GLERL Publication Abstracts: FY 2002

AGY, M. A. Changes in the nearshore and offshore zooplankton communities of southeastern Lake Michigan. Master’s Thesis, University of Michigan, School of Natural Resources and Environment, Ann Arbor, MI, 52 pp. (2001).

Zooplankton populations in southeastern Lake Michigan were analyzed across both space and time by examining nearshore to offshore collections on approximately a monthly basis from 1998through 2000. Zooplankton density and biomass were significantly different among sites during all seasons, with differences more prevalent during spring and summer. Twice during the study, there was an increase in the proportion of small-bodied zooplankton. In fall 1998, there was a decrease in calanoid populations and subsequent replacement by smaller-bodied cyclopoids. Specifically, the number of Diaptomus ashlandi declined by over 50% between winter 1998 and winter 1999 at all sites. Changes in calanoid populations coincided with a strong year-class of alewives in 1998. A shift to smaller species of Ciadocera also occurred at both of the deeper sites between 1999 and 2000. In summer 2000, the smaller Bosmina longirostris exhibited a two-fold increase in abundance relative to 1999, and Daphnia galeata mendotae decreased from over 2400 x m-3 in summer 1999 to less than 200 x m-3 in 2000. Both the low densities of Daphnia and the inshore-offshore patterns of cladocerans observed in this study were consistent with sizeselective predation by fish. A comparison between 1998-2000 data with 1970s data showed significant decreases in zooplankton density and biomass in southeastern Lake Michigan. In summer and fall, zooplankton biomass was three to five times lower in the nearshore region during 1998-2000 relative to the 1970s and two to four times lower in the mid-depth region. Decreases were most likely due to reduced food availability caused by declines in both phosphorus concentrations and phytoplankton abundance nearshore. Predation and competition from exotic species may have also been responsible for longterm changes in zooplankton populations.

ASSEL, R. A., and L. R. HERCHE. Coherence of long-term lake ice records. Verh. Internat. Verein. Limnol. 27:2789-2792 (2000).

Lake ice records are important in studies of climate (Assel and Robertson 1995) and aquatic ecosystems (Magnuson et al. 1997). Further analysis of historical lake ice records is needed to improve knowledge of global cryospheric trends (Fitzharris 1996). An International workshop on Lake Ice and Climate was held at the University of Wisconsin in 1996 (Magnuson et al. 2000) with the general goal of establishing a lake ice database and using it to analyze and interpret long-term ice data for their climatic and ecological content. The analysis described here is made under the auspices of an international "Lake Ice analysis Group" (LIG) established at that workshop. In this paper we present a preliminary analysis of 1) variations of long-term average ice-on, ice-off, and ice duration with latitude, and 2) an index of the coherence of ice event dates among five sites over the Northern Hemisphere with relatively continuous records from 1850 to 1995. Our objective is to provide information useful for the assessment and analysis of climate variability, cl imate change, and aquatic systems.

ASSEL, R. A., D. C. NORTON, and K. C. CRONK. A Great Lakes ice cover digital data set for winters 1973-2000. NOAA Technical Memorandum GLERL-121, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 45 pp. (2002).

A 28-winter digital ice cover data set consisting of 1122 ice charts was established for the Great Lakes. Data reduction and quality control procedures are described in Norton et al. (2000). The data are available in ARC/INFO export and ASCII grid formats. Three types of ice attribute data are given: ice concentration class (the fraction of a unit of surface area covered by ice), ice stage class (range of ice thicknesses), and ice form class (size of ice floes). Ice attribute data coding conventions are described and discussed. The temporal and spatial distribution of the ice chart dates and ice attribute data are summarized in a table and in graphs. Metadata is provided as appendices.

BELETSKY, D. Modeling wind-driven circulation in Lake Ladoga. Boreal Environment Research 6:307-316 (2001).

The goal of this paper is to present circulation patterns in Lake Ladoga occurring during episodes of strong wind. Hydrodynamics of episodic events are studied with a three-dimensional barotropic numerical model. Model results are presented for a variety of wind directions and, therefore, can be used for analysis of various biogeochemical data. As an illustration, an analysis of sediment distribution in Lake Ladoga is presented. It is suggested that location of maximum sediment deposition in southeastern Lake Ladoga is due to sediment transport during episodes of strong northwesterly winds. These events generate significant waves in southern Lake Ladoga, causing sedment resuspension and subsequent offshore advection and dsposition.

Bogdan, J. J., J. W. Budd, B. J. EADIE, and K. C. Hornbuckle. The effect of a large resuspension event in southern Lake Michigan on the short-term cycling of organic contaminants. Journal of Great Lakes Research 28(3):338-351 (2002).

In January and March, 1998, a series of intense, northerly wind-driven storms suspended sediment over the entire coastline of the southern basin of Lake Michigan. The effect of large scale resuspension on organic contaminant cycling was investigated using a two-pronged sample collection strategy that included analysis of settling sediment trap material and discrete air and water samples collected before and after a major resuspension event. It was found that major resuspension events result in a large flux of contaminants. For example, 6.2 ng/cm2 �PCB (sum of 89 congener peaks) and 175 ng/cm2 �PAHs (sum of 31 compounds) fell through the water column in the southern basin between November and May but almost half of that occurred in the month of March after a series of intense storms induced a large-scale resuspension event in that month. Assuming the concentration of contaminants in settling sediments is similar throughout the basin, the March event brought ~400 kg of �PCBs and -13,000 kg PAHs into the water column. Furthermore, the data indicate that concentrations of dissolved phase PCB and �PAHs declined significantly (_ = 0.05) after the event and after resuspended sediment had settled from the surface waters. As a result of the depressed dissolved concentrations at the surface, the potential for gas-phase input to the lake increases on the southwestern coastal region near Chicago, IL and Gary, IN. The potential input of gas-phase contaminants was 8 kg for �PCBs and 2,200 kg for �PAHs over the 40-day lifetime of the nearshore event.

BRANDT, S. B., D. M. MASON, M. J. McCORMICK, B. M. LOFGREN, T. S. HUNTER, and J. A. TYLER. Climate change: implications for fish growth performance in the Great Lakes. American Fisheries Society Symposium 32:61-76 (2002).

Climate change will alter the thermal regime in the Great Lakes, including the onset, duration, and structure of thermal stratification. Such changes may, in turn, affect spatial distributions of planktivores, rates of food web interactions, and growth rate potential of fishes. We use predicted changes in water temperatures for the years 2030 and 2090 to evaluate growth rate potential of lake trout Salvelinus namaycush, chinook salmon Oncorhynchus tshawytscha, and striped bass Morone saxatilis in Lake Michigan. Changes in the timing and extent of thermal stratification changed the predicted distributions of prey fish and the spatio-temporal patterns of growth potential. Overall, growth rate potential of all piscivores increased under climate warming simulations. For chinook salmon, an assumed 15% reduction of prey abundances reduced mean growth rate potential by 9%. A comparison of measured temperatures for 1996 and 1998 showed that current warm years (1998) are similar to mean conditions predicted between years 2030 and 2090. We suggest that studies of interannual variations in food web dynamics may provide insights into the potential impact of climate on fishes.

Bundy, M. H., and H. A. VANDERPLOEG. Detection and capture of inert particles by calanoid copepods: the role of the feeding current. Journal of Plankton Research 24(3):215-223 (2002).

Although there is a scarcity of supporting empirical evidence, it has long been suspected that calanoid copepods use mechanoreception to detect the presence and location of potential prey items entrained in the feeding current. In this study, we document the first observations showing a freely swimming calanoid copepod, Skistodiaptomus oregonensis, attacking prey-sized, non-motile, inert particles entrained in the feeding current before the particles contact the copepod's sensory appendages. Feeding current geometry, fluid velocities and associated behaviours that characterize these interactions are described. The results of this study show how copepod swimming behaviour, coupled with a low-velocity feeding current, not only increases copepod encounter rates with inert prey by increasing direct contact rates, but also increases the probability of detecting and capturing remotely located prey that have well-developed escape responses. In turbulent regimes, a far-reaching, low-velocity feeding current should increase encounter rates, but only if coupled with behaviours that quickly minimize separation distances once prey is detected.

Carrick, H. J., A. Padmanabha, L. Weaver, G. L. FAHNENSTIEL, and C. R. Goldman. Importance of the microbial food web in large lakes (USA). Verh. Internat. Verin. Limnol. 27:3170-3175 (2000).

The traditional view of food web structure categorizes all organisms within an ecosystem into one of several feeding guilds (i.e. primary producers, decomposers, herbivores, and consumers), where energy is transferred from one guild to the next (Lindeman 1942). The biomass of these guilds decreases geometrically with successive trophic levels to form a pyramid, with a large biomass of plants at the base (Elton 1927). Metabolic inefficiencies, such as excretion and sloppy feeding, produce significant losses at each trophic level, with the greatest loss at the highest trophic level (Rich & Wetzel 1978). Deviations from this paradigm have been described for planktonic communities in the ocean, where the biomass of heterotrophic organisms can rival phytoplankton, thus indicating a tight coupling between plants and animals (e.g. Odum 1971). However, our view of food web structure in aquatic ecosystems is being further revised based upon the knowledge that small heterotrophic organisms are more quantitatively important than previously thought (Azam et al. 1983). Recent technological advances now allow more accurate censusing of natural microbial populations, as well as measurement of their high rates of metabolic activity (Kemp et al. 1993). Furthermore, large concentrations of non-living pools of organic carbon and detritus are common features of aquatic ecosystems, and appear to be responsible for fueling a portion of this high microbial metabolic activity (e.g. Ducklow 1994). In this way, organic wastes produced at all levels of the food chain are available to support significant levels of heterotrophic production, that can often rival rates of primary production (e.g. Scavia 1988).

CARTER, G. S. Environmental assessment of the benthic macroinvertebrate community of Muskegon Lake, MI 1999 and evaluation of changes since 1972. Masters Thesis, University of Michigan, School of Natural Resources and Environment, Ann Arbor, MI, 67 pp. (2002).

Benthic macroinvertebrate community composition is widely considered an effective tool for evaluating environmental conditions. In fall 1999, 27 sites were sampled for benthic macroinvertebrates to assess the habitat quality of Muskegon Lake, a drowned river mouth lake connected to eastern Lake Michigan. The oligochaete-based, trophic condition index indicated the lake was meso-eutrophic to eutrophic, and the community was largely dominated by Aulodriluspigueti and Quistadrilus multisetosus. Cluster analysis of the benthic community was used to assess distributions relative to known areas of environmental degradation; four groups of sites were discriminated. The site group closest to the river (the southeastern end of the lake) consisted of several species indicative of enriched conditions, likely due to its proximity to the river. The two site groups on the western end were similar in community composition and reflected similarities in depth. Despite similarities, the western-most group had relatively higher mean densities for total benthos, oligochaetes, total Aulodrilus spp., A. pigueti, Gammarus sp., chironomids, and Chironomus sp. than the more central group in the western part of the lake; suggesting the western group may be more productive. The community at the HA site group (central eastern area near the southern shore) indicated better environmental conditions existed at these sites than the other three groups; however, heavy-metal toxicity was found that might have affected benthic composition. Comparisons between benthic communities in 1972 and 1999 indicated broad changes in the community and environmental conditions since diversion of wastewater, which began in 1973. Increases in total benthos, oligochaetes, chironomids, Gammarus sp., and Pisidium sp., coupled with increased Shannon-Weaver diversity, number of taxa, and decreased proportion of oligochaetes, were indicative of generally improved environmental conditions. Changes in the benthic community likely reflected the diversion of wastewater rather than colonization of the lake by Dreissena polymorpha.

Chen, C., R. Ji, D. J. SCHWAB, D. BELETSKY, G. L. FAHNENSTIEL, M. Jiang, T. H. JOHENGEN, H. A. VANDERPLOEG, B. J. EADIE, J. W. Budd, M. H. Bundy, W. Gardner, J. Cotner, and P. Lavrentyev. A model study of the coupled biological and physical dynamics in Lake Michigan. Ecological Modeling 152:145-168 (2002).

A coupled physical and biological model was developed for Lake Michigan. The physical model was the Princeton ocean model (POM) driven directly by observed winds and net surface heat flux. The biological model was an eight-component, phosphorus-limited, lower trophic level food web model, which included phosphate and silicate for nutrients, diatoms and non-diatoms for dominant phytoplankton species, copepods and protozoa for dominant zooplankton species, bacteria and detritus. Driven by observed meteorological forcings, a 1-D modeling eeriment showed a controlling of physical processes on the seasonal variation of biological variables in Lake Michigan: diatoms grew significantly in the subsurface region in early summer as stratification developed and then decayed rapidly in the surface mixed layer when silicate supplied from the deep stratified region was reduced as a result of the formation of the thermocline. The non-diatoms subsequently grew in mid and late summer under a limited-phosphate environment and then declined in the fall and winter as a result of the nutrient consumption in the upper eutrophic layer, limitation of nutrients supplied from the deep region and meteorological cooling and wind mixing. The flux estimates suggested that the microbial loop had a significant contribution in the growth of microzooplankton and hence, to the lower-trophic level food web system. The model results agreed with observations, suggesting that the model was robust to capture the basic seasonal variation of the ecosystem in Lake Michigan.

CROLEY, T. E. II. Evaluation of NOAA climate outlooks in extended Great Lakes water levels forecast. Proceedings, Conference on Water Resources Planning and Management, Roanoke, VA, May 19-22, 2002. Environmental Water Resources Institute, American Society of Civil Engineers, Washington, DC, 10 pp. (2002).

The Great Lakes Environmental Research Laboratory (GLERL) simulates time series of daily Great Lakes hydrology by first estimating initial hydrological conditions and then using a daily meteorology time series (scenario) taken from the historical record. They do this to make a deterministic hydrology "forecast" (including lake levels) from a representative meteorology scenario. GLERL repeats this for other segments of the historical record in an "operational hydrology" or "ensemble" approach in their Advanced Hydrologic Prediction System (AHPS). The resulting set of lake level scenarios serves as a statistical "sample" for inferring probabilistic lake levels outlooks that properly consider antecedent hydrological conditions. GLERL does this every day to produce six-month outlooks. Meanwhile, the National Oceanic and Atmospheric Administration's Climate Prediction Center publishes each month multiple long-lead probabilistic meteorology outlooks. GLERL transforms these meteorological outlooks into equations for sample weights and solves them simultaneoisly. Their AHPS methodology weights their samples of six-month lake levels scenarios each day to include the effects of these meteorology predictions. GLERL simulated both deterministic and probabilistic lake level outlooks over 1995-2000 without the use of antecedent conditions or meteorology predictions and then added them into the simulation to assess the value of each in making the forecast.

CROLEY, T. E. II. Large basin runoff model. Chapter 17. In Mathematical Models of Large Watershed Hydrology, V. Singh, D. Frevert and S. Meyer Eds., Water Resources Publications, Highlands Ranch, CO, pp. 717-770 (2002).

Large-scale watershed models are required to estimate basin runoff to the Great Lakes and other large-basin applications for use in long-term routing determinations, water resource operation decisions, operational hydrology studies, and long-term forecasting. Data availability over large areas, large-basin applicability, computation requirements, and model application costs often preclude the use of detailed watershed models, designed for small scales, for large-scale applications. An interdependent tank-cascade model is described that uses a mass balance coupled with linear reservoir concepts. It is physically based and uses climatological considerations not possible for small watersheds; analytical solutions are employed to bypass numerical inaccuracies. Snowmelt and net supply computations are separable from the mass balance determinations and are based on simple degree-day empiricism. Partial area concepts are used to determine infiltration and surface runoff. Losses are determined from joint consideration of available energy for actual and potential evapotranspiration and of available moisture in the soil horizons by using climatological concepts. Heuristic calibration procedures are described that give insight into the use of the model. The model is applied in example watersheds and it and its calibration are evaluated. Source code, executable programs, and all examples are available in appendices and over the World Wide Web.

CROLEY, T. E. II, and R. A. ASSEL. Great Lakes evaporation model sensitivities and errors. Proceedings, Second Federal Interagency Hydrologic Modeling Conference, Subcommittee on Hydrology of the Interagency Advisory Committee on Water Data, Las Vegas, NV, July 28-August 1, 2002. 12 pp. (2002).

The Great Lakes Environmental Research Laboratory developed a lumped-parameter model of evaporation and thermodynamic fluxes for the Great Lakes (Croley, 1994). It is based on a point energy balance at the lake's surface (Croley, 1989) and on a one-dimensional (vertical) superposition of lake heat storage (Croley,1992). Ice formation and loss is coupled also to lake thermodynamics and heat stroage (Croley and Assel, 1994). The model is calibrated to observed daily water surface temperatures and ice cover to apply it in a particular setting. Initialization of the model corresponds to identifying water surface temperature, heat storage, and ice cover from field conditions or from previous model runs. The model is used with boundary meteorology conditions (daily time series of air temperature, wind speed, cloud cover, and humiidy) to simulate heat storage and water temperature profiles in a lake from initial conditions forward.

CROLEY, T. E. II, and C. He. Great Lakes large basin runoff model. Proceedings, Second Federal Interagency Hydrologic Modeling Conference, Subcommittee on Hydrology of the Interagency Advisory Committee on Water Data, Las Vegas, NV, July 28-August 1, 2002. 12 pp. (2002).

Agencies concerned with managing water resources of large watersheds, particularly over large time intervals, must be able to assess expected hydrology of an area. Large-scale watershed models are required to estimate basin runoff to the Great Lakes for use in long-term routing determinations, water resource operation decisions, operational hydrology studies, and long-term forecasting. These models must be designed as continuous-time flow representations for assessing water resource questions over the long term (as opposed to flood prediction over the short term). The models must satisfy limited-data requirements, mandated by data availability for large areas such as the Great Lake basins. Allowable data inputs are limited to daily precipitation and air temperature. Also allowed are any data that can be abstracted easily from available maps or climatic summaries. Model concepts must be physically based, so that understanding of watershed response to natural forces is facilitated, and so the models are economical to use. The Great Lakes Environmental Research Laboratory (GLERL) built its Large Basin Runoff Model (LBRM) for modeling river systems 'within the Laurentian Great Lakes Basin. This inter-dependent tank-cascade model is a lumped-parameter model of runoff at the mouth of a water-shed and has been tested on the 121 watersheds of the Great Lakes. It was developed from large-scale (climatological) concepts and designed for weekly or monthly volumes of runoff. The model consists of water and heat balances, as do other water-budgeting models, but with alternative physical interpretations given to its components. The model is physically based and uses climatological considerations not possible with small watersheds. In particular, evapotranspiration losses for large areas may now be considered as a function of readily available data. Analytical solutions are used instead of numerical solutions to bypass associated numerical error. The model is described and applied in an example watershed.

EADIE, B. J., D. J. SCHWAB, T. H. JOHENGEN, P. J. LAVRENTYEV, G. S. MILLER, R. E. Holland, G. A. LESHKEVICH, M. B. LANSING, N. R. MOREHEAD, J. A. ROBBINS, N. HAWLEY, D. N. Edgington, and P. L. VAN HOOF. Particle transport, nutrient cycling, and algal community structure associated with a major winter-spring sediment resuspension event in southern Lake Michigan. Journal of Great Lakes Research 28(3):324-337 (2002).

Over the past decade, intermittent satellite imagery revealed the presence of an extensive plume of resuspended sediments in late winter-early spring with a clear offshore projection coinciding with the region of maximum sediment accumulation in the lake. The large scale of the plume implied that this process was important in sediment, and associated constituent, cycling and transport, but it had never been sampled due to severe conditions. The onset of the 1996 event coincided with a major March storm. Within a few days the plume was approximately, 10 km wide and over 300 km in length, implying that the source of the reflective materials was widely distributed. An estimate of the total mass of resuspended sediment, 12 days after the storm, was similar to the annual external load of (sand-free) particulate material to the southern basin. The high turbidity plume persisted for over a month, progressing northward along the eastern shore with a major offshore transport feature. Sediment traps within this feature recorded a major mass flux event. The plume was sampled on two occasions and was found to contain 5 to 10 times as much suspended matter as open-lake locations outside the visible plume. Total particulate phosphorus was high within the plume making this episodic process important in sediment-water exchange. The diatom community structure within the plume was significantly different from outside the plume and was characteristic of more eutrophic waters. Abundance of non-diatom phytoplankton and microbial food web organisms were highest at the plume edge. The episodic nature of this process makes it difficult to sample, but the scale makes it important in designing monitoring programs and mass-balance modeling efforts.

Fritz, H. M., and P. C. LIU. An application of wavelet transform analysis to landslide-generated impulse waves. Proceedings, Fourth International Symposium Waves 2001, San Francisco, CA, September 2-6, 2001. American Society of Civil Engineers, pp. 1477-1486 (2001).

This paper presents an analysis of applying continuous wavelet transform spectrumanalysis to the results of laboratory measurement of landslide-generated impulse waves. As the measured results are understandably unsteady, nonlinear, and non-stationary, the application of time-localized wavelet transform analysis is shown to be a suitable as well as useful approach. the analysis on correlating the time-frequency wavelet spectrum configurations in connection with the ambient parameters that drive the impulse wave process, with respect to time and space, leads to interesting and stimulating insights not previously known.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Aquatic Invasive Species (AIS) and the Great Lakes: Simple Questions, Complex Answers. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2002).

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Exotic, invasive, alien, nonindigenous, or nuisance species: No matter what you call them, they're a growing problem. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2002).

Human activities are profoundly affecting the earth's surface. Human population growth has been accompanied by a variety of stresses on natural ecosystems, including the unintentional introduction of various nonindigenous invasive species.

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Met Stations and Web Cams. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2002).

GREAT LAKES ENVIRONMENTAL RESEARCH LABORATORY. Selected projects of GLERL's Marine Instrumentation Laboratory. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2002).

The Plankton Survey System, Lake Michigan Wireless Environmental Observatory, and the Sequential Sediment Sampler are described.

Hancock, G., D. N. Edgington, J. A. ROBBINS, J. N. Smith, G. Brunskill, and J. Pfitzner. Workshop on radiological techniques in sedimentation studies: methods and applications. In Environmental Changes and Radioactive Tracers. Proceedings of the South Pacific Environmental Radioactivity Association (SPERA) 2002, J.M. Fernandez and R. Fichez (Eds.), IRD Editions, Paris, France, pp. 232-251 (2002).

The following document summarizes the important issues raised during the 3 hour discussion period of the Workshop on "Radiological Techniques in Sedimentation Studies", held on June 22, 2000. The document includes contributions from the above authors summarizing, and in some cases illustrating important features of the discussion. The discussion issues covered: (1) problems associated with the use of "mapping" algorithms, particulary CRS, to give unsubstantiated 210PB "dates", (2) the necessity to validate 210Pb deposition histories, (3) the trend in research jourjnals to publish 210Pb chronologies with supporting data, (4) the effect of drainagae basin residence times on fallout nuclide sediment profiles, and (5) the low activity of fallout tracers in the southern hemisphere, and the implications for sample core collection, analysis, and geochronological usage.

He, C., and T. E. CROLEY II. A development framework for two-dimensional large basin operational hydrologic models. Proceedings, Second Federal Interagency Hydrologic Modeling Conference, subcommittee on Hydrology of the Interagency Advisory Committee on Water Data, Las Vegas, NV, July 28-August 1, 2002. 12 pp. (2002).

Large-scale operational hydrologic models ae essential tools in support of multiple water resource applications such as flood control, navigation, irrigation,and habitat management, etc. at the regional or continental scales. These models, unlike micro scale watershed models, are defined over large area (>103 km2) and long time scales (typically for use over monthly and annual or longer time scales at a daily interval). Often constrained by l imited data availability, computational requirements,and model application costs over larger areas, large-scale models must have few parameters, use easily accessible meteorolgic and hydrologic databases, and be user-friendly. Horberger and Bioyer (1995) found that better representation of spatial and temporall variability and appropriate parameterization of hydrologic processes have become critical in recent years. They reviewed recent advances in watershed modeling pertinent to use of Geographic Information Systems (GIS), remotely sensed data, and environmental tracers for micro scale modeling. This paper addresses the needs and challenges of large-scale operational hydrologic models through the development of a modeling framework. It focuses on advances in parameterization of the infiltration and evapotranspiration processes and onthe representation of large-scale spatial variability.

Holcombe, T. L., J. S. Warren, D. F. REID, W. T. Virden, and D. L. Divins. Small rimmed depression in Lake Ontario: An impact crater? Journal of Great Lakes Research 27(4):510-517 (2001).

Detailed bathymetry of Lake Ontario reveals a small circular feature and adjoining SW-trending ridge associated with a small topographic high identified as Charity Shoal on nautical charts. The feature consists of a circular basin 1,000 m in diameter and 19+ m deep, completely surrounded by a low-relief rim that rises to within 5 m of the water surface over much of its extent. A N53E tapering ridge is contiguous with the feature and extends southwestward. Bedrock consists of middle Ordovician limestones 100-150 m thick overlying rocks of Precambrian age. The limited information available suggests that the feature may be an extraterrestrial impact crater, but other origins such as sinkhole, volcanic cone, or kettle, are not ruled out. Time of formation is not known, but likely times include the Pleistocene when the area was exposed by glacial erosion, the middle Ordovician near the time of deposition of limestones, or the Cambro-Ordovician or Precambrian when erosion surfaces of this age were exposed. A subtle negative magnetic anomaly coincides with the feature and is consistent with an impact origin, though not positively diagnostic. Relief of the feature is low compared to that typical of an impact crater of this size. Glaciation may have diminished relief by eroding the rim and filling the central basin with drift. Verification as an impact crater will require detailed geophysical surveys and collection and analyses of samples from in and around the structure.

Holmes, C. W., J. A. ROBBINS, R. Halley, M. Bothner, M. Ten Brink, and M. Marot. Sediment dynamics of Florida Bay mud banks on a decadal time scale. Bulletins of American Paleontology 361:31-40 (2001).

Ecosystem management requires knowledge of environmental dynamics. If historical environmental records do not exist, other methods must be employed to obtain this information. A well-known geochemical procedure that supplies this type of data is the use of natural radioactive nuclides to "date" the timing of events. Of the many naturally occurring nuclides, 210Pb is the best suited for gauging the timing of episodes in Florida Bay. The age-depth relationships were calculated using the 210Pb method for thirty-five sites within Florida Bay. The ages were independently confirmed by comparing the distribution of known concentrations of atmospherically anthropogenic lead recorded in dated cores to similar data in an annually banded coral. Sediments in the western and northern fringe of Florida Bay are accumulating at ~0.3 cm/yr. a rate similar to that of sea level rise. In the north-central part of the bay, sediments are accumulating at a taster rate of ~1.0 cm/yr. The highest rate, >=2.0 cm/yr was measured in the northeastern pan of the bay on the bank between Pass and Lake Keys. The rapid rate of accumulation in the northeastern pan of the bay permits the deciphering of biological and geochemical changes with an accuracy of about two years. In contrast. the intermediate sediment rate in the central pan of the bay provides adequate age-depth for relationships deciphering the environmental record of the past 100 years.

Ji, R., C. Chen, J. W. Budd, D. J. SCHWAB, D. BELETSKY, G. L. FAHNENSTIEL, T. H. JOHENGEN, H. A. VANDERPLOEG, B. J. EADIE, J. Cotner, W. Gardner, and M. Bundy. Influences of suspended sediments on the ecosystem in Lake Michigan: A 3-D coupled bio-physical modeling experiment. Ecological Modeling 152:169-190 (2002).

The influence of suspended sediments on the Lake Michigan ecosystem was examined using a 3-dimensional (3-D) coupled biological and physical model developed by Chen et al. (part I). The model was driven by the realistic meteorological forces observed in March 1998, with daily inputs of suspended sediment concentration that were derived from temporally and spatially interpolated satellite imagery. The model results show the significant impact of a seasonally recurring coastal resuspension plume on the spatial and temporal variation of the nutrients and plankton in southern Lake Michigan. The plume-released nutrients played an essential role in maintaining the nutrient level in the lake. Although the growth of phytoplankton in the plume depended on the availability of nutrients and light, the offshore decrease in phytoplankton biomass still satisfied the Sverdrup's relationship. Cross-shore fluxes of nutrients and phytoplankton were controlled by episodic wind events with a period of 5-7 days: offshore during southward winds and onshore during northward winds. The flux estimates for biological variables suggest that the microbial food web is a key contributor to secondary production in southern Lake Michigan and the lower trophic level food web system could be dynamically divided into two decoupled loops: (1) detritus -bacteria-microzooplankton-large zooplankton; and (2) nutrient-phytoplankton-detritus. The model-predicted spatial distributions of nutrients and phytoplankton were in reasonable agreement with observations taken during the 1998 EEGLE interdisciplinary cruises, suggesting that the model was sufficiently robust to capture the basic characteristics of the Lake Michigan ecosystem during the plume event.

LANDRUM, P. F., M. L. GEDEON, G. A. Burton, M. S. Greenberg, and C. D. Rowland. Biological responses of Lumbriculus variegatus exposed to fluoranthene spiked sediment. Archives of Environmental Contamination and Toxicology 42:292-302 (2002).

Lumbriculus variegatus was used as a bioassay organism to examine the impact of the sediment-associated polycyclic aromatic hydrocarbon (PAH) fluoranthene on behavior, reproduction, and toxicokinetics. The number of worms increased between the beginning and end of the experiment at 59 g g-1 fluoranthene, but at the next higher treatment (108 g g-1) the number of worms found was lower and not different from the control.Worms exposed to 95 g g-1 also exhibited increased reproduction when fed a yeast-cerophyl-trout chow mixture. On a total biomass basis, only the 95 g g-1 exposure with food exhibited a statistically significant increase over the nonfed control. Evaluation of reproduction at the two highest treatments was compromised by a brief aeration failure 2 days before the end of the experiment. The behavioral responses were followed as changes in biological burial rate (sediment reworking rate) of a 137Cs-labeled marker layer. The biological burial rate increased toward a plateau as the concentration increased from the control (3.9 g g-1 dry weight total PAH) to 355 g g-1 dry weight fluoranthene in sediment. The aeration failure had minimal impact on the determination of reworking rate because all the data for the rate determination were collected prior to the aeration failure. Uptake and elimination rates declined with increasing treatment concentration across the range of fluoranthene concentrations, 59-355 g g-1 dry weight sediment. The disconnect between the increasing biological burial rates and the decreasing toxicokinetics rates with increasing exposure concentration demonstrates that the toxicokinetic processes are dominated by uptake and elimination to interstitial water. The bioaccumulation factor (concentration in the organisms on a wet weight basis divided by the concentration in sediment on a dry weight basis) ranged from 0.92 to 1.88 on day 10 and declined to a range of 0.52 to 0.99 on day 28 with the lowest value at the highest dose.

LANDRUM, P. F., and J. P. Meador. Is the body residue a useful dose metric for assessing toxicity? SETAC Globe May-June:32-34 (2002).

Clearly the toxicity of a compound depends on its concentration at the receptor site and the duration of site occupation. Aquatic toxicology made use of the concept that the dose at the receptor was proportional to the concentration in the organism which was in turn found to be proportional to the exposure concentrationwith aqueous exposures. The use of external exposure media as the dose metric was severely challenged by the presence of multiple routes of exposure and factors that alter contaminant bioavailability, e.g. s ediment exposures. This suggestion that body residue would serve as a useful dose metric was advocated by McCarty (1986) with the Critical Body Residue (CBR) concept linked to the concentration to cause 50% mortality in a population for non-polar, non-metabilized toxicants (McCarty 1990).

Lee, J.-H., P. F. LANDRUM, and C.-H. Koh. Prediction of time-dependent PAH toxicity in Hyalella azteca using a damage assessment model. Environmental Science and Technology 36:3131-3138 (2002).

A damage assessment model (DAM) was developed to describe and predict the toxicity time course for PAH in Hyalella azteca. The DAM assumes that death occurs when the cumulative damage reaches a critical point and was described by a combination of both first-order toxicokinetic and toxicodynamic models. In aqueous exposures, body residues increase in proportion to the water concentration. Damage is assumed to accumulate in proportion to the accumulated residue and damage recovery in proportion to the cumulative damage when damage is reversible. As a result, the toxicity time course, LC50(t), is determined by both a damage recovery rate and an elimination rate. The constant critical body residue (CBR) and the critical area under the curve (CAUC) models can be derived as two extreme cases from the DAM, and all three models were reanalyzed using a hazard modeling approach. As a result, the critical cumulative damage (DL) is the determinant of the concentration-time response relationship and not simply the CBR or the CAUC. Finally, from the DAM, two parameters, a damage recovery rate constant kr and the killing rate k, were estimated and found to be relatively constant for selected PAH.

Lee, J.-H., P. F. LANDRUM, and C.-H. Koh. Toxicokinetics and time-dependent PAH toxicity in the amphipod Hyalella azteca. Environmental Science and Technology 36:3124-3130 (2002).

The relationship between toxicokinetics and time-dependent PAH toxicity to Hyalella azteca was examined to test the constant critical body residue (CBR) model. A constant CBR model is based on the assumption that the body residue for 50% mortality is constant for each PAH across exposure times. With a constant CBR, kinetic parameters determined through kinetic experiments would be similar to those estimated from time series toxicity data. Time-dependent toxicity was investigated using three types of data: time series LC50 data, LT50(c), and CBR values measured at multiple exposure times for live and dead animals. Kinetic parameters were measured independently. The constant CBR model did not predict the PAH toxicity time course for H. azteca. Since a first-order kinetic model predicted the bioaccumulation of the parent PAH except for naphthalene, this result is not due to a failure to predict the internal dose (body residue). The influence of metabolites on toxicity was negligible except for naphthalene. The LC values at multiple exposure times decreased to an incipient lethal concentration after H. azteca reached steady state. Measured CBR values also decreased with increasing exposure time. Thus, the time course of PAH toxicity is determined not only bythe bioconcentration kinetics but also by the cumulative toxicity with increasing exposure time. Therefore, time-to-death or hazard models must be developed as a complement to toxicokinetic models to describe and predict the toxicity time course.

LESHKEVICH, G. A., and S. V. Nghiem. The 2002 Great Lakes Winter Experiment (GLAWEX 2002) three-dimensional mapping of the Great Lakes ice cover. Proceedings, NASA AirSAR Workshop, Pasadena, CA, March 4-6, 2002. NASA Jet Propulsion Laboratory, Pasadena, CA, 10 pp. (2002).

In his recommendations for Great Lakes ice research, (Marshall, 1966) concludes that "studies are needed to classify Great Lakes ice types, their distribution and drift during the winter, and the subtle changes in albedo and imagery which mark the gradual disintegration of the ice and the imminent breakup." Early investigations by various researchers were conducted to classify and categorize ice types and features (Chase, 1972; Bryan, 1975), to map ice distribution (McMilan and Forsyth, 1976; Leshkevich, 1976), and to monitor and attempt to forecast ice movement with remotely sensed data (Strong, 1973; McGinnis and Schneider, 1978; Rumer et al., 1979; Schneider et al., 1981). Most of the early research on Great Lakes ice cover was done by visual interpretation of satellite and other remotely sensed data (Rondy, 1971; Schertler et al., 1975; Wartha, 1977). Because of the size and extent of the Great Lakes and the variety of ice types found there, the timely and objective qualities inherent in computer processing of satellite data make it well suited for such studies. Moreover, the all-weather, day/night sensing capabilities of Synthetic Aperture Radar (SAR) make it well suited to the short daylight, cloud dominated winter conditions in the Great Lakes region.

LESHKEVICH, G. A., and S. V. Nghiem. Radar remote sensing of Great Lakes ice cover. Proceedings, 2002 IEEE International Geoscience and Remote Sensing Symposium and the 24th Canadian Symposium on Remote Sensing, Toronto, Canada, June 24-28, 2002. Institute of Electrical and Electronics Engineers, Inc., Piscataway, NJ, 1 pp. (2002).

Remote sensing of Great Lakes ice cover uses various classes of radars including scatterometer, polarimetric synthetic Aperture Radar (SAR), and interferometric SAR. Applications of radar mapping of Great Lakes ice cover includes marine resource management, lake fisheries and ecosystem studies, natural hazards such as ice jams and flooding, shipping and hydropower industries, and Great Lakes climatology. Satellite wide-swath scatterometers provide large areal coverage with high temporal resolution data to map Great Lakes ice cover. They compliment the high spatial but lower temporal resolution of satellite SAR data.

Lesht, B. M., and N. HAWLEY. Using wave statistics to drive a simple sediment transport model. Proceedings of the Fourth International Symposium on Waves 2001, San Francisco, CA, September 2-6, 2001. American Society of Civil Engineers, pp. 1366-1375 (2001).

Because both contaminant and nutrient cycles in the Laurentian Great Lakes depend on particle behavior and movement, sediment transport is a critical component of many of the water quality models being developed to understand and manage this important resource. To avoid complicated models that cannot be supported by the available field data, we have used observation-based, empirical analysis as the basis for developing methods of predicting sediment resuspension from relatively simple measurements of the surface wave field. Our modeling is based on data obtained from instrumented tripods designed to measure near-bottom hydrodynamic and sedimentological conditions for extended periods of time. Because of the long duration of the deployments, it usually is impractical to both sample and record the data at the high frequency that would be needed to resolve the effects of individual surface waves. Instead, we have used a system of burst sampling in which we sample the sensors at high frequency during a period of time that is repeated at tn interval appropriate for the deplyment duration. Rather than record the individual samples during the burst, we record only statistics obtained from the individual samples. Our results show that simple representations of the surface wave field obtained from the burst statistics can be used to model sediment transport in wave-dominated enviroments. We also show that once the model parameters are determined, the forcing wave conditions can be derived from other sources, including wind-driven wave models, with comparable success.

Lesht, B. M., J. R. Stroud, M. J. McCORMICK, G. L. FAHNENSTIEL, M. L. Stein, L. J. Welty, and G. A. LESHKEVICH. An event-driven phytoplankton bloom in southern Lake Michigan observed by satellite. Geophysical Research Letters 29(8):18-1 to 18-4 (2002).

Sea-viewing Wide field-of-view Sensor (SeaWiFS) images from June 1998 show a surprising early summer phytoplankton bloom in southern lake Michigan that accounted for approximately 25% of the lake's annual gross offshore algal primary production. By combining the satellite imagery with in situ measurements of water temperature and wind velocity, we show that the bloom was triggered by a brief wind event that was sufficient to cause substantial vertical mixing even though the lake was already stratified. We conclude that episodic events can have significant effects on the biological state of large lakes and should be included in biogeochemical process models.

LIU, P. C., and N. HAWLEY. Wave grouping characteristics in nearshore Great Lakes II. Ocean Engineering 29:1415-1425 (2002).

This is a sequel with extensive new data to Liu's (Liu, 2000a. Wave grouping characteristics in nearshore Great Lakes. Ocean Engineering 27, 1221-1230) exploratory study on wave grouping characteristics in the nearshore Great Lakes. We analyze recent GLERL time-series measurements recorded by pressure sensors deployed at four nearshore stations in southern Lake Michigan during 1998-1999. With the advantage of continued application of time-frequency wavelet spectrum analysis, the extensive new measurements substantially confirmed the effectiveness of the empirical characterization of wave grouping parameters defined in Liu. We show that a wave group is really the basic element for a detailed understanding of wave processes, in contrast to the conventional approach of using a frequency spectrum as the basic element, which depends on the recording length and requires the data to be stationary. While studying wave time-series alone does not really alleviate the vast intricacies of the wind wave processes, the embodiment of wave grouping as the predominant feature in the wind wave processes clearly represents a significant step forward toward sound conceptual advancement.

LIU, P. C., and N. Mori. Characterizing freak waves with wavelet transform analysis. Proceedings, Rogue Waves 2000, M. Alagnon, and G. A. Athanassoulis Eds., Brest, France, November 29-30, 2000. Ifremer, Brest, France, pp. 151-156 (2000).

This paper presents an analysis of a set of available freak wave measurements gathered from several periods of continuous wave recordings made in the Sea of Japan during 1986-1990 by the Ship Research Institute of Japan. The analysis provides an ideal opportunity to catch a glimpse of the incidence of freak waves. The results show that a well-defined freak wave can be readily identified from the wavelet spectrum where strong energy density in the spectrum is instantly surged and seemingly carried over to the high frequency components at the instant the freak wave occurs. Thus for a given freak wave, there appers a clear corresponding signature shown in the time-frequency wavelet spectrum. Since freak waves are primarily transient events occurring unexpectedly, wave transform analysis on continuous, long duration wave measurements clearly represents the most ideal approach to discern the localized characteristics of freak waves for further exploration.

LOFGREN, B. M. Global warming influences on water levels, ice, and chemical and biological cycles in lakes: some examples. American Fisheries Society Symposium 32:15-22 (2002).

Climate change and variability significantly affect freshwater bodies in ways that include effects on the water temperature profiles, total water volumes, inflows and outflows, ice cover, primary productivity and activity at higher trophic levels, and cycling of nutrients and other chemical constituents. Understanding of this large array of potential impacts involves many scientific disciplines, and cases can differ markedly depending on the characteristics of the water bodies, including area, depth, latitude, annual cycle of thermal stratification, nutrient and toxic input, components of the ecosystem, and many other factors. This paper gives brief summaries of several studies that focused on particular examples of these effects, as presented during a special session titled Potential Impacts of Climate Change on Large Lakes, at the meeting of Societas Internationalis Limnologiae (SIL) in Melbourne, Australia on 6 February 2001. These studies include a general overview of the geological and climatological factors that interacted to form the large lakes of China, a study on water quantity and lake levels of the Laurentian Great Lakes, a group of studies regarding effects on the heat content, thermal structure, and ice cover of various lakes, and three studies of nutrient cycling and biological activity in several lakes of northern Europe, using the quasi-periodic North Atlantic Oscillation as a proxy for anthropogenic greenhouse warming. This paper presents the main conclusions of each of these studies; additional details can be obtained from the papers cited here or directly from their authors.

Lotufo, G. R., and P. F. LANDRUM. The influence of sediment and feeding on the elimination of polycyclic aromatic hydrocarbons in the freshwater amphipod, Diporeia spp. Aquatic Toxicology 58:137-149 (2002).

The elimination of non-polar organic contaminants from sediment dwelling aquatic invertebrates was thought to be dominated by fecal elimination. This was particularly thought to be the case for the amphipod, Diporeia spp. that encapsulates the fecal material in a peritrophic membrane. The elimination of selected PAH congeners by Diporeia spp. was determined in the presence of three solid substrates and under water only conditions. The elimination was generally enhanced by the presence of a solid substrate whether or not the organism employed the material as a food source. The greater the sorptive capacity of the substrate, the greater its influence on the elimination process. Elimination via the fecal route was generally insignificant except for the elimination of BaP in the presence of sediment. In this case, the fecal elimination accounted for up to 40% of the total elimination, and the extent of elimination via the fecal route increased with the amount of fecal material produced. Thus, it is clear from the above effort that the main mechanism for elimination of contaminants in the presence of a substrate is primarily via passive diffusion from the organism with subsequent sorption to the solid substrate, which maintains the chemical activity gradient between the organism and the water. This effort refutes the earlier hypothesis that fecal elimination is the dominant route of elimination for Diporeia spp., and that the peritrophic membrane plays any substantial role in the elimination process.

Madenjian, C. P., G. L. FAHNENSTIEL, T. H. JOHENGEN, T. F. NALEPA, H. A. VANDERPLOEG, G. W. Fleischer, P. J. Schneeberger, D. M. Benjamin, E. B. Smith, J. R. Bence, E. S. Rutherford, D. S. Lavis, D. M. Robertson, D. J. Jude, and M. P. Ebener. Dynamics of the Lake Michigan Food Web, 1970-2000. Canadian Journal of Fisheries and Aquatic Sciences 59:736-753 (2002).

Herein, we document changes in the Lake Michigan food web between 1970 and 2000 and identify the factors responsible for these changes. Control of sea lamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus) populations in Lake Michigan, beginning in the 1950s and 1960s, had profound effects on the food web. Recoveries of Lake Whitefish (Coregonus ciupeaformis) and burbot (Lota iota) populations, as well as the buildup of salmonine populations, were attributable, at least in part, to sea lamprey control. Based on our analyses, predation by salmonines was primarily responsible for the reduction in alewife abundance during the 1970s and early 1980s. In turn, the decrease in alewife abundance likely contributed to recoveries of deepwater sculpin (Myoxocephaius thompsoni), yellow perch (Perca flavescens), and burbot populations during the 1970s and 1980s. Decrease in the abundance of all three dominant benthic macroinvertebrate groups, including Diporeia, oligochaetes, and sphaeriids, during the 1980s in nearshore waters (50 m deep) of Lake Michigan, was attributable to a decrease in primary production linked to a decline in phosphorus loadings. Continued decrease in Diporeia abundance during the 1990s was associated with the zebra mussel (Dreissena polymorpha) invasion, but specific mechanisms for zebra mussels affecting Diporeia abundance remain unidentified.

McCORMICK, M. J., G. S. MILLER, C. R. Murthy, Y. R. Rao, and J. H. SAYLOR. Tracking coastal flow with surface drifters during the episodic events: Great Lakes experiment. Verh. Internat. Verein. Limnology 28:365-369 (2002).

In the coastal regions of large lakes and oceans, the horizontal gradients of dissolved chemicals and suspended materials are often far greater in the offshore than in the alongshore direction. Therefore, the mechanisms driving cross-isobath circulation play a critical role in maintaining the water quality in coastal regions. In the Laurentian Great Lakes the absence of any tidal currents and their smaller basin geometry, relative to oceanic conditions, leaves a velocity field that is dominated by wind forcing. Time variability in the surface wind stress in both magnitude and direction results in a relatively weak background circulation pattern (BELETSKY et al. 1999). Under conditions like these there is a greater potential impact for storms to be a major mechanism for the offshore flux of coastal materials. As part of a National Science Foundation- and NOAA-sponsored study, an extensive array of fixed current meter moorings and satellite-reporting drift-ing buoys were used in the coastal region of south-eastern Lake Michigan, as part of an effort to deter-mine the statistics associated with offshore and longshore transport. The observational program began in the fall of 1997 and ended in early summer 2000. With recent improvements in Lagrangian posi-tioning technology, with GPS and sophisticated microprocessor-equipped drifters, they have become even more useful tools for studying coastal circula-tion. PAL et al. (1998) and SANDERSON (1987) used drifters to help describe the mixing and circulation characteristics of Lakes Ontario and Erie, respec-tively. In this report, findings are described from a Lagrangian experiment in April 1999 on the coastal waters of Lake Michigan.

Millie, D. F., G. L. FAHNENSTIEL, H. J. Carrick, S. E. Lohrenz, and O. M. E. Schofield. Phytoplankton pigments in coastal Lake Michigan: Distributions during the spring isothermal period and relation with episodic sediment resuspension. Journal of Phycology 38:639-648 (2002).

Phytoplankton pigment distributions during the spring isothermal periods of 1998 and 1999 and their association with episodic sediment resuspension were characterized in coastal waters of southern Lake Michigan. Total and phylogenetic group chl a concentrations (derived using chemical taxonomy matrix factorization of diagnostic carotenoids) corresponded with assemblage and group biovolumes estimated from microscopic enumeration (P <= 0.001). Diatoms and cryptophytes dominated assemblages and together typically comprised greater than 85% of relative chl a. Total chl a concentrations and both fucoxanthin x chl a and alloxanthin chl a ratios were similar across depths (P > 0.05), indicating uniform distributions of and photophysiological states for assemblages and diatoms and cryptophytes, respectively, throughout the mixed water column. Total chl a concentrations were not always spatially uniform from nearshore to offshore waters, with the greatest variability reflecting the influence of tributary inflows upon coastal assemblages. Sediment resuspension strongly influenced water column particle density and light climate; however, total and group chl a concentrations did not correspond with coefficients of K and suspended particulate matter concentrations (P> 0.05). The correspondence of both light attenuation and suspended particulate matter concentration with relative diatom chl a (P <= 0.001) indicated an apparent association between sediment resuspension and diatoms. This, and the negative association (P<= 0.0001) between relative diatom and cryptophye chl a, corresponded with the spatial dominance of diatom and cryptophyte chl a in nearshore and offshore waters, respectively. The presence of viable chl a and fucoxanthin within the surficial sediment layer, established this layer as a potential source of meroplanktonic diatoms for nearshore assemblages.

Mori, N., P. C. LIU, and T. Yasuda. Analysis of freak wave measurements in the Sea of Japan. Ocean Engineering 29:1399-1414 (2002).

This paper presents an analysis of a set of available freak wave measurements gathered from several periods of continuous wave recordings made in the Sea of Japan during 1986-1990 by the Ship Research Institute of Japan. The analysis provides an ideal opportunity to catch a glimpse of the statistics of freak waves in the ocean. The results show that a well-defined freak wave may occur in the developed wind-wave condition: S(f) f-4, with single-peak directional spectra. The crest and trough amplitude distributions of the observed sea waves including freak waves are different from the Rayleigh distribution, although the wave height distribution tends to agree with the Rayleigh distribution. Freak waves can be readily identified from the wavelet spectrum where a strong energy density occurs in the spectrum, and is instantly surged and seemingly carried over to the high-frequency components at the instant the freak wave occurs.

Mulsow, S., P. F. LANDRUM, and J. A. ROBBINS. Biological mixing responses to sublethal concentrations of DDT in sediments by Heteromastus filiformis (capitellidae) using a 137Cs marker layer technique. Marine Ecology Progress Series 239:181-191 (2002).

Sediment mixing by benthic macroinvertebrates is an important process affecting the fate of sediment-bound and dissolved contaminants in marine environments. A non-invasive, state-of-the-art radiotracer technique was used to study sediment mixing by Heteromastus filiformis (Capitellidae), a common marine head-down deposit feeder, exposed to several sub-lethal concentrations of DDT (0, 5, 10 and 20 pg g-1; control, Treatments 1, 2 and 3). Several horizontal sub-millimeter layers of 137Cs-labeled clay were deposited approximately every 2 cm in each of 3 replicate sediment columns per treatment; 4 polychaetes were then introduced to each column and the y activity of each column was measured vertically using an automated scan detector. Nonlinear least-square fits were applied to obtain parameterized values that were used to determine the mixing rates of each 137Cs layer over time. A simple diffusion model was used to calculate biological diffusion coefficients (Db) for H. filiformis. Overall mixing rates increased towards the surface. Control and Treatment 1 had higher Db values at the surface compared to Treatments 2 and 3. The Db depth profiles were similar in the control and Treatments 1 and 2, with mixing occurring at the sediment water interface and a subsurface maximum at 10 to 12 cm below this interface. This pattern was not clear in Treatment 3, where Db had the lowest values and decreased with depth. Bioturbation besides mixing of solids also changed the water content throughout the sediment column. Porosity profiles at the end of the experiments increased by 10 to 20% at 10 to 12 cm depths compared to above and below this horizon. The DDT depth concentration profiles decreased towards the surface as a result of the mixing by the benthic macroinvertebrates, clearly indicating removal/uptake by the organism. The feeding rate constant (gb, % h-1) in the control showed a maximum at 7 to 12 cm. However, the gb in the treatments was essentially constant with depth. For all treatments and the control, the burial rate (Wb) (downward movement of radiolabeled layers) decreased with depth. The surface layers were buried faster (ANOVA, p < 0.05) in the control than in sediments containing DDT. A sensitivity analysis comparing burial rate, Db, gb (surface only) and worm weights showed that worm weights and burial rate have the highest fractional rate changes per pg g-1 DDT.

MUZZI, R. W., and B. J. EADIE. The design and performance of a sequencing sediment trap for lake research. Marine Technology Society Journal 36(2):23-28 (2002).

Static sediment traps have been successfully used to examine the processes of particle flux and resuspension in large lakes and coastal systems. Although the traps themselves are inexpensive, the deployment and retrieval of them is costly, which restricts both the quantity andfequency of samples. To overcome this, a programmable sequencing sediment trap was designed and tested for use in large lakes and coastal systems. Sediment is collected into a carousel of 23 standard 60 ml (Nalgene) polyethylene sample bottles. The sequencing design incorporates an electric motor and paddle to rotate the carousel so that one sample bottle at a time is exposed according to a preprogrammed schedule. These traps incorporate a cylindrical design with a 20 cm collection opening and an 8:1 aspect ratio. The in icro-controller monitors the operation and records operational parameters allowing confirmation of the exposure time of each bottle. Several field tests were conducted to verify' the precision and uniformity of the sediment collection. Improvements made over the 10 years of deployment experience and field testing have resulted in a very reliable and low-cost instrument.

NALEPA, T. F., D. L. FANSLOW, M. B. LANSING, G. A. LANG, M. FORD, G. GOSTENIK, and D. J. HARTSON. Abundance, biomass, and species composition of benthic macroinvertebrate populations in Saginaw Bay, Lake Huron, 1987-96. NOAA Technical Memorandum GLERL-122, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 32 pp. (2002).

This technical report gives the basic results of benthic macroinvertebrate surveys conducted in Saginaw Bay between 1987 and 1996. Yearly surveys were conducted over this time period to assess trends in macroinvertebrate density, biomass, and species composition. When the surveys were initiated in 1987-88, the main objective was to assess the response of the benthic community to phosphorus abatement programs that were implemented in the mid-1970s. Improvements in water quality were reported after these programs (Bierman et al. 1984), and a two-year sampling program in 1987-88 was designed to determine if similar improvements were evident in the macroinvertebrate community. When the zebra mussel (Dreissena polymorpha) became established in the Great Lakes in 1988 (Hebert et al. 1989), sampling was resumed in 1990 and continued through 1996 with the objective of assessing impacts of Dreissena. Dreissena colonized the bay in 1991 (Nalepa et al. 1995). Thus, the data collected during the time of this study can be divided into two distinct periods: post-phosphorus abatement/pre-Dreissena (1987-90) and post-Dreissena (1991-96). Data are presented in this report with little attempt at interpretation; detailed analysis and discussions of relevance will be provided in other publications. Rather, the purpose of this report is to provide the raw data and basic details of the sampling program, including station locations and characteristics, sampling methods, and laboratory procedures. In addition, results of a comparative study of two samplers, the Peterson and Ponar grabs, is presented. The former grab was used in benthic surveys conducted in the bay in the 1950s and 1960s, while the latter grab has been used since the early 1970s. The relative efficiency of these two grabs was examined to more accurately depict density trends from the 1950s to the present.

NALEPA, T. F., D. J. HARTSON, D. L. FANSLOW, and G. A. LANG. Recent population changes in freshwater mussels (Bivalvia: Unionidae) and zebra mussels (Dreissena polymorpha) in Lake St. Clair, USA. American Malacological Bulletin 16(1/2):141-145 (2001).

To determine trends in abundances, we conducted a survey of freshwater mussels (Bivalvia: Unionidae) and zebra mussels (Dreissena polymorpha) [Pallas, 1771] at five sites in the northwestern portion of lake St. Clair in 1997. Previous, more extensive spatial surveys between 1986 and 1994 showed that unionids were mostly eliminated from the lake as a result of zebra mussel infestation, but at least a few unionids were still present in the northwestern portion in 1994. The 1994 survey also showed that zebra mussel densities were still increasing in this portion of the lake. In the present survey, no live unioninds were collected despite a sampling effort modified from prior surveys specifially to locate live individuals. From these results, we believe that freshwater mussels have been eliminated from the open waters of Lake St. Clair. Zebra mussel populations appear to have reached a steady state in the northwest portion as evidenced by a decrease in mean density from 2,246 m-2 in 1994 to 1,237 m-2 in 1997, and a decrease in the mean size of individuals in the population. Although they were common in previous surveys, we did not collect any zebra mussels with a shell length >20 mm.

Norcross, B. L., E. D. Brown, R. J. Foy, M. Frandsen, S. M. Gay, T. C. Kline, D. M. MASON, E. V. Patrick, A. J. Paul, and K. D. E. Stokesbury. A synthesis of the life history and ecology of juvenile pacific herring in Prince William Sound, Alaska. Fisheries Oceanography 10(1):42-57 (2001).

Physical and biological variables affecting juvenile Pacific herring (Clupea pollosi) in Prince William Sound (PWS) from 1995 to 1998 were investigated as part of a multifaceted study of recruitment, the Sound Ecosystem Assessment (SEA) program. Though more herring larvae were retained in eastern PWS bays, ages-0 and -1 herring used bays throughout PWS as nursery areas. Water transported into PWS from the Gulf of Alaska (GOA) contributed oceanic prey species to neritic habitats. Consequently, variations in local food availability resulted in different diets and growth rates of herring among bays. Summer food availability and possible interspecific competition for food in nursery areas affected the autumn nutritional status and juvenile whole body energy content (WBEC), which differ among bays. The WBEC of age-0 herring in autumn was related to over-winter survival. The limited amount of food consumption in winter was not sufficient to meet metabolic needs. The smallest age-0 fish were most at risk of starvation in winter. Autumn WBEC of herring and winter water temperature were used to model over-winter mortality of age-0 herring. Differences in feeding and energetics among nursery areas indicated that habitat quality and age-0 survival were varied among areas and years. These conditions were measured by temperature, zooplankton abundance, size of juvenile herring, diet energy, energy source (GOA vs. neritic zooplankton), WBEC, and within-bay competition.

POTHOVEN, S. A., G. L. FAHNENSTIEL, and H. A. VANDERPLOEG. Population dynamics of Bythotrephes cederstroemii in southeast Lake Michigan 1995-1998. Freshwater Biology 46:1491-1501 (2001).

1. Population characteristics (density, size, reproductive patterns) of the predatory cladoceran Bythotrephes cederstroemii in south-east Lake Michigan were monitored at an offshore station (110 m) in 1995-98 and at a nearshore station (45 m) in 1997-98. 2. The mean density of B. cederstroemii at the offshore station was generally highest in July-September (145-914 m-2) and at the nearshore station in October-November (168-1625 m-2). In 1995 and 1998, density was also high at the offshore station in November (211-284 m-2). Fish predation may limit B. cederstroemii in nearshore regions in the summer. The maximum annual densities of B. cederstroemii for 1995-98 were generally similar to those reported from the late 1980s, when the species arrived in Lake Michigan. 3. Body size increased rapidly each year to a maximum in August. Thereafter, body size declined and converged for Stage-2 and 3 individuals, suggesting food scarcity or size-selective fish predation was affecting large individuals. 4. Most reproduction occurred asexually (90%), and by stage 2 or 3 females (99%). Asexual brood size was highest when B. cederstroemii first appeared each year, and decreased in August, when larger neonates were produced. There appeared to be differences in reproductive mode for stage 2 and 3 females, with a higher percentage of stage 2 females reproducing sexually.

POTHOVEN, S. A., T. F. NALEPA, P. J. Schneeberger, and S. B. BRANDT. Changes in diet and body condition of Lake Whitefish in southern Lake Michigan associated with changes in benthos. North American Journal of Fisheries Management 21:876-883 (2001).

We evaluated the long-term trends of the benthic macroinvertebrate community (1980-1999) and biological attributes of lake whitefish Coregonus clupeaformis (1985-1999) in southeastern Lake Michigan; We also determined what food types were important to lake whitefish in an area where the amphipod Diporeia had not yet declined in 1998 and how the diet of lake whitefish changed as Diporeia declined during 1999-2000. Zebra mussels Dreissena polymorpha invaded the study area in 1992; Diporeia began to decline in 1993 and was nearly absent by 1999. The body condition of lake whitefish decreased after 1993 and remained low thereafter The length at age and weight at age of lake whitefish was lower in 1992-1999 than in 1985-1991- After declines of Diporeia off the city of Muskegon, Michigan, between 1998 and 1999-2000, the proportion of Diporeia in the diet by weight fell from 70% to 25% and the percent occurrence decreased from 81% to 45%. In contrast, the proportion of lake whitefish that ate other prey, such as Mysis relicta (an opossum shrimp), ostracods. oligochaetes, and zooplankton, increased in the same period; At sites south of Muskegon, where the density at Diporeia has been low since 1998, chironomids, zebra mussels, and fingernail clams (Shaeriidae family) were the most important diet items of lake whitefish. Decreases in body condition and growth are associated with the loss of the high-energy prey resource Diporeia, the consumption of prey with lower energy content, such as zebra mussels, and possible density-dependence. Commercial harvests of lake whitefish will probably decrease because of low body condition and growth. Future management may require changes in harvest quotas, size restrictions, and depth restrictions as zebra mussel-related impacts spread northward in Lake Michigan.

QUIGLEY, M. A., P. F. LANDRUM, W. S. GARDNER, C. R. STUBBLEFIELD, and W. M. GORDON. Respiration, nitrogen excretion, and O:N ratios of the Great Lakes amphipod, Diporeia sp. NOAA Technical Memorandum GLERL-120, NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 16 pp. (2002).

Diporeia sp. (formerly Pontoporeia hoyi) Amphipoda, Crustacea obtained from a 24-29 m deep site in southeastern Lake Michigan were held in stoppered 60 mL BOD bottles in darkness and at 4oC during 24-hour intervals. Change in dissolved oxygen concentration of filtered lakewater within test vessels indicated that mean Diporeia sp. oxygen consumption ranged from 13.9 to 33.9 mg O2 g-1 DW d-1. Test vessel acclimation studies revealed a minor increase in oxygen uptake early in the incubation interval that that was not reflected in overall oxygen consumption measured over the entire 24-hour period. Mean oxygen consumption of amphipods provided with a coarse, ignited sand substrate was not significantly different (P<0.05) from O 2 consumption of animals in test vessels where no substrate was provided. In a series of 10 other experiments, where initial ambient oxygen concentration was varied (from 95 to 23% saturation), Michaelis-Menten kinetics analysis indicated that Diporeia sp. was able to maintain a relatively uniform level of oxygen consumption over the upper portion of oxygen concentrations tested. Vmax (predicted O2 consumption at 100% saturation) was 25.5 mg O2 g-1DW d-1 and fell within the 13.9-33.9 mg O2 g-1DW d-1 range noted in 24-hour oxygen consumption experiments at near-saturation O2 levels. Km (the predicted O2 concentration where oxygen consumption had declined to 50% of the Vmax value) was 2.2 mg L-1. Diporeia sp. nitrogen (ammonia) excretion, simultaneously measured during three of the oxygen consumption experiments, ranged from 0.45 to 0.77 ng-atom N mg -1 DW h-1. Calculation of O:N ratios (atoms of oxygen consumed per atom of N excreted) implied that substrates catabolized by Diporeia sp. consisted primarily of lipids since most (62%) O:N values were greater than 60. These results complement previously observed high lipid content of Diporeia sp. and further suggest that the economy of lipids is a prominent aspect of the amphipod�s life history.

QUINN, F. H. Secular changes in Great Lakes water level changes. Journal of Great Lakes Research 28(3):451-465 (2002).

The three primary scales of Great Lakes water level fluctuations are interannual, seasonal, and episodic. Of, these three, the seasonal water level fluctuations have received relatively little attention. The Great Lakes water levels have a well defined seasonal cycle driven primarily by snowmelt in the spring and summer and lake evaporation in the fall and winter. The present average seasonal cycle ranges from 26 cm on Lake Superior to 38 cm on Lake Ontario. Great Lakes monthly water levels from 1860 to 2000 were used to assess changes in the seasonal cycle of each of the Great Lakes and Lake St. Clair over the past 140 years. Changes are found on all of the lakes during the period of record. They usually resulted in a decrease in seasonal range and a time shift in the months of seasonal maximum and minimum. The effects of lake regulation were found to be negligible in the case of Lake Superior and significant for Lake Ontario. The major changes on Lakes St. Clair and Erie are likely a result of changes in the connecting channels ice retardation rather than changes in seasonal hydrometeorology. Seasonal cycle regimes are delineated for each of the lakes and possible rationale for the changes discussed.

QUINN, F. H., R. A. ASSEL, and C. E. SELLINGER. Hydro-climatic factors and socioeconomic impacts of the recent record drop in Laurentian Great Lakes water levels. Preprints of the 13th Symposium on Global Change and Climate Variations, Orlando, Florida, January 13-17, 2002. American Meteorological Society, Boston, MA, pp. 91-93 (2002).

The Laurentian Great Lakes, comprise the United States premier surface water resource with a basin area of 770.000 km2. This water resource is shared between the U.S. and Canada and supports many important uses including recreational boating, commercial navigation, sports fishing, hydroelectric power, industry, municipal water supply, recreation, and fish and wildlife habitat. The Great Lakes system, Figure 1, which includes the five Great Lakes, Superior, Michigan, Huron, Erie. and Ontario, and Lake St. Clair and the connecting channels is naturally well regulated due to the large lake surface areas and constricted outlet channels. Two of the lakes, Superior and Ontario, are regulated. This has resulted in the lakes fluctuating through a relatively small range in levels, about 1.8 m. Because of the small range in water levels, industrial and recreational uses are sensitive to even small changes in lake levels. The lakes had been in an extremely high levels regime from the late 1960s through the late 1990s with record highs being set in 1973 and 1986. However, beginning with the 1997-1998 El Nino, the lakes began a dramatic decline in water levels that was notable for both the magnitude and the rapidity of the drop. Currently Lake Michigan-Huron is the lowest since 1965, while this spring Lake Superior was the lowest since 1925. In this study we compare the drop in levels with similar past events, examine the hydroclimatological factors leading to the decline in levels and look at both positive and negative impacts. We will concentrate on Lakes Michigan and Huron, one lake hydraulically, which have had the largest impacts.

Rao, Y. R., C. R. Murthy, M. J. McCORMICK, G. S. MILLER, and J. H. SAYLOR. Observations of circulation and coastal exchange characteristics in southern Lake Michigan during 2000 winter season. Geophysical Research Letters 29(13):9-1 to 9-4 (2002).

Intermittent satellite images collected over in the last few years have revealed episodic late winter-spring plumes coinciding with northerly storms in southern Lake Michigan. A major inter-disciplinary observational program was initiated to study the importance of these episodic events on nearshore-offshore transport and the subsequent ecological consequences. In this paper, high density observations of winds and currents made during the winter of 2000 are analyzed to study the variability of the coastal circulation and the physical mechanisms resulting in the alongshore and cross-shore transport in the lake. The southern measurements of currents show the signature of forced two-gyre circulation in the southern basin. During northerly storm episodes the combination of directly wind forced currents and northward propagating vorticity wave generate significant offshore transport in this region.

REID, D. F., and M. I. Orlova. Geological and evolutionary underpinnings for the success of ponto-caspian species invasions in the Baltic Sea and North American Great Lakes. Canadian Journal of Fisheries and Aquatic Sciences 59:1144-1158 (2002).

Between 1985 and 2000, ~70% of new species that invaded the North American Great Lakes were endemic to the Ponto-Caspian (Caspian, Azov, and Black seas) basins of eastern Europe. Sixteen Ponto-Caspian species were also established in the Baltic Sea as of 2000. Many Ponto-Caspian endemic species are characterized by wide environmental tolerances and high phenotypic variability. Ponto-Caspian fauna evolved over millions of years in a series of large lakes and seas with widely varying salinities and water levels and alternating periods of isolation and open connections between the Caspian Sea and Black Sea depressions and between these basins and the Mediterranean Basin and the World Ocean. These conditions probably resulted in selection of Ponto-Caspian endemic species for the broad environmental tolerances and euiyhalinity many exhibit. Both the Baltic Sea and the Great Lakes are geologically young and present much lower levels of endemism. The high tolerance of Ponto-Caspian fauna to varying environmental conditions, their ability to survive exposure to a range of salinities, and the similarity in environmental conditions available in the Baltic Sea and Great Lakes probably contribute to the invasion success of these species. Human activities have dramatically increased the opportunities for transport and introduction and have played a catalytic role.

RODIONOV, S., R. A. ASSEL, and L. R. HERCHE. Tree-structured modeling of the relationship between Great Lakes ice cover and atmospheric circulation patterns. Journal of Great Lakes Research 27(4):486-502 (2001).

Seasonal maximum ice concentration (percentage of lake surface covered by ice) for the entire Laurentian Great Lakes and for each Great Lake separately is modeled using atmospheric teleconnection indices. Two methods, Linear Regression (LR) and Classification and Regression Trees (CART), are used to develop empirical models of the interannual variations of maximum ice cover. Thirty-four winter seasons between 1963 and 1998 and nine teleconnection indices were used in the analysis. The ice cover characteristics were different for each Great Lake. The ice cover data lent itself better to CART analysis, because CART does not require a priori assumptions about data distributions characteristics to perform well. The stepwise LR models needed more variables, and in general, did not explain as much of the variance as the CART models. Two variables, the Multivariate ENSO index and Tropical/Northern Hemisphere index, explained much of the interannual variations in ice cover in the CART models. Composite atmospheric circulation patterns for threshold values of these two indices were found to be associated with above-and below-normal ice cover in the Great Lakes. Thus, CART also provided insight into physical mechanisms (atmospheric circulation characteristics) underlying the statistical relationships identified in the models.

RUBERG, S. A., H. A. VANDERPLOEG, J. F. CAVALETTO, G. A. LANG, J. R. LIEBIG, T. C. MILLER, and M. AGY. Plankton survey system. Proceedings of the Oceans 2001 MTS/IEEE Conference, Honolulu, HI, November 5-8, 2001. Marine Technology Society, Washington, DC, pp. 1899-1903 (2001).

The Plankton Survey System (PSS), developed at the National Oceanic and Atmospheric Administration's (NOAA) Great Lakes Environmental Research Laboratory (GLERL), has been designed to collect high temporal and spatial resolution marine environmental data in three dimensions. The system has proven effective in providing valuable survey information before, during and after sediment re-suspension events in Lake Michigan in support of GLERL's NOAA/NSF funded Episodic Events Great Lakes Experiment (EEGLE) program. The PSS is a towed multi-sensor platform capable of measuring turbidity, chlorophyll a, photosynthetically active radiation (PAR), conductivity, temperature, and zooplankton spatial distributions. All sensors are integrated using a serial data interface. All data are geo-referenced and registered with time, depth, and vehicle pitch, roll, and speed information. A deck unit supplies power for the underwater vehicle components and provides interfaces for data collection and system monitoring. System software provides real-time display of all marine environmental measurements and vehicle status. Zooplankton spatial and individual size distributions are measured using an optical plankton counter (OPC). The OPC measures particle size distributions (0.25 -14mm) using an LED array and a photodiode receiver. Deflections caused by particles crossing the LED generated light beam (4x20x100 mm) are detected by the receiver and digitized. Present work is focused on moving the OPC beyond use as merely a survey tool to calibrating the instrument using laboratory and field measurements. Laboratory calibration plans include the use of specified particles to establish a reference and subsequent investigations using live zooplankton samples. A range of issues involving the implications of variations in zooplankton body characteristics on OPC detection threshold, turbidity on OPC signal-to-noise ratio, tow vehicle orientation and vehicle and OPC channel turbulence will also be investigated.

Schloesser, D. W., and T. F. NALEPA. Comparison of 5 benthic samplers to collect burrowing mayfly nymphs (Hexagenia spp: Ephemeroptera:Ephemeridae) in sediments of the Laurentian Great Lakes. Journal of the North American Benthological Society 21(3):487-501 (2002).

The recent return of burrowing mayfly nymphs (Hexagenia spp.) to western Lake Erie of the Laurentian Great Lakes has prompted a need to find a sampler to obtain the most accurate (i.e., highest mean density) and precise (i.e., lowest mean variance) abundance estimates of nymphs. The abundance of burrowing nymphs is important because it is being used as a measure of ecosystem health to determine management goals for fisheries and pollution abatement programs for waters in both North America and Europe. We compared efficiencies of 5 benthic grab samplers (Ponar, Ekman, petite Ponar, Petersen, and orange-peel) to collect nymphs from sediments of western Lake Erie and Lake St. Clair. Samplers were used at one site with soft substrates in both lakes in 1997 (Ponar, Ekman, petite Ponar, and Petersen) and 1998 (Ponar and Ekman), and at one site with soft and one site with hard substrates in Lake St. Clair in 1999 (Ponar and orange-peel). In addition, the Ponar, Ekman, and Petersen samplers were used at one site with soft substrates of western Lake Erie in 2000 to examine the causes of differences among samplers. The Ponar was more accurate than the other samplers; it collected the highest densities of nymphs for 31 of 32 date and site comparisons. In soft substrates, the order of decreasing overall densities was: Ponar>Petersen>petite Ponar>Ekman in western Lake Erie and Ponar>Petersen> Ekman>petite Ponar in Lake St. Clair in 1997, Ponar>Ekman in both lakes in 1998, and Ponar>orange-peel in Lake St. Clair in 1999. In hard substrates, the Ponar was more accurate than the orange-peel in Lake St. Clair in 1999. Precision of the Ponar was generally greater than the Ekman, petite Ponar, and Petersen but similar to the orange-peel. Higher densities of nymphs obtained with the Ponar than other grabs are attributed to its relatively heavy weight, which allows it to sample deeper in sediments than the Ekman and petite Ponar. Also, the Ponar has a screened top, which allows it to minimize hydraulic shock waves more than the Petersen, and uniform sides, which allow it to sample nymphs more uniformly through sediments than the orange-peel. We recommend that future estimates of burrowing mayfly densities be obtained with a standard Ponar sampler similar to the one used in our study because it will yield the most accurate and precise measurements of burrowing mayfly nymphs such as Hexagenia spp.

Schneider, A. R., B. J. EADIE, and J. E. Baker. Episodic particle transport events controlling PAH and PCB cycling in Grand Traverse Bay, Lake Michigan. Environmental Science and Technology 36(6):1181-1190 (2002).

To evaluate the influence of episodic events on particle and hydrophobic organic contaminant (HOC) cycling in the Great Lakes, we deployed sequencing sediment traps at two locations in the western arm of Grand Traverse Bay, Lake Michigan. The traps collected integrated samples of settling particles every 2weeks from May 1997 to September 1999. The total polycyclic aromatic hydrocarbon (t-PAH) and total polychlorinated biphenyl (t-PCB) settling fluxes from the surface waters in the southern site were significantly greater than those from the northern site. In addition, there were more frequent brief increases in the mass flux to the southern site than to the northern site. These episodic events, which occurred only 20% of the time, accounted for 65% of both the mass flux and t-PAH flux. The t-PCB flux was not influenced by these episodic events, and only 18% of the t-PCB flux occurred during these events. PAHs and PCBs appear to be tracing different types of particles in the water column. Several large mass flux events characteristic of seiches were observed simultaneously in the benthic nepheloid layer (BNL) at both the northern and the southern sites. The particles settling as a result of these resuspension events had lower t-PCB and t-PAH concentrations than particles settling at other times. This suggests that the material settling into the traps on the high mass flux days is composed of a mixture of the less contaminated underlying resuspended sediment and the "regular" contaminant-rich particles settling into the BNL.

SCHWAB, D.J., and D. BELETSKY. Hydrodynamic and sediment transport modeling of episodic resuspension events in Lake Michigan. Proceedings of the 7th International Conference on Estuarine and Coastal Modeling, St. Petersburg, FL, November 5-7, 2001. American Society of Civil Engineers, pp. 266-279 (2001).

This paper describes an integrated hydrodynamic, wind-wave, and sediment dynamics modeling project for simulating episodic, storm-generated resuspension events in lake Michigan. Each of these events resuspends up to several million metric tons of fine-grained sedimentary material, which is several times the estimated total annual input of fine grained material to the lake from shoreline erosion, atmospheric deposition, and tributary runoff combined. The numerical models used in this study are the Princeton Ocean Model for hydrodynamics, the GLERL-Donelan parametric wind-wave model, and a simple two-dimensional sediment dynamics model with one particle size class. The results of the large resuspension event which occurred in March 1998 show many of the characteristics of the lake-wide turbidity pattern as observed in satellite imagery. However, a large vortex-like feature about 20 km in diamter, which is prominent in the satellite imagery, is not reproduced in the model simulations. The modeled net sediment transport during this episoide shows a simlar distribution to the observed long-term net sediment deposition rate in southern Lake Michigan, possibly indicating theat most of the net fine-grained sediment transport occurs during these episodic events.

Soster, F. A., G. Matisoff, P. L. McCall, and J. A. ROBBINS. In situ effects of organisms on porewater geochemistry in Great Lakes sediments. In Organism-Sediment Interactions, J.Y. Aller, S. A. Woodin and R. C. Aller Eds., University of South Carolina, Columbia, SC, pp. 279-294 (2001).

Soft-bottom habitats in the Great Lakes are numerically dominated by deposit-feeding oligochaete annelids; tube-building filter-feeding chironomid insect larvae, and deposit-feeding amphipods, this last group being relatively abundant only in deeper oligotrophic bottoms. The abundance of macrobenthos colonizing uninhabited sediment trays and residing in natural bottom sediments at two sites in Lake Erie were compared with geochemical profiles obtained from porewater peepers. Differences in geochemical profiles were due more to differences in abundances of chironomid larvae (Chironomus plumosus) than to differences in tubificid oligochaete abundance. Porewater concentrations of soluble reactive silicate (SRS), ammonium, carbonate alkalinity, and soluble reactive phosphate (SRP) were lower in western Lake Erie tray sediments, where C. plumosus were more abundant; than in natural bottom sediments where C. plumosus were relatively rare. The opposite abundance pattern was observed in the central basin, where C. plumosus were more abundant in natural sediments and porewater concentrations of SRS, ammonium, and ferrous iron were lower than in tray sediments from the same site. In similar sediments from Lower Saginaw Bay, Lake Huron, geochemical fluxes were determined from changes in concentrations of water overlying sediment cores incubated shipboard at in situ temperatures. There were significant correlations between ammonia flux, SRS flux, and chironomid abundance, between SRP flux and mature tubificid abundance, and between nitrate flux (into the sediment) and immature tubificids. A faunal succession from a community with abundant Chironomus larvae to one with abundant tubificid worms might cause a geochemical succession. Early colonizing Chironomus larvae decrease porewater concentrations of SRS, ammonium, and bicarbonate alkalinity and increase the flux out of the sediment (and for ammonium, also may indirectly increase the rate of nitrification). Concentrations of ferrous iron and SRP are also depressed, but there is no enhanced flux because iron is precipitated near burrow walls after contact with oxygen and adsorbs phosphate, so iron and phosphate do not accumulate in the burrow pore waters. Porewater concentrations of SRS, ammonium, bicarbonate alkalinity, ferrous iron, and SRP are high in the presence of slower colonizing tubificid worms, but the effect that worms have on the flux of most of these species is more complicated.

Steevens, J. A., and P. F. LANDRUM. Development of a biological-effects-based approach to assess the significance of contaminant bioaccumulation. ERDC/TN EEDP-01-48, U.S. Army Engineer Research and Development Center, EEDP Technical Notes Collection, 9 pp. (2002).

This technical note describes the development of an alternative approach to evaluate chronic toxicity and the significance of contaminant bioaccumulation in dredged material assessments. It describes potential approaches and outlines the experimental progress of a project focusing on an effects-based approach to assess bioaccumulation.

VANDERPLOEG, H. A., T. F. NALEPA, D. J. Jude, E. L. MILLS, K. T. HOLECK, J. R. LIEBIG, I. A. Grigorovich, and H. Ojaveer. Dispersal and emerging ecological impacts of Ponto-Caspian species in the Laurentian Great Lakes. Canadian Journal of Fisheries and Aquatic Sciences 59:1209-1228 (2002).

We describe, explain, and "predict" dispersal and ecosystem impacts of six Ponto-Caspian endemic species that recently invaded the Great Lakes via ballast water. The zebra mussel, Dreissena polymorpha, and quagga mussel, Dreissena bugensis, continue to colonize hard and soft substrates of the Great Lakes and are changing ecosystem function through mechanisms of ecosystem engineering (increased water clarity and reef building), fouling native mussels, high particle filtration rate with selective rejection of colonial cyanobacteria in pseudofeces, alteration of nutrient ratios, and facilitation of the rapid spread of their Ponto-Caspian associates, the benthic amphipod Echinogamarus ischmus and the round goby, Neogobius melanostomus, which feeds on zebra mussels. The tubenose goby, Protemrhinus marmoratus, which does not feed on zebra mussels, has not spread rapidly. Impacts of these benthic invaders vary with site: in some shallow areas, habitat changes and the Dreissena -> round goby -> piscivore food chain have improved conditions for certain native game fishes and waterfowl; in offshore waters, Dreissena is competing for settling algae with the native amphipod Diporeia spp., which are disappearing to the detriment of the native deep-water fish community. The predatory cladoceran Cerocopagis pengoi may compete with small fishes for zooplanktonand increase food-chain length.

Willete, M. T., R. T. Cooney, V. Patrick, D. M. MASON, G. L. Thomas, and D. Scheel. Ecological processes influencing mortality of juvenile pink salmon (s) in Prince William Sound, Alaska. Fisheries Oceanography 10(1):14-41 (2001).

Our collaborative work focused on understanding the system of mechanisms influencing the mortality of juvenile pink salmon (Oncorhynchns gorbuscha) in Prince William Sound, Alaska. Coordinated field studies, data analysis and numerical modelling projects were used to identify and explain the mechanisms and their roles in juvenile mortality. In particular, project studies addressed the identification of major fish and bird predators consuming juvenile salmon and the evaluation of three hypotheses linking these losses to (i) alternative prey for predators (prey-switching hypothesis); (ii) salmon foraging behaviour (refuge-dispersion hypothesis); and (iii) salmon size and growth (size-refuge hypothesis). Two facultative planktivorous fishes. Pacific herring (Clupea pallasi) and walleye pollock (Theragra chalcogramma), probably consumed the most juvenile pink salmon each year, although other gadids were also important- Our prey-switching hypothesis was supported by data indicating that herring and pollock switched to alternative nekton prey, including juvenile salmon, when the biomass of large copepods declined below about 0-2 g m-3. Model simulations were consistent with these findings, but simulations suggested that a June pteropod bloom also sheltered juvenile salmon from predation. Our refuge-dispersion hypothesis was supported by data indicating a five-fold increase in predation losses of juvenile salmon when salmon dispersed from nearshore habitats as the biomass of large copepods declined. Our size-refuge hypothesis was supported by data indicating that size- and growth-dependent vulnerabilities of salmon to predators were a function of predator and prey sizes and the timing of predation events. Our model simulations offered support for the efficacy of representing ecological processes affecting juvenile fishes as systems of coupled evolution equations representing both spatial distribution and physiological status. Simulations wherein model dimensionality was limited through construction of composite trophic groups reproduced the dominant patterns in salmon survival data. In our study, these composite trophic groups were six key zooplankton taxonomic groups, two categories of adult pelagic fishes, and from six to 12 groups for tagged hatchery-reared juvenile salmon. Model simulations also suggested the importance of salmon density and predator size as important factors modifying the predation process.

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