Researchers at Acadia Trace Mercury Through Forests, Streams
Contact: Sarah Nelson, 581-3254
While Acadia National Park is often perceived as remote and pristine, the park’s fish, wildlife, and human visitors are vulnerable to mercury contamination that persists throughout North America. New research has documented that fish, amphibians, and even tree swallows from Acadia carry heavy burdens of mercury.
Now, in a series of papers published in a special issue of the journal Environmental Monitoring and Assessment, a group of researchers from the University of Maine, Plymouth State University, the U.S. Geological Survey, National Park Service, and Harvard University have revealed why concentrations of mercury in the environment are higher in some places than in others.
Using Acadia National Park as an “outdoor laboratory,” the ten lead scientists were able to trace mercury as it moves from the sky to the mountains of Acadia, down through the forest canopy, and into streams and lakes, where it builds up in zooplankton, insects, fish and fish-eating wildlife. The research was conducted over seven years by scientists from a number of institutions, making Acadia one of the most intensively studied areas for mercury in the United States.
“These research projects demonstrated that the forested landscape and its history play a role in the cycling of mercury and nitrogen through the environment. This means we need to consider land cover type when assessing contaminants like mercury in our environment,” said Sarah Nelson, co-editor of the special issue and an assistant scientist at Senator George J. Mitchell Center for Environmental and Watershed Research at the University of Maine.
Evergreen forests of spruce, fir, and pine act as air filters, raking mercury from the air; as a result, the amount of mercury that falls through the canopy of these forested areas is much higher than that detected in rain alone. The mercury is washed to the ground with rain, snow, and falling needles and twigs, where it collects in the soil, and eventually moves into streams and lakes. Evergreen forests capture more mercury from the air than hardwood forests, because needles have more surface area to grab the mercury than leaves. Forests that are located on southwest-facing slopes are hardest hit, because they directly intercept polluted air masses drifting eastward across the United States.
Events such as fire can have tremendous influence, even decades later, on an area’s susceptibility to mercury and other air pollutants. Reconstructing the history of Acadia’s landscape, the UMaine team showed that the southeast slope of Cadillac Mountain, which burned during a major fire in 1947 (which covered nearly a third of Mount Desert Island) and was re-vegetated by hardwoods, is much better at retaining mercury than other areas of the park that have remained undisturbed for hundreds of years. The unburned areas are “leaky,” and flush more mercury and nutrients into streams. As evidence of this, salamanders living in unburned forests had higher levels of mercury in their bodies than those in the burned areas.
These results may cause park officials, who are charged with protecting ecosystem health in Acadia National Park for both current visitors and future generations, to wonder whether they should perform controlled burns on more areas of the park to keep mercury out of streams and soils, but this would be taking too simple a view. Burning a forest would release mercury back into the atmosphere, and eventually the mercury held by all vegetation will make its way into soils and streams, fish and other animals. The problem is further amplified at Acadia because of the large extent of wetlands in the park, which are very effective at converting mercury to its more toxic form. Instead, managers are focusing on controlling the major source of mercury in the park, air pollution. “We can use the information from this study, in cooperation with our federal, state, and local air quality partners, to look for ways to reduce deposition and impacts of mercury,” said David Manksi, chief of the resource management division at Acadia National Park.
The research was funded by U.S. EPA, in collaboration with the National Park Service’s Northeast Temperate Inventory and Monitoring Network, Schoodic Education and Research Center and North Atlantic Cooperative Ecosystem Studies Unit, the U.S. Geological Survey, Patuxent Wildlife Research Center-Orono, and Maine Department of Environmental Protection.