Acid Rain Still Taking a Toll on Northeast Forests

May 30, 2008 -- Acid rain may seem, like, so 1980s, but the problem has not gone away.

Researchers reported this week that soils throughout the Northeast are continuing to acidify, despite a 50 percent decrease in acid rain since the peak in 1973.

This may be contributing to declines in sugar maples and red spruce in the region, the researchers said.

"The quality of water is improving, but the soils are continuing to get worse," said study lead author Richard Warby, now at Environ International Corporation in Princeton, N.J.

Warby, who conducted the study while at Syracuse University in N.Y., presented the findings this week at a meeting of the American Geophysical Union in Fort Lauderdale, Fla.

Acid rain in the United States is caused primarily by emissions from coal power plants, especially sulfur dioxide. Acid rain has decreased since restrictions on sulfur dioxide emissions were enacted under the Clean Air Act in 1970 and 1990.

In 2001, Warby repeated surveys done in 1984 by the Environmental Protection Agency of 145 watersheds throughout the Northeast region. He gathered soil and water samples and compared the change over 17 years.

"What we found is rather alarming," Warby said. The levels of calcium ions in the soil had halved throughout the region while aluminum ions had doubled.

Calcium ions are basic, and provide the soil with a way to neutralize acid it is exposed to. They also provide essential nutrition to trees like red spruce and sugar maple.

Aluminum ions, on the other hand, are acidic, and soil aluminum shifts from an inert form into an available form under acidic conditions. The available form is toxic to plants at high concentrations.

"You're replacing a nutrient by a toxic substance," said Charles Driscoll of Syracuse University, who was a part of the study.

"The soils appear to be more sensitive than surface waters," he added. The amount of acid rain seems to have dropped enough that lakes and streams can recover, perhaps with the help of shoreline wetlands and lake sediments, Driscoll said.

But it is not sufficient for soils.