Rain and snow melt make up a third of global rivers, says University of Calgary researcher

Researchers from the University of Calgary discovered that roughly one-third of water flowing into rivers around the world is "young water" and is more likely to have been exposed to contamination.
Calgary researchers find most river systems in the world that are impacted by snow or rain melt — like the Bow River — are more easily exposed to pollutants, such as pesticides. (Devin Heroux/CBC)

Researchers from the University of Calgary have discovered that roughly one-third of water flowing into rivers around the world is "young water" and is more likely to have been exposed to contamination. 

The finding has serious implications for water pollution and ecosystem health, according to a new study published in the journal Nature Geoscience.

Young water is made up of rain and snow melt that has flowed into rivers within three months. The water is measured using methods based on water "fingerprints" — tracking oxygen isotopes found in water molecules. 

"Calculating how long it takes for rain and melting snow to move into rivers is important because this information helps us predict the nutrition levels in rivers and the time lags before a pollutant arrives downstream," said Scott Jasechko, an assistant professor with the University of Calgary's geography department.

The U of C collaborated with universities in Saskatchewan, Switzerland and Alaska to calculate the age of water in more than 250 global rivers.

Flat landscape challenges

"Consequently, for some pollution events, there may be little time to detect the pollutant and prepare for its arrival downstream," said Jasechko.

Scott Jasechko stands at the riverbank at the confluence of the Colorado River and the Little Colorado River, at the bottom of the Grand Canyon, Ariz. (

The findings also reveal that flat landscapes can carry pollutants into river channels more easily and at a faster pace.

It's typically harder for water to be absorbed underground in flatter areas, because the underlying bedrock is less fractured, so the snow and rain melt moves into streams.

Jasechko said this is troubling because most of the world's farmlands are in flatter regions and about two-thirds of the water that humans use comes from surface waters.

"These findings can be used to help urban and agricultural planners better assess their practices and improve the quality of water in downstream rivers and lakes," said Jasechko. 


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