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Acid rain in Shenandoah National Park, Virginia

Printed on recycled paper Visitors to Shenandoah National Park (SNP) enjoy the animal and plant life and the scenery but may not realize how vulnerable these features are to various threats, such as invasion of exotic plants and insects, improper use of park resources by humans, and air and water pollution. The National Park Service strives to protect natural resources from such threats to ensure that the resources will be available for enjoyment now and in the future. Because SNP has limited influence over the air pollution that envelops the region, acidic deposition— commonly known as acid rain—is one of the more challenging threats facing park managers. With the help of U.S. Geological Survey (USGS) scientists, park managers can understand how acid rain interacts with groundand surface-water resources, which enables them to explain why reductions in air pollution can help preserve park resources. Such understanding also provides essential insight into ecosystem processes, as managers strive to unravel and resolve other environmental problems that are interrelated to acid rain. Even though reductions in emissions of acid-forming compounds mandated by the Clean Air Act and Amendments have occurred since 1990, acid rain continues to fall in the eastern United States, including SNP. The combination of acid rain (currently about 4.6 pH units) falling onto an environment that has little inherent ability to neutralize the acidic input and decades of exposure to acid rain have resulted in a fragile environment. When the effects of acid rain are combined with stressors, such as forest defoliation caused by the gypsy moth or coniferous tree demise caused by the hemlock woolly adelgid, significant environmental problems can develop, and park resources become threatened.