Over the past two decades, Lake Erie has experienced recurring harmful algal blooms (HABs), attributed primarily to agriculture practices in the Western Basin and other confounding factors including climate variables, individual management practices, and internal nutrient loading. Modeling this transport is an active area of research with major focus on empirical statistical regression (LOADEST, WRTDS), which lack explanatory power, and highly parameterized physical frameworks (SWAT, SPARROW), which lack flexibility to propagate observational uncertainty and handle dynamic temporal data without massive recalibration. We present a hierarchical Bayesian architecture using a robust Student-t likelihood to jointly estimate hydroclimatic drivers of monthly Total Phosphorus (TP) concentrations and apply it to the Maumee, Sandusky, and Cuyahoga watersheds. Multiple Imputation by Chained Equations (MICE) formally propagates uncertainty from missing data through the posterior, with additional sensitivity analysis determining the effects of prior specification and climate data sources on estimation. Data were retrieved from 1985–2020 from numerous sources covering nutrient, hydroclimate, and land use information. Results indicate discharge and lagged TP are consistent predictors across watersheds. Higher precipitation is associated with increased TP, while higher air temperature generally shows no association, particularly in the Maumee and Sandusky rivers. Results suggest watershed-specific climate metrics may offer improvements over basin-wide averages in capturing the climatic effects on monthly concentrations. Our Bayesian approach provides robust inference into nutrient concentration drivers across diverse systems and our results have practical applications, including potential development of data-driven, targeted water quality management policies, improved forecasting of HABs, and support for adaptive land-use planning.
Diatoms are key players in the silicon (Si) cycle in aquatic ecosystems. Diatom cells assimilate dissolved Si and utilize it to synthesize their silica frustules. This study aimed to assess the activity of cells of different diatom species in both cell division and biogenic silica deposition, under experimental conditions and in natural populations in Lake Baikal across seasons. We employed a staining technique using PDMPO and Lumitracker LysoGreen dyes, which specifically label newly formed frustules. The percentage of stained cells for a given species was defined as the Cell Division and Silica Deposition (CDSD) index. When culturing Ulnaria acus and Fragilaria radians diatom strains, we demonstrated that Si deficiency in the medium caused a decrease in CDSD. In the natural environment no correlation was found between the CDSD index and dissolved Si concentrations. Observations revealed the highest CDSD values (up to 95% of cells) during the ice-covered period. In June, U. acus cell activity resumed and CDSD ranged from 9 to 24%. During direct stratification in July, diatom abundance and CDSD were low. Diverse patterns of abundance and species composition were observed throughout the lake during homothermy in June 2022 and 2023. CDSD could vary significantly with the simultaneous development of different species. When abundances of U. acus, Nitzschia graciliformis, and Stephanodiscus meyeri were high, the CDSD index did not exceed 42%. Conversely, its peak values in 2022 (78–84%) were recorded at stations with low species abundances. These findings advance our understanding of diatom life cycle dynamics in natural environments.
Analysis of Lake Huron's benthic community structure from the 1950s to 2022 provides a long-term perspective on the effects of environmental change on the benthic community and the potential for ecosystem recovery. The lake's four major basins differ markedly in benthic community composition and abundance, as well as in the environmental drivers shaping these assemblages. In Saginaw Bay, major shifts corresponded to periods of eutrophication, subsequent improvements in water quality, and the introduction of Dreissena. The mayfly Hexagenia, common in 1954, was nearly extirpated in the 1960s–1980s, while densities of pollution-tolerant species increased. Partial recovery of the Saginaw Bay benthic community began in the 1990s, characterized by declining oligochaete abundances, increasing chironomid densities, and, since 2017, further gains in both density and diversity across multiple taxa. In contrast, the main basin of Lake Huron and Georgian Bay were historically dominated by Diporeia, which nearly disappeared following zebra (D. polymorpha) and, especially, quagga (D. rostriformis bugensis) mussel invasions in the 1990s–early 2000s. In the North Channel, Diporeia declined after 2002 despite low dreissenid densities, and this decline was accompanied by an increase in chironomid abundance. Across all basins, quagga mussels have become a key component of benthic communities, with densities highest in the main basin and lowest in the North Channel.
Slimy sculpin (Cottus cognatus) abundance has substantially declined in many regions of the Laurentian Great Lakes coincident with the arrival and range expansions of invasive round goby (Neogobius melanostomus). Previous studies have shown that round goby can outcompete native mottled sculpin (C. bairdii) for shelter and negatively affect native spoonhead sculpin (C. ricei) growth, but direct behavioral interactions of slimy sculpin and round goby have not been observed. We conducted a laboratory experiment in which a pair of slimy sculpin were placed in an aquarium that contained an artificial spawning shelter and one round goby (treatment, n = 10) or no other fish (control, n = 10) for at least 30 days at temperatures reflective of their potential offshore overlap. We measured slimy sculpin egg deposition, aggressive interactions, artificial shelter occupancy, growth, and survival. Slimy sculpin were less likely to occupy shelters and experienced increased intraspecific competition when a round goby was present. In contrast, round goby rarely chased slimy sculpin, slimy sculpin were more likely to chase round goby, and slimy sculpin growth, egg deposition, and survival were not significantly different between groups. Differences in density between treatments and the relative size of fish could confound our observations. However, the dominant slimy sculpin occupied the shelter at similar rates between experimental groups if the round goby was smaller. Our results indicate that larger round goby overlapping with slimy sculpin could affect slimy sculpin shelter and space use, but the Great Lakes environment may create more stress for slimy sculpin than we observed.
The Michigan the Beautiful (MtB) initiative, led by the state of Michigan, aligns with the United Nations' goal of protecting 30% of land and water by 2030. This paper analyzes this initiative by addressing three questions: How could and should the 30 by 30 (30 × 30) goal apply to Michigan's Great Lakes coastal and open waters? What percentage of Michigan's waters are already protected? What policies, programs, and resources would be most effective to increase this protection to 30%? To answer these questions, the research team interviewed 48 experts, facilitated three focus groups, and utilized GIS. Results indicate that approximately 23% of Michigan's Great Lakes currently fall within protected area designations, although the level of protection and enforcement is highly variable. To increase this percentage to 30% and enhance existing protections, three core implementation strategies emerged: Facilitating education and engagement, enhancing coastal management, and increasing protections. Across these strategies, seven key recommendations arose. Utilizing the Great Lakes as a central messaging strategy for MtB, in part by establishing a Great Lakes Bottomland State Park and education center, would significantly bolster engagement opportunities. Strengthening regional planning organizations, implementing a “Great Lakes Forever” pledge, and advancing policies and programs to protect coastlines would significantly enhance coastal management. Bolstering and expanding the Michigan Underwater Preserve System while prioritizing stewardship of Manoomin (wild rice) would increase protections for Great Lakes open waters. Michigan has strong potential for leadership by implementing these recommendations for implementing MtB.
Climate migration research overwhelmingly examines socioeconomic and cultural aspects of people moving from their origin communities, yet minimal studies address what happens at receiving regions. This leaves potential receiving regions without guidance on infrastructure needs, service demands, or integration capacity. This literature review synthesizes definitions, theoretical frameworks, empirical evidence, methodological limitations, and critical research gaps, with particular attention to the Great Lakes region as a potential destination for climate-induced migrants. By establishing theoretical and empirical foundation for understanding climate migration through the lens of receiving communities, this review, together with companion analysis of infrastructure and capacity questions, aims to equip Great Lakes municipalities with informed analysis to stimulate on-time preparations.
Lake Erie experiences annual harmful algal blooms (HABs), particularly in the western basin, due to factors including anthropogenic and climatic drivers. Western Lake Erie (WLE) is subject to high-load, low-volume inputs from the Maumee River and high-volume, nutrient-poor inputs from the Detroit River. We assessed water quality and phytoplankton along a ∼ 31-km transect between the two inflows, sampling monthly May–October in 2021 and 2022. Coupled with satellite imagery analysis, findings suggest that the transect grouped into distinct zones characterized by either system or the mixing zone between them. Temperature and specific conductivity increased and photosynthetically active radiation attenuated more rapidly nearer the Maumee River, particularly during active-bloom months. We found less temporal variability in water quality parameters nearer the Detroit River and less spatial variability during pre-bloom than active- and post-bloom months. Total phosphorus consistently increased nearer the Maumee River, and soluble reactive phosphorus remained low. Inorganic nitrogen concentrations were typically higher in May–June than July–October. Ammonium consistently decreased towards the Maumee River and nitrate did so during bloom periods, indicating the Detroit River could supply inorganic nitrogen to the bloom. Suspended materials and chlorophyll concentration increased nearer the Maumee River during the active-bloom months. Phytoplankton community composition and abundance differed spatially and temporally, with important differences between years that echo bloom dynamics, including being more widespread but less concentrated in 2021 than 2022. It is imperative to understand how annual variability in climatic and non-climatic drivers affect WLE’s most influential sources of inflow and the transition zone between them.
Empiricists and modellers use information on energy density, proximate composition, stable isotopes, fatty acids, thiamine, and bioaccumulative tracers (e.g., PCBs and mercury) to understand the state and inter-relationships of aquatic food webs. Data exist in many published and unpublished sources, but are not consolidated in an easily accessible database that would serve as a vital resource to i) provide basic estimates of these diet-derived measures of body composition, ii) understand sources of variation in the underlying data, iii) facilitate exploration and development of data proxies, and iv) assist in study design. We designed GLATAR (Great Lakes Aquatic Tissue Analysis Repository, glatar.org) to address this need. GLATAR is an open-access, searchable database linked to a web-based toolbox to visualise and generate user-defined summaries on diet-derived ecological metrics, with a focus on taxa of importance to the Great Lakes. GLATAR currently contains over 50,000 records on energy density, chemical tracers, and proximate body composition from 67 species of fish and 72 invertebrate taxa. We hope this user-friendly interface will entice others to upload their published and unpublished data to the repository, enriching the breadth of data accessible to researchers. In this way, GLATAR will become a ‘living’ and interactive resource for empiricists and modellers working in freshwater ecosystems as they make critical decisions related to growth, production, and consumption across a diverse group of economically and ecologically important aquatic species.
Extreme lake levels across the Great Lakes basin have significantly impacted society, with record low and highstands during the historical record known back to 1860C.E. Geologists have extended water level history further back in time using strandline landforms and sedimentary records with drowned forests and trees being the most reliable evidence for lower water levels. We describe an in-situ 17th century white pine tree stump submerged in Georgian Bay adjacent to Winkler Island that is 0.53 m below the 175.57 m International Great Lakes Datum (IGLD) 1985 historical record low-water level of Lake Huron. Considering water depth during sampling, glacioisostatic adjustment of the lake bed, and a ∼0.5 m freeboard, the stump records a >40-year lowstand between ∼1650 and 1690 about 2 m below the historical record low lake level. Additional stumps and standing dead trees ∼0.5 m above and below lake level record tree colonization during the most recent historical lowstand that started in 1998. The number of rings present in these recent stumps suggests that the young trees colonized exposed land in a matter of years before they were submerged during the rapid rise in lake level between 2014 and 2016. The 17th century lowstand is unprecedented in magnitude and duration (>40 years) relative to the historical record, which may reflect a drier, cooler and perhaps windier climate during the Little Ice Age (∼1300–1850C.E.).
Eukaryotes are important for nutrient cycling and ecosystem functioning in freshwater lakes, yet their spatiotemporal dynamics and assembly mechanisms under eutrophic conditions remain poorly understood. Here, we examined the seasonal and spatial variations in the eukaryotic community structure and function in eutrophic south Lake Taihu using high-throughput 18S rRNA gene sequencing, co-occurrence network analysis, and metabolic functional prediction; in addition to microeukaryotes (protists, unicellular algae, and fungi), our analyses also included small metazoans and early life stages of some macrofauna. The results revealed a distinct seasonal inversion of α-diversity, with peaks in spring rather than summer. Deterministic processes were dominant in autumn, whereas community similarity prevailed in spring and winter. Taxonomic composition also varied seasonally, whereas the dominant metabolic functions remained relatively stable. Community assembly was co-dominated by stochastic (ecological drift) and deterministic (homogeneous selection) processes, with their relative contributions shifting seasonally. Co-occurrence networks also exhibited clear seasonal restructuring. Summer networks were more connected and dominated by positive associations, whereas winter networks were denser and competitively oriented. Keystone taxa also varied seasonally and showed strong associations with specific metabolic pathways, highlighting their functional roles in maintaining network stability and ecosystem processes. Based on these findings, eutrophication management requires an integrated approach that addresses phosphorus control, organic matter, and algal biomass reduction, considering the seasonal dynamics of microbial interactions and assembly processes to sustain ecosystem resilience. Seasonal shifts in community assembly mechanisms and network structures are fundamental to maintaining functional redundancy in eutrophic lakes. We provide mechanistic insights into microbial interactions that contribute to ecosystem stability, extending beyond Lake Taihu to inform predictive frameworks for temperate eutrophic ecosystems under environmental change.
Recruitment indices for rare or intermittently recruiting fishes are needed to compare year classes and evaluate recruitment drivers, but sparse trawl data with many zero-catch observations complicate estimation. We used fall bottom trawl data from New York, Pennsylvania, and Ohio surveys in Lake Erie's central and eastern basins to estimate annual relative cohort strength of age-0 lake whitefish (Coregonus clupeaformis) from 1992 to 2021 and evaluate whether a Bernoulli-Bernoulli presence-absence model retained enough information for an annual relative cohort strength index compared with a Binomial-Poisson count model. We fixed detection probability at 0.31 in the primary analysis and refit both models using alternative fixed values in sensitivity analyses. Among 2879 tows, 173 were positive and 368 fish were collected, with positive catches ranging from 1 to 20 fish. Annual catch per unit area and both models recovered a similar recruitment pattern, with variable recruitment from 1992 to 2005, little to no recruitment from 2006 to 2014, and renewed recruitment in most years from 2015 to 2021. Cohort rank order was stable across fixed detection values (Spearman rs = 0.996 to 1.000), and annual median estimates maintained high agreement with the primary analysis (Pearson r = 0.966 to 1.000). However, Bernoulli-Bernoulli estimates were not one-to-one with Binomial-Poisson estimates, and relative magnitude depended on assumed detection probability. These results indicate that the Bernoulli-Bernoulli simplification is adequate for recovering cohort strength patterns, but the Binomial-Poisson model is more appropriate for distinguishing relative cohort strength among years.
The Boguchany Reservoir was formed in 2012 after construction of a hydroelectric power plant on the Angara River, 1335 km from its Lake Baikal source. After a nearly decade-long break, the spring and summer phytoplankton of the Reservoir was studied. A total of 83 planktonic microalgae species were identified. Summer phytoplankton showed greater species richness (67) compared to spring (27). In spring, at water temperatures of 4.1–7.6 °C, the dominant complex varied spatially: abundance dominance shifted from the diatom Aulacoseira islandica to small centric diatoms (Stephanodiscus minutulus); biomass dominance shifted from A. islandica to Peredinium sp. In a bay 6 km from the town of Kodinsk, Asterionella formosa and Fragilaria crotonensis dominated. In summer, at water temperatures of 16.5–19.2 °C, the cyanobacterium Aphanizomenon flos-aquae and the green alga Sphaerocystis planctonica dominated in abundance across all stations, while the large-celled diatom F. crotonensis dominated in biomass. Mid-reservoir and near the dam, large-celled subdominants included the dinoflagellate Ceratium hirundinella and the diatom Tabellaria flocculosa. Diversity indices indicated that the main seasonal signal was increased taxonomic richness rather than a shift in dominance structure. Principal Component Analysis (PCA) identified water temperature as the key factor structuring phytoplankton communities. Maximum spring abundance reached 640 thousand cells/L (biomass: 752 mg/m3); summer values were 1795 thousand cells/L and 470 mg/m3, respectively. These values are lower than those recorded in 2016, characterizing the reservoir as oligotrophic. The findings are important for ongoing ecological monitoring, trophic status assessment, and developing biodiversity conservation strategies under climatic and anthropogenic pressures.
Multi-annual studies focusing on seasonal nearshore current dynamics and its effect on nearshore-offshore exchange in large lakes are scarce, even though such information is essential for determining the long-term evolution of a lake's ecosystem. To help address this lack, 8-year-long, near-bottom temperature and current data at 26 m depth, combined with meteorological data, were collected in the northern nearshore zone of Lake Geneva. An analysis revealed that persistent, well developed alongshore currents in the nearshore zone are structured as events driven by two strong, dominant winds coming from the northeast and from the southwest. Current events typically last from several hours to ∼3 days. Alongshore near-bottom currents can exceed 20 cm s−1 causing bursts of sediment resuspension and increased horizontal mixing. Mean alongshore-current direction changed consistently on a seasonal scale from predominantly westward during summer to eastward during winter. Correlated with westward alongshore transport, Ekman transport leads to coastal downwelling mainly in summer. In winter, downwelling at the downwind shore dominated and was correlated with eastward alongshore transport. Thus, during both seasons, offshore transport prevailed near the bed. Offshore currents reached up to 20 cm s−1. Waters of different origin passed through the nearshore zone as reflected by near-bottom summer temperatures continuously changing, within hours, from near-surface values to those recorded at greater depth. Such three-dimensional exchange and mixing between the nearshore zone and the lake interior can significantly affect a lake's bio-geo-chemical equilibrium. The findings of this study reveal the importance of seasonal variability on long-term nearshore zone dynamics.
The ecological function of Netley Marsh, a lacustrine fringe wetland situated between the Red River and Lake Winnipeg in Manitoba, Canada, has undergone substantial transformation over the past century. Historically, it was a diverse hemi-marsh system characterized by aquatic and terrestrial wetland vegetation interspersed with interconnecting channels, ponds, and small lakes. Over time, it has been transformed into a single large, shallow water body. The reconnection of the Red River to the Marsh through the Netley Cut around 1970, and the subsequent enlargement of the Cut itself, is widely viewed as one of the major drivers of ecological degradation. This study compares sediment properties, Cesium-137 (137Cs) radionuclide dating, historical maps, aerial photographs, and satellite imagery as well as long-term hydrological records in the Lake Winnipeg sub-watersheds to reconstruct historical environmental degradation in Netley Marsh. Results from historical map and satellite imagery analysis reveal a 70% loss of marshland habitat between 1934 and 1977 due to a near doubling of open water area. 137Cs profiles and inventories in sediment cores indicate that post-depositional redistribution of sediment and/or 137Cs itself within the deposited sediment profile has been minimal and that direct atmospheric fallout was the predominant source of 137Cs to Netley Marsh. This study demonstrates that degradation processes were already underway prior to the re-opening of the Cut around 1970. Results further suggest that sediment delivered by the Red River has slowed the process of wetland loss by infilling Netley Marsh and re-establishment of hemi-marsh conditions.
Per- and polyfluoroalkyl substances (PFAS) are a large group of synthetic fluorinated compounds with a variety of industrial and consumer product uses. Owing to their environmental persistence and tendencies to bioaccumulate, PFAS are found in fish across the globe, especially in waterbodies located near PFAS sources (e.g., Aqueous Film Forming Foam [AFFF] training sites or industry users). Less is known about fish fillet concentrations along gradients of PFAS exposure, especially in less densely populated areas, such as the Minnesota portion of the Lake Superior basin. Here, examining 663 fish tissue samples across 22 species and 62 sampling locations, we sought to quantify the extent of PFAS contamination within the basin and clarify determinants of PFAS variability among coresident fish. Fish from impaired sites had higher Σ27PFAS concentrations (108 ± 105 [mean ± standard deviation] ng g−1 wet weight) than fish from inland non-impaired sites (2 ± 5 ng g−1) and Lake Superior (4 ± 5 ng g−1), suggesting that outside of known PFAS sources, PFAS in fish in this region are low relative to average national levels. Across ecosystems, we found a significant positive relationship between Σ27PFAS concentrations and δ15N, suggesting trophic magnification of PFAS in freshwater fish. Specifically, the estimated trophic magnification factor for PFOS was 2.1 ± 1.1 (estimate ± standard error). These findings underscore the importance of systematic monitoring of PFAS in fish across ecological contexts to better understand their distribution and potential impacts on aquatic ecosystems, thereby informing effective management and remediation strategies across watersheds.
