Permafrost thaw changing chemistry of Peel River

Permafrost thaw changing chemistry of Peel River
An aerial photo shows a massive, 1-km wide permafrost “slump” on the Peel River system.Photo by NWT Geoscience Office.

Permafrost degradation in the Peel Plateau is having far-reaching effects on the chemistry of water downstream as the river system becomes exposed to ancient sediments, deposited for the first time in high concentrations via melting ice.

A new study by the NWT’s foremost expert on permafrost, Steven Kokelj, who works out of the NWT Geoscience Office, shows a very noticeable increase in the presence of certain ions over the last forty years as the area becomes more and more affected by permafrost thaw.

In his study, Kokelj states that warming temperatures resulting from climate change are causing ice that has been preserved within permafrost for millions of years to rapidly melt as it is exposed by erosion.

The result has been massive landscape disturbance across the region known as “slumping,” which sees giant, gradual landslide-type formations build up over time and move into the river system, filling the water with ions that, though naturally occurring, are in much higher concentrations than is normal for the water because the sediments have never been leached of their ions before.

“What we’re able to do is look at water that runs from these slumps and compare it to just normal surface water, and the concentrations can be ten, 100 times greater, and in some cases even 1,000 times greater,” Kokelj said.

Chemically speaking, the results are being felt further downstream in the Peel River. Despite its size, a definite increase in the most popular permafrost-related ions, such as sulphate and calcium, has been recorded in the river over the last 40 years thanks to Environment Canada water quality monitoring data.

“We can look at sulphate – which is sort of the main ion in the Peel River – and the amounts of sulphate have almost tripled over the period of record. So to see an increase like that in a system that’s as big as the Peel, it really kind of highlights the fact that the change is actually quite substantial on a landscape scale,” Kokelj said.

While sulphates only start to negatively impact drinking water in the thousands of milligrams per litre range – in the Peel, concentrations are still below 100 mg/litre – Kokelj said the data is noteworthy.

“The fact that they’ve increased that much in a river that has water coming from – I think it drains like 70,000 square-kilometres – is pretty significant.”

Slumping is also affecting streams on a local scale, sometimes by blocking them or forming lakes upstream.

“Normally after a heavy rain all the creeks get turbid and full of sediment and as the water goes down, they clear up…but because these slumps tend to melt more when it’s hot and dry, normally as the streams would clear up, that’s when these big slumps are thawing more, so the streams never really clear up,” Kokelj explained. “As the water goes down in the summer when it’s hot and dry, these streams that are impacted are actually even muddier.”

Kokelj’s data is being used to provide context to other studies on the impacts of permafrost melt in the Lower Peel Basin. Researchers from Wilfrid Laurier University are studying how sediment levels are affecting the physiology of northern fish species, while scientists from the University of New Brunswick and the Cumulative Impacts Monitoring Program are looking at benthic communities – the organisms that live at the bottom of the river – near permafrost slumps.

Though results have yet to be released from either study, Kokelj said preliminary results on the benthics research show it’s having an impact.

“There’s huge differences in the abundance of benthics in association with disturbance. Once these disturbances occur, the abundance of benthics decreases substantially,” he said.

Kokelj is now working on establishing an inventory of permafrost in the Northwest Territories in order to track these disturbances on a broader level. This summer, he and a team will be mapping the entire NWT using aerial photographs.

He said the maps will help scientists decipher the extent of permafrost disturbance and what types of ecosystems – coastal, streams, rivers – may be getting impacted.

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