Freshwater ecosystems around the world are getting saltier. Many anthropogenic factors contribute to the salinization of fresh water, including irrigation of agricultural land, oil extraction,potash mining and road de-icing.
Read more: Accumulation of de-icing salts in lakes threatens those who live there
Consequently, the salts enter the waterways. But since bad news never comes alone, salts are often accompanied by a toxic cocktail of other pollutants, whose combined effects on health are largely unknown.
While the problem of increasing freshwater salinization has been largely ignored for many decadesit 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? Review the adequacy of water quality toxicity thresholds for the protection of aquatic life.
Salinization, a major 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 clear the roads).
With climate change and the increased 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. For what ? Because the availability of freshwater resources will become a critical factor for humanity over the next 50 years.
Researchers from all over the world mobilized
We recently featured a series of articles in a special issue on freshwater salinization in the journal 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 the zooplankton (small microscopic crustaceans) on a regional 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 increased abundance of algaeon which it feeds, due to reduced predation pressure;
Salinization of fresh water systematically leads to a loss of abundance and diversity of zooplankton In every region]; 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.
A matter of regulation
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 ; US: 860mg 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 seen 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
Water quality guidelines for the protection of aquatic life are usually established using laboratory tests (called toxicological tests) relating to 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, the collective research published in this special issue also highlights the importance of understanding the ecological responses in multispecies communities in the wild to assess the responses of freshwater life to human impacts.
Overall, we should develop alternative applications and technologies more durable and more efficient.
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.