The salinity of freshwater ecosystems caused by road de-icing salts, agriculture fertilizers, mining operations and climate change is increasing worldwide and current water quality guidelines don’t do enough to address the issue, an international study led by Queen’s University and The University of Toledo has found.

The research, conducted in collaboration with dozens of scientists across North America and Europe, shows significant damage is being done to freshwater lakes by salt concentrations that are below ranges government regulators have deemed safe and protective of freshwater organisms.

Using an experimental network of 16 sites in four countries, the research recently published in the Proceedings of the National Academy of Sciences indicates freshwater salinization triggers a massive loss of zooplankton, a major food source for fish, and an increase in algae — even at the lowest chloride thresholds established in Canada and the U.S. and throughout Europe.

Researchers say the results indicate a major threat to the biodiversity, water quality and functioning of freshwater ecosystems and the urgency for governments to reassess current threshold concentrations to protect lakes from salinization sparked by sodium chloride, one of the most common salt types leading to the salinization of freshwater lakes.

“More algae in the water could lead to a reduction in water clarity, which could affect organisms living on the bottom of lakes as well,” said Dr. Shelley Arnott, professor of aquatic ecology at Queen’s University and co-leader of the project and paper. “The loss of zooplankton leading to more algae has the potential to alter lake ecosystems in ways that might change the services lakes provide, namely recreational opportunities, drinking water quality and fisheries.”

The lowest threshold for chloride concentration in the U.S. established by the Environmental Protection Agency is 230 milligrams of chloride per liter. In Canada, it’s 120 milligrams of chloride per liter. Throughout Europe, thresholds are generally higher.

It can take less than a teaspoon to pollute five gallons of water to the point that is harmful for many aquatic organisms.

“Salt pollution occurring from human activities such as the use of road de-icing salts is increasing the salinity of freshwater ecosystems to the point that the guidelines designed to protect fresh waters aren’t doing their job,” said Dr. Bill Hintz, assistant professor of ecology at The University of Toledo, author of the paper and co-leader of the project. “Our study shows the ecological costs of salinization and illustrates the immediate need to reassess and reduce existing chloride thresholds and to set sound guidelines in countries where they do not exist to protect lakes from salt pollution.”

Additional information

Scientists across the globe contributed to the new project, from the University of California Irvine, University of Barcelona, Ohio Wesleyan University, Wilfrid Laurier University, Ryerson University, Rensselaer Polytechnic Institute, the Ontario Ministry of Environment, Purdue University, University of California San Diego, Dartmouth College, University of Évora, University of Vic – Central University of Catalonia, University of Helsinki, Ontario Tech University, McGill University, Linnaeus University, Uppsala University, Swedish University of Agricultural Sciences, Karlstads University, Montclair State University, Wayne State University, Carl-von-Ossietzky University Oldenburg, Lund University and Université du Québec à Montréal.

Additional papers led by other authors from the 16-site study as part of the Global Salt Initiative led by Arnott and Hintz include:

• Marie-Pier Hébert et al. 2022 in the journal Limnology and Oceanography Letters, titled “Lake salinization drives consistent losses of zooplankton abundance and diversity across coordinated mesocosm experiments.”

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Victoria Klassen
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Queen’s University
Victoria.klassen@queensu.ca
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Queen’s University has a long history of scholarship, discovery, and innovation that has shaped our collective knowledge and helped address some of the world’s most pressing concerns. Home to more than 25,000 students, the university offers a comprehensive research-intensive environment with prominent strengths in physics, cancer research, geoengineering, data analytics, surveillance studies, art conservation, and mental health research. Welcoming and supporting students from all countries and backgrounds to a vibrant, safe, and supportive community is an important part of the Queen’s experience. Diverse perspectives and a wealth of experience enrich our campus and our community. A core part of our mission is to engage our students, staff, and faculty in international learning and research, both at home and abroad.

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