National Park Service

Northeast Temperate Network (NETN)

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What is Atmospheric Deposition?

Atmospheric deposition occurs when pollutants are transferred from the air to the earth's surface. Atmospheric deposition has been shown to be a significant source of pollutants to the Great Lakes and other water bodies of the northeastern U.S. Pollutants travel from the air into the water through rain and snow, falling particles, and absorption of the gas form of the pollutants into the water.

Why Persistent Toxic Substances are a Problem

The persistent bioaccumulative toxic substances (PBTs) of PCBs, organochlorine pesticides, and polycyclic aromatic hydrocarbons (PAHs) are sometimes present in the air and precipitation. They can accumulate in wildlife, causing reproductive problems and other harmful effects. Many fish in northeastern lakes have high concentrations of these pollutants (thousands or even millions of times higher than levels in the water), making them unsafe for both people and wildlife to eat. In humans, PBTs have been linked to reduced birthweight, developmental problems in children, neurological problems, and immune system disorders. Many are also suspected carcinogens.

Importance & Issues

Atmospheric deposition is a stressor to terrestrial and aquatic systems throughout NETN and has been implicated in the decline or degradation of many ecological systems in the region. Estimates of atmospheric deposition are critical for understanding water chemistry and stress It has been estimated that 90% of the mercury entering remote lakes in Voyageurs National Park (Minnesota) was derived from atmospheric deposition. Acidic deposition stresses terrestrial vegetation and alters system functioning and biogeochemical cycles. Compiling acidic deposition data is important for any long-term monitoring program because this stressor has demonstrated negative effects on aquatic systems and can alter wetland function and biogeochemical processes. The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) is a nationwide network of precipitation monitoring sites. We will work closely with the NPS Air Resources Division to acquire and summarize these existing data to interpret changes at the park level. 


Wet and dry deposition rates, soil nitrification, soil base cation availability, soil Ca:Al ratio, streamwater ANC, streamwater nitrate concentration 

Monitoring Objectives

ARD is developing strategies for estimating the amount of deposition that causes harm to ecosystems. This "critical load" is defined as the amount of pollutant deposition below which significant harmful effects to sensitive resources do not occur. Deposition monitoring and research on ecosystem effects will facilitate the identification of critical loads for park resources. Deposition monitoring will enable managers to evaluate whether deposition is below or above critical or target loads.

For Appalachian Trail managers, awareness of the problem is the main goal. Remediation is not practical considering the configuration of the trail, but through awareness, education and communication the A.T. will eventually benefit from reduced sulphur and nitrogen emissions. The A.T. Environmental Monitoring Program intends to rely on projects such as the Deposition Effects study (outlined below), the Baseline Water-Quality Inventory as well as data collected by other agencies and programs to assess resource condition.


Last Updated: December 30, 2016 Contact Webmaster