Shenandoah National Park Streams too Acid for Fish

WASHINGTON, DC, September 25, 2007 (ENS) - Acid rain is one of the most serious environmental problems affecting Shenandoah National Park in northcentral Virginia, according to new research from the U.S. Geological Survey, USGS.

"Because of acid rain, Shenandoah is the third most contaminated park in the national park system," said Karen Rice, the USGS scientist who led the study.

Acid rain affects headwater streams in the park by temporarily reducing the acid-neutralizing capacity of the water. In turn, the increase in acidic components in streamwater can have negative effects on aquatic life.

Steep slopes, small watersheds, and underlying geology, combined with acid rain make many streams inhospitable to native fish for extended periods of time, the study found.

"Many streams in the park have low acid neutralizing capacities for periods lasting from six hours to one week. About 14 percent of the park's watersheds will have three day episodes of acidity sufficient to kill native fish such as brook trout. These high acid episodes occur at least once every two years."

Acid neutralizing capacity is an important factor in stream water quality and biologic health. In Shenandoah National Park, the rains are typically 10 times more acidic than normal rainfall. The pH of rainfall in the park is usually 4.6, although it has dipped well below 4.0.

Normal rain has a pH of 5.6. Rice explains that pH is a logarithmic scale, therefore each whole number denotes a 10-fold change.

While this study did not look at likely impacts to fish populations, the long-term outlook for fish inhabiting streams with the lowest acid neutralizing capacity is not good, Rice said. Over the next 40 to 100 years, there is a greater than 90 percent probability in the most vulnerable streams of at least one acid episode every year for four consecutive years.

The USGS and the University of Virginia, in cooperation with the National Park Service, began this study in 2002 to predict stream response to acid rain.

They found that the vulnerability of a stream to acid rain was controlled by a combination of factors including watershed size, elevation, steepness of gradient and underlying rock type.

Streams with the greatest vulnerability were in small watersheds with a high elevation, steep gradient, and were underlain by silicate bedrock. Those with basaltic rock underneath have a greater capacity to neutralize acid rain, all other factors being equal, the scientists said.

Copyright Environment News Service (ENS) 2007. All rights reserved.