Lake Erie Oxygen Depletion Controversy

A summary of a special workshop held at the Canada Centre for Inland Waters, Burlington, Ontario, 2–3 December 1981, is presented. The purpose of the workshop was to air some differences of opinion regarding the response of the hypolimnetic anoxia of Lake Erie to phosphorus controls. The workshop confirmed the validity of the 1978 U.S.-Canadian Great Lakes Water Quality Agreement's goals on restoring year-round aerobic conditions in the hypolimnion of the central basin of Lake Erie through phosphorus loading reduction. The author served as workshop chairman and convenor.     

Oxygen Depletion in Lake Erie: Modeling the Physical,Chemical, and Biological Interactions, 1972 and 1979

Models of the thermal structure, transport, and oxygen uptake within the water column and sediment are combined to examine the interaction of physical and biochemical processes resulting in oxygen depletion in the central basin hypolimnion of Lake Erie. While the oxygen demand in water and sediment may vary slightly from year to year, the oxygen supply to the hypolimnion due to physical processes is quite variable. Detailed calculations show that in years with relatively calm weather (e.g., 1979), physical processes supply only about 10% of the amount needed to offset demand due to uptake in the water and sediment during stratified periods. As the hypolimnion also tends to be relatively shallow in such years, the available oxygen is often quickly depleted. In contrast, during windy years (e.g., 1972) physical sources can supply about 40% of the oxygen consumed and, since the hypolimnion tends to be thicker, the oxygen concentration seldom reaches the anoxic level. It is concluded that analysis with oxygen depletion as an indicator of Lake Erie's recovery due to phosphorus control must consider variability in oxygen sources as a result of physical processes.     

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.     

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.     

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.     

Modeling Dissolved Oxygen in a Dredged Lake Erie Tributary

A two-dimensional numerical model was developed to study dissolved oxygen (DO) kinetics in a dredged Lake Erie tributary. The model design was aimed to specifically address the fact that many tributaries to the Great Lakes are dredged periodically for navigation, and that resultant changes in morphology and hydraulics can have significant impacts on DO. Due to the greater depths caused by dredging, river velocities slow considerably and vertical mixing is not as effective, leading to thermal stratification and potential short-circuiting of warmer upstream flow. The model solves the two-dimensional (laterally averaged) hydrodynamic and mass balance equations to simulate transport and transformation relevant to dissolved oxygen using an alternating direction, implicit finite difference method. Effects of oxygen-demanding pollutants from municipal and industrial discharges and also from nonpoint sources are included. A model application was developed for the Black River (Ohio), a tributary of Lake Erie. The river is dredged periodically, becomes stratified during the low flow summer months, and is affected by changing lake levels associated with seiching in Lake Erie. After calibration and confirmation, the model was used as a diagnostic tool to understand the impact of various loading sources on low DO levels observed along the bottom of the river. It is shown that sediment oxygen demand (SOD), combined with the river hydraulics, is the primary cause for low DO levels in the Black River.     

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.     

Oxygen use by nitrification in the hypolimnion and sediments of Lake Erie

Nitrification is an oxygen consumptive process, consuming 2 mol of oxygen per mol of ammonium oxidized. Hypolimnion and sediment samples were collected during the summers of 2008–2010 in Lake Erie to determine the total oxygen consumption and oxygen consumption from nitrification by blocking nitrification with selective inhibitors. Oxygen consumption by nitrification in the hypolimnion was 3.7 ± 2.9 (mean ± 1 SD) μmol O₂/L/d, with nitrification accounting for 32.6 ± 22.1% of the total oxygen consumption. Nitrification in the hypolimnion contributed more to oxygen consumption in the eastern sites than western sites and was lowest in September. The nitrification rate did not correlate with environmental factors such as oxygen, nitrate or ammonium, or nitrifier numbers. Oxygen consumption by nitrification in sediment slurries was 7.1 ± 5.8 μmol O₂/g/d, with nitrification accounting for 27.0 ± 19.2% of the total oxygen consumption with the lowest rates in July and the lowest percentages in June. Oxygen consumption by nitrification in intact sediment cores was 682 ± 61.1 μmol O₂/m/d with nitrification accounting for 30.4 ± 10.7% of the total oxygen consumption. Nitrification rates in intact cores were generally highest in September. The proportion of oxygen consumed by nitrification corresponds closely with what would be predicted from complete oxidation of a Redfield molecule (23%). While nitrification is unlikely to be the dominant oxygen consumptive process, the rates observed in Lake Erie were sufficient to theoretically deplete a large portion of the hypolimnetic oxygen pool during the stratified period.     

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.     

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.     

Relationships Between Bacterial Populations and Oxygen Levels in the Central Basin of Lake Erie

Studies were made to ascertain the relationships between bacteria and particulate organic carbon, particulate nitrogen, and the depletion of oxygen from the hypolimnetic waters of the central basin of Lake Erie. Heterotrophic bacterial populations, dissolved oxygen, particulate organic carbon, and total particulate nitrogen were determined during May, August, and September. Data indicate 1) a relationship between heterotroph populations and dissolved oxygen; 2) epilimnion oxygen concentrations of 9 mg/L were associated with bacterial levels of ?4 × 10³ colonies per mL; 3) bacterial densities started to increase from the thermocline downward; 4) hypolimnion oxygen levels of ?l mg/L were associated with bacterial densities of approximately three times the epilimnion values; 5) bacterial oxygen uptake rate in the hypolimnion varied from 1.5 to 7.4 × 10^?10 mg/L/hr; 6) particulate organic carbon and bacteria showed similar distribution patterns in the water column; 7) particulate nitrogen remained unchanged at 0.1 mg/L in the water column showing no relationship to the other parameters measured.     

Sediment Resuspension and Currents in Lake Manitoba

The physical resuspension of bottom sediment during periods of high winds is thought to be important for nutrient recycling in large shallow lakes. In order to study resuspension, prototype instrumentation designed to collect gram quantities of suspended sediment at 38.1-cm intervals in the water column was deployed in 4.2 m of water in the shallow southern basin of Lake Manitoba for 1-month periods in 1978 and 1981. At about 2.7 m depth a sharp discontinuity was observed in the vertical distribution of total mass of suspended sediment collected. The mean current speed varied linearly with depth above the discontinuity but was more uniform near bottom. Although the water column was not thermally stratified, drogues frequently displayed a two-layer structure in the currents with a high skew in direction between layers. The particle size distributions were similarly discontinuous in the vertical, with large quantities of sand in the upper layer samples and a high silt load in the lower. The unusual particle size distribution, which was explained in terms of the origin of resuspended sediments and subsequent transport by lake currents, suggests a decoupling of lake turbulence between the two layers during high winds.     

Lake whitefish (Coregonus clupeaformis) energy and nutrient partitioning in lakes Michigan,Erie and Superior

A concurrent decrease in lake whitefish (Coregonus clupeaformis) condition and Diporeia spp. abundance in Lake Michigan has spurred investigations into possible links between the two phenomena. We examined female lake whitefish δ¹³C and δ¹⁵N stable isotopes, growth, reproductive investment, dorsal muscle total lipid and docosahexaenoic acid (DHA) contents from lakes Erie, Michigan and Superior to determine whether differences in food source were correlated with measures of stock success. Stocks with higher somatic growth rates and mean reproductive potential had higher energy stores in terms of percent total lipid. Stocks with low muscle lipid concentration also had smaller egg sizes as egg number increased. Diet varied among stocks as evidenced by δ¹³C and δ¹⁵N stable isotope analyses; however, muscle total lipid and DHA were not correlated to apparent Diporeia spp. prey use. When compared to stocks from lakes Erie and Superior, Lake Michigan stocks had lower growth, reproduction, and lipid stores. While stocks in Lake Michigan with access to declining Diporeia spp. populations may still feed on the amphipod, it appears that they are unable to consume the quantities necessary to maintain historical growth and reproduction. Stable isotope analyses of lakes Erie and Superior stocks, with higher growth rates and lipid values, indicated different feeding strategies with no indication of reliance on Diporeia spp. While differences in prey resources may have an effect on lake whitefish stocks, differences in Diporeia spp. abundance alone cannot explain differences in lake whitefish condition observed among the Great Lakes included in this study.     

Diffuse (Non-Point) Source Loading of Chemicals to Lake Erie

Studies of chemical loadings to Lake Erie over the last two decades show that the lake, because of its small volume to drainage area ratio, and the intensive agricultural, industrial, and urban land uses of its watersheds, has been a receptor of a myriad of natural and anthropogenic chemicals. Of these, phosphorus, trace metals, PCBs and other organics and pesticides have received the most attention. Phosphorus reduction plans already in place have produced dramatic decreases in point-source P loadings and observable improvements in lake water quality. Target P loads for complete lake restoration will not be met, however, until substantial reductions of agricultural non-point sources are obtained, and gains in this area are likely to be much slower and more difficult to attain. Source reductions of trace metals and the older chlorinated insecticides have produced some decreases in diffuse loadings of these chemicals although their biomagnification in lake biota means that their impact on the lake will continue for many years. Today, the emphasis has shifted to a broader range of anthropogenic organic chemicals including highly mobile herbicides which have been shown to contaminate Lake Erie basin drinking water supplies, and to easily biomagnified toxics which, with relatively small loadings, can have a major impact on higher species.     

Evidence of lake trout (Salvelinus namaycush) natural reproduction in Lake Erie

Native lake trout were extirpated from Lake Erie around 1965 and committed restoration efforts began in 1982. In 2021 and 2022, a total of six lake trout (Salvelinus namaycush) in the free embryo or post-embryo life stage were captured in lake trout embryo traps in Lake Erie offshore of Shorehaven Reef, NY. This represents the first conclusive evidence of successful natural reproduction since extirpation. Trapping locations were identified using the results of a fine-scale positioning acoustic telemetry array, visual observations of adult lake trout exhibiting spawning behavior, and underwater cameras to visually identify possible spawning locations. Lake trout utilized a very specific spawning habitat type—the eastern side of shallow offshore humps in 5–8 m of water. These sites were comprised of habitat typically associated with lake trout spawning with slopes of 5–14° and clean rubble-cobble sized rock with visible interstitial spaces. Genetic barcoding was used to identify the post-embryo stage salmonids to species, and microsatellite genotypes assigned strongly to the Seneca strain which comprises the majority of the adult population. These findings represent a significant milestone for lake trout rehabilitation efforts in Lake Erie, confirming that successful reproduction to the post-embryo stage is possible and supporting continued rehabilitation efforts by Lake Erie management agencies.     

Occurrence of the Deepwater Sculpin (Myoxocephalus thompsoni) in Western Lake Erie

Reported here is the collection of two specimens of deepwater sculpin (Myoxocephalus thompsoni) from Ohio waters of western Lake Erie in 1995. Both specimens were collected while sampling for pelagic walleye (Stizostedion vitreum) larvae. A 15.0-mm TL deepwater sculpin larva was collected over Toussaint Reef on 29 April 1995 and a 17.0-mm TL juvenile was collected west of South Bass Island State Park on 12 May 1995. It appears that there are no references to collections of deepwater sculpins from western Lake Erie in the literature or from communications with local management agency personnel. While these young deepwater sculpin may have come from ballast water or from a reproducing population in Lake Erie, the collection of 21 deepwater sculpin (12 to 19 mm TL) in the St. Clair River in May 1990 provides evidence of downstream transport from Lake Huron where indigenous populations exist.     

The Value of Steelhead (Onchorhynchus mykiss) Angling in Lake Erie Tributaries

Steelhead (Onchorhynchus mykiss) have been stocked in Ohio tributaries to Lake Erie for over a decade yet little information on the value of this fishery exists. A steelhead angler intercept survey was conducted in fall, winter, and spring of 2002–2003. Almost 77% of the anglers surveyed (375) responded to a mail survey with useful information. Typical steelhead anglers were 46 years old, middle class, male, and had 9 years steelhead angling experience. Less than two-thirds of respondents fished with spinning tackle and one-third used fly tackle. On average, individuals traveled with 1.7 people in their group. They mostly took single day trips (94% of respondents), traveling approximately 84 kilometers round trip. Steelhead catch rates are positively related to number of trips taken, angler experience, number of streams visited per trip, number of hours fished per trip, and type of tackle used. The value of the steelhead angling experience to participating anglers is estimated at $36 to $46 per trip while the money spent to participate in steelhead fishing is estimated at $26 per trip. Annual value of the Lake Erie tributary steelhead fishery in Ohio could be as high as $12 to $14 million compared to the $600,000 cost for the stocking program. The fishery provides economic benefits to the coastal areas where adequate access for stream steelhead anglers exists during parts of the year when recreational demand is lowest. This information can be used by policy makers to justify expenditures on stocking, public access, and water quality improvements that enhance angling.     

Summer Food Habits of Pumpkinseeds (Lepomis gibbosus) and Bluegills (Lepomis macrochirus) in Presque Isle Bay,Lake Erie

Zebra mussels (Dreissena polymorpha) and quagga mussels (D. bugensis) have received much attention since they were first reported in the Great Lakes. Predation by fishes may be an important factor in regulating dreissenid populations, but the extent to which fish prey on them is not entirely clear. Pumpkinseeds (Lepomis gibbosus) are known to be effective predators of mollusks, but bluegills (Lepomis macrochirus) do not generally prey heavily on mollusks. Analysis of stomach contents of pumpkinseeds and bluegills collected from Presque Isle Bay of Lake Erie (Erie, Pennsylvania) revealed considerable differences in the diets of the two species. Specifically, dreissenids were the most important food item in the diet of pumpkinseeds and composed 63% of the volume of their diet. In contrast, dreissenids were relatively unimportant in the diet of bluegills and composed only 2.3% of the volume of their diet. Although bluegills and pumpkinseeds differed considerably in their consumption of dreissenids and other prey items, no clear differences in PCB concentrations were detected between the two species. Thus bluegills must acquire most of their PCBs from prey other than dreissenids.     

Lake Erie Nutrient Loads, 1970–1980

The Buffalo District, Corps of Engineers’ Lake Erie Wastewater Management Study and Heidelberg College's Water Quality Laboratory supported a tributary water quality monitoring program from 1974 to 1980 of the major United States tributaries to Lake Erie. This program was designed to measure nutrient loads by monitoring concentration changes occurring in association with increased streamflow. Soluble orthophosphate loads, chloride loads, and silica loads decreased from 1970 to 1980. Nitrogen species were highly variable and increased over the period. Total phosphorus loads to Lake Erie have decreased during the period as a result of phosphorus removal at wastewater treatment plants. The effect of the phosphorus reductions can be seen in the lake concentrations and were predicted by a three-basin phosphorus budget model developed in the early 1970s. The results show that phosphorus removal programs are having the predicted effect on Lake Erie water quality.     

Status,causes and controls of cyanobacterial blooms in Lake Erie

The Laurentian Great Lakes are among the most prominent sources of fresh water in the world. Lake Erie's infamous cyanobacterial blooms have, however, threatened the health of this valuable freshwater resource for decades. Toxic blooms dominated by the cyanobacterium Microcystis aeruginosa have most recently been one of primary ecological concerns for the lake. These toxic blooms impact the availability of potable water, as well as public health and revenues from the tourism and fishery industries. The socioeconomic effects of these blooms have spurred research efforts to pinpoint factors that drive bloom events. Despite decades of research and mitigation efforts, these blooms have expanded both in size and duration in recent years. However, through continued joint efforts between the Canadian and United States governments, scientists, and environmental managers, identification of the factors that drive bloom events is within reach. This review provides a summary of historical and contemporary research efforts in the realm of Lake Erie's harmful cyanobacterial blooms, both in terms of experimental and management achievements and insufficiencies, as well as future directions on the horizon for the lake's research community.