A Tale of Two Acids
by Andy McAllister, Watershed Coordinator
Acidity in our streams can come from a variety of sources; some natural and some not. The water in some streams, swamps and wetlands can be naturally acidic due in part, to the breakdown of plant material releasing Tannins or Tannic Acid. Tannins are responsible for the dark root beer-like appearance and slightly lower pH levels of some waterways.
However, very acidic conditions are most often the result of man’s influence on the environment. Two examples of this are Acid Mine Drainage (AMD) and Acid Rain.
Acid Mine Drainage forms principally from something called Iron Pyrite or “Fools Gold” that is associated with most coal deposits. Acid rain on the other hand, is caused by smoke from automobiles, manufacturing emissions, fossil fuel (oil, coal, and gas) combustion, forest fire smoke, and volcanic gases interacting with rain. When fossil fuels are burned they release sulphur dioxide and nitrogen oxides. These substances, when not removed from the emissions, mix with water vapor in the atmosphere to form Sulfuric Acid and Nitric Acid. Generally, rain with a pH lower than 5.5 qualifies as Acid Rain.
Acid rain eventually flows into streams and lakes, and if those streams cannot buffer the increasing acidity with naturally occurring limestone, they become acidic. The acidity causes such toxins as aluminium and other metals to become dissolved in the stream water. Once dissolved in the water, these metals become poisonous to fish and birds. Acidity in also kills trees and slowly eats away at limestone buildings and stone statues.
The byproducts of combustion that contribute to our acid rain find their way to us from other areas of the country “downwind” of Pennsylvania. The clouds form due in part to our mountainous topography wringing out the water from the atmosphere. The moisture-laden air bumps into the ridgetops in Western and Central PA and forms clouds which then release their acid in the form of rainfall. As a result, the coal regions of Pennsylvania get a “double dose” of acid, both in the form of acid rain and in the form of AMD.
Acid rain has been a widely recognized environmental threat in Europe since the 1950s but has only been acknowledged to be an increasing problem in the US since the 1970s. Technological improvements in fossil fuel combusion for powerplants have resulted in significant reductions of Sulfur compounds over the years but similar success in reducing Nitrogen compounds has yet to be realized.
Acid Rain
from Environment Canada