Saline pollution threatens freshwater ecosystems •

Throughout North America and Europe, human activities are responsible for introducing salt pollution into freshwater ecosystems. Sodium chloride is widely used to melt ice on roads in winter, and inorganic fertilizers contain various salts that can dissolve in rainwater and run off into local waterways. Mining operations also introduce salts into the environment, many of which end up in freshwater ecosystems.

Freshwater organisms are very sensitive to increased concentration of salts, and too high levels can lead to a decrease in biodiversity. In particular, zooplankton are killed by increased salt (sodium chloride) concentrations and, as these microscopic animals feed on algae and are eaten by young fish and many invertebrates, the entire food web is threatened when zooplankton populations decline.

Many governments have environmental guidelines that limit acceptable levels of salt in freshwater ecosystems. However, these vary widely and, as a new study shows, negative impacts on zooplankton populations generally occur at concentrations below these limits. The study, led by researchers from the University of Toledo and Queen’s University at Kingston, found that even at salt concentrations well below the ranges that government regulators have deemed safe and protective of water bodies freshwater, significant damage is caused to freshwater lakes.

“It is clear that saline pollution of freshwater lakes, streams and wetlands, even when limited to levels specifically chosen to protect the environment, threatens biodiversity and the overall function of ecosystems in ‘pure water. This is a global problem that has the potential to impact ecosystems and human health,” said study co-author Rick Relyea, an expert on the impacts of road salt on freshwater ecosystems and director of Rensselaer’s Darrin Fresh Water Institute.

Dr. Relyea, a fellow at the Rensselaer Center for Biotechnology and Interdisciplinary Studies and director of the Jefferson Project in Lake George, has conducted extensive research on the impacts of road salt pollution on aquatic environments. His previous work established that road salt masculinizes developing frogs and that population sex ratios are biased towards males.

Additionally, previous research has shown that although some small zooplankton species can adapt to high salt levels, it erases the circadian rhythm in these individuals. In recent work, Dr. Relyea collaborated with an experimental network of 16 sites in four countries in North America and Europe. Earlier this year, Dr. Relyea and this network produced experimental findings led by Canadian scientist Marie-Pier Hébert, which showed that salinization of lakes reduces the abundance and diversity of zooplankton.

In the present study, researchers measured chloride concentration in freshwater bodies in North America and Europe. They also quantified the population diversity and number of zooplankton present in the natural communities of these habitats. The objective was to determine whether current chloride-based water quality guidelines protect lake organisms in regions with different geology, water chemistry, land use, and species catchments. .

In the United States, the limit for acceptable levels of chloride concentration in freshwater bodies is 230 milligrams of chloride per liter. This limit was established by the US government’s Environmental Protection Agency. In contrast, the limit in Canada is 120 milligrams of chloride per litre. Throughout Europe, the thresholds are generally even higher. For example, in Germany, chloride concentrations between 50 and 200 milligrams per liter are classified as “slightly polluted with salts”, while concentrations between 200 and 400 milligrams per liter are classified as “moderately polluted”. The drinking water recommendation is 250 milligrams per liter in much of Europe.

Alarmingly, the results of the current study, published today in the Proceedings of the National Academy of Sciences, finds that the negative impacts of salinization occur well below these limits. At nearly three-quarters of the study sites, chloride concentration thresholds that resulted in more than 50% reduction in zooplankton were at or below government-established chloride thresholds.

Where zooplankton populations have been reduced, many cascading ecosystem changes have been recorded. For example, the biomass of phytoplankton (tiny plants, also called algae) increased where the number of herbivorous zooplankton was reduced, and this phytoplankton bloom blocked the passage of sunlight to plants growing lower in the ocean. water.

“More algae in the water could lead to reduced water clarity, which could also affect organisms living at the bottom of lakes,” said Shelley Arnott, professor of aquatic ecology at Queen’s University. and co-responsible for the project and the article. “Loss of zooplankton leading to more algae has the potential to alter lake ecosystems in ways that could alter the services lakes provide, namely recreational opportunities, drinking water quality, and fisheries. .”

The researchers say their findings indicate a major threat to biodiversity and the functioning of freshwater ecosystems and urge governments to reassess current threshold concentrations to protect lakes from salinization caused by sodium chloride.

“Many salt-contaminated lakes with chloride concentrations near or above established thresholds in North America and Europe may have already experienced food web changes,” said Bill Hintz, assistant professor of ecology. at the University of Toledo, author and co-director of the study. project. “This applies to lakes around the world, not just study sites. And the variability of our experimental results shows how new thresholds should incorporate the susceptibility of ecological communities at local and regional scales. Governments can protect freshwater organisms in some areas, but many areas in the United States, Canada and Europe cannot.

“Salt pollution resulting from human activities such as the use of road de-icing salts is increasing the salinity of freshwater ecosystems to the point that guidelines designed to protect freshwaters are not doing their job,” said Dr. Hintz. “Our study shows the ecological costs of salinization and illustrates the immediate need to reassess and reduce existing chloride thresholds and establish robust guidelines in countries where they do not exist, to protect lakes from pollution by salt.”

Experts conclude that potential solutions need to be identified, including finding ways to strike a careful balance between human use of salt and ecological impacts on freshwater ecosystems. This could mean reducing the amount of road salt used to melt snow and ice in the winter to keep people and traffic safe.

By Alison Bosman, Personal editor