Acid rain is still a threat to more than one-third of Maine's forestland, according to a new study presented Tuesday in Portland.
While not the urgent and unregulated threat it was in the 1980s, enough acidic pollutants are settling across the landscape today to gradually weaken forests in sensitive areas, the study found.
The amount of forestland at risk statewide totals about 5.9 million acres, with most of that area spread throughout the valuable commercial forests of northern and western Maine.
"Acid rain is still very much an issue in Maine and New England," said David Littell, commissioner of the Maine Department of Environmental Protection.
The report does not include evidence of slowing forest growth or weakened and diseased trees, but it warns that sensitive areas eventually could face such problems at the current rate of acidification. It is expected to focus scientific attention back on the problem and provides state forest managers and private landowners a map of where to look for impacts.
"It should be considered the first step in a more detailed assessment," Littell said.
Acid rain, or acid deposition, occurs when chemicals react in the atmosphere to form acids that settle onto forests and waterways in precipitation or as dry particles. The primary pollutants responsible for the phenomenon are sulfur dioxide and nitrogen oxides from power plants and motor-vehicle exhaust.
Acid deposition damages buildings and monuments, and it changes the chemistry in the environment. It can increase the acidity of lakes and streams and kill aquatic animals and plants. In forests, the acids react with the soils, removing important plant nutrients such as calcium. Once those nutrients are removed beyond the soil's capacity to replace them, trees grow more slowly and become vulnerable to freezing, insects and disease.
Power plants have dramatically cut acid rain pollution since 1990, when federal regulations kicked in. As a result, precipitation in New England is significantly less acidic than it was 20 years ago, officials said. The success of a cap-and-trade system to cut sulfur dioxide pollution has been so successful it is often cited as a model for fighting global warming pollution.
State and regional officials knew acid rain hadn't been eliminated, but did not know what effect it might still be having.
The study presented Tuesday at the University of Southern Maine was conducted by Ecosystems Research Group of Norwich, Vt., as part of a regional mapping effort across New England and eastern Canada. The Maine DEP provided $40,000 for the project, and other sources, including the federal government, contributed another $40,000.
Officials hope to expand the findings to include bodies of water as well as forests.
The study is based on a complex model that considers such factors as geology and nutrient capacity, the rate of nutrient removal through logging, and the amounts of acid deposition in different parts of the state. Although more acid deposition occurs in coastal Maine, the geology and logging practices in northern and western Maine make those areas more susceptible to acidification, said Eric Miller, the lead scientist on the project.
Similarly, while other New England states receive more acid rain pollution from the Midwest, Maine has a higher percentage of at-risk forestland than all but Rhode Island.
Still, Maine has no known areas that are so sensitive that they are showing signs of damage.
"We do not see growth reductions at this point," said David Struble of the Maine Forest Service. There is more wood in the Maine forests now than 50 years ago, he said. "That doesn't mean, necessarily, we don't have a problem looming," he said.
Walter Emrich of J.D. Irving Ltd., one of Maine's largest forestland owners, said the study doesn't put acid rain back at the top of forest ecology concerns. "I don't think anything's going to impact us immediately," he said.
But Emrich does plan to take a closer look at the maps to see which Irving lands might be most susceptible and worth monitoring.
Miller, the scientist, said it's impossible to say what the continuing effects of acid rain will mean as global warming disrupts the climate and the forest ecology.
Heat actually speeds up the process of replenishing soil nutrients for trees and other plants. On the other hand, droughts, which are expected to accompany a global warming, can slow down that process.
"It's going to be a complicated trade-off," he said.Portland Press-Herald
