Mercury is a metallic element that that is present in elevated levels in some lakes in southwest Alaska. It can build up in fish that live in these lakes year-round. Then as birds, people and other animals dine on fish from those lakes, mercury can make its way up the food chain. The National Park Service and the United States Geological Survey are among the agencies that study mercury levels in southwest Alaska’s lakes in order to better understand mercury’s effect on ecosystems and how it gets there.
In 2005, the National Park Service began monitoring mercury levels in non-migratory lake fish in Katmai National Park and Preserve and the Lake Clark National Park Preserve.
“Since then we’ve collected around 400 fish samples, representing nine species from 20 lakes, said Krista Bartz, an aquatic ecologist with the NPS’ Southwest Alaska Network inventory and monitoring program. “We’ve found that filets from long-lived predator species, like lake trout and northern pike, can have elevated concentrations of mercury and they tend to increase with fish age.”
The amount of mercury in lakes varies widely throughout the parks. Researchers observed the highest concentrations in lake trout in Katmai’s Lake Brooks, an average of 0.53 parts per million. The state recommends women of childbearing age, nursing mothers and young children limit their consumption of fish with mercury concentrations greater than 0.20 ppm. In contrast, the concentration of mercury in the trout found in Lake Clark National Park and Preserve’s Turquoise Lake is well below that limit.
In high enough levels, mercury can cause a host of physical problems for vertebrates, including neurological and reproductive issues. A 2014 study by the United States Geological Survey noted that in Lake Clark National Park and Preserve concentrations of mercury in Lake Kontrashibuna and Lake Clark could cause impairment to fish-eating birds.
Mercury enters ecosystems in several ways. Industrial processes can release it into the atmosphere, and it can settle continents away. It can also enter a system naturally through volcano vapor, melting glaciers and latent reservoirs of atmospherically deposited mercury. Bartz said the differences in mercury levels between all these lakes in a relatively small area is a good clue to how mercury got into them.
“If the thing that was driving the variation among lakes was something caused by the atmospheric deposition of coal burning in another continent, then I don’t think that we would see this strong variation at the scale that we’re seeing it. However, if that variation is caused more by like bedrock geology or surficial geology, like something going on in the soils, then you might expect to see these regional localized hotspots of mercury. So I think it could be, at this point, it’s just a natural cause,” Bartz said, stressing that there are many contributing factors to these elevated mercury levels, including mercury emissions from distant sources.
The point of research like this is to understand the situation with mercury in Southwest Alaska parks—how much is there, what is the affect, and is it changing over time?
That data then makes its way to natural resource managers, park superintendents, state agencies and the public. As a result of the 2014 USGS study, for example, the Lake Clark National Park and Preserve began providing information on its websitefor visitors about which species in which lakes have high mercury levels and how many servings are safe for women and children to eat.
Bartz said that there is still plenty of research to be done. Soil analysis, for example, could shed more light on the way mercury travels throughout these ecosystems. She anticipates that the NPS will publish results from the past three years of study on resident lake fish in Katmai and Lake Clark in 2018.