INDEX Conference Page Paper Titles Abstracts Poster Titles Posters Abstracts

Poster Abstracts

The fate of Nemadji River sediment in western Lake Superior

D. R. Albrecht¹, E. T. Brown¹, J. B. Swenson¹, N. J. Wattrus¹, G. Parker²

¹Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55812; ²St. Anthony Falls Laboratory University of Minnesota, Minneapolis, MN 55414

The Nemadji River Watershed, located in Wisconsin and Minnesota, is unique in that it contains easily erodible soil and high riverbanks that contribute large amounts of sediment to the river through mass wasting events. Sediment is then transported and ultimately deposited in Western Lake Superior. Presumably, the finest material from the river is carried the greatest distance into the lake. This fine-grained sediment adsorbs trace metals as it is moved out of the river. By using ICP-MS technology on sediment cores from Western Lake Superior we will determine the geochemical fingerprint of the Nemadji River sediment in Lake Superior and ascertain anthropogenic changes to the watershed. The suspended sediment load of the Nemadji River is also thought to create turbidity currents on the lake bottom. Sediment grain size analysis will help provide quantitative evidence for the existence of turbidity currents in this region. These data will help establish the dominant physical processes taking place in this region of the lake (i.e., wave processes, turbidity currents, lake circulation).

University research vessels on Lake Superior

M. T. Auer¹, T. C. Johnson²

¹Department of Civil & Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; ²Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55812

Long the ‘unstudied’ Great Lake, Lake Superior has experienced a resurgence of research in the past decade. This resurgence has been fueled by an increase in the availability of funds and platforms suitable for the support of lake research. Historically, research vessels plying the waters of Lake Superior have largely been affiliated with state, provincial, and federal agencies. While these resources remain critical to scientific efforts, recent vessel acquisitions at universities in the region speak to the future vitality of Lake Superior research. This poster presents information on vessels presently available at Michigan Technological University in Houghton and at the University of Minnesota’s Large Lakes Observatory in Duluth. Scientists are welcome to contact university representatives about using these quality platforms to explore the waters of this greatest lake.

Lake Superior varves: archives of paleoclimate and geomorphic history

A. J. Breckenridge, T. C. Johnson, D. E. Rausch, N. J. Wattrus, Y. Chan

Large Lakes Observatory and Department of Geological Sciences, University of Minnesota Duluth, 229 Heller Hall, 10 University Drive, Duluth, MN 55812

Withdrawal of the Laurentide Ice Sheet (LIS) from the Lake Superior watershed resulted in the deposition of at least 1,900 glaciolacustrine varves, approximately spanning the interval between 9.2 and 11.1 thousand years ago. These varves should provide a high resolution record of regional climatic variability, LIS meltwater fluxes and ice margin positions. Preliminary analyses reveal quasi-periodic varve thickness patterns similar to modern El Niño-Southern Oscillation (ENSO) patterns. Furthermore, an unusually thick package of correlative varves near the top of the section suggests the final withdraw of the LIS from the watershed was preceded by a 40 year period of catastrophic meltwater discharge. This meltwater discharge, which ultimately spilled into the St. Lawrence Seaway, may have been responsible for short term cooling in the North Atlantic around 9,400 ybp.

Determination of particle residence times in Lake Superior

Y. Chai, N. R. Urban

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

Using radioactive tracers, cross-margin transport of biogeochemically important materials along the coastal region of Keweenaw Peninsula has been studied in the KITES project, a multi-disciplinary study of Lake Superior. Particle-reactive radioisotopes are being utilized to determine the particle residence times in the nearshore zone, i.e. the rate and time scale of cross-margin transport. In addition to determining the time scale of the particle movements (sediment transport) in the nearshore region of Lake Superior, this study also is investigating the factors regulating the particle movements. Inventories of several naturally occurring or artificial radionuclides (210Po, 210Pb, 137Cs) have been measured along transects running perpendicular to shore. Isotope residence time is defined as the inventory divided by the flux. For isotopes (such as 210Pb) with nearly constant inputs from atmospheric fallout, residence times can be determined. Box models with different boundaries are used to determine the influence of bathymetry, waves, and currents. This residence time is the collective result of all processes affecting isotope transport in the system, as well as the isotope decay. Particle residence times can be determined from the residence times of particulate-bound isotopes. This approach allows determination of particle residence time in non-depositional zones of the lake, as well as the rate of cross-margin transport. Preliminary results indicate isotope residence times vary from a few weeks in the very shallow nearshore region to a few years at water depths of 100 meters, and up to several years in water depth of more than 150 meters. Ratios of 210Pb: 137Cs and 210Po: 210Pb change systematically along the transect in response to changing rates of resuspension and changes in sediment provenance.

Burrowing mayflies (Hexagenia) as indicators of ecosystem health

T. A. Edsall, C. Edsall

U.S. Geological Survey, Great Lakes Science Center, 1451 Green Road, Ann Arbor, MI 48105

The U.S. Environmental Protection Agency and Environment Canada are supporting the development of indicators of ecosystem health to aid in restoring and maintaining the Great Lakes ecosystem, as called for in the Great Lakes Water Quality Agreement. This poster describes the development and application of an indicator of ecosystem health that is based on burrowing mayflies (Hexagenia). Burrowing mayflies were selected for use as an indicator because they were historically abundant in mesotrophic habitats in the Great Lakes, were extirpated by pollution in the 1940s to 1950s in most of those environments, and have recovered in some them following pollution abatement. They were also selected because they are key trophic integrators, linking detrital energy directly to fishes which feed preferentially on them. In spring 2001, we sampled at 117 stations on 1,870 km² of lake bed in western Lake Erie, Saginaw Bay, and Green Bay to establish baseline biomass and production data for the mayfly populations and to further the technical development of an indicator of ecosystem health based on those data. Study results indicate that the burrowing mayfly population is recovered in western Lake Erie, and that recovery in Saginaw Bay and southern Green Bay has not yet begun. Study results suggest burrowing mayflies could be used as indicators of ecosystem health elsewhere in the northern United States and Canada.

Cross margin transport and the timing of the spring runoff event and thermal bar formation in Lake Superior

T. M. Gatzke¹, M. T. Auer¹, J. W. Budd²

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

A thermal front or bar develops in large lakes associated with increases in solar radiation in spring. The, defined as the position of the 4°C isotherm physically separates warmer nearshore waters from colder offshore waters. As warming continues, the location of the bar moves lakeward and eventually dissipates with the onset of vertical thermal stratification. In Lake Superior, the thermal bar typically forms in May and exists until June when the lake becomes vertically stratified in July. It has been suggested that the thermal bar may play a role in mediating cross-margin transport in large lakes, trapping nutrients discharged from the watershed behind the front and resulting in enhanced nearshore production. The timing of the spring runoff event (SRE), delivering ~70% of the annual solids load, vis-à-vis the timing of thermal bar formation is important in this regard, as it influences the amount of terrigenous material available for trapping. USGS flow records and results from a tributary monitoring program supported the development of a model for the fate of total suspended solids (TSS) in the Lake Superior nearshore off of Michigan’s Keweenaw Peninsula. The model was used to calculate the fraction of the SRE TSS load remaining in the nearshore at the time of thermal bar formation. Estimates of the timing of bar formation were developed from remote sensing images and water intake records at Ontonagon, Michigan. The SRE was found to typically precede bar formation by 3-6 weeks. Model calculations indicate that, on average, 17% of the SRE TSS load remains in the nearshore at the time of thermal bar formation. These findings are consistent with satellite images which show the Ontonagon River plume present in the lake, well beyond the location of the thermal bar, at the time of spring runoff.

Copper and mercury in Keweenaw Waterway and Lake Superior sediments: ore sources revealed

S. L. Harting¹, W. C. Kerfoot¹, R. Rossmann², J. A. Robbins³

¹Lake Superior Ecosystem Research Center and Department of Biological Sciences, 1400 Townsend Drive, Michigan Technological University, Houghton, MI 49931; ²U.S. Environmental Protection Agency, Large Lakes Research Station, 9311 Groh Road, Grosse Ile, MI 48138; ³NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, Michigan 48105

Total copper flux to Lake Superior averages 5.0±2.5 µg cm^-2 yr^-1 (mean±95%CL), whereas total mercury flux averages 7.3±4.8 ng cm^-2 yr^-1. These values are much higher than atmospheric inputs into regional remote lakes (Cu, 0.31-0.39 µg cm^-2 yr^-1; Hg, 1.0-1.3 ng cm^-2 yr^-1). High metal inventories are typical of coastal margins, simply because metals are contributed by shoreline anthropogenic sources and bedrock erosion, yet particles do not disperse evenly across the enormous expanses of Lake Superior. Copper inventories from NOAA/KITES cores around the Keweenaw region suggest an enriched halo surrounding the Peninsula. Moreover, copper, mercury and silver inventories are highly correlated and can be traced back to shoreline tailing piles, smelters, and parent ores. Elemental mercury occurs as a natural amalgam in native metal (copper, silver, gold) deposits and as an accompanying trace metal in copper- and silver-rich mineral deposits. Native copper stamp mills discharged at least 364 million metric tons of “stamp sand” tailings into waters, whereas native copper smelters refined five million metric tons of copper, liberating together at least 42 tons of mercury. We show that the Keweenaw situation is not unique geographically, as mineral-bound trace mercury is commonplace in U.S. and Canadian Greenstone Belts and of worldwide occurrence in gold, silver, copper and massive base metal ores.

Comprehensive evaluation of satellite-based chlorophyll a algorithms for Lake Superior

H. Li¹, J. W. Budd¹, S. A. Green²

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

In remote sensing, a simple, but useful, optical classification has evolved to distinguish open ocean (case 1) waters, where the optical properties are dominated by chlorophyll and covarying detrital pigments, and coastal ocean (case 2) waters, where chlorophyll, as well as other substances (e.g., gelbstoff, suspended sediments and bacteria) that do not covary with chlorophyll, affect the optical properties. In Lake Superior, the typical range of chlorophyll concentration of 0.2 to 1.5 ug L-1 might indicate case 1 optical classification; however, the influence of the other major absorbing species, i.e., chromophoric dissolved organic matter of terrigenous origin and suspended solids, makes the system very complex optically, necessitating a case 2 optical classification. Using published marine bio-optical retrieval algorithms, we evaluated nine empirical algorithms using in situ optical and discrete water samples collected during three field seasons on Lake Superior. The bio-optical retrieval algorithms overestimated chlorophyll concentrations by as much as 45:1. The presence of low concentrations of the three major absorbing species (i.e., sediment, chlorophyll and CDOM) in Lake Superior, make it difficult to separate and quantify the species individually. Here, we present the initial results of new bio-optical retrieval algorithm for Lake Superior based on a semi-analytical approach.

Linking sediment microbial activity with the abundance and community composition of coastal and profundal macroinvertebrates in Lake Superior

A. E. Maskey, M. Strand

Department of Biology, 1401 Presque Isle Ave., Northern Michigan University, Marquette, MI 49855

We sampled macroinvertebrates and measured CO2 efflux from coastal and profundal sediments (1.5 - 100m) to assess the relative importance of biotic and abiotic factors in shaping Lake Superior macroinvertebrate assemblages. Microbial respiration rates in shallow coastal sites were similar and varied seasonally. Respiration rates in deep profundal sediments were similar to those in shallow coastal sediments during mid-summer, but were much lower than coastal sediments by fall. Overall, microbial activity was lowest in mid-depth profundal sediments and highest at a harbor site warmed by power plant effluent water. Macroinvertebrate abundance was positively correlated with sediment microbial activity. This effect is most pronounced in oligochaete populations. Conversely, abundances of chironomid midges and amphipods were influenced more by depth than by sediment microbial activity. Littoral and mid-depth infaunal communities were dominated by vermiform taxa (midges, oligochaetes, and nematodes), while burrowing amphipods (Diporeia hoyi) and clams (Sphaeriidae) were the dominant detritivores in deep profundal sediments.

Turbulent mixing in western Lake Superior

B. D. May

Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55803

Temperature microstructure profiles obtained in western Lake Superior are used to estimate intensity of turbulent mixing. Data were obtained under a variety of conditions, from early spring (May) through late fall (December). Mixing intensity, characterized by vertical eddy diffusivity K, was found to vary significantly. There is a clear seasonal cycle with high rates of mixing during spring and fall with much weaker mixing during summer. The differences in diffusivity are related to variations in the stratification,

characterized by the buoyancy frequency N.

Late quaternary glacial history of the lower St. Louis River and estuary

K. P. Norton

School of Science, Penn State University at Erie, Station Road, Erie, PA 16563

The morphology of the Lower St. Louis River and its estuary with Lake Superior is the product of Late Quaternary glaciation and glacial retreat. Volcanics from the failed Proterozoic rifting of the Lake Superior region were further scoured by Pleistocene glacial flow and helped to form the Superior Basin. The St. Louis River most likely began life in the Late Pleistocene as a drainage channel of Glacial Lake Upham 1. Sedimentation in Glacial Lake Duluth built up the clays, sands, and gravels exposed in the estuary and the glacial lake plains to the south. The final retreat of the Superior Lobe caused the draining of Glacial Lake Duluth and began a time of extensive erosion in the region. Glacial isostatic rebound caused rapid uplift, leaving multiple terraces and abandoned meanders along the river. ¹⁴C dates were obtained from organic material in abandoned meanders. The dates and total river downcutting indicate that erosion was initially fast, but slowed to approximately 30 cm per century. Following the final retreat of the Superior Lobe from the Superior Basin, sedimentation and erosion in the lower river and estuary has been controlled by fluctuations in lake level and erosion rates in the upper St. Louis River watershed. Late Holocene lake level fluctuations, Nipissing highstand and Sault lowstand, are recorded in the subsurface stratigraphy of the estuary.

Spatial and temporal distribution of zooplankton in Lake Superior's Keweenaw Peninsula region

D. J. Osterberg¹, J. W. Budd²

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

The study of the spatial distributions of populations is essential to gaining an understanding of the influence of environmental forcing factors on the trophic dynamics of a system. In aquatic ecosystems, zooplankton populations fluctuate in response to a variety of physical, chemical, and biological stimuli (e.g. thermal regime and water movements, limiting nutrients, competitive and predatory interactions). However, it has hitherto been difficult to sample and describe the geographical distribution and seasonal dynamics of planktonic communities due to their extreme spatial heterogeneity. Our study utilized an Optical Plankton Counter (OPC) to document the spatial and temporal transformation processes of the lower trophic level food web along the northwest coast of Lake Superior's Keewenaw Peninsula. Three transects were visited intermittently from April through October 2000, with routine sampling consisting of vertical OPC/CTD profiles, as well as circular tows of Clarke-Bumpus nets to obtain quantitative zooplankton samples for validation of the OPC data. Meso-scale dynamics were monitored through the development of two-dimensional images of the physical and biological structure of the system. Analyses will concentrate on identifying relationships between the observed phenomena and zooplankton dynamics, which will further our understanding of the relative importance of physical and biological factors in the control of ecosystem structure in Lake Superior.

Physical processes governing transport within Superior's Keweenaw Current

E. A. Ralph¹, H. J. Niebauer², J. H. Churchill³

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

The Keweenaw Current is a vigorous coastal jet that serves as transport mechanism between the western and eastern basins of Lake Superior. Time series of currents and temperatures were collected between May 1998 and May 2001 and provide the first measurements on annual to interannual time scales of its transport. The mean volume transport through the Eagle Harbor section was approximately 100 milli-Sverdrups. The net volume over the three-year experiment was approximately equivalent to the entire volume of Lake Superior. Transports were largest during the winter months (which were primarily ice-free during the KITES study) with barotropic current speeds reaching 85 cm/sec. Spring and mid-summer transports are similar in magnitude to transports measured in 1972 and 1973. The mean transport is primarily barotopic and appears to be due to cross-lake surface pressure gradients that are established by the zonal winds crossing the basin.

Status of the amphipod Diporeia spp. in Lake Superior, 1994-2000

J. V. Scharold¹, S. L. Lozano²

¹U.S. Environmental Protection Agency, Mid-Continent Ecology Division, 6201 Congdon Blvd., Duluth, MN 55804; ²NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105

The amphipod Diporeia spp. is the dominant component of the Great Lakes benthic macroinvertebrate fauna in terms of both numbers and biomass, and plays an important role in the ecosystem. The Great Lakes Water Quality Agreement calls for the use of Diporeia as an indicator of ecological condition, with a goal of 220-320^.m^-2 at depths less than 100 m and 30-160^.m^-2 at greater depths. Recent studies have revealed drastic declines in Diporeia populations in the lower Great Lakes, but little information is available on abundance of benthic macroinvertebrates in Lake Superior. During 1994-2000, the US EPA Mid-Continent Ecology Division conducted a series of benthic macroinvertebrate surveys in Lake Superior to support development of ecological indicators and monitoring designs. A probability based survey of 27 sites representing the U.S. nearshore waters of Lake Superior was conducted in 1994. During 1995-1998 a subset of 11 of these nearshore, non-depositional sites, plus 6 sites from major depositional basins, in the western half of the lake were revisited yearly to examine variability. The original 27 sites were sampled again in 2000. In 1994, nearshore Diporeia abundance ranged from 550 to 5500^.m^-2, and all sites met or exceeded the ecosystem objective. In 2000, abundance ranged from less than 10 to 2800^.m^-2, and 11% of sites did not meet the objective. These sites were located in the eastern half of the lake. Examination of yearly abundance data in western Lake Superior did not reveal a significant trend at nearshore or offshore sites. This abstract does not necessarily reflect US EPA policy.

Daphnia bioassay: testing the Keweenaw Peninsula waters for acute toxic effects

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

Elevated concentrations of dissolved copper in the Keweenaw Peninsula region of Lake Superior have persisted more than one century during active copper mining in the area. In this study, we tested if (1) copper concentrations near shore are sufficient to reduce survivorship of zooplankters and whether (2) zooplankton grown at the increased copper concentrations exhibit higher resistance to copper toxicity. Ultra clean technique (Nriagu et al., 1993) was used for water sampling and analysis. Field samples were collected from both surface and bottom at 12 different sites, including two stations in Gay tailing ponds, two in Torch Lake, two in Portage Lake, and six in Lake Superior (near Freda-Redridge, near North Entry, and near Gay). Dissolved copper concentrations in the samples ranged from 0.7 to 219 µg Cu l-1. We used 72-hour acute toxicity tests with Daphnia magna neonates in accordance with testing conditions prescribed by both international (OECD) and national standard methods (ISO, USEPA, ASTM). Experimental animals from the same clone were acclimated to two different synthetic mediums (copper-free or 27 µg l-1) prior to testing. As multiple generations of Daphnia were grown successfully under the above conditions, we assume that acclimation was complete. Animals showed rather good resistance to dissolved Cu concentrations within 0.72-27 µg l-1, though the survivorship of non-acclimated animals was lower compared to the survival of Cu-acclimated animals. Both sets of Daphnia showed 100% mortality after 12-h exposure to the highest Cu concentration tested, i.e. 219 µg l-1 (Gay stamp pond-11) that was much above levels potentially lethal for Daphnia (7-90 µg l-1). The major finding of this study is that the Daphnia acclimated to the copper concentration of 27 µg l-1, showed significantly higher resistance at 61 µg Cu l-1 (Gay stamp pond-3) than non-acclimated animals. This difference in resistance may be related to the increased metallothionien production induced by copper present in culture medium. More research is needed to clarify if metallothionien production in zooplankton can be used as a biomarker for monitoring trace element contamination.

Spectral irradiance and backscattering measurements in Lake Superior

A. Vodacek

Center for Imaging Science, 54 Lomb Memorial Dr, Rochester Institute of Technology, Rochester, NY 14623

Spectral measurements across the visible spectrum, at ~0.45 nm resolution, of irradiance, net vertical irradiance, and scalar irradiance were acquired at a number of stations along the Keweenaw Peninsula in Lake Superior. The scalar and net irradiance data were analyzed to obtain the total spectral absorption coefficient. Water collected at the stations was examined using standard spectrophotometric methods for particle absorption and CDOM absorption. Two channel backscattering measurements were made in situ. The sum of particle absorption, CDOM absorption and water absorption compared well with the radiometric determination of total absorption.

Satellite-based chlorophyll and turbidity estimates using SeaWiFS (Sea-Viewing Wide Field-of-View Sensor) imagery of Lake Superior

D. S. Warrington¹, J. W. Budd¹, R. P. Stumpf², S. A. Green³

¹Department of Geological Engineering & Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; ²NOAA National Ocean Service, Center for Coastal Monitoring and Assessment, N/SCI1 rm 9115, 1305 East West Highway, Silver Spring, MD 20910; ³Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931

Cross-margin transport processes in the coastal margins of Lake Superior were studied using satellite-based chlorophyll and turbidity maps from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS). We used remote sensing reflectance at 555 nm to estimate suspended solids concentrations, while chlorophyll concentrations were obtained from an empirically based algorithm that is a ratio of bands 3 (490 nm) and 5 (555 nm). Analysis of Advanced Very High Resolution Radiometer (AVHRR) lake surface temperature (LST) imagery, provided ancillary information about the location of physical fronts in relation to sediment concentrations and chlorophyll biomass. Validation of SeaWiFS chlorophyll indicate a linear fit of the data with R2 values of 0.90 in Lake Superior; however, satellite-based chlorophyll was overestimated by a factor of 3:1 in Lake Superior, indicating that oceanic chlorophyll algorithms won't suffice for Lake Superior. Work is ongoing to develop a chlorophyll bio-optical retrieval algorithm for Lake Superior (see poster by Li et al., 2002). Time series satellite images of Lake Superior in 1998 and 1999, indicate a productive southern coastal corridor from Duluth Harbor to the tip of the Keweenaw Peninsula during spring and summer months (May to August). Images obtained during the unstratified period from November to mid-April revealed a persistent sediment plume in the Ontonagon River region during both years. Cross-margin transport of materials at the tip of the Keweenaw Peninsula was dependent on wind direction, with evidence of materials being broadcast northward, eastward and southeastward depending on prevailing winds.