Dark Waters Stem from Organic Carbons

Many lakes and rivers in northern Europe and North America are darker than they used to be but not because of pollution. Data taken from more than 500 lakes and streams show rising levels of dissolved organic carbons was darkening the waters.

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Elsewhere on the globe, many of the lakes and rivers in Northern Europe and North America are darker than they used to be. It turns out it's not because of pollution. A new study says the darker waters actually prove that the lands near these lakes and rivers are healthier than they've been in decades.

NPR's John Nielsen has more.

JOHN NIELSEN: The lakes in New York's Adirondack Mountains are twice as dark as they were 20 years ago. The once light amber lochs found in the Scottish highlands now look more like dark Guinness Stout. For many years, these kinds of changes were dismissed as strictly local, according to water quality expert Jon Stoddard of the Environmental Protection Agency. But then, five years ago, the subject of darkening waters started coming up at scientific meetings.

Dr. JOHN STODDARD (Water Quality Expert, Environmental Protection Agency): And somebody would stand up and say, well, you know, I noticed the site that I monitor, but I thought it was just me. I didn't know it was happening everywhere. And sort of the consensus began to grow that this was not a - just one place that was doing this, but, in fact, it was going on almost everywhere where we have good monitoring data, which is largely Canada or the U.S. and almost all of Europe.

NIELSEN: Stoddard says data taken from more than 500 lakes and streams showed what was darkening the waters: rising levels of dissolved organic carbons, produced by things like decomposing leaves and bugs. Apparently, these organic materials were breaking down and then clouding up all of the northern lakes and streams. The question was why.

Researcher Donald Monteith of the Environmental Change Research Centre in London says a lot theories have been offered. And for a time, the most compelling one hypothesized a link to global climate change.

Mr. DONALD MONTEITH (Researcher, Environmental Change Research Centre, London): The idea was that as the climate warmed, the rate of decomposition of organic matter in soils would increase. And so this would potentially release a larger amount of carbon into our (unintelligible).

NIELSEN: But in the current issue of the journal Nature, Monteith and Stoddard say they found a very different answer after combing through the records kept at all those lakes and rivers. They say this change is due to a successful effort to control acid rain.

Twenty years ago, high levels of acid in the soil helped preserve dead leaves and organic matter, they say. Now, according to Stoddard, the acid is disappearing, and the dead things are decomposing more quickly.

Dr. STODDARD: And so they're ending up being washed out of soils and into lakes and streams and making those places more colored.

NIELSEN: Stoddard says he has no idea how much darker these northern streams and lakes will get, or how much longer this trend will last. But he's not too worried about it.

Dr. STODDARD: And, in fact, rather than being bad news - because it's being driven by an increase in temperature or Co2 - it's probably good news. It's a return to a more pre-industrial, natural condition.

NIELSEN: There is one group that does have reason to worry about these changes. That's the drinking water companies that may have to pay extra to make the colored water clear again.

John Nielsen, NPR News, Washington.

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