New Study Reveals Causes of Mercury and Nitrogen Pollution at Acadia

February 16th, 2007 by Adam

For years, scientists have wondered why some fish and birds show very high mercury levels while others from adjacent areas are normal. A Plymouth State University professor has provided insight on that issue with the release of a long-term study on understanding mercury and nitrogen pollution at Acadia National Park.

Steve Kahl, director of PSU’s Center for the Environment, is co-editor of a special issue of the science journal Environmental Monitoring and Assessment, titled, “Mercury and Nitrogen Biogeochemistry in Paired Watershed Studies at Acadia National Park, Maine, USA”.
The special issue documents the results from the research in 11 scientific papers. Kahl authored the first paper in the issue, providing an overview of the research findings, and is co-author of 5 other papers in the issue.

Using Acadia National Park as an “outdoor laboratory,” the scientists followed mercury, nitrogen and other substances that occur in acid rain, down through the forest canopy and into streams and lakes. The purpose of the research was to identify how and why mercury and nitrogen vary across landscapes. Kahl points out that, “mercury in the environment falls everywhere on the landscape, yet some lakes have high mercury in fish and loons, and other nearby lakes are low”. As he describes it, understanding what controls the seemingly random occurrence of high mercury in organisms, called ‘bioaccumulation’, is the ‘holy grail’ of mercury research today. Similarly, some watersheds ‘leak’ nitrogen that is normally retained by forests as a nutrient and some watersheds do not.

The findings will influence how park managers educate the public about issues such as mercury consumption advisories in lakes. The information is being provided to agency regulators and Congress for the debate about future regulatory reductions in mercury emissions and changes in clean air legislation that relate to acid rain, to which nitrogen deposition is a contributor.

The special issue summarizes the results of long-term research regarding mercury, nitrogen, and forest disturbance in two paired gauged watersheds at Acadia National Park. A wildfire that burned one of the watersheds in 1947 provided a natural experimental design – a burned/unburned contrast that relates to how watersheds process nitrogen and mercury and the park manages its natural resources. The research team used paleo-ecological techniques to re-construct the vegetation history of the paired research watersheds for the past several hundred years, before written historical information was available.

The controls on mercury and nitrogen are now known to include fire history of watersheds—previous fires mean less mercury is available for ‘bioaccumulation’ and less nitrogen is lost from the forest. More wetlands mean that more mercury is available, and more softwood trees mean that more mercury and nitrogen is captured from rain and snow year around. Varied terrain—such as mountains and steep slopes—also mean that higher amounts of contaminants are deposited to the landscape. Steep slopes mean that contaminants are flushed into waters and are ‘bioavailable’ for organisms such as loons and fish.

Research at the paired watersheds was initiated, in part, to help determine why the most mercury-contaminated fish in the U.S. were found in Acadia National Park and why some tree swallow tissues at Acadia were higher in mercury than their counterparts in a Superfund site in Massachusetts.

These research projects were funded to Kahl and co-workers from UMaine and other universities and federal agencies by the Environmental Protection Agency, the National Park Service, United States Geologic Survey, the Canon Foundation and the Maine Department of Environmental Protection.

For more information, contact Bruce Lyndes, PSU Media Relations Mgr., (603) 535-2775 or