by Mary Ann Gratton
The levels of contamination to water and sediment in Frenchman’s Bay in Pickering, Ontario greatly exceed provincial water quality standards, in some cases by as much as 250 per cent, according to a new study by researchers at the University of Toronto Scarborough. This is mostly due to large amounts of road salt applied in winter, especially to Highway 401, the study finds.
Transportation infrastructure – roads, parking lots and railways – is the primary source of contaminated water and sediment and a decline in aquatic life in the watershed and lagoon, according to a recent article in Sedimentary Geology written by geology professor Nick Eyles and recent PhD graduate Mandy Meriano.
The densely populated area along Highway 401 and its accompanying traffic volume have profoundly affected the geology and characteristics of water in the bay and nearby city, according to the article, “Road-impacted sediment and water in a Lake Ontario watershed and lagoon, City of Pickering, Ontario, Canada: An example of urban basin analysis.” The growing city of Pickering, with a current population of 100,000, is sprawled across a densely urbanized watershed that has been “hardened” by roads, rail lines, buildings and parking lots, the authors write.
The researchers conducted an extensive study of the streams and groundwater entering Frenchman’s Bay over a five-year period using sophisticated field testing and groundwater modeling methods. Some 7,600 tonnes of de-icing salt are applied to nearby roads each year, with more than half of it accumulating in groundwater and returning as brackish (salinated) baseflow into creeks year round, they note. “The remainder is rapidly delivered by surface runoff to Frenchman’s Bay, where chloride contents are more than double the average values in waters across the Great Lakes,” the report states. “Highway 401 is the largest single source of salt contamination to the lagoon, which receives 26 per cent of all road salt applied to the watershed but covers just 1.3 per cent of its area.”
The authors also found that levels of other urban contaminants such as metals, E. coli and coliform were all elevated well above Canadian water quality standards. The authors describe “finger-like plumes of contaminated water” in the bay due to excavation trenches backfilled with gravel as well as leakage from municipal drinking water pipes and sewers, creating “local dilution and/or contamination.”
A decline in ecosystem diversity in Frenchman’s Bay is also noted in the report, reflected in the absence of fish in creeks, significant changes in the age structure of fish populations and a much lowered diversity of aquatic species. The report highlights the loss of wetlands by urban runoff.
“Our findings are pretty dramatic, and the effects are felt year round,” says Eyles. “This is a really bad news story about the relentless chemical assault on a watershed, with bleak implications that go far beyond the lagoon itself. We now know that 3,600 tonnes of road salt end up in that small lagoon every winter from direct runoff in creeks and effectively poison it for the rest of the year. The future of Frenchman’s Bay is not bright, but this also affects the Great Lakes.”
The contaminated water from Frenchman’s Bay flows directly into Lake Ontario and Eyles says it is typical of many urban watersheds across the Great Lakes basin. This basin is home to 36 million Canadians and Americans. The urban impact on the lakes is a major concern because these waters are used for drinking supplies. The water quality of the Great Lakes was identified as being at risk from urban development when the International Joint Commission’s Great Lakes Water Quality Board report was released in 2003, he notes.
The $500,000 study by Eyles and Mariano is one of the most specific and detailed geological research projects on any watershed in Canada, and one of the most well financed studies of its kind, with thorough multi-year monitoring of conditions in both summer and winter.
The authors hope the report will highlight the impact of urban development and infrastructure on water quality, not just in Frenchman’s Bay but in all bodies of water near urban areas. “The world is increasingly urban, but very few studies have been done of how contaminated water and sediment move through urban basins with their built landscapes and complexly disturbed geology,” the report states. Eyles notes that many other bodies of water near urban areas likely have similar results, but such extensive watershed studies of this kind are rare, due to the cost and time involved.
“We as a society haven’t recognized the magnitude of the problem,” Eyles said. “We talk about the need to clean up rivers and lakes, but the discussions are like telling someone they have a cold when they actually have cancer.”
Using traditional sedimentological and stratigraphic methods, Eyles and Mariano tested water samples from boats and on land. They used depth probes in the water and drilled wells into the earth to extract groundwater samples in a comprehensive study of the effects of salt and sediment.
These findings reveal the need for better planning and improved urban design that take into account the impact of development on water quality, Eyles said.
Road salt and sediment are not the only contaminants in Frenchman’s Bay and surrounding waters, the report notes. “Surface waters in the basin are badly impacted by other urban contaminants, indicating persistent bacterial sources in the watershed. These sources included leaking sewer mains, illegal connections, or, most probably, the presence of combined sewers that handle both storm runoff and sewage, and which are prone to overflows during storms. High maintained values of total nitrate and total phosphate during flood events are typical of sewage-impacted urban waters. Creek waters contain elevated levels of metals, such as cobalt, copper, chromium, iron, zinc, phosphorus, aluminum and anadium typical of automobile-related contaminants found in urban surface waters draining roadways and parking lots, at concentrations that exceed water quality standards by considerable margins regardless of season. Waters remain brackish year-round.”
The report warns that the volume of people and cars in the Pickering area, a major transportation corridor in southern Ontario, will be compounded when the new community of Seaton, Ontario, now in development in the region, is built, bringing in another 85,000 people. That development “represents a new and very large source of contaminated urban water that will move south through the basin to Lake Ontario,” Eyles notes. The land earmarked for the Seaton development, he notes, is sitting on a huge aquifer -- an underground layer of water-bearing permeable rock or materials such as gravel, sand, silt or clay from which groundwater can be usefully extracted using a well. “But if you plunk a massive urban development on there, you are saying goodbye to that aquifer. How will people look back on that decision in 100 years, when water is in short supply?”
The current situation in the City of Pickering and the impact on the watershed “is not environmentally sustainable in the face of continued urban development and continued increases in population density, the report states. The research was conducted with the financial support and co-operation of the City of Pickering, Eyles said. The city has created a Waterfront Committee that is considering the implications of the report to decide on future steps.
Funding for the research also came from grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Ontario Innovation Foundation. The Eyles and Mariano study builds on previous studies, including research by fellow UTSC professor Ken Howard and the Toronto and Region Conservation Authority.