U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005-3123

December 2005

Expanding the Mercury Deposition Network in Virginia and 

the U.S. Mid-Atlantic Region

Printed on recycled paper

Mercury in the Environment

Mercury is a toxic metal having known detrimental health 

effects on the central nervous system. Mercury in the environment is derived from natural sources (such as volcanic eruptions) and from human activities (such as combustion of fossil 

fuels, metal processing, and some mining activities). Mercury 

added to the atmosphere by these sources may circulate globally 

or may be deposited locally, depending on its chemical form. 

Levels of mercury present in the air and in precipitation (rain 

and snow) generally do not pose a direct threat to humans; however, mercury derived from the atmosphere is thought to be a 

primary source of mercury in fish. Fish consumption is the main 

avenue for human exposure to mercury in the United States, and 

fish consumption advisories for mercury now account for more 

than three-quarters of all State fish consumption advisories 

(fig. 1). 

Monitoring atmospheric mercury deposition provides 

estimates of the amount of mercury added to lakes, rivers, 

estuaries, and wetlands. In an aquatic environment, a portion of 

the mercury may be converted by bacteria to organic forms (for 

example, methylmercury) that can be taken up by organisms. 

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States/Provinces with

at least one mercury

advisory

Statewide/Provincewide

mercury advisories

Coastal mercury

advisory

States/Provinces with no

mercury advisory

Columbia

Saskatchewan Ontario

Quebec

Newfoundland

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Active MDN sites

Pending MDN sites

STUDY

AREA

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Culpeper

VA-08

VA28

Shenandoah

National Park

Figure 1A. Map showing distribution of 

operating Mercury Deposition Network 

(MDN) stations, pending sites, and fish 

consumption advisories as of 2003. Prior 

to 2003, there were no operating MDN 

sites in Delaware, Maryland, Virginia, or 

West Virginia. Map compiled by National 

Atmospheric Deposition Program 

- Mercury Deposition Network (http://

nadp.sws.uiuc.edu/mdn), with data from 

U.S. Environmental Protection Agency 

National Listing of Fish and Wildlife 

Advisories (http://oaspub.epa.gov/nlfwa/

nlfwa.bld_qry?p_type=advmap&p_

loc=on).

Figure 1B. Location map showing 

the sites of MDN stations in northern 

Virginia. Stations VA–08, near 

Culpeper (latitude 38.42; longitude 

−78.10), and VA–28, at Big Meadows 

(latitude 38.52; longitude −78.44), 

are about 100 and 130 kilometers 

southwest of Washington, D.C., 

respectively.

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B
Levels of methylmercury in the tissues of organisms increase 

upward in the food chain; that is, there are higher concentrations 

at increasingly higher levels in the chain. This bioaccumulation 

poses a potential hazard to humans and long-lived wildlife.

The Mercury Deposition Network

The Mercury Deposition Network (MDN) of the National 

Atmospheric Deposition Program (NADP) was started in the 

mid-1990s to meet the need for information on rates of mercury 

deposition from precipitation in North America (information 

on the NADP is available on the Web at http://nadp.sws.uiuc.

edu). The goal of the MDN is to develop a national database of 

weekly mercury data to determine spatial and seasonal trends 

in mercury wet deposition (that is, mercury deposited from the 

atmosphere via rain, sleet, and snow). Mercury deposition under 

dry conditions, which accounts for a portion of the mercury 

deposited from the atmosphere, is not measured by the MDN. 

Most MDN stations are in the eastern third of the United States, 

where predicted levels of mercury deposition are greatest due 

to prevailing weather conditions and the number of coal-fired 

power-generating stations, a significant source of atmospheric 

mercury, in the Midwest, the mid-Atlantic States, and the 

Southeast. 

The MDN in the U.S. Mid-Atlantic Region

In autumn 2002, two MDN stations began operation in 

Virginia (fig. 1), helping to fill a significant gap in the network 

in the mid-Atlantic region. Station VA–08, located southwest of 

Culpeper, Va., at an elevation of 163 meters, is operated jointly 

by the U.S. Geological Survey and George Mason University 

(fig. 2). Station VA–28, located at Big Meadows in Shenandoah 

National Park, at an elevation of 1,074 meters, is operated by 

the National Park Service. These sites greatly improve MDN 

coverage immediately west of the Washington, D.C., metropolitan area. The proximity of the Culpeper and Big Meadows sites 

Figure 2. Views of MDN sites VA–08 , Culpeper (top), and VA–28, 

Shenandoah National Park-Big Meadows (bottom). Each station 

consists of a recording rain gauge (cylinders) and a precipitation 

collector (boxes). Mercury sample is collected through a 

glass funnel exposed when a moisture sensor activates the lid 

covering the sample chimneys at the left side of the collector. 

Top photograph by Allan Kolker, USGS; bottom photograph from 

National Atmospheric Deposition Program (http://nadp.sws.uiuc.

edu/sites/siteinfo.asp?net=MDN&id=VA28).

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Figure 3. MDN results for 2003 for U.S. mid-Atlantic stations (black dots), including two stations in Virginia. A, Average yearly mercury 

concentration, weighted by volume, in nanograms per liter (1 nanogram equals 10-9 grams). B, Total mercury deposition for the year, in 

micrograms per square meter. Each site also showed seasonal variation in mercury concentrations, with the highest values occurring 

in the summer months. Variation in total mercury deposition mainly reflects differences in precipitation for the year. Color bands 

indicate contoured 2003 results. Maps from National Atmospheric Deposition Program - Mercury Deposition Network (http://nadp.

sws.uiuc.edu/mdn/).

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Pennsylvania

Maryland

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Figure 5. Map showing locations of U.S. mid-Atlantic MDN 

sites active in 2003 (solid symbols) and sites used to calculate 

average mercury concentrations (red symbols; see fig. 6 for 

concentration data) for the weeks leading up to and following 

Hurricane Isabel (September 18–19, 2003). Precipitation 

amounts (black numbers; in centimeters) are shown for the 

week ending September 23, 2003, as are the path (hurricane 

symbols) and wind speed (blue numbers; in mph) of the 

hurricane. Open symbols indicate MDN sites added after 

September 2003. Black symbol for MDN site VA–28 indicates 

that this site was excluded from the mercury concentration 

averages shown in figure 6 due to loss of power, which resulted 

in shutdown of the station during the hurricane. Storm track 

for Hurricane Isabel is plotted from information available at 

http://hurricane.csc.noaa.gov/hurricanes/. Modified from Kolker, 

Allan, Mose, D.G., and Spitzer, Shane, 2004, Filling a gap: MDN 

stations VA–08 (Culpeper) and VA–28 (Shenandoah National 

Park–Big Meadows) in Virginia [abs.]: National Atmospheric 

Deposition Program (NADP), 2004 Scientific Symposium, Halifax, 

Nova Scotia, Canada, 2004.

to each other (31 kilometers) is among the closest in the MDN, 

allowing comparisons of local mercury deposition at different 

elevations. Station VA–28 is also used to monitor potential mercury exposure by wildlife in Shenandoah National Park.

Annual MDN results for 2003 (fig. 3) showed a gradual 

southward increase in mercury deposition across the mid-Atlantic region. These results are consistent with the high levels of 

mercury deposition that occur in the southeastern States. A longer period of observation, however, is needed to assess nationwide patterns and differences among MDN sites in the region. 

Most MDN sites also show seasonal variations, with 

increases in mercury concentration and total deposition in the 

warm weather months. For the year 2003, mercury concentrations were higher at Culpeper (lower elevation) than at Big 

Meadows (higher elevation). Because precipitation was greater 

at Big Meadows, however, total mercury deposition at both 

sites was nearly the same. Additional yearly results will soon 

be available as data for 2004 and for three new MDN stations 

in Virginia and Maryland—VA–98 (Harcum; lower Chesapeake Bay), MD–08 (Piney Reservoir; Garrett County, western 

Maryland), and MD–99 (Beltsville; suburban Washington, 

D.C.)—are finalized.

Generally, weekly MDN samples cannot be linked to 

specific weather events. For samples taken the week ending 

September 22, 2003, however, most mid-Atlantic MDN sites 

showed unusually low mercury concentrations. These samples 

consisted predominantly of precipitation from Hurricane Isabel, 

which came ashore along the North Carolina coast and followed 

a path northward through the region (figs. 4, 5). Mercury concentrations in precipitation from Hurricane Isabel were much 

below average for that time of year (fig. 6), consistent with the 

depletion of mercury from the atmosphere by the heavy rain and 

the origin of the storm far from anthropogenic mercury sources. 

The Need for Measuring Mercury Deposition 

Recent work (for example, see http://www.umanitoba.

ca/institutes/fisheries/METAALICUS.html) suggests that new 

mercury added to the environment by atmospheric deposition 

is more prone to become methylmercury than mercury already 

present in sediments. It is therefore very important to quantify 

Figure 4. Satellite view of Hurricane Isabel, September 18, 

2003, 11:50 a.m. From NASA Terra satellite, http://science.nasa.

gov/headlines/y2003/18sep_isabel.htm.
the amount of mercury deposited each year from atmospheric 

sources. 

Currently, coal-fired powerplants are the largest industrial 

source of U.S. mercury emissions. The U.S. Environmental Protection Agency (USEPA) has approved a long-term plan to cap 

and reduce mercury emissions from coal-fired power-generating 

stations (see http://www.epa.gov/oar/mercuryrule/ for information on the USEPA Clear Air Mercury Rule). The MDN will be 

a primary tool for measuring the overall effectiveness of the new 

mercury rule. For example, the growth of the MDN has led to 

an increased ability to map regional patterns of mercury deposition. Documenting these patterns will help establish baseline 

mercury levels prior to the implementation of the USEPA plan. 

The impact of the USEPA plan should be greatest in the 

eastern third of the United States, where the levels of mercury 

deposition are highest. A similar plan to limit emissions of sulfur dioxide resulted in a large decrease in deposition of sulfate 

(the main component of acid rain) in the East in the last decade.

Summary

The addition of new MDN stations in the mid-Atlantic 

region has greatly improved the ability to assess the impact 

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of reduced mercury emissions from coal-fired powerplants in 

the region and in neighboring States. As the density of MDN 

stations increases, the network will also become more effective 

in defining local variations and improving yearly estimates of 

mercury deposited from the atmosphere to ecosystems in different regions.

By Allan Kolker,1 Douglas G. Mose,2 Shane Spitzer,3

and Joseph A. East1

1

U.S. Geological Survey, MS 956, National Center, Reston, VA 20192.

2

George Mason University, Department of Chemistry, Fairfax, VA 22030.

3

National Park Service, Shenandoah National Park, Luray, VA 22835.

For further information on Station VA–08, please contact

Allan Kolker 

U.S. Geological Survey

956 National Center 

Reston, VA 20192 

Prof. Douglas G. Mose

Department of Chemistry

George Mason University

Fairfax, VA 22030

For further information on Station VA–28, please contact

Gordon Olson

Division of Natural and Cultural Resources

National Park Service

Shenandoah National Park

Luray, VA 22835-9036

Additional Resources

Shenandoah National Park Air Monitoring Program

http://www.nps.gov/shen/SHEN_IM/m_prog_air.htm

National Park Service, Center for Urban Ecology, 

Air Resources Page

http://www.nps.gov/cue/programs/air/air_resources.htm

USGS Mercury Research

http://minerals.usgs.gov/mercury/

Fish and wildlife studies, methylation, and mercury in plants 

and/or organisms 

http://co.water.usgs.gov/trace/

Mercury cycling in watersheds and aquatic ecosystems 

http://toxics.usgs.gov/about.html

Figure 6. Mercury concentration averages of nine U.S. midAtlantic MDN stations affected by Hurricane Isabel, normalized 

to quarterly averages for the respective stations for the period 

shown. Plot shows a pronounced mercury concentration low 

for the first samples taken after the hurricane (red circle). 

Results for site VA–28 (Shenandoah National Park) are 

excluded due to site operation problems resulting from the 

hurricane. Modified from Kolker, Allan, Mose, D.G., and Spitzer, 

Shane, 2004, Filling a gap: MDN stations VA–08 (Culpeper) and 

VA–28 (Shenandoah National Park–Big Meadows) in Virginia 

[abs.]: National Atmospheric Deposition Program (NADP), 2004 

Scientific Symposium, Halifax, Nova Scotia, Canada, 2004.