: wkerfoot@mtu.edu

Because so many species enter and leave coastal planktonic communities, there is debate about biodiversity and the intensity of biotic (predator-prey, competitive) interactions. Lake Superior is characterized by one of the most diverse zooplankton communities, with species falling into three broad categories (embay¬ment, coastal, and open-water). To what degree is diversity a reflection of spatial and temporal scale? Here we advocate application of a new perspective (metacommunity) to examine if embayment and coastal zooplankton communities conform to an exchange-dispersal structure. Both assemblages (embayment and coastal) are seasonal warm-water communities that recruit largely from overwintering eggs or stages. Because of the restricted spatial distribution of viable resting eggs and “egg banks”, we postulate that embayment communities contribute species to developing coastal assemblages, as water is periodically pumped out of openings and long-shore currents disperse individuals from these multiple sources around the coastal zone. Circumnavigation is risky, interrupted by eddies and offshore excursions, potentially iso¬lating populations in different embayments along an irregular coastal zone.

Modeling and experimental paleoecological approaches offer opportunities to test the metacommunity concept. Linked embayment-coastal zone models offer insight into mechanisms of dispersal of endoge¬nous and introduced species. Diapausing eggs can be retrieved from embayment sediment cores to docu¬ment species colonization, extinction, and turn-over rates. Embayment sediments can be dated by a combination of radioisotope (137Cs and 210Pb) techniques and varves, and the timing and successional responses to perturbations (deforestation, mining, eutrophication) quantified. Moreover, diapause eggs can be hatched from different sediment levels for genetic characterization (allozyme electrophoresis, mDNA 12S/16S, microsatellite sequences) and “common garden” experiments. Preliminary studies docu¬ment active species exchange between coastal waters and embayments.

Keywords: plankton, spatial-temporal scales, embayments, dispersal, egg bank, currents

Trends in Spring Crustacean Zooplankton Communities of Lake Superior: Evidence of Planktivory by Lake Herring

Owen T. Gorman*, Lori M. Evrard, Michael H. Hoff, and James H. Selgeby

U.S. Geological Survey, Lake Superior Biological Station, 2800 Lake Shore Drive East, Ashland, WI 54806

*Corresponding author: owen_gorman@usgs.gov

Spring (early May to mid-June) crustacean zooplankton communities were monitored over a 12-year period (1989-2000) across four ecoregions of Lake Superior. Composition, density, areal biomass and mean zooplankter size varied across ecoregions. Of 12 species of zooplankton that were identified, three copepods comprised ~98% of the community: the calanoids Diaptomus sicilis and Limnocalanus macrurus, and the cyclopoid Diacyclops thomasi (listed in order of importance). On average, the largest zooplankton and greatest density and areal biomass were found in the eastern ecoregions, Keweenaw Bay and Whitefish Bay and were intermediate in the western ecoregion, Minnesota North Shore. The zooplankton community in the western Apostle Islands was the most divergent; on average, zooplankton density, areal biomass, mean zooplankter size, and the proportion of larger calanoid copepods were lower than in other ecoregions. Consistent with predictions of the top-down effect of size-selective planktivory, we found that spatial and temporal patterns of zooplankton biomass and mean size were related to temporal and spatial variation in the biomass of the principal planktivore, lake herring (Coregonus artedi). During 1988-1990, large cohorts of lake herring were produced across Lake Superior and the maturation of these cohorts in the early 1990s coincided with subsequent declines in density, areal biomass, and mean size of the calanoid copepods, particularly the larger L. macrurus. The appearance of a moderate 1998 year class of lake herring only in western Lake Superior was correlated with sharply different zooplankton community structures in eastern vs. western ecoregions. Under conditions of low lake herring abundance, zooplankton biomass increased in the eastern ecoregions largely as a result of increased density and mean size of the larger calanoid, L. macrurus. The build-up of zooplankton biomass observed in the eastern Lake Superior in the late 1990s suggests that the relatively small resident lake herring populations were not food-limited in this portion of the Lake, but their principal predator, lake trout may be food limited. A greater understanding of zooplankton productivity and the trophic links between zooplankton, lake herring and lake trout will help managers determine the size of lake trout populations that can be sustained over the long term in Lake Superior.

Keywords: population trends, trophic, predation, recruitment, calanoid, cyclopoid, copepod, bloater, rainbow smelt, lake trout

Spatial patterns of water quality and plankton from high-resolution continuous in situ sensing along a 537-km nearshore transect of western Lake Superior, 2004

Peder M. Yurista* and John R. Kelly

Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U. S. Environmental Protection Agency, 6201 Congdon Boulevard, Duluth, Minnesota 55804 USA

*Corresponding author: yurista.peder@epa.gov

We conducted an extensive survey of the nearshore waters in western Lake Superior along a continuous segment (537 km) from Grand Marais, Minnesota to near Eagle Harbor, Michigan on the Keweenaw Peninsula. A depth contour of 20 m was targeted using a towed CTD, fluorometer, transmissometer, and laser optical plankton counter (LOPC) to gather data on temperature, conductivity, fluorescence, light transmittance, and zooplankton size and abundance. The continuous electronic data stream provided a high resolution image of spatial variability both vertically and horizontally for each parameter. We describe the character of local, regional, and complete transect with goals of revealing spatial patterns not easily detected by other technologies, and briefly compare patterns to published historical trends. Preliminary relationships are presented among water quality and plankton measures. Regional patterns within the lake were related to gradients in landscape character along this stretch of coastline. Strong correlations to landscape characteristics provide suggestions that nearshore water quality may reflect the quality and nature of adjacent watersheds. We have demonstrated that the adaptation of electronic instrumentation and towed survey strategies are effective in providing rapidly collected and spatially extensive data for nearshore assessment of the Great Lakes.

Status of benthic macroinvertebrates in southern nearshore Lake Superior, 1994-2003

J. Scharold1*, S. J. Lozano2, T.D. Corry1

1U.S. Environmental Protection Agency, Mid-continent Ecology Division, 6201 Congdon Blvd., Duluth, MN, 55804, USA

2National Oceanic and Atmospheric Agency, Great Lakes Enviromental Reserarch Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI, 48105, USA

*Corresponding author: scharold.jill@epamail.epa.gov

Recent changes to benthic communities in the lower Laurentian Great Lakes raise concerns about the status of benthic macroinvertebrates in Lake Superior. This lakewide study was conducted to ascertain their status in nearshore waters of Lake Superior. Benthic macroinvertebrates were collected from 27 sites representing the U.S. nearshore waters (20 to 110 m) of Lake Superior in 1994, 2000, and 2003. No significant differences in total benthic macroinvertebrate abundance, or abundances of oligochaetes, clams, or chironomids were detected among years. Abundance of the amphipod Diporeia was lower in 2000 than in 1994 or 2003. The oligochaete trophic index, a measure based on tolerance of oligochaete species to organic enrichment, did not differ between years. Diporeia exhibited a bimodal depth distribution, with peaks in abundance at depths of 30 to 40 m and 60 to 70 m. Oligochaetes were most abundant at 50 to 60 m depth, clams between 30 and 70 m, and chironomids at less than 30 m. The spatial and temporal variability observed in Lake Superior’s benthic macroinvertebrate communities has implications for environmental assessment.

Keywords: Diporeia, Oligochaeta, Chironomidae, Sphaeriidae, abundance, depth distribution

Changes in the Lake Superior fish community during 1978-2003: Chronicling the recovery of a native fauna

Owen T. Gorman* and Michael H. Hoff

U. S. Geological Survey, Lake Superior Biological Station, 2800 Lake Shore Drive East Ashland, Wisconsin 54806

*Corresponding author: owen_gorman@usgs.gov

Status and trends of the fish community of the inshore waters of Lake Superior (<80 m depth, <5 km from shore) were monitored through annual bottom trawl surveys conducted around the perimeter of the Lake during 1978-2003 in U.S. waters and 1989-2003 in Canadian waters. Of 35 species captured over the 26-year period, 17 were commonly caught and represented 99.4% of the total community biomass. Four prey species, lake herring (Coregonus artedi), bloater (Coregonus hoyi), lake whitefish (Coregonus clupeaformis), and rainbow smelt (Osmerus mordax), represented 76.3% of the total community biomass. At the start of the monitoring period, biomass and commercial yields of the exotic rainbow smelt were at historic highs while biomass and commercial yields of native lake trout (Salvelinus namaycush), lake whitefish and lake herring were at historic lows because of decades of overharvest and depredation by the exotic sea lamprey (Petromyzon marinus). In an effort to reverse the declines in native fish stocks, management agencies implemented lamprey control programs, lake trout stocking programs, and closed or restricted commercial trout fisheries in the 1960s and 1970s. The structure of the Lake Superior fish community changed considerably over the 26-year monitoring period. During the first phase (1978-1979), the inshore fish community was dominated by non-native species: rainbow smelt was the principal prey fish and accounted for ~50% of the total community biomass, and planted hatchery strains of lake trout were the principal predator and accounted for ~10% of total community biomass. The second phase (1980-1983) was marked by a transition in community structure: biomass of rainbow smelt populations declined sharply while wild lake trout populations rebounded and small, but successful new cohorts of lake herring began to emerge. The appearance of the large 1984 lake herring year-class and a rapid increase in wild lake trout biomass signaled the beginning of the third phase of the Lake Superior fish community. During 1984-1996, recovery of the native fish community became evident; biomass of lake herring, bloater, lake whitefish, and wild lake trout (lean and siscowet) increased while biomass of rainbow smelt increased over levels observed during the transition period, but remained well below their 1978-1979 level. After 1996, the fish community entered the final phase in which biomass of the principal prey species, lake herring, and wild lake trout gradually declined, and by 2003 approached the low levels observed in 1980-1983. Primary factors that affected the structure and dynamics of Lake Superior fish communities since 1978 included recovery of wild lake trout and lake herring populations and the decline in dominance of rainbow smelt populations. Rapid shifts in community structure were linked to recruitment of large year classes of lake herring and a sharp increase in mortality of rainbow smelt. Changes in the structure of the Lake Superior fish community are likely to continue in the future as lake trout populations continue to evolve in response to new conditions, and fishery managers implement new strategies to continue the restoration of prey fish populations.

Keywords: lake herring, bloater, lake whitefish, lake trout, rainbow smelt, prey fish, population trends, monitoring

Western Lake Superior benthic fish community structure during the summers of 1972-1995

Michael H. Hoff

U. S. Geological Survey, Great Lakes Science Center, Lake Superior Biological Station, 2800 Lake Shore Drive East, Ashland, Wisconsin 54806.

*Corresponding author: michael_hoff@fws.gov

Lake Superior benthic fish community structure was studied during the summers of 1972-1995 by analysis of samples collected in bottom trawls. Nine hundred twenty-eight trawl tows at 21 stations collected 395,077 fish from 26 taxa. Redundancy analysis showed that fish community structure was not well explained by depth and temperature gradients, because they explained only 10% of fish community structure. Instead, discriminant analysis correctly classified 80% of the trawl tows to three depth zones that were revealed using principal components analysis. Some taxa were rarely collected, and densities of 10 taxa explained most of the data variation. Multivariate analysis of variance of those 10 taxa densities across depths showed that three significantly different assemblages existed; one inhabited shallow water (5.0-39.9 m), one inhabited intermediate depths (40.0-79.9 m), and one inhabited the deepest depths sampled (80.0-141.0 m). Analysis of variance showed that rainbow smelt (Osmerus mordax) and trout-perch (Percopsis omiscomaycus) densities were highest in the shallowest zone, whereas lake whitefish (Coregonus clupeaformis) density was highest in the intermediate zone, ninespine stickleback (Pungitius pungitius) and slimy sculpin (Cottus cognatus) densities were highest in the shallow and intermediate zones, siscowet lake trout (Salvelinus namaycush siscowet), bloater (Coregonus hoyi), kiyi (Coregonus kiyi), and deepwater sculpin (Myoxocephalus thompsoni) densities were highest in the deepest zone, and spoonhead sculpin (Cottus ricei) densities were similar across zones. Management objectives can be developed for each assemblage and each of the 10 most structurally important taxa. Understanding the existence and structure of each assemblage will aid in the scientific management of them, the taxa that compose them, and their habitats. Information on assemblage existence and structure will be useful for assessing changes in those assemblages that result from management actions and changes in the lake and its habitats.

Keywords: assemblages, habitats, bathymetry, ecosystem management

Community structure and trends in abundance of breeding birds in the Apostle Islands National Lakeshore, Wisconsin

Michael H. Hoff1* and Julie Van Stappen2

1U. S. Geological Survey, Great Lakes Science Center, Lake Superior Biological Station, 2800 Lake Shore Drive East, Ashland, Wisconsin, USA

2National Park Service, Apostle Islands National Lakeshore, Bayfield, Wisconsin, USA *Present address: U.S. Fish and Wildlife Service, Bishop Henry Whipple Federal Building,1 Federal Drive, Ft. Snelling, Minnesota, USA

*Corresponding author: michael_hoff@fws.gov

We analyzed breeding bird community structure in the Apostle Islands National Lakeshore, Wisconsin, from data collected at 106 points during 1995-1997. We also analyzed the trends in abundance during 1991-2000. Eighty-four species were identified by sight or sound, but we found that relative abundances for 9 species described most of the community structure variability. Abundance data for the 9 species showed that 3 significantly different assemblages existed in the Lakeshore. One assemblage (herein termed conifer-dominant forest) was found in a mixture of habitats, including old-growth (virgin) coniferous forest, coniferous forest, northern hardwood-hemlock (Tsuga canadensis) forest, and northern hardwood-mixed forests. A second assemblage was found mostly in northern hardwood-sugar maple (Acer saccharum) forest stands, and the third assemblage was found in pine savanna, sandscape, and shrub areas. The pine savanna-sandscape-shrub assemblage differed greatly from the other 2, and abundances of black-throated green warbler (Dendroica virens), common yellowthroat (Geothlypis trichas), red-winged blackbird (Agelaius phoeniceus), song sparrow (Melospiza melodia), yellow warbler (Dendroica petechia), ovenbird (Seirus aurocapillus), and red-eyed vireo (Vireo olivaceus) caused much of that difference. Differences in abundances of American redstart (Setophaga ruticilla), Nashville warbler (Vermivora ruficapilla), ovenbird, and red-eyed vireo caused much of the separation between the conifer-dominant forest assemblage and the northern hardwood-sugar maple assemblage. The black-and-white warbler, mourning warbler, Swainson’s thrush, veery, and Nashville warbler declined during the study period in both the Apostle Islands and United States. Black-and-white warbler, Swainson’s thrush, and Nashville warbler were found in greatest abundances in the old-growth, conifer-dominant habitat. That habitat is rare in the Lake Superior basin, so we recommend conserving it to conserve black-and-white warbler, Swainson’s thrush, Nashville warbler, and other species for future generations in the Apostle Islands, Lake Superior Basin, and United States.

Keywords: assemblages, conservation, species, habitats, vegetation

Colonial nesting waterbirds in the Canadian and U.S. waters of Lake Superior: patterns in colony distribution and breeding population numbers (1976-2000)

Ralph D. Morris1*, D.V. Chip Weseloh2 and Cynthia Pekarik3

118 Timmsdale Crescent, Fonthill, ON, L0S 1E5

2Canadian Wildlife Service, Ontario Region, 4905 Dufferin St. Downsview, Ontario M3H 5T4

3Canadian Wildlife Service, Canada Centre for Inland Waters, 867 Lakeshore Road, Burlington, Ontario L7R 4A6

*Corresponding author: rmorris@brocku.ca

Personnel of Canadian and United States wildlife agencies completed three major surveys (1976-1980; 1989-1991; 1997-2000) to census colonially nesting waterbirds breeding on the North American Great Lakes. We here summarize and comment on the numerical and distributional patterns of the five species breeding on Lake Superior during these census periods: Double-crested Cormorants (Phalacrocorax auritus), Great Blue Herons (Ardea herodias), Ring-billed Gulls (Larus delawarensis), Herring Gulls (Larus argentatus) and Common Terns (Sterna hirundo). There were orders of magnitude differences among maximum numbers of nesting pairs in periods of their highest count (DCCO – 5,359 pairs in third census; GBHE – 1,016 pairs in second census; RBGU – 26,920 pairs in second census; HERG – 27,135 pairs in second census; COTE – 944 pairs in third census). Numbers of Great Blue Herons and Herring Gulls increased between the first and second census, then decreased by the third census. Common Terns and Double-crested Cormorants increased in each census period, while Ring-billed Gulls increased between the first two periods then remained stable in the third. Numbers of all species increased from the first to the third census but with wide variation in the average annual rate of increase (from +0.7% for herons to 30.3% for cormorants). We identify major differences in the census and timing techniques used within and among years. We suggest that while these techniques underestimated the size of the actual breeding populations, the data can be taken as a valid index of trends in numbers of breeding pairs. The second census of Lake Superior was the only one coordinated and completed in one year (1989). We strongly recommend that future censuses of each Great Lake be coordinated between the two national agencies using standardized techniques, and be conducted by lake rather than by species.

Keywords: population trends, gulls, herons, cormorants, terns

Trophic linkages in the Lake Superior food web: A synthesis of empirical and modelling studies 1970-2003

Timothy B. Johnson

Aquatic Research and Development Section, Ontario Ministry of Natural Resources 320 Milo Road, Wheatley, Ontario, N0P 2P0 Canada

*Corresponding author: tim.johnson@mnr.gov.on.ca

Ecological studies describing the food web of Lake Superior are reviewed and synthesised from 1970 through 2003. Basic information on lower trophic levels (phytoplankton, zooplankton, and benthos) is much weaker than knowledge of economically important fishes. Extensive spatial and temporal (multi-year and seasonal) databases exist for diets and growth of dominant prey and predatory fishes. Bioenergetic analyses commenced in the mid-1990s to link predator demand with prey supply from invertebrates (zooplankton and benthos) to small (forage) fishes to piscivores. All studies concluded data were collected with inadequate spatial (vertical and horizontal) and temporal intensity to fully address questions of system carrying capacity. Stable isotopes and contaminants have proven useful for identifying pathways of material transfer from atmospheric sources, tributaries and coastal wetlands through to offshore feeding relationships between predators and prey. Recent surveys have extended further offshore, providing valuable information on the biota, their behaviour and interrelationships. Whole lake hydroacoustic surveys and food web models have recently been developed on Lake Superior, providing managers and scientists alike with information needed to understand the structure and productive potential of this Great Lake as it responds to anthropogenic stresses associated with climate change, invasion by non-indigenous species, and development of its watershed.

Keywords: stable isotope, bioenergetics, model, diet, growth, contaminant

Fish Fauna of Lake Superior: Past, Present and Future

Nicholas E. Mandrak

Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada, 867 Lakeshore Road, Burlington, ON L7R 4A6
*Corresponding author: nicholas.mandrak@dfo-mpo.gc.ca

Lake Superior has the most depauperate fish fauna of all of the Great Lakes as a result of historical and environmental factors. Seventy-one native species, including three species endemic to the Great Lakes (Bloater, Kiyi, Shortjaw Cisco), and 15 non-native species are established in the Lake Superior basin. Historically, the fish fauna was exposed to threats related to overexploitation, habitat degradation and aquatic invasive species. Recently, habitat degradation and aquatic invasive species appear to be increasing threats, which may be exacerbated by climate change. In the future, non-native species will likely be added to the Lake Superior fish fauna through natural dispersal, and deliberate and accidental introduction through various pathways, and some of these species will likely become invasive. The successful establishment, spread and impact of these species will ultimately depend on the magnitude and extent of human-related vectors (e.g. ballast water, bait fish), dispersal capability, propagule pressure, extent of climate change and subsequent habitat change, and the nature of their interactions with species native to the lake.

Keywords: biodiversity, aquatic invasive species, introduced, species at risk, threats