Quagga mussels (Dreissena bugensis) as biomonitors of metal contamination: A case study in the upper St. Lawrence River

In this study, the utility of quagga mussels (Dreissena bugensis) as biomonitors was investigated by measuring total concentrations of three trace metals, cadmium, copper, and zinc, in soft tissues. Quagga mussels were sampled from five sites along the upper St. Lawrence River, including one industrially influenced site, from 1999 through 2007. Mussels were collected from near-shore areas, divided into 5 size classes based on maximum shell length, and tissues were pooled for analysis of each size group. Two-way analysis of variance and a posteriori range tests were used to test for differences among sites along a distance gradient from the outflow of Lake Ontario and to examine inter-annual variability within and among sites. Cadmium concentrations were higher nearer the outflow of the lake. Copper concentrations varied among sites and years, but were generally highest near the industrial site. Zinc concentrations were relatively uniform, possibly reflecting internal regulation. Animal size measured as shell length was not an important factor in this section of the river, but warrants further consideration in a wider range of ecosystems and contaminant exposure levels. In general, concentrations of the three metals were not high compared to reports in the published literature for dreissenid mussels in contaminated environments. However, few studies have utilized quagga mussels rather than zebra mussels. The two species may differ in bioaccumulation patterns and may not be interchangeable as biomonitors. Further studies of bioaccumulation of contaminants by quagga mussels in a wider range of contaminant exposures would be useful particularly as quagga mussels displace zebra mussels in the Laurentian Great Lakes and the St. Lawrence River.     

Replacement of Zebra Mussels by Quagga Mussels in the Canadian Nearshore of Lake Ontario: the Importance of Substrate,Round Goby Abundance,and Upwelling Frequency

The invasion of the Great Lakes by zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) has been accompanied by tremendous ecological change. In this paper we characterize the extent to which dreissenids dominate the nearshore of the Canadian shoreline of Lake Ontario and examine mussel distribution in relation to environmental factors. We surveyed 27 5-m sites and 25 20-m sites in late August 2003. Quagga mussels dominated all sites (mean: 9,404/m²; range 31–24,270), having almost completely replaced zebra mussels. Round gobies (Neogobius melanostomus) were associated with quagga populations dominated by large mussels. Quagga mussel total mass was low at 5-m sites with high upwelling frequency; we believe this is the first documentation of reduced benthic biomass in areas of upwelling in Lake Ontario. Overall, we estimated 6.32×10¹² quagga mussels weighing 8.13×10¹¹ g dry weight and carpeting ∼66% of the nearshore benthic habitat. Quagga mussels are a dominant and defining feature of the Lake Ontario nearshore, and must be accounted for in management planning.     

Contrasting shell/tissue characteristics of Dreissena polymorpha and Dreissena bugensis in relation to environmental heterogeneity in the St. Lawrence River

The zebra mussel, Dreissena polymorpha, is widespread in the St. Lawrence River while the conspecific quagga mussel, Dreissena bugensis, is found only in the Lake Ontario outflow region of the river. This situation provided an opportunity to evaluate in situ environmental and interspecific heterogeneity in shell and tissue growth. Shell dry weight, carbon content, and shell strength of D. polymorpha from the four spatially discrete water masses differed significantly. For instance, D. polymorpha total and tissue mass increased over the summer in the shallow fluvial Lac Saint-Pierre but decreased in the upstream and downstream water masses. Standardized shell mass and strength of D. polymorpha was lowest where the mussels experienced salinity or low calcium. Although the response pattern of mass and glycogen content for D. polymorpha was spatially complex, mussels from the stressful oligohaline estuary population had the weakest shells and lowest glycogen content, even though their standardized tissue mass was the heaviest. This disparity in shell and tissue response suggests that some aspect of shell physiology alone may be limiting these mussels in estuarine environments. Tissue characteristics of D. polymorpha and D. bugensis were similar at the site where both were present, but the shell strength of D. bugensis was only equivalent to the weakest of D. polymorpha. We also conclude that lighter shells might make D. bugensis more susceptible to predation or mechanical damage but may also offer a bioenergetic advantage that is contributing to its rapid displacement of D. polymorpha where the two species co-occur.     

Heavy metal concentrations in fish of Lake Balaton

The concentration of heavy metals (cadmium, copper, lead, mercury and zinc) found in muscle, gills and liver of eel, bream and pike‐perch living in Lake Balaton (Hungary) varied significantly between fish species and organs. The toxic metals in the muscle of fish, except for cadmium in bream, were below the maximum permissible level for human consumption. Cadmium concentrations above the maximum permissible level occurred in autumn in a few small individuals of bream, which, because they have poor culinary value and are seldom consumed, does not represent a risk for humans. Cadmium, copper, lead and zinc levels proved to be higher in eel and bream compared to pike‐perch, while high mercury concentrations were found in the predator fish, pike‐perch. Mercury accumulated most in the muscle in each species, while other metals were found in higher levels in the gills and liver. Seasonal differences were found for cadmium in each species and for lead in eel; the concentrations being elevated in autumn compared to spring. The fish species studied as bio‐monitors demonstrated that the overall heavy metal pollution of Lake Balaton is not significant, although, during summer an increase of cadmium and lead loading could occur at the catchment area and in the lake. Studies on the size (age) dependency of heavy metal concentrations showed that, in most cases, none or a negative relationship exists for each organ and metal in all species studied, and a positive regression coefficient was characteristic only on some occasions for mercury, cadmium and lead.     

Trends in Total Phosphorus in Canadian Near–Shore Waters of the Laurentian Great Lakes: 1976–1999

Beginning as early as 1976 at many locations, total phosphorus concentrations (TP) were measured weekly in samples collected year-round in the intake water of 18 municipal water treatment plants in Canadian (Ontario) waters of the Laurentian Great Lakes. No consistent long-term trends were evident at two north-shore Lake Superior sampling locations, but there were significant long-term declines in TP measured at all three Lake Huron locations; however, concentrations there have remained relatively constant during the past decade. Declines in TP averaging about 1 μg/L/yr during 1976 to 1990 were prevalent at lower Great Lakes sampling locations and by the early 1990s TP had declined to 15–25 μg/L in Lake Erie and 10–20 μg/L in Lake Ontario. Declines generally levelled out in Lake Ontario after 1990, but TP increased substantially at some Lake Erie locations in the late 1990s. Recent (1996 to 1999) total phosphorus concentrations in north-shore Lake Erie locations in the range of 20 to 30 μg/L were 2 to 3 times higher than at Lake Ontario near-shore locations in the 8 to 11 μg/L range. Rates of decline of TP were generally highest for the March–April period (−1.88, −1.61, and −1.34 μg/L/yr in Lakes Ontario, Erie, and Huron, respectively for 1976 to 1990). The March–April Lake Ontario near-shore rate of TP decline was nearly twice as high as that reported previously for off-shore Lake Ontario (attributed to proximity to P loading sources and to lower net sedimentation losses of P in the near-shore environment). There were substantial declines in chlorophyll-to-TP ratios and in the slopes and Y-intercepts of chlorophyll-TP regressions for both Lake Erie and Lake Ontario following the establishment of dreissenid mussels.     

Lakewide dominance does not predict the potential for spread of dreissenids

In recent years, quagga mussels (Dreissena rostriformis bugensis) have almost completely replaced zebra mussels (Dreissena polymorpha) in the Lower Great Lakes. As recreational boats are the main vector of spread for dreissenids in North America, this study examined whether lakes Erie and Ontario could still be sources for the spread of zebra mussels. In the summer–fall of 2010, the abundance of each species of Dreissena on 196 boats from 5 marinas in lakes Erie and Ontario was examined. Additional samples of Dreissena in 2010–2012 were collected in tributaries, bays, and in the upper littoral zones of these lakes. A total of 77 boats were fouled by Dreissena, and of those 61 were fouled by both species, 13 were fouled just by zebra mussels, and only 3 were fouled solely by quagga mussels. Although quagga mussels compose ~ 99% of dreissenids in eastern Lake Erie and in Lake Ontario, on boats at most marinas sampled, zebra mussels were usually more abundant and significantly larger than quagga mussels. Refugia for zebra mussels were found in bays, tributaries, and upper littoral zones with high wave activity. Thus, although quagga mussels are now more abundant than zebra mussels within the Lower Great Lakes, these waterbodies still have the potential to be a source for the spread of zebra mussels, and for some vectors, the propagule pressure from zebra mussels is likely greater than that from quagga mussels.     

Dreissenidae in Lake Ontario: Impact Assessment at the Whole Lake and Bay of Quinte Spatial Scales

The total abundance in Lake Ontario of Dreissena polymorpha (Dreissenidae), the zebra mussel, and D. bugensis (Dreissenidae), the quagga mussel, was calculated by aggregating data from several surveys carried out in 1991 to 94. In 1993, there were between 3.0 × 10 and 8.7 × 10¹² Dreissenidae mussels in Lake Ontario. A filtration model was contructed using depth-specific density estimates, a digital bathymetric map of the lake, and literature estimates of clearance rates for individual mussels. With reasonable estimates of both densities and filtration rates, the mean, area-weighted, turnover time of Lake Ontario water by dreissenid mussels was about 1 year. At the smaller spatial scale of the Bay of Quinte, the same model estimated turnover times of 0.05, 0.2, and 10 days for the lower, middle, and upper areas of the bay, respectively. Depth-specific secondary production estimates for dreissenids, combined with literature estimates of net primary production and energy transfer efficiencies, were incorporated into a food demand model that indicated about 1.25 gC/y mussel of food in Lake Ontario and a consumption efficiency of 50%. At the smaller spatial scale of the Bay of Quinte, the same model estimated one to two orders of magnitude less food per mussel and 62%, 130% and 115% consumption efficiency for the lower, middle and upper areas of the bay, respectively. Dreissenidae mussels may not have a huge impact on the Lake Ontario food web when considered at a whole-lake scale, but their potentially striking impact at the smaller spatial scale of embayments like the Bay of Quinte indicate that they may be locally important. When these effects are aggregated across several sub-systems, Dreissenidae mussels may have unpredictable, larger scale effects in the Lake Ontario ecosystem as a whole.     

Distribution of Chlorinated Organic Contaminants in Dreissenid Mussels Along the Southern Shores of the Great Lakes

Samples of dreissenid mussels were collected from 21 sites along the U.S. shores of the southern part of the Great Lakes and their connecting channels. These samples were analyzed for tissue levels of 16 chlorinated organic compounds, mostly pesticides, as well as for lipid levels. Aldrin, endrin, and lindane were found above detection levels at less than one-half of the sites, primarily at sites in Lake Michigan. Mirex was detected at nine sites mostly in Lake Ontario and the Niagara River, but also near Detroit and in Saginaw Bay. Heptachlor was detected at only two sites, both in Lake Erie. Cis-chlordane, dieldrin, hexachlorobenzene, heptachlor, trans-nonachlor, and total DDTs were detected at all or almost all of the sites. Except for hexachlorobenzene, which was highest near Buffalo, these chemicals were found at higher concentrations in Lake Michigan, especially near Milwaukee, than in the other areas studied. A comparison of the concentrations of chlorinated organic compounds to the levels of lipids showed that differences in dreissenid lipid levels among sites were not the major cause of the observed differences in concentrations in the chlorinated organic compounds.At most sampling locations, the category total DDTs was composed primarily of the DDT breakdown products DDD and especially DDE. However, a substantial percentage of the total DDTs detected at sites in eastern Lake Erie and western Lake Ontario was composed of the parent DDT compounds, suggesting the presence of a relatively recent input of this compound in this area.Comparison of the concentrations of chlorinated organic compounds measured in Great Lakes dreis-senids with concentrations of these compounds in marine mussels and oysters found generally similar levels for most of the compounds. Exceptions to this were hexachlorobenzene and mirex which had mean concentrations more than 5 times greater in mussels from the Great Lakes than from marine locations and lindane which had concentrations in mussels from the Great Lakes less than one-tenth of those from marine mussels.     

Lake-wide Distribution of Dreissena in Lake Michigan, 1999

The Great Lakes Science Center has conducted lake-wide bottom trawl surveys of the fish community in Lake Michigan each fall since 1973. These systematic surveys are performed at depths of 9 to 110 m at each of seven index sites around Lake Michigan. Zebra mussel (Dreissena polymorpha) populations have expanded to all survey locations and at a level to sufficiently contribute to the bottom trawl catches. The quagga (Dreissena bugensis), recently reported in Lake Michigan, was likely in the catches though not recognized. Dreissena spp. biomass ranged from about 0.6 to 15 kg/ha at the various sites in 1999. Dreissenid mussels were found at depths of 9 to 82 m, with their peak biomass at 27 to 46 m. The colonization of these exotic mussels has ecological implications as well as potential ramifications on the ability to sample fish consistently and effectively with bottom trawls in Lake Michigan.     

CUSUM Phytoplankton and Chlorophyll Functions Illustrate the Apparent Onset of Dreissenid Mussel Impacts in Lake Ontario

Untreated lake water samples were collected weekly, year-round from the drinking water intakes of five municipal water treatment plants on Lake Ontario and one plant with an intake in the upper St. Lawrence River and analyzed for chlorophyll a and phytoplankton density. CUSUM (cumulative sums of the differences between monthly means and the grand mean of each data set) chlorophyll and phytoplankton functions revealed rapid and dramatic reductions in chlorophyll and phytoplankton at four of the six sampling locations. Break-points in the CUSUM functions were in 1991 for western Lake Ontario, 1993 for the upper St. Lawrence River, 1994 for the Kingston (eastern) outlet basin of the lake, and 1995 for the central, north-shore area of the lake. These dates reinforce the anecdotal information available on the invasion history and spatial distribution of Dreissena spp. (zebra and quagga mussels) in Lake Ontario. Three-year “before and after” comparisons revealed that the highest percentage reductions in phytoplankton (several exceeding 90%) occurred during fall, winter, and spring, despite water temperatures near 0°C (during winter), and were similar to reductions previously reported for the north shore of Lake Erie using similar methods.     

Polymethylene-interrupted fatty acids: Biomarkers for native and exotic mussels in the Laurentian Great Lakes

Freshwater organisms synthesize a wide variety of fatty acids (FAs); however, the ability to synthesize and/or subsequently modify a particular FA is not universal, making it possible to use certain FAs as biomarkers. Herein we document the occurrence of unusual FAs (polymethylene-interrupted fatty acids; PMI-FAs) in select freshwater organisms in the Laurentian Great Lakes. We did not detect PMI-FAs in: (a) natural seston from Lake Erie and Hamilton Harbor (Lake Ontario), (b) various species of laboratory-cultured algae including a green alga (Scenedesmus obliquus), two cyanobacteria (Aphanizomenon flos-aquae and Synechococystis sp.), two diatoms (Asterionella formosa, Diatoma elongatum) and a chrysophyte (Dinobryon cylindricum) or, (c) zooplankton (Daphnia spp., calanoid or cyclopoid copepods) from Lake Ontario, suggesting that PMI-FAs are not substantively incorporated into consumers at the phytoplankton-zooplankton interface. However, these unusual FAs comprised 4-6% of total fatty acids (on a dry tissue weight basis) of native fat mucket (Lampsilis siliquoidea) and plain pocketbook (L. cardium) mussels and in invasive zebra (Dreissena polymorpha) and quagga (D. bugensis) mussels. We were able to clearly partition Great Lakes' mussels into three separate groups (zebra, quagga, and native mussels) based solely on their PMI-FA profiles. We also provide evidence for the trophic transfer of PMI-FAs from mussels to various fishes in Lakes Ontario and Michigan, further underlining the potential usefulness of PMI-FAs for tracking the dietary contribution of mollusks in food web and contaminant-fate studies.     

Abundance and distribution of benthic macroinvertebrates in offshore soft sediments in Western Lake Huron, 2001–2007

Invasive species have had major impacts on the Great Lakes. This is especially true of exotic dreissenid mussels which are associated with decreased abundance of native macroinvertebrates and changes in food availability for fish. Beginning in 2001, we added a benthic macroinvertebrate survey to the USGS-Great Lakes Science Center's annual fall prey fish assessment of Lake Huron to monitor abundance of macrobenthos. Mean abundance of Diporeia, the most abundant benthic taxon in Lake Huron reported by previous investigators, declined greatly between 2001 and 2007. Diporeia was virtually absent at 27-m sites by 2001, decreased and was lost completely from 46-m depths by 2006, but remained present at reduced densities at 73-m sites. Dreissenids in our samples were almost entirely quagga mussels Dreissena bugensis. Zebra mussels Dreissena polymorpha were virtually absent from our samples, suggesting that they were confined to nearshore areas shallower than we sampled. Loss of Diporeia at individual sites was associated with arrival of quagga mussels, even when mussel densities were low. Quagga mussel density peaked during 2002, then decreased thereafter. During the study quagga mussels became established at most 46-m sites, but remained rare at 73-m sites. Length frequency distributions suggest that initial widespread recruitment may have occurred during 2001–2002. Like other Great Lakes, Lake Huron quagga mussels were associated with decreased abundance of native taxa, but negative effects occurred even though dreissenid densities were much lower. Dreissenid effects may extend well into deep oligotrophic habitats of Lake Huron.     

Assessment of heavy metal contamination in coastal lake sediments associated with urbanization: Southern Kerala,India

The study of the spatiotemporal variation of heavy metals in lake sediments is of great importance because heavy metals can result in toxic effects on aquatic biota through bioaccumulation. This study was undertaken to evaluate the degree of heavy metal contamination in the lacustrine sediments and the corresponding environmental deterioration in a tropical, urban, coastal lake (Akkulam–Veli), located in Kerala, India. The spatiotemporal variations of the cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) concentrations in the lake sediments, as well as various indices of anthropogenic contamination, including Contamination Factor (CF), Pollution Load Index and Geoaccumulation Index (Igeo), were used to assess the degree of contamination. This study indicated contamination of the lake sediments with Cu, Pb and Zn. Urban domestic sewage and land run‐off are the major drivers of the heavy metal loads to the lake. During the pre‐monsoon, sediment contamination occurs in the upstream portion of Akkulam Lake because of a high clay content in the sediments. During the monsoon period, Akkulam Lake and the upstream portion of Veli Lake exhibit sediment contamination owing to high silt content. Domestic sewage is the main source of copper and zinc to the lake. Sewage bypass into the drains in the lake basin is largely responsible for the copper and zinc sediment contamination. High traffic levels and wastewater discharges from service stations/workshops are the main cause of the Pb loads entering the lake. Rubber particles of vehicle tires contain zinc and copper pigments that can accumulate on the surface of busy streets, entering the drains during rainfall events. Based on these study results, the accumulation of copper, zinc and lead in lake sediment can be controlled to a great extent by restricting the above‐noted activities. As the sediment content of lead, zinc and copper is confined to the clay fraction during the non‐rainy season and to the silt fraction during other seasons, lake restoration work should largely incorporate treating the clay and silt fractions, respectively, during both the non‐rainy season and rainy season.     

Spatial and seasonal variations and ecotoxicological significance of sediment trace metal concentrations in Kebir-Rhumel basin (Northeast of Algeria)

This study sought to assess sediment contamination by trace metals (cadmium, chromium, cobalt, copper, manganese, nickel, lead and zinc), to localize contaminated sites and to identify environmental risk for aquatic organisms in Wadis of Kebir Rhumel basin in the Northeast of Algeria. Water and surficial sediments (0-5 cm) were sampled in winter, spring, summer and autumn from 37 sites along permanent Wadis of the Kebir Rhumel basin. Sediment trace metal contents were measured by Flame Atomic Absorption Spectroscopy. Trace metals median concentrations in sediments followed a decreasing order: Mn > Zn > Pb > Cr > Cu > Ni > Co > Cd. Extreme values (dry weights) of the trace metals are as follows: 0.6-3.4 microg/g for Cd, 10-216 microg/g for Cr, 9-446 microg/g for Cu, 3-20 microg/g for Co, 105-576 microg/g for Mn, 10-46 microg/g for Ni, 11-167 microg/g for Pb, and 38-641 microg/g for Zn. According to world natural concentrations, all sediments collected were considered as contaminated by one or more elements. Comparing measured concentrations with American guidelines (Threshold Effect Level: TEL and Probable Effect Level: PEL) showed that biological effects could be occasionally observed for cadmium, chromium, lead and nickel levels but frequently observed for copper and zinc levels. Sediment quality was shown to be excellent for cobalt and manganese but medium to bad for cadmium, chromium, copper, lead, nickel and zinc regardless of sites.     

Assessment of heavy metals in sediments and aquatic organisms in West Lake (Ho Tay), Hanoi, Vietnam

West Lake (Ho Tay) is the largest freshlake in Hanoi, Vietnam. It has a surface area of ≈ 500 ha and a total volume of >10⁷ m³, and is 1–3.5 m in depth. West Lake has been classified as needing protection because of its valuable freshwater genetic resources. Noting that it has been extensively affected by pollution, the objective of the present study was to examine the extent of heavy metal contamination of the sediments and commercially important biota in the lake. Heavy metal concentrations in the sediment from most of 24 samples in West Lake exceeded the Ontario Ministry of Environment Screening Level for chromium (Cr), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) concentrations. Aquatic organisms from the lake also were found to be contaminated by heavy metals. The average Zn concentrations in snails and mussels tissues ranged between 174 and 415 µg g⁻¹, and the Pb concentrations between 3.5 and 5.2 µg g⁻¹. The Cu concentration in shrimp (52 µg g⁻¹) and snail (189 µg g⁻¹), and the Pb concentration in all fish species and shrimp from the lake (2.0–5.2 µg g⁻¹) exceeded the Food Standard Australia‐New Zealand (FSANZ) health standards for human consumption. The Cd concentration in Cyprinus carpio also exceeded the FSANZ standard. The implications of these study findings for the effective management of the food and ecological resources of West Lake are discussed.     

The distribution,density, and biomass of the zebra mussel (Dreissena polymorpha) on natural substrates in Lake Winnipeg 2017–2019

The distribution, density, biomass and size-structure of the zebra mussel (Dreissena polymorpha) population in Lake Winnipeg were examined between 2017 and 2019. Zebra mussels have colonized most of the available hard substrate in the south basin and Narrows region, but colonization of the north basin remains low at present, even on suitable substrate. Numerical densities and shell free biomass peaked at 5530 ± 953 m^?2 and 64.7 ± 57.9 g shell free dry mass m^?2 respectively. The distribution appeared to be strongly limited by substrate type and availability, with further limitations on the distribution imposed by physical disturbance in shallow waters and unsuitable substrate in deeper areas of the lake. Zebra mussels <1 year old dominated the populations, and individuals >18 mm were exceedingly rare. Poor recruitment was observed at sites along the eastern side of the south basin compared to elsewhere in the lake. The proximate causes of these differences in colonization success and recruitment are not clear, but may be in part due to heterogeneous patterns of key physico-chemical environmental conditions such as calcium concentrations required for successful development of juvenile mussels and colder water temperatures in the north basin. This study provides a baseline of information on which to track further expansion of zebra mussels in Lake Winnipeg and assist efforts to develop an understanding of how zebra mussels may affect the ecology of Lake Winnipeg.     

Twenty five years of changes in Dreissena spp. populations in Lake Erie

Lake Erie has the longest history of colonization by both Dreissena polymorpha and Dreissena rostriformis bugensis in North America and is therefore optimal for the study of long-term dynamics of dreissenid species. In addition, the morphometry of Lake Erie basins varies dramatically from the shallow western to the deep eastern basin, making this waterbody a convenient model to investigate patterns of Dreissena distribution, as well as interspecies interactions among dreissenids. We compare our data on the distribution, density and wet biomass of both dreissenid species in Lake Erie collected in 2009 and 2011–2012 with previous data. We found that Dreissena spp. distribution in Lake Erie varied depending on the time since the initial invasion, collection depth, and lake basin. In 2009–2012, zebra mussels were smaller than in 1992 and were consistently smaller than quagga mussels. During 2009–2012, quagga mussels were found at all depths and in all basins, while zebra mussels were common in the western basin only, and in the central and eastern basins were limited to shallow depths, resulting in an almost complete replacement of D. polymorpha with D. rostriformis bugensis. In the shallowest western basin of Lake Erie, zebra mussels represented > 30% of the combined dreissenid density even after more than 20 years of coexistence, providing strong evidence that, even in lakes as large as Lake Erie (or at least its western basin), D. polymorpha may sustain a significant presence for decades without being displaced by quagga mussels.     

The Influence of the Niagara River on Contaminant Burdens of Lake Ontario Biota

Top predator and forage fish species, netplankton (> 153 μm), zooplankton, and benthic macroinvertebrates from Lake Erie and Lake Ontario were analyzed for whole body levels of trace metals and organic contaminants. Comparison of contaminant concentrations in similar aquatic food chains from both lakes indicated that levels of PCB, DDT, mirex, and mercury are significantly greater (P <0.05) in the biota of Lake Ontario. The Niagara River, the single largest tributary to Lake Ontario, was confirmed as a major source of organic contaminants and trace metals. Organic contaminants are adsorbed to the particulate load of the river and dispersed throughout Lake Ontario by the circulating currents. There was no significant regional difference (P<0.05) in the degree of contaminant accumulation by the pelagic food chain of Lake Ontario. Conversely, both inorganic and organic contaminant levels in the demersal amphipod, Pontoporeia affinis, were significantly different (P<0.05) between the eastern and western basins of Lake Ontario. The uptake and concentration of contaminants at the sediment-water interface is suggested as a possible mechanism to explain this observed difference.     

Impacts of the Introduced Round Goby (Apollonia melanostoma) on Dreissenids (Dreissena polymorpha and Dreissena bugensis) and on Macroinvertebrate Community between 2003 and 2006 in the Littoral Zone of Green Bay,Lake Michigan

We show that the invasion of round gobies (Apollonia melanostoma) in Green Bay, Lake Michigan, has changed the benthic food web in fundamental ways related to their impact on invasive dreissenid mussels. Dreissenid mussels are of specific interest because they are one of the primary dietary items for round gobies. In this study, we collected rocks from each of 10 study sites along approximately 60 km of the eastern shoreline of Green Bay, Lake Michigan, to assess a temporal change in macroinvertebrate abundance related to the northward movement of the round goby invasion front from a point about midway along the shoreline in 2003 to the entire coast in 2006. The pattern of macroinvertebrate abundance in 2003 suggested that round gobies had already caused significant decreases in macroinvertebrate abundances south of the invasion front (interpretation of the data could have been compromised by confounding environmental gradients). In subsequent sampling in 2006 macroinvertebrates were picked off of sampled rocks in the field and underwater transects were videotaped to estimate round goby abundance at each site. Round gobies were collected for stomach analysis to assist in determining which invertebrates would likely be impacted by goby predation. Our results indicated that by 2006, round gobies had become abundant at those sites where they were absent in 2003 and zebra mussels (Dreissena polymorpha), quagga mussels (Dreissena bugensis), isopods, amphipods, trichopterans, and gastropods in the newly invaded sites had significantly decreased at the newly invaded sites.     

Sediment Contamination in the St. Lawrence River Along the Cornwall,Ontario Waterfront

Studies from 1970 to 1997 repeatedly showed that sediment was contaminated with mercury and zinc and, to a lesser extent, lead and copper in the north channel of the St. Lawrence River along the Cornwall, Ontario waterfront. Mercury contamination was greatest at two depositional zones: downstream of the Cornwall canal discharge near Lamoureux Park boat launch (maximum 18.0 μg/g, 1975) and downstream of Windmill Point (maximum 44.0 μg/g, 1975). Contaminant concentrations decreased with increasing distance from local point sources. The latter depositional zone extended approximately 2 km downstream and had the highest concentrations of mercury as well as high zinc, copper, and lead concentrations. Concentrations of As, Fe, Mn, Cd, Ni, Cr, TP, TKN, and TOC showed no significant local enrichment. Patterns of sediment contamination suggest local sources of PAHs; however, concentrations were not high enough to be of concern. The studies indicated that mercury and zinc were primarily from local industrial sources, a conclusion supported by patterns of contamination in the north versus south channels and downstream into Lake St. Francis. Although mercury concentrations in surface sediment appear to be decreasing over time, contaminants remain at high concentrations in Cornwall waterfront sediment. The two major local point sources of mercury closed their Cornwall industrial operations in the 1990s, but contaminated sediment can act as an important long-term source of mercury to the aquatic food chain. Conclusions drawn from this review will be used in the development of a strategy for managing contaminated sediment in Cornwall and may be applicable to other areas of contaminated sediment for which similar assessments are required.