Field measurements of pH values from the National Atmospheric Deposition Program National Trends Network

PR20 4.8 VI01 4.9

Note: AK is Alaska; HI is Hawaii; PR is Puerto Rico; VI is Virgin Islands.

PR20 4.8 VI01 4.9

Note: AK is Alaska; HI is Hawaii; PR is Puerto Rico; VI is Virgin Islands.

source: Adapted from "Hydrogen Ion Concentration as pH from Measurements Made at the Field Laboratories, 2003," in Hydrogen Ion Concentration as pH from Measurements Made at the Field Laboratories, 2003, National Atmospheric Deposition Program, Champaign, IL, 2005, http://nadp.sws.uiuc.edu/ isopleths/maps2003/phfield.pdf (accessed August 4, 2005)

EFFECTS OF ACID RAIN ON OUR ENVIRONMENT

In nature the combination of rain and oxides is part of a natural balance that nourishes plants and aquatic life. However, when the balance is upset, the results to the environment can be harmful and destructive. (See Table 5.1.)

Aquatic Systems

Although pH levels vary considerably from one body of water to another, a typical pH range for the lakes and rivers in the United States is six to eight.

Low pH levels kill fish eggs, frog eggs, and fish food organisms. The degree of damage depends on several factors, one of which is the buffering capacity of the watershed soil—the higher the alkalinity, the more slowly the lakes and streams acidify. The exposure of fish to acidified freshwater lakes and streams has been intensely studied since the 1970s. Scientists distinguish between sudden shocks and chronic (long-term) exposure to low pH levels.

Sudden, short-term shifts in pH levels result from snowmelts, which release acidic materials accumulated during the winter, or sudden rainstorms that can wash residual acid into streams and lakes. The resulting acid shock can be devastating to fish and their ecosystems. At pH levels below 4.9, damage occurs to fish eggs. At acid levels below 4.5, some species of fish die. Below pH 3.5, most fish die within hours. (See Table 5.2.)

Because many species of fish hatch in the spring, even mild increases in acidity can harm or kill the new life. Temporary increases in acidity also affect insects and other invertebrates, such as snails and crayfish, on which the fish feed.

Gradual decreases of pH levels over time affect fish reproduction and spawning. Moderate levels of acidity in water can confuse a salmon's sense of smell, which it

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