Grain Size and Mineralogy of Sediment Cores from Western Lake Huron

Grain size and mineralogical analyses along the lengths of 12 cores recovered from the Alpena and Manitoulin Basins, when combined with ages determined by C-14 dating of surficial and basal sediments, reveal an approximate sedimentary history of this part of Lake Huron. Reddish glaciolacustrine clays, essentially all 10 ?, crop out on the flanks of the sublacustrine basins and underlie gray post-glacial muds in the central basin regions. The post-glacial muds become more coarse in their upper portions where they are very fine silt. Detrital carbonates which comprise approximately 30% of older sediments are reduced in abundance by an order of magnitude in more recent deposits. We interpet these phenomena as recording lowered lake levels and reduced sedimentation rates since the Nipissing high stand which ended about 4,000 years ago.     

Conceptual Framework for Coordinated Great Lakes Monitoring

The utility of conceptual models is discussed as a basis for effective development of coordinated monitoring efforts on the Great Lakes. The use of conceptual models is illustrated in two ways: (1) the development of a methodology for specifying monitoring objectives of the Great Lakes, based on a conceptual model, and (2) presentation of a comprehensive method for defining resource needs to achieve monitoring objectives.     

Factors in the Determination of Selected Trace Elements in Near-Shore U.S. Waters of Lakes Superior and Huron

Determinations of total As, Cr, Cu, Fe, Mn, and Pb in acidified unfiltered water samples from 48 stations representing the near-shore U.S. waters of Lake Superior, Lake Huron, and selected incoming streams gave overall mean concentrations and standard deviations (μg/L) of 1.0 ± 0.7, 0.9 ± 1.8, 2.0 ± 1.8, 236 ± 819, 14 ± 34, and 0.7 ± 0.8, respectively, using flameless atomic absorption analytical methods. Total concentrations of Ni and Hg were usually less than the instrumental detection limits (μg/L) of 0.8 and 0.02, respectively. Small losses of Hg, As, and Cr from solutions are possible in addition to a molecular spectral interference in the determination of As using the graphite furnace method. River waters usually were only slightly higher in total element concentrations than lake waters, except for Fe andMn. Nearshore waters of both lakes were very similar in elemental composition.     

Modelling Ice Dissipation in Eastern Lake Erie

A previously developed mathematical model, which considered both the heat exchange processes at the air-ice interface and the ice transport rate via the Niagara River Was used to simulate the ice dissipation process in eastern Lake Erie. The model, which assumed the ice thickness to be constant over the lake, has been further developed to take into account variable ice thickness. Buffalo meteorological data were used for the computation of the net heat exchange at the air-ice interface. Results of the model application illustrate the relative importance ofin-lake ice melt to ice transport via the Niagara River during the dissipation period. Model results were found to give reasonably good agreement with the limited ice information available for the 1976 dissipation period.     

First Occurrence of Cercopagis pengoi in Lake Michigan

Adults and juveniles of the predaceous cladoceran Cercopagis pengoi, native to the Ponto- Caspian region, were found in nearshore waters of southern Lake Michigan during August and September 1999. This invasive cladoceran was previously reported from Lake Ontario, but this is the first report of C. pengoi from Lake Michigan. In Lake Michigan, densities of C. pengoi peaked at about 75/m3 on 22 September when water temperature was 16°C, and first and second instars comprised up to 90% of the samples. Of the third and fourth instar reproductive forms, parthenogenetic females were most abundant (up to 33% of all individuals sampled) and were present on all sampling dates. Males and females with resting eggs appeared in low abundance on the last two sampling dates perhaps in response to decreasing temperatures. The impact of this invader on the Lake Michigan food web is yet undetermined, but C. pengoi individuals were found in the stomachs of alewife on 22 September indicating that fishes will feed on C. pengoi.     

Recent Changes in the Phytoplankton of Lake Michigan Near Chicago

Daily counts show that during the years 1972-75, phytoplankton population density near the Chicago shoreline of Lake Michigan averaged 50% lower than during the preceding 4 years, and lower than in any 4-year period since 1953-56. The decrease from 1968-71 to 1972-75 resulted mainly from large decreases in the spring and fall maxima of diatoms. Proportionally, by far the greatest decreases were in Stephanodiscus binderanus and other Stephanodiscus species. Fragilaria, Asterionella, and Tabellaria decreased, while there was a statistically insignificant increase in Melosira. Very small populations of flagellates and green algae were not significantly different in the two periods; Blue-green algae increased in abundance, but remained a very small fraction of the total phytoplankton. The changes suggest a partial reversal of cultural eutrophication in this region of Lake Michigan, although other explanations cannot be ruled out.     

Status and Trends of Benthic Populations in a Coastal Drowned River Mouth Lake of Lake Michigan

Muskegon Lake was designated an Area of Concern because of severe environmental impairments from direct discharge of industrial and municipal wastes. Since diversion of all municipal and industrial wastewater in 1973, few studies have assessed ecological changes associated with improved water quality. We examined distributions and long-term changes in the benthic macroinvertebrate community at 27 sites. Distributions were evaluated relative to distance from the river mouth, water depth, grain size, and known areas of sediment contamination. Temporal changes were assessed relative to wastewater diversion. Oligochaeta and Chironomidae dominated the community, and the oligochaete trophic condition index indicated that, in 1999, the lake was generally mesotrophic to eutrophic. Cluster analysis resulted in four distinct site groupings. A cluster of sites near the river mouth had the highest total density (9,375 m⁻²) and lowest diversity (Shannon Weaver Index 1.05) suggesting an enriched habitat. A site cluster in the south central region had the lowest oligochaete density (2,782 m⁻²), lowest oligochaete trophic condition index scores (1.00), and highest diversity (2.24), suggesting the best habitat. The chironomid community in this site cluster was dominated by predatory species, possibly resulting from high concentrations of heavy metals at some sites. Densities of all major taxonomic groups increased significantly between 1972 and 1999. Decreasing proportions of oligochaetes (0.85 to 0.68) and increasing diversity suggest improved environmental conditions over this period. Evidence suggests that changes in Muskegon Lake's benthic community were more a result of wastewater diversion than Dreissena invasion.     

Sources and Sinks of Escherichia coli in Benthic and Pelagic Fish

Escherichia coli and fecal coliform bacteria were isolated from five benthic and four pelagic fish species to determine their role in the fecal contamination of recreational waters. All fish were collected during fall 2006 from Southworth Marsh in the Duluth-Superior Harbor, a public beach that is commonly posted to minimize water contact due to high E. coli levels. Although fecal coliform bacteria were isolated from each fish species, they were only isolated from 66% and 72% of the individual benthic and pelagic fish, respectively. While 42% of the fecal coliforms from benthic fish were E. coli, only 4% of these bacteria from pelagic fish were E. coli. Cluster analysis showed different fish species harbored identical strains of E. coli and some fish contained multiple E. coli strains. The potential source for 65% of the E. coli isolates obtained from fish were identified by using the HFERP DNA fingerprinting method and libraries of E. coli DNA fingerprints from warm-blooded animals and environmental isolates collected in the area. The E. coli strains whose source could be identified were most similar to strains isolated from sediments, Canada geese, mallard ducks, and wastewater. None of the fish E. coli had DNA fingerprints matching those from any water or beach sand isolates. Although our results demonstrate that benthic fish contain E. coli, it may be more appropriate to consider these fish as a vector of E. coli from other sources, rather than a new source of E. coli contamination in aquatic environments.     

Benthic macroinvertebrate community structure in Lake Taihu,China: Effects of trophic status,wind-induced disturbance and habitat complexity

Lake Taihu, the third largest lake in China, is subjected to severe eutrophication and cyanobacterial blooms as a result of development and urbanization. However, little is known about the macroinvertebrate assemblages and their relationship with eutrophication and other environmental factors in this lake. To characterize the community structure of macroinvertebrates and to examine the benthos-environmental relationships in Lake Taihu, a quarterly investigation was conducted from February 2007 to November 2008. A total of 42 taxa was recorded; Limnodrilus hoffmeisteri, Rhyacodrilus sinicus, Corbicula fluminea, Bellamya aeruginosa, Tanypus chinensis and Gammarus sp. dominated the community in abundance and biomass. Cluster analysis and one-way analysis of similarity (ANOSIM) identified three groups of stations that had significantly different macroinvertebrate communities. Stations in the north bays and three river mouths had the lowest diversity and were dominated by pollution-tolerant species such as L. hoffmeisteri and R. sinicus while Gonghu Bay, the Central Region and the Western Region contained intermediately diverse communities mainly dominated by C. fluminea. Diversity and evenness were highest in the East Bays where aquatic macrophytes were abundant; the zoobenthos were characterized by gastropods. One-way ANOVAs revealed that environmental characteristics differed significantly among the three groups of stations. Canonical correspondence analyses showed that community structure and spatial patterns of macroinvertebrates in Lake Taihu were strongly correlated to three ecological factors—trophic status, wind-induced disturbance and habitat complexity. Our results could provide valuable information that could be used by managers and policy makers to evaluate and modify restoration practices.     

Some Fungi and Water Molds in Waters of Lake Michigan with Emphasis on Those Associated with the Benthic Amphipod Diporeia spp.

To determine types of fungi in the water and associated with the benthic amphipod Diporeia spp., samples were collected at various depths in Lake Michigan in an area where the Diporeia population was in a severe state of decline. No fungi were found associated with living, freshly-dead, or dried Diporeia cultured separately from Lake Michigan water. When dead Diporeia and other organic substrates (snake skin and hemp seeds) were used to grow fungi in Lake Michigan water, a rich and diverse fungal and water mold community was revealed. A total of 31 species were found, with the most common genera being Achlya, Aphanomyces, Myzocytium, and Pythium. In general, species were homogeneously distributed in the water; that is, few differences were found in species richness between nearshore (10–15 m) and offshore (60–80 m) waters, and between near-surface (1 m) and near-bottom waters (1 m off bottom). Sampling occurred during the unstratified period (April and October) to maximize the number of species collected, which may have contributed to the uniform spatial pattern observed. While conclusions must be placed in context with our methods of detection, we found no evidence that a fungal infestation was associated with Diporeia in this region of the lake.     

Distribution and Fate of Escherichia coli in Lake Michigan Following Contamination with Urban Stormwater and Combined Sewer Overflows

Escherichia coli distribution and persistence in nearshore Lake Michigan were assessed following heavy rains and sanitary sewer overflow (SSO) and combined sewer overflow (CSO) events over a 5-year period, including an 18-day period following 25.4 cm of rainfall in which intensive studies were conducted following multiple CSO and SSO events. E. coli levels in the Milwaukee estuary and harbor following SSO and CSO events ranged from 10⁴ to nearly 10⁵ CFU/100 mL, which were significantly higher (p ≤ 0.05) than levels following rainfall alone. Sites outside of the breakwall but within the contamination plume (e.g., within 2 km of the harbor) were an order of magnitude lower. Locations 2–5 km from the harbor ranged from below detection limits, of < 1 to 5 CFU/100 mL. E. coli levels corrected for dilution based on specific conductivity measurements were lower than what would be expected for loss due to dilution alone, suggesting a combination of die-off and dilution, were responsible for the rapid disappearance of these organisms outside of the harbor. E. coli and fecal coliforms measured concurrently demonstrated that fecal coliforms could be recovered longer than E. coli in the open waters of the lake. E. coli isolated directly from sewage treatment plant influent were found to have a marked increase in antibiotic resistance traits for ten antibiotics commonly used in the human population compared with isolates from two animal sources of fecal pollution. However, E. coli obtained from sewage impacted water (n = 2,513) and from stormwater impacted water (n = 1,465) collected the previous year when there were no sewage overflows, were found to have no significant difference (p < 0.05) in the frequency of resistance when comparing the two conditions. E. coli survival characteristics and population dynamics are most likely influenced by multiple factors in complex systems such as the watershed/estuarine/lake environments of the Great Lakes.