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Chlorophyll-a (Chl-a), a proxy for phytoplankton biomass, is one of the few biological water quality indices detectable using satellite observations. However, models for estimating Chl-a from satellite signals are currently unavailable for many lakes. The application of Chl-a prediction algorithms may be affected by the variance in optical complexity within lakes. Using Lake Winnipeg in Canada as a case study, we demonstrated that separating models by the lake's basins [north basin (NB) and south basin (SB)] can improve Chl-a predictions. By calibrating more than 40 commonly used Chl-a estimation models using Landsat data for Lake Winnipeg, we achieved higher correlations between in situ and predicted Chl-a when building models with separate Landsat-to-in situ matchups from NB and SB (R2 = 0.85 and 0.76, respectively; p < 0.05), compared to using matchups from the entire lake (R2 = 0.38, p < 0.05). In the deeper, more transparent waters of the NB, a green-to-blue band ratio provided better Chl-a predictions, while in the shallower, highly turbid SB, a red-to-green band ratio was more effective. Our approach can be used for rapid Chl-a modeling in large lakes using cloud-based platforms like Google Earth Engine with any available satellite or time series length. [ABSTRACT FROM AUTHOR]

Lake Winnipeg in Manitoba, Canada is heavily impacted by harmful algal blooms that contain non-protein amino acids (NPAAs) produced by cyanobacteria: N-(2-aminoethyl)glycine (AEG), β-aminomethyl-L-alanine (BAMA), β-N-methylamino-L-alanine (BMAA), and 2,4-diaminobutyric acid (DAB). Our objective was to investigate the impact of microbial diversity on NPAA production by cyanobacteria using semi-purified crude cyanobacterial cultures established from field samples collected by the Lake Winnipeg Research Consortium between 2016 and 2021. NPAAs were detected and quantified by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) using validated analytical methods, while Shannon and Simpson alpha diversity scores were determined from 16S rRNA metagenomic sequences. Alpha diversity in isolate cultures was significantly decreased compared to crude cyanobacterial cultures (p < 0.001), indicating successful semi-purification. BMAA and AEG concentrations were higher in crude compared to isolate cultures (p < 0.0001), and AEG concentrations were correlated to the alpha diversity in cultures (r = 0.554; p < 0.0001). BAMA concentrations were increased in isolate cultures (p < 0.05), while DAB concentrations were similar in crude and isolate cultures. These results demonstrate that microbial community complexity impacts NPAA production by cyanobacteria and related organisms. [ABSTRACT FROM AUTHOR]

Chlorophyll-a (Chl-a), a proxy for phytoplankton biomass, is one of the few biological water quality indices detectable using satellite observations. However, models for estimating Chl-a from satellite signals are currently unavailable for many lakes. The application of Chl-a prediction algorithms may be affected by the variance in optical complexity within lakes. Using Lake Winnipeg in Canada as a case study, we demonstrated that separating models by the lake’s basins [north basin (NB) and south basin (SB)] can improve Chl-a predictions. By calibrating more than 40 commonly used Chl-a estimation models using Landsat data for Lake Winnipeg, we achieved higher correlations between in situ and predicted Chl-a when building models with separate Landsat-to-in situ matchups from NB and SB (R2 = 0.85 and 0.76, respectively; p < 0.05), compared to using matchups from the entire lake (R2 = 0.38, p < 0.05). In the deeper, more transparent waters of the NB, a green-to-blue band ratio provided better Chl-a predictions, while in the shallower, highly turbid SB, a red-to-green band ratio was more effective. Our approach can be used for rapid Chl-a modeling in large lakes using cloud-based platforms like Google Earth Engine with any available satellite or time series length.

The sun had not yet risen over Lake Winnipeg when Jim Brennand stepped into its cold, calm waters. It was early in the morning of 29 August 1955 and Brennand [...]

Lake Winnipeg in Manitoba, Canada is heavily impacted by harmful algal blooms that contain non-protein amino acids (NPAAs) produced by cyanobacteria: N-(2-aminoethyl)glycine (AEG), β-aminomethyl-L-alanine (BAMA), β-N-methylamino-L-alanine (BMAA), and 2,4-diaminobutyric acid (DAB). Our objective was to investigate the impact of microbial diversity on NPAA production by cyanobacteria using semi-purified crude cyanobacterial cultures established from field samples collected by the Lake Winnipeg Research Consortium between 2016 and 2021. NPAAs were detected and quantified by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) using validated analytical methods, while Shannon and Simpson alpha diversity scores were determined from 16S rRNA metagenomic sequences. Alpha diversity in isolate cultures was significantly decreased compared to crude cyanobacterial cultures (p < 0.001), indicating successful semi-purification. BMAA and AEG concentrations were higher in crude compared to isolate cultures (p < 0.0001), and AEG concentrations were correlated to the alpha diversity in cultures (r = 0.554; p < 0.0001). BAMA concentrations were increased in isolate cultures (p < 0.05), while DAB concentrations were similar in crude and isolate cultures. These results demonstrate that microbial community complexity impacts NPAA production by cyanobacteria and related organisms.

In this first comprehensive study of Lake Winnipeg's microbial communities, limnetic and littoral euphotic zones were examined during each season from 2016 through 2020. Classical cultivation and modern high-throughput sequencing techniques provided quantification and identification of key phototrophic populations, including aerobic anoxygenic phototrophs (AAP). Annual dynamics found total heterotrophs reached 4.23 × 106 CFU/g in littoral sands, and 7.69 × 104 CFU/mL in summer littoral waters on oligotrophic media, higher counts than for copiotrophic compositions. Limnetic numbers inversely dipped to 4.34 × 103 CFU/mL midsummer. Cultured AAP did not follow heterotrophic trends, instead peaking during the spring in both littoral and limnetic waters as 19.1 and 4.7% of total copiotrophs, or 3.9 and 4.9% of oligotrophs, decreasing till autumn each year. Complementary observations came from environmental 16S V4 rRNA gene analysis, as AAP made up 1.49 and 1.02% of the littoral and limnetic sequenced communities in the spring, declining with seasonal progression. Spatial and temporal fluctuations of microbes compared to environmental factors exposed photosynthetic populations to independently and regularly fluctuate in the ecosystem. Oxygenic phototrophic numbers expectantly matched the midsummer peak of Chl a and b, oxygenic photosynthesis related carbon fixation, and water temperature. Independently, AAP particularly colonized spring littoral areas more than limnetic, and directly corresponded to habitat conditions that specifically promoted growth: the requirement of light and organic material. [ABSTRACT FROM AUTHOR]

Copyright of Avian Conservation & Ecology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lakes are important sites for carbon fixation and carbon dioxide (CO 2) exchange with the atmosphere. Carbon fixation rates have not previously been published for Lake Winnipeg but are important for quantifying the lake's role in the regional greenhouse gas budget and the lake's trophic structure and fish habitat. This study measured net ecosystem production (NEP), gross primary production (GPP), and gross respiration (GR) across the lake using a custom-built automated incubator connected to a ship's water intake during a research cruise between July 31 and August 17, 2018 on Lake Winnipeg. The incubator estimated NEP, GR, and GPP every 60 min while moving along the ship's track and at anchor, providing high-resolution data that are not obtainable through conventional incubations. The mean NEP for Lake Winnipeg during our survey was −8.4 ± 5.6 g C m−2 d−1, suggesting that the lake was net heterotrophic and thus a net CO 2 source to the atmosphere during the 2018 summer cruise. The high-resolution data revealed significant spatiotemporal variability, including short-lived, highly net productive events that preceded remotely sensed chlorophyll a blooms by several days. Conversely, in regions with high chlorophyll a concentrations, we observed strong net heterotrophy and low nutrients, suggesting respiration was fueled by the degradation of mature, nutrient-limited phytoplankton blooms. The incubator system used in this study demonstrated its utility for monitoring rapid changes in NEP over short spatial scales in a lake which shows heightened regional variability in its physical, biogeochemical, and biological make-up. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the sedimentation dynamics within Lake Winnipeg (surface area: 23,750 km2) and its role in sediment transport in the downstream river system was achieved by determining the properties of lake bottom sediment and patterns of sediment accumulation rates and by constructing a conceptual total (i.e., organic and inorganic) sediment budget. Net deposition was the governing process in the South and North Basins, whereas transportation dominated in the Narrows. The largest fluvial source of sediments to the lake, the Red River, supplies 35% of the total sediment load. Although accumulation rates in profundal zones progressively decreased northward from this source at the south end of the lake, high accumulation rates with low inventories of fallout radionuclides in the northern margin of the North Basin indicate a second sediment source, which was determined to be erosion of north shore banks, which accounts for up to 50% of the total sediment load to the lake. The nearshore-offshore gradient in bottom sediment properties in the North Basin confirmed that the signature of this source can reach at least 20 km southward into the lake. However, the properties of bottom sediments, sedimentation dynamics, and sediment budget suggested that some of the materials eroded from the north shore are exported without interaction with the lake bottom and this local sediment source is the dominant source for the downstream river system. It was concluded that Lake Winnipeg effectively disconnects the downstream Nelson River from sediment transport processes in its upstream watershed (953,250 km2). [ABSTRACT FROM AUTHOR]

Freshwater lakes are increasingly recognized as significant sources of atmospheric methane (CH 4), potentially offsetting the terrestrial carbon sink. We present the first study of dissolved CH 4 distributions and lake-air flux from Lake Winnipeg, based on two-years of observations collected during all seasons. Methane concentrations across two years had a median of value of 24.6 nmol L-1 (mean: 41.6 ± 68.2 nmol L-1) and ranged between 5.0 and 733.8 nmol L-1, with a 2018 annual median of 24.4 nmol L-1 (mean: 46.8 ± 99.3 nmol L-1) and 25.1 nmol L-1 (mean: 38.8 ± 45.2 nmol L-1) in 2019. The median lake-air flux was 1.1 µmol m−2 h−1 (range: 0.46–70.1 µmol m−2h−1, mean: 2.9 ± 10.2 µmol m−2 h−1) in 2018, and 5.5 µmol m−2h−1 (range: 0.0–78.4 µmol m−2 h−1, mean: 2.7 ± 8.5 µmol m−2 h−1) in 2019, for a total diffusive emission of 0.001 Tg of CH 4 -C yr−1. We found evidence of consistent spatial variability, with higher concentrations near river inflows. Significant seasonal trends in CH 4 concentrations were not observed, though fluxes were highest during the fall season due to strong winds. Our findings suggest Lake Winnipeg is a CH 4 source of similar mean magnitude to Lake Erie, with lower concentrations and fluxes per unit area than smaller mid- to high-latitude lakes. Additional work is needed to understand the factors underlying observed spatial variability in dissolved gas concentration, including estimations of production and consumption rates in the water column and sediments. [ABSTRACT FROM AUTHOR]

Concentrations of total mercury (THg) in the axial musculature of northern pike (Esox lucius), walleye (Sander vitreus), lake whitefish (Coregonus clupeaformis), and sauger (Sander canadensis) were analyzed from several regions of Lake Winnipeg and three main inflows, focusing on Mossy Bay in the North Basin of the lake. Length-standardized means (standard means) indicated THg concentrations in pike of 550 mm fork length (0.44 ppm) and walleye measuring 400 mm (0.38 ppm) from Mossy Bay were highest in 1971 and declined to 0.13 and 0.22 ppm, respectively, by 1974. Standard means of both these species have been similar since 2010 (walleye; approximately 0.11 ppm) and 2013 (pike; approximately 0.17 ppm), except for a significant increase to 0.15 ppm in walleye in 2019, potentially related to concurrent changes in trophic interactions with invasive fish and invertebrate species. Standard means of 300 mm long sauger (0.23–0.29 ppm) did not decline significantly between 1971 and 1974, and those of 350 mm long whitefish ranged from 0.006 to 0.028 ppm from 1983 to 2016 with no clear temporal trend. In concert with data from other areas of Lake Winnipeg and the three inflows for 2000–2019, these results indicate higher contemporary concentrations in the South Basin of the lake. This latitudinal gradient in fish THg is assumed to be a result of continuous mercury inputs from the Red and the Winnipeg River, whereas a former point source of industrial mercury in the Saskatchewan River is no longer relevant. According to human consumption limits based on tolerable daily intake calculations and current THg concentrations of fish from Mossy Bay, substantial quantities of whitefish, pike, and walleye fish can be safely eaten. [ABSTRACT FROM AUTHOR]

Lake Winnipeg has undergone extensive changes in environmental conditions and fish community structure during recent decades. The presence of cyanobacteria and invasive species as well as eutrophication, flow regulation, fishing pressure, and climate change all have potential impacts on the native fish community. Since 2002, pelagic forage fish species and early life stages of large-bodied fish species in the pelagic zone in Lake Winnipeg (Manitoba, Canada) have been monitored. Catch data were used to study the temporal variation in species-specific occurrence and catch-per-unit-effort (CPUE) and to analyse the effects of lake condition on species occurrence and CPUE estimates. To account for the temporal variation observed for commonly caught prey species in Lake Winnipeg, we used a Bayesian approach, Integrated Nested Laplace Approximation (INLA), to compare the effects of environmental variables on occurrence and CPUE. The pelagic fish community composition varied among years, and CPUE declined by 2.2-fold between 2005–2008 and 2015–2018. Emerald shiner was the most dominate prey fish species but decreased in the catches since the early 2000's, while rainbow smelt have almost entirely disappeared from the catches in recent years. Overall, we observed a decrease in CPUE in four of six most caught, pelagic species. Important environmental variables explaining occurrence and CPUE of the six most caught species in the survey were temperature and Secchi, trawl, and water depths. The trawl survey serves as a valuable long-term monitoring tool to study trends in responses of both native and non-native species to ecosystem changes in Lake Winnipeg. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new high-resolution (500 × 500 m), three-dimensional hydrodynamic model was applied to Lake Winnipeg to study summer and winter water circulation, temperature, and ice-cover during 2016–17. The model was run with a combination of buoy-based observations and the outputs from the Global Environmental Multiscale model forcing. Four primary riverine inflows and two outflows were considered in the model. The bathymetry from a previous study by the authors was revised using a 2018 survey covering the South Basin and the Narrows. Comparisons of this new model with the previous model setup (2 km resolution) show noticeable improvements in all simulated parameters. In the Narrows, where seiche-driven flows have predominant oscillation periods of ~27 h and ~17 h, the RMSE of simulated currents is 0.1 m s−1, half of that of the previous simulations. The new model was able to reasonably simulate the spatial development of ice-cover over the lake. The ice-free period circulation results show that there are two clockwise and counterclockwise gyres in the North Basin, and a weak seasonal clockwise gyre in the South Basin. Monthly circulation patterns differ from those during short wind events due to spatiotemporal variability of wind patterns. The materials from the Red and the Winnipeg Rivers need ~50 days to reach the Narrows before transported from the South Basin to the North Basin. The daily inter-basin exchange flow oscillations during the ice-free period can range up to ~3.5 × 104 m3 s−1, while under-ice daily exchanges are always northwards with values depending on inflowing riverine discharge up to ~0.5 × 104 m3 s−1. [ABSTRACT FROM AUTHOR]

While nutrient loading has affected all levels of Lake Winnipeg's ecology, its greatest influence has likely been on the microbial community. In addition to eutrophication, zebra mussels (Dreissena polymorpha) have recently invaded the ecosystem and threaten food web dynamics. Their filter-feeding predation and association with bacteria, specifically phototrophs, was investigated. A sampling trip to Lake Winnipeg in October 2017, focused on the isolation, enumeration, and identification of aerobic anoxygenic phototrophs in littoral water, sediment, and tissues of mussels. Gimli, Patricia, and Grand beaches, separated by >15 km across the South Basin, had similar bacterial counts when cultivated on rich organic, BG-11, purple non-sulphur, and K 2 TeO 3 -supplemented media. Culture-based enumeration on rich organic medium revealed 1.74% of heterotrophs from littoral waters were aerobic anoxygenic phototrophs, and represented 13.98% within sediments. In contrast, 0.48, 1.15, and 0.16% of cultured heterotrophs were aerobic anoxygenic phototrophs within zebra mussel gill, gut, and gonadal tissues, respectively. High-throughput sequencing of bacterial 16S V4 rDNA maintained similar trends in respective bivalve organs, where 0.22, 1.13, and 0.20% of total 16S genes belonged to these phototrophs. Several Sphingomonadaceae isolates were recovered from gut tissues, all with filamentous morphology large enough for predation. Bioaccumulation of metals was also studied in D. polymorpha. All tested associated aerobic anoxygenic phototrophs were capable of resisting the metalloid oxide tellurite. The consistent distribution of aerobic anoxygenic phototrophs within microbial communities across Lake Winnipeg, and their predominance in the gut tissues of zebra mussels suggested bacterial consumption by this invasive species. [ABSTRACT FROM AUTHOR]

Lake Winnipeg has undergone rapid eutrophication over the last several decades with a large portion of the associated nutrient loads delivered via the Red River. Consequently, subcatchments of the Red River Valley (RRV) are priorities for nutrient management, an aim that requires identification of key nutrient sources to stream food webs. We identified the primary sources of nitrogen to food webs of rural streams of the RRV, as well as variation in nitrogen input between spring and summer. We measured δ15N of particulate organic matter (POM) and collector-gatherer invertebrates collected in spring and summer from 20 subcatchments, which exhibited a range of agricultural intensity and size of municipal wastewater lagoons. δ15N values of POM and collector-gatherer invertebrates were best predicted by the presence of wastewater treatment lagoons, with δ15N values increasing with the number of people served by lagoons in spring and summer. When present, wastewater contributed a greater proportion of nitrogen to stream food webs than agricultural sources. Waste sources also had a greater relative contribution to food webs in summer than spring. Despite wastewater lagoons releasing nitrogen in short-term, pulsed discharges, the influence of wastewater on food web nitrogen persisted from the summer release into the following spring. Based on the observed importance of wastewater as a source of nitrogen to stream food webs, we recommend management agencies consider additional actions to reduce nutrient losses from wastewater treatment facilities as well as agricultural lands to more effectively protect aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Water resources on the Canadian Prairies are at risk due to human settlement, agricultural intensification, and climatic change. The Red River Valley (RRV), Manitoba, Canada, represents a nexus of these cumulative stressors. Here land use change, combined with a recent increase in precipitation and runoff, imperils the protective function of tributaries draining to Lake Winnipeg. A concerted research effort over the past decade has greatly improved availability of data and knowledge about the RRV. However, a full synthesis of these data and information remain lacking. We undertook a review to identify and compare contemporary and historical land use, climatic, hydrologic, and water quality condition within the RRV. Then, using current knowledge of the ecological condition of streams in the RRV and elsewhere, we completed an ecological causal assessment of RRV tributaries to identify linkages and knowledge gaps between anthropogenic drivers and ecological endpoints. We found wastewater to be the candidate cause of ecological effects in RRV streams best supported by empirical evidence. A lack of complete lines of evidence linking agriculture, the greatest diffuse source of nutrient inputs, and ecological effects in RRV tributaries underscored a need for stressor-specific indicators and improved biomonitoring strategies to better detect likely impacts of land use. We also identified a need for research to connect well-known causal elements in the RRV, such as climatic variables and hydrological alteration, to ecological effects. Our findings provide direction for future research and can aid in development of an adaptive management strategy for tributaries of the RRV. [ABSTRACT FROM AUTHOR]

Variation in the timing and quantity of diffuse versus point-source inputs of phosphorus (P) to streams can be evaluated by examining P concentration-flow relationships. Diffuse load inputs usually increase with stream flow (due to increased delivery caused by precipitation); whereas, point-source concentrations decrease with rising river flow (due to increased dilution). This study tested the suitability of a load apportionment model (LAM), a power-law function of flow, to estimate contributions of diffuse and point inputs to P loads for eight sub-watersheds in the Red River Valley, a cold-climate rural region of Manitoba, Canada. For all but two sub-watersheds, annual and seasonal (snowmelt and summer) models of P concentration versus flow best fit a strictly diffuse source contribution. The models identified significant point-source inputs (in addition to diffuse sources) in two sub-watersheds, during summer in both watersheds (consistent with the fact that wastewater from sewage lagoons is discharged to upstream reaches between June and September) and during snowmelt for one watershed. Application of a LAM proved to be a simple and rapid method for nutrient source apportionment as well as detection of unknown sources for cold-climate, rural sub-watersheds. Such information is critical for developing the most effective mitigation strategies to reduce P concentrations and eutrophication risk. [ABSTRACT FROM AUTHOR]

Violet and purple bacterial pigmentations are uncommon when considering strict aerobes. Here we report discovery of two novel isolates, P102 and P117 from the freshwater Lake Winnipeg, each with violet to deep purple colony colouration. The relationship between pigment production and growth was investigated under different conditions, including a variety of carbon sources, pH, and temperatures. The violet compounds were purified using polar organic solvents, and then structurally characterized via mass spectrometry and nuclear magnetic resonance to be violacein and deoxyviolacein. Strain P117 produced higher concentrations of the darker pigment deoxyviolacein, which resulted in a deeper hue of violet than in cultures of P102. Strain P102, synthesized violacein maximally in liquid rich organic medium at pH 8 and 20 °C, and had 99.3% sequence similarity to the 16S rDNA from Janthinobacterium lividum. Strain P117, related to Massilia violaceinigra sharing 99.2% 16S rDNA sequence similarity, also produced violacein at similar optimal conditions, but developed higher concentrations of pigment at 15 °C. Culture-based methods found that violacein producers composed 0.001% or 0.023% CFU of environmental heterotrophic populations using BG-11 and potato-based media, respectively. Culture-independent high-throughput ribosomal 16S V4 sequencing of environmental DNA was used to detect Gram-negative species known for their production of violacein. Of all bacterial and archaeal sequences present during the fall in littoral waters and sediment of Lake Winnipeg, 5.5% and 6.3%, respectively, belonged to species that have similar pigment, demonstrating the scarcity of violacein producers in this aquatic freshwater system. [ABSTRACT FROM AUTHOR]

Copyright of Avian Conservation & Ecology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this first comprehensive study of Lake Winnipeg’s microbial communities, limnetic and littoral euphotic zones were examined during each season from 2016 through 2020. Classical cultivation and modern high-throughput sequencing techniques provided quantification and identification of key phototrophic populations, including aerobic anoxygenic phototrophs (AAP). Annual dynamics found total heterotrophs reached 4.23 × 106 CFU/g in littoral sands, and 7.69 × 104 CFU/mL in summer littoral waters on oligotrophic media, higher counts than for copiotrophic compositions. Limnetic numbers inversely dipped to 4.34 × 103 CFU/mL midsummer. Cultured AAP did not follow heterotrophic trends, instead peaking during the spring in both littoral and limnetic waters as 19.1 and 4.7% of total copiotrophs, or 3.9 and 4.9% of oligotrophs, decreasing till autumn each year. Complementary observations came from environmental 16S V4 rRNA gene analysis, as AAP made up 1.49 and 1.02% of the littoral and limnetic sequenced communities in the spring, declining with seasonal progression. Spatial and temporal fluctuations of microbes compared to environmental factors exposed photosynthetic populations to independently and regularly fluctuate in the ecosystem. Oxygenic phototrophic numbers expectantly matched the midsummer peak of Chl a and b, oxygenic photosynthesis related carbon fixation, and water temperature. Independently, AAP particularly colonized spring littoral areas more than limnetic, and directly corresponded to habitat conditions that specifically promoted growth: the requirement of light and organic material.

Common Tern (Sterna hirundo) breeding populations in inland North America have declined significantly since the 1970s. A 2012 survey of the large Manitoba lakes, previously the largest known inland population stronghold, reported a 57–67% decline in 20 years. A further 38% decline by 2017 highlights the urgent need for research and management. We use ground-based estimates of productivity and analysis of microsatellite markers to provide the first detailed insight into breeding status and movements of Common Terns in this region. At six breeding colonies in 2012, we recorded breeding success in fenced plots, counted fledglings, documented predators and floods, and collected blood samples for microsatellite analysis of movement. Productivity ranged from 0.0 to 2.0 chicks fledged per nest, being highest at large colonies (> 1000 nests) located far away from human settlements (20–30 km). Large-scale breeding failure from predation occurred at smaller colonies close to human settlement. The most common predators were Black-crowned Night Herons (Nycticorax nycticorax) and Great Horned Owls (Bubo virginianus), but we also report three novel predators: Bald Eagles (Haliaeetus leucocephalus), gray wolves (Canis lupus), and river otters (Lontra canadensis). Microsatellite analysis suggested little eastward emigration, but instead a 100-fold increase in immigration from the Great Lakes between the 1990s and 2010s. Substantial population declines in the Manitoba Lakes despite this influx imply that net losses are occurring within inland-breeding populations. Terns now appear to switch frequently between breeding colonies in the region, possibly in response to predation and/or flooding. Although some colonies achieved productivity during the one-year study, continued population decline indicates that monitoring and studies of adult survival and movement are needed, especially given the on-going environmental changes within the region. Only by coupling these data with further efforts in unsurveyed boreal regions can the status of inland-breeding Common Terns be determined and strategies developed to curb apparent, large-scale population declines.

Johansson ML, Lavigne SY, Ramcharan CW, Heath DD, MacIsaac HJ. Detecting a spreading non-indigenous species using multiple methodologies. Lake Reserv Manage. 36:432–443. Non-indigenous species (NIS) are often introduced to novel environments at very low population abundance. Detecting the presence of such an NIS can be very challenging, particularly as it spreads from the initial establishment site. This provides an opportunity to test detection limits using different approaches. This study tested the detection capability of 3 methods as zebra mussels (Dreissena polymorpha) spread from south to north through Lake Winnipeg, Manitoba, Canada. Zebra mussel veliger larvae were detected using cross-polarized light microscopy (CPLM), flow cytometry and microscopy (FlowCam), and conventional polymerase chain reaction (cPCR) analysis of environmental DNA (eDNA) on the same samples. Abundance generally declined from south to north in the lake but was lowest at Calder's Dock (central). Although abundances could be quite low (i.e., <1 veliger/m3, Calder's Dock) CPLM prevalence—the percentage of samples with at least one veliger—was high throughout the lake (99–100% of samples). Prevalence was lower for cPCR and FlowCam but was statistically associated with veliger abundance. Using standardized 3 mL subsamples (0.06–0.18 m3 of lake water sampled), all 3 methods had a high probability of veliger detection if large numbers of samples were processed. FlowCam was the most expensive method to process these 3 mL subsamples, while cPCR was least expensive and fastest. eDNA combined with intensive sampling is the most practical method for wide-scale monitoring programs for early detection. However, all 3 methods are complementary and could be deployed sequentially, with rapid initial sample processing using PCR, confirmation and density estimation with FlowCam, and detailed veliger counts using CPLM. [ABSTRACT FROM AUTHOR]

Management of colonial waterbirds at regional, national, and continental scales requires up-to-date monitoring information on breeding locations, population sizes, and trends. The large lakes of southern Manitoba, Canada (Winnipeg, Winnipegosis, and Manitoba), and the inter-lake region host nationally and continentally significant populations of colonial waterbirds, but the area has been surveyed only irregularly in the past. We conducted surveys in 2017 to produce updated information on population abundance and trends for the six most abundant species breeding on the lakes: Ring-billed Gull (Larus delawarensis), Herring Gull (Larus argentatus), Caspian Tern (Hydroprogne caspia), Common Tern (Sterna hirundo), Double-crested Cormorant (Phalacrocorax auritus), and American White Pelican (Pelecanus erythrorhynchos). We also examined the relationship between lake water levels and breeding pair abundance on Lake Winnipegosis. All species but American White Pelicans showed declines in recent years, and most notably populations of Caspian Tern and Common Tern were as low as or only just above 1970s levels, respectively. Higher water levels were associated with fewer breeding pairs of colonial waterbirds. The effects of water regulation in this region on colonial waterbirds and their habitat warrants further research, as does the degree to which the species use smaller lakes spread throughout the western boreal forest for breeding, especially during high water years on the lakes in southern Manitoba.

Abstract Hydrogen isotope (δ2H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with δ13C and δ15N analyses to evaluate complex trophic relationships in aquatic systems. However, δ2H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix‐equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, δ2H (and δ15N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007–2010, and were assessed for the effects of species, feeding habits, and ambient water δ2H values. After lipid removal, we used comparative equilibration to calibrate muscle δ2H values to nonexchangeable δ2H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic δ2H enrichment by comparing δ2H values with δ15N values. Our results showed a significant logarithmic correlation between fork length and δ2H values, and no strong relationships between δ15N and δ2H. This suggests the so‐called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for δ2H enrichment. We evaluated the importance of water in controlling δ2H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The δ2H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using δ2H measurements.

Lake Winnipeg has experienced dramatic increases in nutrient loading and phytoplankton biomass over the last few decades, accompanied by a marked shift in community composition towards the dominance of cyanobacteria. Comprehensive lake-wide observations of algal blooms are critical to assessing the lake's health status, its response to nutrient management practices, and an improved understanding of the processes driving blooms. We present an analysis of the spatial and temporal variability of algal blooms on Lake Winnipeg using satellite-derived chlorophyll and indices for algal bloom intensity, spatial extent, severity, and duration over the period of ESA's MERIS mission (2002–2011). Imagery documented extensive blooms covering as much as 93% of the lake surface. Bloom conditions were analysed in the context of in-lake and watershed processes to gain further insight on the drivers of bloom events. Day to day bloom variability was driven primarily by intermittent wind mixing events, with quiescent periods leading to the formation of dense surface blooms. Seasonal bloom distribution was consistent with light limitation in the south basin and lake circulation transporting bloom material towards the north-east shore. Inter-annual variability in average bloom severity was related to both total phosphorus (TP) loadings and summer lake surface temperatures. Results provide a valuable historical time series of bloom conditions to which ongoing observations from Sentinel-3's OLCI sensor can be added for longer term monitoring and change detection. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms have affected Lake Winnipeg since the mid-1990s due to an increased phosphorus loading into the lake, which has been exacerbated by stressors such as climate change and eutrophication. Aquatic ecosystems involving cyanobacteria have been found to contain N-β-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB), non-protein amino acids that are associated with neurodegenerative disease, as well as two of the naturally occurring isomers, N-2(amino)ethylglycine (AEG) and β-amino- N-methylalanine (BAMA). We hypothesized that the cyanobacterial bloom in Lake Winnipeg produces BMAA and/or its naturally occurring isomers. Samples of cyanobacteria were collected by the Lake Winnipeg Research Consortium from standard sampling stations and blooms in July and September of 2016 and were analyzed for BMAA, DAB, AEG, and BAMA using previously published validated analytical methods. BMAA and BAMA were found in the highest concentration in the center of the north basin, the deepest and lowest-nitrogen zone of the lake, at an average concentration of 4 μg/g (collected in July and September 2016) and 1.5 mg/g (collected in July 2016), respectively. AEG and DAB were found in the highest concentration in cyanobacterial blooms from the nearshore region of the north basin, the slightly shallower and more nitrogen-rich zone of the lake, at 2.1 mg/g (collected in July 2016) and 0.2 mg/g (collected in July and September 2016), respectively. These findings indicate that the production of non-protein amino acids varies with the depth and nutrient contents of the bloom. It is important to note that we did not measure food or water samples directly and further study of the Lake Winnipeg food web is required to determine whether BMAA bioaccumulation represents an increased risk factor for neurodegenerative disease in the region. [ABSTRACT FROM AUTHOR]

Lake Winnipeg (Manitoba, Canada), the world’s 12th largest lake by area, is host to yearly cyanobacterial harmful algal blooms (cHABs) dominated by Aphanizomenon and Dolichospermum. cHABs in Lake Winnipeg are primarily a result of eutrophication but may be exacerbated by the recent introduction of dreissenid mussels. Through multiple methods to monitor the potential for toxin production in Lake Winnipeg in conjunction with environmental measures, this study defined the baseline composition of a Lake Winnipeg cHAB to measure potential changes because of dreissenid colonization. Surface water samples were collected in 2013 from 23 sites during summer and from 18 sites in fall. Genetic data and mass spectrometry cyanotoxin profiles identified microcystins (MC) as the most abundant cyanotoxin across all stations, with MC concentrations highest in the north basin. In the fall, mcyA genes were sequenced to determine which species had the potential to produce MCs, and 12 of the 18 sites were a mix of both Planktothrix and Microcystis. Current blooms in Lake Winnipeg produce low levels of MCs, but the capacity to produce cyanotoxins is widespread across both basins. If dreissenid mussels continue to colonize Lake Winnipeg, a shift in physicochemical properties of the lake because of faster water column clearance rates may yield more toxic blooms potentially dominated by microcystin producers.

Spatial, seasonal, and inter-annual variation in zoobenthos was examined in Lake Winnipeg which has experienced accelerated nutrient loading and multiple environmental stressors over the last several decades leading to increased overall productivity. Qualitative zoobenthos data (1928–29) and quantitative data (1969–2013), revealed two prevailing patterns: (1) a substantial increase in density, mainly Oligochaeta (Tubificinae), Mollusca (Sphaeriidae), and Diptera (Chironomidae) in the North basin, but a less consistent pattern of increase in density overall and of Ephemeroptera (Ephemeridae) and Trichoptera (Leptoceridae) in the South basin, and (2) disappearance of Amphipoda ( Diporeia ) from the South basin and a decline in Diporeia as a dominant taxon in the North basin, although it remained prevalent in the Narrows where higher total organic carbon (TOC) concentrations have persisted. Permutational analysis of variance (PERMANOVA) revealed that over time, inter-basin variation overwhelmed the seasonal component of variation in zoobenthos abundance. The benthic environment has changed (e.g. food resources, sediment particle sizes and nutrients) over the decades, contributing to the substantial changes in zoobenthos abundance and community composition that may constitute a regime change in the lake. [ABSTRACT FROM AUTHOR]

The spiny water flea (Bythotrephes longimanus), an aquatic invasive zooplankton species native to Eurasia, was first recorded from Manitoba waters at the Pointe du Bois Generating Station on the Winnipeg River using a larval fish drift net with 950 µm mesh, on 18 July, 2009. Bythotrephes drift density upstream and downstream of the station was highly variable with maximum densities of 23.3 individuals/100 m³ (9 samples) in June 2010 and 9.4 individuals/100 m³ in June 2012 (60 samples). In August and October of 2011, Bythotrephes were identified from the stomachs of eight cisco (Coregonus artedi) collected from the South basin of Lake Winnipeg near the mouth of the Winnipeg River, indicating that the invader had become part of the local food web. Subsequent targeted sampling for Bythotrephes with ship-based vertical plankton net (76 µm mesh) tows at 65 offshore/pelagic sites in Lake Winnipeg during summer and fall of 2012 indicated that the invader had colonized the South basin by early August and had expanded its distribution into most of the North basin by early October. No individuals were captured at a site just past the lake outlet in the Nelson River. Densities of Bythotrephes in Lake Winnipeg ranged from 0 to 93.1 and 0 to 39.2 individuals/m³ among sites for the summer and fall sampling, respectively. The highest mean density (9.2 individuals/m³) was observed for the South basin in the summer of 2012. Non-targeted kick-net sampling at Playgreen Lake, located on the Nelson River approximately 27 km north of the Lake Winnipeg outlet in August of 2012, confirmed the rapid northward expansion of Bythotrephes through Lake Winnipeg. This represents the first evidence for further downstream dispersal. However, as of August 2015, multiple kicknet and Ekman/Ponar grab samples from Cross and Sipiwesk lakes further downstream on the Nelson River have not captured any Bythotrephes. [ABSTRACT FROM AUTHOR]

Dietary niche overlap between invasive rainbow smelt ( Osmerus mordax ) and the native cisco ( Coregonus artedi) of similar size in Lake Winnipeg was examined using stomach content analysis throughout the open water period in 2010 and 2011. Although smelt and cisco were caught together in the North Basin ( n = 7 stations), rainbow smelt were exclusively caught in the North Basin ( n = 39 stations), whereas cisco were predominantly caught in the South Basin ( n = 31 stations). Substantial dietary overlap was evident when found together and apart, illustrating little dietary niche differentiation between the two species in sympatry and allopatry in the lake. Both smelt and cisco appear to shift from copepods in spring to large-bodied cladocerans in summer and fall. Although high dietary overlap suggests that these species have the potential to compete for prey, differential abundance in each basin of Lake Winnipeg suggests possible environmental niche divergence between these two species. Overall, this study provides important baseline information to examine the impact of another recent invasive planktivorous species (e.g. Bythotrephes longimanus , spiny water flea) on the smelt-cisco competition as well as the commercially important piscivorous walleye ( Sander vitreus ) population in Lake Winnipeg. [ABSTRACT FROM AUTHOR]

Changes in the crustacean zooplankton community composition and abundance in Lake Winnipeg (1969–2006) provide a rare opportunity to examine their response to environmental changes in the largest naturally eutrophic lake on the Canadian prairies. Since 1929, zooplankton species composition in Lake Winnipeg has changed little except for the addition of the invasive cladoceran, Eubosmina coregoni in 1994. The dominant taxa in the lake in summer include: Leptodiaptomus ashlandi , Acanthocyclops vernalis , Diacyclops thomasi , Daphnia retrocurva , Daphnia mendotae , Diaphanosoma birgei , Eubosmina coregoni , and Bosmina longirostris . Climate-accelerated nutrient loading to southern Lake Winnipeg over the last two decades has led to increased phytoplankton abundance and higher frequency of cyanobacterial blooms especially in its northern basin. Crustacean zooplankton have likewise increased especially in the North Basin, but less so in the more nutrient rich South Basin, possibly as a consequence of higher densities of pelagic planktivorous fish and light-limited primary production compared with the more transparent North basin (Brunskill et al., 1979, 1980). Calanoid copepods play a larger role in the South basin food web in contrast to cyclopoid copepods and Cladocera in the North basin. The study begins to fill the recognized gap in understanding of Lake Winnipeg's food web structure and provides a baseline for evaluating ongoing changes in the zooplankton community with the arrival of new non-indigenous taxa, e.g. Bythotrephes longimanus and Dreissena polymorpha . It reinforces previous work demonstrating that zooplankton provide valuable indices toward evaluating the health of an ecosystem. [ABSTRACT FROM AUTHOR]

Severe algal blooms in Lake Winnipeg since the late 1990s have been attributed to increased watershed nutrient loading, much of which is associated with suspended particles. Within-lake transport and fate of this nutrient fraction and the importance of internal loading via resuspension, however, are unknown. We measured radioisotopes ( 7 Be, 210 Pb, 137 Cs), metal and nutrient contents of suspended solids in major tributaries and lake-water, in sediment traps and in bottom sediments to estimate sediment resuspension and mass accumulation rates using two models. Sedimentation rates calculated from 137 Cs and 210 Pb dated cores and sediment traps indicated that most (95–99%) suspended material is derived from bottom sediment; mixing models using 7 Be/ 210 Pb and 137 Cs yielded similarly high estimates (82 and 84%, respectively). 137 Cs profiles in cores indicated that up to ~ 7 cm remains actively resuspended for times up to 23 years before incorporation into deeper sediments. Total and bioavailable phosphorus (TP, BAP) in this top sediment layer were generally lower in the North than the South Basin, likely reflecting inputs from the Assiniboine and Red Rivers at the southern end of Lake Winnipeg, with an average of ~ 30% TP as BAP. Estimates of average sediment-associated internal TP loading for the South Basin (0.264 g/m 2 /y) were ~ 2 × those for the North Basin (0.146 g/m 2 /y). Together, this internal loading is comparable to the magnitude of the external loading. Our results indicate that surficial sediments in Lake Winnipeg will remain a significant and active source of internal nutrient loading for several decades, a process which may delay the response of the lake to external nutrient management. [ABSTRACT FROM AUTHOR]

River ice can pose considerable challenges to hydropower operations in cold regions. Relative to open-water conditions, the presence of ice in various forms contributes to lower hydraulic efficiency. At the outlet of Lake Winnipeg, maintaining winter conveyance through the channels of the Outlet Lakes Area (OLA) is of paramount importance for downstream energy production on the Nelson River. The complex hydraulic conditions of the OLA are attributed to various factors, including the influence of hydraulic system operation, flow routing through lakes and rivers with non-uniform attributes, and the presence of dynamic ice processes throughout winter. In this study, a methodology was designed to quantify the impacts of ice on the OLA hydraulics using a combination of numerical modelling and statistical techniques. This approach includes adaptation and configuration of a two-dimensional river ice model, selection of suitable performance metrics, and derivation of hydraulic datasets for model simulations using historical observations and statistical relationships. Numerical modelling simulations feature treatments for predominant ice processes in the OLA, including freeze-up jamming, thermal growth and decay of a stable ice cover, and under cover transport and deposition of brash ice. The methodology was evaluated using historical winters 1996–1997 to 2020–2021, with most results falling within an acceptable performance range, even in response to varying hydro-meteorological conditions. Instances of error exceeding accepted thresholds were attributed mainly to factors outside of the study, including uncertainty in discharge estimation and the effects of mid-winter forebay operation. Influence of Lake Winnipeg water levels on winter hydraulics was identified as significant, as higher upstream Lake Winnipeg water levels can mitigate ice impacts by providing more hydraulic head for conveyance. As expected, ice restriction severity also varies in accordance with heat fluxes. Targeted areas for improvement of the methodology and future work are discussed, including enhancing the simulation of the thawing ('pre-breakup') period and field verification of flow split quantities during winter. The methodology presented provides an estimate of ice-impacted hydraulic conveyance which serves to benefit hydropower operators, regional water resources studies, and further investigations of river ice impacts that can be attributed to future climate change. • Channel hydraulics at the outlet of Lake Winnipeg are seasonably impacted by ice. • A methodology is presented to quantify effects of ice on lake-outlet hydraulics. • A test using historical years shows that most results fall within an acceptable performance range. • Valuable insights into regulated cold regions rivers and lake-outlet systems are presented. [ABSTRACT FROM AUTHOR]

Hydrogen isotope (δ2H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with δ13C and δ15N analyses to evaluate complex trophic relationships in aquatic systems. However, δ2H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix-equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, δ2H (and δ15N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007-2010, and were assessed for the effects of species, feeding habits, and ambient water δ2H values. After lipid removal, we used comparative equilibration to calibrate muscle δ2H values to nonexchangeable δ2H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic δ2H enrichment by comparing δ2H values with δ15N values. Our results showed a significant logarithmic correlation between fork length and δ2H values, and no strong relationships between δ15N and δ2H. This suggests the so-called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for δ2H enrichment. We evaluated the importance of water in controlling δ2H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The δ2H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using δ2H measurements. [ABSTRACT FROM AUTHOR]

Intensification of agricultural production worldwide has altered cycles of phosphorus (P) and water. In particular, loading of P on land in fertilizer applications is a global water quality concern. The Lake Winnipeg Basin (LWB) is a major agricultural area displaying extreme eutrophication. We examined the eutrophication problem in the context of the reemerging global concern about future accessibility of phosphate rock for fertilizer production and sustainable phosphorus management. An exploratory action research participatory design was applied to study options for proactivity within the LWB. The multiple methods, including stakeholder interviews and surveys, demonstrate emerging synergies between the goals of reversing eutrophication and promoting food security. Furthermore, shifting the prevalent pollutant-driven eutrophication management paradigm in the basin toward a systemic, holistic and ecocentric approach, integrating global resource challenges, requires a mutual learning process among stakeholders in the basin to act on and adapt to ecosystem vulnerabilities. It is suggested to continue aspects of this research in a transdisciplinary format, i.e., science with society, in response to globally-expanding needs and concerns, with a possible focus on enhanced engagement of indigenous peoples and elders. [ABSTRACT FROM AUTHOR]

Commercial and sport fishes are subject to rigorous monitoring for concentrations of elements that could pose threats to human health, with numerous advisories issued by authorities annually for those fisheries with high mercury (Hg) concentrations. In Lake Winnipeg, Manitoba, Canada, the commercial walleye fishery is valued at more than $20 million/year, but has historically been subject to Hg advisories. We used an information theoretic approach to evaluate the utility of non-destructive fish-scale sampling to predict As, Mn and Hg concentrations, as well as stable isotope values in walleye muscle by analysing paired samples. Hg concentrations in scales were significantly related to those in muscle (r2 = 0.75), but the relationships were weaker for As and Mn. Theδ15N values in scales predictedδ15N in muscle reasonably well (r2 = 0.72), whereas scaleδ13C andδ34S had less predictive power for estimating their respective muscle stable isotope values. For all three isotope values, sex was a marginal predictor, with parameter confidence intervals bounding zero. Analytical constraints currently limit the utility of non-destructively analysing scales for Hg, but hindcasting trophic changes using archived walleye scales may be useful in understanding shifts in nutrients and production, particularly in impacted lake systems. [ABSTRACT FROM AUTHOR]

Lake Winnipeg has the second largest commercial walleye ( Sander vitreus ) fishery in North America. The lake has experienced and will continue to undergo comprehensive changes such as eutrophication, invasion of non-indigenous aquatic species, and climate change. The North and South Basins of the lake differ in many ways, e.g. mean water depth and temperature, turbidity, and fish community. The study objectives were to establish a baseline for diet of walleye and sauger ( Sander canadensis ) in Lake Winnipeg, to determine whether the diets currently differ between basins and among seasons, and to investigate whether the non-indigenous rainbow smelt ( Osmerus mordax ) contributes substantially to their diet. Walleye and sauger diets in the South Basin had more diverse species composition, whereas in the North Basin, the diet consisted almost entirely of the introduced rainbow smelt (as well as troutperch ( Percopsis omiscomaycus ) for sauger). Some seasonal variation was also documented and found to be attributable to the emergence of young-of-year fish and mayfly larvae. The predominant incorporation of the abundant and large rainbow smelt in the diets of walleye and sauger in the North Basin may lead to increased growth and condition of fish in this basin. These data provide a baseline for comparison in future investigations of walleye and sauger diets as changes occur in the food web of the lake with invasion of zebra mussels ( Dreissena polymorpha ) and spiny water fleas ( Bythotrephes longimanus ). [ABSTRACT FROM AUTHOR]