Monitoring Surface Water Chemistry
Surface water chemistry is a direct indicator of the effects of acid rain on water bodies. Networks that monitor surface water chemistry over long time periods provide valuable information on aquatic ecosystem health and how water bodies respond to changes in acid-causing emissions. EPA oversees the Long-Term Monitoring (LTM) program, which tracks changes in surface water chemistry in response to changing air emissions and acid deposition.
The goal of this long-term program is to track whether the Clean Air Act Amendments (CAAA) (Plain English Guide to the Clean Air Act) have been effective in reducing the acidity of surface waters in New England, the Northern Adirondack Mountains, Appalachian Plateau, and the Central Appalachians and advance the science of air pollution impacts on water resources.
What are Acidified Surface Waters?
Acid precipitation (commonly known as acid rain) primarily affects sensitive bodies of water, which are located in watersheds whose soils have a limited ability to neutralize acidic compounds (called “buffering capacity”). Acidification is a result of acidic deposition and the soil’s capacity to buffer what is deposited. As water moves through and over the soil, it picks up the acid deposited and transfers it into lakes and streams. As lakes and streams become more acidic, the numbers and types of fish and other aquatic plants and animals that live in these waters decrease.
Locations for the LTM Program
The LTM program tracks changes in surface water chemistry in the four regions shown below, known to be sensitive to acid rain: New England, the Adirondack Mountains, the Northern Appalachian Plateau, and the central Appalachians.
Data for the LTM Program
This dataset compiles surface water chemistry data for 172 sites (lakes and streams) from 1980 to 2018 and will be updated annually with an approximate lag time of one year. Data are currently collected from 158 sites in four regions sensitive to acid rain in the eastern United States: Central Appalachians (Virginia), Adirondack Mountains (New York), Catskills (New York), New England (Maine, New Hampshire, Vermont). The fifth region/state (Pennsylvania) is no longer sampled but is still included in the dataset. Fourteen sites in the four regions are no longer sampled, but are also included in the dataset. These data are used to calculate trends in surface water chemistry to assess aquatic ecosystem response to changes in sulfur and nitrogen deposition. Water chemistry in this data can be influenced by the ambient flow conditions, such as spring snowmelt or intense rainfall. To be included in the dataset, sites needed to have regular sampling (at least once per year for 20 years).
Number of Currently Sampled Streams and Lakes per Region
Virginia: 73 Streams
New York: 55 Lakes, 7 Streams
Maine and New Hampshire: 20 Lakes
Vermont: 12 Lakes
Pennsylvania: 5 Streams
Main Water Quality Parameters Sampled
Acid Neutralizing Capacity
Dissolved Organic Carbon
U.S. Environmental Protection Agency Clean Air Markets Division
EPA Long-Term Monitoring of Acidified Surface Waters
Date accessed: [month day, year]