National Water Quality Program

National Atmospheric Deposition Program (NADP)

Featured: Atmospheric Deposition of Mercury on Eastern Forests

Featured: Atmospheric Deposition of Mercury on Eastern Forests

Atmospheric mercury (Hg) deposition to forests is of concern because half of the land cover in the eastern USA is forest. Scientists learned that forests canopies record changes in atmospheric mercury over time.

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Featured: Reversals in Soil Acidification from Acid Rain

Featured: Reversals in Soil Acidification from Acid Rain

Reduced acid rain levels resulting from American and Canadian air-pollution control measures have begun to reverse soil acidification across the northeastern United States and eastern Canada.

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Since 1981, the USGS has been the lead Federal agency for the monitoring of wet atmospheric deposition (chemical constituents deposited from the atmosphere via rain, sleet, and snow) in the United States for the interagency National Atmospheric Deposition Program (NADP). The USGS supports about one-third (79 of approximately 250) of the NADP-National Trends Network sites, which measure acidity, sulfate, nutrients and other major ions in precipitation. The USGS also supports sites in the 100-site NADP-Mercury Deposition Network and the NADP-Mercury Litterfall Network. These networks provide scientists, resource managers, and policymakers with long-term, high-quality atmospheric deposition data used to support research and decision-making in the areas of air quality, water quality, agricultural effects, forest productivity, materials effects, ecosystem studies, watershed studies, and human health.

Below are several highlights of recent accomplishments and planned activities.

  • The NWQP’s National Atmospheric Deposition Program released two studies that explored how landscape characteristics such as soils, slope steepness, and vegetation affect ecosystem sensitivity to acidic atmospheric deposition in upland watersheds in the northeast and west. 

  • In the first study (Siemion and others, 2018), three northeastern streams have become less acidic during 1999 – 2013 as sulfuric and nitric acid concentrations have declined in precipitation. However, soil chemistry shows a mixed response, with improvements only at the site where acid deposition has declined by the greatest amount. 

  • In the second study (Clow and others, 2018), soil, vegetation, and topographic characteristics were found to be strongly related to the nitrate concentrations in upland streams in Colorado, California, and Washington.


Stakeholder Quotes 

Litterfall and throughfall monitoring for mercury dry deposition

Litterfall and throughfall monitoring for mercury dry deposition.

(Public domain.)

NADP has played a key role in providing long-term monitoring data to assess policies aimed at reducing air pollution and ecological impacts of atmospheric deposition. The program includes monitoring networks for programs including acid rain, mercury, and reactive nitrogen. Policy implementation for acid rain mitigation is relatively mature and the evolution of these policies is reflective in NADP monitoring data. Programs for regulating mercury and reactive nitrogen deposition are less mature and NADP monitoring will be critical in future years to assess control program efficacy.”  

James Schauer, PhD, PE, MBA, Director, Wisconsin State Laboratory of Hygiene, August 2018


Douglas A Burns

Research Hydrologist (RGE)
New York Water Science Center
Phone: 518-285-5662