Detroit River Research Articles

Macroinvertebrate Diversity of Submerged Detroit River Coastal Wetlands

Macroinvertebrate Diversity of Submerged Detroit River Coastal Wetlands

Aquatic Bacterial Community Connectivity: The Effect of Hydrological Flow on Community Diversity and Composition

Microbial communities are vital components of freshwater ecosystems due to their role in nutrient cycling and energy flow; however, the mechanisms driving their variation are still being explored. In aquatic systems, water flow (hydrology) can impact microbial community composition through community connectivity; however, the details of hydrology’s effects on microbial connectivity remain unclear. To address this question, we used 16S rRNA metabarcoding to determine bacterial community composition and connectivity across flow transects in three connected Great Lakes waterbodies with very different water-flow regimes: the Little River (high flow), the Detroit River (moderate flow), and Lake Erie (low flow). Bacterial alpha diversity (Chao1) did not differ among the three locations or sample sites along the transects. Analyses of beta diversity using community dissimilarity matrices identified significant differences among the three locations and among sample sites within locations. Bacterial community connectivity varied among the three locations, with a significant distance–decay relationship observed only in the low-flow location, which is indicative of connectivity driven by spatial proximity. Directional analyses showed that the water-flow direction affected bacterial similarity, consistent with the expected hydrological effects on community connectivity and previous published work. Our results indicate that (1) microbial community composition varies within and among even geographically close sampling locations and (2) the specific water-flow regime appears to affect bacterial community connectivity. Including hydrology in models of bacterial community composition will improve our understanding of the relative roles of selection versus stochastic effects on bacterial community diversity and composition in freshwater ecosystems.

Increasing broad-spectrum aquatic invasive species early detection program efficiency through biased site selection and gear allocation

Invasive species cause severe environmental and economic damage throughout the globe. Aside from preventing their introduction, early detection of newly introduced species is the most successful method to prevent their establishment, spread, and eventual negative impacts. Broad-spectrum monitoring for the early detection of novel non-native species is oftentimes heavily burdened by the inherent difficulty in maximizing the detection probabilities of numerous high priority species simultaneously with only finite resources. We attempted to increase the efficiency of broad-spectrum monitoring in four locations across Lake Erie (USA)—the Detroit River, Maumee Bay, Sandusky Bay, and Cleveland—by targeting our site and gear selections to maximize overall species richness and detection rates of rare and non-native species, with the results compared to a random sampling design. Overall species richness was significantly higher in all four locations, while non-native species detection rates were significantly higher in every location except for Cleveland. Detection rates of rare species was significantly higher in Maumee Bay only. Our results indicate this selective sampling design is more likely to detect a newly introduced non-native species than a random sampling design and are in support of the established literature for broad-spectrum monitoring for novel aquatic invasive species.

Why Windsor deindustrialized differently than Detroit

ABSTRACT This paper examines the divergent trajectories of automotive investment and employment in Detroit, Michigan and Windsor, Ontario. Located on opposite shores of the Detroit River, in the United States and Canada respectively, Detroit and Windsor are the founding cities of the North American auto industry. Long dominated by the Big Three, their factories have produced vehicles for the same continental market since 1965. Each has weathered parallel challenges since then, including spikes in the price of oil, the Big Three’s loss of market share, the transition to lean production, and the near-collapses of Chrysler and GM. Yet Detroit began deindustrializing decades earlier and lost much more employment than Windsor. To determine why, we compared their automotive sectors from 1900 to the 2010s. Since the Depression, each city has repeatedly confronted the prospect of deindustrialization, but three factors have made Windsor more resilient: (1) federal and provincial interventions on its behalf, (2) Windsor’s greater competitiveness with respect to factor costs, quality, and innovation, and (3) Windsor’s annexation of outlying territory to capture new factories. These differences show how national, subnational, and regional/local policies have mediated corporate decision-making to produce a variegated North American Rust Belt, with Canada outperforming the United States.

Temporal Trends of Great Lakes Legacy Contaminants: Ecological and Biological Considerations Applying the Age-Trend Model.

The USEPA Great Lakes Fish Monitoring and Surveillance Program (GLFMSP) has been monitoring top predator lake trout and walleye contaminant concentrations since the early 1970s. Our research revealed that select legacy contaminant groups (∑PCBs, ∑DDTs, ∑chlordanes, and ∑5PBDEs) have similar t1/2 and k2 values across the Great Lakes, with the exception of both Lake Erie sites and the Lake Superior─Keweenaw Point site. The slower halving times determined at both Lake Erie sites are consistent with legacy contaminant remobilization due to extreme weather climate effects and past remedial actions on the Detroit River, whereas the Lake Superior─Keweenaw Point site demonstrates contaminant halving times approaching the exponential minimum. Overall, Great Lakes select contaminant groupings have decreased between 25.8 and 97.9% since 2004. An age-normalized Great Lakes Contaminant Index (GLCI) was devised, indicating both Lake Michigan sites as the most highly impacted. The mean absolute deviation statistic was applied, documenting the need to age-correct contaminant trends due to highly variable age profiles. With the noted exceptions, the uniformity of age-corrected trend modeling suggests that a combination of the fundamental biological and physicochemical mechanisms of natural contaminant sequestration, declining dissolved water concentrations, accumulation/metabolism/depuration, and the overall reduction of legacy contaminant loading are driving the generally consistent rates of declines in the Great Lakes. Many of the biological and ecological stressors currently associated with climate change appear to be accounted for by the age-trend model.

Genetic origins of a resurging lake whitefish, Coregonus clupeaformis, population in the Detroit River, Laurentian Great Lakes

The Detroit River connects Lake Huron and Lake Erie of the Laurentian Great Lakes. The river once supported a substantial lake whitefish (Coregonus clupeaformis) fishery until the early 1900s, when habitat loss, pollution, and overfishing contributed to the collapse of the fishery and loss of spawning populations in the river. In the early 1970s, efforts were initiated to improve water and habitat quality, and in December 2005 a spawning male lake whitefish and viable eggs were collected; the first documented evidence of spawning since 1916. Researchers have tracked the spawning magnitude of the lake whitefish population in the Detroit River since 2005 by assessing the number of eggs deposited on egg mats. Genetic analysis of larval fish hatched from eggs collected in the field between 2005 and 2018 was used to determine the relative contributions of Lake Erie and Lake Huron to the resurging population. Over 80% of the hatched larvae had parents originating from Lake Erie in all the years sampled. The estimated number of full-sibling families sampled at Belle Isle was the same in 2010 and 2014 and varied between 2009 and 2016 at Fighting Island. The estimated number of lake whitefish parents at Fighting Island decreased in the most recent collections possibly due to loss of habitat on spawning reefs due to sedimentation. Our results provide additional evidence that restored spawning habitat in the Detroit River is again being used by lake whitefish and continued reproduction at these sites may improve the Great Lakes portfolio of ecological and genetic diversity.

Mercury concentrations and potential methylation rates in Lake Erie

Abstract Little is known about external and internal loading and cycling of bioaccumulative methylmercury in Lake Erie, despite the lake having a world-renowned sport fishery. During the summer/early fall of 2018 to 2021, concentrations and fluxes of total mercury and methylmercury in the water column were examined near the Detroit and Maumee River discharges into western Lake Erie, as well as the junction between Sandusky Bay and central Lake Erie. Average unfiltered total mercury concentrations were similar near the Detroit River (5.4 ± 0.8 pM) and Sandusky Bay inputs (5.3 ± 0.9 pM), which were less than half of those near the Maumee River mouth (11.6 ± 2.8 pM). Similarly, unfiltered methylmercury concentrations near the Detroit River (0.29 ± 0.09 pM) and Sandusky Bay inputs (0.24 ± 0.06 pM) were less than half of those near the Maumee River mouth (0.63 ± 0.21 pM). Potential specific mercury methylation rates measured in central Lake Erie were 0.062 ± 0.027 day-1, 0.045 ± 0.012 day–1 near the Sandusky Bay input, and 0.031 ± 0.006 day–1 at the Detroit River input (Maumee Bay was below detection; rates were not different; Tukey, p >0.87). Compared to previous work, total mercury concentrations in the western basin observed in this study indicate a decrease of about 3.3% yr–1, which may reflect positive impacts of state, provincial, and national legislation (U.S. National Clean Water Act 1990, Ohio Clean Air and Water Act 2004, Ontario Clean Water Act 2006). However, methylmercury concentrations have increased in western Lake Erie from 2010 to 2019, which may reflect the impact of legacy mercury pollution.

Broad scale community-level larval fish survey of southern Lake Erie

Abstract The early-life history stages of fish are sensitive to environmental change and therefore can indicate habitat quality as well as help predict recruitment of resident and transient fishes. In 2019, as part of the Lake Erie Cooperative Science and Monitoring Initiative, we conducted a lake-wide assessment of the ichthyoplankton community in U.S. nearshore waters and international offshore waters. The goal of this work was to characterize the larval fish community across the lake and assess species composition, phenology, and distribution of larvae. Ichthyoplankton were sampled weekly using bongo nets at ports beginning at the Detroit River and along the southern shore of Lake Erie to Dunkirk, NY, and less frequently in the Niagara River and offshore areas. Larval fish were present from March 26 through August 29, 2019. The first taxon to emerge was Lake Whitefish in all basins, followed by Walleye, Yellow Perch, and catostomids, depending on port. Mean total density peaked in mid-June due to high catches of Gizzard Shad, Morone spp., and Freshwater Drum in the western basin. Few fish were collected in the offshore sites. Taxa richness, diversity, and larval density were higher in the western basin and lower in the central and eastern basins, generally following the productivity gradient. This was the first study to provide a comprehensive community assessment of the ichthyoplankton community of Lake Erie and can provide a baseline to assess future change, especially in community composition or phenology, of larvae which are likely to respond to climate and habitat change.

Buried but not dead: The impact of stream and wetland loss on flood risk in redlined neighborhoods

The United States government sponsored the Home Owners’ Loan Corporation (HOLC) in the 1930s to assess and grade neighborhoods based on perceived financial risk. The grades were influenced by the presence of minority racial groups, immigrants, and residents with lower socioeconomic statuses and, even though the practice was eventually outlawed, the impact on low income and underrepresented minorities is still prevalent today. This study was designed to assess spatial patterns and intensity of flood risk to (a) HOLC grade, (b) proximity to coastal zones, (c) intensity of vegetative cover, and (d) relationship to buried (ghost) streams and wetlands to determine which variable has the most impact on flood risk. Flood risk data, acquired from First Street Foundation’s Flood Factor dataset, was summarized by HOLC grade, and ghost streams and wetlands were digitized from historical maps and aggregated by HOLC grade. The results show flood risk is higher in C and D graded neighborhoods, compared to A and B. Regardless of HOLC grade, neighborhoods near the Detroit River and Lake St. Claire have 10 times higher flood risk than inland neighborhoods. Interestingly, B-graded neighborhoods exhibit minimal impact from buried rivers and wetlands, but that risk increases substantially if there is a history of stream or wetland burial within a D graded neighborhood. Flood risk is disproportionately distributed, caused in part by outlawed, racist housing policies. Understanding where risk is highest can help identify optimum locations for adaptation measures to minimize flood damage in these neighborhoods.

Contaminated sediment in the Detroit River provokes acclimated responses in wild brown bullhead (Ameiurus nebulosus) populations

In a previous study, adaptive responses to a single polycyclic aromatic hydrocarbon (PAH), benzo[a]pyrene (BaP), were identified in brown bullhead (Ameiurus nebulosus) captured from contaminated sites across the Great Lakes. The tumor suppressor p53 and phase I toxin metabolizing CYP1A genes showed a elevated and refractory response, respectively, up to the F1 generation (Williams and Hubberstey, 2014). As an extension to the first study, bullhead were exposed to sediment collected from sites along the Detroit River to see if these adaptive responses are attainable when fish from a contaminated site are exposed to a mixture of contaminants, instead of a single compound. p53 and CYP1A proteins were measured again with the addition of phase II glutathione-s-transferase (GST) activity in the present study. Three treatment groups were measured: acute (treated immediately), cleared (depurated for three months and subsequent treatment), and farm raised F1 offspring. All three treatment groups were exposed to clean and contaminated sediment for 24 and 96 h. Acute fish from contaminated sites exposed to contaminated sediment revealed an initial elevated p53 response that did not persist in fish after long-term contaminated sediment exposure. Acute fish from contaminated sites exposed to contaminated sediment revealed refractory CYP1A expression, which disappeared in cleared fish and whose F1 response overlapped with clean site F1 offspring. Decreasing GST activity was evident in both clean and contaminated fish over time, and only clean site fish responded to long-term contaminated sediment deliberately with increasing GST activity.Because p53 and CYP1A gene expression and GST activity responses did not overlap between contaminated fish treatment groups, our study suggests that contaminated fish have acclimated to the contaminants present in their environments and no evidence of adaptation could be detected within these biomarkers.

Host species and habitat shape fish-associated bacterial communities: phylosymbiosis between fish and their microbiome

BackgroundWhile many studies have reported that the structure of the gut and skin microbiota is driven by both species-specific and habitat-specific factors, the relative importance of host-specific versus environmental factors in wild vertebrates remains poorly understood. The aim of this study was to determine the diversity and composition of fish skin, gut, and surrounding water bacterial communities (hereafter referred to as microbiota) and assess the extent to which host habitat and phylogeny predict microbiota similarity. Skin swabs and gut samples from 334 fish belonging to 17 species were sampled in three Laurentian Great Lakes (LGLs) habitats (Detroit River, Lake Erie, Lake Ontario). We also collected and filtered water samples at the time of fish collection. We analyzed bacterial community composition using 16S metabarcoding and tested for community variation.ResultsWe found that the water microbiota was distinct from the fish microbiota, although the skin microbiota more closely resembled the water microbiota. We also found that environmental (sample location), habitat, fish diet, and host species factors shape and promote divergence or convergence of the fish microbiota. Since host species significantly affected both gut and skin microbiota (separately from host species effects), we tested for phylosymbiosis using pairwise host species phylogenetic distance versus bacterial community dissimilarity. We found significant phylogenetic effects on bacterial community dissimilarity, consistent with phylosymbiosis for both the fish skin and gut microbiota, perhaps reflecting the longstanding co-evolutionary relationship between the host species and their microbiomes.ConclusionsAnalyzing the gut and skin mucus microbiota across diverse fish species in complex natural ecosystems such as the LGLs provides insights into the potential for habitat and species-specific effects on the microbiome, and ultimately the health, of the host.13rgRWqcw5pvG7aonCbZg2Video

Habitat modelling of native freshwater mussels distinguishes river specific differences in the Detroit and St. Clair rivers of the Laurentian Great Lakes

Native freshwater mussels (Bivalvia: Unionidae) were seemingly pushed to extirpation following the establishment of dreissenid mussels in the St. Clair (SCR)–Detroit River (DR) System and the current state of unionids in the main channels of the SCR remains unknown. To assess remnant unionid populations, the DR and SCR were surveyed in 2019 and 2021, respectively, using a mixture of stratified random, historical, potential refuge, and model-selected (SCR sampling only) sites (n = 56 DR sites and 51 SCR sites). Data collected from the DR (2019) were used to create unionid species distribution models in MaxEnt, which produced the model-selected sites for sampling the SCR. A total of 14 live unionids representing 9 species were found among 7 sites in the SCR; however, the DR model projected to the SCR failed to be predictive for unionid presence in the SCR (0 % success). Additional models were created for the DR and SCR using MaxEnt and classification and regression tree (CART) Analysis to elucidate the characteristic differences between the two rivers. MaxEnt modelling showed the highest contributing variable for the DR model was water velocity (m/s) while the highest contributing variable for the SCR model was river distance to the outlet which could be one explanation for why the DR model did not accurately predict unionid presence in the SCR. Additionally, when DR and SCR data were combined in the CART model, the model failed to predict any live unionid sites from the SCR. Variability in model predictions demonstrate the characteristic differences between the DR and SCR. Therefore, model verification for both rivers specific models took place in 2022 (n = 8 DR sites and 6 SCR sites). The DR unionid species distribution model identified 3 additional sites with live unionids (38 % of predicted sites), but the SCR model did not locate any additional live unionid locations (0 % of predicted sites). This research updated our knowledge on native unionid distributions and habitat use in the DR and SCR which could contribute towards unionid conservation in the future.

Assessing potential spawning locations of Silver Chub in Lake Erie

AbstractObjectiveSilver Chub Macrhybopsis storeriana, a predominately riverine species throughout its native range, exists within Lake Erie as the only known lake population. Its population declined in the 1950s and never fully recovered. Canada has listed Silver Chub in the Great Lakes–St. Lawrence River as endangered and has initiated a recovery plan that recognized the identification of spawning areas as a critical component to inform Silver Chub's recovery potential.MethodsWe investigated potential spawning locations of Silver Chub using capture records, otolith microchemistry, and daily age analysis. Lapillus otolith Sr:Ca ratios from 27 age‐0 Silver Chub were used to identify potential spawning areas. Daily ages estimated from lapilli were used to calculate hatch dates, which then were compared with capture data of adults and river flows to further inform potential spawning areas.ResultThe Detroit River (and its nearshore area) was all but ruled out as a potential spawning location. The Maumee, Portage, and Sandusky rivers or their nearshore areas were all possible spawning locations. Projected hatch dates spanned the end of May through the end of June and occurred across a wide range of flows, although some peaks in hatch dates corresponded to flow peaks, indicating recruitment is potentially enhanced by high flows.ConclusionSilver Chub spawning period and hypothesized spawning rivers or lacustuaries overlap those of invasive Grass Carp Ctenopharyngodon idella, creating a need to jointly consider Grass Carp control efforts with conservation of Silver Chub when assessing management alternatives. Further research on spawning guild and the use of rivers themselves or nearshore areas influenced by rivers as spawning areas are required to maximize potential for conservation and recovery of Silver Chub.

A mass-balance approach for predicting lake phosphorus concentrations as a function of external phosphorus loading: Application to the Lake St. Clair – Lake Erie System (Canada – USA)

Abstract A mass balance model is presented that links the total phosphorus concentration in lakes to the water residence time, Rw (lake volume divided by the annual water inflow) and the total phosphorus residence time, Rp (average standing stock of lake total phosphorous divided by the external annual total phosphorus input). Following a change in the external load, the lake total phosphorus concentration asymptotically approaches a new value that depends on the Rp:Rw ratio, with the rate of approach controlled by Rp. We applied this approach to a recent reanalysis of the water and total phosphorus budgets of the Lake Erie system of the Laurentian Great Lakes for the 2003-2016 period. We generated load–response relationships and response matrices that relate the steady state total phosphorus concentrations to external total phosphorus loads, for the whole Lake Erie system and for the individual basins (Lake St. Clair, western basin, central basin, eastern basin) and connecting channels (St. Clair River, Detroit River). These relationships and matrices provide a simple but robust framework to gauge the potential response of total phosphorus concentrations to total phosphorus load reductions, such as the 40% reduction proposed for Lake Erie under the Canada-United States Great Lakes Water Quality Agreement. The mass balance analysis further highlights the importance of inter-basin total phosphorus transfers. For example, around 70% of the total phosphorus concentration in the eastern basin is contributed by inflow from the central basin. Consequently, total phosphorus load abatements in watersheds upstream of the eastern basin, rather than in the direct watershed itself, will have the greatest impact on the eastern basin's concentration. Overall, our results illustrate how simple mass balance calculations can provide useful guidance to efforts to manage phosphorus enrichment of lakes.

Rewilding the Detroit, Michigan, USA–Windsor, Ontario, Canada Metropolitan Area

Rewilding attempts to increase biodiversity and restore natural ecosystem processes by reducing human influence. Today, there is growing interest in rewilding urban areas. Rewilding of the Detroit, Michigan, USA and Windsor, Ontario, Canada metropolitan area, and its shared natural resource called the Detroit River, has been delineated through the reintroduction of peregrine falcons and osprey, and a return of other sentinel species like bald eagles, lake sturgeon, lake whitefish, walleye, beaver, and river otter. Rewilding has helped showcase the value and benefits of environmental protection and restoration, ecosystem services, habitat rehabilitation and enhancement, and conservation, including social and economic benefits. Improved ecosystem health and rewilding have become a catalyst for re-establishing a reconnection between urban denizens and natural resources through greenways and water trails. The provision of compelling outdoor experiences in nature, in turn, can help foster a personal attachment to the particular place people call home that can help inspire a stewardship ethic.

Lake Sturgeon population trends in the St. Clair–Detroit River system, 2001–2019

AbstractObjectiveThe Lake Sturgeon Acipenser fulvescens is listed as threatened or endangered in 15 states or provinces within the species' native range. Accordingly, investments in habitat and population restoration for this species have increased throughout the Great Lakes. To aid in the evaluation of restoration efficacy, robust population parameters are needed to inform management decisions. The St. Clair–Detroit River system (SCDRS) contains one of the largest self‐sustaining Lake Sturgeon populations in the Great Lakes; however, recent estimates of population abundance and growth parameters have not been assessed.MethodsOur study used baited setline and mark–recapture data collected between 2001 and 2019 to estimate whether the number of Lake Sturgeon captured varied annually and/or with water temperature and whether population abundance and the population growth rate (λ) varied among three subpopulations located in the SCDRS.ResultTrends in the number of Lake Sturgeon captured on setlines varied among subpopulations and by life stage. Annual trends in the number of Lake Sturgeon captured remained consistent over time in the upper St. Clair River, decreased for adults and increased for subadults in the lower St. Clair River, and increased in the Detroit River. With subpopulation abundances of 20,184 (95% confidence interval [CI] = 12,533–27,816) in the upper St. Clair River/southern Lake Huron, 6523 (95% CI = 5720–7327) in the lower St. Clair River, and 6416 (95% CI = 4065–8767) in the Detroit River, our study confirms that the SCDRS contains the largest Lake Sturgeon population with unimpeded access to the Great Lakes. The geometric mean λ for all subpopulations indicated stable populations and ranged from 1.00 to 1.16.ConclusionOur study provides an updated assessment of Lake Sturgeon population parameters that serve as a baseline to evaluate habitat restoration efforts and to inform management of the SCDRS recreational Lake Sturgeon fishery.

Lingering Effects of Legacy Industrial Pollution on Yellow Perch of the Detroit River.

We used yellow perch (Perca flavescens) captured at four sites differing in legacy industrial pollution in the Lake St. Clair-Detroit River system to evaluate the lingering sublethal effects of industrial pollution. We emphasized bioindicators of direct (toxicity) and indirect (chronic stress, impoverished food web) effects on somatic and organ-specific growth (brain, gut, liver, heart ventricle, gonad). Our results show that higher sediment levels of industrial contaminants at the most downstream Detroit River site (Trenton Channel) are associated with increased perch liver detoxification activity and liver size, reduced brain size, and reduced scale cortisol content. Trenton Channel also displayed food web disruption, where adult perch occupied lower trophic positions than forage fish. Somatic growth and relative gut size were lower in perch sampled at the reference site in Lake St. Clair (Mitchell's Bay), possibly because of increased competition for resources. Models used to determine the factors contributing to site differences in organ growth suggest that the lingering effects of industrial pollution are best explained by trophic disruption. Thus, bioindicators of fish trophic ecology may prove advantageous to assess the health of aquatic ecosystems. Environ Toxicol Chem 2023;42:2158-2170. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Constraining carbon and sulfur dynamics in Lake Erie nearshore waters: A chemical and isotopic reconnaissance study

Past studies have documented contrasting geochemical responses of the Great Lakes to anthropogenic disturbances of the carbon and sulfur cycles. Yet, it is unclear whether these responses were induced by differences in tributary inputs or different behaviors controlled by in-lake biogeochemical processes. To yield insight into the carbon and sulfur dynamics across the land-lake interface, concentrations of chloride (Cl-), sulfate (SO42-), dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC) were measured in water samples from nearshore and offshore sites at Lake Erie, the Detroit River, and other tributaries. The stable isotope ratios of water (δ18O and δ2H), sulfate (δ34SSO4 and δ18OSO4), and the stable and radio isotope ratios of DIC (δ13CDIC and Δ14CDIC) were also measured. Our results confirm that waters from Lake Erie characterized by low Cl- and SO42-, low deuterium excess (d-excess = δ2H – 8 δ18O), and high δ13CDIC, Δ14CDIC, δ34SSO4, and δ18OSO4, were chemically and isotopically different from tributary waters. The nearshore waters exhibited significant correlations between various pairs of chemical and isotopic parameters revealing the influence of inputs from the tributaries. Moreover, the nearshore waters had lower averages of Cl-, SO42-, DOC, DIC, and δ18O, but higher averages of δ13CDIC, Δ14CDIC, and δ34SSO4 than those estimated from binary mixing between lake and tributary waters, suggesting an effect of in-lake biogeochemical transformations. But the rates of carbon and sulfur transformations differed considerably. Thus, we suggest that the contrasting geochemical responses were induced by both their different in-lake transformation rates and their different histories of tributary inputs.

Detroit River load estimation; the need for a new monitoring approach

The Great Lakes Water Quality Agreement (GLWQA) established new Lake Erie phosphorus loading targets, including a 40% total phosphorus load reduction to its western and central basins. The Detroit and Maumee rivers’ loads are roughly equal and contribute about 90% of the load to the western basin and 54% to the whole lake. They are key drivers of central basin hypoxia and western basin algal production. So, accurate estimates of the Detroit River load are important. Direct measurement of that load near its mouth is difficult due to requiring real-time knowledge of flows around islands and the influence of Lake Erie’s seiches. Consequently, most estimates sum the loads to the St. Clair/Detroit River system. But this approach is complicated by uncertainties in the Lake Huron load and load retention in Lake St. Clair. Routine GLWQA reassessments will confirm or adjust over time the goals, loading targets, and approaches based on evolving information. So, there is a need to improve monitoring approaches that ensure accurate Detroit River loads. New approaches should take into account both the characteristics of this dynamic connecting channel and the uses of monitoring results: 1) determining the Detroit River loads to drive models, develop mass balances, set load reduction targets, and track progress; and 2) assessing the sources and processing of the loads to help guide reduction strategies. Herein, we review temporal and spatial variability in the St. Clair/Detroit River system, and suggest adjustments to monitoring that address those variabilities and both uses.

Biological Investigation of the Endangered Northern Madtom in the North Channel St. Clair River

AbstractAquatic organisms and the habitats they live in are declining globally, yet managers often lack even basic biological information for individual imperiled species. This makes assessment of the current status, management needs, and recovery targets for these species challenging. One such organism is the Northern Madtom Noturus stigmosus, a small, bottom‐dwelling catfish of the family Ictaluridae. Northern Madtom are listed as endangered in the state of Michigan and the province of Ontario, with only a handful of isolated populations known in each region. To address life history uncertainties and to provide fisheries managers with baseline information to inform decision making, the Michigan Department of Natural Resources annually sampled Northern Madtom in the St. Clair River using minnow traps and amassed the largest known data set for this species. We handled 871 individuals from 2010 to 2022, with yearly catch rates ranging from 0.17 to 1.33 individuals/trap. Age estimates derived from otoliths and dorsal spines of 17 individuals showed no clear pattern of bias, indicating that nonlethally collected dorsal spines provide a suitable age estimation method. We developed an age–length key to assign ages to all individuals in our data set, calculated growth parameters, and determined that annual mortality rates across all ages ranged from 46% to 69%. Diet analysis revealed that caddisfly (order Trichoptera) larvae were the dominant prey item and fecundity averaged 178 eggs/female. We compared microsatellite allele frequencies and mitochondrial DNA haplotypes among samples collected in the St. Clair River and the Detroit River. Significant evidence of genetic structure was present, indicating limited gene flow and suggesting that separate management of these two populations may be warranted. Collectively, these data provide context for managers interested in the development of biological reference points and planning for the conservation and management of this species.