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Water Today Title December 12, 2018

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Update 2017/4/26
Groundwater

IT TAKES THOUSANDS OF YEARS TO REPLACE GOUNDWATER, HERE'S WHY


By Cori Marshall


The United Nations World Water Development Report states that "groundwater provides drinking water to at least 50% of the global population," and makes up almost half of the water used in irrigation. The Earth's groundwater resources are what "2.5 billion depend [on], to satisfy their basic daily needs." Environment and Climate Change Canada says that "in Canada, 8.9 million people,or 30.3% of the population, rely on groundwater for domestic use."

With so many people in Canada and worldwide depending on groundwater to meet their water needs, what do really know about the character, age, and make-up of the of the planet's groundwater and aquifers? Surprisingly not that much. There is an international collaboration of researchers that have made some important findings. I had the opportunity to speak with one of them.

Scott Jasechko, assistant professor in the Geography Department at the University of Calgary is part of this international collaboration; according to him, the group confirmed that "99% of all fresh, unfrozen water resources are stored in groundwater."

A very important aspect of the group's findings revolves around how much time has passed since the water first fell in the form of precipitation. Jasechko said that the researchers explored the question of "how much [groundwater] is replenished over a typical human lifespan." The findings revealed that "though there is a great deal of groundwater on our planet, only a small fraction is replenished," within a human life.

This raises the question of how much of this groundwater is old. Jasechko said that the group also looked at "how much of this water fell as rain and snow within the last geological age?"

The findings show that most of the planet's groundwater is "rain and snow that fell more than 12 thousand years ago," Jasechko said. The group refers to this as "fossil groundwater." What this means is that it takes millennia for groundwater aquifers to completely renew their contents.

Jasechko suggests that "there are places on our planet where the groundwater that exists today is from a very old climate state." Meaning that areas of the world that are arid today had much more temperate climates in the past. Examples of this are found in Libya and Northern Africa.

Jasechko said that there is groundwater beneath massive sand dunes in the Sahara [Desert]." This is an area of the world that receives very minimal groundwater replenishment, because "use of the groundwater in hyper-arid climates is unsustainable."

The slow rate of renewal in groundwater aquifers underlines the need for accurate studies and figures to enable the world to know how much water is really beneath our feet. Jasechko views the importance of groundwater studies and the relationship with use as a type of bank account. "Without understanding how much is in your account, it becomes very difficult to manage in a sustainable manner."

He believes that, if the world wants to preserve this resource, "we need to set long-term groundwater management and use goals." Ultimately these goals would have to be much lower than contemporary usage rates. Jasechko added that if we set "groundwater management agendas to help meet those goals, it is possible that we can reverse some of the unsustainable groundwater use and aquifer depletion."

Sustainable management of groundwater necessitates an understanding "of the rate with which this resource is renewed." This water is deep and slow moving. Jasechko added that when this water is pumped it mixes with modern water and "is not immune to contaminants found in modern landscapes." Many practices of contemporary land use contaminate shallow waterways.

Modern society has a very large impact on fossil groundwater. The contaminants that are in our modern environment can seep into deep groundwater aquifers. Jasechko said that "because these aquifers are flushed so slowly, any contamination of these resources will likely persist well beyond a human lifespan and will effectively cause irreversible harm to fossil groundwater."








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