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Scientists Quantify Export of Mercury from the Yukon River

Thawing permafrost in the Yukon River watershed may be a source of naturally occurring mercury being conveyed by rivers into the environment, according to USGS research scientists.

The Yukon River watershed, home of the longest free-flowing river in the world, releases nearly 5 tons of mercury per year into the environment. This is 3 to 32 times more mercury than eight other major northern hemisphere rivers.

Methylated mercury, the type toxic to humans, was also found in the Yukon River, but at very low levels.

Mercury measured in the Yukon River is strongly correlated with concentrations of organic matter originating from boreal forest soils. Seventy-five percent of the Yukon River watershed is covered by organic-rich permafrost, in which mercury has been accumulating since the end of the last ice age, 10,000 years ago.

"It is important to measure the amount of mercury from river watersheds so that a baseline is established to compare against future conditions," said lead USGS researcher Paul Schuster.

As a result of cyclical warming and changing climatic conditions, the permafrost in this region is thawing at an increased rate that may result in increased mobilization and export of mercury from the Yukon River, the fourth-largest in North America. Moreover, due to rapid expansion of Eurasian industrialization, it is anticipated that northern regions of the hemisphere will see increased atmospheric deposition of mercury, according to the team of USGS researchers.

The five-year study analyzed surface-water samples for total mercury concentrations and measured water discharge from the Yukon River at Pilot Station, Alaska.

The study, "Mercury Export from the Yukon River Basin and Potential Response to a Changing Climate," appears in the journal Environmental Science & Technology.

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