This text is part of the special Environment section
In North America and Europe, fresh waters are increasingly saline due to human activity. An international team of researchers reveals that ecosystems and biodiversity are threatened, and wants measures to be taken so that lakes and rivers are further protected.
In Canada, a lake is considered too saline when it contains 120 milligrams of chloride per liter of water. Above this concentration, aquatic species would be in danger. This threshold established by the federal government is based on recommendations resulting from laboratory tests. Researchers thus observe in the laboratory the effect of salinization on the components of lakes, isolating each element, explains Alison Derry, professor in the Department of Biological Sciences at the University of Quebec in Montreal (UQAM), who criticizes this methodology.
“We must study the responses in aquatic environments, with entire communities, with competition between individuals of the same species or of other species, with predators. When we have pollution, it is not an individual who is exposed, it is all the species together, ”she illustrates.
Alison Derry is part of the Global Salt Initiative, an international group of researchers. In 2018, the latter conducted field analyzes in Europe, Canada and the United States. In lakes that had salt levels below regulatory thresholds, she and her colleagues observed a decrease in the populations and varieties of zooplankton.
Zooplankton are tiny organisms found in pools of water. They mainly eat algae. With their decline, the team also noted an increase in blue-green algae. These little creatures are also a very important food source for fish larvae and small fish. Their decline could therefore cause an imbalance in the food chain and jeopardize the survival of larger fish.
However, this assertion remains speculative. If we know well the effect of methane and carbon dioxide on the environment, we measure much less that of the salinization of lakes and rivers. “Salt is not like heavy metals. Chloride, in fact, is quite natural, it is found in geology, on our table. We do not consider salinity to be a pollutant,” emphasizes Alison Derry.
The latter co-edited a special edition of the scientific journal Limnology and Oceanography Letters, entirely devoted to the observation of the effect of chloride in fresh water. She hopes that new research will emerge in the wake of this publication published at the beginning of the year. “We really need to conduct more studies to better understand the phenomenon. Salt does not arrive alone in the lakes, it is often a cocktail that contains other substances, such as oils, metals. »
Whose fault is it ?
De-icing salts applied to roads in winter to make them less slippery are identified as the main culprits. When the snow melts, they run off or are absorbed by the soil and make their way to lakes and rivers. The spreading of chemical fertilizers in agricultural areas, oil extraction, mining, rising sea levels are also blamed.
Bad news: climate change is likely to make the situation worse. Some regions will experience more precipitation, which will lead to even greater use of salt on the streets during the cold season, while other areas will face drought, evaporation from freshwater sources and therefore to the increase in their chloride content.
Each territory should thus imagine its own tailor-made solutions to protect aquatic life. “In Quebec, there are so many things that could be done. The first step is to review the policies. How we manage the de-icing problem of the boulevards. How fertilizers are used in the fields. Proximity to highways and aquatic environments. Development rates…” enumerates Alison Derry.
The researcher would like government guidelines on salinity to be stricter — to lower the scale of 120 milligrams of chloride per liter of fresh water set by Ottawa. We would also have to increase surveillance and control of our resources, which would leave something to be desired. “There are probably lakes with high salinity [dans la province]but we don’t necessarily know, because we don’t have the data taken over time, ”assumes Alison Derry.
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