Global warming is increasing the concentration of pollutants in rivers, but the same phenomenon is also boosting beaver populations in the western United States, whose dams improve water quality, according to a study released Tuesday.

The conclusion, published in the journal Nature Communications by Stanford University scientists, is based on a simple observation: more frequent and more intense heat waves and droughts reduce the amount of water in rivers and, as a result, increase the concentration of pollutants such as nitrates. , which are present in large quantities in fertilizers.

At the same time, human-caused global warming has increased the range of American beavers, cousins ​​of the Eurasian beaver, expanding the benefits of their dams.

When beaver dams raise the river upstream, the water is diverted to the surrounding soil and secondary streams in the basin.

“These zones act as filters, removing excess nutrients and pollutants before the water re-enters the main channel downstream,” according to a news release.

Nitrogen, in particular, promotes the growth of algae, which deprives the water of oxygen necessary for living things in this ecosystem.

The study found that beaver dams improve water quality in the extremes of climate change—whether hot, dry weather or heavy rain and melting snow.

In both cases, “the beaver dam pushed more water and nitrate into the surrounding soil than the two seasonal extremes, resulting in much greater nitrate removal,” lead author Christian Dewey told AFP.