We use data from inundated-area surveys of 58 coastal wetlands spanning a gradient of anthropogenic impacts across all five Laurentian Great Lakes to describe the distribution of nine exotic and invasive taxa of aquatic plants. We found plants that were exotic or have invasive strains to be substantially more prevalent in wetlands in Lakes Erie and Ontario than in Lakes Superior and Huron, with Lake Michigan wetlands intermediate. Najas minor (slender naiad), Butomus umbellatus (flowering rush), and Hydrocharis morsus-ranae (European frogbit) were restricted to the lower lakes and rarely dominant. Myriophyllum spicatum (Eurasian milfoil), Potamogeton crispus (curly pondweed), Lythrum salicaria (purple loosestrife), Phalaris arundinacea (reed canary grass), Phragmites australis (common reed), and Typha sp. (cattail) were more widespread and except for P. crispus, often among the dominant taxa. None of the submerged or floating-leaf exotic taxa were associated with altered total plant cover or richness, although M. spicatum, P. crispus, and native Stuckenia pectinatus (sago pondweed) were positively associated with agricultural intensity in the watershed (a surrogate for nutrient loading). Emergent P. australis, L. salicaria, and Typha were more likely to be present and dominant as agricultural intensity increased, and were associated with elevated emergent cover and decreased emergent genera richness. Effects of dominant taxa on plant cover and richness were readily detected using ordinal data from 100 m inundated segments but were harder to discern with data aggregated to the wetland scale. The sum of shoreline-wide abundance scores for four easily identified taxa (S. pectinata, P. australis, Typha, and L. salicaria) is proposed as a rapidly-measured indicator of anthropogenic disturbance across the Great Lakes.

For remote sensing of Great Lakes ice cover, a field experiment campaign was conducted in the 1997 winter season across the Straits of Mackinac and Lake Superior. The campaign was coordinated in two expeditions on two different United States Coast Guard icebreaker vessels, the Biscayne Bay in February and the Mackinaw in March. Aboard these icebreakers, the Jet Propulsion Laboratory C-band polarimetric scatterometer was used to measure backscatter signatures of various ice types and open water at incidence angles from 0° to 60°. The radar measurements include incidence angles and polarizations of spaceborne Synthetic Aperture Radars (SAR) on ERS, RADARSAT, and Envisat satellites. The radar data together with in situ measurements form a signature library that can be used to interpret SAR data for ice classification and mapping. Results are presented for backscatter signatures of Great Lakes ice types from thin lake ice to thick brash ice with different snow-cover and surface conditions. The signature library indicates that several ice types can be identified with multi-polarization SAR data; however, single-polarization data can result in misclassification of ice and open water at different ranges of incidence angle and wind conditions. For incidence angles larger than 30°, thick brash ice, the most difficult for icebreaking operations and the most hazardous for ship navigation, can be uniquely identified by co-polarized backscatter for all wind conditions below the gale force.

During the 1997 winter season, shipborne polarimetric backscatter measurements of Great Lakes (freshwater) ice types using the Jet Propulsion Laboratory C-band scatterometer, together with surface-based ice physical characterization measurements and environmental parameters, were acquired concurrently with Earth Resource Satellite 2 (ERS-2) and RADARSAT Synthetic Aperture Radar (SAR) data. This polarimetric data set, composed of over 20 variations of different ice types measured at incident angles from 0° to 60° for all polarizations, was processed to radar cross-section to establish a library of signatures (look-up table) for different ice types. The library is used in the computer classification of calibrated satellite SAR data. Computer analysis of ERS-2 and RADARSAT ScanSAR images of Great Lakes ice cover using a supervised classification technique indicates that different ice types in the ice cover can be identified and mapped, and that wind speed and direction can have an influence on the classification of water as ice based on single frequency, single polarization data. Once satellite SAR data are classified into ice types, the ice map provides important and necessary input for environmental protection and management, ice control and ice breaking operations, and ice forecasting and modeling efforts.

Integrated, GIS-based, wetland predictive models were constructed to assist in predicting the responses of wetland plant communities to proposed new water-level regulation plans for Lake Ontario. The modeling exercise consisted of four major components: 1) building individual site wetland geometric models; 2) constructing generalized wetland geometric models representing specific types of wetlands (rectangle model for drowned river mouth wetlands, half ring model for open embayment wetlands, half ellipse model for protected embayment wetlands, and ellipse model for barrier beach wetlands); 3) assigning wetland plant profiles to the generalized wetland geometric models that identify associations between past flooding/dewatering events and the regulated water-level changes of a proposed water-level-regulation plan; and 4) predicting relevant proportions of wetland plant communities and the time durations during which they would be affected under proposed regulation plans. Based on this conceptual foundation, the predictive models were constructed using bathymetric and topographic wetland models and technical procedures operating on the platform of ArcGIS. An example of the model processes and outputs for the drowned river mouth wetland model using a test regulation plan illustrates the four components and, when compared against other test regulation plans, provided results that met ecological expectations. The model results were also compared to independent data collected by photointerpretation. Although data collections were not directly comparable, the predicted extent of meadow marsh in years in which photographs were taken was significantly correlated with extent of mapped meadow marsh in all but barrier beach wetlands. The predictive model for wetland plant communities provided valuable input into International Joint Commission deliberations on new regulation plans and was also incorporated into faunal predictive models used for that purpose.

A particle tracking model (PTM) is linked with a hydrodynamic model to evaluate mean seasonal circulation patterns in Lake Ontario, and also to provide a basis for predicting movement of algal blooms. The PTM is based on a random walk algorithm that combines a deterministic advective component with a stochastic component associated with the turbulent diffusivity field to calculate trajectories of neutrally buoyant particles, where both the advective and diffusive velocities are obtained from the hydrodynamic model. Mean circulation is calculated using 30-year average meteorological forcing data collected from five stations around the lake. Seasonal variations in lake circulation are demonstrated, and a clockwise flow in the eastern basin during summer and early fall is identified, contrary to some previous observations that suggest counterclockwise flow. The impacts of Niagara and St. Lawrence river flows on general lake circulation are found to be small, except within approximately 10 km of the river mouth. Development and application of the PTM demonstrate its potential to provide calculations of (Lagrangian) movements as determined from the hydrodynamic output, and to serve as a first step toward development of an algal transport model. Particle tracking helps to visualize flow patterns and provides a means of evaluating the probability a bloom will reach a specified area, given an initial position and the predicted velocity and diffusivity fields. This capability, when set up for real-time applications, can provide an important tool to support management decisions that may be needed when a bloom is observed, for example in predicting potential impacts of the bloom on a beach or a water intake.

We examined a suite of environmental contaminants and exposure endpoints in black-crowned night-heron (Nycticorax nycticorax, BCNH) embryos collected in 2002 from colonies in Illinois, Minnesota, and Virginia. Embryos from the Lake Calumet, IL, colony had greater exposure to polychlorinated biphenyls (PCBs), 4,4′-dichlorodiphenyldichloroethylene (DDE), dieldrin, transnonachlor, oxy-chlordane, cobalt, copper, and selenium than did those from northwest MN and coastal VA. Embryos from IL and VA contained greater concentrations of mercury and zinc than those from MN, whereas the latter had greater accumulation of lead. Greater exposure of IL embryos to PCBs was reflected in greater ethoxyresorufin-O-deethylase and benzyloxyresorufin-O-dealkylase induction. However, measures of oxidative stress and genotoxicity were similar to those in embryos from the other colonies examined, and no overt toxic effects of contaminant exposure such as embryo mortality or malformations were observed. Although efforts to clean up the south Chicago environment are ongoing, Lake Calumet BCNH, and undoubtedly other piscivorous wildlife foraging in the region, continue to be exposed to a variety of environmental contaminants. Life-history characteristics of this species make it ideal as an environmental sentinel for the success of the cleanup of the south Chicago environment.

In this study, we measured growth trends in oxygen and carbon isotopic ratios in whole sagittal otoliths from three adult centropomid fish (Lates stappersii) from each of three sub-basins of Lake Tanganyika, East Africa. Sampling density was 20 to 50 samples per otolith. Both δ¹⁸O and δ¹³C values increase with age. The δ¹⁸O data suggest that otoliths were precipitated near the expected equilibrium with the ambient environment (ca. 3.5‰) and support a migration pattern from surface waters during larval stages to deeper waters (40 to 80 m) for mature fish. Relatively high δ¹⁸O values in the southern sub-basin are consistent with cooler temperatures in the region during seasonal upwelling. The δ¹³C increase from otolith core to edge is large (up to 4‰) and is interpreted as due to ontogenetic changes in diet and contributions from a decrease in the proportion of respired CO₂ incorporated into otolith carbonate as metabolic rates of the fish dropped with maturity. The data seem to successfully reveal life strategy and migration patterns of L. stappersii, document regional differences in lake conditions, and provide a record of temperature within the water column during which the fish lived. Higher resolution studies and analyses of historical samples could be used to constrain modern and past growth patterns, and to reconstruct past temperature gradients and productivity patterns in the lake.

Time series measurements of current velocity, wave action, and water transparency were made at two sites—one in 24 m of water and the other in 53 m—in Lake Erie during the fall and winter of 2004–2005. The observations at the shallow site show that bottom resuspension occurred several times during the deployment. Although local resuspension did not occur at the deeper station, several advection episodes were observed. The storms during the observation period were not unusually large, so the processes observed are probably typical of those that occur on a yearly basis. The observations agree reasonably well with previous estimates for both the bottom shear stress during storms, and for the critical shear stress needed to resuspend bottom sediment, but previous estimates of the particle settling velocity are probably too low, while previous estimates of the sediment entrainment rate are too high. The results show that bottom material in the central basin is reworked numerous times before it is finally buried. Deposition in the eastern basin is a more continuous process, but the events observed were not sufficient to match the long-term accumulation rate, so deposition at this site is probably also due in part to larger, more infrequent storms.

Satellite observations of aquatic colour enable environmental monitoring of the Great Lakes at spatial and temporal scales not obtainable through ground-based monitoring. By merging data from the Coastal Zone Color Scanner (CZCS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), monthly binned images of water-leaving radiance over the Great Lakes have been produced for the periods 1979–1985 and 1998–2006. This time-series can be interpreted in terms of changes in water clarity, showing seasonal and inter-annual variability of bright-water episodes such as phytoplankton blooms, re-suspension of bottom sediments, and whiting events. Variations in Secchi disk depth over Lakes Erie and Ontario are predicted using empirical relationships from coincident measurements of water transparency and remotely-sensed water-leaving radiance. Satellite observations document the extent to which the water clarity of the lower Great Lakes has changed over the last three decades in response to significant events including the invasion of zebra mussels. Results confirm dramatic reductions in Lake Ontario turbidity in the years following mussel colonization, with a doubling of estimated Secchi depths. Evidence confirms a reduction in the frequency/intensity of whiting events in agreement with suggestions of the role of calcium uptake by mussels on lake water clarity. Increased spring-time water clarity in the eastern basin of Lake Erie also corroborates previous observations in the region. Despite historical reports of localised increases in transparency in the western basin immediately following the mussel invasion, image analysis shows a significant increase in turbidity between the two study periods, in agreement with more recent reports of longer term trends in water clarity. Through its capacity to provide regular and readily interpretable synoptic views of regions undergoing significant environmental change, this work illustrates the value of remotely sensing water colour to water clarity monitoring in the lower Great Lakes.

Potential for large-scale physical transport processes to affect recruitment of Lake Michigan yellow perch (Perca flavescens) was studied by examining the variation in larval distribution, growth rate, and settlement during June–August 1998–2003 using a 3D particle transport model linked with an individual-based bioenergetics growth model. In all years, virtual larvae were released nearshore in southwestern Lake Michigan, a known and important spawning region for yellow perch. For any given year, the same circulation pattern and water temperature either promoted or reduced yellow perch settlement depending on the consumption rates and settlement size chosen in the growth model. Increased consumption increased the number of settled larvae and expanded the total area where larvae settled, whereas increased settlement size reduced the number of settled larvae and reduced the overall settlement area. Interannual variability in circulation patterns and water temperature also resulted in contrasting larval settlement rates, settlement locations, and size of settlement areas between years. Model predictions were most consistent with field observations of age-0 yellow perch from Illinois and Michigan waters when settlement was assumed to occur at 50 mm. Moreover, our model suggests that larvae originating from southwestern Lake Michigan can recruit anywhere within the southern basin and even in the northern basin. Future model improvement will require information on the relative contribution of various sectors to the larval pool, their distribution with reference to the hydrodynamic landscape, the feeding and growth of yellow perch during their pelagic phase, and the size at transition to demersal stage.

Many nonindigenous species (NIS) present in the Laurentian Great Lakes are expanding their ranges to inland lakes and streams. This study used cladoceran microfossils to examine the invasion history of Eubosmina coregoni, the first known nonindigenous zooplankter to invade Lake of the Woods (LOW), Ontario, Canada. Sediment cores from 16 sites in LOW were used to analyze broad-scale presence/absence of E. coregoni prior to human development (bottom sediment samples) in comparison with present-day distribution (top sediment samples). E. coregoni had the highest relative abundance in the northern and eastern regions of LOW and the abundance of all cladoceran remains was low in the southern region of the lake. A long core (time core) from Clearwater Bay provided a more detailed historical account of E. coregoni's abundance in the northern region of LOW, indicating that E. coregoni was first detected in the lake in the early 1990s, approximately 25 years after it was discovered in the Laurentian Great Lakes. Results obtained in this study have illuminated temporal and spatial patterns of colonization of this inland water body. Study of the early invasion dynamics of NIS in these inland lakes may aid in the prevention of future invasions of taxa that have already altered the food web dynamics in the Laurentian Great Lakes.

We propose a radiometric chronology bracket for the last glacial advance/retreat, called the Marquette readvance, in the Upper Peninsula of Michigan (Upper Peninsula) using organic material from kettle lakes and previously published age determinations on wood buried by glaciofluvial sediments. The lakes are located both inside and outside the ice-contact margin of the Marquette readvance. Wood buried in glaciofluvial sediments from the Marquette readvance was previously dated at 10,025 ± 100 ¹⁴C yr BP (Hughes and Merry 1978, Lowell et al. 1999, and Pregitzer et al. 2000). Ackerman Lake, a kettle lake located inside the ice-contact margin, yielded a basal radiocarbon date of 9,495 ± 70 ¹⁴C yr BP representing the time of organic accumulation after ice retreat. These dates above and below the glacial deposit bracket the age of the Marquette readvance/retreat to 360–700 ¹⁴C yr, or the midpoint of 530 ¹⁴C yr. Ackerman Lake yielded multiple radiocarbon dates, including an average date of 8,811 ± 11 ¹⁴C yr BP (9,736–9,913 cal yr BP) at a change in stratigraphy from red clay to gray silt. This transition along the northern Upper Peninsula is interpreted to represent ice sheet retreat into Lake Superior and the reworking of older glacial sediments by ~8,500 ¹⁴C yr BP. Organic material from the kettle lake sediments spanning multiple geomorphic locations (both inside and outside of the ice-contact margin) and previous radiocarbon dates from the entire Upper Peninsula yielded dates concentrating around 9,500 14C yr BP. We attribute this synchronous organic accumulation in the Upper Peninsula to be a result of climatic signature corresponding with the Preboreal Oscillation, so the duration of the Marquette glacial cover may have been less then implied by the Ackerman Lake basal age.

Between 1998 and 2002, surface water samples were collected from several sites in the Don River and Humber River watersheds, both tributaries to Lake Ontario, and analyzed for a variety of pesticides, including those used for urban lawn care. Analyses included 152 pesticide active ingredients and eight metabolites. Samples were collected during base flow periods (i.e., dry events) and rainfall events (i.e., wet events). The objectives of the study were to determine which pesticides were detectable, whether there was a difference in the detection frequency between the two watersheds and between upstream and downstream in each river, and whether precipitation influenced the frequency of detection. Eleven pesticides and one metabolite were detected in surface waters of the Don and Humber rivers or their tributaries, with approximately 72% of samples containing at least one pesticide attributable to lawn care use. The pesticides and pesticide metabolite detected in this study included 2,4-D, atrazine, bromacil, carbofuran, chlorpyrifos, cypermethrin, diazinon, dicamba, MECOPROP, metolachlor, metribuzin, and an atrazine metabolite (des-ethyl atrazine). Four pesticides exceeded federal or provincial water quality guidelines/objectives. Diazinon exceeded the provincial water quality objective in 28% of the samples taken. For the three other pesticides (atrazine, carbofuran and chlorpyrifos) exceedance of a water quality criteria occurred in less than 1% of the samples.

Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) have established naturalized populations throughout the Great Lakes. Young-of-year of these species occur sympatrically for about one month in Lake Ontario tributaries. This study examined the diets of subyearling Chinook salmon and steelhead relative to available food in the Salmon River, New York. Terrestrial invertebrates and trichopterans were the major prey of Chinook salmon, whereas steelhead fed primarily on baetid nymphs and chironomid larvae. Diet overlap was low (0.45) between the species. The diet of Chinook was closely associated to the composition of the drift (0.88). Steelhead diet drew equally from the drift and benthos during the first year of the study, but more closely matched the benthos during the second year. Differences in prey selection, perhaps associated with differences in fish size, in addition to apparent differences in feeding mode (drift versus benthic), likely reduce competitive interactions between these species.

We investigated the potential for using carbon and oxygen isotope values of otolith carbonate as a method to distinguish naturally produced (wild) lake trout (Salvelinus namaycush) from hatchery-reared lake trout in Lake Ontario. We determined δ ¹³C_(CaCO3) and δ ¹⁸O_(CaCO3) values of otoliths from juvenile fish taken from two hatcheries, and of otoliths from wild yearlings. Clear differences in isotope values were observed between the three groups. Subsequently we examined otoliths from large marked and unmarked fish captured in the lake, determining isotope values for regions of the otolith corresponding to the first year of life. Marked (i.e., stocked) fish showed isotope ratios similar to one of the hatchery groups, whereas unmarked fish, (wild fish or stocked fish that lost the mark) showed isotope ratios similar either to one of the hatchery groups or to the wild group. We interpret these data to suggest that carbon and oxygen isotope values can be used to determine the origin of lake trout in Lake Ontario, if a catalogue of characteristic isotope values from all candidate years and hatcheries is compiled.

Localized natural reproduction of lake trout Salvelinus namaycush in Lake Huron has occurred since the 1980s near Thunder Bay, Michigan. During 2004–2006, USGS spring and fall bottom trawl surveys captured 63 wild juvenile lake trout at depths ranging from 37–73 m at four of five ports in the Michigan waters of the main basin of Lake Huron, more than five times the total number captured in the previous 30-year history of the surveys. Relatively high catches of wild juvenile lake trout in bottom trawls during 2004–2006 suggest that natural reproduction by lake trout has increased and occurred throughout the Michigan waters of the main basin. Increased catches of wild juvenile lake trout in the USGS fall bottom trawl survey were coincident with a drastic decline in alewife abundance, but data were insufficient to determine what mechanism may be responsible for increased natural reproduction by lake trout. We recommend further monitoring of juvenile lake trout abundance and research into early life history of lake trout in Lake Huron.

Lake whitefish (Coregonus clupeaformis Mitchill), an important commercial species in the Laurentian Great Lakes, have experienced decreased growth and condition in regions of the upper Great Lakes over the past 20 years. Increases in lake whitefish density and decreases in the density of Diporeia spp., an energy rich and historically important part of the lake whitefish diet, have been implicated in the recent declines in lake whitefish growth and condition. The goal of this study was to describe lake whitefish fecundity, egg lipid content, and total ovary lipid content in selected regions of Lakes Huron, Michigan, and Superior in 1986–87 and 2003–05, two time periods with different lake whitefish and Diporeia densities. Under conditions of high lake whitefish density and low Diporeia density, female lake whitefish in the upper Laurentian Great Lakes generally produced fewer eggs. Egg lipid content was higher in 2003–05 than in 1986–87 at all sites, regardless of changes in lake whitefish or Diporeia densities. Total ovary lipid content and lake whitefish abundance were inversely related, while there was no significant relationship between total ovary lipid content and Diporeia density. The amount of energy that lake whitefish invested in egg production was more closely associated with lake whitefish abundance than with Diporeia density. This study provides evidence that recent changes in production dynamics of Great Lakes lake whitefish have not been driven solely by declines in Diporeia but have been significantly influenced by lake whitefish abundance.