Farming, dams and agricultural runoff are the biggest threats to freshwater biodiversity globally, with Europe and Northwest Africa the hardest-hit regions, McGill researchers have found.
Applying a mapping methodology previously used to study terrestrial species, the researchers identified where freshwater species are under threat, and which human activity seems to be responsible.
Their study could help conservationists prioritize where interventions are most urgently needed, they said.
"At a time when global biodiversity frameworks risk overlooking freshwater species, these maps give us a new, freshwater-specific baseline for conservation, helping to highlight where different types of conservation action may be most needed," said Christophe Brabant , lead author and PhD candidate. "That matters to everyone, not just biologists, because freshwater systems provide services we all depend on: clean drinking water, fisheries, flood protection and more.
"These all depend, to some extent, on the species found in freshwater," he said.
Forty-five global threats mapped
Using data from the International Union for Conservation of Nature (IUCN) Red List, which tracks the global conservation status of species worldwide, the team mapped the effects of 45 threats on more than 21,000 species across five major freshwater taxonomic groups: mammals, reptiles, fish, amphibians and odonates (dragonflies and damselflies). This resulted in 225 maps showing the impact of each threat on each group, which they combined to create a cumulative index of all threats to all freshwater species.
They then compared their results to previous global threat mapping work focused on terrestrial vertebrate biodiversity and found that freshwater species faced greater threat and distinct spatial patterns of impact.
"By combining this data, we could calculate, for any sub-watershed, the probability that a species occurring there is affected by a particular threat," Brabant said.
The dominant threats shifted by species group: amphibians and some insects, such as dragonflies, are mostly threatened by agricultural activities, while reptiles and mammals are affected by hunting, they said.
Freshwater species have largely been omitted from previous research or included only through the lens of human benefits rather than species conservation, yet many of the most biodiverse freshwater regions are also under the greatest pressure, the researchers said.
Further analysis required
This study is also the first to create a unified spatial framework across terrestrial and freshwater realms and make a fair comparison between threats at this scale.
Future research will focus more closely on which species and areas to prioritize for conservation, said Lars Lønsmann Iversen , senior author, Professor of Biology and member of the Bieler School of Environment .
"If we identify areas that should be protected and know there are high levels of pressure or threats in those places, it can help indicate what actions should be taken," he said.
About the study
" The Global Geography of Threats to Freshwater Biodiversity ," by Christophe Brabant, Laura Pollock, Jonas Geldmann, Mette Bendixen, Lise Comte, Harith Farooq, Katherine Hébert, Bernhard Lehner, Catherine A. Sayer and Lars Lønsmann Iversen, was published in Science.
The study was funded by Fonds de recherche du Québec – Nature et technologie, the Natural Sciences and Engineering Research Council of Canada, the New Frontiers in Research Fund, the Danish Independent Research Council and the Villum Center for Global Mountain Biodiversity.
