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Listening to Loons: Mercury and MERGANSER

An EPA-led collaborative effort produces a model for predicting mercury levels in New England fish and loons.

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The distinctive, almost haunting call of the common loon is to New England what the howl of the wolf is to the American West: it’s the sound of wilderness. If you’re fortunate enough to be listening to a loon, you’re almost certainly surrounded by forests and lakes, and a long way from the nearest office building, shopping center, or interstate. But the seemingly pristine waters of even the most remote New England lake—loon habitat—may contain troubling levels of mercury. 

The loon’s diet is composed exclusively of fish. And while all 50 states currently have fish consumption advisories for some of its rivers and lakes due to elevated mercury levels, water bodies in New England are particularly vulnerable, the unfortunate result of geography and chemistry. New England is located downwind from some major industrial emissions sources.

And when mercury does arrive, it is likely to find its way to wetlands and water, where it is converted through chemical reactions into methylmercury, a form that is not only hazardous, but easily absorbed into living tissue and passed along the food chain.

To protect human health, advisories are issued to warn people not to eat fish from lakes where the fish tissues exceed EPA’s recommended levels for mercury consumption. Loons, of course, don’t have the option of avoiding fish. High mercury levels can disrupt the bird’s reproductive success.

To get a better idea of the health of New England’s lakes, EPA researchers and their partners developed a model that estimates current and future mercury concentrations in fish and loons for more than 4,400 lakes across the region. The model is the Mercury Geospatial Assessments for the New England Region, or MERGANSER (the name of another aquatic bird).  

According to biologist Diane Nacci, Ph.D., one of the EPA scientists on the development team,   MERGANSER “will  help scientists to better understand factors that increase risk of mercury contamination in wildlife, regulatory agencies to prioritize their sampling efforts, and the public to better understand the risk associated with eating fish from a particular lake in New England.”

The model uses geographical information systems (GIS) technology to link fish mercury levels and spatial, water quality, and environmental data for 20-acre and larger lakes. The model was developed using fish mercury levels stored in the EPAsWildlifeDatabase

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MERGANSER has many potential uses. It predicts whether fish mercury levels for a given lake will exceed EPA’s recommended human health criteria limit of 0.3 parts per million (ppm). The model can also help scientists determine whether mercury levels in a given lake are likely to result in reproductive, behavioral, or physiological changes in loons.

Another aspect of MERGANSER is that it predicts how mercury levels will fluctuate in the face of changing environmental conditions. For example, users could address such questions as: “If atmospheric mercury declined by 10 percent, how much would fish mercury decline in my lake? Or in every lake in Massachusetts?” It allows users to identify areas where fish mercury levels will change most if environmental conditions change.

Working with a model offers some advantages over reliance on collecting fish specimens or loon feathers for chemical analysis in a laboratory. With so many lakes across the region, MERGANSER can be used to identify those where mercury levels are likely to be a concern. This can help officials target field sampling operations, saving resources in a time of shrinking budgets. “We obtain a lot of data without actually having to visit a site…that is the real payoff and innovation of MERGANSER,” explains EPA research ecologist John Johnston, Ph.D.

Among other uses, the researchers hope that the tool will help health officials to identify lakes that are good candidates to be removed from advisories—reopening them to fishing activities—while actions are taken to reduce mercury emissions.

The MERGANSER methodology also has the potential to be applied in other areas of the country. “We’ve provided a framework and initial modeling results that researchers in other regions of the country could use as a starting point using local data,” says EPA environmental scientist Alison Simcox, Ph.D. “MERGANSER makes maximum use of existing data. And that’s rarely done,” she explains.

Researchers from multiple EPA offices collaborated with partners from the U.S. Geological Survey, research institutes, and state environmental organizations to establish MERGANSER. “It’s rare to be able to pull a team like this together and keep it together for almost a decade,” says Simcox.

The developers of MERGANSER intend to share the model through a publicly available web-based interactive tool and publication in a scientific journal. Johnston notes that “the methodology is going to be published in a pretty transparent way…and then the database will be shared because the more we can make it available and the easier it is to use the better for everyone.”

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