Virginia Is Losing Its Native Trout Streams To Acid Rain

Presently only about 50 percent of Virginia's mountain streams support trout, down from an estimated 82 percent before the mid-1800s, according to a University of Virginia study. "Our study indicates a substantial decline in trout stream water quality since the start of the industrial age," says Art Bulger, research scientist in the Department of Environmental Sciences at U.Va.

Unless acidic emissions from power plants and other sources are reduced dramatically from current levels, Bulger says, only about 42 percent of Virginia's streams will support trout before the midpoint of the 21st century. Similar decline is expected throughout the Southern Appalachians, representing thousands of miles of streams that may become troutless. Fifty-nine percent of the wild trout streams throughout the Southern Appalachians are considered highly vulnerable to acidification.

"Very importantly, a 70 percent reduction in acid deposition ("acid rain") from 1991 levels (when Amendments to the Clean Air Act became effective) will be needed just to keep healthy the trout streams we presently have," Bulger says. "Even this reduction will not increase to previous levels the number of streams suitable for brook trout."

The Amendments to the Clean Air Act require that by the year 2000, coal-fired power plants must have cut in half sulfur dioxide and nitrogen oxide emissions.

Bulger and his colleagues used detailed water chemistry data from 60 geologically representative Virginia trout streams collected each quarter from 1989 to 1992. A computer model was used to analyze this data to predict future stream chemistry, and to reconstruct past water chemistry. The results were printed last year in a report produced by Trout Unlimited, a national conservation organization headquartered in Arlington, Va.

Acid deposition, which is often called "acid rain," is the deposit of airborne acidic material from sources such as coal-burning power plants into streams, rivers and lakes as wet precipitation (rain, snow, fog, cloud) and dry precipitation (dust and gases). Acid deposition is responsible for the documented loss of hundreds of fish populations in Europe and North America.

The burning of fossil fuels releases sulfur and nitrogen oxides into the atmosphere, which are converted to sulfuric and nitric acids. Coal-burning power plants in the Ohio River Valley are a major source of this pollution, which is carried east on prevailing winds.

Depending on the bedrock geology of a particular stream, these acids can create a situation that is deadly to fish. Acids release aluminum from the soil, resulting in an environment that is toxic to fish and aquatic insects. In basin waters at lower elevations, acids are usually neutralized because weathered bedrock has a buffering effect on acids that have entered streams and lakes. But at the higher elevations where brook trout live, the hard unweathered bedrock of headwaters has little buffering effect, allowing excessively high acidic conditions to develop. These acids accumulate over time, and even when the source of the pollution has been reduced, it may take years for the stream chemistry to respond. During that time the entire population of fish in a stream may become extinct.

"The hydrogen ion that is derived from sulfuric and nitric acids and the soluble aluminum create a poisonous combination for the fish," says Bulger. "The toxic action occurs at the gill, resulting in blood and body fluid disturbances leading to circulatory collapse. The fish basically has a heart attack."

Of the three species of trout in the eastern U.S., the brook trout is the only native to the region, and is the most acid tolerant, Bulger says. Non-native rainbow trout and brown trout are more sensitive to acidification, and may experience greater declines due to this process. Bulger limited his study to brook trout (and other native fish species) because they are intrinsically valuable to mountain stream fish communities. These communities include fish species that are sensitive to many kinds of pollution.

The study was sponsored by the National Park Service, the USDA Forest Service, Virginia Department of Game and Inland Fisheries, and Trout Unlimited.