Air Resource Management Program - Monitoring Pollutants Deposited to Ecosystems
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Forest Service managers directly monitor and use models to measure or estimate the amount of acid deposition occurring in the national forests and how this deposition is affecting forest resources. Long-term air quality and resource monitoring in and near the national forests and Class I areas has helped establish air pollution trends and existing conditions of the resources. Based on these existing conditions and documented cause-and-effect relationships, the air resource specialists in the Forest Service are identifying critical loads and resource concern thresholds for evaluating potential impacts of new sources of air pollution for each Class I Area.
The Forest Service conducts deposition monitoring as a participating agency in the National Atmospheric Deposition Program (NADP). Air Program staff are also members of the Critical Loads of Atmospheric Deposition Science Committee, which facilitates coordination of the efforts of multiple federal and state agencies, scientists, and other partners related to the science of critical loads.
Resources:
Critical Loads Assessment by Site (CLAS; tool to query lichen community air scores and critical loads exceedances and view unit level reports on critical loads exceedances for all ecosystem components)
Sulfur and Nitrogen Deposition
Wet deposition of sulfate and nitrate are monitored through the National Trends Network, which provides information on precipitation chemistry. The chemicals and analytes measured include acidity (measured as pH), sulfate, nitrate, ammonium, chloride, and base cations.
Depositional loading refers to the amount of deposition moving from a pollutant source to a water body. By measuring sulfur and nitrogen deposition in precipitation, we can assess the depositional loading of pollutants from the atmosphere to surface vegetation and waterways. These pollutants have acidifying and fertilizing effects. Estimating the pollutant load is critical for effective ecosystem and natural resource management plans.
Aquatic Ecosystems
Assessing the effects of air pollutant deposited to aquatic ecosystems requires understanding the processes that control the chemistry and biology of each lake or stream. Aquatic monitoring often begins with a chemical and biological survey of surface waters to identify sensitive ecosystems.
Water chemistry is generally monitored directly. Many studies combine water quality monitoring with biological monitoring of plankton, aquatic insects, amphibians, and fish.
Resources:
Surface water sample collection
Surface water sample analysis at Forest Service laboratories. Please contact the laboratory directly for the most up-to-date forms, instructions, protocols, and methodologies.
Northern Research Station, Grand Rapids Laboratory
Rocky Mountain Research Station, Fort Collins Biogeochemistry Laboratory
See the lab’s 2024 Quality Assurance Procedure for more information.
Southern Research Station, Coweeta Hydrologic Laboratory
Surface water data access
Monitoring Protocols
Surface water chemistry: USDA Forest Service national protocols for sampling air pollution-sensitive waters.
Precipitation chemistry: National Trends Network (National Atmospheric Deposition Program).
Terrestrial Ecosystems
Monitoring current conditions, tracking changes, and predicting ecosystem responses to changes in climate and air pollution can be expensive and challenging tasks through instrumentation alone. Biological indicators such as lichens can provide an economical and practical means to maximize monitoring resolution, especially in remote areas.
Lichens have a long history of use as air pollution indicators, with records dating back from the mid 1800’s. Epiphytic lichens are lichens found growing off the ground in trees and shrubs that absorb the bulk of their nutrients from the air, lack a waxy cuticle and stomata which, in plants, helps slow the absorption of pollutants, and have no roots (in which elemental transfer can take place). Because of these characteristics, lichens are highly sensitive to changes in habitat structure, climate, and air pollution, especially fertilizing and acidifying nitrogen- and sulfur-containing pollutants.
Lichens also have a long history of use as air pollution indicators, with records dating back from the mid 1800’s. Epiphytic lichens are lichens found growing off the ground in trees and shrubs that absorb the bulk of their nutrients from the air, lack a waxy cuticle and stomata which, in plants, helps slow the absorption of pollutants, and have no roots (in which elemental transfer can take place). Because of these characteristics, lichens are highly sensitive to changes in habitat structure, climate, and air pollution, especially fertilizing and acidifying nitrogen- and sulfur-containing pollutants.
Resources:
Forest Service lichen samples analysis at Northern Research Station, Grand Rapids Laboratory. Please contact the laboratory directly for the most up-to-date forms, instructions, protocols, and methodologies.
Monitoring protocols:
Mercury Deposition
Wet mercury deposition is monitored through the Mercury Deposition Network, part of the National Atmospheric Deposition Program (NADP). Mercury accumulation can be measured directly in any part of the ecosystem. Mercury in fish tissue can be orders of magnitude higher than mercury concentrations found in water and sediments and has been measured for decades in many states. Mercury monitoring is accomplished in each region of the Forest Service as needed using methods appropriate for that area. In some cases, the Forest Service has partnered with state and other federal agencies to determine the rate of mercury deposition and its effects on the ecosystem.
The Mercury Litterfall Network was created as a complement to the Mercury Deposition Network. These measurements provide an estimate of dry deposition to a forested landscape.
Snow Deposition
The United States Geological Survey Snowpack Chemistry Network is a long-term monitoring network that measures chemistry in snowpack and estimates wintertime total deposition, both dry and wet. This network encompasses the northern, central, and southern Rocky Mountains and is a collaboration between U.S. Geological Survey, federal land management agencies, and nonprofit sponsors. Snowpack sites tend to be located at high elevations and are collected once per year in the Spring before the snowpack begins to melt. There are 16 sites in the Greater Yellowstone Area, and most were first sampled in 1993.
Resources
United States Geological Survey