Water Resources Institute Research
Pollutant quickly finds its way into fish
By Marie Zhuikov
They took to the remote lake in Canada under the cover of dusk, dripping pollution into the water via the boat’s prop wash. Were these culprits improperly disposing of industrial waste? No. They were researchers, and their actions were in the name of science.
The setting was a unique area in Ontario, about 40 miles east of Kenora on the Trans-Canada Highway and then due south another 10 miles. The Experimental Lakes Area (ELA) is one of the only places in the world where researchers can practice experimental limnology; in other words, instead of relying on computer models or other simulated conditions, they can study a real lake and see what happens.
The water body in question is Lake 658, a smallish 19-acre lake in the ELA surrounded by wetlands and an upland habitat. Water Resources Institute-funded scientists wanted to observe how the lake and surrounding environment reacted when mercury was added to the system, with the ultimate goal of seeing how it recovered once the mercury addition was discontinued.
The project was part of a larger study called METAALICUS (Mercury Experiment to Assess Atmospheric Loadings in Canada and the United States), designed to discover how a watershed and its lake would respond to changes in mercury loading.
For this study, researchers added enriched stable (non-radioactive) isotopes of mercury to Lake 658 and the surrounding watershed. They used different isotopes for the lake, the upland and the adjoining wetland so they could trace which contributed more to the eventual mercury pollution of the plankton and fish. They also wanted to see how quickly this “new” mercury reacted with the “old” mercury already stored in the environment.
The mercury was added to the lake at night because sunlight can vaporize it. The amount added was not excessive — only about two to three times what would typically occur in background levels. The lake was dosed with a colorless mixture of mercury premixed with a batch of lake water once every two weeks from ice-on to ice-off over the course of seven years (three years for this particular study). Mercury was applied to the watershed with the help of a crop duster plane once per year.
Researchers found that this new mercury, as opposed to the old mercury, got assimilated into the environment very quickly and that the new lake-deposited mercury made up the bulk of the mercury in fish. They also discovered that it took much longer for mercury added to the watershed to be taken up by plants and animals in the lake food chain. Their findings were published online in “Science of the Total Environment” in an article titled “Importance of Hypolimnetic Cycling in Aging of ‘New’ mercury in a northern Temperate Lake” aqua.wisc.edu/channel/40.
“It was amazing how fast the mercury got into fish,” said James Hurley, project researcher and director of the Water Resources Institute (WRI). “In order to get to that point, the mercury has to get to parts of the lake where it is transformed by microbial processes into methyl mercury. Then it has to get through the food web to accumulate in fish. We started seeing the isotope we added in June accumulate in yellow perch by early fall. By the start of the second year, we were clearly seeing it even in predatory fish.”
“Before this study and the other METAALICUS work, we really didn’t really have any idea about how long it took for mercury to move through the environment,” said David Krabbenhoft, a lead investigator for METAALICUS and a research hydrologist with the U.S. Geological Survey’s Wisconsin Water Science Center. “This study has been very useful for that.”
“The other amazing thing was that after we stopped adding the mercury isotope, we quickly started to see the mercury concentration in predatory fish drop,” Hurley said. These findings were discovered in follow-up studies.
Results from the study of Lake 658 are already being used by environmental regulators to protect lakes on a nationwide basis. Hurley and Krabbenhoft said the Environmental Protection Agency used them to help justify rules for decreasing mercury emissions from power plants through the Mercury and Air Toxics Standards passed in 2011.
A basic part of the scientific method is replication. It may be very challenging for other scientists to try to replicate these results or attempt further whole-lake manipulations because funding for the ELA has been cut by the Canadian government and the scientific area may be closed if other funding sources or operators can’t be found.
According to Kevin Hill, communications manager for the Central and Arctic Region for Fisheries and Oceans Canada, discussions about the fate of the ELA are ongoing and “for reasons of confidentiality, we cannot provide additional information at this time.”
For more information about mercury and the METAALICUS study, listen to this WRI-produced podcast aqua.wisc.edu/channel/41.