UNITY, Maine — Two Maine scientists are celebrating good news about the environment, after a decades-long study has shown that the negative effects of acid rain have been reversed much faster than expected.

Steve Kahl, a sustainability professor at Unity College, said Thursday that the study looked at lakes throughout most of New England and New York, and it found that environmental regulations and the voluntary actions of industry have sharply reduced sulfur emissions in rain and snow. It also found that soils are recovering quickly, without taking centuries to bounce back that some had predicted would be necessary. Finally, the scientists learned that some of the acidity in the watersheds is organic, occurring naturally, and should not be targeted by the Clean Air Act policy.

“Success stories are possible,” Kahl said, adding that the reduction of emissions since the 1970s and 1980s has been critical for water quality. “This is a huge success story for the environment.”

The study was published this spring on the website for the journal Environmental Science & Technology.

Acid rain was an environmental hot button issue in the 1980s. It occurs when factories and coal-burning power plants emit sulfur dioxide and other acidic chemicals that mix in the atmosphere and produce acid rain. Because of the prevailing winds, pollution that was generated in the midwest would blow east and damage lakes, forests and streams in Maine and other parts of the Northeast, killing fish and alarming residents.

At that time, photos of dying trees were shown by environmentalists to generate support for regulatory measures aimed at reducing chemical emissions.

According to Kahl, sulfur emissions in rain and snow have dropped by about 70 percent from the peak in the 1980s. He said that industry was able to save money by switching to lower-emissions fuels, and the formerly-controversial cap-and-trade practice that was established by the federal government has proved to be a success. That practice allows companies flexibility in complying with a mandatory cap on emissions, and it has helped reduce sulfur dioxide emissions from 17.3 million tons in 1980 to about 7.6 million tons in 2008, according to the EPA.

“It’s not controversial anymore,” Kahl said. “It just works. It should be a model for environmental issues. It provides a flexible way to reach the same target and use whatever methods to get there.”

The professor has been studying Maine lakes since 1983, when he was selected to be the team leader for the EPA’s regional acid rain assessment. Although he stopped running the study in 2010, he remains involved, along with Sarah Nelson, an associate research professor at the University of Maine’s Mitchell Center and School of Forest Resources.

Nelson said that the study really shows the value of long-term monitoring.

“Because these lakes have been sampled for so long, they’re really sentinels of what’s been going on in the Northeast,” she said. “It’s really an amazing resource.”

Kahl, Nelson, and another scientist from the University of New Hampshire, take samples at least once a year from 74 lakes in Maine, Massachusetts, Vermont, New Hampshire, Rhode Island and New York. The lakes were chosen to represent the Northeast, with some located in busy suburbs of Boston and some on remote Maine mountaintops. She said that the sampling at Maine’s high-elevation lakes takes place in the fall, usually by helicopter.

“You hop out on the pontoon, dump a bottle in the water and take off,” she said.

Those high-elevation lakes serve as the canary in the coal mine for water quality, Nelson said. Because they are essentially granite bowls without much soil around them, acidic precipitation can be measured more easily.

Although scientists continue to learn about new issues in the environment, including climate change and major weather events, the acid rain study shows that change is possible, Nelson said.

“I think sometimes there can be a perception of doom and gloom, and there are lots of problems, and it’s hard to figure out how to solve them,” she said. “Even though we keep finding new challenges, it’s nice to see that there can be changes made.”