Permafrost melt changing chemistry of the Yukon River
Ryan Toohey/USGS Alaska Climate Science Center
Melting permafrost is one of the best-known impacts of climate change in the North.
Now, new research out of Alaska suggests that vanishing permafrost is having a major impact on the Yukon River.
The study, led by the U.S. Geological Survey, found that the Yukon River has seen a significant increase in calcium, magnesium and sulphate levels over 30 years.
Ryan Toohey, a hydrologist with the Alaska Climate Science Center and the study’s lead author, said the results indicate that a deepening layer of soil is thawing and freezing each year, instead of staying frozen year-round.
As more of the ground thaws, water can seep through and carry minerals from the soil into waterways, including the Yukon River.
“I think we were surprised at the scale that this was happening on,” Toohey said.
For instance, the level of sulphate in the river has increased by 60 per cent since 1982.
There are other changes, too. The researchers found that the level of phosphorus in the river has more than doubled over 30 years.
Toohey said that’s likely because the Yukon River is freezing later in the fall and thawing earlier in the spring, giving the running water more time to erode the riverbanks. Phosphorus often seeps into water from eroding soil.
The researchers don’t yet know what the changing water chemistry means for fish stocks in the river or for the chemistry of the Arctic Ocean.
But Toohey said the trend is significant.
“It’s a large-scale, landscape-type change that is being observed, and something that we need to pay attention to,” he said.
The Yukon River isn’t the only major waterway experiencing these changes.
Suzanne Tank, an assistant professor at the University of Alberta, published her own research on the Mackenzie River in the Northwest Territories last spring, and also found an increase in calcium, magnesium and sulphate in the water.
But Tank’s most notable finding was a 39 per cent increase in dissolved organic carbon flowing into the Arctic Ocean over the last 40 years, something Toohey didn’t find in the Yukon River.
“I was really surprised by that,” Tank said. “I was really surprised by the magnitude of the change.”
Tank said there are some “pretty vast peat deposits” along the Mackenzie River that aren’t as common in the Yukon River watershed, which could explain the difference between her results and Toohey’s.
But like Toohey, she thinks the changing water chemistry is related to melting permafrost. And she said all that dissolved organic carbon in the water is a concern, because it’s liable to turn into carbon dioxide, which contributes to ocean acidification.
Increasing organic carbon could also affect food webs in the Arctic Ocean, as it’s a major food source for bacteria.
“I’m pretty shocked by what I found,” Tank said. “It really says something about how rapidly the North is changing.”
Edda Mutter, science director at the Yukon River Inter-Tribal Watershed Council, said Toohey’s results “definitely show that permafrost (melt) is happening in the (Yukon River) watershed.”
She said the river this year was full of sediment, which she believes is eroding from the riverbanks left unstable by the disappearing permafrost.
“Personally, I’ve never seen river erosion so intensive,” she said.
The watershed council includes 73 First Nations and tribes in the Yukon and Alaska. About 50 of them have been collecting water chemistry data from different points all along the Yukon River for the last decade. Toohey used some of those data alongside data from the U.S. Geological Survey for his study.
Toohey’s study used data from just two sites in Alaska, where data were available from 1982 until 2014. But he said future research will look more closely at regional differences along the river, including in the Yukon.
Mutter said she’d like to look more closely at whether changing water chemistry poses any threat to fish stocks or subsistence activities on the river. She’s especially interested in levels of contaminants in the water, including mercury.
But she said it wouldn’t be possible to gather detailed information about the changing Yukon River if it weren’t for the participation of Indigenous communities throughout the watershed. She said the council’s 10-year data set, stretching from the headwaters to the mouth of the Yukon River, is something unique.
“It’s really, really rare for Arctic rivers,” she said. “And that’s just possible due to citizen science.”