How healthy is the water?

A hidden salamader enjoys neutral water.

Most salamanders, such as the one hiding on this streambank, can't tolerate acidic water.

NPS photo.

Over many years, researchers at the University of Tennessee noticed that the water is becoming more acidic, especially at high elevations above 4000 feet. Even though our water looks clear and pristine, lab analysis reveals that it is contaminated with acidic sulfates and nitrates from air pollution.

Why does acidification matter? If you are a fish or insect larva, you prefer water that is neither acidic (like sour vinegar) nor basic (like smooth milk). You like neutral water with a pH around 7.0. Pure rainwater without any buffering minerals is slightly acidic—pH 5.6 or so—but minerals from rocks and soil capture this acidity and buffer it, so streams stay near-neutral. When rainwater is not just slightly acidic, but very—pH of 4.0 or even less—rocks and soil cannot buffer all of the acid. Much of it runs into streams, making them acidic as well. When stream water drops to pH 6.0—that’s 10 times more acidic than neutral 7.0 water—acid-sensitive fish and other creatures cannot survive. As the pH drops further, to 3.0-4.0 (as acidic as that sour vinegar), aquatic life cannot survive.

University of Tennessee-Knoxville doctoral students Keil Neff and Mei Cai are busy studying trends in water quality. Find out what questions they're asking and what they've found.

Fewer streams will have a healthy pH above 6.0 in the future.

If acid pollution continues, the percent of Smokies streams that are good habitat (pH of 6.0 or above) will drop in the next 50 years.

NPS graphic.

What’s the future for aquatic plants and animals?
We’ve already seen brook trout disappear from streams where they were common just 15 years ago as the pH drops below 6.0 and flushes more toxic aluminum into the water. With continued drops in pH, scientists think that brook trout may be gone from the Park entirely in 25-50 years. By 2070 all of the Park’s streams could have a pH less than 4.0, a level that is unlivable for most aquatic animals here today.

But it's not all doom and gloom. There is hope to alter these trends by reducing air pollution so the predictions never come true. Through a combination of individual, community, and legal actions, we can change the way we live and, by doing so, improve water quality. The most recent check-up, from the 2008 Annual Water Quality Report, says that we can even be cautiously optimistic about at least some of the results:

  • pH range across 43 sample sites in Park = 4.8-7.4
  • Average pH = 6.3 (up from 17-yr average)
  • Average pH of rain = 5.64 (up from 17-yr average)
  • Average pH of throughfall (rain through trees) = 4.7 (up from 4.2, the 17-yr average)
  • Trends in sulfate & nitrate deposition = less acid is falling, due to long-term drought (less acid precipitation) and/or emissions reductions from power plant scrubbers

We hope to continue seeing good news for Park streams. Find out more on page 3: reversing trends through research and action.

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