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Abstract

We present an overview of physical processes that drive water circulation within the extended system of coastal embayments in the Toronto Harbour. The different water circulation patterns occur at various spatial and temporal scales, and our paper provides context for the various efforts to improve water quality by the Toronto and Region Remedial Action Plan. Velocity profiles and water level measurements showed that the harbour’s Helmholtz pumping mode drives a 1- hour period oscillation, which can influence flushing of the shallow embayments. This process likely persists year-round and would lead to flushing time-scales of between 1-11 days for these shallow embayments. If this ubiquitous pumping is combined with solar heat fluxes, it partially explains the persistent temperature gradients amongst the shallow embayments. In the larger and deeper (∼10 m) Inner Harbour, the prevailing westerly winds drive most of the mean circulation, with a current entering through the Western Gap and leaving through the Eastern Gap. This wind driven circulation leads to a residence time of water in the Inner Harbour between 7-14 days. In addition, periodic strong and sustained westerly winds can induce frequent upwelling events in Lake Ontario (between 4 to 10 times during the stratified season) that mildly increase the exchange flow and help maintain good water quality by exchange nearshore waters with cleaner hypolimentic waters. The intrusion of cold water into the harbour can also lead to highly variable temperature regimes with sudden drops in temperature that could have negative effects on aquatic organisms.

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... The biomass and composition of zooplankton is controlled by factors which can be broadly grouped as environmental (e.g., temperature or flow), bottom-up (nutrients and system productivity) and top-down (predation) (Shuter and Ing, 1997;Jeppesen et al., 2000;Dodson et al., 2009). Within the TRAOC, a range of factors have been suggested to influence phytoplankton and zooplankton communities, including flushing of the IH with Lake Ontario water (Haffner et al., 1982;Hlevca et al., 2018), contaminants (Munawar et al., 1993), blooms of inedible or potentially toxic phytoplankton (de Bernardi and Giussani, 1990) and changes in populations of fishes (Bowlby and Hoyle, 2017) and invasive predatory zooplankton (Warner et al., 2006). Water quality within Toronto Harbour fluctuates both spatially and temporally via loading gradients, weather and lake circulation . ...
... Additionally, Munawar et al. (2018) postulated that combined sewer overflows emptying into the IH via the Don River have resulted in extremely high microbial biomass and production, which could alter the transfer of energy and nutrients to zooplankton. Also influencing zooplankton populations within the harbour and surrounding coastal area are frequent upwelling events, which result in increased flow from Lake Ontario and decreased water temperatures (Hlevca et al., 2018). ...
... The direction of the relationship is shown by the slope (positive or negative). (Hlevca et al., 2018). This compares to 95-140 days in Hamilton Harbour, which has a single narrow channel entering Lake Ontario (Haffner et al., 1982). ...
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To better understand zooplankton dynamics in Lake Ontario’s Toronto Harbour and adjacent coastal area (CA), we sampled zooplankton, phytoplankton, nutrients and physical parameters on six dates in 2016. Despite higher levels of nutrients, chlorophyll and primary production in the inner harbor (IH), the areas supported similar May to November zooplankton biomass (IH = 32 ± 7 and CA = 42 ± 10 mg/m³). IH values were much lower than other nutrient-enriched embayments in Lake Ontario, yet CA biomass was twice that of nearshore sites away from Toronto. Small zooplankton such as rotifers and Bosmina dominated IH; and large taxa (Daphnia, calanoids and predatory cladocerans) were more important in the CA. Daphnia, Bosmina, cyclopoids and calanoids were larger in the CA, and adult cyclopoids had higher egg ratios. This led to low annual IH production estimates for both cyclopoid and calanoid copepods. Total phosphorus and chlorophyll did not appear to regulate zooplankton biomass, but positive relationships were found with bacterial biomass in the IH and with temperature in the cool season. Atypically high fish planktivory rates likely suppressed larger IH zooplankton in 2016, allowing small, resilient Bosmina to flourish and contribute 84% of total production in the IH. Comparing 2016 data to previous zooplankton surveys revealed considerable inter-annual variation in proportions of Daphnia, Bosmina and predatory cladocerans over the 1994 to 2016 period, and the strong top-down controls observed in 2016 were not typical. Elevated microbial production may serve as an important alternate trophic pathway supporting cladoceran populations in Toronto Harbour.
... The rapid water circulation in the Toronto Harbour is a key process that determines many of the chemical and nutrient gradients between the Don River and Lake Ontario, as well as the temperature variability within the harbour. Hlevca et al. (2018) identify four main processes that drive circulation at various scales. Large-scale upwelling events in Lake Ontario are perhaps the most well-known process, and result when sustained westerly winds cause offshore movements of the summer thermocline, and lead to intrusions of cold water into a warmed harbour. ...
... The prevailing westerly winds drive the main circulation through the harbour, with flows from the eastern gap out through the western gap flushing the harbour on a period of 7-14 days. In addition, Hlevca et al. (2018) identify a 1-hour water level oscillation throughout the harbour, which can drive a strong oscillating flow between shallow embayments and the main body of the harbour. ...
... These basic issues that affect water quality in the TR AOC also resonate up the food web Staley et al., 2018) and are reflected in fish and wildlife habitat impairments in watersheds and waterfront locations, shown through fish distributions (Veilleux et al., 2018), local fish contamination (Bhavsar et al., 2018;Gilroy et al., 2018) and fish community metrics (Hoyle et al., 2018). Important factors to consider for the ecological potential of the area are the natural and urban constraints on lower food web dynamics (Munawar et al., 2018) and fish and wildlife populations, such as large-lake water A c c e p t e d M a n u s c r i p t movements (Hlevca et al., 2018) affecting both currents and water levels, stream fragmentation (Choy et al., 2018), and urban runoff and natural terrestrial feature loss (Stille et al., 2018). Regaining those lost features will not only improve our ecosystem but provide other valued outcomes (Greene et al., 2018). ...
Article
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Of the 14 possible Beneficial Use Impairments (BUIs) listed by the International Joint Commission (IJC 1987), the Toronto and Region Area of Concern (TR AOC) had listed in 2016: a. six as impaired (eutrophication/algae, beach closings, aesthetics, fish/wildlife habitat, fish consumption, fish/wildlife populations); b. one as requiring further assessment (phytoplankton/zooplankton communities); c. four re-designated as not impaired after assessment (fish tumours/deformities, bird/animal deformities/reproductive problems, benthos, dredging restrictions), and; d. three that were never considered impaired (flavour of fish/wildlife, drinking water restrictions/taste/odour problems, and added costs to agriculture/industry). The articles in this special issue provide needed insight into the 7 Beneficial Use Impairments (BUIs) that remain impaired or require further assessment within the large area that the TR AOC covers. This includes multiple watersheds, as well as the nearshore waters of Lake Ontario. This special issue provides new and additional data on water quality and circulation (Hlevca et al., 2018; Howell et al., 2018; Snodgrass et al., 2018), beaches (Edge et al., 2018; Staley et al., 2018), aesthetics (Dahmer et al., 2018), phytoplankton and zooplankton populations (Munawar et al., 2018), fish and wildlife habitat (Choy et al., 2018; Stille et al., 2018; Veilleux et al., 2018), restrictions on fish consumption (Bhavsar et al., 2018), and fish populations (Hoyle et al., 2018). Only wildlife populations were not addressed directly. We summarize the findings of these contributions and provide a synthesis of the results as we move towards delisting the Toronto and Region AOC.
... The Don River (average annual flow 4 m 3 s À1 ) contributes substantial loadings to the north east corner of the Inner Harbour via the Keating Channel (D' Andrea and Anderton, 1996), which have been shown to contribute to highly variable water quality in the harbour that is at times poorer than much of the waterfront, and broader Lake Ontario nearshore (Howell et al., 2012a). Mixing of water masses driven by lake circualtion and water exchange between Toronto Harbour and Lake Ontario is also an important contributor to variability in water quality (Hlevca et al., 2018). ...
... The OH is connected directly to Lake Ontario. Water circulation in Toronto Harbour is described by Hlevca et al. (2018). ...
... The spatial patterns in water quality seen in 2008 resemble those reported in earlier studies which highlight the influence of the Don River discharge on the NE corner of the harbour (Poulton, 1977;Poulton and Griffiths, 1986), the variability within the IH as affected by mixing (Poulton, 1977), and the contrasting conditions among the inner and outer harbours and the nearshore adjacent to Toronto Island (OME, 1980). Frequent upwelling with intrusion of cold lake water into the IH and increased exchange flows (Hlevca et al., 2018) at times attenuates or amplifies the broader gradient in water quality extending from IH to nearshore over the study area. ...
Article
Toronto Harbour, adjacent to a large urban centre on Lake Ontario, receives inputs from storm sewers, combined sewer overflows, and urban runoff that lead to contrasting water quality over the waterfront. Toronto’s Inner and Outer Harbours, mesotrophic and meso-oligotrophic, respectively, were investigated in 2008 to assess how water quality conditions were affected by loading gradients, weather and lake circulation. Spatially-intensive measurements of UV fluorescence, turbidity, conductivity, and chlorophyll a, together with lab-based analysis of chemistry at discrete sites, were used to depict patterns and contrasts in water quality in the harbour. Spatially-integrated field sensor data were also employed to examine the efficacy of using discrete water quality sampling to represent average conditions. Nitrogen, total phosphorus, dissolved organic carbon, major ions and E. coli gradients were a recurrent feature among surveys with concentrations decreasing away from the Don River mouth. The limited point-sample data reasonably depicted average conditions among areas of the harbour on the days of survey as did the results interpolated for a long-term monitoring station in the Inner Harbour (IH). The strong variability seen within the IH indicates that the most affected water quality conditions are likely under represented by area-wide conditions. Temporal variability in water quality, correlated with the discharge from the Don River, was strong yet under represented by the field-based sampling. Empirical prediction of TP concentrations in the IH, and correlated with Don River discharge, were used to demonstrate both the critical need to address temporal variability in monitoring design and the possibility of using empirical predictive approaches drawing upon field sensor data to fill this gap.
... For instance, near the cities of Burlington and Hamilton in Ontario (combined population 750,000), the Hamilton Harbour in Lake Ontario has a residence time of approximately 100 days (Lawrence et al., 2004). The city of Toronto has a population of nearly 3 million, and much of the urban runoff passes through the Toronto Harbour which has a residence time of order 10 days (Hlevca et al., 2018). The mean depth of Hamilton Harbour is 13 m and 10 m for Toronto Harbour, so Eq. ...
Article
Buoyant microplastic pollution disperses widely from sources via strong wind-driven water currents in lakes and oceans. This ability for dispersal depends critically upon the particle's density, which can change over time due to microbial growth (biofilm). This study quantifies biofilm-induced sinking rates of irregularly-shaped polypropylene granules (~125–2000 μm) via ex-situ experiments emulating a Great Lakes freshwater environment. Biofilm development increases particle density and lowers microplastic rise velocities, eventually causing sinking. We observed sinking for 100% of small and intermediate microplastics, and 95% of large microplastics. Under constant environmental conditions, sinking onset was observed sooner for smaller particles (~125–212 μm, 18 days) than for larger particles (~1000–2000 μm, 50 days). Differences in settling onset would lead to size-fractionation of particle sedimentation, whereby smaller particles are deposited closer to their sources relative to larger particles. Our study demonstrates a novel mechanism by which buoyant microplastics can selectively sink from the lake surface.
... The restricted circulation of lake water into Toronto Harbour accounts for the contrasting water quality compared with nearby areas of shoreline; nonetheless, strong water exchange with the lake moderates water quality as evident from the gradients within the Inner Harbour and between the Inner and Outer Harbours. Hlevca et al. (2018) estimated the residence time of Toronto Inner Harbour and outer Harbour were 7 and 4 days, respectively. The persistent pattern in the Inner Harbour of poorer water quality in the NE corner and on the NE and SE shoreline attributable to mixing of the Don River discharge is consistent with hydrodynamic modeling describing the movement of the Don River as initially flowing west into the harbour and then towards the Eastern Gap (Snodgrass et al., 2018) and previous water quality studies (Howell et al., 2018), and biological studies (Brinkhurst, 1970). ...
Article
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Urban centers line western Lake Ontario where urban rivers, wastewater treatment plants and stormwater load nutrients, major ions and suspended solids to the nearshore. In 2018, nearshore water quality and associated physical conditions bordering the cities of Toronto and Mississauga were assessed as a benchmark for future effects of urban growth and municipal infrastructure projects to improve water quality. Conductivity and UV-fluorescence were used as water quality surrogates and mapped over blocks of shoreline stratified by distance offshore. Patterns in UV-fluorescence aligned with loading points, and generally higher levels near the shoreline, were correlated with concentrations of nutrients, major ions and suspended solids. Water quality was more land-impacted over the shoreline from the Credit River to Humber Bay contrasting with the more lake-like conditions from Toronto Eastern Beaches to the Rouge River. Within Toronto Harbour, cross-harbour gradients in water quality varied with weather-related changes in river and storm water loading. Mixing areas at wastewater treatment plant outfalls and tributary mouths, frequently shaped by alongshore lake circulation, resulted in a mosaic of water quality over the shoreline. Area-wide elevation of chloride and conductivity, and poorer water quality in late spring, was linked to heightened river discharge. Thermal stratification affected how discharges were distributed in the water column, but measurements at the lake surface reflected the strongest overall land-effects on water quality. The patterns of temporal-spatial variability identified within geographically-defined areas of shoreline can be used as past footprints in future monitoring to detect change.
... The Don River is a highly urbanized watershed with approximately 30 CSO discharge points and 872 storm sewer outfalls along its length (Boyd et al., 2001). The Don River is the most significant water input source to the inner harbour, with an average flow of 345,600 m 3 per day (Hlevca et al., 2018). Suspended sediments have historically accumulated in the northeast section of the harbour near the mouth of the Keating Channel, which requires regular dredging. ...
Article
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Sediment quality of the Toronto and Region Area of Concern (AOC) waterfront was assessed using a weight of evidence approach following the Sediment Quality Triad, with the addition of contaminant bioaccumulation data, to determine current status following the 2013 re-designation of the “degradation of benthos” Beneficial Use Impairment as “no longer impaired.” Five stations within the AOC were sampled in 2015 and compared to lower Great Lakes nearshore reference areas (n = 22) selected based on similarity of sediment physicochemical properties. Sediment chemistry was comparable except for a localized instance of elevated perfluorinated compounds at one AOC site. Laboratory sediment toxicity bioassays indicated chronic toxicity associated with point sources to the AOC, corresponding to increased invertebrate body burdens measured in laboratory exposures. Diversity metrics and multivariate analysis showed that benthic invertebrate community composition present at the AOC sites was not significantly different from reference conditions of the lower Great Lakes. The weight of evidence from this study indicates benthic invertebrate communities continue to show effects of degraded sediment conditions at sites impacted by point sources. While the 2013 RAP decision was to re-designate the “degradation of benthos” BUI to “no longer impaired,” our results support the notion that life after AOC delisting must continue to prioritize monitoring efforts.
... The model domain ends as the Don River enters Keating Channel and Toronto Harbour, where water velocities are lower (Hlevca et al., 2018(Hlevca et al., , 2015. Eggs settle in areas of low velocity and turbulence, indicating that eggs will settle in these areas before entering Lake Ontario. ...
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Asian carps are threatening to establish in the Great Lakes basin and the examination of factors leading to spawning success is vital for preventive efforts. Hydrodynamic modelling can determine if successful hatching of carp eggs can occur in a tributary, by predicting egg movement during a spawning event to see if hatching can occur before eggs settle. A 3-D hydrodynamic model, coupled with a Lagrangian particle tracker, was used to assess hatching rates of three Asian carp species (bighead, grass, and silver carps) in different temperature and flow scenarios in the east Don River, a potential spawning tributary to Lake Ontario. In-river hatching rates were highest in scenarios with warmer summer water temperatures (23–25 °C) and flow magnitudes of 15–35 m³/s, which occur at least once every year. Using a 3-D hydrodynamic model allowed the inclusion of low-velocity zones where eggs become trapped in lower flow scenarios, thereby reducing modelled hatching success. In-river hatching rates were significantly reduced when the spawning location was moved close to the mouth of the river, with no modelled hatching if spawning occurred in the lower 8 km of the Don River, indicating that preventing Asian carp movement upstream would viably reduce the chances of successfully spawning occurring in this tributary. The magnitude of reduction in spawning success caused by limiting Asian carp passage upstream can guide preventative strategies and the method of using a 3-D hydrodynamic model as a predictive tool could be applied in similar tributaries across the Great Lakes basin.
... Despite the recent advances in the development of CMEMS global and regional core products, many downstream services for user uptake require information on even smaller spatial scales, such as ocean forecasting for small island chains (Caldeira et al., 2016), intricate bights , or port approach areas where sharp topobathymetric gradients pose special difficulties for accurate local predictions (Hlevca et al., 2018;Federico et al., 2017;Sánchez-Arcilla et al., 2016;Sammartino et al., 2014;Grifoll et al., 2012). A variety of operational products for harbours have been recently developed, although most of these coastal applications are wave and water-level forecasting sys-P. ...
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In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface, ranging from global to local scales in a two-phase stepwise strategy. Firstly, a comparison of CMEMS-GLOBAL and the nested CMEMS-IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL direct data assimilation in open-waters and the increased horizontal resolution of IBI in coastal areas, respectively. Besides, IBI proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI and SAMPA high-resolution coastal forecast system (partially nested to IBI) in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamic. A quantitative validation against High Frequency radar (HFR) hourly currents highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales though a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2-day quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the added value of imposing accurate meteorologically-driven barotropic velocities in the open boundaries (imported from NIVMAR storm surge model) to take into account the remote effect of the atmospheric forcing over the entire Mediterranean basin, which was only partially included in IBI and GLOBAL systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the Western Alboran Sea to put in a broader perspective the context of the onset, development and end of such flow reversal episodes.
... In addition to the lack of a BACI design, in it is important to emphasize some fundamental differences in habitat between the western and eastern slips (as mentioned previously). First, water clarity in both Jarvis and Parliament slips is heavily influenced by high amounts of suspended sediments and nutrients flowing from the Don River relative to the other two slips, which are more influenced by Lake Ontario water that flows through the western gap (Hlevca et al., 2018). While reduced water clarity undoubtedly contributes to the observed differences among slips in the proportional coverage of SAV, its direct influence on Northern Pike is less clear. ...
Article
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Hardening of natural shorelines in urban aquatic ecosystems can result in a loss of fish habitat and productivity. The north shore of Toronto Harbour (Lake Ontario) has been converted to hardened boat slips for commercial, industrial and recreational purposes, but its potential utility as fish habitat has not been evaluated. The objective of this study was to determine whether fish frequented and utilized four slips in the inner harbour of Toronto. Two western boat slips are adjacent to some natural features and have undergone some rehabilitation to increase the complexity of aquatic habitat (i.e. addition of large substrate, overhead cover, and in-water structure). In contrast, the two eastern slips are deeper and more influenced by the turbid Don River. We assessed the timing and duration of occupancy within all four slips for seven fish species using acoustic telemetry. In just under a year, tagged fishes spent a limited amount of time in any one slip. However, there was evidence for increased use at the two western slips by Northern Pike (Esox lucius) in spring, which is likely linked to the proximity of these slips to a known spawning area. Overall, there was no reliable evidence that the majority of the seven adult fish species evaluated frequented either the western or eastern slips. Despite efforts to track and tag a variety of species, insufficient detections prevented a detailed assessment of habitat selection for the majority of species of interest. A more detailed study of the spatial ecology of these fishes is therefore needed to understand the scale of their habitat use and inform the design of habitat rehabilitation projects for hardened shorelines.
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This paper evaluates the role that different levels of control for combined sewer overflows have in addressing the recreational water quality objectives of the Toronto Inner Harbour of the Toronto and Region Remedial Action Plan. Three models are used to establish the predictive methodology: the Infoworks model for the combined sewer service area, the Hydrologic Simulation-F model for the remainder of the watershed, and the MIKE 3 computer code to evaluate Lake Ontario response to control. Each model was calibrated with E. coli densities observed respectively in sewer discharges, instream, and in the Inner Harbour. Two indices are used to evaluate the response of water quality in the Inner Harbour – fraction of the surface area achieving Blue Flag status, and portion of the swimming season (June to August) above recreation objectives. Analyses of control options led to the recommendation that virtual elimination of combined sewer overflows (one overflow per season control strategy) should be pursued, rather than the lower level of control of 90% volumetric control, which is the minimum provincial environmental requirement. Implementation of priority projects for improving water quality along the Toronto waterfront, including the Don River and Central Waterfront project, are integral to delisting Toronto as a Great Lakes Area of Concern.
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Hardening of natural shorelines in urban aquatic ecosystems can result in a loss of fish habitat and productivity. The north shore of Toronto Harbour (Lake Ontario) has been converted to hardened boat slips for commercial, industrial and recreational purposes, but its potential utility as fish habitat has not been evaluated. The objective of this study was to determine whether fish frequented and utilized four slips in the inner harbour of Toronto. Two western boat slips are adjacent to some natural features and have undergone some rehabilitation to increase the complexity of aquatic habitat (i.e. addition of large substrate, overhead cover, and in-water structure). In contrast, the two eastern slips are deeper and more influenced by the turbid Don River. We assessed the timing and duration of occupancy within all four slips for seven fish species using acoustic telemetry. In just under a year, tagged fishes spent a limited amount of time in any one slip. However, there was evidence for increased use at the two western slips by Northern Pike (Esox lucius) in spring, which is likely linked to the proximity of these slips to a known spawning area. Overall, there was no reliable evidence that the majority of the seven adult fish species evaluated frequented either the western or eastern slips. Despite efforts to track and tag a variety of species, insufficient detections prevented a detailed assessment of habitat selection for the majority of species of interest. A more detailed study of the spatial ecology of these fishes is therefore needed to understand the scale of their habitat use and inform the design of habitat rehabilitation projects for hardened shorelines.
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Along 25 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (0.4–32 ha) have been constructed or modified by lake-infilling to restore warmwater fish habitat. The variation in thermal habitat quality for warmwater fishes among these embayments is very high; temperatures range from those found within a small pond to those of much cooler Lake Ontario. Since meteorological conditions and surface heat fluxes are almost identical, the temperature variation among embayments must be caused by differences in bathymetry or exchange with Lake Ontario. However, a previous study on these embayments found paradoxically that temperatures were not strongly associated with channel size or embayment bathymetry. This paper resolves the paradox by showing that flushing times for almost all of the constructed embayments were less than 1 day, and often less than 12 h. With so little time to warm within the embayments, water temperatures of almost all embayments remained very close to the temperatures of the adjacent lake waters. The coldest embayments connected directly to open Lake Ontario and warmer embayments connected to Lake Ontario through other embayments or protected harbors, where the inflowing water from Lake Ontario had already substantially warmed. To allow embayments along the exposed shoreline of Toronto to reach acceptable temperatures for warmwater fish, we use heat budgets to calculate that average summer flushing times must be increased from their current length of 1.5 to 5.5 h to approximately 30 h. Such changes could be achieved through large reductions in the channel cross section.
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Along 40km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (4.38–848×103m2) have been constructed or modified by lake-infilling to restore warmwater fish habitat. We describe how the thermal regimes of these embayments differ from those of small inland lakes, how embayment bathymetry alters the degree of exchange with Lake Ontario, and predict how embayment thermal regimes affect warmwater fish growth. The accumulated growing-degree days, calculated from a 14°C baseline (∑GDD14), of seven South-Central Ontario inland lakes and an embayment disconnected from Lake Ontario ranged from 844 to 1157GDD. Compared to the inland lakes and disconnected embayment, the coastal embayments connected to Lake Ontario achieved fewer ∑GDD14 and had a greater range, 390–1047, reflecting differences in their degree of exchange with and the cooling effect of Lake Ontario. The thermal regime of coastal embayments differs most from inland lakes during May–late-July. During early summer, mean embayment depth explains over 50% of the variability in ∑GDD14, with deeper embayments cooling more from lake exchange than shallow embayments. After mid-summer, the cooling embayments are warmed by exchanges with Lake Ontario. This late-summer warming is insufficient to compensate for the cooling effect of the Lake earlier in the summer. Bioenergetic simulations of bluegill, Lepomis macrochirus, growth indicate that most of these embayments are too cool for adequate summer growth of YOY sunfish. Nevertheless, small coastal embayments that are shallow with suitable controls on exchange with the Lake can provide acceptable warmwater fish habitat.
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We discuss a laboratory model of dipole formation due to tidal flow through a channel connecting a bay to the sea. Tidal changes in water elevation lead to periodic flow in and out of the bay through the narrow channel. Due to flow separation there is an asymmetry between the flow entering and leaving the channel on different phases of the tide. A consequence of this asymmetry is that every tidal cycle a fraction of fluid is not returned through the channel, so that a passive tracer in the bay is successively flushed away. We consider what happens when the creation of vorticity in the channel leads to the formation of a dipole that can propagate away from the returning flow of the later phase of the tide. When the dimensionless ratio of maximum channel velocity , width of channel and tidal period is such that , we find that dipoles can propagate away from the source region without being drawn back into the sink. Some results of this process are also presented from a depth-averaged numerical model of a realistic oceanographic situation.
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This paper evaluates the role that different levels of control for combined sewer overflows have in addressing the recreational water quality objectives of the Toronto Inner Harbour of the Toronto and Region Remedial Action Plan. Three models are used to establish the predictive methodology: the Infoworks model for the combined sewer service area, the Hydrologic Simulation-F model for the remainder of the watershed, and the MIKE 3 computer code to evaluate Lake Ontario response to control. Each model was calibrated with E. coli densities observed respectively in sewer discharges, instream, and in the Inner Harbour. Two indices are used to evaluate the response of water quality in the Inner Harbour – fraction of the surface area achieving Blue Flag status, and portion of the swimming season (June to August) above recreation objectives. Analyses of control options led to the recommendation that virtual elimination of combined sewer overflows (one overflow per season control strategy) should be pursued, rather than the lower level of control of 90% volumetric control, which is the minimum provincial environmental requirement. Implementation of priority projects for improving water quality along the Toronto waterfront, including the Don River and Central Waterfront project, are integral to delisting Toronto as a Great Lakes Area of Concern.
Article
Toronto Harbour, adjacent to a large urban centre on Lake Ontario, receives inputs from storm sewers, combined sewer overflows, and urban runoff that lead to contrasting water quality over the waterfront. Toronto’s Inner and Outer Harbours, mesotrophic and meso-oligotrophic, respectively, were investigated in 2008 to assess how water quality conditions were affected by loading gradients, weather and lake circulation. Spatially-intensive measurements of UV fluorescence, turbidity, conductivity, and chlorophyll a, together with lab-based analysis of chemistry at discrete sites, were used to depict patterns and contrasts in water quality in the harbour. Spatially-integrated field sensor data were also employed to examine the efficacy of using discrete water quality sampling to represent average conditions. Nitrogen, total phosphorus, dissolved organic carbon, major ions and E. coli gradients were a recurrent feature among surveys with concentrations decreasing away from the Don River mouth. The limited point-sample data reasonably depicted average conditions among areas of the harbour on the days of survey as did the results interpolated for a long-term monitoring station in the Inner Harbour (IH). The strong variability seen within the IH indicates that the most affected water quality conditions are likely under represented by area-wide conditions. Temporal variability in water quality, correlated with the discharge from the Don River, was strong yet under represented by the field-based sampling. Empirical prediction of TP concentrations in the IH, and correlated with Don River discharge, were used to demonstrate both the critical need to address temporal variability in monitoring design and the possibility of using empirical predictive approaches drawing upon field sensor data to fill this gap.
Conference Paper
Reversing currents in inlets on the Great Lakes are generated primarily by long wave seiching modes of the lakes rather than by the tide. In order to investigate the nature of long wave excitation and the generating mechanism for significant inlet velocities, to establish techniques for predicting inlet-harbor system response, and to develop base data for future planning and design studies, field measurements were conducted in 1974-75 at several harbors on the Great Lakes. Data collected includes continuous harbor water level measurements at all sites, inlet velocity measurements at the primary site (Pentwater, Michigan), and channel hydrographic surveys at the sites where more recent data were needed. Historic water level and velocity data for some of the harbor sites was also available. Amplification of harbor oscillations and generation of the highest inlet velocities are caused by the Helmholtz resonance mode which has a period of 1 to 3 hours for the inlet-harbor systems studied. A recently developed simple lumped-parameter numerical model is shown to be quite effective in predicting inlet-harbor response over the range of excitation periods encountered. Selected data from Pentwater are presented to demonstrate the hydraulic response of the inlet harbor system and the applicability of the lumped-parameter numerical model.
Article
This article presents an overview of selected physical processes and their effects on water quality in Hamilton Harbour. An understanding of circulation and mixing processes are essential to assess the fate and transport of water quality constituents in Hamilton Harbour. Water level measurements showed that in addition to harbour and lake seiches, the Helholtz mode, due to pumping action from Lake Ontario, is important in generating harbour water movements while the circulation patterns in the open waters of the harbour are influenced by prevailing winds. In general, the mean summer circulation consists of two counter-rotating gyres occupying the harbour. Hamilton Harbour physical processes are further characterized by substantial water exchanges with Lake Ontario. These exchange flows play a major role in determining the retention time of the harbour, thereby exerting a large influence on water quality, including hypolimnetic dissolved oxygen concentrations.
Article
Helmholtz resonance basically represents the balance between the kinetic energy of the water flowing in through a narrow connecting channel, and the potential energy from the rise in mean water level within the harbor. It is an additional gravitational mode of substantially longer period than the fundamental free oscillation and can be significant in the contamination of spectra of water levels collected in harbors and in the consideration of harbor flushing times. Theoretical estimates for the Helmholtz periods for an idealized multi-channel basin are computed by means of a multi-degree of freedom resonator and for a more realistic geometry by means of a numerical model. Power spectral analysis of water level records measured during the IFYGL study compare favorably with the theoretical predictions for the Toronto and Hamilton harbors.
Article
Many coastal embayments in the Laurentian Great Lakes have highly variable temperatures due to pronounced movements of the thermocline in the nearshore zone. As an example, we document the diverse thermal regimes in Toronto Harbour, which is also the site of some of the most extensive fish habitat restoration activities in Lake Ontario. Toronto Harbour is characterised by considerable thermal variability as a result of diurnal heat fluxes and large amplitude movements of the thermocline of Lake Ontario. During the ice-free period from April–November 2013, an array of benthic and surface temperature loggers were deployed to obtain the spatio-temporal distribution of water temperatures. Complementary measurements of stratification were made in Lake Ontario at a site 5 km offshore. The dominant periods of short-term thermal variability were 12, 17, and 24 h, reflecting both diurnal heat fluxes and inertial oscillations of Lake Ontario's thermocline. The thermocline in Lake Ontario was observed to oscillate by as much as 15 m, around a mean depth of 9 m, which is comparable to the mean depth of Toronto Harbour. Cold intrusions were found to quickly flow from the lake into the harbour and lead to rapid drops in temperature (e.g., as much as 15 °C in less than 4 h). Such “cold shock” events may be associated with a variety of negative effects on many aquatic organisms, especially warm-water fishes. We consider the potential impacts of the observed temperature variability on cool and warm-water fish species that are the target of restoration activities.
Article
Abstract Lake water level fluctuations provide an important role in flushing shallow coastal embayments in the Great Lakes, specially if the embayment has a resonant response. pecifically, long-period waves (of periods 4 to 30 minutes) can excite resonance in coastal embayments, which greatly increases the lushing rates. We describe how resonance can explain the difference in responses of three shallow (≈2 m) coastal embayments of Lake Ontario and Lake Huron to similar long-period waves. Higher frequency water level fluctuations were analyzed to determine the most influential frequencies within the embayments. Observations in two adjacent embayments in Lake Huron show dramatic differences between their amplified responses to identical forcing, while in Frenchman's Bay the oscillations are damped for the whole forcing spectrum. We model the water level response of the shallow coastal embayments to lake long-period wave forcing using a driven Helmholtz harmonic resonator. We compare and find favourable agreement (R2=78%) between the amplification of water level fluctuations predicted by our model and field values for nearly enclosed embayments, where the Helmholtz mode dominates the energy of the oscillations. Additionally, strong peaks corresponding to the first three natural modes are observed in the water level oscillations of one of the Lake Huron embayments. This embayment has a wider entrance and its stronger amplified response can be explained using an analytical model based on an asymptotic theory of nonlinear resonance of free long-period oscillations induced by wind waves.
Article
Numerical simulations were carried out to determine the residence (or flushing) time of water in Vidy Bay (north shore of Lake Geneva) for different meteorological conditions. A hydrodynamic model (Delft3DFLOW) was applied to simulate the flow field in the embayment during 2010 and January 2011. Using these results, particle tracking was applied to estimate transport of wastewater effluent discharged into the embayment. The model predictions compared well with published field measurements of dissolved species (as given by electrical conductivity profiles) within the wastewater. The pelagic boundary of the embayment was defined by the largest within-bay gyre. Based on this definition, particle tracking was used to quantify the residence time under dominant wind conditions. Similarly, particle tracking was used to determine the travel time (i.e., time to exit the embayment) for each of Vidy Bay’s three inflows (stream, stormwater and wastewater effluent). Although the wind field over the lake is variable, current patterns in the embayment can be simulated using the hydrodynamic model forced by a spatially uniform wind field. For a given wind speed, the main factor influencing residence and travel times is the wind angle. The presence of gyres leads to high mean residence times with large variability. As the wind direction becomes more aligned with the shoreline (i.e., with increasing westerly or easterly components), longshore currents dominate. These disrupt gyre formation and markedly reduce the mean and variability of embayment residence time. The numerical model was utilized to assess the potential for plume movement (in plan) from above the wastewater effluent outfall towards one of Lausanne’s drinking water intakes. In the most direct pathway, westward longshore currents can move water from the embayment to the water column above the intake location.
Article
We present laboratory experiments for tidal starting jet vortices forming at idealized barotropic inlets using dye visualization and particle image velocimetry (PIV) of the surface velocity field. Vortices are identified in the PIV data using the local swirl strength, and metrics are calculated for each identified vortex, including position, equivalent circular diameter, maximum vorticity, circulation, and upwelling potential. These quantitative metrics are presented for four different inlet layouts, including narrow and wide barrier islands and short and long jetties. In each case, starting jet eddies initially form attached to the inlet mouth, with a rapid increase in vorticity, circulation, and size as water exiting the inlet flows directly into the starting jet dipole. Once the vortices reach a critical size, they are entrained into the tidal jet and detach from the inlet. As they advect away from the inlet, their size remains steady while the maximum vorticity and circulation gradually decrease because of the effect of bottom friction and the reduction of input to the vortices from the tidal flow as a result of their advection within the tidal jet. Secondary vortices shed from the inlet during the quasi-steady tidal jet are also entrained into the starting jet vortices, decreasing the overall rate at which their vorticity and circulation decay downstream of the inlet. The quantitative results indicate that the starting jet eddies grow, detach from the inlet mouth, and decay at predictable non-dimensional rates and times.
Article
Standard l-h readings of water level are shown to be unsuitable for determining the periods of seiches of Lake Ontario due to contamination by high-frequency noise (aliasing). During an extensive study of the physical limnology of Lake Ontario, readings of water level at 17 tidal gauges and at 5-min intervals were used to form smoothed 30-min estimates of water level. Spectral analyses of these data revealed that numerically calculated periods by the finite element method were within several percent of observed periods and that computed distriblltions of amulitutle and Dhuse of the four lowest gravitational modes generally agreed - with field data.
Article
A reservoir with distinct shallow and deep regions can produce stratification in response to uniform surface heat loss. The shallow region cools more rapidly, and a cold dense gravity current forms that results in stratification at the base of the deep region and an upwelling of cold water. The surface mixed layer deepens by convective entrainment, and a steady mixed-layer depth can result when the cold upwelling balances the rate at which the mixed layer deepens. The steady depth of the mixed layer depends on the ratio of the area of the shallow region to the area of the deep region. Significant stratification only results when the reservoir has shallow regions that account for more than 50% of the surface area. The depth of the surface mixed layer also depends on the ratio of the depths of the shallow and deep regions, and no significant stratification can form if this ratio is greater than 0.5. For a wedge-shaped geometry, these observations can be generalized by considering the ratio of the average depth to the maximum depth in a reservoir; the gravity current can produce stratification in more than 50% of the depth when this ratio is less than 0.5. Results from a laboratory study and field data from Chaffey Reservoir, Australia, are presented on the surface mixed-layer depth, along with estimates of the time scales needed for atmospheric forcing to lead to the development of stratification.
Article
Accurate simulations of the flow and the transport of water quality constituents in such coastal zones of large lakes as the western end of Lake Ontario and Hamilton Harbour are needed to assess the impact on pollutant levels of cleanup operations and sewage diversions. Coastal models in temperate zone lakes are classified in terms of density stratification, uniform in winter and stratified during summer. During the winter period a 1-D model of the flow between a lake and adjacent harbour is shown to agree favourably with advanced acoustic measurements of the flow in the connecting passage, but does not account for the observed winter buildup of salinity in the harbour. A calibrated 2-D hydrodynamic and salt transport model is used to show that significant exchange does not take place unless the excursion of the inflow is several times greater than the length of the connecting channel, an infrequent occurrence. The exchange is also shown to depend on the flow field at the entrances of the channel. In summer a 1-D vertical model illustrates the dramatic effect of the inflow from Lake Ontario on hypolimnetic temperatures of the harbour. Three-dimensional hydrodynamic and temperature–salt transport models are validated by extensive field observations taken in 1996. The stratified exchange is much stronger than its winter counterpart and more steady. Winter exchange is forced by short-term water level fluctuations, whereas summer or stratified exchange by slowly fluctuating density contrasts between the two water bodies.Key words: exchange flows, hydrodynamic and transport modelling, lakes, harbours, water quality.
Article
Water movements due to temperature gradients and short-term water level fluctuations control the flushing timescale of the many shallow embayments in the Great Lakes. In this article the water circulation within Frenchman's Bay is reported and estimates made of the hydraulic flushing timescale. This shallow freshwater embayment is permanently connected to Lake Ontario through a channel of width 30 m and depth of 2 m. The water flushing timescale is estimated by using a salt mass budget, leading to a flushing timescale of 7–10 days. During the summer, the exchange of water between the bay and the lake can be driven by a combination of horizontal thermal gradients, and by small but ubiquitous 1–5 cm oscillations in the water level of Lake Ontario. The water movements that are predicted due to water level fluctuations (caused by seiches, storm surges and tides) and due to horizontal thermal gradients leads to estimates of the flushing time of water within Frenchman's Bay in the range of 12–13.5 days, i.e. the same order of magnitude as the salt budget. One consequence of the temperature driven exchange flows is to cause strong and persistent temperature stratification within the bay, which in combination with high nutrient loading and low winds in summer leads to frequent anoxic events.
Article
The resonant response of a harbour H of depth scale d and area A to excitation of frequency ω through a mouth M of width a is calculated in the joint limit a2/Aω2A/gd[downward arrow]0. The results are relevant to the tsunami response of narrow-mouthed harbours. 16 is assumed that an adequate approximation to the radiation impedance of the external domain is available (Miles 1972). The boundary-value problem for H is reduced to the solution of [nabla del, Hamilton operator]. (h[nabla del, Hamilton operator]φ) = −1/A, where h is the relative depth, the normal derivative of φ is prescribed in M and vanishes elsewhere on the boundary of H, and the spatial mean of φ must vanish. The kinetic energy in H is proportional to an inertial parameter M that is a quadratic functional of φ. It is demonstrated that decreasing/increasing h increases/decreases M. Explicit lower bounds to M are developed for both uniform and variable depth. The results are extended to coupled basins (inner and outer harbours). Several examples are considered, including a model of Long Beach Harbor, for which the calculated resonant frequency of the dominant mode is within 1% of the measured value. The effects of entry-separation and bottom-friction losses are considered; the latter are typically negligible, whereas the former may be comparable with, or dominate, radiation losses.
Article
Biological responses to physical-chemical processes were examined in Toronto and Hamilton Harbours of Lake Ontario. Nutrient loadings to the harbors are large and are of similar magnitude, yet the trophic conditions of the harbors were considerably different. Lake oscillations were found to determine the flushing rates and environmental stability of the harbors. LOW residence times (<10 days) resulted in homogenous chemical conditions in Toronto Harbour, and prevented the establishment of large phytoplankton crops. The longer retention time of Hamilton Harbour permitted the establishment of huger phytoplankton crops. There probably exists a critical retention time where nutrient input events persist for a sufficient period of time for the algal community to adapt to and exploit the environmental conditions of nearshore areas.
Article
A field study conducted in the summer of 1996 investigated exchange flow between Hamilton Harbour and Lake Ontario through the Burlington Ship Canal. Prevailing westerly winds during July caused upwelling of cold water in Western Lake Ontario. A two-layer exchange flow through the canal was driven by the resulting density difference between Lake Ontario and Hamilton Harbour. In the canal, a lower layer of cold lake water flowed into the harbour while an upper layer of warm harbour water flowed out into Lake Ontario. The intrusion of fresh, cool, oxygenated Lake Ontario water had a dramatic impact on the hypolimnion of Hamilton Harbour. When the prevailing winds shifted to the east in early August downwelling in Western Lake Ontario resulted in a reduced exchange flux that included an episode of 'reverse' exchange with an upper layer of warmer lake water flowing into the harbour. The volume of the exchange during July 8–28 was estimated to be 23% of the harbour volume, with daily mean exchange fluxes of 25–50 m 3 /s. During sustained upwelling, July 16–28, the exchange was 54% less than predicted by inviscid two-layer hydraulics. Frictional effects accounted for 45% of this reduction, while recirculation due to interfacial mixing accounted for the remaining 9%.
Article
As a river flows through shallow littoral regions such as wetlands, forebays, and side arms, the temperature of the water is modified through atmospheric heat exchange. This process, which we call thermal mediation, can control the initial fate of river-borne nutrient and contaminant fluxes within a lake or reservoir. This paper presents temperature observations that demonstrate the occurrence of thermal mediation and directly support the theoretical results derived by AndradOttir and Nepf [2000]. The measurements show that the wetland warms the river inflow by approximately 1-3øC during summer and fall nonstorm conditions. Less thermal mediation occurs during storms, both because the residence time is significantly reduced and because the wetland circulation shifts from laterally well mixed (low flows) to short-circuiting (storms). The dead-zone model can simulate both these regimes and the transition between the regimes and is therefore a good choice for wetland modeling.
Article
We discuss a laboratory model of the flushing and mixing between a bay and a sea connected by a narrow channel. Tidal changes in water elevation lead to periodic flow in and out of the bay through the narrow channel. Due to flow separation there is an asymmetry between the flow entering and leaving the channel on different phases of the tide. A consequence of this asymmetry is that every tidal cycle a fraction of fluid is not returned through the channel, so that a passive tracer in the bay is successively flushed away. We consider what happens when the creation of vorticity in the channel leads to the formation of a dipole that can propagate away from the returning flow of the later phase of the tide. When the dimensionless ratio of maximum channel velocity U, width of channel W and tidal period T is such that W/UT<0.13, we find that dipoles can propagate away from the source region without being drawn back into the sink. This process leads to a larger exchange of water between the estuary and sea, than the classical model of tidal flushing by the jet-sink asymmetry of [Stommel, H., Farmer, H. G., 1952. On the nature of estuarine circulation WHOI Tech. Rep. 52–88, 131].
Ueber die Bewegung tropfbarer Flu€ssigkeiten in Gefa€ssen (On the movement of drippable liquids in vessels
  • J R Merian
Merian, J. R., 1828. Ueber die Bewegung tropfbarer Flu€ssigkeiten in Gefa€ssen (On the movement of drippable liquids in vessels. In German.) Basel, Schweighauser. Reproduced by Vonder-Mu€hll, K., 1886. Mathematische Annalen 27(4), 575-600.
Hydraulics of Great Lakes Inlets, Department of the Army
  • W N Seelig
  • R M Sorensen
Seelig, W. N., Sorensen, R. M., 1977. Hydraulics of Great Lakes Inlets, Department of the Army, Corps of Engineers, Coastal Engineering Research Center, VA.
On the nature of estuarine circulation. Woods Hole Oceanographic Institution
  • H M Stommel
  • H G Former
Stommel, H.M., Former, H.G., 1952. On the nature of estuarine circulation. Woods Hole Oceanographic Institution, Mass. Available at http://hdl.handle.net/1912/2032
Toronto Inner Harbour Water Quality Modelling Report
  • R Dewey
Dewey, R., 2012. Toronto Inner Harbour Water Quality Modelling Report, Environmental Assessment Study Report, MMM Group, 80 Commerce Valley Dr. E., Thornhill, Ontario. Available online at: https://www1. toronto.ca/city_of_toronto/toronto_water/files/pdf/drncwesr-appendix-3-3-toronto_inner_harbour_water_quality_report. pdf
Physical processes and eutrophication
  • G D Haffner
  • D J Pouiton
  • B Kohli
Haffner, G. D., PouIton, D. J., Kohli, B., 1982. Physical processes and eutrophication. J. Amer. Water Res. Assoc. 18(3), 457-464.
Direct effects of dominant winds on residence and travel times in the wide and open lacustrine embayment
  • A M Razmi
  • D A Barry
  • U Lemmin
  • F Bonvin
  • T Kohn
  • R Bakhtyar
Razmi, A. M., Barry, D. A., Lemmin, U., Bonvin, F., Kohn, T., Bakhtyar, R., 2014. Direct effects of dominant winds on residence and travel times in the wide and open lacustrine embayment: Vidy Bay (Lake Geneva, Switzerland). Aquat Sci 76(Suppl 1): 59. doi:10.1007/s00027-013-0321-8
Ueber die Bewegung tropfbarer Flu¨ssigkeiten in Gefa¨ssen (On the movement of drippable liquids in vessels. In German.) Basel, Schweighauser
  • Merian
Summer exchange between Hamilton harbour and Lake Ontario
  • Lawrence