Freshwater at risk: Dalhousie University research into precious resource on Sable Island

It may be surrounded by the Atlantic Ocean, but inland, there is fresh water on Nova Scotia’s Sable Island – ponds which provide drinking water for the Island’s diverse and unique wildlife, including its population of about 450 wild horses.

But new research from scientists with Dalhousie University’s Coastal Hydrology Lab suggests the groundwater supply is being threatened by changing weather and coastal erosion.

“There's historical ground water monitoring data on Sable Island,” explains PhD candidate Julia Cantelon, “and the goal of my work was to go back to the island and make repeat measurements to see if there had been change since the 1970s.”

The results of that work have been published in the October edition of the journal “Water Resources Research.”

Cantelon and study co-author Barret Kurylyk, the Canada Research Chair in Coastal Hydrology at Dalhousie, travelled with team members to the crescent-shaped island 190 kilometres off the coast several times to install and monitor sophisticated equipment which allowed them to “see” underground.

Researchers set up equipment to measure if the groundwater supply at Sable Island is being threatened by changing weather and coastal erosion. (Courtesy: Dalhousie)That allowed them to find and measure freshwater and saltwater present on the island.

Sable Island’s groundwater supply comes from rainfall that filters into a sand aquifer.

Their findings indicate that supply has been compromised in areas particularly on the south shore of the island where the iconic dunes have eroded, even as waves and powerful storms keep washing more saltwater in.

“In areas where the dunes were completely lost, we saw a complete loss of the fresh groundwater, a loss of up to 10 metres,” explains Cantelon.

Researchers install equipment which allows them to "see" underground to allow them to measure freshwater and saltwater present on Sable Island. (Courtesy: Dalhousie)The ecosystem typically “flushes” the saltwater out, allowing the groundwater supply to recovery.

But Cantelon and Kurylyk say the increasing frequency and severity of hurricanes like Fiona last year are making that more difficult.

“These findings have some concern in terms of the trajectory, so (that) over time potentially the part of Sable Island that is eroding, could experience more and more saltwater intrusion into the coming decades,” says Kurylyk.

He says the work has implications not only for understanding the changes happening on Sable Island, but also for other islands and coastal communities around the world.

“People think about coastal erosion and surface flooding because…they can see it, but what happens in the subsurface is important too,” he explains.

“And so what Julia’s work shows is that over time, those changes at the surface, whether its coastal erosion or flooding or in combination, they can really drive profound and long-lasting subsurface changes to groundwater salinity,” Kurylyk says

“We can take those findings and apply them in other places where coastlines are changing, and so even here in Nova Scotia we have issues with saltwater intrusion into our coastal wells,” he adds.

Kurylyk and Cantelon say the research is also valuable for Parks Canada staff who live and work on the island, as they, too, rely on the groundwater supply for drinking water.

Researchers set up equipment to measure is the groundwater supply at Sable Island is being threatened by changing weather and coastal erosion. (Courtesy: Dalhousie)Cantelon’s last trip to Sable Island is Thursday, where she will collect the team’s remaining instruments to officially wrap up the project. But she hopes there will be more work on the subject in the future.

“For the sake of the freshwater resources, I hope it will be an ongoing research relationship between the Lab and Parks Canada.”

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