Background

Atmospheric deposition is the process by which airborne particles and gases are deposited to the earth’s surface either through precipitation (rain, snow, clouds, and fog) or as a result of complex atmospheric processes such as settling, impaction, and adsorption, known as dry deposition. Wet deposition is the component of atmospheric deposition that is deposited by rain or snow commonly known as acid rain. Deposition can include a wide variety of natural and anthropogenic pollutants, including inorganic elements and compounds (e.g., nitrogen, sulfur, basic cations, mercury and other metals) and organic compounds (e.g., pesticides and herbicides). Once deposited, pollutants can have a variety of ecosystem effects. Nitrogen and sulfur compounds, for example, can result in acidification of freshwaters, loss of aquatic species, eutrophication of estuarine and near-coastal waterways, soil nutrient and base cation leaching, and vegetation changes.

The Chesapeake Bay Watershed (which includes the NCRN) receives some of the highest fluxes of N and S among the estuarine watersheds of the eastern seaboard. Deposition of S (10-14 kg S ha-1 yr-1) and the associated hydrogen ion create "acid rain" have decreased markedly since the implementation of the Clean Air Act Amendments (CAAA) of 1990. Wet deposited NO3- and NH4+, although an incomplete measure of total N deposition, will be used as an indicator N deposition trends. Combined with SO42- wet deposition data, these numbers will also provide an indicator for acidification caused by atmospheric pollutants. Because N and S deposition can affect water quality parameters (i.e., nitrate, ammonia, and/or DON), soil characteristics (ion exchange characteristics), and encourage invasive plants (i.e., grasses through excess N), these parameters should be tracked along with the deposition numbers to ensure that any correlations and underlying linkages are quantified.

Objectives

• Report on seasonal and annual status and trends of nitrogen, sulfur and other pollutant concentrations in precipitation and depsition amounts.

Measures

Since N and S deposition may affect water quality parameters (e.g., acid neutralizing capacity) and soil characteristics (ion exchange capacity) and N deposition is hypothesized to encourage invasive plant establishment, any significant trends in N or S deposition may affect surface waters, soils or plant communities in NCRN parks. NCRN will evaluate correlations between N and S concentration and deposition and other ecological parameters, and initiate monitoring or research in this area, if warranted.

Status

State and federal agencies, and others, who monitor wet deposition chemistry through the National Atmospheric Deposition Program/National Trends Network (NADP/NTN), use NADP/NTN’s monitoring protocol and follow the program’s quality assurance/quality control guidelines. NADP/NTN posts site-specific and programwide data on their website. NPS ARD will provide trend data annually for parks with NADP/NTN monitoring. As appropriate, NCRN will supplement information obtained from ARD with data summaries, interpretations and graphics available on the NADP/NTN website.

Contacts
Patrick Campbell, NCRN Network Coordinator
202.342.1443 ext. 229