But, while the situation may be improving, many of the lakes still have a long way to go before they can fully support aquatic life. If current levels of acid rain are maintained, it will be several decades before the region sees total recovery, the researchers predict.
The findings are scheduled to appear in the May 15 print edition of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society. The article was initially published April 11 on the journal's Web site.
"This is clear evidence that the Clean Air Act is working," says Charles Driscoll, Ph.D., a professor of civil and environmental engineering at Syracuse University and lead author of the paper. "This is the first time in a peer-reviewed journal that we can say the Adirondacks are showing significant numbers of lakes recovering. It means we've now turned the corner and we're starting to see some improvement."
Acid rain generally occurs when sulfur dioxide in the air (mostly from electric utility emissions) mixes with precipitation to form sulfuric acid, which is then deposited in watersheds. Sulfur dioxide emissions have decreased dramatically since the 1970 Amendments to the Clean Air Act. Emissions peaked in 1973 and have declined almost 40 percent since that time, according to the U.S. Environmental Protection Agency.
The Adirondack region encompasses a giant swath of land in northern New York, including the 6-million-acre Adirondack Park -- a densely forested cluster of mountains spattered with almost 3,000 lakes and ponds.
The area's proximity to the population centers of the Northeast, along with heavy rainfall and shallow soils, has made it incredibly sensitive to the effects of acid rain over the years. In a 2001 study published in the journal BioScience, Driscoll and his colleagues reported that more than 40 percent of the lakes in the Adirondack Mountains periodically have acid levels that can harm aquatic life.
But acid rain is not just a concern for fish; it can be detrimental to an area's economy. Acid rain leads to empty lakes and streams, dead trees, and even reduction in visibility -- major concerns for regions that rely on fishermen and outdoor enthusiasts for tourism dollars. And while acid rain is not directly harmful to human health, the pollutants that cause acid rain (sulfur dioxide and nitrogen oxides) have been associated with increased illness and premature death from heart and lung disorders, such as asthma and bronchitis, according to the U.S. EPA.
In the new study, Driscoll and his colleagues studied data from 48 lakes distributed fairly evenly across the Adirondack region. The lakes are part of the Adirondack Long-Term Monitoring Program (ALTM), which was established in 1982 to assess patterns in lake chemistry in the region through a monthly sampling routine.
Almost all of the lakes showed marked decreases in levels of the sulfate ion -- a part of the sulfuric acid molecule that breaks down upon contact with water. These decreases have in turn caused increases in pH, as well as increases in a key indicator known as Acid Neutralizing Capacity (ANC) -- the ability of a body of water to neutralize acid.
ANC is an important measurement, according to Driscoll. "If it's a positive value ... that's a good thing. But if you have a negative value, you've got more acids than bases."
A body of water with a negative ANC may be "fishless." In fact, any level below about 50 microequivalents per liter -- a measurement used in evaluating water's ANC -- can be dangerous to fish and other aquatic life, depending on the species, Driscoll says. For example, Lake Trout is a more sensitive species than Brook Trout, so certain lakes may be too acidic for one but not the other.
The goal is to get ANC up to a level where the water can support a diverse biological community. An ANC of about 200 microequivalents per liter is considered highly positive.
The good news is that ANC is increasing in many of these lakes, but the caveat, Driscoll says, is that the levels are increasing rather slowly. Extrapolation of the current rates suggests that many lakes will not be fully recovered for several decades. "I don't want to give the impression that the job is done," Driscoll says, "but I think we can say with great confidence that if we cut emissions further, we'll get faster recovery."
Support for this study was provided by the New York State Energy Research and Development Authority, the New York State Department of Environmental Conservation, and the U.S. Environmental Protection Agency.
-- Jason Gorss