Surficial Sediment Contamination in Lakes Erie and Ontario: A Comparative Analysis

Sediment surveys were conducted in Lakes Erie and Ontario to characterize spatial trends in contamination, to assist in elucidation of possible sources of contamination, and for identification of areas where contamination exceeded Canadian sediment quality guidelines for protection of aquatic biota. Sediment levels of metals including nickel, lead, zinc, chromium, and copper were compared to pre-colonial concentrations, and sediment enrichment factors, defined as the ratio of surficial concentrations to background concentrations determined from benthos cores, were calculated. Sediments in Lake Ontario exhibited elevated contamination compared to Lake Erie. The average enrichment factor for Lake Ontario (2.6) was comparable to the western basin in Lake Erie but greater than those for the central (1.3) and eastern (1.0) basins. There was a gradient toward decreasing sediment contamination from the western basin to the eastern basin of Lake Erie, and from the southern to the northern area of the central basin. Sediment contamination in Lake Ontario was similarly distributed across the three major depositional basins. The spatial distribution of metals was similar to those of other contaminants including mercury, polychlorinated biphenyls (PCBs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs). Lake-wide averages of sediment mercury, PCBs and PCDDs/PCDFs in Lake Erie were 0.185 μg/g, 96.5 ng/g, and 18.8 pg/g TEQs, respectively. Lake-wide averages of sediment mercury, PCBs and PCDDs/PCDFs in Lake Ontario were 0.586 μg/g, 100 ng/g, and 101 pg/g TEQs, respectively.     

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.     

Analysis of Models and Measurements for Sediment Oxygen Demand in Lake Erie

In situ measurements of water column oxygen consumption and sediment oxygen demand (SOD) in the central basin of Lake Erie are historically 50% to 100% larger than observed from decreases in stocks of dissolved oxygen. Recent statistical and modeling analyses of observed oxygen data, and in situ measurements of SOD using a dome with gentle mixing, suggest consistent values for SOD of 0.2 to 0.3 g/m²/d. These values are lower than historical estimates. Three SOD models applicable to Lake Erie are examined. One (Walker) describes SOD as a function of oxygen concentration, and of biological and chemical components. The second (Klapwijk) describes SOD as a function of carbonaceous oxidation, nitrification, denitrification, and ammonia produced by diffusion and in the aerobic, anoxic, and anaerobic zones of the sediments. The third (DiToro) describes SOD as a function of settling fluxes of algae and organics from the water column, and assumes that all anaerobically produced carbon is oxidized in the sediments. It is suggested that aspects of the latter two models are required for future modeling of SOD in Lake Erie. More measurements of sediment profiles of POC are required to resolve certain modeling questions.     

Sediment Oxygen Demand in the Central Basin of Lake Erie

Three separate procedures were used to estimate the sediment oxygen demand (SOD) in the central basin of Lake Erie and were compared with other estimates determined previously and with historical data. First, whole core incubations involved sealing sediment cores at 12°C to ensure no interaction between the overlying water and the atmosphere and monitoring continuously to define the linear disappearance of oxygen. Second, sediment plugs were placed inside flow-through reactors and the influent and effluent concentrations were monitored to obtain steady-state reaction rates. Third, an extensive data set for the central basin of Lake Erie was compiled for input into the diagenetic BRNS model, and the SOD was calculated assuming all primary redox reactions, but no secondary reactions. All three procedures produced estimates of SOD that were in reasonable agreement with each other. Whole core incubations yield an average SOD of 7.40 × 10⁻¹² moles/cm²/sec, the flow-through experiments had an average SOD of 4.04 × 10⁻¹² moles/cm²/sec, and the BRNS model predicts an SOD of 7.87 × 10⁻¹² moles/cm²/sec over the top 10 cm of sediment and appears to be calibrated reasonably well to the conditions of the central basin of Lake Erie. These values compare reasonably well with the 8.29 × 10⁻¹² moles/cm²/sec obtained from diffusion modeling of oxygen profiles (Matisoff and Neeson 2005). In contrast, values reported from the 1960s to 1980s ranged from 10.5–32.1 × 10⁻¹² moles/cm²/sec suggesting that the SOD of the central basin has decreased over the last 35 years, presumably, in response to the decrease in phosphorus loadings to Lake Erie. However, since hypoxia in the hypolimnion persists these results suggest that improvement in hypolimnetic oxygen concentrations may lag decreases in loadings or that the hypolimnion in the central basin of Lake Erie is simply too thin to avoid summer hypoxia during most years.     

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.     

Oligochaete Fauna of Western Lake Erie 1961 and 1982: Signs of Sediment Quality Recovery

The oligochaete fauna at 40 stations in western Lake Erie were collected in 1982 and compared to oligochaete fauna collected similarly in 1961. A total of 34 taxa, representing 18 Tubificidae and 16 Naididae, were identified. Changes in the proportions of low, moderate, and heavy polluted sediments, as determined by ranges of total numbers of oligochaetes, indicate that, in general, heavy pollution substantially decreased near shore and moderate pollution increased and low pollution decreased in open waters over the 21-year comparison. The most common taxon, the eutrophic species, Limnodrilus hoffmeisteri, decreased in abundance in open water, indicating decreased eutrophication, whereas the distribution and abundance of other indicator taxa, including the eutrophic species L. maumeensis, L. cervix, Quistadrilus multisetosus multisetosus, and mesotrophic species Ilyodrilus templetoni and three species of Aulodrilus indicate increased eutrophication in open water. In general, oligochaete trophic indices (based on tubificid species and abundances) in traditional area designations used in 1961, the nearshore designation (<3.5 km from shore), and areas defined by cluster analysis confirm results of less eutrophic substrates near shore. However, traditional analysis indicates that low pollution was replaced by moderate pollution in open waters and cluster analysis indicates that the zone of least detectable pollution increased in open waters over the 21-year comparison. It may be that the open waters of western Lake Erie were in a stage of transition between pollution designations when sampled in 1982. The present study is valuable because it provides a baseline to assess environmental changes observed in western Lake Erie after many years of pollution abatement programs and before the exponential increase in densities of the trophic shifting zebra mussel Dreissena polymorpha.     

Observations of Sediment Transport in Lake Erie during the Winter of 2004–2005

Time series measurements of current velocity, wave action, and water transparency were made at two sites—one in 24 m of water and the other in 53 m—in Lake Erie during the fall and winter of 2004–2005. The observations at the shallow site show that bottom resuspension occurred several times during the deployment. Although local resuspension did not occur at the deeper station, several advection episodes were observed. The storms during the observation period were not unusually large, so the processes observed are probably typical of those that occur on a yearly basis. The observations agree reasonably well with previous estimates for both the bottom shear stress during storms, and for the critical shear stress needed to resuspend bottom sediment, but previous estimates of the particle settling velocity are probably too low, while previous estimates of the sediment entrainment rate are too high. The results show that bottom material in the central basin is reworked numerous times before it is finally buried. Deposition in the eastern basin is a more continuous process, but the events observed were not sufficient to match the long-term accumulation rate, so deposition at this site is probably also due in part to larger, more infrequent storms.     

Overview of USEPA/CLEAR Lake Erie Sediment Oxygen Demand Investigations During 1979

In situ hypolimnetic oxygen depletion measurements were conducted during four summer cruises in 1979 at two central basin stations in Lake Erie to evaluate the relative contribution of the sediments to the oxygen demand. Sediment oxygen demand (SOD) rates were determined by measuring the rate of oxygen decrease within a triangular benthic chamber; water column oxygen demand (WOD) rates were determined using 24-hour light and dark bottles placed in situ. Results indicated that the SOD contribution to the hypolimnetic oxygen depletion rate decreased throughout the summer from about 81% to only 30% with an initially high rate due to spring algal biomass sedimentation and lower rates in late summer due to depressed oxygen levels. The WOD rate contribution increased from 19% to 70% throughout the stratified period due to the decomposition of settling algal cells. Comparing the overall volumetric summer in situ rates (0.126 mg O₂/L/day) with cruise-interval depletion rates (0.365 mg O₂/L/day), the in situ rates were about 300% higher. This is attributed to unaccounted oxygen sources to the hypolimnion and because the in situ rates measure the gross WOD and SOD rather than measuring the net effects they exert.     

Values of Sediment Oxygen Demand Measured in the Central Basin of Lake Erie, 1979

The results of sediment oxygen demand (SOD) measurements for the central basin of Lake Erie, 1979, are presented. Two chambers were used. One, a triangular chamber, has a mixing velocity of 5 cm/sand gives values for SOD of 0.86 ± 0.42 gm²/d (n = 52). The second chamber, a hemispherical dome with gentle mixing, gives values of 0.32 ± 0.11 g/m²/d (n = 13). There are no significant differences in measured values between two stations, located 50 km apart, when measurements from the same chamber design are compared. There are no measurable effects of photosynthesis when daytime values are compared with nighttime values or when light and dark chambers are compared. A comparison of these two SOD values with rates observed for hypolimnetic oxygen decline in the water column shown that the value measured by the dome (0.32 gm/m²/d) is the most plausible value. It is hypothesized that the fluid mechanics of the triangular chamber do not properly emulate the hydrodynamics of the lake, causing the higher values.     

Spatial Distributions and Temporal Trends in Sediment Contamination in Lake St. Clair

The sediments of Lake St. Clair were surveyed in 2001 for a range of compound classes including metals (such as total mercury and lead), polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, organochlorine pesticides, polycyclic aromatic hydrocarbons, and short- and medium- chain chlorinated paraffins, in order to evaluate the spatial distribution and temporal trends of contamination. Concentrations of contaminants were generally low compared to the lower Great Lakes (Erie and Ontario), and were typically below the Canadian Sediment Quality Probable Effect Level (PEL) guidelines. The only exceptions were for mercury and DDE, where concentrations exceeded their respective PEL at one of the thirty-four sites sampled. With the exception of mercury, it was difficult to interpret spatial trends in contaminant concentrations due to these low levels, although relatively elevated concentrations of several contaminants were found in L’Anse Creuse Bay and at the outflow of the Thames River. In the case of mercury, historically-contaminated sediments in the St. Clair River associated with chlor-alkali production appeared to contribute to loadings to Lake St. Clair. There have been substantial reductions in sediment contamination in Lake St. Clair over the past three decades, as determined through sediment core profiles as well as through comparison of current data to those from historical surveys conducted in the early 1970s. These results indicate that management actions to reduce contaminant loadings to Lake St. Clair have been generally successful.     

Sediment Loading During the 20th Century in Presque Isle Bay,Lake Erie,Pennsylvania

Mud-dominated sediments in Presque Isle Bay are contaminated with metals and hydrocarbons derived from developed watershed and atmospheric sources. Prior to this study, the quantities, rates, and spatial distribution of long-term sedimentation and erosion in the bay were largely unknown. As a result, the fate of contaminated bay-floor sediments and possible rates of natural recovery for this Area of Concern (AOC) could not be determined. To provide baseline data useful to state and federal agencies monitoring recovery of the bay, this paper identifies: (1) the quantities, rates and patterns of 20^th Century sedimentation and erosion, (2) the major sediment inputs and outputs for the bay, and (3) the implications of the sedimentary regime on possible future rates of bay recovery. Bathymetric and sedimentological data show that 20th Century net accumulation totaled approximately 3.94 × 10⁶ m³ which is equivalent to a dry sediment loading of 5.92 × 10⁹ kg (5.92 × 10⁶ t), or 6.29 kg/m²/yr (1.28 lb/ft²/yr) when averaged over the accretional 70% of the bay. This external loading represents approximately 50% of total accretion because externally derived sediments are augmented with resuspended sediments from shallow-water parts of the bay. The principal sediment inputs were littoral drift from ephemeral and permanent inlets (∼42%), artificial infilling along the shoreline (∼28%), streams (∼16%), bank/bluff erosion (∼12%), and biological production (∼2%). Dredging was the principal output. Based on long-term average sedimentation rates and patterns, recovery of the AOC through natural sediment capping will take at least several decades if source contaminants are removed.     

Sediment Mixing by Lampsilis Radiata Siliquoidea (Mollusca) from Western Lake Erie

The sediment reworking activities of an abundant Lake Erie unionid bivalve, Lampsilis radiata siliquoidea, have been studied by field observations and laboratory experiments. Unionid burrowing in laboratory microcosms increased sediment water content 10-20%, decreased water content variability, homogenized sedimentary structures, and increased tenfold the volume of oxidized sediment over that in microcosms with no unionids. Incomplete mixing of sediment took place to a depth of 10 cm during burrowing by L. r. siliquoidea. Burrowing by other unionids may extend the depth of maximum reworking to 20 cm. Unionid burrowing, feeding, and respiratory activities may alter the profiles of various elements and radionuclides associated with sediment particles and alter the location and intensity of microbial activity in sediments.     

History of Lake Ontario Contamination from the Niagara River by Sediment Radiodating and Chlorinated Hydrocarbon Analysis

Contamination of Lake Ontario by persistent organic compounds began with the development of the chemical industry along the Niagara River. These compounds are discharged to the river where they are scavenged from the water column by sedimenting particulates which in turn settle out in depositional areas of Lake Ontario. We have determined ²¹⁰Pb, ¹³⁷Cs, and chlorinated hydrocarbon profiles of sediment cores taken about 3 km from the mouth of the Niagara River. Age profiles of the sediments were constructed from the radionuclide measurements and used to determine historic trends of chlorinated hydrocarbon input to Lake Ontario. The historical record found in the sediments for chlorobenzenes, chlorotoluenes, hexachlorobutadiene, octachlorostyrene, mirex, and PCBs is in good agreement with known production and usage patterns of the chemicals. Pollution of Lake Ontario with chlorinated hydrocarbons from the Niagara River is still occurring, but the worst contamination of the lake occurred in the 1960s.     

A hydrodynamic approach to modeling phosphorus distribution in Lake Erie

The purpose of this paper is to show how a high-resolution numerical circulation model of Lake Erie can be used to gain insight into the spatial and temporal variability of phosphorus (and by inference, other components of the lower food web) in the lake. The computer model simulates the detailed spatial and temporal distribution of total phosphorus in Lake Erie during 1994 based on tributary and atmospheric loading, hydrodynamic transport, and basin-dependent net apparent settling. Phosphorus loads to the lake in 1994 were relatively low, about 30% lower than the average loads for the past 30 years. Results of the model simulations are presented in terms of maps of 1) annually averaged phosphorus concentration, 2) temporal variability of phosphorus concentration, and 3) relative contribution of annual phosphorus load from specific tributaries. Model results illustrate that significant nearshore to offshore gradients occur in the vicinity of tributary mouths and their along-shore plumes. For instance, the annually averaged phosphorus concentration can vary by a factor of 10 from one end of the lake to the other. Phosphorus levels at some points in the lake can change by a factor of 10 in a matter of hours. Variance in phosphorus levels is up to 100 times higher near major tributary mouths than it is in offshore waters. The model is also used to estimate the spatial distribution of phosphorus variability and to produce maps of the relative contribution of individual tributaries to the annual average concentration at each point in the lake.     

A Post Audit of a Lake Erie Eutrophication Model

A post audit of a eutrophication-dissolved oxygen model of Lake Erie is presented. The model had been calibrated using data from 1970 and 1975. Projections were then made for use in establishing the IJC target loadings for phosphorus that would essentially eliminate the anoxia in the central basin. In the latter 1970s the phosphorus discharges to Lake Erie dropped substantially due to increased removal from point sources. The observed response of the lake to this change in loading is compared to the predicted response. A 10-year computation from 1970 to 1980 is made using measured lake loadings. Concentrations of total and dissolved phosphorus, nitrate, chlorophyll, dissolved oxygen, and anoxic area are compared to observations. Both agreements and deviations are examined. It is concluded that the IJC target loadings were reasonably accurate forecasts of the loadings required to achieve the goal of elimination of anoxia.     

Statistical Analysis of the 1975 Intercomparison Study on Lake Erie

An intercomparison experiment was carried out at two sampling stations on Lake Erie on June 10, 1975 by three laboratories that are conducting environmental monitoring programs on the lake. The laboratories simultaneously collected water samples from three sampling depths at each station. The samples were divided into thirds, one third to be analyzed by each of the laboratories using their standard procedures. A number of physical, chemical, and biological properties were determined from each of the water samples. One of the principal results of the statistical analyses is that significant differences exist for most of the properties under study due to which laboratory analyzed the samples. However, the effect due to which laboratory obtained the samples is much less important. These results are in direct agreement with results reported in 1974 by Robertson, Elder, and Davies, IFYGL Chemical Intercomparisons, Proc. 17th Conf. Great Lakes Research.     

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.     

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.     

Diatoms abound in ice-covered Lake Erie: An investigation of offshore winter limnology in Lake Erie over the period 2007 to 2010

The limnology of offshore Lake Erie during periods of extensive (> 70%) ice cover was examined from ship borne sampling efforts in 2007 to 2010, inclusive. Dense and discrete accumulations of the centric filamentous diatom Aulacoseria islandica (> 10 μg Chl-a/L) were located in the isothermal (< 1 °C) water column directly below the ice and only detectable in the ship wake; viable phytoplankton were also observed within ice. Evidence from these surveys supports the notions that winter blooms of diatoms occur annually prior to the onset of ice cover and that the phytoplankton from these blooms are maintained in the surface waters of Lake Erie and reduce silicate concentrations in the lake prior to spring. The mechanisms by which high phytoplankton biomass rise at this time of year requires further investigation, but these winter blooms probably have consequences for summer hypoxia and how the lake responds to climate change.