Why wetlands are effective at purifying water

Pourquoi les zones humides sont efficaces pour dépolluer l’eau


Wetlands play a vital role in ecosystems, especially in terms of water purification. A new joint study between the University of Waterloo, Canada, and the University of Illinois exhaustively measured the influence of restoring wetlands on improving water quality. 

Focusing on wetlands in the United States, the study’s authors discovered that they could remove 8% of the excess nitrogen in the environment, mostly from runoff from farming land. 

This 8% figure is a national average across the United States, but it is higher in certain regions. In the Midwest, wetlands can remove 439 kilotons of nitrogen, which would otherwise end up in the Gulf of Mexico. Without these areas, 51% of the excess nitrogen would be found in the ocean. 

In their work, the researchers not only evaluated the disastrous consequences of wetlands’ disappearance. They also put forward a very optimistic point of view concerning their potential for restoration in the United States. 

According to one scenario, if 10% of farm land, i.e. 5.1 million hectares, were restored as wetlands, this would reduce by 54% the amount of nitrogen found in river basins, such as the Mississippi, one of the rivers most affected by excess nitrates.

Restoring wetlands: a low-cost solution 

What would the transformation of 10% of farmland into wetlands cost? The good news: it is affordable. This restoration would require 2.75 billion euros, i.e. more or less what the United States already spends each year on water quality improvement projects. 

The researchers hope that their study will help politicians make better-informed decisions about financing wetland conservation and restoration. Their work confirms the extent to which these areas play a key role in the water cycle and how necessary it is to protect them as a priority. 

Combined with the adoption of more sustainable and regenerative farming practices, restoring wetlands would help transform the entire American as well as global farming system, allowing it to become more environmentally friendly. 


“Restoring wetlands near farms would dramatically reduce water pollution,” Waterloo News, December 16, 2020 - uwaterloo.ca/stories/news/restoring-wetlands-near-farms-would-dramatically-reduce

“Maximizing US nitrate removal through wetland protection and restoration,” Nature, December 16, 2020 - www.nature.com/articles/s41586-020-03042-5