Something peculiar is happening to rivers and streams in large parts of the United States — the water's chemistry is changing. Scientists have found dozens of waterways that are becoming more alkaline. Alkaline is the opposite of acidic — think baking soda or Rolaids.
Research published in the current issue of Environmental Science and Technology shows this trend to be surprisingly widespread, with possibly harmful consequences.
What's especially odd about the finding is its cause: It seems that acid rain actually has been causing waterways to grow more alkaline.
The story started back in 1963 in a New Hampshire forest. A young scientist named Gene Likens found a stream there that was as acidic as tomato juice.
Likens eventually found the culprit: acid rain. Industrial air pollution was acidifying water that rained down from the sky, killing trees and the ecosystems of streams in the East.
Now — 50 years later — there's less acid rain. But rivers aren't neutral, they're alkaline, and that seems to be the trend in lots of places. "The real shocker to me," Likens says, "was [that] we found it from New Hampshire to Florida, and in rivers and streams that drained agricultural land, forest land and urban land."
Two-thirds of the 97 streams and rivers his team studied in the East have been growing more alkaline — from the mighty Susquehanna to small urban streams, like Gwynns Falls in downtown Baltimore.
I recently visited Gwynns Falls with one of Likens' team members, Sujay Kaushal, a geologist from the University of Maryland. He guided me down to the stream, directly below an overpass of Interstate 95. It's anything but bucolic. Traffic roars overhead, and there's trash in the stream, and plastic bags hanging from the lower limbs of trees along the banks.
This stream is where Kaushal first found signs of rising alkalinity about six years ago, after a local water quality official told him he'd been noticing changes in water chemistry.
"We couldn't explain it," Kaushal says. Initially the scientists thought maybe the concrete and cement of pavement, highway overpasses or other structures were to blame. "One of the key ingredients of concrete is actually limestone," he says, and the mix of water and limestone release bicarbonate — essentially the same stuff that remedies acid indigestion.
But when Kaushal and Likens looked at waterways outside cities — running through forests, for example, or farmland — they found that these rural rivers and streams have been growing more alkaline over the past 25 years, too.
Acid rain is largely behind the phenomenon, the scientists say. It's been eating away chunks of rock, especially limestone rock, and the runoff produces carbonates that flow into rivers. "We're basically dissolving the surface of the Earth," says Kaushal. "It's ending up in our water. It's like rivers on Rolaids. There's a natural antacid in these watersheds."
Now, that's not an immediate health threat, but it has environmental effects. Kaushal invited me to wade into the stream. Mops of stringy green stuff coated the rocks. It was thick and slippery underfoot.
"You can feel that?" he asks. "All that scum, all that slime is algae and bacteria." The alkalinity stimulates the growth of certain types of algae. And too much algae will suck the oxygen out of the water — bad news for whatever else lives there.
Something else is worrisome about alkaline water: If it mixes with sewage, it creates a particularly toxic stew by converting ammonia in the sewage into a more toxic form.
It just so happens, the day I visited Gwynns Falls, there was a sewage leak just upstream that Kaushal was eager to show me. "So ... why don't we walk up along this?" He seemed disappointed when I declined to observe sewage chemistry firsthand. I took his word for it.
Gwynns Falls is a small stream, and it doesn't take a lot to alter its chemistry. But even big rivers that usually can dilute moderate levels of noxious pollutants are growing more alkaline.
"We've changed the chemistry of the Mississippi," says Peter Raymond, an ecologist at Yale University. "These aren't small systems."
Some of the growing alkalinity of the Mississippi and its tributaries comes from farmers putting lime on fields to counteract the acidity produced by fertilizers, Raymond says. Acid rain likely contributes, too.
He says it's not clear what kind of damage all this is doing, though a number of freshwater organisms are likely to be affected. "Some will be winners, and some will be losers," Raymond says.
If there's any good news here, it's this: There's less acid rain falling now. Still, it's enough, says Gene Likens, to keep eating away the rock. Likens, now at the Cary Institute of Ecosystem Studies in Millbrook, N.Y., says he never dreamed acid rain would have such a long reach. "The impacts are large," he says, "larger than we ever thought 50 years ago they might be."
STEVE INSKEEP, HOST:
Researchers are paying close attention to waterways in some other parts of the country. Freshwater rivers and streams are not so fresh any more. Their chemistry is changing. Scientists have found dozens of waterways along the East Coast that are becoming more alkaline, less acidic.
As NPR's Christopher Joyce reports, new research shows this trend to be surprisingly widespread, with possibly harmful consequences.
CHRISTOPHER JOYCE, BYLINE: Let's go back to 1963 for a minute. In a New Hampshire forest, a young scientist named Gene Likens found a stream that was incredibly acidic like tomato juice. Likens eventually found the culprit: acid rain, industrial air pollution raining down from the sky. It was killing trees and streams in the East. Now 50 years later, there's less acid rain. But Likens and other scientists are finding that many rivers are now becoming the opposite of acidic- they're becoming alkaline, and it seems to be happening all over the place.
GENE LIKENS: The real shocker to me was we found it from New Hampshire to Florida, and rivers and streams that drained agricultural land, forest land, urban land.
JOYCE: Likens and his team has found that two-thirds of the 97 streams and rivers they studied in the East have been growing more alkaline, from the mighty Susquehanna to small urban streams like this one, Gwynns Falls in downtown Baltimore, Maryland.
SUJAY KAUSHAL: So we can climb down in there.
JOYCE: Sujay Kaushal walks down slope to the stream, directly below an overpass of Interstate 95. Kaushal teaches geology at the University of Maryland and works with Likens. This stream is where he first found signs of rising alkalinity.
KAUSHAL: We couldn't explain it. At first we thought it was simply just, there's more concrete and cement and that's causing it. One of key ingredients of concrete is actually limestone.
JOYCE: When rain and limestone come into contact, the runoff can contain a lot of bicarbonate, basically the stuff you take for acid indigestion. Its alkaline. Maybe that was polluting the stream.
But when Kaushal and Likens looked at waterways elsewhere - in forests, in farmland, they found they too have been growing more alkaline for the past 25 years.
And the really surprising thing is it appears acid rain is doing this. It's been eating away at rocks, especially limestone rocks, and that produces bicarbonate that runs down into rivers.
KAUSHAL: We're basically dissolving the surface of the Earth. It's ending up in our water. It's like rivers on Rolaids. There's a natural antacid in these watersheds.
JOYCE: Now, that's not an immediate health threat, but it does have environmental effects. Kaushal invites me to wade into the stream. Mops of stringy green stuff coat the rocks. It's thick and slippery underfoot.
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KAUSHAL: You can feel that?
KAUSHAL: OK, all that scum, all that slime is algae and bacteria. And the alkalinity actually can stimulate growth of certain types of algae.
JOYCE: Too much algae will suck the oxygen out of the water - bad news for whatever lives in it.
Another thing about alkaline water, if it mixes with sewage, it creates a toxic stew. And it just so happens, there's a sewage leak just upstream of us.
KAUSHAL: So why don't we, why don't we walk up along this...
JOYCE: I'm not going to walk in it.
KAUSHAL: OK, you're not? I can't get you to go in there? It can be highly dangerous.
JOYCE: I kinda figured that.
Now, Gwynn's Falls is a small stream, it doesn't take a lot to alter its chemistry. But even big rivers are growing more alkaline.
PETER RAYMOND: We've changed the chemistry of the Mississippi. These aren't small systems.
JOYCE: Ecologist Peter Raymond at Yale University found that the country's biggest river is also growing more alkaline. He says it's not clear what kind of damage all this is doing.
RAYMOND: It can be pretty important, I think, for a lot of different freshwater organisms. But, you know, for some are winners and some will be losers.
JOYCE: If there's any good news here, it's this: there's less acid rain now. But enough, says Gene Likens, to keep eating away the rock. Likens, who's now at the Cary Institute of Ecosystem Studies, says he never dreamed acid rain would have such a long reach.
LIKENS: The impacts are large, they're larger than we ever thought 50 years ago, they might be, I must say.
JOYCE: The research is published in the journal Environmental Science and Technology.
Christopher Joyce, NPR News.
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