NPS Look Rock remote photo.
Understanding how pollution comes in from outside the park. The most harmful air pollutants—nitrates and sulfates—cause acid deposition in the form of rain, fog, snow, and dry particles. All of these deposits come from outside the park, carried in on warm air masses that rise and cool to form clouds, rain, and fog over the Smokies’ high peaks.
Acidic water also flushes nutrients and metals out of the soil (see the next section for more details). One metal that washes into streams is aluminum. High levels of aluminum are toxic to fish, so biologists expect to see increased die-offs as this common metal rushes into streams from soil after storms.
Are plants and animals on land affected by acid deposition?
Normal rain is slightly acidic, with a pH of about 6.0, but that’s not enough acid to cause any problems. In fact, scientists are beginning to think that the slight acidity of normal rainwater helps the soil capture the small amounts of acid that normally fall, creating a chemical “sponge” so the soil can hold and buffer low amounts of sulfates.
Adding more sulfate and nitrate to the nutrient system disrupts the balance. Plants can store a certain amount of nitrates (they need them to grow—this is a common ingredient in fertilizer), and soils can store a certain amount of sulfates, but we have already exceeded this necessary amount. Excess acid then washes straight into the stream, taking with it metals and nutrients such as calcium from the soil. This disrupts natural levels of magnesium, potassium, and sodium. Changes in soil chemistry have serious consequences for plants and animals:
How do we measure what’s in our water?
For more detail and photos of water quality monitoring, click to go to the Partner Profile: Taking the pulse of Smoky Mountain streams.