The state of Toronto and Region’s ecosystem: Synthesis and highlights

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: six as impaired (eutrophication/algae, beach closings, aesthetics, fish/wildlife habitat, fish consumption, fish/wildlife populations);one as requiring further assessment (phytoplankton/zooplankton communities);four re-designated as not impaired after assessment (fish tumours/deformities, bird/animal deformities/reproductive problems, benthos, dredging restrictions), and;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 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. This usually occurs between 4–10 times every summer. In addition there are pronounced spatial temperature differences within the harbour that result from the isolation of many shallow embayments from the main body of the harbour or lake; these temperature gradients can drive weak exchange flows. The harbour is polymictic in that there is only intermittently weak vertical stratification. The prevailing westerly winds drive the main circulation through the harbour, with flows from the western gap out through the eastern gap flushing the harbour on a period of 7–14 days. In addition, Hlevca et al. (2018) identify a 1-h water level oscillation throughout the harbour, which can drive a strong oscillating flow between shallow embayments and the main body of the harbour.There is considerable variability, in both space and time, of the water quality parameters in the Central Toronto Waterfront, due to loading gradients, weather and lake circulation. The inner Harbour receives inputs from a variety of sources including storm sewers, combined sewer overflows, and urban runoff. In general Howell et al. (2018) found an improvement in water quality going from the Inner Harbour to the open waters of Lake Ontario. Much of the variability of water quality in the Inner Harbour is due to loading from the Don River – there were spatial gradients in water quality away from the river mouth, and temporal variability associated with storm events. The second largest source of variability was on seasonal timescales; phytoplankton growth in summer led to decreases in nitrate and silicates, whilst changes in runoff correlated with increases in turbidity and DOC. Howell et al. (2018) noted that the variability of water quality in Toronto Harbour complicates the design of monitoring programs, due in part to the episodic lake circulation events and weather events. They recommend the use of mechanistic models of hydrodynamic, water quality and tributary loading processes in order to better understand these temporal changes of water quality to help design better sampling strategies.Combined sewer overflows have a large impact on water quality of the Toronto Inner Harbour (Snodgrass et al., 2018). After heavy rains or snowmelt, discharges from combined sewer overflows can release a mixture of stormwater and untreated sewage into the Don River and the Inner Harbour. Snodgrass et al. (2018) investigated how various control options can be used to achieve blue flag status for the inner harbour during the period when swimming is possible in summer. Model results suggest that given current conditions in the Inner Harbour, most of the waters would exceed the provincial water quality objectives at least 20–40% of the time during the summer swimming period, while near the mouth of the Don River this would occur more than 40% of time. If the control option with a 90%-volume-capture of wet weather flows generated in the combined sewer system is implemented, only the western part of the harbour would have good water quality, where 0-20% of it would meet guidelines. Snodgrass et al. (2018) showed that the preferred control level is the ‘one overflow per season’ scenario, as then most of the recreationally-used parts of the harbour would only exceed guidelines between 0–20% of the time.Water quality impairment is a persistent issue for many Great Lakes Areas of Concern, with excess phosphorus causing eutrophication and algal blooms and E. coli causing beach postings. Legacy sewage contamination sources have long been the focus of remediation efforts, but stormwater and urban wildlife (e.g. waterfowl) can also contribute phosphorus and E. coli into the system. Assessing the variability of total phosphorus (TP) and soluble reactive phosphorus (SRP) as well as E. coli concentrations and sources among stormwater outfall sites and foreshore beach sands will allow for an assessment of how these different areas influence regional eutrophication. Not surprisingly, stormwater outfall sites had elevated SRP and E. coli from human sources suggesting that there are human sewage cross-connections at the surveyed outfalls. Foreshore beach sand typically had the highest TP levels and was more associated with gull fecal contamination. Furthermore, beach sand can act as a reservoir of TP and consequently a source for adjacent water bodies via wave action or groundwater discharge. More research, however, is needed to understand the role of these reservoirs for contributing to localized changes to microbial communities and eutrophication along beach shorelines.Bluffer’s Park Beach, located in the eastern portion of the Toronto and Region Area of Concern, has a long history of being closed for swimming and recreation due to E. coli contamination. Edge et al. (2018) documented how an expanded E. coli surveillance program coupled with microbial source tracking techniques found that animal fecal pollution primarily from gulls and Canada Geese was the source of the contamination which was further affected by runoff from an adjacent marsh and parking lot. Importantly, the findings showed that human sewage was not the primary source. A bird management program implemented in 2006 in addition to the construction of a berm to prevent runoff from the wetland and the redirection of drainage from the parking lot resulted in dramatic improvements in water quality. The beach, which was unsafe for swimming as much as 80% of the time prior to remediation, is now closed less than 20% of the time.Degradation of aesthetics was one of the BUIs identified as impaired in the Stage 1 RAP report. The re-designation (i.e. restoration) criterion was defined as when “waters are free of any substance that produces a persistent objectionable deposit, unnatural colour or turbidity, or unnatural odour (for instance, oil slick or surface scum)” (IJC, 1991). The article by Dahmer et al. (2018) used an Aesthetics Quality Index (AQI) adapted by Heidtka and Tauriainen (1996) to assess the current state of the impairment in the TR AOC. The index includes 4 categories (clarity, colour, odour and debris) which were applied to sites inside and outside the TR AOC. The assessment found that no persistent objectionable deposit, unnatural colour or turbidity, or unnatural odour were perceived in the Toronto Region during the period of study (2012–2015) and recommended future monitoring to assess the impacts of land use and development on aesthetic conditions.Eutrophication is often assessed through standard water quality indicators (total phosphorus, nitrogen, chlorophyll a) but such measures offer little insight into the dynamics of the foodweb they are intended to represent. Munawar et al. (2018) used both autotrophic and heterotrophic indicators to assess ecosystem health in the TR AOC. Autotrophic measures like phytoplankton biomass and primary productivity suggested a range of oligotrophic to mesotrophic conditions. Heterotrophic measures including extremely high bacterial growth rates and elevated microbial biomass, particularly near the mouth of the Humber and Don Rivers, showed that a significant amount of organic matter is being deposited into the receiving waters and shunted through the microbial foodweb. This excess microbial production shows a potential impairment in the phytoplankton and zooplankton communities with the AOC.Much of the central waterfront of the Toronto and Region AOC has been hardened (particularly along the north and eastern shore) and is used for recreational and commercial vessels, which has contributed to the listing of the Loss of Fish and Wildlife Habitat BUI as impaired. To assess the extent of fish use of these hardened shorelines in Veilleux et al. (2018), several 2D acoustic telemetry arrays were deployed in four urban boat slips along the north shore of the central waterfront. Based on the timing and duration of occupancy for seven fish species over one year, there was no reliable evidence that most of these fishes frequented the slips. The sole exception was Northern Pike (Esox lucius), which were found in the two western most slips across all seasons, but in the spring in particular. This coincides with their spawning period and the authors (Veilleux et al., 2018) suggest that Northern Pike in the western slips are staging in preparation for spawning in the adjacent created Spadina Quay Wetland. Overall results from the Veilleux et al. (2018) study support the notion that hardened shorelines provide only limited habitat for many freshwater fishes, with the caveat that tracked individuals were all adults and that future work should explore the use of urban boat slips across a broader range of slip types, (e.g. marinas), fish species and life-history stages.Instream barriers (e.g. dams, weirs and road crossings) fragment aquatic habitat and prevent the upstream movement of fish, impairing the ability of fishes to complete critical life stages, access critical habitat, and dispersal among local populations. Mitigation efforts have improved aquatic connectivity to some degree, but it has been challenging to quantify the overall improvement in connectivity without long-term and costly field assessments. The development of spatially-explicit habitat connectivity indices by Choy et al. (2018) helped identify impediments to fish movement and reviewed and evaluated past restoration actions in five watersheds (i.e. full TR AOC area but excluding west Don and Humber Rivers). Aquatic connectivity improved for diadromous species up to 14.5% and for potadromous species between 0.1 and 4.4% in the five studied watersheds. Some variation in improvement among the watersheds can likely be attributed to differences in mitigation strategies among the watersheds and a historical emphasis on mitigating instream barriers to benefit migratory salmonid species. Recommended next steps by Choy et al. (2018) included using best practices across mitigation and restoration projects that need coordination through a systematic approach using good spatial information.Through various long term monitoring and modeling initiatives, Toronto and Region Conservation Authority (TRCA) has amassed a wealth of knowledge on terrestrial biodiversity, aquatic ecosystems, hydrology, and headwater conditions in 6 AOC watersheds. Using this information, Stille et al. (2018) developed Integrated Restoration Prioritization (IRP) methods to identify impairments and threats to ecosystem function building upon existing TRCA strategies, data systems and monitoring programs. Specifically, the IRP identifies where impairments to ecological function are located, ensures habitats and corridor linkages are protected or restored, and prioritizes local and upstream catchments that could contribute most to improving the natural system where most watersheds are only between 10–40% natural cover, below the 50% target. High priority catchments (12% of total) were identified for restoration, mostly within the Highland watershed but also Etobicoke, Mimico and Rough watersheds.Terrestrial restoration through improved connectivity was mainly identified by Stille et al. (2018) along the Oak Ridges Moraine which is under intense development pressure. High value natural areas requiring protection included northern sections of Humber and Duffins watersheds. The tools developed for the IRP will continue to be updated and identify important areas for protection and restoration and aide in re-designating the fish and wildlife habitat BUI as no longer impaired in the TR AOC watersheds as targets are reached.The health of the fish community in TR AOC was evaluated by Hoyle et al. (2018) by comparing the status for 16 nearshore areas in Lake Ontario and the upper St. Lawrence River. Using data from 2006 to 2016, the authors used complementary fish sampling gear types and protocols, boat electrofishing and trap nets, and published aquatic ecosystem health indicators to evaluate TR AOC fish communities. Indices of Biotic Integrity (IBI) scores were related to the degree of exposure to the open-waters of Lake Ontario, effective fetch, and land cover and use in surrounding watersheds. Focusing on Toronto Harbour, the authors determined that IBI scores were lower (45.1 and 45.6 for electrofishing and trap net gear types respectively) than predicted (55.5 and 59.6) compared to other Lake Ontario nearshore areas with similar physical/environmental conditions but this is not unexpected given the significant influence of Canada’s largest urban area, the City of Toronto. The proportion of fish community biomass comprised of piscivores (0.21 and 0.18 for electrofishing and trap nets respectively) approached target levels (0.20) set for the Toronto Harbour fish community, and indicated a balanced trophic structure. Ongoing aquatic habitat remediation and creation projects around Tommy Thompson Park and the Toronto Islands should ensure maintenance or improvement in fish community health and aquatic ecosystem health in general.Many Great Lakes AOCs have restrictions on fish consumption due to elevated contaminants and are still listed as impaired. In the years since 1987, targets for this BUI were set but there have been changes in fish consumption benchmarks (i.e. more restrictive), angler behaviours, and our understanding of fish ecology, such that there is a need to revisit the BUI criteria. As such, a novel re-designation criterion was developed by Bhavsar et al. (2018) that uses reference sites as a measure of the restrictiveness of consumption guidelines and also narrows the focus solely on locally controllable sources of contaminants (i.e. those that can be managed within the AOC). Additionally, a three-tier Assessment Framework for this BUI was developed and applied to the TR AOC as a case study. For the TR AOC, the Tier 1 criteria were not met due to consumption restrictions for many migratory fishes and some resident species. Similarly, Tier 2 criteria were also not met due to higher PCB levels in Common Carp and White Sucker than reference sites; however, mercury restrictions were comparable to reference areas. Finally, various lines of evidence (e.g. temporal trends in contaminants, angler consumption patterns) were evaluated for Tier 3 and assessed as either not conclusive or not impaired. Ultimately, it was recommended that this BUI continue to be listed as impaired until the Remedial Action Plan (RAP) team has explored whether there are any additional feasible actions that can be taken to improve the BUI locally (i.e. remediating potential PCB sources in some tributaries).Although not all the ongoing scientific work in the TR AOC is included in this special issue, substantial headway has been made in recent years in the continued refinement and assessment of BUI targets and criteria towards delisting. The results in this special issue represent a substantial addition to the scientific literature on relevant topics in the TR AOC in the last decade. The broader literature stems from many of the same research groups but also adds context to the multiple threats to water quality (Dobbs et al., 2012; Nirupama et al., 2014; Wallace and Biastoch 2016), habitats and fish and wildlife (McKenzie et al., 2018; Cusa et al., 2016; Robinson et al., 2015) in Toronto’s urban setting. Within this context the TR AOC special issue papers have shown that water quality continues to be impaired at select locations and along known gradients but there is a path forward for its future remediation (Snodgrass et al., 2018). Similarly beach sources of contamination are better known so targeted actions have and can continue to make improvements. The aesthetics of the local waters are now considered excellent or good throughout the AOC according to Dahmer et al. (2018). Therefore, we are moving the bar closer to re-designating 3 BUIs as no longer impaired, given continued perseverance and action.The basic issues that affect water quality in the TR AOC also resonate up the foodweb (Edge et al., 2018; 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 foodweb dynamics (Munawar et al., 2018) and fish and wildlife populations, such as large-lake water 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).Linked efforts and research on BUIs not presented in this issue are also still ongoing. Recognizing that manmade features can be slightly improved, but larger more natural features are likely to make a bigger impact ecologically, Aquatic Habitat Toronto is focussed on a waterfront restoration et al., that is more and similar to terrestrial presented in this of fish and wildlife such as biodiversity, are being tracked in the Toronto Region but are impaired in the urban (McKenzie et al., 2018; Hoyle and compared to other the to needed habitat improvements and restoration efforts moving forward and Cusa et al., and and Ontario, of and of

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