In vivo and in vitro phenotypic differences between Great Lakes VHSV genotype IVb isolates with sequence types vcG001 and vcG002

Viral hemorrhagic septicemia virus (VHSV) is an aquatic rhabdovirus first recognized in farmed rainbow trout in Denmark. In the past decade, a new genotype of this virus, IVb was discovered in the Laurentian Great Lakes basin and has caused several massive die-offs in some of the 28 species of susceptible North American freshwater fishes. Since its colonization of the Great Lakes, several closely related sequence types within genotype IVb have been reported, the two most common of which are vcG001 and vcG002. These sequence types have different spatial distributions in the Great Lakes. The aim of this study was to determine whether the genotypic differences between representative vcG001 (isolate MI03) and vcG002 (isolate 2010-030 #91) isolates correspond to phenotypic differences in terms of virulence using both in vitro and in vivo approaches. In vitro infection of epithelioma papulosum cyprini (EPC), bluegill fry (BF-2), and Chinook salmon embryo (CHSE) cells demonstrated some differences in onset and rate of growth in EPC and BF-2 cells, without any difference in the quantity of RNA produced. In vivo infection of round gobies (Neogobius melanostomus) via immersion exposure to different concentrations of vcG001 or vcG002 caused a significantly greater mortality in round gobies exposed to 10² plaque forming units ml^− 1 of vcG001. These experiments suggest that there are phenotypic differences between Great Lakes isolates of VHSV genotype IVb.     

Great Lakes ice classification using satellite C-band SAR multi-polarization data

The objective of this study is to advance development of algorithms to classify and map ice cover on the Laurentian Great Lakes using satellite C-band synthetic aperture radar (SAR) multi-polarization data. During the 1997 winter season, shipborne polarimetric backscatter measurements of Great Lakes ice types, using the Jet Propulsion Laboratory C-band scatterometer, were acquired together with surface-based ice physical characterization measurements and environmental parameters, concurrently with European Remote Sensing Satellite 2 (ERS-2) and RADARSAT-1 SAR data. This fully polarimetric dataset, composed of over 20 variations of different ice types measured at incidence angles from 0° to 60° for all polarizations, was processed and fully calibrated to obtain radar backscatter, establishing a library of signatures for different ice types. Computer analyses of calibrated ERS-2 and RADARSAT ScanSAR images of Great Lakes ice cover using the library in a supervised classification technique indicate that different ice types in the ice cover can be identified and mapped, but that wind speed and direction can cause misclassification of open water as ice based on single frequency, single polarization data. Using RADARSAT-2 quad-pol and ENVISAT ASAR dual-pol data obtained for Lake Superior during the 2009 and 2011 winter seasons, algorithms were developed for small incidence angle (< 35°) and large incidence angle (> 35°) SAR images and applied to map ice and open water. Ice types were subsequently classified using the library of backscatter signatures. Ice-type maps provide important input for environmental management, ice-breaking operations, ice forecasting and modeling, and climate change studies.     

Diatom-based Weighted-averaging Transfer Functions for Great Lakes Coastal Water Quality: Relationships to Watershed Characteristics

In an effort to develop indicators for Great Lakes near-shore conditions, diatom-based transfer functions to infer water quality variables were developed from 155 samples collected from coastal Great Lakes wetlands, embayments and high-energy shoreline sites. Over 2,000 diatom taxa were identified, and 352 taxa were sufficiently abundant to include in transfer function development. Multivariate data exploration revealed strong responses of the diatom assemblages to stressor variables, including total phosphorus (TP). Spatial variables such as lake, latitude and longitude also had notable relationships with assemblage characteristics. A diatom inference transfer function for TP provided a robust reconstructive relationship (r² = 0.67; RMSE = 0.28 log(μg/L); r²jackknife = 0.55; RMSEP = 0.33 log (μg/L)) that improved following the removal of 13 samples that had poor observed-inferred TP relationships (r² = 0.75; RMSE = 0.22 log(μg/L); r²_jackknife = 0.65; RMSEP = 0.26 log (μg/L)). Diatom-based transfer functions for other water quality variables, such as total nitrogen, chloride, and chlorophyll a also performed well. Measured and diatom-inferred water quality data were regressed against watershed characteristics (including gradients of agriculture, atmospheric deposition, and industrial facilities) to determine the relative strength of measured and diatom-inferred data to identify watershed stressor influences. With the exception of pH, diatom-inferred water quality variables were better predicted by watershed characteristics than were measured water quality variables. Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, it appears they can better integrate water quality information than snapshot measurements. These results strongly support the use of diatoms in Great Lakes coastal monitoring programs.     

Consistent individual differences in sea lamprey (Petromyzon marinus) behaviour: Implications for control via trapping

We tested if consistent individual differences (CIDs) in the behaviour of sea lamprey (Petromyzon marinus) from the Laurentian Great Lakes could influence their vulnerability to trapping. The sea lamprey is invasive in the Upper Laurentian Great Lakes and the target of a binational control program. Trapping could be used for control if trapping efficiency is unbiased and effective. Our test involved comparing the behaviour of sea lamprey collected in the field from a trap (n = 42) at a barrier and electrofished (n = 9) downstream of the barrier. We quantified each individual's latency to exit an enclosure (a measure of exploration), proportion of time spent moving (a measure of general activity), and change in activity in response to a putative predator cue (a measure of boldness). CIDs were detected for each behaviour measured (intraclass correlations: 0.3–0.5). CIDs in behaviour also differed between trapped individuals and those collected downstream using electrofishing, irrespective of size, sex, and maturity status. Trapped individuals decreased their activity in response to a putative predator cue, while individuals collected using electrofishing increased their activity in response to the cue. Trapped individuals also tended to spend a greater proportion of time moving than individuals sampled downstream of the trap. However, the two samples of lamprey did not differ significantly in time taken to exit an enclosure. The behavioural differences between sea lamprey sampled from a trap and those sampled downstream of the trap suggest that CIDs in behaviour can influence an individual's vulnerability to trapping.     

Great Lakes rivermouth ecosystems: Scientific synthesis and management implications

At the interface of the Great Lakes and their tributary rivers lies the rivermouths, a class of aquatic ecosystem where lake and lotic processes mix and distinct features emerge. Many rivermouths are the focal point of both human interaction with the Great Lakes and human impacts to the lakes; many cities, ports, and beaches are located in rivermouth ecosystems, and these human pressures often degrade key ecological functions that rivermouths provide. Despite their ecological uniqueness and apparent economic importance, there has been relatively little research on these ecosystems as a class relative to studies on upstream rivers or the open-lake waters. Here we present a synthesis of current knowledge about ecosystem structure and function in Great Lakes rivermouths based on studies in both Laurentian rivermouths, coastal wetlands, and marine estuarine systems. A conceptual model is presented that establishes a common semantic framework for discussing the characteristic spatial features of rivermouths. This model then is used to conceptually link ecosystem structure and function to ecological services provided by rivermouths. This synthesis helps identify the critical gaps in understanding rivermouth ecology. Specifically, additional information is needed on how rivermouths collectively influence the Great Lakes ecosystem, how human alterations influence rivermouth functions, and how ecosystem services provided by rivermouths can be managed to benefit the surrounding socioeconomic networks.     

A reference inventory for aquatic fauna of the Laurentian Great Lakes

The Laurentian Great Lakes encompass an expansive and diverse set of freshwater ecosystems that contain a concordantly large and diverse vertebrate and invertebrate fauna. Although numerous publications exist concerning the composition and distribution of this fauna, there is at present no single readily available resource that brings all this information together. Here, we present and describe the compilation process for a comprehensive Great Lakes aquatic fauna inventory covering fishes, reptiles, amphibians, zooplankton, mollusks, annelids, insects, mites, and various other aquatic invertebrates. Inventory entries were developed via an extensive search of literature and internet sources and are attributed with detailed nomenclature information, general lake and habitat occurrences, and supporting citations and links to life history and genetic marker information. The inventory scope is the Laurentian Great Lakes proper and their connecting rivers, and their fringing coastal wetlands and lower tributaries. Over 2200 unique taxa are contained in the inventory – 85% resolved to species and 14% to genus. The listing substantially expands previous richness estimates for invertebrates in the Great Lakes, but taxonomic resolution and spatial distribution information for them remains quite uneven. Example pattern analyses for fauna in this inventory show that aquatic vertebrates are generally more widely distributed than invertebrates, and that biodiversity is concentrated in the coastal margins. The inventory is being packaged into a public, searchable database that showcases the biodiversity of the Great Lakes aquatic fauna and can assist the research and management community in their biological investigations.     

Molecular characterization of bacterial communities associated with sediments in the Laurentian Great Lakes

The Laurentian Great Lakes freshwater ecosystem comprises a series of interconnected lakes exhibiting wide spatial differences in hydrogeochemistry, productivity, and allochthonous inputs of nutrients and xenobiotics. Bacterial communities associated with offshore sediments in this ecosystem have been rarely studied. We evaluated bacterial communities associated with sediments from 10 locations in four of the five Great Lakes (Lakes Superior, Michigan, Huron, and Ontario) by generating16S rRNA pyrosequence libraries. Pyrosequencing analysis revealed the presence of 26 bacterial phyla and proteobacterial classes among Great Lakes sediment samples. Actinobacteria, Acidobacteria, Betaproteobacteria, and Gammaproteobacteria were the most abundant groups of bacteria. Redundancy analysis was used to examine the role of sediment properties, including depth and chemical composition, in shaping bacterial community structure. One sample from Lake Huron was distinctly different from all other samples. Phylogenetic analysis revealed that the sample contained greater abundances of groups of bacteria associated with polluted environments. This study constitutes the most extensive examination of bacteria associated with Laurentian Great Lakes sediments and sheds useful insight into the microbial ecology of the Great Lakes.     

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

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

Influence of lake levels on water extent,interspersion, and marsh birds in Great Lakes coastal wetlands

Coastal wetlands in the Laurentian Great Lakes undergo frequent, sometimes dramatic, physical changes at varying spatial and temporal scales. Changes in lake levels and the juxtaposition of vegetation and open water greatly influence biota that use coastal wetlands. Several regional studies have shown that changes in vegetation and lake levels lead to predictable changes in the composition of coastal wetland bird communities. We report new findings of wetland bird community changes at a broader scale, covering the entire Great Lakes basin. Our results indicate that water extent and interspersion increased in coastal wetlands across the Great Lakes between low (2013) and high (2018) lake-level years, although variation in the magnitude of change occurred within and among lakes. Increases in water extent and interspersion resulted in a general increase in marsh-obligate and marsh-facultative bird species richness. Species like American bittern (Botaurus lentiginosus), common gallinule (Gallinula galeata), American coot (Fulica americana), sora (Porzana carolina), Virginia rail (Rallus limicola), and pied-billed grebe (Podilymbus podiceps) were significantly more abundant during high water years. Lakes Huron and Michigan showed the greatest increase in water extent and interspersion among the five Great Lakes while Lake Michigan showed the greatest increase in marsh-obligate bird species richness. These results reinforce the idea that effective management, restoration, and assessment of wetlands must account for fluctuations in lake levels. Although high lake levels generally provide the most favorable conditions for wetland bird species, variation in lake levels and bird species assemblages create ecosystems that are both spatially and temporally dynamic.     

Mapping invasive Phragmites australis in the coastal Great Lakes with ALOS PALSAR satellite imagery for decision support

The invasive variety of Phragmites australis (common reed) forms dense stands that can cause negative impacts on coastal Great Lakes wetlands including habitat degradation and reduced biological diversity. Early treatment is key to controlling Phragmites, therefore a map of the current distribution is needed. ALOS PALSAR imagery was used to produce the first basin-wide distribution map showing the extent of large, dense invasive Phragmites-dominated habitats in wetlands and other coastal ecosystems along the U.S. shore of the Great Lakes. PALSAR is a satellite imaging radar sensor that is sensitive to differences in plant biomass and inundation patterns, allowing for the detection and delineation of these tall (up to 5 m), high density, high biomass invasive Phragmites stands. Classification was based on multi-season ALOS PALSAR L-band (23 cm wavelength) HH and HV polarization data. Seasonal (spring, summer, and fall) datasets were used to improve discrimination of Phragmites by taking advantage of phenological changes in vegetation and inundation patterns over the seasons. Extensive field collections of training and randomly selected validation data were conducted in 2010–2011 to aid in mapping and for accuracy assessments. Overall basin-wide map accuracy was 87%, with 86% producer's accuracy and 43% user's accuracy for invasive Phragmites. The invasive Phragmites maps are being used to identify major environmental drivers of this invader's distribution, to assess areas vulnerable to new invasion, and to provide information to regional stakeholders through a decision support tool.     

Widespread prevalence of hypoxia and the classification of hypoxic conditions in the Laurentian Great Lakes

Aquatic hypoxia within the Laurentian Great Lakes has contributed to various adverse ecological consequences and stimulated research interest in recent decades. An analysis of published peer-reviewed journal articles from 2000 to 2020 demonstrates an increasing trend of studies related to hypoxia in the Laurentian Great Lakes. However, the majority of these studies (78%) focus on Lake Erie and in particular the well-documented hypolimnetic hypoxic conditions that develop in the central basin of Lake Erie. This hypoxic zone is relatively large (up to 1.5 million ha), has substantial ecological effects, and motivates monitoring programs and water quality improvement initiatives. Nonetheless, the hypoxic zone in the central basin of Lake Erie is only one of over twenty documented hypoxic zones in the Laurentian Great Lakes. Moreover, hypoxic conditions in the Great Lakes are quite diverse. Here, we define and characterize a four-fold classification of Great Lakes hypoxic conditions: 1) hypolimnetic hypoxia, 2) over-winter hypoxia, 3) diel hypoxia, and 4) episodic hypoxia. We suggest that Great Lakes research and monitoring programs should seek to more broadly document hypoxic conditions and develop models to predict the temporal and spatial occurrence of hypoxia. Such efforts are particularly timely as future climatic conditions contributing to warmer temperatures, longer and more intense stratified periods, increased spring nutrient loading and more variable allocthonous inputs are expected to exacerbate three of the four hypoxic conditions described for the Great Lakes (hypolimnetic, diel, and episodic hypoxia).     

Legacy polychlorinated organic pollutants in the sediment of the Great Lakes

Legacy, organic pollutants, including polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), and diphenyl ethers (PCDEs) were quantified in sediments of the Laurentian Great Lakes of North American. A total of 40 cores (939 core segments) and 198 Ponar surface grab samples were collected from the five Great Lakes between 2010 and 2014. Median concentrations in Ponar grab samples were 8.4, 0.27, 0.05, 0.19 and 0.01 ng/g dry weight (dw) for total-PCBs, ∑₇PCDDs, ∑₁₀PCDFs, ∑₁₂PCNs, and ∑₇PCDEs, respectively. By using Geographic Information Systems Analysis with the inverse distance weight (IDW) interpretation of the spatial distribution of the chemical inventory at coring sites, total mass loads in the five lakes combined were estimated to be 511, 15.3, 5.3, 20.7 and 2.9 t for total-PCBs, ∑₇PCDDs, ∑₁₀PCDFs, ∑₁₂PCNs, and ∑₇PCDEs, respectively. Patterns of spatial distributions revealed pollution hotspots and provided evidence for historical local sources. Concentrations of residues in Ponar grabs and inventories at coring sites, when normalized to concentrations of organic carbon, exhibited statistically significantly correlations with latitude and longitude of the sampling sites for all five chemical groups. At most coring sites, concentrations have been decreasing towards the sediment surface. At locations relatively close to known or suspected sources, estimated half-times for all classes of chemicals were approximately 20 years. The declining trends of PCDDs and PCDFs were unclear at some locations, suggesting the presence of currently active emission sources.     

U.S. EPA Great Lakes National Program Office monitoring of the Laurentian Great Lakes: Insights from 40 years of data collection

The U.S. EPA Great Lakes National Program Office (GLNPO) implements long-term monitoring programs to assess Great Lakes ecosystem status and trends for many interrelated ecosystem components, including offshore water quality as well as offshore phytoplankton, zooplankton and benthos; chemical contaminants in air, sediments, and predator fish; hypoxia in Lake Erie's central basin; and coastal wetland health. These programs are conducted in fulfillment of Clean Water Act mandates and Great Lakes Water Quality Agreement commitments. This special issue presents findings from GLNPO's Great Lakes Biology Monitoring Program, Great Lakes Water Quality Monitoring Program, Lake Erie Dissolved Oxygen Monitoring Program, Integrated Atmospheric Deposition Network, Great Lakes Fish Monitoring and Surveillance Program, and Great Lakes Sediment Surveillance Program. These GLNPO programs have generated temporal and spatial datasets for all five Great Lakes that form the basis for assessment of the state of these lakes, including trends in nutrients, key biological indicators, and contaminants in air, sediments and fish. These datasets are used by researchers and managers across the Great Lakes basin for investigating physical, chemical and biological drivers of ongoing ecosystem changes; some of these analyses are presented in this special issue, along with discussion of new methods and approaches for monitoring.     

Diets,population structure,and seasonal activity patterns of mudpuppies (Necturus maculosus) in an urban,Great Lakes coastal habitat

Freshwater species native to the Laurentian Great Lakes region face numerous environmental stressors, and the conservation status and ecological relationships of many remain poorly understood. One such species, the mudpuppy (Necturus maculosus), is declining, but better information on their natural history and development of more effective population monitoring techniques is needed. We assessed seasonal variation in capture success, biases in capture techniques, and feeding ecology of mudpuppies in Wolf Lake, a highly perturbed and urban former estuarine wetland complex to Lake Michigan. Trapping periods of ≥ 3 consecutive nights occurred from January to May 2015, and October 2015 to March 2016. Overall trapping success differed among trapping periods (p = 0.01) and declined precipitously at water temperatures above 14.1 °C (p < 0.001). Mudpuppies in traps (mean 26.9 ± 0.5 cm) were larger than those caught with hand nets (mean 14.7 ± 0.8 cm, p < 0.0001), suggesting that multiple methods may be needed to accurately assess demographics. Stomach contents obtained through gastric lavage included mollusks, leeches, insects, isopods, amphipods, crayfish, fish, a frog, and a juvenile conspecific. Invasive species, including rusty crayfish (Orconectes rusticus), round gobies (Neogobius melanostomus), and zebra/quagga mussels (Dreissena spp.) were present in guts, suggesting mudpuppy foraging has changed along with aquatic communities in the region. Prey community analyses revealed differences in overall diet among size classes of mudpuppies (p = 0.001), but relatively weak similarity within size classes. Results suggest that mudpuppies in lake ecosystems occupy a broad niche that changes as they grow.     

High frequency radar and its application to fresh water

High frequency (HF) radar has become an important tool for remotely mapping the spatial distribution and temporal evolution of waves and currents of the nearshore coastal ocean. Its acceptance along ocean coasts has resulted in the development of several commercially available systems and a planned nationwide coastal network to routinely measure coastal currents. Because HF radiation is known to propagate less efficiently over fresh water than seawater, it has been largely overlooked as a viable tool for freshwater application. However, its potential utility in freshwater was clearly demonstrated by a deployment along Lake Michigan as part of the 1999–2001 Episodic Events Great Lakes Experiment. As part of this experiment, the University of Michigan Multi-frequency Coastal Radar consistently produced reliable near surface current measurements to a range of approximately 25 km offshore showing strong correlation with both in-situ measurements and numerical hind-casts. This paper provides background on HF radar technology, a summary of the current state of the art with respect to freshwater and describes the results of a recent experiment to measure the propagation of HF radar signal over freshwater using CODAR Ocean Sensors SeaSondes, operating at 5 and 42 MHz with 21 W and 90 W average radiated powers, respectively. The effective offshore range for these radars was found to be 18 km at 5 MHz and 4–5 km at 42 MHz. These findings are consistent with currently available models for the prediction of propagation loss, verifying that they can reliably be used to estimate ranges in freshwater settings.     

Diel timing of lake sturgeon (Acipenser fulvescens) activity revealed by satellite tags in the Laurentian Great Lake Basin

Lake sturgeon (Acipenser fulvescens) are slow-growing and long-lived residents of the Laurentian Great Lakes Basin, making them vulnerable to anthropogenic stressors. The behavior of lake sturgeon, and how it may result in conflict with human activities, remain incompletely understood. Our goal was to describe how environmental conditions, such as depth, temperature, and time of day, influence lake sturgeon activity. Data were recorded using pop-up archival satellite tags, which have provided insight into the ecology, physiology, and behavior of challenging to study marine megafauna, yet are rarely deployed within freshwater ecosystems despite parallel research needs. Adult lake sturgeon were fitted with satellite tags containing integrated accelerometers near spawning grounds in the Niagara River between Canada and the United States. We used the time-series of acceleration in recovered tags to test the hypothesis that lake sturgeon exhibit diel activity cycles in situ. We defined activity as acceleration greater than two standard deviations from a running average. We applied this classification to partial records obtained from satellite transmission, an approach that can render incomplete datasets a useable product for analysis. Lake sturgeon were most active nocturnally with a significant mean at 22:32 h. Generalized linear mixed-effect models showed temperature and time of day to be significant predictors of activity. Temporal cycles of fish activity should be understood and could be exploited to reduce human-fish conflict in the increasingly altered waterways of the globe.     

A model for determining satellite-derived primary productivity estimates for Lake Michigan

A new MODIS based satellite algorithm to estimate primary production (PP) has been generated and evaluated for Lake Michigan. The Great Lakes Primary Productivity Model (GLPPM) is based on previous models that required extensive in situ data but it can utilize remotely sensed observations as input for some model variables and therefore allows greater spatial resolution for primary productivity estimates. The Color Producing Agent Algorithm (CPA-A) is utilized to obtain robust chlorophyll a values and the NASA KD2M approach is used to obtain the diffuse attenuation coefficient (K_d). Only incident PAR and carbon fixation rates are additionally needed to generate the primary productivity estimate. Comparisons of the satellite derived PP estimates from single monthly images to average monthly field measurements made by NOAA/GLERL found good agreement between estimates. Satellite derived PP estimates were used to estimate a preliminary Lake Michigan annual primary production of 8.5 Tg C/year. The new algorithm can be easily adapted to work on all the Great Lakes and therefore can be used to generate time series dating back to late 1997 (launch of SeaWiFs). These time series can contribute to improved assessment of Great Lakes primary productivity changes as a result of biological events, such as Dreissenid mussel invasions, climatic change and anthropogenic forcing.     

Age and growth of round gobies in Lake Michigan,with preliminary mortality estimation

The round goby (Neogobius melanostomus) is a prevalent invasive species throughout Lake Michigan, as well as other Laurentian Great Lakes, yet little information is available on spatial variation in round goby growth within one body of water. Age and growth of round goby at three areas of Lake Michigan were studied by otolith analysis from a sample of 659 specimens collected from 2008 to 2012. Total length (TL) ranged from 48 to 131 mm for Sturgeon Bay, from 50 to 125 mm for Waukegan, and from 54 to 129 mm for Sleeping Bear Dunes. Ages ranged from 2 to 7 years for Sturgeon Bay, from 2 to 5 years for Waukegan, and from 2 to 6 years for Sleeping Bear Dunes. Area-specific and sex-specific body–otolith relationships were used to back-calculate estimates of total length at age, which were fitted to von Bertalanffy models to estimate growth rates. For both sexes, round gobies at Sleeping Bear Dunes and Waukegan grew significantly faster than those at Sturgeon Bay. However, round goby growth did not significantly differ between Sleeping Bear Dunes and Waukegan for either sex. At all three areas of Lake Michigan, males grew significantly faster than females. Based on catch curve analysis, estimates of annual mortality rates ranged from 0.79 to 0.84. These relatively high mortality rates suggested that round gobies may be under predatory control in Lake Michigan.     

Temporal and spatial differences in deposition of organic matter and black carbon in Lake Michigan sediments over the period 1850–2010

Inorganic carbon (IC), total organic carbon (OC), and black carbon (BC) were analyzed in eight sediment cores obtained from deep water (>30 m) sediments in the Chippewa and south Chippewa basins, as well as Green Bay in Lake Michigan. These cores were segmented at high resolution and radio-dated to reconstruct a detailed history of deposition to the lake both spatially and temporally since ca. 1850 CE. To help interpret the depositional record, cores were also characterized for stable isotopes (¹³C and ¹⁵N), as well as particle size distribution, density, organic matter (OM), and other parameters. Fine (silt and clay) sediment particles contained OM of primarily lacustrine algal biomass origin. Sedimentation fluxes showed large increases in OM and OC fluxes through much of the lake during the onset of industrialization and the period of rapid industrialization to onset of Great Lakes environmental legislation. In contrast, fluxes and loading of BC increased dramatically in the southern basin until the 1930's, then decreased substantially after the 1940's. This observation was due largely to results from site M009 nearest the steel mills and industrial zones of Chicago and northern Indiana. Together, whole lake loadings of OM and BC provide evidence that changing industrial activity and legislation intended to curb air pollution in the Great Lakes region have had a fairly rapid and dramatic impact. In contrast, legislation intended to decrease eutrophication through reductions in nutrient loading to the lake have not had a similar impact on sedimentation of OM in the lake.