The study, “Decadal Trends Reveal Recent Acceleration in the Rate of Recovery from Acidification in the Northeastern U.S.” was published online in March on the Environmental Science & Technology website.

Steve Kahl, Director and Professor of Sustainability, had the research report published in March in the journal Environmental Science and Technology along with colleagues from UMaine and UNH. This paper is a follow-up to the previous assessment of recovery published as a cover article in the same journal in 2004 (Kahl et al., Response of surface water chemistry to changes in acidic deposition: implications for future amendments to Clean Air Act). Kahl was the EPA-funded team leader of this regional acid rain assessment from 1983 to 2010.

Acid rain — which contains higher than normal amounts of nitric and sulfuric acid and is harmful to lakes, streams, fish, plants and trees — occurs when sulfur dioxide and nitrogen oxide in the atmosphere mix with water and oxygen. In the United States, about two-thirds of sulfur dioxide and one-quarter of nitrogen oxide result from burning fossil fuels, according to the U.S. Environmental Protection Agency.

“We now know that lakes are more resilient to pollution from the atmosphere than previously thought” Kahl says. Part of the answer lies in the change in air emissions over the past decade. “Remarkably, the use of coal in power plants, which is responsible for emissions of both carbon dioxide (a greenhouse gas) and sulfur dioxide (a precursor to acid rain) has decreased from half of our power production to only one-third”. The other part of the answer lies in watersheds of the lakes. “First, organic acidity has been shown to be important as a natural acidifier and we can’t — and shouldn’t — try to decrease natural acidity with Clean Air Act policy. Second, the recovery in pH is being facilitated by soil processes that were incorrectly thought to be only slowly reversible”.

Sulfate concentration in rain and snow dropped 40 percent in the 2000s and sulfate concentration in lakes in the Northeast declined at a greater rate from 2002 to 2010 than during the 1980s or 1990s, says the team’s leader, Kristin Strock, a former doctoral student at UMaine, now an assistant professor at Dickinson College in Pennsylvania. Also during the 2000s, nitrate concentration in rain and snow declined by more than 50 percent and its concentration in lakes also declined.

The research team analyzed data collected since 1991 at 31 sites in Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and southern New York and 43 sites in the Adirondack Mountains of New York.

While results reveal a recent acceleration in recovery, say continued observation is necessary due to variability of results caused by climate change and other factors, including road salt, on lakes. According to Kahl, perhaps most problematic complication is a proposal to flood the upper atmosphere with sulfur dioxide particulates which reflect sunlight back into space and are presumed to cool the planet. Such an action would have the unintended consequence as the SO2 gradually fell back into the atmosphere and became acid rain.

Tuesday, August 26, 2014