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The deep chlorophyll maximum in Lake Superior

M.T. Auer¹, L.A. Bub¹, K.D. Elenbaas²

¹Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931; ²Blasland, Bouck & Lee, Engineers and Scientists, 6723 Towpath Rd., P.O. Box 66, DeWitt, NY 13214

One of the most fascinating features of the annual cycle of the plankton, the deep chlorophyll maximum (DCM) has been observed in a variety of fresh- and saltwater environments.  In Lake Superior, the DCM forms in July, consistent with the onset of vertical stratification and remains in place until destratification in late fall.  The DCM typically lies at the base of the metalimnion and exhibits chlorophyll concentrations 2-4 times those of the well-mixed surface layer.  Researchers studying the DCM at sites around the world have offered a wide variety of explanations for the phenomenon, including favorable conditions of light, temperature, and nutrients, variation in C:Chl ratios, reduced grazing pressure, and accumulation through sedimentation and have generally supported their positions with reasonable science.  Efforts to identify a common paradigm explaining the presence of the DCM fall generally into two camps: those who believe that the peak reflects conditions particularly suitable for phytoplankton growth and those who believe that the maximum simply reflects the accumulation of chlorophyll sedimented from the epilimnion.  Here we present the results of field measurements, laboratory experiments, and model calculations which follow these two lines of reasoning.   

Carbon flux and the distribution of Diporeia in Lake Superior

M. T. Auer¹, J. E. Kahn², N. A. Auer², N. R. Urban¹

¹Department of Civil & Environmental Engineering,; ²Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931 

The benthic macroinvertebrate Diporeia occurs in zones of concentration in Lake Superior.  While distributional structure relating to depths and/or sediment type has been reported from other Great Lakes, reasons for this association remain unclear.  A favored hypothesis relates zones of concentration and enhanced delivery of particulate organic matter, the food source for Diporeia.  Here we report on the distribution of Diporeia along three transects in Lake Superior extending offshore of Michigan’s Keweenaw Peninsula and examine sediment and water column conditions relating to food supply.  Bathymetric surveys, sediment particle size distributions, and rates of sediment and organic carbon deposition are utilized to infer variations in organic carbon flux along these transects.  Determinations of the organic carbon content of the sediment, the abundance and activity of sediment bacteria, and rates of sediment oxidation are applied in characterizing the quality of sediment along the transect as a food source.  Finally, the abundance of diatom frustules in the water column and in sediment are quantified as a measure of the availability and utilization of this food resource.  Finally, these observations are integrated with Diporeia  surveys to test the organism concentration - food delivery hypothesis.

Lake sturgeon in Lake Superior - status and rehabilitation

N. A. Auer¹, H. Quinlan²

¹Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931; ²U.S. Fish and Wildlife Service, Ashland Fishery Resource Office, 2800 Lakeshore Drive East, Ashland, WI 54806

The Great Lakes Fishery Commission Lake Superior Committee developed fish community objectives for the lake in 1990.  In an effort to reach those objectives agencies responsible for fisheries management agreed that several native species should be rehabilitated. To that end the Lake Superior Technical Committee formed the Lake Sturgeon Subcommittee in 1994. This subcommittee was composed of individuals from state, tribal, provincial and federal agencies and academic institutions from the U.S. and Canada. The charge to the subcommittee was to describe the current status of lake sturgeon stocks in Lake Superior and then to develop a basin wide plan for lake sturgeon rehabilitation. Information on current and historic status of this fish was complied in "Status of lake sturgeon in Lake Superior" in 1997 and the "Lake sturgeon rehabilitation plan for Lake Superior" was finalized in April 2002. This plan is the first of its kind for the Great lakes and will serve as a guiding document for habitat and fisheries management strategies for lake sturgeon.

Current status of offshore phytoplankton, zooplankton and benthos communities in Lake Superior

R. P. Barbiero¹, M. L. Tuchman²

¹Dyncorp S&S Inc., 1359 W. Elmdale Ave. #2, Chicago, IL 60660; ²U.S. Environmental Protection Agency, Great Lakes National Program Office, 77 W. Jackson Boulevard, Chicago, IL 60604

Long-term surveillance of bald eagles nesting along Lake Superior

W. W. Bowerman

Clemson University, Department of Environmental Toxicology, P. O. Box 709, Pendleton, SC 29670

The bald eagle (Haliaeetus leucocephalus) has been suggested as one of the best avian indicator species for monitoring the impact of environmental pollutants under the Great Lakes Water Quality Agreement. It and the peregrine falcon (Falco peregrinus) were the first predatory birds in North America that alerted us to the impacts of DDT on avian reproduction. Numbers of eagles along the shorelines and islands of Lake Superior declined during the 1950s and early 1960s, and total reproductive failure occurred in this population by 1970. Since the ban of DDT and many other organochlorine pesticides and PCBs in the early 1970s, the bald eagle population has rebounded. Concentrations of organochlorine pesticides and PCBs have declined in samples of unhatched eggs and blood plasma of nestlings. A program to monitor trends in concentrations of these compounds using blood plasma and mercury in feathers of nestling eagles has been initiated under the Clean Michigan Initiative and the Great Lakes Initiative. The sampling strategy and results of this program will be described.

Spatiotemporal distributions of phytoplankton standing crop and production in Lake Superior

L. A. Bub and M. T. Auer

Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

Physical processes, e.g. thermal fronts (horizontally) and stratification (vertically) are known to manifest themselves in nearshore-offshore differences and seasonal dynamics in phytoplankton standing crop and primary production.  In Lake Superior, as in other large lakes, a thermal bar develops in spring as shallow nearshore waters warm, potentially trapping nutrients and stimulating phytoplankton growth.  The thermal stratification process influences phytoplankton dynamics through changes in the mixed layer depth, i.e. the light available to support photosynthesis as algae circulate over the water column.  These phenomena were investigated by sampling along three transects (Ontonagon, Houghton, and Eagle Harbor) perpendicular to Michigan’s Keweenaw Peninsula in Lake Superior in 1999 and 2000.  The sampling period, May - October, bracketed the development and dissipation of the thermal bar and vertical thermal stratification.  Strong nearshore-offshore (high to low) gradients in phytoplankton biomass (chlorophyll) and production (¹⁴C uptake) were noted in spring.  No differences in dissolved phosphorus or C:P ratios, indicating favorable nearshore nutrient status, were observed.  Spring gradients are largely resolved in summer, resulting in horizontally homogenous conditions when the lake is thermally stratified.  This and other evidence suggests temperature, and especially mixing depth, are the forces driving spatiotemporal distributions of phytoplankton in Lake Superior.

Remote sensing of biological and physical variability in Lake Superior

J. W. Budd¹, S. A. Green², T. Yu1¹, H. Li¹

¹Department of Geological Engineering & Sciences; ²Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931 

The detection and measurement of temporal and spatial variability in biomass is important for studying large-scale coastal processes and dynamics including those controlling carbon cycling in the Great Lakes. There are a number of unknown factors, namely: (1) the unique sources of lake color variability in the Great Lakes; (2) the temporal and spatial variability of phytoplankton production; and (3) the effect of warmer temperatures on lower trophic food web dynamics.  Ocean color sensors, such as SeaWiFS, have a unique role in understanding these processes because of the potential for estimating bio-optical parameters and production.  The importance of this role depends on the ability of the sensors and algorithms to accurately discern and measure chlorophyll a concentrations, under varying optical conditions.  The launch of SeaWiFS in 1997 resulted in the first ever daily [chl] estimates of the Great Lakes.  In Lake Superior, evaluation of nine marine bio-optical retrieval algorithms with in situ data indicates the satellite-based chlorophyll concentrations are overestimated by as much as 45:1.  Here, we present the initial results of a new bio-optical retrieval algorithm for Lake Superior based on empirical and semi-analytical approaches.  Satellite imagery are used to investigate large scale events and transport processes in the coastal regions of Lake Superior.  Seasonal and interannual time series provide new insights about particle transport phenomena and productivity pulses along the southern shore of Lake Superior. 

The Lake Superior binational program

J. Cantrill

Department of Communication and Performance Studies, Northern Michigan University, 1401 Presque Isle Avenue, Marquette, MI 49855

In 1991, under the auspices of the International Joint Commission and the 1987 Great Lakes Water Quality Agreement, the governments of Canada and the United States created the Lake Superior Binational Program.  The twofold intent of this multi-agency, multi-jurisdictional initiative is to promote the "zero discharge" of several bioaccumulative toxic substances and to promote a broader program to restore and protect the Lake Superior basin.  The combined efforts of several agencies, nongovernmental organizations, and private citizens has resulted in the completion of a comprehensive Lakewide Management Plan (LaMP) in 2000.  This presentation will outline the components of the Binational Program, discuss work related to meeting program goals, and center on efforts to promote sustainable lifestyles in the Lake Superior watershed.

A watershed perspective on the dispersal of stocked brook trout between Lake Superior tributaries

A. J. Carlson, C. J. F. Huckins

Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton MI, 49931

Coasters are a large form of brook trout (Salvelinus fontinalis) which typically inhabit the tributaries and near shore regions of Lake Superior. Populations of coaster brook trout began to decline in the late 1800's likely due to intense fishing pressure, the widespread stocking of exotic salmonids, and loss of critical habitat. Since coaster stocks have been reduced to a few remnant populations they are currently a focus of native species restoration around Lake Superior. In 1999, The Michigan Department of Natural Resources initiated a 5-year program of stocking Nipigon strain brook trout in the Gratiot River on the Keweenaw Peninsula. The goal of this program was to reestablish viable coaster brook trout populations in this region. In 2001, we surveyed the fish communities and stream habitat in 24 streams around the Keweenaw Peninsula as part of an evaluation of this stocking effort. To compliment these data, we used GIS tools to analyze the quaternary geology, bedrock geology, land use / land cover, groundwater upwelling, and hydrologic characteristics for the watershed of each survey tributary. Watershed level characteristics shape many of the physical and ecological functions in these systems and may consequently influence the suitability of local habitat conditions for brook trout populations. The variation in the physical characteristics at the watershed level help to explain the dispersal of coaster brook trout around the Keweenaw Peninsula. This information should be helpful in guiding management decisions on future local and regional coaster brook trout restoration programs.

Dynamics of the Keweenaw Waterway: remote forcing, summertime convective overturning and local wind effects

J. H. Churchill¹, W. C. Kerfoot², M. T. Auer³, J. W. Budd⁴, E. A. Ralph⁵

¹Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; ²Lake Superior Ecosystem Research Center and Department of Biological Sciences, ³Department of Civil and Environmental Engineering; ⁴Department of Geological Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; ⁵Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55812

The Keweenaw Waterway is a deep-draft navigation passage that bisects Lake Superior's Keweenaw Peninsula. It includes a relatively large inland lake, Portage Lake, and supports numerous species of plankton and pelagic fish, including several that depend on a resting egg stage for reproduction. Over 1998-1999, temperature records were obtained from a number of locations within the Waterway. These have shown that exchange of water between Lake Superior and the Waterway is predominantly wind-driven, but involves two processes. One is direct acceleration of the surface current within the Waterway by the along-waterway component of the wind stress. The other is flow driven by surface elevation gradients at Waterway's entrances, and is essentially the result of along-shore wind stress forcing of Lake Superior coastal waters. The data have also revealed rapid thermal stratification of Portage Lake during late spring, followed by a series of convective overturning events during summertime periods of cold air passage. As shown by heat flux calculations, carried out using meteorological data from a nearby airport, these overturning events were the result of sensible and latent heat loss from the lake coupled with reduced solar heat input due to predominately cloudy conditions. Each event increased the temperature of water within the lake basin and thus reduced the vertical temperature gradient established with the resumption of stratification. Contrary to expectations, this process effectively made the Lake more susceptible to convective and wind-driven overturning as the summer progressed.

Transoceanic shipping patterns in Lake Superior: a hotspot without invaders

R. I. Colautti, I. A. Grigorovich, I. C. Duggan, H. J. MacIsaac

Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N8Y 1P7

Human-mediated introductions of non-indigenous species (NIS) into novel environments are having profound impacts on the economy and ecology of the Great Lakes. Shipping and related activities (primarily ballast exchange) have been implicated as the primary vector of introduction for 28 of 40 NIS that were discovered subsequent to the completion of the St. Lawrence Seaway in 1959. We reviewed the spatial and temporal patterns of transoceanic shipping traffic on the Great Lakes to infer areas of ballast release by ships declaring both 'ballast-on-board' (BOB ships) and 'no-ballast-on-board' (NOBOB ships). Regional sources of transoceanic shipping on the Great Lakes were generally consistent with sources of recent Great Lakes invaders. However, approximately 55 and 75% of BOB and NOBOB ships, respectively, released ballast in the Lake Superior basin. Given the 'propagule pressure' model of invasion, our analysis of ballast patterns suggest that Lake Superior should be an invasion hot-spot; a result largely inconsistent with the sites of first discovery of established NIS in the Great Lakes. We are exploring this discrepancy from two angles: 1) a field survey of Lake Superior biota to confirm this disparity, and 2) to better understand abiotic restraints on invasion, modeling the conditions for the survival of organisms during the stages of uptake, transport and release of ballast.

Small size class fish suffering the consequences for consuming Bythotrephes cederstroemi

J. A. Compton, W. C. Kerfoot

Lake Superior Ecosystem Research Center and Department of Biological Sciences, Department of Biological Sciences, 1400 Townsend Drive, Michigan Technological University, Houghton, MI 49931

Microbial-dissolved carbon dynamics in Lake Superior

J. B. Cotner, B.A. Biddanda

Department of Ecology, Evolution, and Behavior, 100 Ecology Building, 1987 Upper Buford Circle, St. Paul, MN 55108

Lake Superior is one of the Earth’s greatest freshwater resources and the biogeochemistry of this very large ecosystem is dominated by microbial metabolism and physical processes. We have demonstrated that as much as 90% of the total respiration in Lake Superior passes through Bacteria and Archaea in surface waters. Sunlight also plays an important role in the carbon and, likely phosphorus, biogeochemistry of Superior as well as other Laurentian Great Lakes. We exposed water from both lakes Superior and Michigan to natural sunlight and examined its effects on the bioavailability of carbon to bacterioplankton. Exposure of water collected from offshore surface layers to sunlight caused a net reduction in bioavailability (bacterial growth ~20-30% of dark control), whereas both exposure of deep water and river water to sunlight resulted in a net enhancement in bioavailability of dissolved organic matter (bacterial growth ~150-260% of dark control). Irradiated water from the nearshore exhibited an intermediate response in terms of changes in bioavailability (bacterial growth ~75-115% of dark control).  Thus, the net effect of photochemical alterations appeared to depend on spatial factors and this suggests that previous exposure to sunlight may play an important role in its bioavailability.

Sustainability science and the future of Lake Superior

J. C. Crittenden

Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931

The discipline of environmental science and engineering (ESE) has adopted new approaches, insights and techniques from the finer scales of cellular and molecular biology, chemistry and physics to address multimedia problems of regional and global impact and complexity.  Unfortunately, problem-solving efforts have been aimed primarily at evaluating the quantity of pollutants that could be discharged into the environment with acceptable impact.  There has been little or no focus on alternatives such as pollution prevention.  The domain of the ESE discipline has been calculation of the carrying capacity of the natural world with respect to these emissions.  ESEs have been led to assume that pollutant generation and release were a normal part of commerce.  With increased public pressure for greener products, processes and practices, industry has begun to consider a number of environmentally responsible manufacturing (ERM) initiatives.  These efforts have led to life cycle analyses (LCA), which provide a cradle-to-grave evaluation of environmental impacts including extraction of natural resources, manufacture, product use, and reuse, recycle or disposal.  Through industrial ecology, the concept has been expanded further to consider material and energy flows from multiple, often inter-related industries, and through local environments, regions, national economies and global trade.  While the union of industrial ecology and environmental impact and risk assessment has spawned new management, research and educational initiatives, there are further challenges to ensure that this approach has a broad and lasting impact.  Public education and associated social processes of knowledge diffusion have not been explicitly included in decision support tools. Active involvement of user groups and stakeholders in the decision making process is vital to successful implementation of sustainable goals, i.e. estimation of the triple bottom line: economic, social and environmental impacts that can form the basis for integrated decision support.  An example will be provided, illustrating the application of sustainability science in maintaining a quality environment in the Lake Superior basin.

Environmental forcing conditions mediating bacterioplankton populations in Lake Superior

K. D. Elenbaas¹ and M.T. Auer²

¹Blasland, Bouck & Lee, Engineers and Scientists, 6723 Towpath Rd., P.O. Box 66, DeWitt, NY 13214; ²Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

As part of the microbial loop, bacteria play a major role in the cycling of organic matter in aquatic ecosystems.  The distribution of bacterioplankton biomass and production, in time and in space, is mediated by temperature and the availability of a carbon source, with grazing additionally influencing biomass.  Bacterioplankton abundance (numbers) and production (thymidine incorporation) were surveyed over the May - October period of 1999 and 2000 in the waters of Lake Superior near Michigan’s Keweenaw Peninsula.  With a very few exceptions, nearshore-offshore gradients in bacterioplankton numbers were minimal.  This is consistent with the findings of others that, while bacterial abundance may vary with trophic status, spatiotemporal structure is often muted by grazing pressure.  Results were similar for nearshore-offshore differences in bacterioplankton production where increases observed system wide were not manifested in spatial gradients.  In contrast, marked temporal signals in bacterioplankton production (and to a lesser extent numbers) were observed.  Nearly order-of-magnitude increases in the rate of secondary production were observed in 1999 and 2000, closely tracking patterns in primary production.  These findings suggest that internal processes, i.e. the coupling between primary and secondary production are more significant in Lake Superior than external processes, i.e. stimulation of secondary production by carbon introduced through the spring runoff event.  The behavior of bacterioplankton populations in Lake Superior is consistent with their role in recycling byproducts of primary production within the food web.

Effects of planktivory by pelagic prey fishes on zooplankton in the Apostle Islands region of Lake Superior

O. T. Gorman, L. M. Evrard

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

Composition, abundance, and size of prey fishes and zooplankton were monitored over a 12-year period (1989-2000) in the Apostle Islands region of Lake Superior. Prey fishes were sampled each spring at 9 locations using a bottom trawl towed cross-contour from nearshore (depth ~15 m) toward offshore (depth ³ 60 m). Zooplankton were sampled by vertically towing a conical net from near bottom to surface at the deep end of each trawl sampling location. Both prey fish and zooplankton showed wide fluctuations in abundance and composition over the period of study. Density and size composition of the zooplankton community was inversely related to densities of planktivore fishes, particularly rainbow smelt (Osmerus mordax). As has been observed in other Great Lakes, our results indicate an important link between planktivore fishes and the zooplankton community. In the Apostle Islands region of Lake Superior, top-down control of planktivores by piscivores was not sufficient enough during our study to suppress strong top-down effects of planktivores on the zooplankton community.

Status and trends in the Lake Superior fish community, 1978-2001

O. T. Gorman¹, M. H. Hoff¹, K. Cullis²

¹U. S. Geological Survey, Lake Superior Biological Station, 2800 Lake Shore Drive East, Ashland, WI 54806; ²Ontario Department of Natural Resources, 435 James Street South, Thunder Bay, Ontario, P7C5G6

Status and trends in the Lake Superior fish community were monitored through annual bottom trawl surveys conducted around the perimeter of the Lake between 1978-2001 in U.S. waters and during 1989-2001 in Canadian waters. Principal species included in the analysis were lake trout, lake whitefish, lake herring, bloater, rainbow smelt, ninespine stickleback, trout perch, slimy sculpin, and burbot. The structure of the Lake Superior fish community changed considerably over the 24-year monitoring period. During the twenty years that preceded the monitoring period, densities of the principal prey species, lake herring and rainbow smelt, declined from historic levels and have oscillated about reduced levels since the beginning of the monitoring period. Populations of bloater have remained more stable but at much lower densities than lake herring. Prior to the monitoring period, abundance of lake trout was greatly reduced from overharvest and sea lamprey depredation. Recovery of wild lake trout (lean and siscowet) populations was evident in our trawl samples beginning in the mid-1980s. Like wild lake trout, lake whitefish densities were relatively low at the beginning of the monitoring period and began to increase in the mid-1980s, peaked in the mid-1990s and declined substantially over the past 5 years. Unlike trends for pelagic species, bottom fishes (nine-spine stickleback, trout perch, slimy sculpin, burbot) showed higher densities at the beginning of the monitoring period but subsequently showed substantial declines. The success of the sea lamprey control program was a major factor in the increase in lake trout and lake whitefish densities in the mid-1980s. The recovery of lake trout, the top predator in the Lake Superior fish community, may be a likely factor in the changes in some prey fish populations, most notably the bottom fishes. Changes in the structure of the Lake Superior fish community are likely to continue in the future as lake trout populations continue to recover and fishery managers implement new strategies to restore other fish populations.

The optical environment of Lake Superior

S. A. Green¹, A. Vodacek², X. Ma¹

¹Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; ²Center for Imaging Science, 54 Lomb Memorial Dr, Rochester Institute of Technology, Rochester, NY 14623

The optical environment of Lake Superior will be introduced based on data from three field seasons of the Keweenaw Interdisciplinary Transport Experiment in Superior (KITES).  Results include measurements of penetration of UV and visible light into the water column, indicating the depth of the photic zone and regions of harmful UV exposure.  Concentrations of the major absorbing component (chromophoric organic carbon, CDOM) have been determined and photoxidative loss rates of CDOM were measured. Reflectance ratios have been calculated and implications for remote sensing will be discussed.  Spatial and temporal variations in optical properties in the Keweenaw region will also be presented.

Environmental chemical contamination of Lake Superior

K. Groetsch¹, M. Neilson², D. M. Whittle³, P. McCann⁴

¹Great Lakes Indian Fish and Wildlife Commission, Odanah, WI 54861; ²Environment Canada, Burlington, Ontario L7R 4A6; ³Department of Fisheries and Oceans, Burlington, Ontario L7R 4A6; ⁴Minnesota Department of Health, St. Paul, MN 55164

Over the past 10 to 15 years, much of the chemical contaminant monitoring and research has been focused on persistent, bioaccumulative and toxic (PBT) chemicals found throughout the Lake Superior basin and its biota. This presentation is an overview of temporal trends of commonly monitored PBT chemicals in air, water, and two types of biota [herring gull eggs and whole lake trout] as well as recently published data on PBDE. This overview finds that many regulated-out-of-use chlorinated organic chemicals, with the exception of toxaphene, show a significant decline in concentration over time. Furthermore, this presentation demonstrates the benefit of long-term monitoring data and the need to expand these studies to “emerging” chemicals of concern. Finally, Lake Superior has unique characteristics that make it susceptible to retaining chemicals, which in turn, results in longer exposure times for Lake Superior biota.

Lakewide survey of significance of microbial activities in C- and P-dynamics in Lake Superior

R. T. Heath¹, M. Munawar²

¹Department of Biological Sciences and Water Resources Research Institute, Kent State University, Kent, OH 44242; ²Great Lakes Laboratory for Fisheries & Aquatic Sciences, Fisheries & Oceans Canada, 867 Lakeshore Road, Burlington, Ontario L7R 4A6

A lakewide survey of the importance of bacterioplankton in carbon and phosphorus transfers through the base of the food web was conducted in Lake Superior in August 2001.  The purpose of this survey was to examine the significance of the microbial shunt in C- and P- dynamics in nearshore and offshore stations.  We investigated intensively 5 nearshore stations and 4 offshore stations.   Determination of primary production (14-C method), bacterial production (3-H leucine method), and phosphate uptake (33-P-phosphate method) were conducted on shipboard, generally within 1 hour of collection.  Primary production ranged from 0.7 - 2.1 µg C L^-1 hr^-1, with significantly higher primary productivity shown at nearshore stations.  Bacterial numbers ranged from 0.5 - 1.0 x 10⁶ cells L^-1, with somewhat higher numbers observed at nearshore stations.  Bacterial production ranged from 0.5-4 x10^-2 µg C L^-1 hr^-1, was significantly correlated with primary production and was significantly greater at nearshore stations.  Bacteria-sized particles (particles less than 1µm effective spherical diameter) took up 55 - 81 percent of the phosphate, with no significant differences between nearshore and offshore stations.  We observed a weak negative correlation between phosphate uptake and primary production. 

Genetic structure and community DNA similarity of picoplankton communities from the Laurentian Great Lakes

R. E. Hicks, D. A. Pascoe

Department of Biology, University of Minnesota-Duluth, Duluth, MN 55812

The similarity of picoplankton communities in the epilimnia (5 m) and mid-hypolimnia (45-70 m) of several Laurentian Great Lakes was compared by quantitative 16S rRNA-based and community DNA membrane hybridizations. Total nucleic acids were extracted and purified from picoplankton collected in Lakes Erie, Ontario, Huron, Michigan, and Superior during July and August 1992. Based on 16S rRNA hybridizations, the majority of picoplankton nucleic acids (91-98%) were from bacteria. Microeucaryotes accounted for less than 3% of the total nucleic acids. Surprisingly, up to 2% of the picoplanktonic nucleic acids in the epilimnia and hypolimnia of these lakes were from prokaryotic archaeons. The genetic similarity of these communities was estimated by pair wise hybridization of heterogeneous DNA samples. This similarity is an estimate of the fraction of DNA shared in common between two communities. Total picoplanktonic DNA in the epilimnia of all lakes examined was similar during August (*70% similarity), except for comparisons to Lake Superior. However, the community DNA composition of epilimnetic picoplankton was usually different from picoplankton in the hypolimnia at the same sites. Total picoplanktonic DNA was different in the epilimnion and hypolimnion at four sites in Lakes Erie, Ontario, and Michigan. Epilimnetic and hypolimnetic picoplanktonic DNA was similar at only two sites investigated in Lakes Ontario and Superior. A large enough proportion of DNA was shared in common between the epilimnetic and hypolimnetic picoplankton at this second site in Lake Ontario to be considered marginally similar (71% similarity). It is possible that not enough time had elapsed for a different picoplankton community to develop in the epilimnion at the Lake Superior site when it was sampled in July because this lake was probably not stratified as long as the other lakes that were sampled later in August. Together, the results verify that bacteria account for the majority of the picoplanktonic-sized organisms in these great lakes but also indicate that different picoplankton communities can form in the epilimnion and hypolimnion during summer after these lakes become thermally stratified.

Annual and offshore changes in bacterioplankton abundance and productivity in the western arm of Lake Superior during 1989 and 1990

R. E. Hicks, P. Aas, C. Jankovich

Department of Biology, University of Minnesota-Duluth, Duluth, MN 55812

The abundance and productivity of heterotrophic bacterioplankton were measured in the western arm of Lake Superior to determine if seasonal, annual, and offshore differences occur. A shallow site (35 m) in the Duluth basin near Duluth, MN was sampled approximately bimonthly from spring to late fall in 1989 and 1990 to identify seasonal and annual changes. Although some seasonal changes in cell abundance were observed, the greatest change in bacterioplankton abundance was between 1989 and 1990. Bacterioplankton were more abundant and larger during 1989 (0.71-2.17 x 109•L-1; 0.52 ±0.08 µm) than in 1990 (0.62-1.84 x 109•L-1; 0.35±0.03 µm). The majority of bacterioplankton cells were coccoid shaped at this Duluth basin site. Although thymidine incorporation varied from 0.6 to 21.0 pmol•L-1h-1, no seasonal or annual changes were detected. Prior to thermal stratification, bacterioplankton were less abundant during both years. Bacterial abundances usually decreased from the epilimnion to the sediment-water interface after the lake was thermally stratified. Cell volumes were slightly smaller during early summer in 1989 but similar in size during all 1990 ranging from 0.02 to 0.03 µm3. Thymidine incorporation decreased with depth only during August 1989 and October 1990. Three sites along a transect from the Duluth basin northeast to the Chefswet basin were also sampled during late August and early September 1990 to identify any differences in the spatial distribution of bacterioplankton abundance and productivity in the western portion of Lake Superior. Bacterioplankton abundances were higher at the nearshore sites in the Duluth basin compared to sites further offshore in the Duluth and Chefswet basins, except in the mid-hypolimnion. More bacteria were present near the sediment at shallower sites that had high, suspended solid concentrations. Epilimnetic cells were similar in volume within the Duluth basin but smaller than cells in the Chefswet basin. There were no differences in cell volumes at other depths or in thymidine incorporation rate when the Duluth and Chefswet basins were compared. In conclusion, bacterioplankton were more abundance and larger in 1989 than 1990, they were more abundant at nearshore sites but epilimnetic cells were largest at the furthest site offshore. However, consistent seasonal, annual, or spatial differences in thymidine incorporation by heterotrophic bacterioplankton were not evident in the western arm of Lake Superior during the same period.

Biogeochemical cycling of copper in Lake Superior

J. Jeong, N. R. Urban

Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49930

Ecosystems in the Keweenaw Peninsula region of Lake Superior were directly affected by dumping approximately one billion tons of copper-rich mine tailings during the past 100 years. Understanding the fate and transport of the copper in this area is important for management and remediation of the lake. The objective of this study was to identify factors controlling concentrations of dissolved copper in the water column. Dissolved copper concentrations in the water column and total copper in sediments were determined over 3 years from 1998 to 2000 in the western coastal area of the Keweenaw Peninsula. Concentrations of dissolved copper in nearshore areas (>800 ng/L) are elevated relative to those offshore (<600 ng/L). Total copper concentrations in sediments from this area (0.150 - 0.640 mg/g) are high compared to background reference sites (0.030 - 0.070 mg/g). Wet chemical extractions of the size-fractionated surface sediments, settling particles and cores revealed that Cu-rich particles have been transported into the lake and released copper into the water in the nearshore region. Unlike the oceans, depth profiles of dissolved copper concentrations and high Cu:C ratios of suspended particles indicate that surface depletion resulting from biological activity is not a major process for regulating copper in Lake Superior. Scavenging by suspended particles is a major process controlling the dissolved copper concentrations in Lake Superior. Also, chemical (i.e., dissolution of copper minerals) and physical processes (i.e., the fast mixing of the entire water body and transportation by currents) appear to be significant factors for regulating the dissolved copper in this ultraoligotrophic and high-energy lake.

Sedimentation in Lake Superior: big lake, big questions

T. C.  Johnson

Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55812

Lake Superior is the most complex sedimentary basin that I have investigated.  There is extensive erosion by bottom currents in many of the deep basins offshore, including the deepest site in the lake, which is nearly 400 m deep. New high-resolution seismic reflection profiles (28 kHz) and multi-beam sonar records are allowing us for the first time to map the erosional features in great detail, in many parts of the basin. We do not know the cause, frequency or intensity of the erosional deep currents, but suspect that they are generated by passing atmospheric storms, especially during the non-stratified time of the year.  Are the bottom currents primarily large-scale, wind-driven features, possibly associated with seiches, or perhaps associated with "laddies," the large lake eddies recently reported by E. Ralph to be widespread in Lake Superior?  In addition to the large erosional areas found in many regions, the deep-basin floor is dissected by numerous ring-shaped troughs.  While the presence of these features has been known for decades, their origin still remains a mystery.  N. Wattrus has generated new, high-quality acoustic images of the ring depressions, and is investigating the potential ties between them and the ubiquitous polygonal fault system in the underlying sediments.  New information is being generated on the varved, glacial lacustrine sediments laid down beween 8200 and 9600 radiocarbon ybp.  A. Breckenridge is generating a fascinating stratigraphy based on carbonate content and varve thickness that can be correlated across broad expanses of the lake basin.  One of the key questions to be addressed in the varve study is how to distinguish between the input of meltwater off the Laurentide Ice Sheet at the time of its retreat and the catastrophic inflow from Glacial Lake Agassiz.  This is a new era of sedimentological investigations of the Lake Superior basin, one that will provide important new insights into the dispersal and fate of sediments and that will shed new light on the environmental history of this complex Great Lake.

Preliminary report of late holocene lake-level variation in southeastern Lake Superior: Tahquamenon Bay, Michigan

J. W. Johnston¹, T. A. Thompson², S. J. Baedke³

¹Department of Geological Sciences, Indiana University, 1005 E 10th St., Bloomington, IN 47405; ²Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405; ³Department of Geology and Environmental Science, MSC 7703, James Madison University, Harrisonburg, VA 22807

Endemism and invasion in the Great Lakes diatom community

M. L. Julius

Department of Biological Sciences, St. Cloud State University, St. Cloud, MN 56301

Population dynamics and health for individual Great Lakes diatom species is explored. Information dealing with how these taxa compete with introduced species and rapid environmental changes in modern times is examined. Diatomists have identified a number of these taxa, but discussion is limited with little or no information covering the ecological range of the taxa over time. Some of these include: Cyclotella americana Fricke; Cyclotella bodanica var. stellata Skvortzow; and Stephanodiscus superiorensis Theriot. A number of taxa endemic to the Great Lakes undescribed in the literature also exist. These are species wedged into taxonomic categories from the European taxonomic system. Recent advances in the understanding of diatom species boundaries, suggest these names are inappropriately used for a number of taxa identified in paleolimnological investigations of the Great Lakes. This problem developed because taxonomic information outside of the European flora is not readily available to researchers, and because the focus of paleolimnological studies is primarily environmental reconstruction minimizing the time that can be spent unraveling taxonomically troublesome species. Examples of these are Cyclotella bodanica var. glabriscula and Cyclotella bodanica var. oligactis. Great Lakes populations of these taxa are significantly different from the original populations described from alpine lakes in Austria and Switzerland and merit taxonomic separation. Many of the endemic taxa are no longer present in the modern Great Lakes assemblages. The precise time of their disappearance from the system is not know, but modifications in Great Lakes diatom populations clearly coincided with the development of substantial European settlement of the Great Lakes region. Cyclotella americana, for example, was always limited to Lakes Erie and Ontario but disappeared from both of these lakes prior to 1900. With the disappearance of these taxa, came a number of introductions to the lakes. This work represents the first attempt to document these floristic changes.

The abundance and distribution of benthic macroinvertebrates along the Keweenaw Peninsula, Lake Superior

J. E. Kahn, N. A. Auer

Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

The benthic invertebrate community in Lake Superior is important to the well being of both fish and humans, however, there have been few investigations describing this community.  The purpose of this study was to identify the key benthic invertebrate taxa, and discern what physical and chemical factors may influence their abundance and distribution along  the Keweenaw coast.  Sampling, using a ponar, was conducted from 1998-2000, along three transects with distinctly different bathymetry.  During the three years of sampling, Diporeia was found to be the most abundant invertebrate, accounting for 48% of the invertebrate community, followed by chironomids (21.3%), oligochaetes (18.7%), and sphaeriids (8.4%).  Only chironomids showed a statistically significant difference in seasonal density, being more abundant in September than earlier or later in the year.  The Diporeia, Sphaeriidae, and Nematoda groups were most densely distributed along the slope of the Keweenaw Peninsula, with lower abundances in the shelf and profundal regions.  The distribution of  chironomids and oligochaetes was best explained by depth, showing peak densities at 50 meters on all three transects.  The Keweenaw Current may play a role in the distribution of invertebrates, concentrating benthic invertebrates at the north of the Keweenaw Peninsula.  This study is an important step towards understanding the factors that influence the abundance and distribution of the benthic invertebrates in this region, as well as providing the first thorough description of this benthic community.

Historical metal footprints across the bottom sediments of Lake Superior

W. C. Kerfoot¹, J. A. Robbins², J. Jeong³

¹Lake Superior Ecosystem Research Center and Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; ²Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105; ³Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive Houghton, MI 49931

Around the turn-of-the-century, native copper stamp mills on the Keweenaw Peninsula sluiced at least 71 Mt of copper-rich tailings directly into Lake Superior. Coarse, fine ("slime clay"), and dissolved fractions left historical imprints varying distances from the discharge site. High metal inventories are typical of coastal shelf margins, leaving a "halo" around the Peninsula. Fine particles and particle-bound Cu dispersed further, following the track of the Keweenaw Current. There is even evidence for a perhaps smelter-derived "Old-Cu" signal as far as the lake outlet (Lake George portion of St. Marys drainage).

Documenting frequent species replacements and rapid evolution in Daphnia: an example of “resurrection ecology”

W. C. Kerfoot¹, X. Ma¹, C. S. Lorence¹, L. J. Weider²

¹Lake Superior Ecosystem Research Center and Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; ²The University of Oklahoma Biological Station, HC-71, Box 205, Kingston, OK 73439

We address the dilemma of evaluating historical (paleolimnological) inferences by retrieving resting eggs from sediment cores for genetic studies and experiments. The development of present day species distributions around the Keweenaw Waterway and southern shoreline of Lake Superior is clarified by describing changes in species composition, gene frequency, and morphology through time. Genetic changes are examined at mega-(mtDNA RFLP), meso-(allozyme), and micro-evolutionary (common garden) levels. Mitochondrial DNA 12S/16S sequences and allozymes (Pgi, Pgm, Ao, Got) were characterized for 211 clonal isolates, whereas Pgi allozymes were analyzed on over 2400 Portage Lake and L'Anse Bay resting eggs, reaching back 60-80 years. A surprising revelation is the recent arrival of Daphnia mendotae and D. retrocurva in nearshore Lake Superior assemblages, frequent species replacements and rapid evolution. The replacements and microevolution suggest rapidly changing nearshore environments around a lake noted for lack of physical, chemical, and biological change.

Long-term variations in the Lake Superior water budget

J. D. Lenters

Department of Geology and Physics, Lake Superior State University, 650 West Easterday Avenue, Sault Ste. Marie, MI 49783

Development of a satellite synthetic aperture radar (SAR) and scatterometer approach for Lake Superior ice cover mapping

G. A. Leshkevich¹, S. V. Nghiem²

¹NOAA / Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105; ²Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109

Ice cover mapping over Lake Superior is a regional-scale problem that requires a satellite sensor to provide data with large spatial and high temporal coverage. In this paper, we present the development of an approach using satellite synthetic aperture radar (SAR) and scatterometer to map Lake Superior ice cover. With the launch of ERS-1 and ERS-2 (1991 and 1995) and the subsequent launch of RADARSAT (1995) with its wide swath (~500 km), high resolution (100 m) ScanSAR Wide data, algorithms to classify and map lake ice, based on in situ measurements and observations, have been developed. In addition, NSCAT was operated at approximately 14 GHz on the Advanced Earth Observing Satellite (ADEOS) from June 1996 to July 1997 covering the entire ice season over the Great Lakes. The results from NSCAT lake ice mapping are in good agreement with field observations and National Ice Center (NIC) ice analysis charts. With the launch of the SeaWinds Ku-band scatterometer on the QuikSCAT satellite in June 1999, techniques in the scatterometer approach to Great Lakes ice mapping have been developed specifically for SeaWinds data with preliminary results verified with field observations. Moreover, the results from the Great Lakes Winter Experiment 2002 (GLAWEX02) employing the NASA AIRSAR aircraft and the recent launch of the ENVISAT satellite will facilitate the development of algorithms to map ice thickness and to better utilize the all-weather, day/night imaging capabilities of satellite SAR and scatterometer data for applications in ice forecasting and modeling, climate and winter ecology research, hazard mitigation, as well as operational use.

Changes in the Lake Superior crustacean zooplankton community

J. S. Link¹, J. H. Selgeby², R. E. Keen³

¹National Marine Fisheries Service, Northeast Fisheries Science Center, Food Web Dynamics Program, 166 Water St., Woods Hole, MA 02543; ²National Biological Service, Great Lakes Science Center, Lake Superior Biological Station, Ashland WI 54806 (retired at P.O. Box 37, Revillo SD 57259); ³Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton,  MI 49931

We examined crustacean zooplankton densities at five locations in Lake Superior during a time period that spanned two decades, for three years in the early 1970's and again in the early 1990's. This sampling covered all seasons except limnological winter. We used a coupled multivariate and univariate approach to detect whether the zooplankton community had changed over these decades, and to determine if such changes had occurred consistently across all stations. Seasonal variation was also elucidated. Although life history processes generally conformed to previous reports, there were distinct differences in the timing of life history events for a number of species. The presence of various species in different habitats also varied within a year, between years, and between decades. It appears that seasonally mediated thermal tolerances of habitat use and life history patterns were more rigorously delineated in the 1990s. Evidence for top-down effects, demonstrated as shifts in the size composition of the zooplankton community, are observed in Lake Superior concurrent with an increase in the abundance of a major endemic planktivore, the lake herring (Coregonus artedi). Evidence for bottom-up effects, demonstrated as shifts in taxonomic composition and related indices of secondary productivity, are observed in Lake Superior concurrent with increased nitrogen loading to this lake and climate shifts. The spatial and temporal scale of this study confirm that size-selective planktivory and increased productivity can occur in large lakes, and of the two it appears the planktivory more strongly influences the zooplankton community in this lake. However, the magnitude of these processes is less in Lake Superior than commonly observed in smaller and shallower lakes, including the lower Great Lakes.

Multiple lines of evidence support phytoplankton Fe deficiency in Lake Superior

R. M. L. McKay¹, D. Porta¹, G. S. Bullerjahn¹, E. T. Brown², J. Agnich², R. Sherrell³, M. P. Field³, T. Smutka⁴, R. Sterner⁴

¹Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43402; ²Large Lakes Observatory, University of Minnesota- Duluth, 10 University Drive, Duluth, MN 55803; ³ Institute of Marine and Coastal Sciences, Rutgers University, Piscataway, NJ 08854-8066; ⁴Department of Ecology, Evolution and Behavior, 1987 Upper Buford Circle, University of Minnesota, St. Paul, MN 55108. 

Despite the fact that limitation of primary producers by phosphorus remains a central tenet of modern day limnology, an increasing body of evidence supports the concept of trace metal deficiency in freshwater lakes. Here, we present data collected during a 2-year survey (2000-2001) of the western basin of Lake Superior in which trace metal distributions were measured using metal-clean sampling techniques. These data demonstrated that trace metals were generally present in low nanomolar levels (e.g. Fe: 1-10 nM) in pelagic regions of the lake with modest enrichment observed in some coastal areas. Whereas total concentrations of dissolved trace metals provide a first-order indication of potential limitations to productivity, they may not relate directly to biological availability. To address this uncertainty, we adopted several complementary approaches to assess the bioavailability of Fe. Microcosm enrichments of epilimnetic water conducted during July and September demonstrated a positive effect of phosphate-P on the accumulation of biomass (chl). Addition of Fe, while having no effect alone, appeared to act in synergy with added P and resulted in further accumulation of biomass over that provided by P alone. In experiments examining size-fractionated effects, the picoplankton fraction (0.2 - 2 microns) actually appeared to be co-limited by Fe and P. The Fe status of endemic phytoplankton was also assessed using in situ immunological probes for flavodoxin and ferredoxin. Under periods of Fe deficiency, flavodoxin replaces ferredoxin as a redox catalyst in phytoplankton. Whereas flavodoxin did not accumulate in samples collected in May when the water column was essentially isothermal and presumably subject to mixing, flavodoxin accumulation was evident in samples collected during July and September with some evidence of differences in accumulation between nearshore and offshore samples. Finally, we have developed a cyanobacterial Fe bioreporter for use in freshwater systems. The bioreporter contains the Fe-responsive promoter for isiAB ligated to luxAB reporter genes. As such, the cells emit variable luminescence under different levels of Fe deficiency. The bioreporter response observed at most stations surveyed indicated relative Fe deficiency in epilmnetic waters compared to water sampled from the hypolimnion where bioreporter luminescence was quenched. Water sampled during May also elicited a quenched luminescent response suggesting that Fe was available at that time.

Effects of water temperature on copepod abundance in Lake Superior

R. O. Megard¹, W. C. Kerfoot²

¹Department of Ecology, Evolution and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul MN 55108; ²Lake Superior Ecosystem Research Center and Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931

Copepods are the most abundant planktonic animals in Lake Superior, usually varying between 10^2 and 10^6 animals per cubic meter. Some species are most abundant during summer in warm water within or above the thermocline, but others are mostly below the thermocline or in cold unstratified water offshore. The effect of temperature on metabolism and growth cannot account for these aggregations, but they can be explained with a simple three-component kinetic model, which assumes that the composition of aggregations is due to differential migratory behavior of three kinds of thermosensitive individuals: thermoreactive vagrants, thermotrophic immigrants and thermophobic emigrants. Different thermokinetic parameters of species can account for the proportions of species in aggregations. Thermokinetic parmeters also explain the abundance and spatial distributions of the three copepods that are most abundant in Lake Superior and other large northern lakes.

Lake trout stocking and survival in the Keweenaw Bay waters of Lake Superior

H.E. Mensch and M. Donofrio

Keweenaw Bay Natural Resources Department, Keweenaw Bay Indian Community, PO Box 10,

L’Anse, MI 49946

In cooperation with the United States Fish and Wildlife Service (USFWS) and other fishery management

agencies, strategic stocking of hatchery reared lean lake trout Salvelinus nemaycush into Keweenaw Bay

by the Keweenaw Bay Indian Community (KBIC) has occurred annually since 1995.  Assessments of

juvenile and adult lake trout populations in Keweenaw Bay by KBIC staff indicate increases in both lake

trout abundance and the numbers of hatchery vs. wild origin lake trout in survey catches.  A trend has also

been noted in improving relative survival of stocked fish: the number of age-7 stocked lake trout captured

per 304m of gillnet divided by the number (in 100,000s) of lake trout stocked seven years earlier.  The

Great Lakes Fishery Commission (GLFC) recommends discontinuation of stocking in areas of Lake

Superior where populations of lake trout are considered rehabilitated, or in areas with declination of

stocked-yearling survival.  KBIC will continue to monitor lake trout populations and hatchery fish survival,

and anticipates an eventual phasing out of stocking efforts in Keweenaw Bay as multi-agency lake trout

rehabilitation goals are achieved. 

Temporal dynamics of nutrients and hydrology in a Lake Superior coastal wetland

J. A. Morrice, J. R. Kelly, A. S. Trebitz, A. M. Cotter, M. L. Knuth

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

The base of the food web at the top of the Great Lakes

M. Munawar¹, I. F. Munawar², R. Dermott¹, O. Johannsson¹, H. Niblock¹, S. Carou¹, S. Lozano³, D. Lynn⁴, T. Weisse⁵

¹Great Lakes Laboratory for Fisheries & Aquatic Sciences, Fisheries & Oceans Canada, 867 Lakeshore Road, Burlington, Ontario, L7R 4A6; ²Plankton Canada, 685 Inverary Road, Burlington, ON., Canada, L7L 2L8; ³NOAA Great; Lakes Environmental Research Laboratory,2205 Common wealth Blvd, Ann Arbor, MI. 48105-1593, USA; ⁴Department of Zoology,University of Guelph, Guelph, ON, Canada NIG 2W1; ⁵Institute for Limnology, Austrian Academy of  Sciences, Mondsee, Austria.

Since the publication of “ Limnology of Lake Superior” in the J. Great Lakes Res., 1978 (M. Munawar, ed.) limited information has been published about the state of Lake Superior ecosystem and its biological components. Very little is known about the microbial communities and microbial loop interactions (bacteria, autotrophic picoplankton-APP, heterotrophic nanoflagellates-HNF, ciliates, nanoplankton). Similarly since the detailed lakewide surveys of 1973, phytoplankton monitoring has been sparse during the past 30 years. Fisheries & Oceans Canada continued its moderate lakewide coverage during 1983 and more recently in the spring and summer of 2001. This presentation summarizes our recent findings of the spring and summer lake wide cruises which attempts to assess changes not only in phytoplankton communities but in the entire microbial food web. The 2001 cruises consisted of 14 stations distributed across Lake Superior. The stations were divided in to 3 categories: Northern, Offshore and Southern. Bacteria showed higher abundance in the Northern and Southern stations compared to the Offshore. The APP and HNF showed higher abundance in summer than spring. The size-fractionated primary production was higher in the summer dominated by nanoplankton (2-20 µm) and picoplankton (<2 µm) size assemblages. Phytoplankton biomass was relatively lower at the Offshore stations dominated by Diatomeae and flagellates (Chrysophyceae+Cryptophyceae+Dinophyceae). Highest biomass was recorded at Thunder Bay dominated by Diatomeae (70%).

The only major spatial and temporal survey of the lake Superior zooplankton community was undertaken in 1973 at the height of eutrophication by Watson and Wilson.  Calanoids were the dominant taxonomic group, comprising 75% of the April-November numerical abundance.  In the early 1980s, the proportion of calanoids and average individual size increased suggesting an increase in the ratio of piscivores to planktivores in the system.  Cladocerans contributed only 20% of the summer (September) biomass.  The zooplankton community had changed little by 1998 according to EPA studies.  Calanoids, principally Limnocalanus macrurus and Septodiaptomus sicilis together with the cyclopoid Diacyclops thomasi were the dominant species.  Cladocerans still contributed less than 20% of the summer (August) biomass; however the dominant species had switched from Bosmina longirostris and Daphnia galeata mendotae/D. retrocurva to D. g. mendotae and Holopedium gibberum.

The benthic macroinvertebrate composition and abundance were compared from samples collected in 1973 and 2000.  In 1973, Cook concluded that the extreme western basin of the lake was in ecological danger from mining activities on the northwest shore. Currently, Diporeia is still the dominant benthic invertebrate based on density and biomass.  Within seven of nine benthic zones identified by Cook, there were large increases in Diporeia and total abundance.  The greatest change occurred in the western end of the lake where Diporeia densities reached values between 2,058 and 3,741 m^-2 in 2000 compared to values between 112 and 262 m^-2 in 1973.  In conclusion, the status of macroinvertebrates in Lake Superior is very good including the western end of the lake.

Transport processes in Lake Superior

H. J. Niebauer

Atmosphere and Ocean Sciences, 1225 W. Dayton St., University of Wisconsin, Madison, WI., 53706-1695

Transport processes and transport itself have been sporadically studied and documented in Lake Superior for at least a century.  This includes both horizontal and vertical transport in the coastal margin as well as in the open Lake.  Documented phenomena include coastal jets associated with coastal upwelling and downwelling, wind-driven currents, near inertial frequency currents and Kelvin waves, convection in the thermal bar as well as assorted internal and external waves and seiches.  An important dynamically significant feature is the episodic, seasonal and interannual variability in winds, heat, runoff etc.  This variability occurs on many time scales so conditions tend not to be steady state.  In this presentation, several of the above transport processes are illustrated using hydrographic sections, time series of winds and coastal temperatures, as well as U.S. and Canadian current meter moorings from the northern Keweenaw Peninsula region from projects in the 1970's and in 1990's-2000.  In some cases we are able to compare mass transport calculations and temperature differences between the programs.

Episodic events and transport in the Keweenaw Current:  a 1970s retrospective

H. J. Niebauer¹, E. A. Ralph², J. H. Churchill³

¹Atmosphere and Ocean Sciences, 1225 W. Dayton St., University of Wisconsin, Madison, WI., 53706-1695; ²Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55812; ³Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543

A major goal of the Lake Superior portion of the NSF Coastal Oceans Project (CoOP) on the Great Lakes is to improve the understanding of transport processes in the Keweenaw Current off the Upper Peninsula Michigan.  This paper sets the stage for comparing and contrasting  episodic physical transport processes and characteristics of Lake Superior observed in the 1970s with those observed in the recent Keweenaw Interdisciplinary Transport Experiment in Superior (KITES) program. In this retrospective we present documentation of episodic events from wind, temperature and surface current meter time series as well as hydrographic sections for July and August of 1972 and 1973.  The episodic events are primarily wind driven coastal upwelling and downwelling, and the effect on the Keweenaw Current.  While some of these data have been published (e.g., Yeske and Green, 1975; Niebauer et al., 1977), almost all of the 1972 data, and most of the hydrographic sections and half the current meter data from 1973 have not been published.  In addition, 6 current meter records (both Canadian and American) from 1973 have been combined to generate a time series of longshore mass and heat transport of the Keweenaw Current.  These data are corroborated by the hydrographic observations.  This retrospective provides the background against which the recent KITES data are presented in the poster by Ralph et. al. 

Numerical modeling of Lake Superior coastal biogeochemical and physical interaction: a hypothesis for phosphorus cycling

H. J. Niebauer¹, N. R. Urban², M. T. Auer², L. A. Bub²

¹Atmosphere and Ocean Sciences, 1225 W. Dayton St., University of Wisconsin, Madison, WI., 53706-1695; ²Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

The Lake Superior portion of the Coastal Oceans Project (CoOP) is called KITES (Keweenaw Interdisciplinary Transport Experiment in Superior). A major goal of KITES is to improve the understanding of transport processes in the region of the Keweenaw Current in the coastal margin off the Upper Peninsula Michigan. Our goal is to use numerical modeling to simulate primary production and its interaction with episodic physical processes such as coastal upwelling and downwelling, and coastal jets. The idea is to use the biogeochemistry as tracers in the episodic events. However, using a simple nutrient-phytoplankton-zooplankton model to generate biochemical tracers, with soluble reactive phosphorus (SRP) as the limiting nutrient, did not work. The problem is that SRP in Lake Superior shows little variation, yet there are gradients in time and space of primary productivity and production. The main problem was getting the right concentrations and rates of change of SRP. Our solution, or hypothesis, is a loop of dissolved organic phosphorus (DOP), SRP and phytoplankton, with quick acting hydrolysis of DOP, to model the SRP. With this loop, we now get reasonably good comparison of SRP, DOP, chlorophyll, zooplankton, vertical flux and primary production concentrations and rates, with KITES data. We also show some effects of modeled episodic events such as wind-driven coastal upwelling and downwelling.

Distribution of larval lake herring (Coregonus artedii) in the Keweenaw Current, Lake Superior

J. K. Oyadomari, N. A. Auer

Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

The Keweenaw Current located in Lake Superior off the western shore of the Keweenaw Peninsula, Michigan, may greatly influence fish survival by transporting larvae into either favorable or unfavorable locations. We sampled mainly from three locations along the western coast of the Keweenaw Peninsula in 1998-2000 to determine the distribution of larval fishes, lake herring (Coregonus artedii) in particular. Larval lake herring occurred only briefly, from late spring to mid-summer, with a peak in early to mid-May. Variation in abundance was evident among the three years with 1998 having very low densities and 2000 having the greatest. Among stations, Hancock, being deeper and colder, had greater densities compared to Ontonagon, being shallower and warmer, in 1999 but not in 2000. The density and size of larval lake herring were typically greater inshore than offshore. However, Ontonagon in 2000 had much greater densities offshore, even though the inshore larvae remained comparably larger. This pattern suggest that larval may hatch out from offshore locations then migrate inshore where they remain for some time.

Micrometeorological measurement of air-water exchange fluxes of PBTs in Lake Superior

J. A. Perlinger, D. E. Tobias, P.S. Morrow

Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

High-volume air sampling using solid sorbents such as XAD resin or polyurethane foam downstream of a filter for particle collection has become the preferred method for semi-volatile organic compound (SVOC) collection.  Various studies have shown that use of these samplers can lead to artifacts due to repartitioning of compounds within the sampler.  Diffusion denuders have been shown to avoid these sampling artifacts, but have been used to a much lesser extent for SVOC collection.  We are fabricating and testing a diffusion denuder based upon an original design by Krieger and Hites (1994) and a custom-built desorber.  The denuder employs ca. 250, 25-cm, parallel fused silica capillary column sections with an appropriate coating to denude air of organic vapors but not particles.  Ambient air is drawn through the denuder, trapping SVOCs, and then through a particulate filter using a vacuum pump.  Trapped SVOCs are thermally desorbed into a cryogenically-cooled gas chromatograph (GC) inlet followed by separation on an analytical GC column and detection in a micro-electron capture detector.  We will present results of laboratory and field experiments designed to optimize trapping and desorption of SVOCs, the design of our micrometeorological system for SVOC flux measurement, and hypotheses for measurement of the temporal and spatial variability in SVOC fluxes.  Fieldwork planned for summer 2002 will measure SVOC fluxes to Lake Superior onboard research vessels off the Keweenaw Peninsula.

Comparisons of lake trout spawning regions along Minnesota’s north shore

C. Richards¹, J. Bonde², D. Schreiner³

¹Minnesota Sea Grant College Program, University of Minnesota, 2305 East 5^th St., Duluth, MN 55812; ²Natural Resources Research Institute, University of Minnesota, 5013 Miller Trunk Hwy, Duluth, MN, 55811; ³Minnesota Dept. of Natural Resources, 5351 North Shore Drive, Duluth, MN 55804

Seven regions approximately ten kilometers in length along Minnesota’s North Shore were compared with respect to physical characteristics of bottom substrates in waters < 30 m in depth.  Detailed substrate and bathymetric data for the regions were compiled with hydroacoustic surveys and were stored and manipulated in a Geographical Information System. The amount and distribution of good lake trout spawning substrates (dominated by cobble and boulders) and poor spawning substrates (high proportion of sand and fines) varied considerably among the seven regions.  The percentage of good habitat was greatest (> 50%) along the middle and upper regions of the Minnesota shoreline and lower (23 to 38%) in regions closer to Duluth. These regions also differed with respect to average size of good habitat patches and composition of good substrate. Patch size was greatest in the middle and upper regions (10 to 18.5 hectares) than the lower regions (1.8 to 3.9 hectares). Good habitat substrates had higher proportions of conglomerate and boulder materials than in the middle and upper regions and the lower regions had more cobble materials. Analysis of fisheries data indicate significant increased numbers of wild (as opposed to stocked) lake trout in fisheries surveys with these physical dimensions of habitat.

Evaluating methods for assessing sediment quality in a Great Lakes embayment

C. Richards¹, J. Crane², D. Breneman³, G. Petersen⁴, J. Scharold⁴, S. Lozano⁵

¹Minnesota Sea Grant College Program, University of Minnesota, 2305 East 5^th St., Duluth, MN 55812; ²Minnesota Pollution Control Agency, Water Quality Division, 520 Lafayette Rd., St. Paul, MN 55155; ³Natural Resources Research Institute, University of Minnesota, 5013 Miller Trunk Hwy, Duluth, MN, 55811; 4 U.S. Environmental Protection Agency,  Mid-Continent Ecology Division, 6201 Congdon Boulevard, Duluth, MN, 55804;5 NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd,  Ann Arbor, MI 48105-2945

Various sediment monitoring techniques are routinely utilized to assess environmental  health and provide recommendations for remediation. We compared the results from toxicity tests, sediment chemistry analysis, and a benthic community survey to evaluate sediment quality within the Duluth/Superior Harbor located at the western end of Lake Superior. Data from 20 training sites (10 a prior sites selected as undisturbed and 10 as disturbed) were used to establish standard criteria for evaluating sediment conditions at 87 randomized sites within the harbor.  Lethality exhibited during Microtox® tests with Photobacterium phosphoreum prompted 10-day single-species toxicity tests on Hyalella azteca and Chironomus tentans.  Sediments from only 2 of 56 sites produced a deleterious response to either test organism during acute exposures. Training site sediments produced mortality in 33% of the sites, with only one a prior selected “undisturbed” site exhibiting a lethal response. Discriminate function analysis and multimetric analysis were used to categorize biological metric scores from macroinvertebrate assemblage data. Discriminant function analysis categorized 75.9 % of the sites as disturbed while the multimetric technique classified 33% of the sites as disturbed and 12% indeterminate.  Comparisons of macroinvertebrate data to other benthic measures suggest that the multimetric approach may best for depicting benthic conditions.

Dynamics of lake trout recruitment in Michigan waters of Lake Superior

J. M. Richards¹, M. J. Hansen², C. R. Bronte³, S. P. Sitar⁴

¹U.S. Fish and Wildlife Service, Marquette Biological Station, 1924 Industrial Parkway, Marquette, MI 49855; ²University of Wisconsin-Stevens Point, College of Natural Resources, 1900 Franklin Street, Stevens Point, WI 54481; ³U.S. Fish and Wildlife Service, Green Bay Fishery Resources Office, 1015 Challenger Court, Green Bay, WI 54311; ⁴Michigan Department of Natural Resources, Marquette Fisheries Research Station, 484 Cherry Creek Road, Marquette, MI 49855

Is the Lake Superior wave zone just another stream to aquatic insects?

M. Strand, S. Rybczynski, J. Scanlan, B. Thierry

Department of Biology, Northern Michigan University, Marquette, MI 49855

Many of the aquatic insect species that inhabit the wave zones of large lakes are more typically associated with riverine habitat. The prevailing hypothesis used to explain these lotic/coastal distributions is that erosional habitat specialists are preadapted for life in the wave-swept shores of large lakes and thus, through drift and/or oviposition, extend their distributions from tributaries to coastal sites. In this study, we used quantitative invertebrate sampling, water temperature loggers, and periphyton and sediment respirometry to determine the extent to which benthic communities and physical characteristics vary among Lake Superior wave zone and tributary habitats. Although some populations did seem to fit the lotic/coastal distribution model, most did not. The physical and biotic conditions in wave zone sites also differed from tributary conditions. Average summer water temperatures were similar in tributaries and wave zone sites, but diel amplitude and timing of daily minimum and maximum temperatures were markedly different, which is predicted to have profound influences on benthos. As expected, periphyton activity was much greater in lotic sites. However, respiration rates from coastal sands were higher than those from river mouth sands. Invertebrate abundance was greater in stream sites than in wave zone sites. Abundance was similar in sand and sandstone substrate sites and was not related to proximity to river mouths. The Lake Superior wave zone along the south-central shore is inhabited by disturbance-tolerant lentic species and lotic species that face relatively low food availability and very different environmental conditions than those experienced by conspecifics in nearby streams.

Reconstructing past lake-level change in Lake Superior from relict shorelines

T. A. Thompson¹, J. W. Johnston², S. J. Baedke³

¹Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405; ²Department of Geological Sciences, Indiana University, 1005 E 10th St., Bloomington, IN 47405; ³Department of Geology and Environmental Science, MSC 7703, James Madison University, Harrisonburg, VA 22807

Copper in Keweenaw Peninsula Waters: Toxic Effects on Algae and Daphnia

I. L. Trubetskova, W. C. Kerfoot

Lake Superior Ecosystem Research Center and Department of Biological Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931

Due to more than one century of mining activity, copper extensively contaminated the Keweenaw Peninsula waters. Copper released from stamp sands/sediments can reach concentrations that are toxic for biota, and thereby may severely impact different trophic levels and the food web. Using standard bioassay techniques and life table experiments, we attempted to quantify possible toxic effects of water taken from different local sources on both phytoplankton and zooplankton. Growth of green algae, Chlorella sp. and Chlamydomonas sp., was not affected within a particular range of copper concentrations. However, the accumulation rate of dissolved copper by algae was rather high, especially for treatments with higher initial copper concentration. Several species of Daphnia fed on these algae showed definite signs of chronic toxicity stress. Copper dissolved in the water directly affected Daphnia fed with algae not contaminated with copper, though the effect was less pronounced compared to indirect impact via food. Negative changes in Daphnia performance (i.e. deteriorated survivorship, development, growth and reproduction) accumulated in subsequent generations, resulting in a reduced intrinsic rate of population increase (r). This study provides evidence that elevated copper concentrations in aquatic environments might negatively affect zooplankton production both directly through water and/or indirectly via food (due to eating algae contaminated with copper).

Relationships between copper and manganese and its effect on phytoplankton productivity in Lake Superior: laboratory and field studies

M. R. Twiss¹, K. J. Rattan¹, R. M. Sherrel², R. M. L. McKay³

¹Department of Chemistry, Biology and Chemical Engineering, 350 Victoria St., Ryerson Polytechnic University, Toronto, Ontario, M5B 2K3; ²Institute of Marine and Coastal Sciences, Rutgers University, Piscataway, NJ 08854-8066; ³Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43402

Despite the size and importance of the North American Great Lakes, our knowledge of trace metal speciation in these waters in almost entirely absent. At present, the Great Lakes Water Quality Agreement has defined objectives for ensuring water quality with respect to numerous contaminants including trace metals. However, the GLWQA (1978) objectives for copper (78.7 nM Cu) may be acutely toxic to phytoplankton in Lake Superior. In natural waters dissolved metal is present as free metal ions (for cationic forms of trace metals) and complexed metal. Trace metals are complexed to varying degrees by a range of inorganic and organic ligands, both in solution, on particle surfaces (>0.2-0.45 µm), and associated with colloids (<0.2-0.45 µm). Biological availability and toxicity of an element depend on the chemical speciation of that element. In the case of copper, toxicity is proportional to the concentration of the free ion, Cu2+. We tested the sensitivity to Cu of natural phytoplankton assemblages from the western arm of Lake Superior in September 200 and May/June 2001. The photosynthetic efficiency of the assemblage tested in September was sensitive to as little as 2 nM added Cu, suggesting a tight balance of buffered Cu2+ concentrations. In contrast, water examined in May/June lacked any response, measured as change in size-fractionated chlorophyll-a abundance. Ambient total dissolved metal concentrations were 10-12 nM Cu and 1.2-2.1 nM Mn. To further examine the potential role played by low dissolved [Mn], laboratory toxicity tests were conducted at two light intensities using environmentally realistic concentrations of metal ([Cu2+] = 10-13 -10-10 mol/L; [Mn2+] = 0.08-4.8 nM), on two Great Lakes phytoplankton species, Chlorella and Microcystis. Responses to the toxicity tests suggest that light and [Mn] play an important role in the expression of Cu toxicity and both factors may play a role in phytoplankton community structure.

Carbon and nutrient cycling in Lake Superior: a retrospective

N. R. Urban

Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931

It is well known that Lake Superior is a large, dilute, freshwater, lake with low productivity. The common paradigm has it that the lake is strongly P-limited, with primary production of only 30-50 g C m-2 yr-1. Both silica and nitrate exhibit only minor epilimnetic depletion, because both are available much in excess of phosphorus. Carbon burial has been reported to follow the same dependence on sedimentation rate as observed in the ocean. This talk will address two central themes: (1) has the lake changed over time with respect to carbon and nutrient dynamics, and (2) what can carbon and nutrient dynamics in Lake Superior teach us that is relevant to today's important questions in limnology and oceanography? The talk will draw together the sporadic data available in the literature as well as some of the new findings from recent intensive studies.

Carbon cycling in Lake Superior

N. R. Urban¹, M. T. Auer¹, S. A. Green², D. A. Apul¹, P. F. Siew¹, X. Lu¹, J. Jeong¹, Y. Chai¹, L. A. Bub¹, K. D. Elenbaas³

¹Department of Civil & Environmental Engineering; ²Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI  49931; ³Blasland, Bouck & Lee, Engineers and Scientists, 6723 Towpath Rd., P.O. Box 66, DeWitt, NY 13214

Relatively little is known about carbon cycling in Lake Superior. Even rates of the basic processes of photosynthesis and respiration have been quantified very seldom. Questions that remain unanswered include: Is the lake a net source or sink of CO2 to the atmosphere? What role does the lake play in the carbon cycle of the entire watershed? What factors limit rates of primary production? What will be the effects of climatic warming on carbon cycling? Is annual primary production more tightly coupled with nutrient loading or the physical structure of the water column? Intensive measurements carried out over the past three years as part of the KITES project have allowed us to augment our understanding of this large ecosystem. This talk will focus on (1) the balance of photosynthesis and respiration, (2) factors limiting autotrophic production, and (3) factors regulating the distribution of DOC.

Evidence of post-depositional mobility in Lake Superior's glacio-lacustrine sediments

N. J. Wattrus¹, A. Sharpe¹, D. E. Rausch¹, J. B. Swenson¹, J. A. Cartwright²

¹Large Lakes Observatory and Department of Geological Sciences, University of Minnesota, Duluth, MN 55812; ²Department of Earth Sciences, University of Cardiff, Cardiff, Wales

We present results from a high resolution "pseudo-3D" seismic survey collected in western Lake Superior in 2001. The data show that the varved glacio-lacustrine clays below the lake floor are deformed and faulted. This deformation can be used to subdivide the subsurface section into distinct tiers. Examination of the tiers reveals that the layer-bound deformation and faulting can be linked to lateral variations in thickness of a basal layer. These thickness variations are interpreted as evidence of post-depositional mobilization resulting from the formation of overpressure in the fine-grained sediments.