“High-Arctic”: Toxic mercury in arctic lakes

After he was able to identify a link between metal accumulation and climate change in arctic salmon from Tyrolean high mountain lakes in the 1990s, Günter Köck from the Institute for Interdisciplinary Mountain Research of the Academy of Sciences initiated a small research assignment from the Ministry of Science in 1997, the accumulation of heavy metals and the impacts of climate change on Arctic char in the Canadian Arctic.

Together with his Canadian colleague Derek Muir of the Canadian Department of the Environment and the University of Guelph, they have begun a survey of about 30 lakes on six islands in the Canadian High Arctic that has not yet been completed. “High Arctic” is therefore the Austrian Arctic project that has been running for the longest time.

Toxic mercury enters the food chain
Over the years, not only have mercury concentrations in the atmosphere dropped in the Arctic, but also, as expected, in many lakes — “but not everywhere,” Köck told APA. Of the six Arctic lakes with the longest data series, heavy metal loads in Arctic coal are decreasing in four, but increasing in two. The researchers showed that the diet of the arctic char has changed: the fish eat more and more animal food – and thus absorb more mercury. This enters the lakes through the atmosphere, is converted by bacteria into the much more toxic methylmercury and accumulates in the food chain.

Different lakes – different consequences
The scientists also found that different impacts of climate change have different effects on fish’s mercury exposure. For example, at Lake Hazen, the largest and most remote lake in the study, the more ice-free days there are, the higher the mercury concentration. On the other hand, at Amituk Lake and North Lake, which are very different geographically, the mercury concentration depends on the depth of the snow cover. “A climate-related decrease in snowfall could therefore lead to a decrease in mercury concentration in the lakes,” says Köck. In the Amituk Lake, there is also an association with the “North Atlantic Oscillation” weather phenomenon – which is also true for the concentration of persistent organic air pollutants in several lakes. The reason for this may be that during certain phases of this weather phenomenon, air masses – and therefore pollutants – are carried to the pole from Europe, North America and Asia, Köck said.

The scientists explain the fact that the differences in mercury pollution between the Arctic lakes are quite large due to the different concentrations of dissolved and particulate organic carbon: The mercury content of the fish is highest in nutrient-poor lakes because the methylmercury is apparently much better absorbed here. If more carbon ends up in such lakes, for example through more rainfall and the thawing of the permafrost, this should have a positive effect on the development of mercury concentrations.

His last expedition
After Derek Muir retired last year and Köck will also retire next year, the two are now putting the project in younger hands. “This year will certainly be the last time for me – and therefore a difficult goodbye to Resolute Bay,” says the biologist, who always has his base camp in the Inuit settlement of Resolute Bay in the south of Cornwallis Island, which has about 200 inhabitants hits.

But because there is so much data from recent years, the project is continuing and the data situation is improving, he is confident that a number of publications about the work will appear in the coming years.