Science at the lakeshore: measuring cumulative stress in the Canadian Great Lakes nearshore waters

Arial view of the Scarborough Bluffs, Toronto, Ontario.

The Great Lakes Water Quality Agreement includes a commitment to develop a nearshore framework that provides an overall assessment of the state of the nearshore waters. 

The Great Lakes Nearshore Waters Assessment is the first cumulative assessment of the Canadian Great Lakes nearshore waters. Different kinds of data, which were traditionally evaluated separately, were integrated to support better decision making on water quality and ecosystem health.

Understanding nearshore water quality and ecosystem health through collaboration

Data used in the assessment came from existing monitoring programs, such as Ontario’s Nearshore Long-term Monitoring Network, Canada’s Great Lakes Water Quality Monitoring and Surveillance Data, and the U.S. National Oceanic and Atmospheric Administration’s Harmful Algal Bloom Monitoring Program.

Scientists collected data on water quality, coastal processes, ecosystems and advisories on human use from various government and non-government organizations to assess the overall state of the nearshore waters and the potential for impacts on human health. 

Colour coded map marking the Regional Units for Lake Ontario.
The nearshore was classified into Regional Units using physical characteristics such as water depth, lake bottom composition, wave energy and coastal units known as littoral cells. The Regional Units were then classified based on their overall ecological type. Photo credit: Lake Ontario nearshore assessment: 2019 highlights report.

Stressors identified through the assessment

  • Large-scale algae blooms due to excessive loads of nutrients from agricultural runoff
  • Industrial releases of harmful substances
  • Aquatic invasive species from shipping
  • Loss of biodiversity and habitat due to shoreline alterations
  • Closed beaches due to the threat of illness from pathogens such as E. coli

Getting a clear picture of nearshore areas

The results of the nearshore framework allow partners and stakeholders to be more informed in setting priorities and making decisions, as well as to prioritize local management actions and fill science gaps to target the most pressing threats to nearshore ecosystem health. For example, most regions on Lake Ontario were assessed as having moderate cumulative stress, but for a variety of reasons. This highlights how stress on an area can be caused by different sources that may interact together. Assessing these potential issues helps support effective and evidenced-based decision-making.

By continuing to conduct regular cumulative effects assessments of the nearshore, decision makers can prevent negative effects in areas of high ecological value, partners and stakeholders can access information to prioritize action, local citizens and communities are better equipped to discuss priority actions, and scientists are better enabled to inform long-term management measures.

Map showing all the Regional Units for Lake Ontario with legend
2019 Lake Ontario Nearshore Assessment: Results placemat. Source: Lake Ontario Canadian nearshore assessment: 2019 highlights report.

Map showing all the Regional Units for Lake Ontario with the legend: very low stress, low stress, moderate stress, high stress, and concerns to human and ecosystem health due to cyanobacteria. All units are coded as moderate stress. Niagara Peninsula, Hamilton Harbour and Burlington Beach to Humber Bay are labelled “low benthic community quality.” Hamilton Harbour is labelled as having “contaminants detected in sediment that exceed severe effect levels. Burlington Beach to Humber Bay is labelled as having “the most littoral barriers (12) of any Regional Unit.” Pickering to St. Mary’s Cement Pier, St. Mary’s Cement Pier to Cobourg, and Cobourg to Gull Island are labelled as having “low levels of shoreline hardening but multiple littoral barriers present.” Kingston Basin is labelled as having “beaches posted over 20% of July/August 2018.” Bay of Quinte is labelled as having the “longest total length of tributaries of any Regional Unit however dams significantly impede connectivity.” An inset map labelled the St. Lawrence River shows Thousand Islands region, Brockville to Iroquois Dam, and Iroquois Dam to Moses Saunders Dam is labelled as having “beaches posted over 5% of July/August 2018.” Thousand Islands Region is labelled to indicate the “dam at Gananoque impedes tributary connectivity.” Additional labels over Lake Ontario state “nuisance Cladophora wash up can foul shorelines and beaches, high extents were detected from Burlington Beach to Humber Bay, all along the north shore of Lake Ontario and into Kingston Basin,” “shoreline hardening and presence of littoral barriers impede natural coastal processes along much of the Lake Ontario open coast,” and “cyanobacteria is a concern to human and ecosystem health in Hamilton Harbour, Bay of Quinte, and Kingston Basin.”

An innovative approach to understanding cumulative effects

You can view the Great Lakes Nearshore Waters Assessment on the Open Science and Data Platform at various scales and click on the results for each category to better understand sources of stress across eleven individual measures, grouped into four categories: coastal processes, contaminants in water and sediment, nuisance and harmful algae, and human use. Each measure was evaluated as low, moderate or high stress then grouped into an overall cumulative stress score.

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