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.     

Evidence of Lake Whitefish Spawning in the Detroit River: Implications for Habitat and Population Recovery

Historic reports imply that the lower Detroit River was once a prolific spawning area for lake whitefish (Coregonus clupeaformis) prior to the construction of the Livingstone shipping channel in 1911. Large numbers of lake whitefish migrated into the river in fall where they spawned on expansive limestone bedrock and gravel bars. Lake whitefish were harvested in the river during this time by commercial fisheries and for fish culture operations. The last reported landing of lake whitefish from the Detroit River was in 1925. Loss of suitable spawning habitat during the construction of the shipping channels as well as the effects of over-fishing, sea lamprey (Petromyzon marinus) predation, loss of riparian wetlands, and other perturbations to riverine habitat are associated with the disappearance of lake whitefish spawning runs. Because lake whitefish are recovering in Lake Erie with substantial spawning occurring in the western basin, we suspected they may once again be using the Detroit River to spawn. We sampled in the Detroit River for lake whitefish adults and eggs in late fall of 2005 and for lake whitefish eggs and fish larvae in 2006 to assess the extent of reproduction in the river. A spawning-ready male lake whitefish was collected in gillnets and several dozen viable lake whitefish eggs were collected with a pump in the Detroit River in November and December 2005. No lake whitefish eggs were found at lower river sites in March of 2006, but viable lake whitefish eggs were found at Belle Isle in the upper river in early April. Several hundred lake whitefish larvae were collected in the river during March through early May 2006. Peak larval densities (30 fish/1,000 m³ of water) were observed during the week of 3 April. Because high numbers of lake whitefish larvae were collected from mid-and downstream sample sites in the river, we believe that production of lake whitefish in the Detroit River may be a substantial contribution to the lake whitefish population in Lake Erie.     

Lake Erie in Mid-Winter

The results of four surveys of Lake Erie during mid-winter are presented here. The most recent survey, from February 15 to 17, 1977, was conducted during an exceptionally cold winter to determine whether six weeks of complete ice-cover had led to low levels of oxygen concentration in the lake. The results showed that all parts of the lake, even the shallow, normally highly productive areas, contained acceptable levels of oxygen. Apparently, production of oxygen by a small phytoplankton population counterbalanced a fairly low uptake of oxygen and maintained the level of oxygen concentration in most of the water above 90% saturation. The 1976-77 winter phytoplankton biomass was low (0.1 to 1.0 gm biomass per m³) and consisted mostly of diatoms. It appears that some of the phytoplankton were photo-synthetically active under 70 cm of ice and 23 m of water. All surveys of the lake showed the water to be virtually isothermal at a temperature just above the freezing point of water. The maximum temperature differences observed were about 0.2° in magnitude and were found in the East Basin. Nevertheless, the slight temperature differences apparently caused density currents under the ice, which resulted in lowered oxygen concentrations in the deepest part of the East Basin.     

Seasonal Phosphate Demand for Lake Erie Plankton

From April to mid-October 1979, in the eastern and central basins of Lake Erie, the pattern for phosphate demand was assessed by four independent methods: conventional monitoring, measurements of polyphosphate, phosphate turnover time, and a newly developed phosphate deficiency index. Thermal stratification and P limitation occurred faster in the central than in the eastern basin and the plankton remained P limited throughout most of the stratified season. This condition relaxed as the thermocline deepened in the central basin, exposing the epilimnion to a greater area of sediments. In September, when mixing of the entire water column occurred, the plankton were no longer P limited. In contrast, as the thermocline deepened in the eastern basin, metalimnetic water was entrained but the plankton remained P limited until mid-October. These observations support the view that a reduction of phosphorus in Lake Erie would probably affect the phytoplankton biomass during the periods of P limitation.     

Distribution of Freshwater Ostracodes in Lake Erie

Samples collected from the Lake Erie sediment-water interface in 1975 indicate the presence of few live shelled crustaceans (ostracodes). Of the 26 species identified only one, Candona caudata, can be considered as successful today in Lake Erie. Cytherissa lacustris and Candona subtriangulata, primarily recovered as empty shells in this study, indicate that these species have become extinct because of chemical and/or physical change sometime during the last 100 years in Lake Erie.     

Multiple Estimates of Lake Erie Evaporation

Evaporation from large lakes cannot be measured directly, but several methods have been developed to compute lake evaporation. Because of the Great Lakes data limitations, evaporation determined by a single method is’ not sufficiently reliable and requires verification of accuracy by different methods. Monthly evaporation from Lake Erie was derived by the water budget, selected mass transfer, and the energy budget approaches. The period of record varies with the availability of data, 1937-68 for the water budget and mass transfer methods, and 1952-1968 for the energy budget method. Evaporation determined by the water budget method was used to provide control for the other methods. The evaporation rates varied from -9 to 25 cm/month with periods of low, median, and high annual evaporation averaging approximately 80, 90 and 100 cm. The analysis of results indicates that reasonably accurate evaporation estimates during the year can be obtained by the water budget and the modified Lake Hefner mass-transfer equations.     

Calcium Carbonate in Postglacial Lake Erie Sediment

Geotechnical, geochemical, electron-microscopic and biostratigraphic investigation of a 16.8–m long core of a postglacial lacustrine mud collected from the central Lake Erie basin revealed zones containing up to 30% calcite. These zones were associated with a very fine sediment, 80% of which was finer than 4 y.m. Shear strength values of the sediment ranged from 2 kN/m² near the lake bottom to about 9 kN/m² close to the Pleistocene boundary. The concentration of CaO was positively correlated with the concentration of inorganic C and Sr. The concentration of SiO₂, A1₂O₃, Fe₂O₃, K₂O, and Rb gradually decreased with depth. The major crystalline phases were illite (44 wt %), chlorite (10 -13 wt %), calcite (6 - 30 wt %), quartz (6 - 20 wt %), albite (6 - 9 wt %), K-feldspar (2 wt %), and dolomite (2 wt %). The shells of mollusc species present in the lower portion of the postglacial sedimentary column indicated that the carbonate-high sediments were deposited in warmer water than the carbonate-low sediments above and between them.     

Oxygen Depletion in Central and Eastern Lake Erie: Relationship with Bacteria,Chlorophyll, POC,and Morphometry

Hypolimnion oxygen depletion in central and eastern Lake Erie was related to bacteria, particulate organic carbon, and chlorophyll concentrations during 1979. The central basin had the higher oxygen depletion rate and this was associated with more microbiota and particulate organic carbon. After compensation for temperature differences, the rate of oxygen depletion per unit bacteria, chlorophyll, and particulate organic carbon was found to be similar in each basin. These observations are consistent with the hypothesis that lake morphometry affects oxygen depletion through the control of hypolimnion particle concentrations. The implication that most of the hypolimnion oxygen metabolism occurs in the water column means that the role of sediments as a site of oxygen consumption should be reassessed.     

Commentary: Achieving phosphorus reduction targets for Lake Erie

Harmful Algal Blooms (HABs), which were largely absent from Lake Erie from the 1980s until the mid-late 1990s, have been growing steadily worse in intensity. While much of the phosphorus loading into the lake prior to 1972 was caused by point-source pollution, approximately 88% to 93% of current loading comes from nonpoint sources, of which agriculture is the dominant land use. A reduction target of 860?metric?tons, or 40% of the total phosphorus spring loading in 2008, has been set with the expectation that such a reduction could limit the size and associated impact of HABs in 9 out of every 10?years. We review the effectiveness of recommended practices aimed at reducing phosphorus loss in agriculture and pair this knowledge with behavioral data on likely adoption to identify how best to achieve the reduction target. The data suggests that the target is feasible as a majority of the farming population is willing to consider many of the recommended practices. However, increases in adoption over time have been minimal, and farmers will need better cost-benefit information, site-specific decision support tools, and technical assistance in order to more rapidly adopt and execute the placement of recommended practices. A combination of voluntary and mandatory approaches may be needed, but policies and programs promoting voluntary adoption should be designed to better target known barriers and maximize voluntary program effectiveness.     

Commercial Prospects for Natural Gas Extraction from Lake Erie

About four trillion cubic feet of gas are thought to lie beneath Lake Erie. Federal and State officials currently are considering opening U.S. portions of the lake for gas extraction. The generalized resource policy evaluation model (GEN2) is used here to evaluate commercial prospects for such extraction under risk. Using average data, discounted profits appear to be marginal, especially by comparison to the risks encountered. However, higher gas prices, above-average reserves, or slow rates of production decline improve commercial prospects considerably.While public revenues from Lake Erie gas extraction will be modest, output from such wells could help stabilize supplies in a region which is chronically short of gas.     

Hypolimnion Flow Between the Central and Eastern Basins of Lake Erie During 1977 (Interbasin Hypolimnion Flows)

The shallow central basin of Lake Erie (mean depth 19 m) is separated from the deeper eastern basin (mean depth 28.5 m) by the Pennsylvania Ridge which extends southward from the base of Long Point to Erie, Pennsylvania. The crest of the ridge lies at a depth of 15 m except for a narrow notch near Erie, Pennsylvania, where communication between the two basins extends to 24 m depth. Both basins are stratified in summer, and the thin (2 m) hypolimnion of the central basin becomes depleted of oxygen by late summer. Flows to the hypolimnion of the central basin from the mid thermocline water of the eastern basin have been thought to be important sources of dissolved oxygen to the central basin.Data from ship cruises and current meter moorings made in 1977 have been used to form an estimate of the hypolimnion flux across the sill area. A strong correlation between winds and mean flux is observed and the dynamic balance appears to be one where surface pressure gradient created by wind stress is opposed by internal pressure gradients and by bottom friction. While the total quantity of oxygen transported by the subsurface flow is significant in terms of the later summer oxygen consumption of the central basin hypolimnion, its effects are confined to the eastern half of that basin due to the relatively weak horizontal diffusion in the mid-basin hypolimnion.     

Wave Action and Bottom Shear Stresses in Lake Erie

For Lake Erie, the amplitudes and periods of wind-driven, surface gravity waves were calculated by means of the SMB hindcasting method. Bottom orbital velocities and bottom shear stresses were then calculated using linear wave theory and Kajiura's (1968) turbulent oscillating boundary layer analysis. These calculations were made for south-west and north wind directions and a steady wind speed of 40 km hr^?1. Calculated bottom shear stresses are related to the textural properties of surficial Lake Erie sediments as determined by Thomas et al. (1976). The bottom shear stresses, especially under prevailing southwest wind conditions, control the textural characteristics of surface sediments in Lake Erie. In particular, wave-induced bottom shear stresses are probably the most important energy source for sediment entrainment.     

Lyngbya wollei in western Lake Erie

We report on the emergence of the potentially toxic filamentous cyanobacterium, Lyngbya wollei as a nuisance species in western Lake Erie. The first indication of heavy L. wollei growth along the lake bottom occurred in September 2006, when a storm deposited large mats of L. wollei in coves along the south shore of Maumee Bay. These mats remained intact over winter and new growth was observed along the margins in April 2007. Mats ranged in thickness from 0.2 to 1.2 m and we estimated that one 100-m stretch of shoreline along the southern shore of Maumee Bay was covered with approximately 200 metric tons of L. wollei. Nearshore surveys conducted in July 2008 revealed greatest benthic L. wollei biomass (591 g/m² ± 361 g/m² fresh weight) in Maumee Bay at depth contours between 1.5 and 3.5 m corresponding to benthic irradiance of approximately 4.0–0.05% of surface irradiance and sand/crushed dreissenid mussel shell-type substrate. A shoreline survey indicated a generally decreasing prevalence of shoreline L. wollei mats with distance from Maumee Bay. Surveys of nearshore benthic areas outside of Maumee Bay revealed substantial L. wollei beds north along the Michigan shoreline, but very little L wollei growth to the east along the Ohio shoreline.     

Trace Metal Mineral Equilibria in Lake Erie Sediments

The thermodynamic tendency of metal phosphate and carbonate mineral phases to precipitate in Lake Erie sediments has been calculated by means of an ion-pair model of the interstitial water chemistry. The calculations suggest that detrital calcite, aragonite, and dolomite should be dissolving in the sediments, but that iron and manganese carbonates should be precipitating. Regenerated phosphate should be reacting with calcium, iron, manganese, and lead to form authigenic mineral phases and be removed from solution. Whitlockite, Ca₃(PO₄)₂, and not hydrozylapatite, Ca₅(PO₄)₃OH, is the predicted primary controlling phase for phosphate, although apatites are supersaturated and may be precipitating. Zinc and cadmium are apparently controlled by other mechanisms, perhaps as sulfide phases, mixed mineral phases, adsorption, and/or ion exchange equilibria.     

Blueback Herring (Alosa aestivalis) in Lake Ontario: First Record,Entry Route,and Colonization Potential

Two juvenile blueback herring (Alosa aestivalis) were caught in Lake Ontario in October 1995, the first record of this anadromous marine clupeid in the Great Lakes. Blueback herring most likely gained entry to Lake Ontario via the Erie Barge Canal, a navigation canal that links the Mohawk-Hudson rivers, which drain to the Atlantic Ocean, to Oneida Lake, which drains to Lake Ontario through the Oneida-Oswego rivers. Blueback herring ascend the Hudson River to spawn and were first reported from the upper Mohawk River in 1978. They currently spawn in several of the upper Mohawk's tributaries, including one about 430 km from the ocean but only 25 km from Oneida Lake. They were first found in Oneida Lake in 1982 and, in fall 1994, large numbers of juvenile blueback herring were found moving down the Oswego River. In the southern United States, blueback herring established self-reproducing populations in several reservoirs, and thus they have the potential to colonize Lake Ontario. If blueback herring become established in Lake Ontario, they could spread to other Great Lakes and impede recovery of depressed populations of indigenous fishes, like lake herring (Coregonus artedi) and lake trout (Salvelinus namaycush), through competition with, or predation on, their larvae.     

The Entrainment and Deposition of Fine-Grained Sediments in Lake Erie

A series of entrainment and deposition experiments was performed with the general purpose of increasing our understanding of the parameters on which entrainment and deposition depend and the specific purpose of obtaining entrainment rates for a variety of sediments from the western basin of Lake Erie. The experiments were performed in an annular flume. A rotating top produced a turbulent flow which in turn exerted a turbulent shear stress on the sediments deposited on the bottom of the flume. Four different sediments from the western basin of Lake Erie were analyzed. Large variations in entrainment and deposition rates occurred and are shown to be dependent on the shear stress, water content (time after deposition), the type of sediment (grain size and mineralogy), and the manner of deposition. In the interpretation of the experiments, it is necessary to consider the frequency distribution of sediment properties as well as the average properties.     

Lake Whitefish Relative Abundance,Length-at-Age,and Condition in Lake Michigan as Indicated by Fishery-independent Surveys

In the mid 1990s, growth and condition of lake whitefish (Coregonus clupeaformis) declined within commercial catches in Lake Michigan. However, underlying mechanisms responsible for the declines have not been thoroughly explored. Using fishery-independent survey data, we examined growth and relative abundance of adult whitefish over historical (1980–1990) and recent (1996–2005) time periods in three regions of Lake Michigan: north, mid, and south. Relative abundance was assessed from catch-per-unit-effort (CPUE) of independent surveys, and changes in growth conditions were evaluated using size-at-age estimates. Relative abundance increased in the mid and south regions between the two time periods and decreased in the north region. Length-at-age significantly declined between the two time periods in the north, mid, and south regions; the north region consistently had the lowest length-at-age. Condition also declined between the two time periods in each region. The decline in growth and condition coupled with increases in relative abundance suggest density-dependent mechanisms are contributing to the observed population changes in the south region. The north region does not appear to be regulated by density, suggesting density-independent mechanisms, such as food web changes, are influencing stocks. Changes in the mid region are likely from a mixture of increased lake whitefish abundance and food web changes. Using fishery-independent population data, our results suggest that multiple factors are potentially contributing differentially within three Lake Michigan regions to cause similar declines in length-at-age and condition of whitefish. These factors (e.g., food web changes, lake whitefish density) should be considered when managing the commercial fishery.     

Seasonal Variation of Nutrient Limitation in Western Lake Erie

Monthly nutrient enrichment experiments were performed from April through October, 1983, to identify growth limiting nutrients of natural phytoplankton assemblages collected from a station in the Pigeon Bay waters off the north shore of Lake Erie's western basin. Data from these experiments suggest that silica was the major limiting nutrient in April, phosphorus was the major limiting nutrient in May-September, and trace metals were limiting in October. These results show that nutrient enrichment experiments should be performed often enough to account for seasonal changes in the physicochemical environment as well as seasonal succession in phytoplankton. The conclusion that phosphorus was the major limiting nutrient in summer is different from the conclusions of the late 1960s and early 1970s that nitrogen was the major limiting nutrient in the summer in the western basin and suggests a possible shift from nitrogen to phosphorus limitation. Pigeon Bay nutrient trend data show that summer nitrate:soluble reactive phosphorus ratios have increased from approximately 4 in the late 1960s to over 40 in the late 1970s and early 1980s, corroborating that a shift has probably occurred. This shift in nutrient limitation is probably due to reduced bioavailable phosphorus loadings and increased nitrate loadings to the western basin. The southern portion of the western basin is physicochemically different from the northern portion and may not have responded in the same manner.