When Quebec's fresh water becomes salty

Freshwater ecosystems around the world are increasingly salty. Many anthropogenic factors contribute to the salinization of fresh water, including agricultural irrigation, oil extraction, potash mining, and road de-icing.

As a result, the salts enter the waterways. But because bad news never comes alone, salts are often accompanied by a toxic cocktail of other pollutants, the combined health effects of which are largely unknown.

While the problem of the increasing salinization of fresh water has been largely ignored for many decades, it has received considerable attention over the past 20 years.

Scientists around the world, including us, are working together to understand the ecological impacts of increasing salinization on aquatic ecosystems. Our ultimate goal? Examine the adequacy of water quality toxicity thresholds for the protection of aquatic life.

Salinization , a size problem

Canada has the majority of the world's freshwater resources, mainly concentrated in the provinces of Ontario and Quebec), where nearly 5 million tonnes of road salt are applied each year to de-ice roads).

With climate change and increasing frequency and duration of droughts in many parts of the world, the problem is only getting worse. We are talking about a major concern here. Why? Because the availability of freshwater resources will become a critical factor for humanity over the next 50 years.

Inequitable global distribution of the availability of fresh surface water resources (source: Philippe Rekacewicz, February 2006).

Researchers-around-the-world-mobilized

We recently presented a series of articles in a special issue on the salinization of fresh water in the magazine Limnology and Oceanography Letters, published last February).

In this special issue, we focus on sodium chloride (NaCl), the same molecule found in table salt, as a key agent in the salinization of fresh waters. We highlight a series of coordinated field experiments, conducted by researchers from North America and Europe, that addressed the impacts of freshwater salinization on zooplankton (small microscopic crustaceans) at the scale.

Zooplankton are an ecologically essential group in aquatic food webs and are often used as an indicator to detect environmental changes.

The main conclusions of these experiments are as follows:

• Water quality guidelines in Canada and the United States (standards) do not adequately protect freshwater zooplankton, which could lead to an increase in the abundance of algae, on which they feed, in due to reduced predation pressure;
• Salinization of freshwater systematically leads to loss of zooplankton abundance and diversity in all regions]; and
• Individuals of the same zooplankton species do not all have the same salinity tolerance. Thus, this variation may interfere with our ability to predict responses at the community level. Water quality guidelines may therefore need to be adjusted to become more region specific.

Regional coverage of a coordinated mesocosm field experiment, with an example of one of the experiments conducted at Lac Croche (Laurentians, Quebec, Canada) (figure modified from Hintz et al. 2022b).

A regulatory-question

Many questions remain unanswered. However, what we now know is that the long-term water quality guidelines (Canada: 120 mg Cl⁻1L⁻1 and USA: 230 mg Cl⁻1L⁻1 ) and short-term (Canada: 640 mg Cl⁻1L⁻1 ; USA: 860 mg Cl⁻1L⁻1) for chloride concentrations are too high to protect aquatic life in Canada and the UNITED STATES. For reference, a pinch of salt in a boiler of water corresponds to approximately 0.3 mg of Cl⁻1/L⁻1.

In other words, adverse effects are observed at much smaller concentrations. The regulations therefore need to be reviewed in Canada and the United States. In Europe, saline water quality standards for the protection of aquatic life in water ecosystems are mostly absent.

The importance of taking concrete action

The guidelines relating to water quality for the protection of aquatic life are usually established using laboratory tests (called toxicological tests) on a single species.

However, aquatic habitats harbor a complex mix of predators, prey, competitors and pathogens, the interactions of which can limit our ability to predict community and species responses to pollutants.

Thus, collective research published in this special issue also highlights the importance of understanding ecological responses in multispecies communities in the wild to assess the responses of freshwater life to human impacts.

Globally, we should develop more sustainable and efficient alternative applications and technologies.

We also need to establish more appropriate water quality guidelines to improve controls on salts entering our freshwater environments to reduce harmful effects on aquatic life and the quality of our freshwater resources.

Alison Derry, Associate Professor, University of Quebec in Montreal (UQAM); Miguel Cañedo-Argüelles, Profesor lector en Ecología, Universitat de Barcelona, and Stephanie J Melles, Associate Professor, Spatial Ecology, Toronto Metropolitan University

Cet article is republished from The Conversation under a Creative Commons license. Read the original article.