Accumulation of de-icing salts in lakes threatens those who live there
Canada dumps millions of tons of de-icing salts on the roads each year and this causes salt pollution which can become toxic for certain organisms in fresh water. An article by Marie-Pier Hébert, post-doctoral fellow at the University of Vermont and UQAC.
ANALYSIS – Like many countries with cold winters, Canada sprays millions of tonnes of de-icing salt on the roads every year. Although we no longer see them under our feet in the spring, road salts do not disappear by magic: they dissolve, run off and accumulate (in part) in bodies of water.
Saline pollution can, however, quickly become toxic to certain freshwater organisms.
Certain species of microscopic animals, such as crustacean zooplankton (including the famous “water fleas”), can be sensitive to the increase in salinity in their environment. The loss of these small aquatic grazers could lead to significant environmental consequences, such as the proliferation of algae (normally grazed by zooplankton) or the reduction of food intake for young fish.
As an aquatic ecologist, I study how freshwater ecosystems and organisms respond to global change. With colleagues from some twenty universities around the world, including a team from the interuniversity research group in limnology (GRIL) at UQAM and McGill University, I participated in a series of international studies in order to to better understand the response of freshwater plankton to salinization.
An environmental issue on a global scale
Often measured as chloride (an ion commonly found in salts), the salinity of many lakes, rivers, ponds and wetlands is gradually increasing due to human activities. The causes are multiple. Runoff from de-icing salts (such as sodium chloride) applied in winter can play a major role in colder regions, but other practices such as agricultural fertilizer application, mining, raising the sea level or land deforestation also contribute to the salinization of fresh waters.
The catch is that once the salts infiltrate our freshwater supplies, it is difficult, if not impossible, to extract them. Chloride contamination can persist for decades. The accumulation of de-icing salts, for example, can, among other things, pose problems for the management of drinking water and the release of harmful substances into water bodies. In fact, the salinization of fresh waters today represents a global environmental issue.
Loss of zooplankton and associated consequences
To assess the plankton fragility threshold of large-scale lakes, our international research team coordinated to carry out the same study in experimental enclosures in 16 lakes in North America and Europe. Our research indicates that increased salinity can cause loss of biodiversity and high zooplankton mortality at chloride levels similar to those measured in lakes polluted by de-icing salts.
Similarly, in nearly half of the experimental sites in the study, the massive loss of grazing zooplankton allowed algae to proliferate. In lakes, algal blooms can reduce water clarity (which can, among other things, harm organisms living deeper) and compromise certain “services” provided by these ecosystems, such as the quality of drinking water. , fisheries or recreational activities. In other words, the sensitivity of zooplankton to salt pollution can create a domino effect on other links in the aquatic food chain, thus destabilizing the ecological balance of lakes and harming their health.
These research results reinforce the conclusions drawn from other studies, but on a larger scale. Most studies on the subject focus on a single body of water or on model species in the laboratory. By joining forces with researchers elsewhere in the world, this collective effort has made it possible to show that a multitude of zooplankton species commonly found in lakes are sensitive to salinization, even if the environmental conditions differ.
As in many areas of science, there are always certain limits to what can be concluded from a study. That said, when you get the same results repeatedly and in multiple places, you can start thinking about the next step: the application of research findings and sociopolitical issues.
Appeals to public authorities
An important observation resulting from the work: the concentrations of chloride that can cause the mortality of 50% of zooplankton are often lower than the threshold concentrations established by government directives. In other words, whether in Canada, the United States or several places in the European Union, current water quality regulations are not stringent enough to protect lakes from pollution by salt.
In their natural state, freshwater ecosystems contain very little chloride; say, usually less than 20 mg Cl–/L. The threshold concentration considered safe for aquatic life in Canada is 120 mg Cl–/L, while in the United States it is 230 mg Cl–/L (about one or two tablespoons (s) of table salt in a bucket of fresh water).
Although adverse effects (especially on zooplankton) may occur below these chloride concentrations, one might still believe that the more conservative guidelines in Canada are safer. But it would still be necessary for these maximum thresholds to be maintained. This is not always the case, as the World Wildlife Fund of Canada (WWF-Canada) reminds us. In fact, chloride levels in lakes polluted by de-icing salts can reach several hundred, and sometimes even thousands, of mg/L.
Every winter, more than five million tonnes of salt are dumped on Canadian roads, pavements and parking lots; the metropolises in the east of the country, such as Montreal and Toronto, can spread nearly 150,000 tonnes on their own. The researchers call for reducing the application of road salts and considering alternative options. A recent study has also suggested some practices to improve management, such as the use of brine-based liquids to reduce the amount of salt applied. One thing is certain, it seems to have become imperative to develop dialogue with decision-makers and political leaders in order to ensure road safety while protecting environmental health.
Marie-Pier Hébert, Post-doctoral fellow at l’ University of Vermont and at UQAC; Aquatic Ecology Research.
This article is republished from The Conversation under a Creative Commons license. Read the original article.