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Aquatic Ecosystems


A person collecting water samples from a lake

An example of a person collecting water samples from a lake. Photo courtesy of Sharon Grant.

Assessing the effects of air pollutant emissions on aquatic ecosystems requires an understanding of 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 particularly sensitive ecosystems.

Acidic inputs from the atmosphere-mainly sulfur and nitrogen compounds- can negatively impact aquatic and terrestrial ecosystems. Their acidifying effects contribute to degradation of stream and lake water quality by lowering the acid neutralizing capacity (ANC) which represents the water's natural acid buffering system. As the ANC decreases, the pH decreases as the acid levels in the water increase. In some areas of the central and southern Appalachians, forest streams have acidified to the point where they are no longer capable of sustaining aquatic life such as fish or amphibians.

Ecosystem Sensitivity to Pollution

The sensitivity of lakes and streams to acidic deposition are often linked to natural watershed characteristics, most notably the type of bedrock geology. Watersheds containing naturally occurring bedrock that weathers (breaks down) easily and that are made up of minerals containing high levels of base cations like calcium (nutrients that plants need) are more resilient to the impacts of acidic deposition. Likewise, watersheds where the soils are derived from bedrock that is resistant to weathering (e.g. granite) or that contain thin shallow soils are very vulnerable to acidic deposition. Such areas may exhibit lake and stream water chemistry changes that can affect the health of native aquatic organisms sensitive to the acidification of their environment. Acid deposition may also affect soil chemistry in sensitive watershed resulting in nutrient leaching. Nutrient leaching can eventually lead to deficiencies in nutrients that are important for plant growth.

Monitoring Water Chemistry

Water chemistry is generally monitored directly as it will show changes more quickly than plant and animal communities. Many studies combine the monitoring of water quality with biological monitoring of plankton, aquatic insects, amphibians, and fish.

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