Distilled water has a pH of 7, which is neutral. Normal rain is by nature slightly acidic, with a pH of 5.6. Sulfuric and nitric acids from industrial and automotive sources mix with the rain, snow and fog, creating acidic precipitation. Even though Vermont emits the lowest amount of acid precipitation- causing pollutants than any other state in the nation, emissions from Midwestern states blow eastward and contaminate the precipitation that falls in Vermont. Snow retains and accumulates pollutants until the spring snow melt, when these acidic compounds are released all at once into the environment, creating a phenomenon known as acid shock.
Acid shock can cause significant alterations to water chemistry and aquatic life.
Acid shock can be particularly harmful to aquatic communities because it occurs during spawning or the early life stages of many aquatic animals. If the pools become too acidic from spring run-off, the eggs are unable to properly develop and may die. Some naturally occurring levels of nutrients, such as calcium, become less available to aquatic life because they are chemically bound up buffering the effects of the incoming acids. A decrease in calcium concentrations can be detrimental to the shell development of crustaceans and mollusks as well as to the ability of fish to respond to changes in water temperature and alkalinity. The full extent to which streams, rivers and lakes are affected by acid precipitation is determined in large part by the bedrock of the area.