Advancing re-designation of beneficial use impairments in the Toronto and Region Area of Concern: Synthesis and highlights

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Abstract

Since the establishment of the Toronto and Region Area of Concern in 1985 there have been marked improvements in water quality and sediments. These improvements have led to the re-designation of five beneficial use impairments as unimpaired. For the remaining six beneficial use impairments (five listed as impaired and one requiring further assessment), efforts are underway to assess their status and identify actions that could lead towards their re-designation. Here we introduce a series of nine articles that establish benchmarks of current conditions, provide critical supporting information to undertake an assessment, or directly assess (or re-confirm) the status of a beneficial use impairments.

Introduction

Over the past 30 years, there have been dramatic improvements in the condition of the Toronto waterfront. Water quality, beaches, contamination of fish, aesthetics. All have changed for the better. How did this change come about? In 1985, Toronto and Region was identified by the International Joint Commission as one of 42 Great Lakes Areas of Concern (AOC and increased to 43 in 1991) under the Canada-US Great Lakes Water Quality Agreement. Areas of Concern are locations where water quality and ecosystem health are degraded due to local sources of pollution caused by human activities. The Toronto and Region AOC (herein the Toronto AOC) is comprised of six watersheds—Etobicoke Creek, Mimico Creek, the Humber River, the Don River, Highland Creek, and the Rouge River—which drain an area of approximately 2000 square kilometers and spans 42 km of waterfront (Fig. 1). The AOC also includes Canada’s most populous city and is home to over four million people.

Following designation, individual AOCs developed remedial action plans (RAPs) to guide restoration and protection efforts, with the goal of restoring beneficial uses degraded by pollution, such as safe fish consumption, clean beaches, and healthy fish and wildlife populations. In total, the International Joint Commission defined 14 different possible human or ecological beneficial uses and, in 1987, eight of these beneficial uses were deemed impaired in the Toronto AOC, and three required further assessment (Fig. 2). These Beneficial Use Impairments (BUI) largely stemmed from several centuries of agriculture, industrialization, and urban development that drastically reshaped the terrestrial and aquatic environments in and around the region.

Remedial actions over the past 30 years have led to significant and demonstrable improvements in the quality of water and sediments, resulting in the removal of five BUIs that are no longer considered to be impaired in the Toronto AOC: bird and animal deformities or reproductive problems (BUI#5 in 2011); fish tumours or other deformities (BUI#4 in 2011); degradation of benthos (BUI#6 in 2013); restrictions on dredging activities (BUI#7 in 2014); and degradation of aesthetics (BUI#11 in 2020). As of early 2021, five impairments remain: restrictions on fish consumption (BUI#1), degradation of fish and wildlife populations (BUI#3), eutrophication or undesirable algae (BUI#8), beach closures (BUI#10), and loss of fish and wildlife habitat (BUI#14); one, the degradation of phytoplankton and zooplankton communities (BUI#13), requires further assessment.

The improvement of conditions in Toronto AOC watersheds and along the lakefront is largely attributable to collaborative restoration efforts, and more will be done. Currently underway and expected to be completed by 2024, the Don Mouth Naturalization and Port Lands Flood Protection Project will reroute the mouth of one of Toronto’s largest rivers through wetlands and greenspace, adding approximately 14 ha of aquatic habitat to the waterfront. Work also continues on the Don River and Central Waterfront Combined Sewer Overflow project. Estimated at $3 billion, the project is Canada’s most extensive and expensive stormwater management initiative and will take nearly 25 years to build, completion is targeted for 2038. The project will virtually eliminate combined sewer overflow events in the Lower Don River, Taylor-Massey Creek, and Toronto’s inner harbour, using an integrated wet weather flow management system to capture, store, and transport stormwater. It will ensure enhanced climate change adaptation to increased stormwater flow, as well as provide a buffer for future urban growth effects.

With these changes and more on the horizon, this Toronto and Region AOC special issue provides a snapshot of the current state of beneficial use impairments in the Area of Concern. It will serve as a benchmark against which to compare past and future conditions and will help us to better understand the impact of AOC restoration efforts. Here we briefly summarize the findings of these contributions.

Section snippets

BUI#3 – Degradation of fish and wildlife populations

The Toronto AOC has been a focal area for science that has led to the development of multiple special issues in different scientific journals. The most recent special issue noted that a key missing piece was the assessment of the wildlife component of BUI#3 (Doka et al., 2018) and the present special issue summarizes recent research seeking to resolve this deficiency. The sources of much of the impairments to wildlife populations within the Toronto AOC watersheds are the loss or degradation of

BUI#6 – Degradation of benthos

Benthic invertebrate assemblages have long been used as integrative biological indicators of environmental conditions in the AOC, dating back to Brinkhurst (1970) who used the distribution of oligochaetes to diagnose organic enrichment of Toronto Inner Harbour. The composition of benthic invertebrates has been periodically assessed in agency monitoring and research studies that contributed to the removal of the BUI “Degradation of Benthos” from the list of impairments in the Toronto and Region

BUI#8 – Eutrophication and undesirable algae

Howell and Benoit (2021) have provided two articles that summarize extensive field studies in 2018 to advance the assessment of the eutrophication and undesirable algae Beneficial Use Impairments in the Toronto and Region Area of Concern. The results from Howell and Benoit (2021) provide important context for assessing water quality conditions across a broad range of lake characteristics and conditions along 60 km of shoreline including the Toronto and Region (AOC). Using conductivity and

BUI#10 – Beach closures

Microbial pollution of the Toronto AOC adversely affecting water resources and recreational use of the lake has been a longstanding concern. Improvements in beach water quality aided by storm water remediation projects conducted by the City of Toronto have greatly improved access to water recreation at public beaches (Kidd, 2016), however, the BUI of “beach closures” remains impaired with problem areas of microbial pollution and in part attributable to human fecal pollution known in the AOC.

BUI#13 – Degradation of zooplankton and phytoplankton

Studies in recent years examining plankton ecology in the AOC (e.g., Currie et al., 2015) will help resolve whether the BUI addressing the condition of phytoplankton and zooplankton communities should be considered impaired. Munawar et al. (2018) suggested that elevated bacterial growth rates and elevated microbial biomass at mouths of Humber and Don River, attributed to elevated loading of organic material, was impacting phytoplankton and zooplankton communities by altering the microbial food

BUI#14 – Loss of fish and wildlife habitat

Historically, the extensive coastal marshes of the Toronto waterfront supported a diverse and productive fish and wildlife community (Whillans, 1982). Through infilling and shoreline modification much of these natural habitats have been lost or degraded; however, extensive habitat creation and remediation efforts are underway, guided by the recently updated Toronto Waterfront Aquatic Habitat Restoration Strategy (TRCA, 2003). To compile information on the progress that has been made over the

Conclusions

As of early 2021, five BUI remain listed as impaired and one requires further assessment in the Toronto AOC. The research presented in this special section target five of the six outstanding BUIs and reviews one previously delisted BUIs to help inform their re-designation or identify additional works that are required to meet their targets. For BUI#3, Cartwright et al. (2021) determined that birds and amphibians within the Toronto AOC watersheds fall within ranges from comparable wetlands

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