New research, co-authored by Queen’s doctoral candidate Jamie Summers (Biology), has determined that salt levels in many North American lakes are increasing.

The study also determined that a paved surface area of only one per cent around a freshwater lake substantially increased the risk that the salinity (chloride concentration) of the water would increase. Over a quarter of freshwater lakes in the United States had sufficient paved or impervious surface area within 500 metres of their shores to put them at risk of increased salinization.

“We found, across a fairly large region, that many lakes are becoming elevated in salt concentrations and that the run-off from a relatively small amount of development near a lake likely contributes to this,” Ms. Summers explains. “With our population becoming increasingly urbanized, and urban environments expanding, there is a salt threat to our freshwater lakes.”

The researchers examined long-term trends in salinity levels as measured in lakes and reservoirs across North America, with attention paid to the northeastern United States and the province of Ontario – the North American Lakes Region. The team examined lakes with salinity data dating back a minimum of 10 years, and excluded lakes that varied greatly in water levels.

As many of these lakes are in regions that experience cold winters, the team considered road salt as a source of the elevated lake salinity. The percentage of paved surface area within 500 metres of the lakeshore was used as a proxy for salt inputs. The study found a strong relationship between lake salinity and the percentage of paved surface area, with increasing salinity trends in lakes with as little as one per cent of the land area being paved within the 500-metre buffer.

The researchers estimated that more than 7,770 lakes in their U.S. study region were at risk of elevated salinity, with road salt applications as a likely source. Ms. Summers says these figures are likely a conservative estimate, due to often incomplete lake data. The research team further determined that 14 lakes were on track to reach the U.S. Environmental Protection Agency’s aquatic life threshold criterion for chronic chloride exposure by 2050.

“We have known for a long time that human activities, such as applying road salt can have an impact on lake ecosystems, but seeing the extent of the problem and how much of an effect urbanization and road salting can have on lakes is an eye-opener,” Ms. Summers says. “A small amount of development in a watershed can yield substantial risks for important fresh waters.”

The paper is the result of a collaboration between the fellows of the Global Lakes Ecological Observatory Network (GLEON) and data contributions from dozens of sources. An international grassroots network of researchers, GLEON organizes and completes research on lakes and reservoirs all over the world to examine how lakes are responding to a changing global climate. The fellowship consists of 12 PhD candidates who receive 18 months of funding and logistical support to collaborate on a research project in a diverse international team.

The complete study, titled Salting our freshwater lakes, is available online from the Proceedings of the National Academy of Sciences.