Phytoplankton trends in the Great Lakes, 2001–2011

We describe recent trends in phytoplankton composition and abundance in the Laurentian Great Lakes using synoptic spring (April) and summer (August) sampling events from 2001 through 2011, a period of rapid shifts in pelagic food webs and water quality. Data analysis identified qualitative and quantitative changes in algal densities, biovolume, and taxonomic composition of assemblages. Since 2001, Lake Superior has changed subtly with an increase in small-celled blue-green algae in spring and a recent decline in summer centric diatoms, possibly a result of lake warming and changes in water quality. Spring phytoplankton declines mainly attributed to diatoms occurred in Lakes Huron and Michigan, a probable result of invasions by non-native dreissenids that have reduced pelagic nutrients and selectively consumed certain taxa. The decline in Lake Huron's spring phytoplankton biovolume was earlier and more severe than that in Lake Michigan, despite a faster and more abundant dreissenid invasion in Lake Michigan. Lake Erie's central basin had a notable increase in spring centric diatoms (largely Aulacoseira), while the whole of Lake Erie shows a summer increase in cyanobacteria, complementing that found in coastal regions. The composition of Lake Ontario's species assemblage shifted, but little overall change in algal abundance was observed with the exception of higher summer densities of cyanophytes. Additional mechanisms for shifts in the pelagic primary producers are described or hypothesized in the context of concurrent shifts in water quality and invertebrate populations. Tracking these trends and explaining driving factors will be critical to the management of lake conditions.     

Hydrology influences generalist–specialist bird-based indices of biotic integrity in Great Lakes coastal wetlands

Marsh bird habitats are influenced by water levels which may pose challenges for interpreting bird-based indices of wetland health. We determined how much fluctuating water levels and associated changes in emergent vegetation influence the Index of Marsh Bird Community Integrity (IMBCI) using data collected in Great Lakes coastal wetlands by participants in Bird Studies Canada's Great Lakes Marsh Monitoring Program. IMBCI scores for 90 wetlands in Lake Erie and 131 wetlands in Lake Ontario decreased with decreasing water levels due to decreasing number of marsh-dependent species in Lake Erie and perhaps also in Lake Ontario. The average magnitude of the decrease in scores between extremely high and low water periods for wetlands with sufficient data was 15% in Lake Erie where water dropped 0.9 m on average (n = 11 wetlands) and 18% in Lake Ontario where water dropped 0.5 m (n = 7). Scores in Lake Erie increased with increasing Typha due to increasing numbers of marsh-dependent species and decreased with increasing Phragmites due to increasing numbers of generalist species. The opposite was observed in Lake Ontario, perhaps due to denser Typha and sparser Phragmites. Scores were explained by the naturally fluctuating water levels of Lake Erie, which favored Phragmites expansion and the regulated water levels of Lake Ontario which promoted Typha expansion. Scores were influenced by fluctuating water levels and associated changes in emergent vegetation. Inter-annual water level fluctuations should be considered when interpreting any indicator of wetland health that is based on marsh-dependent bird species.     

In-use Pesticide Concentrations in Surface Waters of the Laurentian Great Lakes, 1994–2000

Pesticides are heavily used in agricultural production in the Great Lakes basin. Large-volume surface water samples were collected between 1994 and 2000 from Lakes Ontario, Erie, Huron (including Georgian Bay), and Superior and analyzed for neutral and phenoxy-acid herbicides, and organophosphorus insecticides. Thirty-nine pesticides from these three pesticide classes, including analytes and some metabolites, were measured. Six pesticides—barban, diallate-2, triallate, phorate, phosmet, and disulfoton—were not detected. Atrazine, metolachlor, simazine, and 2,4-D were detected in greater than 50% of the samples. The highest maximum concentrations were observed for atrazine (1,039 ng/L), metolachlor (736 ng/L), and D-simazine (281 ng/L). No pesticide concentrations exceeded water quality guidelines/criteria for the protection of aquatic life and drinking water. In general, an increasing concentration gradient from north to south was observed with Superior < Huron < Ontario < Erie. The spatial and seasonal variability of selected pesticides are discussed in relation to their use and application.     

Nutrient concentrations and loadings in the St. Clair River–Detroit River Great Lakes Interconnecting Channel

Long-term (2001–2015) water quality monitoring data for the St. Clair River are presented with data from studies in the Detroit River in 2014 and 2015 to provide the most complete information available about nutrient concentrations and loadings in the Lake Huron–Lake Erie interconnecting corridor. Concentrations of total phosphorus (TP) in the St. Clair River have reflected declines in Lake Huron. We demonstrate that St. Clair River TP concentrations are higher than offshore Lake Huron values. The recent average (2014 and 2015) incoming TP load from the upstream Great Lakes is measured here to be 980 metric tonnes per annum (MTA), which is roughly three times greater than previous estimates. Significant TP load increases are also indicated along the St. Clair River. We treat the lower Detroit River as three channels to sample water quality as part of a two year monitoring campaign that included winter sampling and SRP in the parameter suite. We found concentrations of many parameters are higher near the shorelines, with the main Mid-River channel resembling water quality upstream measured at the mouth of the St. Clair River. Comparison with past estimates indicates both concentrations and loadings of TP have dramatically declined since 2007 in the Trenton Channel, while those in the Mid-River and in the Amherstburg Channel have remained similar or have possibly increased. The data demonstrate that the TP load exiting the mouth of the Detroit River into Lake Erie is currently in the range of 3740 (in 2014) to 2610 (2015) MTA.     

Great Lakes total phosphorus revisited: 1. Loading analysis and update (1994–2008)

Phosphorus load estimates have been updated for all of the Great Lakes with an emphasis on lakes Superior, Michigan, Huron and Ontario for 1994–2008. Lake Erie phosphorus loads have been kept current with previous work and for completeness are reported here. A combination of modeling and data analysis is employed to evaluate whether target loads established by the Great Lakes Water Quality Agreement (GLWQA, 1978, Annex 3) have been and are currently being met. Data from federal, state, and provincial agencies were assembled and processed to yield annual estimates for all lakes and sources. A mass-balance model was used to check the consistency of loads and to estimate interlake transport. The analysis suggests that the GLWQA target loads have been consistently met for the main bodies of lakes Superior, Michigan and Huron. However, exceedances still persist for Saginaw Bay. For lakes Erie and Ontario, loadings are currently estimated to be at or just under the target (with some notable exceptions). Because interannual variability is high, the target loads have not been met consistently for the lower Great Lakes. The analysis also indicates that, because of decreasing TP concentrations in the lakes, interlake transport of TP has declined significantly since the mid-1970s. Thus, it is important that these changes be included in future assessments of compliance with TP load targets. Finally, detailed tables of the yearly (1994–2008) estimates are provided, as well as annual summaries by lake tributary basin (in Supplementary Information).     

A cross-lake comparison of crustacean zooplankton communities in the Laurentian Great Lakes, 1997–2016

Spring and summer open-water crustacean zooplankton communities were examined across all five Laurentian Great Lakes from 1997 to 2016. Spring communities were dominated by calanoid (lakes Superior, Huron and Michigan) or cyclopoid (lakes Erie and Ontario) copepods. Volumetric biomass of summer communities increased along an assumed trophic gradient (Superior, Huron, Michigan, Ontario; eastern, central and western Erie), as did dominance by cyclopoids and cladocerans. Over the time series of the study, summer communities in lakes Michigan, Huron and Ontario shifted towards greater dominance by calanoids and greater similarity with Lake Superior. Trajectories of changes were different; however, reductions in cladocerans accounted for most of the change in lakes Michigan and Huron while reductions in cyclopoids and increases in Leptodiaptomus sicilis were behind the changes in Lake Ontario. Shifts in the predatory cladoceran community in Lake Ontario from Cercopagis pengoi to occasional dominance by Bythotrephes longimanus, a species much more vulnerable to planktivory, as well as the appearance of Daphnia mendotae in a daphnid community previously consisting almost exclusively of the smaller Daphnia retrocurva, suggest impacts of reduced vertebrate predation. In contrast, strong correlations between cladocerans and chlorophyll in lakes Michigan and Huron point to the possible importance of bottom-up forces in those lakes. Large interannual shifts in cladoceran community structure in the central and eastern basins of Lake Erie suggest intense but variable vertebrate predation pressure. The zooplankton communities of lakes Huron, Michigan and Ontario may be approaching a historic community structure represented by Lake Superior.     

Patterns of long-term dynamics of aquatic communities and water quality parameters in the Great Lakes: Are they synchronized?

Long time series data can provide insights into dynamics of large lakes. We use the USEPA-GLNPO biological monitoring dataset (phytoplankton, benthos, zooplankton and water quality), collected from 1996 through 2016, to identify whether there is evidence of concordant linear or non-linear trends in community composition, density/biomass/biovolume and major environmental parameters. We show changes in biotic assemblages and water quality variables, particularly in Lakes Michigan and Huron. These include changes in phytoplankton biovolume and zooplankton biomass, increasing invasive Dreissena abundance and decreasing densities of other benthos. Biotic changes are accompanied by pronounced changes in water quality and nutrient ratios. Species change-points, identified using threshold indicator taxon analysis, are often less abrupt, but there are clear shifts in a large proportion of species in each assemblage. The concordance of breakpoints among assemblages or lack thereof provides valuable insight into potential drivers of ecosystem change.     

What's in a name? Taxonomy and nomenclature of invasive gobies in the Great Lakes and beyond

The species identities, scientific names, and relationships of Eurasian gobies that invaded the Laurentian Great Lakes – and other species that are predicted to invade in the future – are evaluated here using recently resolved DNA characters. The Round Goby and the Freshwater Tubenose Goby entered the Great Lakes ca. 1990 via ballast water originating from Black Sea ports. The Round Goby spread extensively throughout the Great Lakes and adjacent rivers, whereas the Freshwater Tubenose Goby recently began to expand its range. Both species also are widely invasive in Eurasia, dispersing via canals and shipping. Several of their relatives – the Monkey, Racer, and Bighead gobies – also are invasive in Eurasia, and are predicted to invade the Great Lakes. We discuss results from phylogenetic analyses of DNA sequences from 4 mitochondrial and nuclear gene regions, and provide a revision of their scientific nomenclature. The Freshwater Tubenose Goby was redefined as Proterorhinus semilunaris, which is markedly different and distinctive from the Marine Tubenose Goby Proterorhinus marmoratus. The genus Neogobius, as formerly defined, contained multiple evolutionary lineages and incorrect scientific names. We thus restricted Neogobius to just 4 species—including the Round Goby Neogobius melanostomus and the Black Sea Monkey Goby Neogobius fluviatilis. Several previously recognized subgenera, which were incorrectly grouped in Neogobius, were elevated to the level of genera. Notably, the Racer Goby became Babka gymnocephalus and the Bighead Goby now is Ponticola kessleri. These changes made the names consistent with their true relationships and species characters, which are essential for identifying and characterizing these gobies in invasive and native habitats.     

Parasites of Lake Trout,Salvelinus namaycush,from the Great Lakes: a Review of the Literature 1874–1994

A comparative summary of the literature on parasites reported from lake trout, Salvelinus namaycush, from the Great Lakes is presented. Twenty-four studies on parasites infecting lake trout in these lakes have been published since 1874 with 32 parasite species (1 Monogenea, 3 Digenea, 9 Cestoidea, 6 Nematoda, 6 Acanthocephala, 1 Annelida, 5 Crustacea, 1 Fungi) being reported. The most common parasites are Eubothrium salvelini and Echinorhynchus salmonis in the intestine, and Cystidicola stigmatura in the swim bladder. Most of the parasites occur in the gastrointestinal tract. Twenty (80%) of the 25 helminth species reported from lake trout are represented by adults. The dominance of these helminth species is attributable to the position of lake trout in the food web of the Great Lakes as top predators. Parasitological data from splake, Salvelinus namaycush X Salvelinus fontinalis, from Lake Huron are also presented.     

Groundwater Demand Management in the Great Lakes Basin—Directions for New Policies

Demand-side management should be used to maximize the efficiency of groundwater use. Implementation of conservation measures would decrease the volume of water use and also exert less pressure on the water distribution system as well as the wastewater treatment system. Allocation of ground water in the Great Lakes basin must conform to priorities established at the community level. Groundwater pricing should reflect the full costs arising from ground water use. A differential pricing structure would help conserve water in the residential and industrial sectors. A user-friendly database on ground water use, quality and quantity for the entire Great Lakes basin is also essential. New policies for sustainable groundwater allocation, regulating water prices for water conservation, conservation education, pollution prevention, recycling and reuse of water as well as effective information management provide new directions for managing the groundwater demand in the Great Lakes basin.     

Do existing ecological classifications characterize the spatial variability of stream temperatures in the Great Lakes Basin,Ontario?

Ecological classifications of stream ecosystems have been used to develop monitoring programs, identify reference and impacted systems, and focus conservation efforts. One of the most influential, but highly variable, components of stream ecosystems is water temperature but few geographically broad-scale and long-term programs exist to assess and monitor temperatures. This study evaluated if existing ecological classifications could be used to categorize the similarities and differences in stream temperatures across the Ontario portion of the Great Lakes Basin. Concordance between the spatial variability in temperatures and an existing ecological classification would support the use of that classification to define areas with similar temperatures, guide the development of a monitoring program, and inform management programs. The five classifications evaluated were the ecoregions and ecodistricts defined in the National Ecological Framework for Canada, the ecoregions and ecodistricts defined in the Ecological Land Classification of Ontario, and the aquatic ecosystem units defined in the Aquatic Ecosystem Classification (AEC) for the Ontario portion of the Great Lakes Basin. Hierarchical linear modelling and corrected Akaike Information Criterion indicated that the ecodistrict classifications characterized more of the spatial variability in temperatures than the ecoregion and AEC classification but temperatures were more variable among sites within classes than between classes. Therefore, none of the existing ecological classifications could be used to characterize thermal variability. Future research should examine if the inability of the existing classifications to capture the thermal variability translates into inaccurate classification of other ecosystem components such as water quality, and macroinvertebrate and fish assemblages.     

Trends in Total Phosphorus in Canadian Near–Shore Waters of the Laurentian Great Lakes: 1976–1999

Beginning as early as 1976 at many locations, total phosphorus concentrations (TP) were measured weekly in samples collected year-round in the intake water of 18 municipal water treatment plants in Canadian (Ontario) waters of the Laurentian Great Lakes. No consistent long-term trends were evident at two north-shore Lake Superior sampling locations, but there were significant long-term declines in TP measured at all three Lake Huron locations; however, concentrations there have remained relatively constant during the past decade. Declines in TP averaging about 1 μg/L/yr during 1976 to 1990 were prevalent at lower Great Lakes sampling locations and by the early 1990s TP had declined to 15–25 μg/L in Lake Erie and 10–20 μg/L in Lake Ontario. Declines generally levelled out in Lake Ontario after 1990, but TP increased substantially at some Lake Erie locations in the late 1990s. Recent (1996 to 1999) total phosphorus concentrations in north-shore Lake Erie locations in the range of 20 to 30 μg/L were 2 to 3 times higher than at Lake Ontario near-shore locations in the 8 to 11 μg/L range. Rates of decline of TP were generally highest for the March–April period (−1.88, −1.61, and −1.34 μg/L/yr in Lakes Ontario, Erie, and Huron, respectively for 1976 to 1990). The March–April Lake Ontario near-shore rate of TP decline was nearly twice as high as that reported previously for off-shore Lake Ontario (attributed to proximity to P loading sources and to lower net sedimentation losses of P in the near-shore environment). There were substantial declines in chlorophyll-to-TP ratios and in the slopes and Y-intercepts of chlorophyll-TP regressions for both Lake Erie and Lake Ontario following the establishment of dreissenid mussels.     

Dreissenid mussels are not a “dead end” in Great Lakes food webs

Dreissenid mussels have been regarded as a “dead end” in Great Lakes food webs because the degree of predation on dreissenid mussels, on a lakewide basis, is believed to be low. Waterfowl predation on dreissenid mussels in the Great Lakes has primarily been confined to bays, and therefore its effects on the dreissenid mussel population have been localized rather than operating on a lakewide level. Based on results from a previous study, annual consumption of dreissenid mussels by the round goby (Neogobius melanostomus) population in central Lake Erie averaged only 6 kilotonnes (kt; 1 kt = one thousand metric tons) during 1995–2002. In contrast, our coupling of lake whitefish (Coregonus clupeaformis) population models with a lake whitefish bioenergetics model revealed that lake whitefish populations in Lakes Michigan and Huron consumed 109 and 820 kt, respectively, of dreissenid mussels each year. Our results indicated that lake whitefish can be an important predator on dreissenid mussels in the Great Lakes, and that dreissenid mussels do not represent a “dead end” in Great Lakes food webs. The Lake Michigan dreissenid mussel population has been estimated to be growing more than three times faster than the Lake Huron dreissenid mussel population during the 2000s. One plausible explanation for the higher population growth rate in Lake Michigan would be the substantially higher predation rate by lake whitefish on dreissenid mussels in Lake Huron.     

Trends in Mysis diluviana abundance in the Great Lakes, 2006–2016

With the large Diporeia declines in lakes Michigan, Huron, and Ontario, there is concern that a similar decline of Mysis diluviana related to oligotrophication and increased fish predation may occur. Mysis density and biomass were assessed from 2006 to 2016 using samples collected by the Great Lakes National Program Office's biomonitoring program in April and August in all five Great Lakes. Summer densities and biomasses were generally greater than spring values and both increased with bottom depth. There were no significant time trends during these 10–11 years in lakes Ontario, Michigan, or Huron, but there was a significant increase in Lake Superior. Density and biomass were highest in lakes Ontario and Superior, somewhat lower in Lake Michigan, and substantially lower in Lake Huron. A few Mysis were collected in eastern Lake Erie, indicating a small population in the deep basin of that lake. On average, mysids contributed 12–18% (spring-summer, Michigan), 18–14% (spring-summer, Superior), 30–13% (spring-summer, Ontario), and 3% (Huron) of the total open-water crustacean biomass. Size distributions consisted of two peaks, indicating a 2-year life cycle in all four of the deep lakes. Mysis were larger in Lake Ontario than in lakes Michigan, Superior, and Huron. Comparisons with available historic data indicated that mysid densities were higher in the 1960s–1990s (5 times higher in Huron, 2 times higher in Ontario, and around 40% higher in Michigan and Superior) than in 2006–2016.     

Extinction in Multiple Species Fisheries Harvested with the Same Gear—The Great Lakes Ciscoes

Extinction of four deepwater ciscoe species (Coregonus spp.) in the Great Lakes occurred during a period of heavy exploitation, but during the same period there were several introduced and invading species and there also was widespread deterioration in the quality of the environment. The cause of the extinctions is uncertain, but extinction is a threat in multiple species fisheries harvested with a common gear. The possibility that the ciscoe extinctions resulted from harvesting was investigated using a general form of the surplus production model and computer simulation. In the simulations extinctions occurred even with a moderate fishing effort when a large number of different species were caught with the same gear. In the Great Lakes 4 out of 8 ciscoe species caught with the same gear apparently went extinct. In the simulations 4 extinctions out of 8 species was a common event, and the fishery alone was all that was necessary to cause the extinctions.