Airborne Mercury in Precipitation in the Lake Superior Region

Mercury was measured in accumulated snow (March 1982) sampled from around Lake Superior and in rainfall from Duluth, Minnesota (June–September 1982 and March–November 1983), Forbes Township, and Dorset in northwestern and central Ontario, respectively (May–September 1983). Methods of melting snow and collecting rain samples were investigated to avoid loss of mercury during the melting process and sample shipment and storage. Low concentrations in snow and rain required greater analytical sensitivity. A detection limit of 0.008 ± 0.004 μg/L of mercury (N = 26) was attained using the cold vapor technique; and by utilizing a gold gauze amalgam accessory for preconcentration, a detection limit of 0.005 ± 0.003 μg/L (N = 13) was attained. Regional comparisons of mercury accumulation in the snow pack across the northern parts of Minnesota, Wisconsin, Michigan, and Ontario show highest values, 0.10 ± 0.17 μg/L Hg, in the Grand Rapids, Minnesota, area and lowest values in remote areas of Minnesota and Ontario. Rainfall concentrations of total mercury were substantially higher than snow accumulation and were mainly of inorganic forms (73%). The highest amounts of mercury were measured in rainfall at Duluth, Minnesota (3.4 μg/L) during June 1982 and at Forbes Township, Ontario, (1.2 μg/L) during July 1983. Substantially lower concentrations were observed in the other months of 1982 and 1983. There is no unique association of the observed mercury concentration with the air parcel history. However, the single highest mercury concentration in rainfall observed at Duluth, Minnesota, occurred when the 850-mb air parcel back trajectory indicated upwind corridors to the N-NW and the highest concentration at Forbes Township, Ontario, was associated with an 850-mb trajectory from W-NW. Significant positive correlation coefficients (0.05) were obtained with other measured components in rain at Duluth, Minnesota, including S, B, Ca, Mg, Na, Fe, Mn, and Zn in 1983. Mercury concentrations in precipitation and in lake water for precipitation-dominated lakes are similar and indicate that atmospheric deposition can be the major source of mercury for some lakes in the Lake Superior region.     

Characteristics of nearshore water quality of Lake Ontario coast under Credit Valley Conservation Jurisdiction,Ontario, Canada

The 28.5 km Lake Ontario shoreline along Credit Valley Conservation’s jurisdiction is habitat for native flora and fauna, the source of drinking water for over two million residents, and the location of outfalls for Region of Peel’s two wastewater treatment plants. Some of the significant sources of pollutants to this region are urban tributaries and the Credit River. Instream, shoreside, and nearshore water quality of this region were characterized under this Lake Ontario Integrated Shoreline Strategy study. Eight Parameters of Concern (PoC); water temperature (WT), total suspended solids (TSS), total phosphorous (TP), orthophosphate (OP), nitrate-nitrogen (NO₃-N), Escherichia coli (E. coli), specific conductivity (SC), and pH were studied from 2011 to 2013. Amongst all the PoCs TP was of concern since its instream (75th percentile range: 51.0 µg/L to 188 µg/L), shoreside (75th percentile range: 9.00 µg/L to 53.75 µg/L), and nearshore (75th percentile range: 9.75 µg/L to 19.00 µg/L) concentrations, exceeded their respective objectives of 30 µg/L and 10 µg/L. Other parameters in shoreside/nearshore samples met their respective provincial/federal objectives/guidelines; however, instream E. coli and specific conductivity levels were elevated, reflecting the effects of urbanization. The Lake water temperature moorings recorded lake stratification dynamics, including eight downwelling and five upwelling events during 2011 deployment period. These results provide baseline data for future climate change-related assessment studies.     

Salmonine Consumption as a Source of Mirex in Human Breast Milk near Rochester,New York

Fifty-seven pre-natal classes were attended to recruit 30 donors of human milk samples in the vicinity of Rochester, NY. Donors were categorized into two groups of 15 Lake Ontario fish eaters (LOFE) and non-Lake Ontario fish eaters (NLOFE). A comparison of mirex concentrations in breast milk of Lake Ontario fish eaters with non-Lake Ontario fish eaters indicated no significant difference in median mirex concentrations (0.09 vs 0.06 ng/g milk). When the Lake Ontario fish eaters were divided into panfish and salmonine consumers, significant differences in mirex concentration in breast milk were observed. Women eating Lake Ontario salmonines have significantly higher concentrations of mirex (median = 0.21 ng/g milk) in their breast milk than Lake Ontario panfish consumers (median = 0.03 ng/g milk) and the NLOFE group (median = 0.06 ng/g milk). Photomirex concentrations were consistently higher in both donor groups than mirex and were significantly higher in the breast milk of salmonine consumers than in both the panfish consumers and the NLOFE group. The relatively high concentrations of photomirex in the breast milk of all donors (LOFE and NLOFE) suggest volatilization and an atmospheric transport of this contaminant. The child of a woman salmonine consumer, breast feeding daily at the median concentration level observed for a month, has a loading of mirex (816 ng mirex/kg) that is equivalent to consuming three Lake Ontario salmon meals at the FDA action level and that represents 2.9 times more mirex than an adult male should consume per month according to the NYS Department of Health advisory.     

Estimation of Zooplankton Mean Length for Use in an Index of Fish Community Structure and its Application to Lake Erie

Mills et al. (1987) developed an index of zooplankton mean size to assess the state of fish communities. The use of this index was evaluated in an assessment of the fish community structure in 1993 at nearshore and offshore sites in the three Lake Erie basins. Mills et al.’s index was developed using a 153-μm mesh net, while the samples in this study have been collected with 64-μm and 110-μm mesh size nets. Two methods were used to convert the data to 153-μm equivalent collections: (a) regression relationships based on simultaneous collections with three mesh sizes, and (b) elimination of smaller organisms that would have passed through the 153-μm mesh by determining the minimum length of inclusion (MLI). The regressions employed for the conversion of zooplankton mean length (ZML) between the nets were: ZML₁₅₃ = 0.137 + 0.988 ZML₁₁₀ (mm) (r²= 0.804) (n = 10) and ZML₁₅₃ = 0.042 + 1.330 ZML₆₄ (mm) (r² = 0.931) (n = 9). The MLI that resulted in the same mean length as the 153-μm sample averaged (± 1 SE) 0.267 ± 0.016 mm (n =19).The comparison between zooplankton mean length and fish community structure in the western basin of Lake Erie in 1993 showed good agreement with Mills et al.’s index. However, the same was not true for the 1988 to 1990 data. Reasons for this discrepancy are discussed.     

Effect of the urbanized embayment Toronto Harbour on the composition and production of zooplankton

To better understand zooplankton dynamics in Lake Ontario’s Toronto Harbour and adjacent coastal area (CA), we sampled zooplankton, phytoplankton, nutrients and physical parameters on six dates in 2016. Despite higher levels of nutrients, chlorophyll and primary production in the inner harbor (IH), the areas supported similar May to November zooplankton biomass (IH = 32 ± 7 and CA = 42 ± 10 mg/m³). IH values were much lower than other nutrient-enriched embayments in Lake Ontario, yet CA biomass was twice that of nearshore sites away from Toronto. Small zooplankton such as rotifers and Bosmina dominated IH; and large taxa (Daphnia, calanoids and predatory cladocerans) were more important in the CA. Daphnia, Bosmina, cyclopoids and calanoids were larger in the CA, and adult cyclopoids had higher egg ratios. This led to low annual IH production estimates for both cyclopoid and calanoid copepods. Total phosphorus and chlorophyll did not appear to regulate zooplankton biomass, but positive relationships were found with bacterial biomass in the IH and with temperature in the cool season. Atypically high fish planktivory rates likely suppressed larger IH zooplankton in 2016, allowing small, resilient Bosmina to flourish and contribute 84% of total production in the IH. Comparing 2016 data to previous zooplankton surveys revealed considerable inter-annual variation in proportions of Daphnia, Bosmina and predatory cladocerans over the 1994 to 2016 period, and the strong top-down controls observed in 2016 were not typical. Elevated microbial production may serve as an important alternate trophic pathway supporting cladoceran populations in Toronto Harbour.     

Organochlorines,Mercury, and Selenium in Great Blue Heron Eggs from Indiana Dunes National Lakeshore,Indiana

In 1993, 20 great blue heron (Ardea herodias; GBH) eggs (one per nest) were collected from a colony at the Indiana Dunes National Lakeshore, Indiana (INDU). The eggs were artificially incubated until pipping and were then analyzed for organochlorines, mercury, and selenium. Livers of embryos were analyzed for hepatic microsomal ethoxyresorufin-O-dealkylase (EROD) activity. Brains were measured for asymmetry. Egg-laying began in early April and the mean clutch size was 4.2 eggs per clutch. Organochlorine concentrations were generally low (geometric mean p,p’-DDE = 1.6 /μg/g wet weight; polychlorinated biphenyl [PCB] = 4.9 μg/g); however, one egg had elevated concentrations of p,p -DDE (13 /μg/g) and PCBs (56 /μg/g). EROD activity in the embryos analyzed from INDU was not elevated. The frequency (11%) of brain asymmetry was low. Eggshells averaged 3.4% thinner than eggshells collected prior to the use of DDT. Mercury (geometric mean = 0.9 μg/g dry weight) concentrations in GBH eggs were within background levels. Selenium (4.0 μg/g dry weight) concentrations in eggs were above background levels, but below a concentration threshold associated with reproductive impairment.     

Cladophora,mass transport,and the nearshore phosphorus shunt

The nearshore phosphorus shunt hypothesis and the potential for mussels to excrete phosphorus sufficient to meet the growth requirements of Cladophora are now well accepted by scientists studying Great Lakes biogeochemistry. The response of algal growth to near bottom water column phosphorus concentrations and the interplay between excretion and mass transport in yielding those concentrations have, however, not been elucidated. Here we present soluble reactive phosphorus profiles from the near bottom environment of Lake Michigan at a site near Good Harbor Bay, Michigan, where both mussels and Cladophora were present. Soluble reactive phosphorus was observed to accumulate under quiescent conditions, establishing a concentration boundary layer (CBL), 5–15 cm thick, with near bottom concentrations on the order of 2–8 μg P/L. A one-dimensional model was applied to determine mass transport conditions mediating the transition from CBL formation to CBL destruction. Significant wave height (SWH) was used as an indicator of mass transport intensity, and it was determined that the formation/destruction transition occurred at a SWH of 0.2 m at the 8-m study site depth. The Great Lakes Cladophora Model was applied to determine the time intervals required to saturate (1 day with the CBL present) and deplete (14 days with the CBL absent) algal internal P stores. A review of SWH conditions at the study site indicated that a CBL would be expected to form at a frequency sufficient to support the phosphorus nutrition of Cladophora over the entire May to August interval.     

Contaminant Concentrations and Reproductive Rate of Lake Superior Bald Eagles, 1989–2001

We investigated the trend in contaminant concentrations in Lake Superior bald eagles (Haliaeetus leucocephalus) from 1989–2001, and examined the relationship of contaminant concentrations to eagle reproductive rate during that time. Concentrations of dichloro-diphenyl-dichloroethylene (DDE) and total polychlorinated biphenyls (PCBs) in nestling blood plasma samples decreased significantly from 1989-2001 (p = 0.007 for DDE, p = 0.004 for total PCBs). Mean contaminant concentrations in eaglet plasma, 21.7 μg/kg DDE (n=51) and 86.7 μg/kg total PCBs (n = 54), were near or below the estimated threshold levels for impairment of reproduction as determined in other studies. A preliminary assessment of polybrominated diphenyl ether (PBDE) concentrations indicated a mean of 7.9 μg/kg total PBDEs in Lake Superior eaglet plasma (n = 5). The number of occupied bald eagle nests along the Wisconsin shore of Lake Superior increased from 15 to 24 per year, between 1989 and 2001 (p < 0.001, r² = 0.70, n = 13 years). Eagle reproductive rate did not increase or decrease significantly between 1989 and 2001 (p = 0.530, r² = 0.037, n = 13 years, mean productivity = 0.96 young per occupied nest). The lack of correlation between reproductive rate and contaminant concentrations, as well as the comparison of contaminant concentrations to the estimated thresholds for impairment of reproduction, suggest that DDE and PCBs no longer limit the reproductive rate of the Lake Superior eagle population in Wisconsin.     

A Comparison of Photosynthate Allocation in Lakes

We compared the relationships between photosynthate allocation to protein, carbohydrate, lipid and low molecular weight (LMW) fractions and the variables daylength and water temperature in Lakes Huron, Michigan, and Ontario as well as three smaller headwater lakes in the Lake Ontario drainage. In all lakes investigated the allocation of recently produced photosynthate to carbohydrate was strongly related to daylength (% carbohydrate = −3.5 * daylength (hr) + 72.8; n = 59, r² = 0.56). The percentage of photosynthate allocated to protein was a function of water temperature in all lakes although the y-intercept for the protein-temperature relationship was much lower in the three headwater lakes and Lake Ontario (% protein = 0.50 * temperature (°C) + 6.1; n = 37, r² = 0.52) than in Lake Huron and Lake Michigan (% protein = 0.68 * temperature (°C) + 24.2; n = 23, r² = 0.49). The increase in allocation to protein was related to a decrease in allocation to low molecular weight material (% LMW = −1.1 * % protein + 57.13; n = 60, r² = 0.72). The percentages of photosynthate in lipid and LMW material were not related to any of the environmental variables measured. Assuming that photosynthate allocation is related to biochemical composition, the phytoplankton in Lakes Huron and Michigan were more protein rich for a given temperature than those in Lake Ontario and in the smaller inland lakes. The protein deficit was due to an increase in allocation to LMW material.     

Precision of Ages Determined from Scales and Opercles for Yellow Perch Perca flavescens

Scales and opercles were used to age yellow perch Perca flavescens collected in 1989 from Lake Madison (South Dakota), Dauphin Lake (Manitoba), and southern Lake Michigan (Indiana). Three readers aged fish from Lake Madison and Dauphin Lake once and two readers aged fish from Lake Michigan twice. The coefficient of variation (CV) was calculated to compare precision. Ages determined from opercles were as precise as those from scales for fish from Lake Madison (CV = 0 for both structures), and more precise than ages from scales for fish from Dauphin Lake (CV_opercle = 14.0, CV_scale = 27.4, p < 0.001) and Lake Michigan (CV _opercle = 10.6, CV_scale = 13.9, p < 0.001). The high precision of scale and opercle ages for yellow perch from Lake Madison can be attributed to the fast growth rate of fish from that lake and also that only age 1 and 2 fish were aged. The greater precision of opercle ages in comparison to scale ages for Dauphin Lake and Lake Michigan yellow perch can be attributed to ease of recognition of false annuli on opercles as well as to difficulty in distinguishing between false and true annuli crowded on the edge of scales from mature, slower growing fish. Because true annuli are more easily recognized on opercles, ages determined from opercles may be more accurate than ages determined from scales for yellow perch growing at slow or moderate rates.     

Anthropogenic Copper Inventories and Mercury Profiles from Lake Superior: Evidence for Mining Impacts

During the past 150 years, the mining industry discharged more than a billion tons of tailings along Lake Superior shorelines and constructed numerous smelters in the watershed. Given the vast size of Lake Superior, were sediment profiles at locations far offshore impacted by nearshore activities? Did copper and associated precious metal mining modify regional fluxes for copper and mercury? Samples from thirty sediment cores document that background concentrations of copper are high (mean 60.9 ± 7.0 μg/g), due to the proximity of natural ore sources. Anthropogenic inventories uncorrected for focusing also are high, ranging from 20 to 780 μg/cm² (mean 187 ± 54 μg/cm²). Focusing factor corrections decrease the mean estimate and reduce variance (144 ± 24 μg/cm²). Several approaches to estimating inputs suggest that only 6 to 10% of historic copper deposition originated directly from atmospheric sources, emphasizing terrestrial sources. Moreover, coastal sediment cores often show synchronous early increases in copper and mercury with buried maxima. Around the Keweenaw Peninsula, twenty-two cores trace high copper and mercury inventories back to mill and smelting sources. Direct assays of ores from thirteen mine sites confirm a natural amalgam source of mercury in the stamp mill discharges. Core records from inland lakes (Michigamme Project) also reveal patterns of copper and mercury inputs from a variety of mining sources: historic tailing inputs, amalgam assay releases, and atmospheric smelter plumes.     

Contaminants Associated with Suspended Sediments in Lakes Erie and Ontario, 1997–2000

Sediment traps were installed at individual index stations in the western basin of Lake Erie and the Mississauga (central) basin of Lake Ontario, and refurbished seasonally during the period 1997–2000. In Lake Ontario, sediment down flux rates and corresponding contaminant down flux rates were highest in winter and increased with depth due to the influence of resuspended bottom sediments. Sediment down flux rates in western Lake Erie (22 to 160 g m⁻² d⁻¹) were far greater than in Lake Ontario (0.19–3.0 g m⁻² d⁻¹). Suspended material in western Lake Erie was characterized as predominately resuspended bottom sediments; down flux rates were roughly 5- to 10-fold higher in spring and fall, compared to summer. Suspended sediment concentrations of PCBs and other organochlorine contaminants, represented by both annual means and individual seasonal values, were higher in Lake Ontario throughout the duration of the study, compared to Lake Erie. The mean annual concentration of PCBs in suspended sediments over the period 1997–2000 was 330 ng/g in western Lake Erie and 530 ng/g in Lake Ontario. Based on a comparison with historical data from Lake Ontario, mean contaminant concentrations over the period 1997–2000 for PCBs, hexachlorobenzene, and mirex corresponded to decreases of 38%, 74%, and 40%, respectively, since the mid-1980s. Corresponding down flux rates for PCBs, hexachlorobenzene, and mirex decreased by approximately 70%, 90%, and 80%, respectively, since the 1980s.     

Neonatal Behavioral Assessment Scale Performance in Humans Influenced by Maternal Consumption of Environmentally Contaminated Lake Ontario Fish

Behavioral effects in neonates of their mothers’ consumption of Lake Ontario fish were examined using the Neonatal Behavioral Assessment Scale (NBAS). Newborns of women who had consumed > 40 equivalent pounds of fish were placed in a high-exposure group (n = 152), those of women who had consumed < 40 equivalent pounds of fish were placed in a low-exposure group (n = 243), and offspring of women who reported having never eaten Lake Ontario fish comprised the control group (n = 164). Assessments were given at 12–24 hours after birth, and again at 25–48 hours after birth. Despite relatively low levels of fish consumption, newborns in the high-exposure group scored more poorly than those in both the low-exposure and control groups on the Reflex, Autonomic, and Habituation clusters of the NBAS. No significant group differences were found on the Orientation, Range of State, Regulation of State, or Motor clusters of the NBAS, nor did birth weight or head circumference differ between groups. These results represent the first replication and extension of the neonatal results of the Lake Michigan Maternal Infant Cohort study (Jacobson et al. 1984).     

Diatom-based Weighted-averaging Transfer Functions for Great Lakes Coastal Water Quality: Relationships to Watershed Characteristics

In an effort to develop indicators for Great Lakes near-shore conditions, diatom-based transfer functions to infer water quality variables were developed from 155 samples collected from coastal Great Lakes wetlands, embayments and high-energy shoreline sites. Over 2,000 diatom taxa were identified, and 352 taxa were sufficiently abundant to include in transfer function development. Multivariate data exploration revealed strong responses of the diatom assemblages to stressor variables, including total phosphorus (TP). Spatial variables such as lake, latitude and longitude also had notable relationships with assemblage characteristics. A diatom inference transfer function for TP provided a robust reconstructive relationship (r² = 0.67; RMSE = 0.28 log(μg/L); r²jackknife = 0.55; RMSEP = 0.33 log (μg/L)) that improved following the removal of 13 samples that had poor observed-inferred TP relationships (r² = 0.75; RMSE = 0.22 log(μg/L); r²_jackknife = 0.65; RMSEP = 0.26 log (μg/L)). Diatom-based transfer functions for other water quality variables, such as total nitrogen, chloride, and chlorophyll a also performed well. Measured and diatom-inferred water quality data were regressed against watershed characteristics (including gradients of agriculture, atmospheric deposition, and industrial facilities) to determine the relative strength of measured and diatom-inferred data to identify watershed stressor influences. With the exception of pH, diatom-inferred water quality variables were better predicted by watershed characteristics than were measured water quality variables. Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, it appears they can better integrate water quality information than snapshot measurements. These results strongly support the use of diatoms in Great Lakes coastal monitoring programs.     

Association of Low Reproductive Rates and High Contaminant Levels in Bald Eagles on Green Bay,Lake Michigan

Bald eagles (Haliaeetus leucocephalus) nesting on the shores of Green Bay, Lake Michigan, had reproductive rates significantly lower than those of neighboring eagles nesting in inland Wisconsin (0.55 vs. 1.1 young per occupied territory). This study investigated effects of two factors which have depressed eagle reproductive rates at other locations: exposure to organochlorine contaminants and low food availability. Levels of dichloro-diphenyl-dichloroethylene (DDE) and total polychlorinated biphenyls (PCBs) in addled eggs and eaglet blood samples from Lake Michigan and inland Wisconsin reference sites were measured. An index to food availability, the food delivery rates by parent eagles to nestlings, and other behavioral indices that have been associated with food availability, were measured and compared to inland reference data. Mean contaminant concentrations in addled eggs from Green Bay were 8.3 μg/g wet weight DDE and 31.3 μg/g wet weight total PCBs (1987 to 1996, n = 9). Mean concentrations in nestling blood plasma were 53 μg/kg wet weight DDE and 207 μg/kg wet weight total PCBs (1987 to 1995, n = 8). Indices of food availability were generally normal in comparison to inland reference data. Mean food delivery rate to the nestlings was 2.55 items per nestling per day (n = 7 nests). None of the behavioral measures differed significantly from inland reference values, suggesting that prey was adequate. It was concluded that organochlorine contaminants caused all or most of the depression in reproductive rates of Green Bay bald eagles.     

Measurement of Diporeia respiration rate for Lake Superior

The freshwater amphipod Diporeia is a dominant macroinvertebrate species in Lake Superior’s benthic community and an important prey item for many fish. A capacity to predict growth and production rates of Diporeia using a bioenergetics model requires information on physiological processes of the species. The objective of this study is to quantify oxygen consumption of Lake Superior Diporeia and to determine if respiration rate changes with body length. Diporeia were collected from Lake Superior and kept over natural sediment maintained at 4 °C. Dissolved oxygen levels for groups of immature (2 mm), juvenile (4 mm), and adult (6 mm) Diporeia in 20 ml microcosms were measured using a polarographic microelectrode. Mass-specific respiration rates for Lake Superior Diporeia ranged from 32.0 to 44.7 mg O₂ g DW^− 1 day ⁻¹. A significant relationship between body length and mass-specific respiration rate (p > 0.1) was not found. The estimate of Diporeia respiration presented here is significantly higher (p < 0.05) than previous findings from populations in Lakes Michigan and Ontario. This study provides new data on respiration rates of Lake Superior Diporeia and compares findings to studies for other connecting Great Lakes.     

Distribution of Metals in Different Size Fractions of Sediment from the Niagara River

This study was carried out to demonstrate that the concentration of major and trace elements, determined in sediment samples separated mechanically into different size fractions, gives better information for assessing a potential hazard of in situ, dredged, or resuspended sediments than the bulk total concentration. The concentrations of major elements (Si, Al, Ca, Mg, Na, K, Fe, Ti, Mn, and P), trace elements (Cr, Co, Cu, Zn, V, Ni, and Pb), and organic and carbonate C were determined in six size fractions (< 13 μm, 13–19 μm, 19–27 μm, 27–40 μm, 40–54 μm, and 54–150 μm) of bottom sediments collected at eight stations along the Niagara River. Fine particles (< 13 μm) separated from the river sediments exposed to pollution sources accumulated greater metal quantities than particles in the other size fractions. The contribution of trace elements from specific size fractions was calculated from the particle size distribution and trace elements concentration. With the exception of Ni, significant differences were found between trace elements concentration in specif ic particle size fractions of Niagara River sediments and that from the nearshore zone of Lake Erie.     

Food of Trout and Salmon in Lake Ontario

Stomachs of trout and salmon (n = 1,904) were collected from fish registered at fishing tournaments held in New York State waters of Lake Ontario between April and September 1983 and 1984. Numbers of adult-sized fish containing identifiable food items were 323 lake trout (Salvelinus namaycush), 289 brown trout (Salmo trutta), 24 rainbow trout (S. gairdneri), 164 coho salmon (Oncorhynchus kisutch), and 63 chinook salmon (O. tschawytscha) Proportional similarity in diet between pairs of species was high and normally exceeded 0.70; diet composition of individual species was similar between years. Alewives (Alosa pseudoharengus) were the main prey of all species during all months and were normally 110–149 mm in standard length. Rainbow smelt (Osmerus mordax) was the second most common prey eaten but was generally found in fewer than 20% of the stomachs examined during any month. Diet diversity was generally higher during April-May than during July-September for coho salmon, lake trout, and brown trout. Larger brown trout ate larger alewife in 1983 but not in 1984. Results suggest that the five trout and salmon species in Lake Ontario are potential competitors.     

Mapping cyanobacterial blooms in Lake Champlain's Missisquoi Bay using QuickBird and MERIS satellite data

C-phycocyanin (C-PC) and chlorophyll-a (Chl-a) concentrations for the eutrophic waters of Missisquoi Bay, Lake Champlain (VT–QC) were retrieved from Envisat's MERIS radiance data (300 m spatial resolution) and validated against coincident georeferenced transect observations. Pigment concentrations were also predicted from empirically calibrated QuickBird data (2.4 m spatial resolution) using selected band ratios and principal components analysis. The QuickBird NIR/Red band ratio accounted for approximately 80% of the variability in observed Chl-a concentration, allowing for detailed mapping of phytoplankton spatial distributions. C-PC concentrations, in contrast, were somewhat poorly modeled (R² = 0.68). Use of these data for monitoring purposes, however, is also limited by the need for coincident field observations. Chl-a concentrations were also accurately retrieved from the MERIS data (Mean Relative Error = -0.6%) despite high concentrations of suspended particles and dissolved organic matter in the bay waters. C-PC concentrations were underestimated on average by 2.1%, but by 10–20% at high C-PC concentrations (≥ 80 μg/L) and as the proportion of cyanobacteria in the phytoplankton community decreased. The relatively high overall accuracies observed, however, attest to the robustness of the MERIS semi-analytical retrieval algorithms used to quantify potentially toxic cyanobacteria cell densities without the need for coincident field data. Our analyses over a 17 day period captured the peak and collapse of a late summer cyanobacterial bloom, illustrating the value of remote sensing to provide synoptic and timely information on the abundance and distribution of cyanobacterial populations that, in turn, can facilitate public health risk assessment.     

Reproductive Potential and Fecundity of Lake Trout Strains in Southern and Eastern Waters of Lake Ontario, 1977–1994

We assessed the reproductive potential of various genetic strains of hatchery lake trout (Salvelinus namaycush) in southern and eastern Lake Ontario from indices of fecundity and indices of male abundance. Indices were constructed from catches of mature lake trout in gill nets during September 1980 to 1994 after correcting for mortality from sea lampreys (Petromyzon marinus) which occurred between September sampling and late fall spawning. Strain and age were assigned to individual lake trout based on clipped fins and maxillary bones or coded wire tags. Fecundity-length relationships for fish of the same age, determined from mature females collected in 1977 to 1981 and 1994, were not different (P > 0.05) among genetic strains. For all strains combined, fecundity-length relationships in 1977 to 1981 were not different among fish of various ages but in 1994, age-5 and -6 fish had fewer eggs (P < 0.003) than age-7 fish, and age-7 fish had fewer eggs (P < 0.003) than fish of age 8, 9, or 10. Annual indices of fecundity varied 19 fold and indices of mature males varied 11 fold; both indices were low in the early 1980s, increased sharply in the mid 1980s, and peaked in 1993. The strain which dominated fecundity and mature male indices shifted during the study from Seneca Lake strain to Lake Superior strain and then back to Seneca Lake strain. However, changes in either reproductive potential or genotypes do not appear responsible for the abrupt appearance of naturally-produced yearling lake trout throughout southern and eastern Lake Ontario in 1994–1995, the first widespread occurrence of juveniles produced by hatchery lake trout in Lake Ontario.