Healthy air, healthy soil, healthy forests

Dispatches from the Field > Healthy air, healthy soil, healthy forests

Megan on the way to check lysimeters in winter.

To collect soil water, Megan treks to each site twice. She first “primes” the lysimeter by setting up a vacuum to draw moisture; in the second visit she drains the water-filled tubes. Megan freezes the samples for later testing.

NPS photo.

Many people know that air pollution—from coal-burning factories and gasoline-burning cars—causes acid rain, snow, and fog in the mountains. But what happens to that acidic water after it falls to the ground? How does it impact life on the mountains? Researchers from the University of Missouri and the National Park Service are studying air pollution from the ground level: how acidic water in the soil affects high elevation forests.

To do this, they test water that percolates through the soil. In this “soil water” are dissolved minerals and chemicals from the soil. Each month, technician Megan Cooke treks to 30 different test sites up mountains and along ridges, traversing dozens of miles each time. Her goal is to reach lysimeters—instruments that extract soil water—at high elevations. Lysimeters themselves are made of a ceramic cylinder the size of a water bottle buried in the ground, with a stopper in the top and flexible plastic tubing leading out. Around each is a large study plot, an area in which researchers recorded plant types and exposure to the sun, and took soil samples. The plots are in a habitat subjected to some of the highest levels of acidic deposition: the spruce-fir forest, which tops our mountains above 4000 feet.

Researchers draw water held in the soil through these lysimeters.

The lysimeter includes a buried ceramic cup and plastic tubes to draw water from the soil.

NPS photo.

What’s in the water?

The Missouri researchers are measuring a ratio of two very specific elements in the soil water: calcium and aluminum. When acid rain, snow, or dry particles fall, the acids break the chemical bonds that hold both aluminum and calcium in the soil.

Although these elements have opposite effects—calcium helps plants and animals grow, and aluminum can be toxic—flushing both from the soil can be harmful to park ecosystems. When calcium is lost, some species such as dogwoods, snails, and birds that feed on snails don’t have the mineral they need to grow or build shells. When aluminum is released, it changes from a harmless form held in soil to a highly toxic metal that stunts plants’ growth and upsets fish electrolyte levels in nearby streams.

High elevation habitat in the Smokies.

Healthy soils and forests need clean air.

NPS photo.

Soil what?

Scientific results from this ongoing study will help the park understand what air pollution—such as sulfates and nitrates that come from burning coal and gasoline—does to soil, and therefore plants and animals, in the ecosystems the park protects.

Next time you’re outside, bend down and take a close look at the soil beneath your feet. You may see many colors and textures: grains of sand, tiny flakes of shiny metal, and fragile root filaments. But remember that it’s what you can’t see—chemicals bound together in that handful—that can tell the story of our mountains’ health.

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