Huron-Erie Corridor Research Articles

Assessing trophic position quantification methods for three piscivorous freshwater fish using stable isotopes and stomach contents

Accurate trophic position (TP) estimates are important for the development of ecosystem-based management plans. TPs can be quantified by carbon (δ13C) and nitrogen (δ15N) stable isotopes in tissues, but these can disagree with observed and perceived feeding ecology. A recent method that has used a scaled diet-tissue discrimination factor (DTDF), reflecting the inverse relationship between DTDF and δ15N, was found to better describe TPs of predatory fish species in marine ecosystems, but this has not been tested in freshwater ecosystems. Here, we compare methods of TP estimations in the Lake Huron-Erie corridor (HEC), a system where high diversity of prey items has contributed to the concern that foraging ecology of piscivorous fish species is poorly understood. Using δ15N and δ13C, we quantified TP of longnose gar (Lepisosteus osseus), largemouth bass (Micropterus salmoides), and northern pike (Esox lucius) to assess the efficacy of a scaled DTDF compared to traditional DTDF isotope methods and stomach content analysis (SCA). The scaled DTDF method produced TP estimates that were at times consistent with SCA and were generally higher and with a greater range among individuals than non-scaled DTDFs. The scaled method was not sensitive to baseline choice nor influenced by incorporating carbon source in the model. Greater variability of TP estimates using a scaled DTDF suggests more complex trophic structuring in the upper trophic level guild of the HEC. These results, particularly the lack of baseline sensitivity, provide support for using the scaled DTDF in freshwater food web characterization.

Tributary use and large-scale movements of grass carp in Lake Erie

Infrequent captures of invasive, non-native grass carp (Ctenopharyngodon idella) have occurred in Lake Erie over the last 30+ years, with recent evidence suggesting wild reproduction in the lake’s western basin (WB) is occurring. Information on grass carp movements in the Laurentian Great Lakes is lacking, but an improved understanding of large-scale movements and potential areas of aggregation will help inform control strategies and risk assessment if grass carp spread to other parts of Lake Erie and other Great Lakes. Twenty-three grass carp captured in Lake Erie’s WB were implanted with acoustic transmitters and released. Movements were monitored with acoustic receivers deployed throughout Lake Erie and elsewhere in the Great Lakes. Grass carp dispersed up to 236 km, with approximately 25% of fish dispersing greater than 100 km from their release location. Mean daily movements ranged from <0.01 to 2.49 km/day, with the highest daily averages occurring in the spring and summer. The Sandusky, Detroit, and Maumee Rivers, and Plum Creek were the most heavily used WB tributaries. Seventeen percent of grass carp moved into Lake Erie’s central or eastern basins, although all fish eventually returned to the WB. One fish emigrated from Lake Erie through the Huron-Erie Corridor and into Lake Huron. Based on our results, past assessments may have underestimated the potential for grass carp to spread in the Great Lakes. We recommend focusing grass carp control efforts on Sandusky River and Plum Creek given their high use by tagged fish, and secondarily on Maumee and Detroit Rivers.

Sequence analysis and acoustic tracking of individual lake sturgeon identify multiple patterns of river–lake habitat use

AbstractUnderstanding the spatial ecology of sturgeon (Acipenseridae) has proven to be a challenge due to the life history characteristics of these fish, especially their long life span, intermittent spawning, and long‐distance migrations. Within the Huron‐Erie Corridor (HEC) of the Laurentian Great Lakes, habitat use of 247 lake sturgeon (Acipenser fulvescens) was monitored over a three‐year period (2015–2017) with acoustic transmitters. Extensive spatial coverage of receivers throughout the St. Clair River, Lake St. Clair, and Detroit River between Lake Huron and Lake Erie (~150 km) allowed for continuous monitoring of the movements of acoustic‐tagged individuals. Sequence analysis of individual detection histories was used to describe lake sturgeon habitat use and to determine (1) whether distinct habitat‐use patterns occurred within the HEC; (2) whether the range of habitats occupied varied across seasons among sturgeon grouped by common patterns; and (3) whether variation identified was related to tagging sites in the two rivers or sex. Lake sturgeon were active throughout the HEC, but five distinct habitat‐use patterns were identified. River residents were not broadly distributed across entire rivers, but rather associated with particular segments (middle Detroit River, St. Clair River delta). Variations in habitat‐use sequences were in part related to three river tagging sites, but not sex, and did not produce groups with sequences that reflected all five habitat‐use patterns derived from cluster analysis. Lake sturgeon distribution was reduced to fewer habitat segments during winter and expanded to the maximum extent during the spring and summer. Conservation planning that incorporates behavioral diversity of habitat use is relatively rare due to a lack of observations on movements of individuals at biologically relevant spatial and temporal scales, but using telemetry and sequence analysis methods may promote the success of conservation and restoration efforts.

Telemetry reveals limited exchange of walleye between Lake Erie and Lake Huron: Movement of two populations through the Huron-Erie corridor

Immigration and emigration of individuals among populations influence population dynamics and are important considerations for managing exploited populations. Lake Huron and Lake Erie walleye (Sander vitreus) populations are managed separately although the interconnecting Huron-Erie Corridor provides an unimpeded passageway. Acoustic telemetry was used to estimate inter-lake exchange and movement within St.Clair River and Detroit River. Of 492 adult walleyes tagged and released during 2011 and 2012, one fish from Tittabawassee River (Lake Huron; 1 of 259, 0.39%) and one individual from Maumee River (Lake Erie; 1 of 233, 0.43%) exchanged lakes during 2011–2014. However, both fish returned to the lake where tagged prior to the next spawning season. The one walleye from Maumee River that moved to Lake Huron made repeated round-trips between Lake Erie and Lake Huron during three consecutive years. Of twelve fish tagged in the Tittabawassee River detected in the Huron-Erie Corridor, few (n = 3) moved south of Lake St.Clair to the Detroit River. Ten walleye tagged in the Maumee River entered the Huron-Erie Corridor, and five were detected in the St.Clair River. Our hypothesis that walleye spawning in Maumee River, Lake Erie, served as a source population to Lake Huron (“sink population”) was not supported by our results. Emigration of walleye to Lake Huron from other populations than the Maumee River, such as those that spawn on in-lake reefs, or from Lake St.Clair may contribute to Lake Huron walleye populations.

Polybrominated Diphenyl Ethers (PBDEs) in Sediments of the Huron-Erie Corridor.

Polybrominated diphenyl ethers (PBDEs) were measured in 182 sediments from the Huron-Erie Corridor, North America. The median (5-95 percentile) Corridor ∑PBDE concentration was 1.03ng/g dry wt (0.25-13.48ng/g dry wt). Dry weight ∑PBDEs were elevated in U.S. waters of the Detroit River (US DR) and lowest in Canadian waters of Lake St. Clair (CA LSC). Sediment total organic carbon (TOC) explained some of the variation in ∑PBDEs, particularly in upstream waterbodies except for the Detroit River where local sources were apparent in the US DR and TOC-dilution occurred in CA DR. Canadian Federal Sediment Quality guidelines were exceeded at 19 stations, 14 occurring in the US DR. ∑Hazard Quotients (∑HQ) had a median (5-95 percentile) Corridor value of 0.46 (ND to 2.27). By strata, 43.2% of US DR stations had ∑HQ's greater than 1 while 21.3% of US SCR stations exceeded a value of 1.

Comparison of thermal tolerance and standard metabolic rate of two Great Lakes invasive fish species

Abstract Round goby (Neogobius melanostomus) and western tubenose goby (Proterorhinus semilunaris) invaded the Laurentian Great Lakes at approximately the same time and area yet have shown substantial differences in their post-invasion success with more rapid establishment and development of much larger abundances of round goby populations throughout the invaded habitat. In this study, we compared differences in physiological performance (thermal tolerance and standard metabolic rate) between round and tubenose goby collected from the Huron-Erie corridor. Tubenose goby were observed to have lower thermal tolerance but exhibited similar standard metabolic rate across environmental temperatures compared to round goby. At temperatures exceeding 31 °C, tubenose goby demonstrated significantly higher mortalities and shorter times to death relative to round goby. The observed differences in thermal tolerance were consistent with differences in the native geographic ranges observed for each species at their southern ranges. The observed differences in physiological performance combined with species differences in other life history traits such body size, reproduction, feeding ecology and habitat affiliation may also explain differences in the invasiveness experienced by these two Great Lakes invasive fish including a greater ability of round gobies to occupy extreme habitats with large water temperature fluctuations.

Divergent migration within lake sturgeon (Acipenser fulvescens) populations: Multiple distinct patterns exist across an unrestricted migration corridor.

Population structure, distribution, abundance and dispersal arguably underpin the entire field of animal ecology, with consequences for regional species persistence, and provision of ecosystem services. Divergent migration behaviours among individuals or among populations are an important aspect of the ecology of highly mobile animals, allowing populations to exploit spatially or temporally distributed food and space resources. This study investigated the spatial ecology of lake sturgeon (Acipenser fulvescens) within the barrier free Huron-Erie Corridor (HEC), which connects Lake Huron and Lake Erie of the North American Laurentian Great Lakes. Over 6years (2011-2016), movements of 268 lake sturgeon in the HEC were continuously monitored across the Great Lakes using acoustic telemetry (10years battery life acoustic transmitters). Five distinct migration behaviours were identified with hierarchical cluster analysis, based on the phenology and duration of river and lake use. Lake sturgeon in the HEC were found to contain a high level of intraspecific divergent migration, including partial migration with the existence of residents. Specific behaviours included year-round river residency and multiple lake-migrant behaviours that involved movements between lakes and rivers. Over 85% of individuals were assigned to migration behaviours as movements were consistently repeated over the study, which suggested migration behaviours were consistent and persistent in lake sturgeon. Differential use of specific rivers or lakes by acoustic-tagged lake sturgeon further subdivided individuals into 14 "contingents" (spatiotemporally segregated subgroups). Contingents associated with one river (Detroit or St. Clair) were rarely detected in the other river, which confirmed that lake sturgeon in the Detroit and St. Clair represent two semi-independent populations that could require separate management consideration for their conservation. The distribution of migration behaviours did not vary between populations, sexes, body size or among release locations, which indicated that intrapopulation variability in migratory behaviour is a general feature of the spatial ecology of lake sturgeon in unfragmented landscapes.

Total and soluble reactive phosphorus loadings to Lake Erie

Information about the loads of total and soluble reactive phosphorus entering Lake Erie is required in order to support commitments made under Annex 4 of the Great Lakes Water Quality Agreement. For these purposes, annual (water year) total phosphorus loads to Lake Erie are updated (2003–2013) and soluble reactive loads are reported on a lakewide basis for the first time (2009–2013). Complete documentation including input data and error estimates are provided. The results confirm previously documented long-term declining TP loads and show how these are driven by early and recent improvements in point source discharges, but are confounded by recent increases in nonpoint source loads that may in turn be due to increasing trends in precipitation and river discharge. The record since 2009 for SRP indicates high interannual variability and no discernible change in loadings over time. Recent TP loads are dominated by nonpoint sources (71%), with lower contributions from point sources (19%) and the balance comprising atmospheric deposition and loads from the upstream Great Lakes. Approximately one-half (49%) of the load of SRP is contributed from nonpoint sources, approximately 39% comprises point sources, and atmospheric deposition and upstream loads comprise 6% each. Loads are highest to the western basin for TP and highest to the Huron–Erie corridor for SRP. U.S. sources account for a majority (> 80%) of the phosphorus loads entering the lake. Recommendations for improvements to the study approach are made including the identification of monitoring gaps and the testing of assumptions that require independent verification.

Foraging ecology of Bowfin (Amia calva), in the Lake Huron–Erie Corridor of the Laurentian Great Lakes: Individual specialists in generalist populations

Abstract The foraging ecology of bowfin (Amia calva) is relatively unknown in the Laurentian Great Lakes despite comparable abundances to other piscivorous predators. We investigated bowfin foraging ecology by determining trophic position, isotopic niche size, dietary proportions, and the degree of individual specialization at two locations in the Lake Huron–Erie Corridor using carbon (δ13C) and nitrogen (δ15N) stable isotopes and stomach content analysis. Trophic position did not differ between Mitchell's Bay (4.2) and Peche Island (4.3) using δ15N, but both sites had large ranges in individual estimates (range = 2.8). Bowfin isotopic niche size was large across site, season, and tissue, suggesting a generalist feeding strategy at the population level. However, bowfin had greater between-individual than within-individual variation accounting for 72% and 88% of total niche size at Mitchell's Bay and Peche Island, respectively, suggesting specialist feeding strategies at the individual level. Stable isotope mixing models for Peche Island showed high proportions of crayfish (54%) and small fish (Cyprinidae spp., Lepomis spp.; 38%) in their diet, consistent with high stomach content prevalence for crayfish (spring = 75%, fall = 10%) and small fishes (spring = 19%, fall = 33%) at Peche Island. Overall, our analysis of bowfin suggests a complex foraging ecology with bowfin acting as generalist predators at the species level but exhibiting a high degree of individual specialization, warranting further study to assess their trophic role in this diverse ecosystem of conservation concern.

Bed Scouring During the Release of an Ice Jam

A model is developed for simulating changes in river bed morphology as a result of bed scouring during the release of an ice jam. The model couples a non-hydrostatic hydrodynamic model with the processes of erosion and deposition through a grid expansion technique. The actual movement of bed load is implemented by reconstructing the river bed in piecewise linear elements in order to bypass the limitations of the step-like approximation that the hydrodynamic model uses to capture the bed bathymetry. Initially, an ice jam is modeled as a rigid body of water near the free surface that constricts the flow. The ice jam does not exchange mass or momentum with the stream, but the ice body can have a realistic shape and offer resistance to the flow of water through the constriction. An ice jam release is modeled by suddenly enabling the ice to flow and exchange mass and momentum with the water. The resulting release resembles a dam break wave accelerating and causing flow velocities to rise rapidly. The model is used to simulate the 1984 ice jam in the St. Clair River, which is part of the Huron-Erie Corridor. The jam had a duration of 24 days, and its release was accompanied by high flow velocities. It is speculated that high flow velocities during the release of the jam caused scouring of the river bed. This led to an increase in the river’s conveyance that is partly responsible for the persistence of low water levels in the upper Great Lakes. The simulations confirm that an event similar to the 1984 ice jam will indeed cause scouring of the St. Clair River bed.

A description of the nearshore fish communities in the Huron–Erie Corridor using multiple gear types

Great Lakes coastal wetlands provide a critical habitat for many fish species throughout their life cycles. Once home to one of the largest wetland complexes in the Great Lakes, coastal wetlands in the Huron–Erie Corridor (HEC) have decreased dramatically since the early 1900s. We characterized the nearshore fish communities at three different wetland complexes in the HEC using electrofishing, seines, and fyke nets. Species richness was highest in the Detroit River (63), followed by the St. Clair Delta (56), and Western Lake Erie (47). The nearshore fish communities in the Detroit River and St. Clair Delta consisted primarily of shiners, bluntnose minnow, centrarchids, and brook silverside, while the Western Lake Erie sites consisted of high proportions of non-native taxa including common carp, gizzard shad, goldfish, and white perch. Species richness estimates using individual-based rarefaction curves were higher when using electrofishing data compared to fyke nets or seine hauls at each wetland. Twelve fish species were captured exclusively during electrofishing assessments, while one species was captured exclusively in fyke nets, and none exclusively during seine hauls. Western Lake Erie wetlands were more indicative of degraded systems with lower species richness, lower proportion of turbidity intolerant species, and increased abundance of non-native taxa. This work highlights the importance of coastal wetlands in the HEC by capturing 69 different fish species utilizing these wetlands to fulfill life history requirements and provides insight when selecting gears to sample nearshore littoral areas.

An ecological basis for future fish habitat restoration efforts in the Huron-Erie Corridor

This perspective describes the major natural and anthropogenic forces driving change in the abundance and quality of fish habitats in the Huron-Erie Corridor (HEC), the Great Lakes connecting channel comprised of the St. Clair River, the Lake St. Clair, and the Detroit River. Channels connecting the Laurentian Great Lakes discharge large volumes of water equal to or greater than most other large rivers in the world that is of consistent high quality and volume, all year. Owing to creation of the St. Lawrence Seaway through the Great Lakes, the connecting channels have been modified by dredging over 200km of deep-draft shipping lanes with a maintained depth of no less than 8.2m. Combined with modification of their shorelines for housing and industries, use of the connecting channels for discharges of industrial and municipal wastes and shipping has resulted in numerous beneficial use impairments, such as restrictions on fish and wildlife consumption, degradation of fish and wildlife populations, and losses of fish and wildlife habitat. Various options for remediation of native fish populations and their habitats in the Great Lakes connecting channels, including construction of spawning habitat for threatened and high-value food fishes, such as lake sturgeon (Acipenser fulvescens), walleye (Sander vitreus), and lake whitefish (Coregonus clupeaformis), have been implemented successfully in two of the channels, and form the basis for further recommended research described in this article.

Synthesizing reference conditions for highly degraded areas through best professional judgment

Reference sites, comparable in physical and chemical characteristics to test sites with the exception of the effect of interest, provide a set of species to contrast against test site data and assign a condition to test sites in the Reference Condition Approach. However, what if disturbance is ubiquitous and comparable reference sites are absent? Here, we use the Detroit River as a case study where development and industrialization has rendered reference sites absent. In this paper, a novel application of best professional judgment was developed to generate a set of species characteristic of reference conditions. The synthesized assemblage functions as substitute to a sampled reference site and can be applied analogously towards determining condition and assessing recovery. Members of the Huron–Erie Corridor Steering Committee, comprised of agency partners that manage the corridor, were surveyed to produce a hypothetical data matrix of the fishes present in the river in the absence of anthropogenic disturbance. The synthesized assemblages were assessed using an Index of Biotic Integrity and subsequently integrated into a Principal Coordinates Analysis with test site fish assemblage data. Recovery and response to remediation was determined by the position of the test sites within confidence ellipses. The results indicated signs of recovery in upstream sites of the Detroit River, but no recovery at downstream sites. The application of the best professional judgment approach towards reference conditions provides a novel and versatile method to interpret species assemblage change and allows practitioners the ability to select specific assemblages coincident with restoration objectives.

Genetic connectivity and diversity of walleye (Sander vitreus) spawning groups in the Huron–Erie Corridor

The Huron–Erie Corridor (HEC) connects the upper and lower Great Lakes, providing key fish passage. A century of channelization, dredging, and pollution has led to habitat loss and declining fish numbers. Since 2004, the multi-agency HEC initiative augmented fish spawning habitat at Belle Isle and Fighting Island in the Detroit River, whose populations are examined here. We analyze genetic patterns among seven spawning groups (N=311) of walleye Sander vitreus, a key fishery species, using nine nuclear DNA microsatellite loci and mitochondrial DNA control region sequences. Results reveal that all spawning groups contained appreciable genetic diversity (microsatellites: HO=0.72; mtDNA: HD=0.73) and showed a mixture of connectivity and divergence. Genetic relationships did not fit an isolation by geographic distance hypothesis, with some closely spaced populations being very different. Notably, the Flint River–Lake Huron spawning group was the most divergent, showing no genetic exchange. The Belle Isle and Fighting Island populations markedly differed, with the latter showing some genetic exchange with the Grosse Ile (Detroit River) and the Huron River (northwest Lake Erie) populations to the south. Walleye spawning at Fighting Island experienced no significant change in overall genetic diversity pre- versus post-habitat augmentation, but the allelic frequency changed. Our results comprise an important baseline for future population analyses and habitat assessment of these habitat augmentation areas. Despite habitat degradation and pollution, it appears that historic walleye spawning groups have persisted along the HEC, meriting continued genetic monitoring and further restoration efforts to conserve and enhance this important and diverse fishery.

Genetic diversity and divergence of yellow perch spawning populations across the Huron–Erie Corridor, from Lake Huron through western Lake Erie

The yellow perch Perca flavescens supports one of the largest Great Lakes fisheries, whose populations have varied due to environmental changes, including exploitation and habitat degradation. The Huron–Erie Corridor (HEC) connects the upper and lower Great Lakes, running from Lake Huron through the St. Clair River, Lake St. Clair, and Detroit River to western Lake Erie; it serves as an essential fish migration corridor, and contains key spawning and nursery grounds. Its shipping importance led to its extensive channelization and dredging, destroying and degrading habitats. Since 2004, the HEC Initiative has restored some fish spawning and nursery grounds. Our objective is to assess the genetic diversity, connectivity, and divergence of yellow perch spawning populations along the HEC to provide a baseline for assessing future patterns, including responses to improved habitat. Genetic variation of seven spawning populations (N=248), four in the HEC, one in Lake Huron, and two in western Lake Erie, are analyzed at 15 nuclear microsatellite loci. Results showed appreciable genetic diversity of the seven spawning populations (mean observed heterozygosity=0.637±0.020, range 0.568–0.699), which significantly differed in genetic composition (θST=0.011–0.099, p<0.0001–0.0007), suggesting a history of genetic isolation; relationships did not follow a pattern of genetic isolation by geographic distance. Notably, some nearby spawning populations were very genetically distinctive, with high genetic diversity and high proportions of private alleles, as characterized by the Belle Isle restoration site in the Detroit River. Our study provides a genetic benchmark to assess ongoing and future habitat restoration efforts across the HEC and beyond.

First report of tubenose goby (Proterorhinus semilunaris) in the eastern basin of Lake Erie

The tubenose goby (Proterorhinus semilunaris), native to the Ponto-Caspian region, was first discovered in the Laurentian Great Lakes in 1990 after it was introduced through ballast water discharge. Compared with Neogobius melanostomus, another exotic gobiid from the Ponto-Caspian, colonization of the Great Lakes by P. semilunaris has been slow, with reports of the species being largely confined to the Huron-Erie Corridor (HEC) and western portions of Lake Erie and Lake Superior. This is the first report of P. semilunaris in the Great Lakes east of the western basin of Lake Erie. Between 28 June and 27 July, 2012, 176 P. semilunaris were collected from shallow (<1.2m) water of Marina Lake, a 40ha embayment in Presque Isle State Park (Erie, PA). The large number of P. semilunaris collected at the site and the presence of individuals as small as 17mm total length suggest an established population. However, the mechanism by which P. semilunaris was introduced to Presque Isle Bay is not clear.

Relationships between wind-driven and hydraulic flow in Lake St. Clair and the St. Clair River Delta

A three-dimensional hydrodynamic forecasting model of the Great Lakes Huron–Erie Corridor is used to investigate mixing and the relationship between hydraulic and wind-induced currents in a shallow lake system in which lake inflows come through several channels of a river delta. The hydrodynamics in Lake St. Clair and the channels of the St. Clair River Delta are evaluated for (1) a one-year simulation from 1985 including water age calculation, (2) 8 different wind direction scenarios, and (3) a storm event. Observations and model simulations show distinct regions in the lake in which currents are forced by either hydraulic flow from the river system or from wind stress over the lake. However, during severe storm events, these regions are found to shift or even disappear due to changes in the delta channel inputs into the lake. These changes underscore the need for realistic, unsteady river flow boundary conditions at interfaces between a shallow lake and river delta. Steady inflow conditions will not allow for potential shifting of these current zones, and will also fail to resolve flow retardation or reversals during storm events.

Factors influencing contaminant distribution in the Huron-Erie Corridor sediments

The study discusses the role of natural and anthropogenic factors influencing dispersal of both inorganic and organic pollutants in the sediments based on findings for different aquatic sub-systems (fluvial, deltaic, lacustrine) joined into one waterway (Huron-Erie Corridor, North America). Bottom current velocity, finest fraction (< 0.063 mm), Al, C org, TN, and oil contents have been selected as the potential factors influencing contaminant distribution, most commonly used in the geochemical studies. It was found that studied sub-systems were heterogeneous not only in terms of hydrological and geochemical conditions, but also with respect to the spatial contaminants patterns. Both metals and organic contaminants revealed elevated concentrations in sites localized in proximity of anthropogenic sources. The fact that the finest fraction (< 0.063 mm), Al, C org, and TN were mostly not effective as the contaminant scavengers in the studied area brings more attention to the other than geochemical factors responsible for the distribution of contaminants in sediments. These findings demonstrate that the common approach is not always suitable in describing the contaminants dispersal patterns.

Real-Time Hydraulic and Hydrodynamic Model of the St. Clair River, Lake St. Clair, Detroit River System

The Huron-Erie Corridor serves as a major waterway in the Great Lakes and is the connecting channel between Lake Huron and Lake Erie. The system consists of the St. Clair River, Lake St. Clair, and the Detroit River, and serves as a recreational waterway, source of drinking water for Detroit and surrounding cities, as well as the only shipping channel to Lakes Huron, Michigan, and Superior. This paper describes a three-dimensional unsteady model of the combined system and its application to real-time predictions of physical conditions over the corridor. The hydrodynamic model produces nowcasts eight times per day and 48 h forecasts twice a day. Comparisons between model simulations and observed values show average differences of 3 cm for water levels and 12 cm/s for along-channel currents in the St. Clair River (compared to mean current values of 1.7 m/s) for the period of September 2007 to August 2008. Simulations reveal a spatially and temporally variable circulation in Lake St. Clair as well as significant changes in flow rate and distribution through the St. Clair Delta not accounted for in previous models.

Determination of in situ polychlorinated biphenyl elimination rate coefficients in the freshwater mussel biomonitor Elliptio complanata deployed in the huron–erie corridor, southeast Michigan, USA, and southwest Ontario, Canada

Quantitative mussel biomonitoring studies often use laboratory-measured whole-body elimination rate coefficients (k(tot) in conjunction with concentration data from field-deployed mussels to estimate bioavailable steady-state contaminant concentrations (C(m(ss)) in aquatic systems. However, the validity of applying laboratory k(tot) values to field-deployed mussels has not been verified. The present study quantified in situ k(tot) values by the common mussel biomonitor species Elliptio complanata for a group of performance reference compound polychlorinated biphenyl (PCB) congeners (International Union of Pure and Applied Chemistry 23, 61, 109, and 173) at 11 sites along the Lake Huron-Lake Erie corridor (southeast MI, USA, and southwest ON, Canada). Predictive site-specific k(tot) versus log K(ow) relationships were derived to estimate in situ k(tot) values for the bioaccumulated environmental PCB congeners, and the resultant steady-state concentration estimates were compared against values estimated using laboratory-derived k(tot) values. In situ k(tot) values were almost always faster (1.3-10-fold) than rate coefficients determined by laboratory studies, with a mean difference +/- standard error of 3.89 +/- 0.28-fold. Consequently, control adjusted steady-state concentrations of sum PCBs in the mussels were overestimated by factors ranging from 1.30 to 3.45 across sites when using laboratory-derived k(tot) values in place of in situ k(tot) values and a field deployment period of 90 d. This error was shown to increase with increasing congener hydrophobicity, as represented by their log K(ow) values, and when shorter field deployment times are performed. To more accurately predict the steady-state concentrations of environmentally accumulated PCBs in mussels, it is recommended that future quantitative biomonitoring studies employ the reference compound approach for measuring site-specific in situ k(tot) values.