Seasonal cycles in streamwater quality on Catoctin Mountain, Maryland

In 1980, the U.S. Congress mandated the National Acid Precipitation Assessment Program (NAPAP) to study the effects of acidic precipitation (acid rain). In 1982, the U.S. Geological Survey (USGS) was selected to be the lead Federal agency under NAPAP to monitor the composition of precipitation and its effects on the environment. In 1982, the USGS began to monitor precipitation and streamwater on Catoctin Mountain in north-central Maryland (fig. 1); the effort has continued through the present. Beginning in 1990, funding for these data-collection and interpretation activities was supplemented by the Maryland Department of the Environment and the Maryland Department of Natural Re- sources. The collection and interpretation of long-term precipitation and streamwater-quality records, such as those at Catoctin Mountain, provide valuable information for management decisions. At the local level, the information can be used to identify periods when streamwater quality may pose a danger to aquatic resources, such as finfish; at the national level, the information can be used to assess the effectiveness of the Clean Air Act Amendments.