Surface Waters
When acid rain falls into a lake or stream, it decreases the pH balance of that particular body of water. According to the U.S. Environmental Protection Agency, most streams and lakes have a natural pH level between 6.0 and 8.0. Bodies of water with a pH level of 5.0 or less are considered very acidic. Melting snow and heavy rain with chemical content can cause brief acidic runoff in some areas. Many lakes and streams in the U.S. are sensitive to this episodic acidification, which can cause "fish kills."
Aquatic Animals
When acid rain enters the water, aluminum levels increase in a lake or pond and the pH level decreases. These factors can cause chronic stress to fish, which results in lower body weight; this can make them less capable when competing for food. Younger aquatic animals have a harder time coping with these conditions than adults. Most fish eggs are unable to hatch with a pH level of 5.0 or less. According to the EPA, frogs can withstand a pH level of 4.0 or greater, while clams and snails can only withstand a pH level of 6.0 or more. Because an ecosystem is interdependent, even though an animal higher on the food chain can withstand lower pH levels, its food may not. Reducing the food supply decreases diversity within the acidic ecosystem.
Soils and Forests
Acid rain can cause plants and trees in the forest to grow more slowly or even die. Trees are weakened when chemicals are absorbed through leaves and roots, resulting in damage, injury or death. When acidic rain or snow falls, it seeps into the soil but may become neutralized. According to the EPA, this is called the "buffering zone" and neutralization of the acid depends on the content of the soil. Environments like the Catskill Mountains have low buffering soils, resulting in more trees affected by acid rain. States like Nebraska and Indiana have stronger buffering soils, resulting in less acid rain damage to those forests.