The effect of Lake Erie water level variations on sediment resuspension

Variability in Lake Erie water levels results in variations of the fluid forces applied to the lake bed by free-surface gravity wind-waves. An increase in the bed stress may re-suspend sediment deposited years earlier. This study identifies areas of possible non-cohesive sediment mobilization in response to the forcing conditions and water levels present in Lake Erie. Observations from NOAA buoy 45005 were used to identify wave events generated by a variety of atmospheric forcing conditions. For each event, numerical predictions of significant wave height, wave period, and water level from the Great Lakes Forecasting System (GLFS) were used to characterize the wave event variability over the lake. The Shields parameter was estimated at each 2 km × 2 km grid cell with the local wave forcing as predicted by GLFS assuming an estimate of the wave-induced friction factor. In the Cleveland harbor region of the central basin, the Shields parameter was also estimated by assuming uniform wave conditions as observed by NOAA buoy 45005. The “contour of incipient motion” for both variable and uniform wave events was defined as the offshore contour where the Shields parameter exceeds the critical limit for motion. Comparisons with a radiometrically corrected image from Landsat-7 showed that the spatially varying wave events from GLFS were in qualitative agreement with the satellite observations. A sensitivity analysis of wave height, wave period, and grain size showed the contour of incipient motion to be the most sensitive to wave period. Calculations performed for record high and low water levels showed that the incipient motion of non-cohesive sediments in the relatively flat central basin to be the most sensitive to the historic hydrologic variability present in Lake Erie.     

Beach sediment magnetism and sources: Lake Erie,Ontario, Canada

Measurements were made along the northwestern shore of Lake Erie, Canada to determine whether grain magnetic properties can be used to identify and distinguish sources of beach sediment. Although surface magnetic susceptibilities were highly variable, ranging from 56 to 9867 × 10⁻⁵ SI (Bartington MS2D), there was generally a gradual increase from the low beach (near the waterline) towards the high beach; there were also narrow, shore-parallel bands with high susceptibility at various points on the beach surface. Magnetic mineralogy on the beaches was dominated by low-Ti magnetite (570° < Tc < 580 °C), and the effective grain-size varied from pseudosingle domain in the low beach to multidomain on the high beach. Sandy bluff sediments in the eastern part of the study area had magnetic properties (e.g. S-ratios, hysteresis loops, thermomagnetic curves) that were similar to those on the beaches, whereas the magnetic properties of the extensive till bluffs and river basin sediments were quite different. The data suggested that, whereas the beaches in the western part of the study area are supplied with sediment from bluffs several tens of kilometres to the east, the source of the high magnetic concentrations on the eroding beaches of eastern Point Pelee remains to be determined.     

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.     

Variability of sedimentary phosphorus fractions in the western and Sandusky basins of Lake Erie

Surface sediments and three sediment cores from the western basin and one sediment core from the Sandusky basin were analyzed to document spatial and temporal changes in five phosphorus fractions and total phosphorus (TP). The areal distributions of the bioavailable fractions NaCl-Pi, NaBD-Pi, and NaOH-Pi and the refractory organic fraction Res-P were broadly consistent and contrasted with those of the detrital fraction HCl-Pi which showed that high concentrations occurred mostly in high-energy littoral zones and low concentrations largely in profundal depositional areas. The contrasting distributions were induced by interactions among tributary inputs, wave action, circulation, and biogeochemical cycling and transfer in the basin. As revealed by the Sandusky basin sediment record, the detrital fraction HCl-Pi was dominant (70% of TP) during European settlement and decreased rapidly by 28.0% in the early 1910s due largely to impoundments of the Maumee and Sandusky Rivers. While HCl-Pi has ever since remained relatively constant, NaCl-Pi, NaBD-Pi, and NaOH-Pi increased significantly between 1950 and 1970 in the two basins. However, the post-regulation sediment records differed considerably among these coring sites. There was a marked increase of TP in two cores, corresponding to recent return of eutrophication and massive harmful algal blooms but contrasting with a relatively constant, low loading into the lake. This signified the role of internal loading as derived partialy from legacy pollution. Furthermore, NaCl-Pi has increased progressively throughout all the records. We conclude that the increased levels of NaCl-Pi in surface sediments may have altered the internal loading and contributed to the resurgences of harmful algal blooms in Lake Erie.     

Factors influencing microplastic abundances in nearshore,tributary and beach sediments along the Ontario shoreline of Lake Erie

Sediment samples were collected from nearshore, tributary and beach environments within and surrounding the northern part of Lake Erie, Ontario to determine the concentrations and distribution of microplastics. Following density separation and microscopic analysis of 29 samples, a total of 1178 microplastic particles were identified. Thirteen nearshore samples contained 0–391 microplastic particles per kg dry weight sediment (kg^?1), whereas 4 tributary samples contained 10–462?kg^?1 and 12 beach samples contained 50–146?kg^?1. The highest concentrations of nearshore microplastics were from near the mouths of the Detroit River in the western basin and the Grand River in the eastern basin, reflecting an urban influence. The highest microplastic concentrations in beach samples were determined from Rondeau Beach in the central basin where geomorphology affects plastics concentration. The Welland Canal sample in the eastern basin contained the greatest concentration of microplastics of the tributary samples, which is consistent with high population density and shipping traffic. The overall abundance of microplastic in northern Lake Erie nearshore, tributary and beach samples is 6 times lower than in sediment sampled from northern Lake Ontario. The nearshore and beach sample results potentially reflect the transport patterns of floating plastics modeled for Lake Erie, which predict that the majority of plastic particles entering the lake are transported to southern shoreline regions rather than northern areas.     

Long-term dynamics of Lake Erie benthos: One lake,three distinct communities

Lake Erie has experienced multiple anthropogenic-driven changes in the past century, including cultural eutrophication, phosphorus abatement initiatives, and the introduction of invasive species. The benthos of Lake Erie has been studied infrequently over nine decades and can provide not only insights into the impact of environmental changes but can also be used to examine ecosystem recovery through time. We used multivariate analyses to examine temporal changes in community composition and to assess the major drivers of long-term changes in benthos. Eutrophication, water quality improvement, and dreissenid introduction were the major drivers of changes in benthos in the western basin, while hypoxia was a major factor in the central basin, and dreissenid introduction was most important in the eastern basin. Non-dreissenid community composition of the western basin has changed dramatically over 90 years from benthic species indicative of good water quality in the 1930s, with a diverse community dominated by Hexagenia, to one of low diversity dominated by oligochaetes and other pollution-tolerant species in the 1960s, followed by recovery in the early 2000s to a state similar to that reported in 1930. In contrast, the non-dreissenid benthic community of the central basin over 60 years was consistently dominated by low oxygen-tolerant taxa, signifying the persistence of hypoxia, the major community driver in this basin. The eastern basin community also changed dramatically, including the disappearance of Diporeia after the introduction of Dreissena in the 1990s and more recent declines in oligochaetes, amphipods, gastropods, sphaeriid clams, and leeches.     

Spatial patterns of bacterial community composition within Lake Erie sediments

Lake Erie is a large freshwater ecosystem with three distinct basins that exhibit an east-to-west gradient of increasing productivity, as well as allochthonous inputs of nutrients and xenobiotics. To evaluate microbial community composition throughout this ecosystem, 435 16S rDNA environmental clones were sequenced from 11 sediment samples throughout the Western, Central, and Eastern basins, as well as the hypoxic “dead zone” of Lake Erie in the hypolimnetic region of the Central basin. Rank abundance distributions of bacterial taxa within each location revealed that Gamma- and Betaproteobacteria, microbes capable of metabolizing a wide range of organic matter pools, comprised a greater fraction of the microbial community within inshore sites of the Central and Western basins compared to the Eastern basin. While geophysical characteristics of the three major basins and the dead zone did not drive significant differences in species diversity, Fast UniFrac analyses revealed microbial community spatial structuring, with the Central basin showing higher phylogenetic uniqueness of bacterial lineages. Principal component analyses based on phylogenetic distances consistently grouped the dead zone with the Central basin and highlighted the distinctiveness of microbial communities from the Eastern basin. Results from this study provide evidence for the local adaptation of microbial communities and the potential role of riverine inputs in modulating taxonomic composition of lacustrine bacterial communities. These results are consistent with previous functional studies on microbial metabolism, which showed that differences in geochemistry across the three basins of Lake Erie play an important role in the local adaptation of microbial communities.     

The relative importance of anammox and denitrification to total N2 production in Lake Erie

Production of dinitrogen gas via microbially mediated anaerobic ammonium oxidation (anammox) and denitrification plays an important role in removal of fixed N from aquatic ecosystems. Here, we investigated anammox and denitrification potentials via the ¹⁵N isotope pairing technique in the helium flushed bottom water (~0.2 m above the sediment) of Sandusky Bay, Sandusky Subbasin, and Central Basin in Lake Erie in three consecutive summers (2010?2012). Potential rates of anammox (0–922 nM/day) and denitrification (1 to 355 nM/day) varied greatly among sampling sites during the 3 years we studied. The relative importance of anammox to total N₂ production potentially ranged from 0 to 100% and varied temporally and spatially. Our study represents one of the first efforts to measure potential activities of both anammox and denitrification in the water column of Lake Erie and our results indicate the Central Basin of Lake Erie is a hot spot for N removal through anammox and denitrification activities. Further, our data indicate that the water column, specifically hypolimnion, and the surface sediment of the Lake Erie Central Basin are comparatively important for microbially mediated N removal.     

On hypoxia and fish kills along the north shore of Lake Erie

Hypoxia is a common feature in the offshore central basin of Lake Erie. In the late summer of 2012, a strong wind-induced upwelling event transported oxygen depleted water to the nearshore zones of northern Lake Erie. Wind speed, duration and direction relative to the shoreline of individual wind events determined the extent of nearshore zone affected by the hypoxic waters. The upwelling event resulted in adverse water quality along some stretches of the northern shoreline of Lake Erie with persistent anoxia, which was mainly responsible for the mortality of fish.     

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.     

Three-dimensional modeling of sediment resuspension in a large shallow lake

We simulated bottom resuspension events in Lake Erie, using a coupled three-dimensional hydrodynamic and water quality model. Key parameters in the model, including critical bottom shear stress (${\tau }_{\mathit{cr}}$) and resuspension rate (α) were calibrated and validated by comparing the model output to observations. These included total suspended solid (TSS) concentrations in the bottom boundary layer (RMSE = 0.74 $\text{mg}{\text{L}}^{\text{-1}}$) and water column (RMSE = 0.81 $\text{mg}{\text{L}}^{\text{-1}}$), and to time series of acoustic backscatter signal (R² > 0.8) and turbidity (R² ≈ 0.4) from long-term moorings near the lakebed in 2008–09 and 2013. Signals from phytoplankton, in spring and summer, caused discrepancies between modeled TSS and the observed turbidity data. Although common practice, we show that literature-based or field-observed critical shear stress should not be directly applied in large-scale Reynolds-averaged sediment model as this will likely underestimate resuspension. In agreement with the literature, the model reproduced more frequent and intensive surface-wave driven resuspension in the shallow regions (< ~20 m), particularly in the western basin, compared to the deeper central and eastern basins, where bottom stresses induced by mean currents (${\tau }_c$) were comparable with those due to surface waves (${\tau }_w$). However, on the north-shore of the eastern basin, ${\tau }_c$ often predominated over ${\tau }_w$. We simulated thermocline motion, including up- and down-welling events and swashing of the internal Poincaré wave, to contribute to ${\tau }_c$ in the central basin and form nepheloid layers.     

An ecosystem health assessment of the Detroit River and western Lake Erie

The Canada-U.S. State of the Strait Conference is a biennial forum with a 22-year history of assessing ecosystem status and providing advice to improve research, monitoring, and management of the Detroit River and western Lake Erie. The 2019 conference focused on assessing ecosystem health based on 61 indicators. Although there has been considerable improvement in the Detroit River since the 1960s, much additional cleanup is needed to restore ecosystem health. Western Lake Erie is now at risk of crossing several potential tipping points caused by the interactions of a variety of drivers and their stresses. This assessment identified eight environmental and natural resource challenges: climate change; population growth/transportation expansion/land use changes; chemicals of concern; human health/environmental justice; aquatic invasive species; habitat loss/degradation; nonpoint source pollution; and eutrophication/harmful algal blooms. Specific recommendations for addressing each challenge were also made. Climate change is the most pressing environmental challenge of our time and considered a “threat multiplier” whereby warmer, wetter, and more extreme climatic conditions amplify other threats such as poor air quality effects on vulnerable residents, species changes, and nonpoint source runoff and combined sewer overflow events that contribute to eutrophication and can manifest as harmful algal blooms. Our assessment found that investments in monitoring and evaluation are insufficient and that the region's intellectual and environmental capital is not being leveraged sufficiently to address current challenges. Continued investment in this transnational network is essential to support ecosystem-based management.     

Assessing and addressing the re-eutrophication of Lake Erie: Central basin hypoxia

Relieving phosphorus loading is a key management tool for controlling Lake Erie eutrophication. During the 1960s and 1970s, increased phosphorus inputs degraded water quality and reduced central basin hypolimnetic oxygen levels which, in turn, eliminated thermal habitat vital to cold-water organisms and contributed to the extirpation of important benthic macroinvertebrate prey species for fishes. In response to load reductions initiated in 1972, Lake Erie responded quickly with reduced water-column phosphorus concentrations, phytoplankton biomass, and bottom-water hypoxia (dissolved oxygen < 2 mg/l). Since the mid-1990s, cyanobacteria blooms increased and extensive hypoxia and benthic algae returned. We synthesize recent research leading to guidance for addressing this re-eutrophication, with particular emphasis on central basin hypoxia. We document recent trends in key eutrophication-related properties, assess their likely ecological impacts, and develop load response curves to guide revised hypoxia-based loading targets called for in the 2012 Great Lakes Water Quality Agreement. Reducing central basin hypoxic area to levels observed in the early 1990s (ca. 2000 km²) requires cutting total phosphorus loads by 46% from the 2003–2011 average or reducing dissolved reactive phosphorus loads by 78% from the 2005–2011 average. Reductions to these levels are also protective of fish habitat. We provide potential approaches for achieving those new loading targets, and suggest that recent load reduction recommendations focused on western basin cyanobacteria blooms may not be sufficient to reduce central basin hypoxia to 2000 km².     

The ecological history of Lake Erie as recorded by the phytoplankton community

Lake Erie's water quality has fluctuated since European settlement due to cultural eutrophication and the effects of invasive species. Our attempts to understand the cause-and-effect linkages between observed ecosystem changes and various stressors are evolving. Non-indigenous species, pollutants, land-use and climate change that can alter a lake's physical and chemical environment can manifest rapid changes in community composition and abundance of phytoplankton. As such, for many decades researchers have used phytoplankton data from Lake Erie to track environmental changes. We provide a chronological account of previous and ongoing assessments of pelagic algae to summarize past and present environmental conditions of Lake Erie. This review necessarily focuses on diatom-based assessments as their preserved remains in sediments have been used to hind-cast human-induced impacts and recovery. Because of their uniqueness, this review summarizes where possible the long-term trends according to the western, central and eastern lake basins. Overall, this historical assessment summarizes a period of significant eutrophication throughout most of the 20th century, followed by water quality improvement due to nutrient reductions and establishment of filter-feeding dreissenids. Recent data suggest new issues associated with blooms of diatoms and blue-green algae. The challenges facing Lake Erie underline the need for continued monitoring and evaluation of historical records that will help us distinguish natural from anthropogenic changes, and to reveal the causes and extent of environmental insults in order to make management decisions.     

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.     

Assessing the application of SeaWiFS ocean color algorithms to Lake Erie

The feasibility of satellite-based monitoring of phytoplankton chlorophyll a concentrations in Lake Erie is assessed by applying globally calibrated, ocean-derived color algorithms to spatially and temporally collocated measurements of SeaWiFS remote sensing reflectance. Satellite-based chlorophyll a retrievals were compared with fluorescence-based measurements of chlorophyll a from 68 field samples collected across the lake between 1998 and 2002. Twelve ocean-derived color algorithms, one regional algorithm derived for the Baltic Sea's Case 2 waters, and a set of regional algorithms developed for the western, central and eastern basins of Lake Erie were considered. While none of the ocean-derived algorithms performed adequately, the outlook for the success of regionally calibrated and validated algorithms, with forms similar to the ocean-derived algorithms, is promising over the eastern basin and possibly the central basin of the lake. In the western basin, each of the regional algorithms considered performed poorly, indicating that alternative approaches to algorithm development, or to satellite data screening and analysis procedures will be needed.     

A simple 1-dimensional,climate based dissolved oxygen model for the central basin of Lake Erie

A linked 1-dimensional thermal-dissolved oxygen model was developed and applied in the central basin of Lake Erie. The model was used to quantify the relative contribution of meteorological forcings versus the decomposition of hypolimnetic organic carbon on dissolved oxygen. The model computes daily vertical profiles of temperature, mixing, and dissolved oxygen for the period 1987–2005. Model calibration resulted in good agreement with observations of the thermal structure and oxygen concentrations throughout the period of study. The only calibration parameter, water column oxygen demand (WCOD), varied significantly across years. No significant relationships were found between these rates and the thermal properties; however, there was a significant correlation with soluble reactive phosphorus loading. These results indicate that climate variability alone, expressed as changes in thermal structure, does not account for the inter-annual variation in hypoxia. Rather, variation in the production of organic matter is a dominant driver, and this appears to have been responsive to changes in phosphorus loads.     

Isolation and characterization of Lake Erie bacteria that degrade the cyanobacterial microcystin toxin MC-LR

Microcystin-LR (MC-LR) is a cyclic hepatotoxin produced by cyanobacteria, including Microcystis sp. and Planktothrix sp. Harmful algal blooms (HABs) in Lake Erie have become a major human health concern in recent years, highlighted by the August 2014 City of Toledo, Ohio, municipal water “do not drink” order that affected nearly 500,000 residents for 3?days. Given that microcystin degrading bacteria have been reported from HAB-affected waters around the world, we hypothesized that MC-LR degrading bacteria could be isolated from Lake Erie. To test this hypothesis, 13 water samples were collected from various Lake Erie locations during the summers of 2014 and 2015, MC-LR was continuously added to each water sample for 3 to 5?weeks to enrich for MC-LR-degrading bacteria, and MC-LR was quantitated over time. Whereas MC-LR was relatively stable in sterile-filtered lake water, robust MC-LR degradation (up to 19?ppb/day) was observed in some water samples. Following the MC-LR selection process, 67 individual bacterial isolates were isolated from MC-LR degrading water samples and genotyped to exclude potential human pathogens, and MC-LR degradation by smaller groups of bacterial isolates (e.g., groups of 22 isolates, groups of 11 isolates, etc.) was examined. Of those smaller groups, selected groups of four to five bacterial isolates were found to degrade MC-LR into non-toxic forms and form robust biofilms on siliconized glass tubes. Taken together, these studies support the potential use of isolated bacterial isolates to remove MC-LR from drinking water.     

Episodic nearshore-offshore exchanges of hypoxic waters along the north shore of Lake Erie

We investigate the nearshore-offshore exchange of hypoxic waters during episodic coastal upwelling events in the nearshore waters of northern Lake Erie using intensive field observations and a validated hydrodynamic and water quality model. We observe wind-induced coastal upwelling events to be the dominant nearshore physical process in the lake which are energized every 5–10 days. When the winds were predominantly blowing from the west or south-west, epilimnetic waters were transported to the offshore bringing in hypolimnetic waters with low temperature (8–10 °C), dissolved oxygen (DO: 0–6 mg L^?1) and pH (6–7) to the nearshore zones. During these events, vertical diffusivity coefficients decreased from 10^?2 m² s^?1 to values as low as ~ 10^?7 m² s^?1. In late summer, the coastal upwelling events in the nearshore waters lower the near bottom DO to hypoxic levels (DO < 2 mg L^?1). Lake-wide observations of DO and pH show that they are positively and linearly correlated while in the nearshore DO and pH experience spatial and temporal variability where upwelling events were developed, which were further assessed using a three-dimensional model. The model accuracy to reproduce offshore hypoxia was first assessed on a lake-wide basis using a coarse resolution model for a five-year period (2008–2012) and in nearshore waters using a higher resolution model for 2013. We use the model results to delineate the near bottom areas experiencing hypoxia at time scales longer than 48 h.     

First report of tubenose goby (Proterorhinus semilunaris) in the eastern basin of Lake Erie

The tubenose goby (Proterorhinus semilunaris), native to the Ponto-Caspian region, was first discovered in the Laurentian Great Lakes in 1990 after it was introduced through ballast water discharge. Compared with Neogobius melanostomus, another exotic gobiid from the Ponto-Caspian, colonization of the Great Lakes by P. semilunaris has been slow, with reports of the species being largely confined to the Huron-Erie Corridor (HEC) and western portions of Lake Erie and Lake Superior. This is the first report of P. semilunaris in the Great Lakes east of the western basin of Lake Erie. Between 28 June and 27 July, 2012, 176 P. semilunaris were collected from shallow (< 1.2 m) water of Marina Lake, a 40 ha embayment in Presque Isle State Park (Erie, PA). The large number of P. semilunaris collected at the site and the presence of individuals as small as 17 mm total length suggest an established population. However, the mechanism by which P. semilunaris was introduced to Presque Isle Bay is not clear.