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.     

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.     

Physical Processes Controlling Taste and Odor Episodes in Lake Ontario Drinking Water

Circulation and thermal structure of the coastal waters were studied as a part of an interdisciplinary program to investigate the taste and odor problem in drinking water along the north and western shores of Lake Ontario. The currents and temperature variations were found to be strongly linked to winds, with winds from the west causing upwelling and eastward flowing currents, and winds from the east inducing downwelling and warm westward flowing currents. The downwelling along the north shore during late August and early September of 2000 was associated with a pulse in concentration of the taste and odor causing compound geosmin. This study indicates that during this episode the onshore directed mean currents and cross-shore fluxes in the surface layer transported geosmin to the coastal waters of the north shore.     

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.     

Kelvin waves in Lake Geneva

The passage of Kelvin waves in Lake Geneva after strong wind events was experimentally investigated in 1987 and 2002 using thermistor chains, current meters and Acoustic Doppler Current Profilers (ADCP) probing the whole water column, including the bottom boundary layer. Characteristics of these internal waves such as period, amplitude, exponential decay with distance from the shore and damping were determined. A significant increase of shear was observed in the thermocline region during the passage of a Kelvin wave crest. The passage of a Kelvin wave crest also led to a well-mixed bottom boundary layer characterized by a logarithmic velocity profile, complying with the so-called “law of the wall” up to an average height of 11 m. A bottom drag coefficient of 2.5 × 10^− 3 was determined from our measurements. We estimated that ~ 70% of the Kelvin wave energy is dissipated in the bottom boundary layer. This study shows that the passage of Kelvin waves energizes the thermocline and near bed region and that this process is of fundamental importance in the dynamics of the nearshore region of mid-latitude large lakes.     

Classifying and Forecasting Coastal Upwellings in Lake Michigan Using Satellite Derived Temperature Images and Buoy Data

Coastal upwellings are common in the Great Lakes but have lacked enumeration and systematic classification of spatial extent, frequency, duration, and magnitude. Near real-time sea surface temperature (SST) images derived from the Advanced Very High Resolution Radiometer (AVHRR) provide indices of upwelling events, but visual inspection of daily images can be tedious. Moreover, the definition of what constitutes an upwelling from AVHRR data is subjective. We developed a semi-automated method to classify upwellings during the period of thermal stratification using daily, cloud-free surface temperature charts from AVHRR SST data. Then we statistically evaluated the location, frequency, magnitude, extent, and duration of upwelling events in Lake Michigan from 1992–2000. Further, we analyzed meteorological data from the National Data Buoy Center buoys in an attempt to improve the reliability of the classification and to provide a means for future forecast of coastal upwelling. Although variable, upwelling events along the western shoreline were preceded by 4 days of southerly and west-to-northwesterly winds, while upwelling events occurring along the eastern shore were preceded by 4 days of northerly winds. Probability of an upwelling event occurring was a function of the direction-weighted wind speed, reaching a 100% probability at direction weighted wind speeds of 11 m s⁻¹ for the western shore. Probability of an upwelling occurrence along the east coast reached 73% at 11 m s⁻¹ and 100% at 13 m s⁻¹. Continuous measurements of wind data with a sufficient temporal resolution are required during the entire upwelling season to improve the predictability of upwellings.     

Seasonal variation in the influence of environmental drivers on nearshore water quality along an urban northern Lake Ontario shoreline

We examined drivers of water quality during 2007–2013 in a region of Lake Ontario influenced by various anthropogenic inputs and natural influences. Nutrient concentrations generally declined from shoreline to offshore, with mean concentrations approaching background after 1 km from shore. N species were an exception to this overall pattern, often with higher concentrations coincident with a mid-nearshore Water Pollution Control Plant outfall (WPCPo). The WPCPo, however, did not appear to be a major contributor to shoreline total phosphorus (TP) or ammonia + ammonium. Shoreline TP variability increased in dry years, while E. coli and conductivity variability increased in wet years. The influence of environmental drivers on water quality differed seasonally. In summer, cross-shore winds causing resuspension appeared to be drivers of elevated nearshore TP and suspended solids (SS), while precipitation, light, and water column stability were related to E. coli. Summer biological activity was evident in higher shoreline total Kjeldhal N contributions and lower NO₃ + NO₂ and dissolved inorganic N. In fall and spring, TP, SS, and conductivity were elevated within 400 m of the shore, suggesting tributary inputs were an important P delivery mechanism to the nearshore in addition to spring resuspension events. Fall, however, represented a transitional period representing a shift from drivers dominant in summer to those in spring. The analytical approach used here reveals generalizable patterns in nearshore water quality and their drivers and may be applicable to other regions where there is a confluence of varying drivers of water quality to a nearshore region.     

An Evaluation of Effects of Groundwater Exchange on Nearshore Habitats and Water Quality of Western Lake Erie

Historically, the high potentiometric surface of groundwater in the Silurian/Devonian carbonate aquifer in Monroe County, MI resulted in discharge of highly mineralized, SO₄-rich groundwater to the Lake Erie shoreline near both Erie State Game Area (ESGA) and Pointe Mouillee State Game Area (PMSGA). Recently, regional groundwater levels near PMSGA have been drawn down as much as 45 m below lake level in apparent response to quarry dewatering. From August to November of 2003, we conducted preliminary studies of groundwater flow dynamics and chemistry, shallow lake water chemistry, and fish and invertebrate communities at both sites. Consistent with regional observations, groundwater flow direction in the nearshore at ESGA was upward, or toward Lake Erie, and shallow nearshore groundwater chemistry was influenced by regional groundwater chemistry. In contrast, at PMSGA, the groundwater flow potential was downward and lake water, influenced by quarry discharge seeping downward into nearshore sediments, produced a different lake and shallow groundwater chemistry than at ESGA. Although the invertebrate and young fish community was similar at the two sites, taxonomic groups tolerant of degraded water quality were more prevalent at PMSGA. Sensitive taxa were more prevalent at ESGA. We propose a conceptual model, based on well-described models of groundwater/seawater interaction along coastal margins, to describe the interconnection among geologic, hydrologic, chemical, and biological processes in the different nearshore habitats of Lake Erie, and we identify processes that warrant further detailed study in the Great Lakes.     

Near-Bottom Currents and Suspended Sediment Concentration in Southeastern Lake Michigan

In a study of sediment transport at the edge of the coastal shelf (28 m depth) in southeastern Lake Michigan we used an instrumented tripod to make continuous observations of horizontal current velocity, temperature, and turbidity within 1 meter of the bottom for 4 weeks during October 1981. The concentration of total suspended material (TSM) 0.9 m above the bottom varied from 1 to 5 mg/L in response to coastal upwelling, surface waves, and currents that exceeded 0.28 m/s (0.7 m above the bottom) on occasion. Advection of the Grand River plume also contributed significantly to the variations in the observed TSM concentration. Currents near the bottom were well correlated with surface winds and, although upwelling currents transported sediment upslope, the net horizontal sediment flux during the period of observation was west-southwestward, almost directly offshore. The magnitude of the horizontal sediment flux was approximately 1,000 times the magnitude of the vertical flux estimated from sediment traps deployed as part of earlier studies. We infer that local resuspension occurred roughly 20 percent of the time and the critical mean flow speed (at 0.7 m) for resuspension of the local silty sands was estimated to be about 0.18 m/s.     

Littoral drift by alongshore flow at Visakhapatnam – East Coast of India

The littoral drift in the surf zone of Visakhapatnam has been evaluated using simulated longshore current. In this study we examined littoral processes, driven by longshore currents using a set of numerical models (Mike-21 modeling system). Deepwater waves as they approach shallow water dissipate energy and the water from the broken waves flow parallel to the shoreline known as longshore current. In order to simulate the current from wave breaking, offshore wave data for the period 1995–2004, have been collected from British Meteorological Office (BMO), UK. Waves having an annual exceedance of 20% are allowed to propagate to nearshore using a nearshore spectral wind-wave model from predominant directions. The wave-induced radiation stress obtained from wave model then formed the basis for simulating the longshore current and associated sediment transport. The results of these simulations show the pattern of longshore flow and sedimentation. The net annual discharge at selected coastal stretches is estimated and presented. It has been inferred from the study that the sediment transport for the coast is of the order of 0.4–0.6 million m³/year.     

Variations in the Distribution of Suspended Particles During an Upwelling Event in Lake Michigan in 1980

To test the hypothesis that suspended fine-grained particles moving downslope within the nepheloid layer in Lake Michigan are periodically reintroduced into the nearshore and euphotic zones during upwelling events, temperature and transparency profiles were recorded and water samples analyzed for total suspended materials (TSM) during a strong upwelling event. The resultant data confirmed that there is periodic reintroduction of suspended materials into the nearshore and epilimnion during such events, and provided insight into the importance of the general resuspension process, especially in regard to differences between known sedimentation rates and the rate indicated by trap collections. Both upwelling and downwelling currents are disruptive processes that tend to keep the suspended particulates in motion and prevent them from rapidly becoming a permanent part of the bottom sediment. These currents redistribute suspended particulates and the associated chemical load, and may resuspend surficial sediments, especially from the slope and shelf regions. The reintroduction of fine-grained materials into the euphotic zone through upwelling events can play a large role in the long-term behavior and fate of persistent contaminants.     

Sedimentary in-filling of an urban Great Lakes waterfront embayment and implications for threshold-driven shoreline morphodynamics,Montrose Beach,SW Lake Michigan

This paper addresses subaqueous and subaerial patterns of geomorphic change across Montrose Beach, an urban embayment along Chicago’s engineered SW Lake Michigan coastline. Our goal was to better characterize the urban littoral zone, its sediment-transport processes, and associated shoreline morphodynamics (from the early 1950s to present). Succinct beach geomorphic responses to decadal base-level changes (i.e., regression during lake-level fall and transgression during lake-level rise) occurred once a morphologic threshold in the subaqueous portion of the system had been crossed. Despite continuous sand trapping, nearshore elevations were initially not conducive to promoting expansion of the subaerial beach environment, regardless of water-level condition. Rapid beach expansion after 1990 (by a factor of four in <25 years) was facilitated by prior decades of nearshore accretion. Shoreline morphodynamic trajectories and degree of coupling to nearshore sedimentary processes are important considerations for developing long-term beach-management strategies. Rapid cross-shore movements of the shoreline in response to oscillatory base levels are expected to persist at Montrose and other urban beaches of similar design (and nearshore conditions). This has important implications for managing urban lakefront ecosystems, including coastal dunes and shore-bird habitats. Few datasets have thus far quantified time-variant and threshold-driven patterns of beach geomorphic development along engineered coastlines. Such insights should help coastal managers better understand littoral sediment interconnectivity across the urban lakefront and anticipate future geomorphic trajectories of beach environments with anticipated decadal-scale oscillatory patterns in lake level.     

Nearshore-offshore exchanges by enhanced turbulent mixing along the north shore of Lake Ontario

Seasonal nearshore-offshore exchanges by coastal upwelling events in large lakes can play a significant role in nearshore nutrient dynamics, affecting lake productivity and water quality. We analyzed field observations along the north shore of Lake Ontario, collected in the summer of 2018, focusing on the littoral zone and specifically the Cladophora habitat zone (<15 m), to investigate episodic enhanced vertical mixing by coastal up/downwelling events. Vertical turbulent diffusivity (K_z) based on the buoyancy Reynolds number above the metalimnion layer during downwelling events was generally higher than those below the metalimnion layer during upwelling events; while K_z at the metalimnion layer can increase by ∼ two orders of magnitude during upwelling events. Our results suggest that K_z based on the Richardson number parameterization, which only accounts for large-scale current shear and stability, and incorporates an adjustable parameter is ∼ ten times higher than the K_z based on the buoyancy Reynolds number. Analysis of historical wind records indicates that the frequency of coastal upwelling favorable winds on the north shore of Lake Ontario has increased by > 45% over the last thirty years - suggesting an increasing trend of nearshore-offshore nutrient exchanges as a contributing factor for the nearshore water quality management.     

Application of a 3D hydrodynamic-biological model for seasonal and spatial dynamics of water quality and phytoplankton in Lake Erie

In large lakes, temporal variability is compounded by strong spatial variability associated with mesoscale physical processes such as upwelling and basin-scale circulation. Here we explore the ability of a three dimensional model (ELCOM-CAEDYM) to capture temporal and spatial variability of phytoplankton and nutrients in Lake Erie. We emphasized the east basin of the lake, where an invasion by dreissenid mussels has given special importance to the question of spatial (particularly nearshore-offshore) variability and many comparative observations were available. We found that the model, which did not include any simulation of the mussels or of smaller diffuse nutrient sources, could capture the major features of the temperature, nutrient and phytoplankton variations. Within basin variability was large compared to among-basin variability, especially but not exclusively in the western regions. Consistent with observations in years prior to, but not after, the mussel invasion the model predicted generally higher phytoplankton concentrations in the nearshore than the offshore zones. The results suggest that the elevated phytoplankton abundance commonly observed in the nearshore of large lakes in the absence of dreissenid mussels does not have to depend on localized nutrient inputs but can be explained by the favourable light, temperature and nutrient environment in the shallower and energetic nearshore zone. The model is currently being extended to allow simulation of the effects of dreissenid mussels.     

Replacement of Zebra Mussels by Quagga Mussels in the Canadian Nearshore of Lake Ontario: the Importance of Substrate,Round Goby Abundance,and Upwelling Frequency

The invasion of the Great Lakes by zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) has been accompanied by tremendous ecological change. In this paper we characterize the extent to which dreissenids dominate the nearshore of the Canadian shoreline of Lake Ontario and examine mussel distribution in relation to environmental factors. We surveyed 27 5-m sites and 25 20-m sites in late August 2003. Quagga mussels dominated all sites (mean: 9,404/m²; range 31–24,270), having almost completely replaced zebra mussels. Round gobies (Neogobius melanostomus) were associated with quagga populations dominated by large mussels. Quagga mussel total mass was low at 5-m sites with high upwelling frequency; we believe this is the first documentation of reduced benthic biomass in areas of upwelling in Lake Ontario. Overall, we estimated 6.32×10¹² quagga mussels weighing 8.13×10¹¹ g dry weight and carpeting ∼66% of the nearshore benthic habitat. Quagga mussels are a dominant and defining feature of the Lake Ontario nearshore, and must be accounted for in management planning.     

Spatial Patterns Emphasize the Importance of Coastal Zones as Nursery Areas for Larval Walleye in Western Lake Erie

Lake Erie walleye Sander vitreus exhibits significant interannual variability in year-class strength. Recent research revealed the importance of larval growth and survival rates in determining walleye year-class strength in western Lake Erie, indicating that spatial and temporal overlap of larvae with good habitat conditions (e.g., abundant prey, warm waters) promoted walleye growth and survival. To assess the spatial overlap between walleye larvae and habitat parameters (water depth, temperature, water clarity, prey density) in western Lake Erie, we evaluated the spatial distribution of walleye larvae and these habitat parameters with intensive sampling at 30 to 36 sites during spring 1994–1999. We analyzed spatial relationships among pelagic walleye larvae and various habitat attributes using a geographic information system and principal components analysis. Larval walleye density was consistently highest at nearshore sites during all years and showed a high degree of spatial overlap with high ichthyoplankton density, and warm water temperatures. Larval walleye density was negatively associated with water depth and water clarity. Two principal components represented 79.6% of the total variability in site attributes. Principle components analysis supported our spatial analysis by graphically separating sites into distinct groups based on larval walleye density and habitat attributes. These analyses indicated that similar relationships between larval distribution and habitat attributes occur each year, emphasizing the importance of nearshore coastal zones as nursery areas for walleye.     

Three dimensional modeling of the effects of changes in meteorological forcing on the thermal structure of Lake Erie

A three dimensional hydrodynamic model, the Estuary and Lake Computer Model (ELCOM), validated by field data collected in 2008, is used to investigate the thermal structure response in Lake Erie to changes in air temperature and wind speed. We define spatially and temporally varying regions for the epilimnion, thermocline, and hypolimnion. Increasing the air temperature warms up the epilimnion but has little effect on the hypolimnion. The stratification forms earlier and breaks down later. The thermocline is raised modestly in the warmer air temperature scenario. Stronger winds cool the epilimnion slightly, but warm up the hypolimnion with much larger temperature changes. The stratification duration is shortened, and the thermocline depth is noticeably deepened. Due to the large differences in depths and layer thicknesses of the three basins, the responses to changes in meteorological forcing vary among the basin. Exploiting the power of the three dimensional model to provide a more authentic characterization of thermal stratification in large lakes, it is shown that patterns inferred from simple isotherm dynamics when studying the stratification period as typically done with one dimensional models are not always accurate. The present results for Lake Erie show the potential for complicated and interactive effects of climate forcing on important biogeochemical processes, especially hypolimnetic oxygen depletion.     

Population Characteristics of the Invading White Perch (Morone Americana) in Western Lake Erie

The white perch (Morone americana) is an East Coast estuarine species that invaded Lake Erie in the 1950s, but did not increase in abundance until the mid 1970s. We studied its distribution and population dynamics in western Lake Erie during this period of rapid increase in population size. White perch spawned in riffle areas of tributary streams of western Lake Erie during late April, and then moved downstream into the lake. They were abundant in nearshore and reef habitats throughout most of the year, although a few were collected in deep offshore areas. Increasingly strong year classes were produced each year in 1980–1984. The age structure of the population reflected a surge in recruitment in the 1980s; fish of age–1 and age–2 were abundant, but older fish were still rare. White perch in western Lake Erie grew faster and matured earlier than those in most other populations, but growth rates appeared to be declining as the population expanded. White perch can be expected eventually to colonize suitable habitats throughout the Great Lakes.     

Post-dreissenid Increases in Transparency During Summer Stratification in the Offshore Waters of Lake Ontario: Is a Reduction in Whiting Events the Cause?

Since the dreissenid invasion of the lower Great Lakes, calcium concentrations in the offshore waters of Lake Ontario have decreased by approximately 4–5 mg/L. This decline has coincided with a three-fold reduction in August turbidity values and nearly a doubling of Secchi depths, presumably due to reduced summer calcite precipitation events in the lake. The reductions in calcium have followed a dramatic reduction in alkalinity in the central and eastern basins of Lake Erie, which provides most of the inflow to Lake Ontario. This reduction in alkalinity in Lake Erie corresponds to a period of rapid dreissenid growth in that lake, strongly suggesting calcium uptake by dreissenid mussels as a causative factor. The mass of calcium resident in the dreissenid population in Lake Erie, estimated from published lake-wide census data, is sufficient to account for the observed decreases in alkalinity. In addition, observed changes in alkalinity in Lake Ontario closely match those expected to result from inflows from Lake Erie, based on mass balance considerations. Considered in sum, our data strongly suggest that calcium uptake by dreissenid mussels in Lake Erie has resulted in decreases in the calcium concentration in Lake Ontario, reducing the frequency and/or intensity of whiting events in the latter lake. We believe this is the first report of an increase in transparency that can be reasonably attributed to a chemical change brought about by Dreissena. These increases in transparency may have very different consequences than those of dreissenid filtration activities. For example, rather than decreasing phytoplankton populations, the improved light climate might increase summer phytoplankton populations, particularly sub-epilimnetic ones.     

Modelling the influence of seiche-events on phosphorous-loading dynamics in three Lake Ontario coastal wetlands

Coastal Wetlands (CWs) provide critical ecosystem services that maintain biogeochemical processes and habitats in the coastal zone of the Great Lakes. When nutrient-laden surface waters flow into CWs from their watersheds, internal physical, chemical, and biological processes can alter the final nutrient loadings to the lake. However, CWs can periodically be inundated with lake water from seiche events, and little is known about the impacts of seiches on nutrient processing and loadings from CWs. To evaluate the influence of lake seiches on CW phosphorous-loading dynamics, we built a multi group structural equation model (SEM) using climatic and wave data, and interannual (2009–2018) estimated sediment and phosphorous loadings from three CWs on the north-shore of central Lake Ontario (Rouge Marsh, Duffin’s Marsh, and Carruthers Marsh). Wind speeds, lake levels, and an increased peak period of wave spectra were significant explanatory variables of seiche events (p-value < 0.001). We identified that seiche events caused significant sediment resuspension (p-value < 0.001) in CWs, which contributed to a significant increase of phosphorous loading to the coastal zone of Lake Ontario (p-value < 0.001). Our results indicate that lake-seiche events can influence CW phosphorous-loadings to Lake Ontario, and should be considered when modelling water quality in the nearshore zone.