A new study released by the U.S. Geological Survey involving research on some of Voyageurs' most remote lakes indicates that levels of toxic mercury are dropping in fish and lake water in sync with pollution control regulations. Mercury from man-made pollution is converted in lakes and wetlands to methylmercury, a toxic form of mercury that accumulates in fish and is the main cause of fish consumption concern in Minnesota. USGS and University of Wisconsin – La Crosse scientists recently found that methylmercury levels in water and year-old yellow perch, a type of fish, in Ryan and Peary lakes of Voyageurs National Park decreased significantly from 2001 to 2012. Yellow perch were studied because of their key position in the food chain, consumed by both loons and northern pike.
However, methylmercury levels increased in Brown Lake water and yellow perch during this time, likely as a result of higher inflow from a contaminated lake upstream. No significant trend in methylmercury levels was observed in Shoepack Lake. Variations can be attributed to the complexity of lake ecosystems and can be used to guide future water resource management plans.
Mark Brigham, head of the research team commented, "It's important to monitor wilderness ecosystems like Voyageurs so that we can learn how ecosystems are responding to changes in atmospheric pollutants, without the confounding effects of direct human disturbances like urbanization, industry, or agriculture. And it's encouraging that at least some of the lakes appear to be benefiting from reduced emissions of mercury and acid rain pollutants."
Decreases in levels of mercury, sulfate and hydrogen ion precipitation likely resulted from reduced emissions in the U.S. and Canada related to improved pollution controls on coal-fired utility boilers and other sources implemented in the 1980s, and to regulations that removed mercury from numerous consumer products such as batteries in 1990.
From Ryan Maki, Voyageurs National Park Aquatic Ecologist: Because Voyageurs National Park is located in a mercury sensitive region and the mercury contamination of many lakes within the park is substantial enough to necessitate fish consumption advisories and to harm fish and wildlife, it is important for us to understand whether mercury contamination in fish of the lakes within Voyageurs National Park will decrease in response to decreased atmospheric deposition of mercury. This study shows that in at least some of the lakes within Voyageurs National Park, mercury contamination of water and fish is decreasing in concert with decreases in atmospheric deposition of mercury - our hope is that this decrease in contamination of lakes within Voyageurs National Park will continue for the benefit of the aquatic ecosystem and of people who consume fish from these lakes.
We, at Voyageurs, were thrilled to be able to collaborate with staff from the USGS, the NPS Great Lakes Inventory and Monitoring Network, the University of Wisconsin - La Crosse, and the National Atmospheric Deposition Program on this research and monitoring effort. All of the collaborators have been very generous with their time and resources to ensure that this unique dataset was collected and available for use in research focused on how lake ecosystems are responding to decreases in atmospheric deposition of mercury.
You can download and read the full study here from the journal Environmental Science and Technology.