U of S study lends new insight into the water cycle

A study led by a University of Saskatchewan (U of S) researcher released today in the journal Nature challenges conventional theory on the way water moves through soil to nourish plants, recharge water stocks and discharge into streams.

"The prevailing view in the field assumes that beneath the soil surface lies one huge tank where all water 'meets, greets, and mixes'," said Jaivime Evaristo, lead researcher of the study and PhD student in the School of Environment and Sustainability (SENS) at the U of S. "In fact, what we found was that around the world, water is compartmentalized, with plants using soil water that does not contribute to groundwater recharge or stream flow."

Evaristo's work involved using the scientific equivalent of crowd sourcing to collect data from 47 study sites around the world and using that data to calculate the extent of ecohydrological separation between plant water and groundwater. The area the researchers studied is known as the 'critical zone', which is the layer of the Earth's surface where biology and hydrology meet the most.

"We call this separation between plant water and groundwater the two water worlds hypothesis," said Evaristo.

Evaristo's research follows that of his supervisor and co-author Jeffrey McDonnell, SENS professor and associate director of the Global Institute for Water Security at the U of S. In a paper published in 2010, McDonnell and colleagues first challenged the single-mixing-tank model, tracking for the first time the isotope composition of mobile and immobile water at the watershed scale.

Evaristo and McDonnell collaborated with Scott Jasechko, an assistant professor at the University of Calgary, for the Nature study to test if what McDonnell had previously found was localized to his study sites, or ubiquitous in nature. What they discovered was the latter.

"Jaivime's PhD findings have the potential to change how we view the hydrological cycle - from what we teach in Grade 10 science to academic research in related ecosystem and soil biogeochemical studies. It's a huge finding," said McDonnell.

The team hopes that its findings help improve the hydrological models planners rely on when projecting water resources and the potential problems that occur as water moves through the landscape, like groundwater contamination, flooding and drought.


For more information, contact:
James Shewaga
Media Relations Specialist
University of Saskatchewan
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