Maine's Lakes are Recovering from Acid Rain

Is acid rain finally a thing of the past? Here in Maine, it might be.

I am majoring in geoscience at Smith College and last year I conducted a research project on the recovery of Maine’s lakes from acidic deposition. As you may be aware, acid rain (and other forms of deposition, such as snow) is especially harmful to aquatic ecosystems. Having increased drastically after WWII, it has been a prominent subject of study.

Acidic deposition is defined as having a pH less than 5.6, where a pH of 7 is neutral (non-acidic) and a pH less than 5 is greatly acidic. If this deposition is incorporated into an aquatic ecosystem, it can significantly lower the pH of the water.

Because most aquatic organisms are conditioned to live within a certain pH range, lowering the pH can have deadly consequences. The threshold pH for many organisms, such as crayfish and clams, is between 5 and 6 – below this, they cannot survive.

The biggest source of acidic deposition is the burning of coal, which contains sulfur. When it is burned it releases sulfur dioxide into the atmosphere which eventually comes back to the surface, through deposition, as sulfuric acid. This acid severely lowers the pH and acid neutralizing capacity of the water in aquatic ecosystems.

In 1990 amendments to the Clean Air Act were made to reduce sulfur emissions and stop acidic deposition, and in 2017 I collected water from a random suite of Maine lakes to see if this has truly come to pass. And… it has! I measured the sulfate levels, which is the sulfur component of sulfuric acid, in these lakes and found that the average level in 2017 was almost half of what it was in the 1980s.

None of my samples were acidic. Some, like Blunts Pond in Lamoine, look to be recovering as they have pH values of about 6. Most of the other samples have pH values around 7, meaning they are neutral, such as Chickawaukie Pond in Rockland (7.2).

Our reduction in coal-burning has undoubtedly saved many aquatic ecosystems in the state, but I hope that this research will be continued into the future so we can more fully understand the nature of acid rain impacts and recovery.