SOMA DALAI

Jaivime Evaristo is one of a kind, and it’s not just because the University of Saskatchewan doctoral student has just had a paper published in Nature, one of the pre-eminent science journals in the world. Evaristo began his career in cell biology and chose the field of hydrology for his master’s almost on a whim because he wanted to explore quantitative research.

The paper published in Nature was written by Evaristo, his supervisor Jeffrey McDonnell and University of Calgary professor Scott Jasechko. It was published on Sept. 2, 2015 and is a meta-analysis of numerous studies done previously. Entitled “Global separation of plant transpiration from groundwater and streamflow,” the article takes the occurrence of plants compartmentalizing the water that they use and shows that it could be a global phenomenon.

Most of the water used by a plant is not actually used for growth or metabolism. Up to 99.5 per cent of water absorbed is actually used for a process called “transpiration,” which is the evaporation of water from plant leaves. This is vital for the plant because it helps the process of transforming carbon dioxide into sugar. Previously, scientists believed that once precipitation entered the ground, it mixed into a vast reservoir of ground water that plants absorbed for transpiration. Evaristo’s paper, however, challenges this idea.

Evaristo and his co-authors demonstrated that water used by the plant for transpiration is distinct from the water used to recharge streams and lakes by using the distinct stable isotope ratios of hydrogen and oxygen found in each to “track” them through the water cycle. They found that while the groundwater enriches the water table, only streamflow is used by plants.

Evaristo then explained how this finding leads to another key question.

“You could actually ask the question: ‘Why is this plant using water that is not related, isotopically, to the water that recharges the ground and ends up in streams?’”

The answer to that is still not fully known, but Evaristo’s work has helped establish ecohydrological separation of stream water and groundwater as more the rule, rather than the exception. Evaristo took care to stress that his paper was not the only one to show this phenomenon.

All the papers Evaristo and his co-authors analyzed have shown this process in local sites.   

“What makes our finding surprising is that number one, it is global in scale,” Evaristo said. “It’s one thing to show something that exists at the site and it’s quite another for you to show the same thing globally.”

It is quite another thing to get published in Nature. The journal has existed since 1869 and has stayed at the forefront of scientific research, publishing the first articles on cloning, climate research and the human genome project. It also has a notoriously rigorous peer-review process, publishing an average of 7.4 per cent of the studies submitted to it each year.

Evaristo said his paper is also important because it alters scientist’s conception of the water cycle, which was previously seen as an unbroken loop.

“So now you have a picture of the water cycle that kind of breaks somewhere,” Evaristo said. “At a point that the water infiltrates the ground, some of that water is exclusively related to plant uptake and some of that water recharges the ground. In other words, once that water is within this domain where the plants can access [it], you can forget about groundwater.”

While Evaristo acknowledged there were exceptions to this pattern shown in scientific literature, these exceptions are “not widespread.”

According to Evaristo, it is tempting to “stretch” findings in the field of basic science to the field of applied science, but there are some ways this knowledge can be used. The main application Evaristo outlined is that it will change the models that engineers, water resource managers and urban planners use to understand water allocation.

“The obvious implication for that is if you do a separated model like what we’re finding, like what our results show, there is now less water available for either plant transpiration or water recharge individually than there is if you assume a single mixing tank.”

Despite accomplishing something many scientists only dream of, Evaristo is unsure of what his future holds. 

“I live one day at a time. Quite frankly, I used to plan my life but somewhere along the way things don’t follow as planned… Five years from now, I really have no idea.”

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Photo: Michael Bergen