On the Origins of Magnetic Excursions in the Great Lakes

Paleomagnetic studies of cores from Lake Michigan and Lake Erie exhibit possible excursions of the geomagnetic field at approximately 9,000 to 10,000 years B.P. and 12,000 to 14,000 years B.P. In this report, magnetic data and lithologic data from two cores from Lake Erie and six cores from Lake Michigan are presented. It is shown that the magnetic excursions are predominately associated with deepening waters which followed low lake levels produced by glacial advances and retreats. It is suggested that these excursions are the result of slumping and/or flowing of lacustrine and glaciolacustrine materials, rather than of changes in the magnetic field.     

Deglacial and Lake Level Fluctuation History Recorded in Cores,Beaver Lake,Upper Peninsula,Michigan

Sediment cores collected from the littoral and pelagic zones of Beaver Lake, Michigan record fluctuations in the water level of Lake Superior. Beaver Lake is a small 300 ha lake in Pictured Rocks National Lakeshore (PRNL) now separated from Lake Superior by a dune-capped barrier bar. Cores were collected using a vibracorer from a lake-ice platform in February 1997. A 2.85 m long core in 10 m of water contains well-sorted sand, rhythmites, peat, interbedded sand and gyttja, and is capped with 1 m of massive gyttja. A 9480 BP AMS age from the basal sand provides a minimum deglacial date for the area. Further analysis indicates a sand-dominated depositional environment from a low lake stand at approximately 8500 BP to present. An approximate 8800 BP red to gray sediment color transition records either the cessation of meltwater input from Lake Agassiz or receding ice, while a younger similarly colored transition, 6600 BP in age, likely records sediment reworking in the coastal zone.Four AMS ages on peat range from 8520 to 7340 BP and are indicative of the Houghton low phase. Burial of the peat by stratified sand and gyttja after 7340 BP indicates a rising lake level. Peat at a higher level in the lake basin, encountered in shallow littoral cores, ranges in age from 6800 to 6420 BP, which estimates a 0.91 m rise/century in lake level to the Nipissing level by 5000 BP.     

Circular Rep encoding single stranded (CRESS) DNA virus-like sequences detected in quagga mussels (Dreissena rostriformis bugensis) and sediments from the central Lake Michigan benthos

Circular Rep Encoding Single Stranded (CRESS) DNA viruses are a diverse group of viruses that have been identified in both terrestrial and aquatic ecosystems. Recent work in the Laurentian Great Lakes characterized the ecology and diversity of CRESS-DNA viruses associated with amphipods, Diporeia spp. In the last 20 years the Lake Michigan benthos has changed considerably with drastic population declines of Diporeia spp. concurrent with an increase in invasive quagga mussel (Dreissena rostriformis bugensis) abundance. The purpose of this study was to characterize CRESS-DNA virus-like elements (VLES; which could represent complete, partial/defective, endogenized or satellite viruses) associated with both invasive quagga mussels and in sediment collected in central Lake Michigan. Viral metagenomic libraries were prepared from two size classes (>25 mm and <15 mm shell length) of Lake Michigan quagga mussels and for two different sediment layers (136 mm and 290 mm below the lake floor) in a sediment core extracted from the lake. Viral metagenomes were different between quagga mussels and sediment cores. Nine VLE sequences were present in both the quagga mussel tissues and the sediment core layers analyzed. Cs¹³⁷ radiometric dating results indicate that these VLEs were present in the sediment prior to arrival of quagga mussels in Lake Michigan. These data suggest quagga mussels may interact with CRESS-DNA VLEs and algal DNA VLEs historically present in the Lake Michigan benthos. Overall, these data suggest that quagga mussels interacted with CRESS-DNA VLES present in Lake Michigan benthos since at least 1952.     

Nearshore Versus Offshore Copper Loading in Lake Superior Sediments: Implications for Transport and Cycling

A thorough understanding of the fate and transport of metals in Lake Superior is necessary in order to predict the ability of Lake Superior to recover from anthropogenic perturbations (copper mining). Sediment cores were collected from nearshore and offshore sites in Lake Superior and used to evaluate spatial and temporal variations in copper loading associated with mining-related activities. Although both settings have been strongly affected by anthropogenic releases of copper, copper concentrations in nearshore cores are significantly greater than those found in offshore cores, implying that nearshore copper loading is dominated by simple deposition and burial of sediment generated from mining activities. Temporal variations in copper profiles in sediments from nearshore environments closelymimic copper production rates. Conversely, copper loading histories derived from offshore sediments are not well correlated to production rates. The offshore sediment cores, when compared with analogous cores from Lakes Ontario and Michigan, show that the average, lake-wide intensity of copper loading in Lake Superior is comparable to the other two lakes, despite the fact that Lake Superior has received the largest total burden of anthropogenic copper. Cu/Zn ratios, used to evaluate the amount of copper loading derived from mining discharges, vary strongly in nearshore environments in response to loading. Cu/Zn ratios in offshore sediments are much less variable, implying that copper loading may be regulated by additional mechanisms (solution chemistry and/or biologic uptake). Study of trace metal partitioning within Lake Superior sediments indicates that the organic fraction of the sediment contains the majority of the copper. Copper concentrations in offshore sediments are significantly correlated to organic carbon content of the sediment whereas copper concentrations in nearshore sediments are not. These findings support the model that transport and deposition of particles released from mining discharges dominate copper loading in nearshore sediments, whereas biologic uptake and settling of particulate organic matter may regulate copper loading in offshore sediments.     

Reconstruction of lake-level and climate changes in Lake Qarun,Egypt, during the last 7000 years

Sediment cores from Lake Qarun provide a record of mid-late Holocene climatic changes in Northern and Eastern Africa as well as environmental changes due to the activities of ancient Egyptians. We used sedimentological, mineralogical, and geochemical analyses of the cores to investigate long-term variations in lake level due to changing hydrologic inputs. An age model based on three paired ¹⁴C and paleomagnetic measurements suggests that the base of the sediment cores is as old as ∼ 5000 B.C.E. Geochemical analyses indicated that lake sediments were derived from Nile floods with an admixture of Saharan sand. Laminated endogenic carbonate-rich clayey silt lithofacies with benthic diatoms are indicative of relatively low lake levels, saline waters and dry conditions; massive lithofacies with planktonic diatom species are indicative of relatively high lake levels, fresh waters and humid conditions. Faintly laminated clayey silt lithofacies suggest intermediate conditions. Variations in lithology as well as diatom composition suggest that the lake level has varied from relatively high levels in its early history to lower levels in later years although there have been numerous cycles in water level over the past 7000 years. A combination of climate changes in the source area of the Nile River as a result of monsoon dynamics; climatic changes in the setting area of the Lake Qarun; and human activities through the dynasties in Egypt produced these variations in lake level.     

Distribution of Major Elements and Metals in Sediment Cores from the Western Basin of Lake Ontario

An investigation was made of the relationship between the changes in metal concentrations in sediments with the distance from the Niagara River mouth and the chemical and physical characteristics of the sediments. Sediment cores were obtained at nine sampling stations in the western basin of Lake Ontario. In addition, surface sediment was collected at three stations on the Niagara Bar. Minerals present at all stations were silica, feldspars, illite/muscovite, chlorite, kaolinite, and calcite. Dolomite was found at some sampling stations as grains of 2 to 63 μm size. Significantly elevated concentrations of calcite (up to 20%) in the surface sediment (about 0 to 10 cm) at four sampling stations in the western basin and in the entire 25-cm sediment column at the Niagara River mouth indicated increased input of this mineral into Lake Ontario during the past 100 years. Furthermore, sediment concentration profiles of Zn, Pb, Cr, Cu, Ni, and especially Hg at all sampling stations indicated major transport of metals associated with the clay- and silt-size particles from the Niagara River into Lake Ontario (especially north-north-east and east of the river mouth). A significant decrease in Hg loading from the Niagara River during the past 20 years was also observed. Although smaller in magnitude, a similar decrease was found for Pb, Zn, Cr, Ni, and Cu loading. However, elevated Hg concentrations (up to 7 μg g～^l above background values) existed in the surface 10 cm of sediment at eight sampling stations.     

Sediment distribution and accumulation in Lake Naivasha,Kenya over the past 50 years

Although surface waterbodies are water sources for socio‐economic activities and ecosystems, their functions are threatened by sedimentation. Sedimentation of lakes and reservoirs can result in a loss of storage capacity and altered water quality. The present study assessed the sedimentation status of Lake Naivasha, Kenya, based on sediment distribution and accumulation over the past 50 years, using a Bathymetric Survey System (BSS). The BSS uses multi‐frequency Acoustic Profiling System (APS) to map recently deposited sediments. Sediment core samples were collected with a vibe‐ coring device and dated. Sediment layers corresponding to a period of the past 20 and 50 years were identified. Sediment cores and acoustic images were subsequently used to determine sediment thickness within the lake. The collected depth data from multi‐frequency APS, and dated cores were processed in DepthPic and Surfer software. The sediment depth was extracted in DepthPic, while the sediment volume and distribution were generated from Surfer software. The results from present study indicated that sediment distribution varied from one part of the lake to another for the past 20 and 50 years. High sediment thickness observed in the south‐west and eastern parts of the lake. Between 1996–2016 and 1966–2016 periods, the maximum accumulated sediment thickness was found to be about 0.55 and 1.9 m, with an average sediment thickness of 0.25 and 0.56 m, respectively. The mean sediment load corresponding to the 1966–1996 and 1996–2016 periods was 2.78 × 10⁵ and 4.61 × 10⁵ t/year, respectively. It was found that sediment load into Lake Naivasha has been increasing in the recent past. Based on the present the study, it was found that combined use of BSS, sediment cores and dating can be adopted in many lakes and reservoirs to determine sediment thicknesses even where no prior bathymetric surveys exist for comparison.     

Lead in Lake Michigan and Green Bay surficial sediments

Sediment samples were collected in 1987–1990 from Green Bay and in 1994–1996 from Lake Michigan. Surficial sediments (0–1 cm) from both locations were analyzed for lead for the purpose of describing the horizontal variation of lead in 1994–1996 Lake Michigan and 1987–1990 Green Bay sediments, estimating lead fluxes to surficial sediments, and comparing results to earlier studies. With Lake Michigan concentrations ranging from below the method detection limit to 180 μg/g, the surficial sediments had mean and median lead concentrations of 70 μg/g and 64 μg/g, respectively. Lead concentrations in Green Bay surficial sediments were similar to those in Lake Michigan and ranged between the method detection limit and 160 μg/g. For the bay, mean and median concentrations were 58 and 59 μg/g, respectively. Surficial lead concentrations were highest in the Southern, Waukegan, and Grand Haven basins of Lake Michigan and in the central region of Green Bay in the vicinity of Chambers Island. For Lake Michigan and Green Bay, dated sediment cores illustrate the decline in lead concentrations during the last 30 and 10 years, respectively. Lead fluxes ranged between < 0.049 and 7.2 μg/cm²/yr for Green Bay and between 0.47 and 20 μg/cm²/yr for Lake Michigan. Lead fluxes to Lake Michigan were lower than those reported for 1972. These are the most comprehensive fluxes of lead to Lake Michigan and Green Bay surficial sediments reported to date.     

PCBs in Great Lakes sediments, determined by positive matrix factorization

Previously determined PCB concentrations in 10 dated sediment cores from Lakes Michigan, Huron, Erie, and Ontario are analyzed by positive matrix factorization in order to find characteristic congener patterns including signs of anaerobic dechlorination. Three or four factors are sufficient to describe the PCB data for each lake. All four lakes are dominated by Aroclors 1248A, 1248G, 1254A, and 1254G. Aroclor 1260 is only a significant factor in Lake Michigan prior to 1975, reflecting in part a usage patterns of heavy chlorinated Aroclors early and less chlorinated Aroclors in the phase-out years in the 1970s. Dated records of factors or sources indicate clear PCB concentration maxima for Lakes Erie (1981) and Ontario(1968), while redistribution of PCBs in the less contaminated Lakes Michigan and Huron has occurred after 1980. Using a single data matrix for all four lakes provides a common basis and possibility to examine low degrees of dechlorination, while individual data matrices for each lake provide more accurate results and better separation of factors. Lakes Ontario, Michigan, and Huron undergo dechlorination via reactions such as 66(24-34) → 25(24-3) and 18(25-2) → 4(2-2) consistent with reactions H' + M, while Lake Erie appears to be dominated by 18(25-2) → 4(2-2) and 53(25-26) → 19(26-2) that are typical for processes M + Q.     

Sediment Trap Studies in Lake Michigan: Resuspension and Chemical Fluxes in the Southern Basin

The results of 4 years (1977–80) of sediment trap sample collection in the southeastern region of Lake Michigan are summarized and compared with water column and sediment characteristics. Mass flux data indicate strong seasonal patterns, with maximum fluxes recorded during the unstratified period. The large amount of winter resuspension is a mechanism which provides an intimate coupling of recent sediments and the water column. Also these trap study results indicate that there is a near-bottom (10-m-thick) benthic nepheloid layer whose chemical composition approaches that of deep water (fine grain) sediments. The amount of resuspended NaOH extractable phosphorus injected into the euphotic zone is estimated as approximately equal to the load of new phosphorus entering southern Lake Michigan. The role of resuspension in the cycling of organic carbon and contaminants associated with it appears to be important.     

Identification and Determination of Trace Organic Substances in Sediment Cores from the Western Basin of Lake Ontario

A study was carried out to identify and to determine organic chemicals in sediment from the western basin of Lake Ontario, particularly in the fine-grained sediments near the mouth of the Niagara River. Sediment cores were obtained at five sampling stations, and samples were extracted by the base/neutral and acid method designed by US Environmental Protection Agency for extraction of water samples. The identification of organic compounds in the base/neutral sediment extract was carried out by GC/MS techniques. The major classes of investigated contaminants were aromatics, polynuclear aromatics, alkylated polynuclear aromatics, alkylated benzenes, phthalates, methyl esters of fatty acids, olefins, aldehydes, chlorobenzenes, and benzoates. In addition, all sediment samples were analysed for 2,3,7,8-tetrachloro dibenzo-p-dioxin. In the surface sediments, the abundance of contaminants decreased with the distance from the Niagara River mouth toward the north-west. However, high concentrations of most of the detected organics were present in sediment at the station located east of the River mouth.     

Sedimentary Records of Spheroidal Carbonaceous Particles from Fossil-Fuel Combustion in Western Lake Ontario

Spheroidal carbonaceous particles (SCPs) were quantified in three sediment cores collected from depositional areas in the western basin of Lake Ontario to examine the impact of fossil-fuel combustion on sediment metal concentrations. SCP profiles were similar for the three cores showing the initiation of the SCP record deep in the core, followed by a rapid increase to a sub-surface maximum, and a subsequent decrease towards the sediment surface. Subsurface maximum SCP concentrations ranged from 1.97 to 5.61 × 10⁵ per gram dry matter/gDM. For ²¹⁰Pb dated cores, dates for the initiation of the SCP record (1850 ± 10 years), the initiation of the rapid rise in SCPs (1880 ± 13 years), and the SCP subsurface maximum (1961 ± 3 years) agree well. The rapid increase in sediment SCPs also agrees well with the US bituminous coal consumption during this same period (1880 to 1980). SCPs in surface sediments decreased between 55 to 83% from the subsurface maximum (1961 to 1996) in these cores while U.S. coal usage continued to increase. SCP decreases were attributed to the increased use and efficiency of particle collection devices by utilities and industry. Lead, Cr, Cu, and Zn showed significant correlations (r² = 0.63 to 0.94) with SCPs within each respective sediment core. Calculations show that although SCPs are not the major source of anthropogenic metals in Lake Ontario sediments, they may account for between 4 to 55% of the Zn, 1 to 12% of the Cu, 2 to 22% of the Pb and 1 to 18% of the Cr in these sediments.     

Drought coincident with aeolian activity in a Great Lakes coastal dune setting during the Algoma Phase (3.1–2.4 ka), southwest Michigan

Aeolian studies of Lake Michigan’s coastal dunes have yet to elucidate what factors control their episodic activity over the past 5000 years. High lake levels exposing sand along with increased storminess is generally accepted for high perched dunes. This hypothesis, however, remains poorly tested for low perched dunes along the southeast Lake Michigan coastline. Here, small lakes in the lee of dune complexes contain aeolian sand and various biological proxies. Age and sedimentation rate models from Gilligan Lake cores guide analysis of aeolian sand, charcoal, pollen, and diatoms at high resolution (1 cm [10.4 yr/cm]) during the high-water Algoma Phase (3.1–2.4 ka) of the upper Great Lakes. The diatoms record a transition from a deep, more acidic lake to a shallower, more alkaline lake with fewer wetlands. This transition is accompanied by a stepped increase in the amount of aeolian sand. There is a weak correlation (R² 0.5, p < 0.01) between increasing abundances of charcoal chunks and sand. Peaks of sand follow peaks in charcoal threads and sheets, suggesting fire played a role in removing vegetation, presaging the landscape for increases in storminess. Arboreal pollen records a transition from a mesic forest Fagus-Acer-Quercus-Abies assemblage suggestive of moister conditions to one richer in mesic hardwoods tolerant of drier conditions. Together, the environmental proxy data record a shallowing lake concomitant with increasing aeolian sand, suggesting that drought-like conditions along the coastline conditioned the landscape for renewed aeolian activity. Once initiated, increased storminess and shoreline erosion maintained dune activity through increased sediment supply.     

Influence of Lake Michigan Holocene Lake Levels on Fluvial Sediments of the Lower Pigeon River,Wisconsin

Thirty-seven vibracores, extending up to 4.86 m, collected along the lower Pigeon River north of Sheboygan, Wisconsin, were used to interpret Holocene lake-level fluctuations of Lake Michigan. The sediments reflect numerous cycles of degradation and aggradation as well as marshland and submergence. The basal unit is till and glaciolacustrine silt and clay. The river cut through these sediments prior to 6,500 ¹⁴C years BP, probably during the Chippewa Low stand, and deposited the lowest gravel unit in the cores. Between 6,500 and 5,500 ¹⁴C years BP, yellowish-red fluvial sand and silt were deposited in the northern half of the valley. Aggrading point bar gravel and overbank silt and fine sand throughout the entire valley record the lake rise to the Nipissing level from about 5,500 to 5,000 ¹⁴C years BP. Subsequent deposition of organic-rich, muddy palustrine sediment indicates that Nipissing water flooded the valley. A lack of sediments with ages between 5,000–2,000 ¹⁴C years BP suggests lack of aggradation, indicating a lowering lake level until about 2,000 ¹⁴C years BP. Sandy-silt overbank sediment deposited over the palustrine sediment since 2,000 ¹⁴C years BP marks the return of floodplain aggradation as lake level stabilized or rose slightly to the modern level. While the river-mouth sediments are not useful for refining Holocene lake-level curves, they do corroborate major events such as the Chippewa Low, the rise to the Nipissing level followed by a period of declining lake level and fluvial erosion, and the small rise to the modern lake level.     

Temporal evolution of urban wet weather pollution: analysis of PCB and PAH in sediment cores from Lake Bourget, France.

In order to evaluate the historical impact of urban stormwater runoff on a lacustrine environment, eight sediment cores were collected in October 2006 in Lake Bourget (Savoie, France). Sediment samples were analysed for polycyclic aromatic hydrocarbons (PAH) and polychlorobyphenyls (PCB) in order to correlate the vertical profiles of contamination and the evolution of the urbanisation on the watershed for the last 100 years. Overall, we observe that vertical profiles of PCB and PAH concentrations in Lake Bourget are showing a downward trend, probably resulting from the pollution control measures. Concentrations of PCB and PAH measured in surface sediments are approximately 5-10 fold less than maximal concentrations found in the cores. Maximal PAH concentrations were found at the bottom of the cores ( approximately 40 cm) which approximately correspond to the beginning of the 20th century. Maximal PCB concentrations measured in cores L5 and L6 are respectively 850 and 790 microg/g dw (dryweight). The peak of PCB corresponds to the maximum of PCB production and consumption in the 1970s. In surface sediments total PCB concentrations range between 47 and 79 microg/kg dw. Those concentrations are particularly high compared to other values measured in lake sediments and highlight the problem of a local source of PCB contamination in the watershed. General trends were observed, yet the part of urban stormwater runoff in the total contamination could not be determined.     

Sorption and Sedimentation of Zn and Cd by Seston in Southern Lake Michigan

Recent estimates suggest that inputs of Zn and Cd to southern Lake Michigan exceed losses. We investigated the sorption and sedimentation of Zn and Cd by southern Lake Michigan seston particles using ⁶⁵Zn and ¹⁰⁹Cd in 21 radiotracer experiments. The time-series sorption by total seston >0.45 μm was asymptotic with apparent equilibria of ～100–200 ng Zn/L and ～1.0–2.0 ng Cd/L, occurring in ～24–30h during the summer phytoplankton bloom. Studies of the sorption by different particle size fractions showed that the abundance of phytoplankton and detritus control the concentrations of particle-bound Zn and Cd. The seasonal maximum concentrations of particle-bound Zn and Cd correlated well with the development of both the summer and fall phytoplankton blooms. Serial additions of Zn and Cd in combination with the radiotracers showed that these additions inhibit the sorption of both metals as their toxic effects are expressed. Coupling of the particle-bound Zn and Cd estimates for the period May to December with data on the seasonal variations in the net settling velocity in southern Lake Michigan provided annual sedimentation rates of ～9 μg Zn/cm^2.yr and ～0.1 μg Cd/cm² yr that are in excellent agreement with similar estimates by other investigators. Likewise, dividing our particle-bound estimates by the dry weight of total seston in the samples provided sediment concentration estimates of ～38–185 ng Zn/mg dry weight (ppm) and 0.5–2.3 ng Cd/mg dry weight that agree with measured levels from the surficial Lake Michigan sediment. The results of these experiments suggest that, if the dissolved concentrations of Zn and Cd do increase to toxic levels, the impacts on phytoplankton may potentiate further increases in the dissolved levels by reducing plankton sorption and removal by sedimentation.     

Late Holocene Lake-level Variation in Southeastern Lake Superior: Tahquamenon Bay,Michigan

Internal architecture and ages of 71 beach ridges in the Tahquamenon Bay embayment along the southeastern shore of Lake Superior on the Upper Peninsula of Michigan were studied to generate a late Holocene relative lake-level curve. Establishing a long-term framework is important to examine the context of historic events and help predict potential future changes critical for effective water resource management. Ridges in the embayment formed between about 4,200 and 2,100 calendar years before 1950 (cal. yrs. B.P.) and were created and preserved every 28 ± 4.8 years on average. Groups of three to six beach ridges coupled with inflections in the lake-level curve indicate a history of lake levels fluctuations and outlet changes. A rapid lake-level drop (approximately 4 m) from about 4,100 to 3,800 cal. yrs. B.P. was associated with a fall from the Nipissing II high-water-level phase. A change from a gradual fall to a slight rise was associated with an outlet change from Port Huron, Michigan/Sarnia, Ontario to Sault Ste. Marie, Michigan/Ontario. A complete outlet change occurred after the Algoma high-water-level phase (ca. 2,400 cal. yrs. B.P.). Preliminary rates of vertical ground movement calculated from the strandplain are much greater than rates calculated from historical and geologic data. High rates of vertical ground movement could have caused tectonism in the Whitefish Bay area, modifying the strandplain during the past 2,400 years. A tectonic event at or near the Sault outlet also may have been a factor in the outlet change from Port Huron/Sarnia to Sault Ste. Marie.     

Stimulation of Lake Michigan Plankton Metabolism by Sediment Resuspension and River Runoff

Previous work during a major sediment resuspension event (March 1988) in southern Lake Michigan demonstrated that nutrients and carbon derived from resuspended sediment stimulated intense winter heterotrophic production while simultaneously decreasing light availability and autotrophic biomass. However, the role of riverine inputs on plankton metabolism remained unclear. Here we present results from a simulated enrichment experiment (March 2000) designed to examine the influence of resuspended sediments and riverine inputs on Lake Michigan plankton dynamics. Lake water amended with realistic levels of river water, coastal resuspended sediment and river water + sediment all showed enhanced heterotrophic bacterial production and plankton respiration rates, relative to the lake water control. Bacterial production increased by approximately 4× in river water treatments and by a factor of 2.5× for the sediment only treatment compared to lake water controls. Rates of net primary production were stimulated by river water (8.5×) and resuspended sediment (3×), but most by a combination of river water + sediments (11×). Community respiration showed a similar response with rates approximately 8x higher in river water amendment treatments and 3.5× higher in the sediment treatment. Extrapolating experimentally determined production rates to the southern Lake Michigan basin indicated that heterotrophic and autotrophic production in this nearshore region may be enhanced by as much as 3× and 5.2× due to these source inputs. Indeed, field measurements throughout southern Lake Michigan from 1998–2000 support these experimental results. Experimental and field observations suggest that both seasonal riverine inputs and episodic resuspended sediments influence the regional scale ecosystem metabolism and biogeochemistry in Lake Michigan.     

Climatology of Large Sediment Resuspension Events in Southern Lake Michigan

Lake Michigan, particularly the southern basin, is subject to recurrent episodes of massive sediment resuspension by storm-induced waves and currents. The purpose of this paper is to investigate the climatology of these events for Lake Michigan, including an analysis of associated meteorological conditions. This paper begins by examining turbidity records from two water treatment plants (Chicago, IL and St. Joseph, MI) for which long-term records are available. The turbidity records from the two plants show significant differences indicating that turbidity measurements from a single location would probably not be representative of a basin-wide climatology. A one-dimensional sediment resuspension and deposition model for fine-grained sediments is then developed and calibrated with data from the water treatment plants. The one-dimensional model is applied at 15 points around the southern basin for a 45-year period for which Lake Michigan wave climatology is available and the results are averaged to obtain a basin-wide turbidity index (Southern Lake Michigan Turbidity Index, SLMTI). A frequency distribution of the turbidity index is presented and meteorological conditions associated with the largest events are examined. Our analysis indicates that significant resuspension events in southern Lake Michigan are usually caused by a strong cyclone passing to the east of the lake. The most likely time of the year for this to occur is October to April. There is an average of 1 event per year with SLMTI above 25 mg/L and each event typically lasts about 3 days. Our analysis indicates that events have occurred more frequently since the late 1980s as the number of winter storms has increased and ice cover has decreased.     

A Comparison of Lake Trout Spawning,Fry Emergence,and Habitat Use in Lakes Michigan,Huron, and Champlain

Restoration of self-sustaining populations of lake trout is underway in all of the Great Lakes and Lake Champlain, but restoration has only been achieved in Lake Superior and in Parry Sound, Lake Huron. We evaluated progress toward restoration by comparing spawning habitat availability, spawner abundance, egg and fry density, and egg survival in Parry Sound in Lake Huron, in Lake Michigan, and in Lake Champlain in 2000–2003. Divers surveyed and assessed abundance of spawners at 5 to 15 sites in each lake. Spawning adults were sampled using standardized gill nets, eggs were sampled using egg bags, and fry were sampled using emergent fry traps and egg bags left on spawning reefs overwinter. Spawning habitat was abundant in each lake. Adult lake trout abundance was low in Lake Michigan and Parry Sound, and very high at one site in Lake Champlain. Egg deposition was lowest in Lake Michigan (0.4–154.5 eggs•m⁻², median = 1.7), intermediate in Parry Sound (39–1,027 eggs•m⁻², median = 278), and highest in Lake Champlain (0.001–9,623 eggs•m⁻², median = 652). Fry collections in fry traps followed the same trend: no fry in Lake Michigan, 0.005–0.06 fry•trap⁻¹ day⁻¹ in Parry Sound, and 0.08–3.6 fry•trap⁻¹ in Lake Champlain. Egg survival to hatch in overwinter egg bags was similar in Lake Michigan (7.6%) and Parry Sound (2.3–8.9%) in 2001–02, and varied in Lake Champlain (0.4–1.1% in 2001–02, and 1.8–18.2 in 2002–03). Lake trout restoration appears unlikely in northern Lake Michigan at current adult densities, and failure of restoration in Lake Champlain suggests that there are sources of high mortality that occur after fry emergence.