Ice thickness measurements in Lake Erie during the winter of 2010–2011

Time series measurements of ice thicknesses were made at either 1 or 2?Hz at 6 locations in the western part of Lake Erie's central basin during the winter of 2010–2011. Ice was observed over approximately 80?days beginning in late December and continuing through mid-March. Deformation and ridging of ice occurred frequently and produced ice thicknesses of up to 10?m, and over 6?m at all stations. The measurements show considerable variability (up to several meters) between stations, even when the distance between them is <500?m. Comparison of the measurements to those generated by the National Ice Center show good agreement for undeformed thicknesses, but the Ice Center analyses do not account for increased thicknesses due to ice ridging. Several different measures of ice thickness (based on different averaging times and the parameter used to characterize the resulting distribution of thicknesses) are used to characterize the data, and the results can vary widely depending upon which measure is used. The best measure to use will depend upon the use for which the data is intended.     

Factors affecting Cladophora growth in the eastern basin of Lake Erie: Analysis of a monitoring dataset (2012–2019)

Cladophora is a naturally occurring benthic alga in the Great Lakes which can reach nuisance levels in the nearshore, leading to beach closures and other impacts. A monitoring program was initiated in 2012 in the eastern basin of Lake Erie to identify ecological factors driving its growth. Inflows from the Grand River, the largest river to the north shore, were generally positively associated with phosphorus concentrations in the nearshore and negatively associated with light reaching the lakebed. At the depths sampled (3 m–18 m), Cladophora was strongly influenced by light availability, and due to shading by the Grand River plume, an overall negative association was found between Cladophora biomass and phosphorus inputs. Phosphorus limitation was only observed at shallow sites farthest from the Grand River. Positive associations between dreissenid mussel coverage and both Cladophora biomass and tissue phosphorus suggest that nutrient cycling by dreissenids supports Cladophora growth. Our results indicate that i.) the Grand River has a strong influence on nearshore nutrient levels and water clarity; and ii.) Cladophora is limited by both phosphorus and light to varying degrees within the study area, although light appears to be the dominant factor, at least at these depths, years, and locations. The implication that phosphorus reductions could lead to increased Cladophora biomass by improving light conditions will need to be considered carefully against the known historical success of controlling nuisance algae through nutrient management.     

Studies of Large-Scale Currents in Lake Erie, 1979–80

Currents and water temperatures were recorded at a large-scale grid of fixed moorings in Lake Erie from May 1979 through June 1980. Currents measured in the lower half of the central basin water column were mostly return flows (beneath the surface wind drift) driven by the surface pressure gradient. Often observed was a complex system of Lake Erie circulation gyres as predicted by models. Another common occurrence was for one of the central basin gyres to become dominant and envelop the whole basin in either uniform clockwise or anticlockwise flow. It is not fully certain why one of the circulation cells grows as opposed to the others, but the curl of the wind stress had influence. The currents were more barotropic than predicted by full Ekman layer current models. Tidal-like currents driven by the longitudinal seiches of Lake Erie dominate the island-filled passages between the western and central Lake Erie basins, with currents across the whole island chain very closely in phase. Processes of hypolimnion volume entrainment are suggested from the central basin temperature recordings. Large volume water exchanges between the central and eastern basins occurred after the water mass in the vicinity of the shallow ridge that separates them had become unstratified. These and other topics are discussed as the large data set generated from the experiment is explored.     

Fleet Dynamics of the Commercial Lake Trout Fishery in Michigan Waters of Lake Superior during 1929–1961

Understanding fishing fleet dynamics is important when using fishery dependent data to infer the status of fish stocks. We analyzed data from mandatory catch reports from the commercial lake trout (Salvelinus namaycush) fishery in Michigan waters of Lake Superior during 1929–1961, a period when lake trout populations collapsed through the combined effects of overfishing and sea lamprey (Petromyzon marinus) predation. The number of full-time fishermen increased during 1933–1943 and then decreased during 1943–1957. Addition of new fishermen was related to past yield, market prices, World War II draft exemptions, and lost fishing opportunities in Lake Huron and Lake Michigan. Loss of existing fishermen was related to declining lake trout density. Large mesh (≥ 114-mm stretch-measure) gill net effort increased during 1929–1951 because fishermen fished more net inshore as lake trout density declined, even though catch per effort (CPE) was often higher in deeper waters. The most common gill net mesh size increased from 114-mm to 120-mm stretch-measure during 1929–1957, as lake trout growth increased. More effort was fished inshore than offshore and the amount of inshore effort was less variable over time than offshore effort. Relatively stable yield was maintained by increasing gill net effort and by moving some effort to better grounds. Because fishing-up caused yield and CPE to remain high despite declining lake trout abundance, caution must be used when basing goals for lake trout restoration on historical fishery indices.     

Reproductive Potential and Fecundity of Lake Trout Strains in Southern and Eastern Waters of Lake Ontario, 1977–1994

We assessed the reproductive potential of various genetic strains of hatchery lake trout (Salvelinus namaycush) in southern and eastern Lake Ontario from indices of fecundity and indices of male abundance. Indices were constructed from catches of mature lake trout in gill nets during September 1980 to 1994 after correcting for mortality from sea lampreys (Petromyzon marinus) which occurred between September sampling and late fall spawning. Strain and age were assigned to individual lake trout based on clipped fins and maxillary bones or coded wire tags. Fecundity-length relationships for fish of the same age, determined from mature females collected in 1977 to 1981 and 1994, were not different (P > 0.05) among genetic strains. For all strains combined, fecundity-length relationships in 1977 to 1981 were not different among fish of various ages but in 1994, age-5 and -6 fish had fewer eggs (P < 0.003) than age-7 fish, and age-7 fish had fewer eggs (P < 0.003) than fish of age 8, 9, or 10. Annual indices of fecundity varied 19 fold and indices of mature males varied 11 fold; both indices were low in the early 1980s, increased sharply in the mid 1980s, and peaked in 1993. The strain which dominated fecundity and mature male indices shifted during the study from Seneca Lake strain to Lake Superior strain and then back to Seneca Lake strain. However, changes in either reproductive potential or genotypes do not appear responsible for the abrupt appearance of naturally-produced yearling lake trout throughout southern and eastern Lake Ontario in 1994–1995, the first widespread occurrence of juveniles produced by hatchery lake trout in Lake Ontario.     

Biotic and Abiotic Factors Related to Rainbow Smelt Recruitment in the Wisconsin Waters of Lake Superior, 1978–1997

Lake Superior rainbow smelt (Osmerus mordax) recruitment to 12–13 months of age in the Wisconsin waters of Lake Superior varied by a factor of 9.3 during 1978–1997. Management agencies have sought models that accurately predict recruitment, but no satisfactory models had previously been developed. In this study, modeling was conducted to determine which factors best explained recruitment variability. The Ricker stock-recruitment model derived from only the paired stock and recruit data accounted for 63% of the variability in recruitment data. The functional relationship that accounted for the greatest amount of recruitment variation (81%) included rainbow smelt stock size, May rainfall, and bloater (Coregonus hoyi) biomass. Model results were interpreted to mean that recruitment was affected negatively by increased river flows from increased rainfall, and affected positively by the biomass of bloater, and those results were interpreted to mean that bloater mediated the effects of lake trout predation on rainbow smelt recruits. Model results were also interpreted to mean that stock size caused compensatory, density-dependent mortality on rainbow smelt recruits. Correlations observed here may be of value to managers seeking approaches to either enhance or control populations of this species, which is not indigenous to the Great Lakes.     

Pink Salmon Populations in the U.S. Waters of Lake Superior, 1981–1984

Pink salmon were introduced to Lake Superior in very small numbers at Thunder Bay, Ontario, Canada in 1956. Since that time, they have established themselves as permanent members of the Lake Superior ecosystem. Peak spawner densities were observed in the U.S. tributaries of Lake Superior in 1979 when many streams experienced runs of 10,000 fish or more. To better understand the population dynamics of pink salmon, population characteristics, fecundity and egg deposition of spawners, egg and larval survival, and fry outmigration were studied in several Michigan and Minnesota tributaries in 1980. Population estimates indicate a significant decline of pink salmon in the U. S. waters of Lake Superior since 1979. This decline appears to be related to instream fry survival, which is in turn related to the hydrological conditions of the streams in fall and winter. Lake Superior pink salmon are phenotypically similar to their Pacific Coast counterparts, the major difference being age structure and smaller size of adults. Approximately 90% of the adults mature as 2-year-olds while the remaining 10% mature as 3-year-olds. Pink salmon maturing as 3-year-olds have different growth patterns than those maturing at 2 years of age. Two-year-old pink salmon average 390 mm in length, which is about 30% smaller than 2-year-olds from the Pacific Ocean. Three-year-old females have a lower fecundity and a poorer egg quality than 2-year-old females.     

Resuspension of Bottom Sediments in Lake Ontario During the Unstratified Period, 1992–1993

Time-series measurements of current velocity and water temperature made at a station in southwestern Lake Ontario between October 1992 and June 1993 are combined with analyses of material collected in a sequencing sediment trap moored at the same location. The results show that local resuspension of bottom material occurred several times during November and December. Analyses of total PCBs and Mirex concentrations were used to infer the origins of the material collected in the traps. Material collected during the fall has multiples sources; in addition to material already in suspension and bottom material resuspended from the immediate area, some material appears to be derived from the Niagara River delta. This is the first reported instance of bottom resuspension in the Great Lakes at depths below wave base during the unstratified period that has been confirmed by current velocity measurements.     

Fifty Years of Physical Investigations and Related Limnological Studies on Lake Erie, 1928–1977

To set the scene for the papers which follow, this review presents the principal findings of hydrodynamic and related chemical and sedimentological studies in Lake Erie beginning with the 1928/29 cooperative surveys of the central and eastern basins (Fish 1929, 1960) and ending with the (also cooperative) “Project Hypo” (Burns and Ross 1972) and the papers assembled in the 1976 special number, “Lake Erie in the Early Seventies” (J. Fish. Res. Board Canada, Vol. 33). Attention is also drawn to the far-reaching and interweaving influence of the physical phenomena on biological and sedimentological processes operating in the lake. Where needed to place the half-century's findings in context or to lead into the papers which follow in this issue, some references to work published before 1928 or after 1977 are also included. After an introduction, the review examines: surface surges and seiches; thermal stratification and its coupling with the distribution of oxygen and phosphorus in bottom water; long-term and short-term circulation patterns; sedimentation and sediment transport.     

Piscivory by Lake Superior Lake Herring (Coregonus artedi) on Rainbow Smelt (Osmerus mordax) in Winter, 1993–1995

The stomach contents of 31 lake herring (Coregonus artedi), captured by anglers from western Lake Superior in the winters of 1993–1995, were examined to determine if predation on rainbow smelt (Osmerus mordax) was occurring as indicated by anglers. Twenty-six (84%) of the stomachs contained rainbow smelt, with an average of 7.0 rainbow smelt/stomach. This was the first documentation of piscivory by lake herring on rainbow smelt in the Great Lakes.     

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.     

Broad screening of toxic and bioactive metabolites in cyanobacterial and harmful algal blooms in Lake of the Woods (Canada and USA), 2016–2019

Cyanobacteria produce toxic/bioactive metabolites that affect human and ecosystem health via inhibition of proteases, carboxypeptidases, or phosphatases. From surface water samples collected between 2016 and 2019 inclusive (n = 78), we report intracellular concentrations of more than 30 such compounds in Lake of the Woods (LOW), a large lake system of multinational importance. Although most surface biomass blooms were dominated by the cyanobacteria Dolichospermum (max. ～50 mg/L) and Aphanizomenon (max. ～60 mg/L), there was also significant biomass of other cyanobacteria (Gloeotrichia echinulate along shoreline, max. ～40,000 mg/L; Woronichinia naegeliana max. ～100 mg/L; Lyngbya max. ～10 mg/L; Planktothrix agardhii max. ～6 mg/L) and phytoplankton (Stephanodiscus niagarae max. ～6 mg/L). Microcystins (MCs) were present in ～80 % of samples, peaking at ～33 µg/L (MC variant-LR). Approximately 50 % of samples contained MC concentrations below 0.1 µg/L. Alkaloid metabolites detected included neurotoxin anatoxin-a (～60 % < 0.1 µg/L) and cytotoxic cylindrospermopsins (～30 % < 0.1 µg/L). Anabaenopeptins A/B/F were prevalent (>96 %) and exceeded MCs by >100 fold (max. >4,000 µg/L). Aeruginosamide B was present in ～75 % of samples (max. ～10 µg/L). Cyanopeptolin 1040 MB, microginin 690 methyl ester, and oscillaginin A were not detected however, traces of micropeptin 1106 were detected. Microcystin and anabaenopeptin genes were also detected in the majority of samples (78 % and 79 %, respectively), while saxitoxin, cylindrospermopsin, and anatoxin genes occurred at lower frequencies with 59 %, 36 %, and 38 % detection, respectively. These results will aid assessment of risk from cyanobacterial blooms in LOW and inform ongoing binational lake management and policy development.     

Sudden Disappearance of the Amphipod Diporeia from Eastern Lake Ontario, 1993–1995

Diporeia, Oligochaeta, and Sphaeriidae were sampled at three sites (28 to 35 m depth) in the east basin of Lake Ontario, and at one mid-lake site (125 m) from 1982 and 1996. In addition, Diporeia was sampled at 14 more sites located in the south and eastern part of the lake in 1990 and 1995. Before 1991, densities of all three macroinvertebrate taxa fluctuated with peaks occurring between 1988 and 1991. Between 1992 and 1995, Diporeia declined rapidly from > 6,000 per m² to 0 at all three sites in the east basin, while increasing from 1,050 to 5,230 per m² at the mid lake site. Samples from the south and eastern part of the lake confirmed the decline was extensive at depths < 100 m. Abundance and biomass of the Oligochaeta and Sphaeriidae also fluctuated, but remained more similar before 1991 and after 1993. Direct cause for the disappearance of Diporeia is unknown but declines occurred after establishment of nearshore Dreissena colonies. Lake circulation patterns suggest that the nearshore mussel populations may intercept diatoms and other material that had been consumed by Diporeia located further offshore. A substantial biomass of Diporeia (3 g/m² dry) has been lost from the food web of eastern Lake Ontario, with serious consequences to the coldwater fisheries of the lake.     

Is glyphosate an underlying cause of increased dissolved reactive phosphorus loading in the Western Lake Erie basin?

The western Lake Erie basin has been experiencing increasing dissolved reactive phosphorus (DRP) loads since approximately 1994, the causes of which are not well understood. Changing agricultural practices such as no-till agriculture and tile drainage are certain to have an effect on DRP loads. This study examines glyphosate as a potential driver of the observed increase in the western Lake Erie basin DRP loads since 1994 by examining adoption of herbicide-tolerant crops, glyphosate use, and both DRP loads and concentrations from the mid-1990’s to the present. Glyphosate’s widespread usage contributes to DRP loadings and eutrophication in the western Lake Erie basin.     

Carbon dioxide in the atmosphere-water system and biogenic elements in the littoral zone of Lake Baikal during period 2004–2018

We report long-term comprehensive measurements of CO₂ in the atmosphere, surface water and the major nutrients obtained for the period 2004–2018. The research was conducted at the Baikal Atmospheric and Limnological Observatory (BALO), which is located in the coastal zone of South Baikal (coordinates 51° 54′ N, 105° 05′ E). The seasonal variation of these characteristics was analyzed. For our site, during the open water period (May-December) we assessed average flux of CO₂, which amounted to −155 mmol m⁻² y⁻¹ (sink from the atmosphere to the water surface). Carbon dioxide content in the near-water air of Lake Baikal rises with a rate of 2.46 ppm per year, which is in good agreement with the global trend. The common effect of many factors (often multi-directional), such as variability of weather conditions, hydrological processes and productivity cycles of aquatic plankton in the Baikal waters, cause strong variations in the water characteristics, which we observed in different seasons and years. Under these conditions of strong inter-annual and seasonal variability of all characteristics, trend calculations using our long-term observations did not allow us to reveal reliable tendencies of changes in surface water CO₂ concentrations.     

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.     

The distribution,density, and biomass of the zebra mussel (Dreissena polymorpha) on natural substrates in Lake Winnipeg 2017–2019

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.     

Spatiotemporal trends of polychlorinated biphenyls (PCBs) in surface and suspended sediments from the Lake Ontario Canadian nearshore 1994–2018: A fish consumption advisory perspective

Spatiotemporal trends for polychlorinated biphenyls (PCBs) were examined in surface and suspended sediments collected between 1994 and 2018 from over twenty nearshore stations on the Canadian side of Lake Ontario and the St. Lawrence River. In 2018, PCB concentrations ranged over an order-of-magnitude in surface (<10 ng/g?357 ng/g) and suspended sediments (<10 ng/g–330 ng/g), illustrating the presence of legacy hotspots as well as diffuse urban inputs. PCB concentrations in both surface and suspended sediments were consistently highest in Hamilton Harbour, but were also elevated at other stations around the perimeter of the Niagara basin as well as near Trenton and Kingston, Ontario. Generally, higher PCB concentrations were found in surface sediment relative to paired suspended sediment samples suggesting temporal improvements in nearshore sediment quality. However, many stations demonstrated temporal variability in PCB concentrations, a likely factor in the lack of an overall nearshore declining trend. Given that PCBs are listed as a consumption-limiting contaminant for all fish sampling blocks in the Canadian waters of Lake Ontario and are responsible for 78% of restricted advisories, sediment quality benchmarks that account for bioaccumulation potential should be considered over toxicologically-derived guidelines to gauge severity of PCB contamination of nearshore sediments. Relatively higher TOC-normalized PCB concentrations in the western end of Lake Ontario suggests additional research on PCB bioavailability from nearshore sediment would be beneficial in understanding basinwide trends of PCBs in fish, and that an adaptive approach to sediment management may be needed in the context of consumption advisories.     

The Sustainable Utilization of Lake Resources in the Middle and Lower Reaches of Yangtze River

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Status of the amphipod Diporeia spp. in Lake Superior, 2006–2016

The amphipod Diporeia spp. has historically been an important component of the benthic food web of the Laurentian Great Lakes. The Great Lakes Water Quality Agreement included its population density as an indicator of ecological condition for Lake Superior, with target values of 220–320 m^?2 in nearshore areas (≤100 m depth) and 30–160 m^?2 in offshore areas (>100 m). To assess the status of Diporeia in Lake Superior, we used a probability-based lake-wide survey design to obtain estimates of Diporeia density and biomass in 2006, 2011 and 2016. A PONAR grab sampler was used to collect Diporeia at 50–53 sites each year, with approximately half in the nearshore (<100 m depth) region of the lake and half in the offshore. The mean area-weighted lake-wide density was 395 ± 56 (SE) m^?2 in 2006, 756 ± 129 m^?2 in 2011, and 502 ± 60 m^?2 in 2016. For all years, both density and biomass were greater in the nearshore than in the offshore stratum. The densities for 2006–2016 were 3–5 times higher than those reported from a lake-wide survey conducted in 1973 by the Canada Centre for Inland Waters. The severe declines in Diporeia populations observed in the other Great Lakes during recent decades have apparently not occurred in Lake Superior. Further research is needed to understand spatial and temporal variability of Diporeia populations in Lake Superior to enhance the utility of Diporeia density as an indicator of benthic condition.