A new study from the University of Alberta shows that the lichen eaten by caribou herds along the Arctic coast is being contaminated with mercury from the marine ecosystem.
The study looked at two islands in the Arctic Archipelago – Bathurst and Devon Islands – and found that where there was open water during most of the year, methylmercury concentrations in lichen were higher, with those levels being highest close to the coast and decreasing as researchers moved inland.
“On Bathurst Island, which was near those open water areas, we saw really elevated concentrations and enrichment of that methylmercury over soils in just those coastal sites,” said Kyra St. Pierre, a PhD candidate in the department of Biology, who was lead author on the study.
The pattern showed enrichment of close to 100 times moving inland toward the coast – strong evidence for a marine influence on those concentrations.
“On Devon Island, we saw none of that same pattern,” St. Pierre noted. “It was kind of a flatline all across all of the sites, which told us that the ocean didn’t make a difference there probably because it’s locked in ice for most of the year.”
Methylmercury is a potent neurotoxin that bioaccumulates and thus magnifies as it ascends through the food chain. This study is the first to make a clear link between mercury in the ocean and the toxin present in lichen consumed by caribou along the coast.
St. Pierre said bacteria in the ocean produce diamethylmercury, a gaseous substance, in surface waters. That gas then enters the atmosphere, where it is transformed by sunlight into methylmercury, and is deposited onto the lichen.
As well, inorganic deposits of mercury coming from coal-fired plants as far away as China, due to the structure of global air currents, are also deposited in the Canadian Arctic, contributing to mercury concentrations in lichen.
“Lichen don’t have any root system. They’re a plant-like organism, but actually a kind of fungus. So what happens is that lichen are dependent on the atmosphere for pretty well all of their nutrients. In that case, it also makes it susceptible to airborne pollutants, like mercury,” St. Pierre said.
Though the study wasn’t focused on climate change, specifically, St. Pierre said the results imply that more open water on the Arctic Ocean would likely lead to more mercury deposition on lichen.
“We may see that spatial pattern that we observed between the two islands gone altogether where there’s no sea ice for longer periods for part of the year,” she said.
And while caribou herds that eat lichen off the coast remain safe for human consumption, more monitoring needs to be done to ensure their health – and the health of those who eat them as country food – is protected decades down the line.
“In terms of the health of the caribou, mercury isn’t at a level that’s going to impact them right now, but in terms of a climate change perspective, we really don’t know what the future of the food supply is going to be for them up there,” St. Pierre said. “So if they become more or less dependent on lichen, that would have an impact; as well, the open water is going to determine how much mercury is actually in those lichens.”
She said more research needs to be done to determine the source of mercury in lichen further inland, which is at concentrations higher in lichen than other plant life.