As It Happens

Henry David Thoreau's Walden Pond is being spoiled by climate change — and urine

A new study finds that Thoreau's famous Walden Pond is in a state of decline thanks to all humans whose bladders have been relieved while relaxing in its once-clear waters.

Biologist Curt Stager says increased phosphorus in the water may have spurred growth of new plankton

Henry Thoreau's cove in Walden Pond, which has been changed by human activity. (Submitted by Curt Stager)

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After Henry David Thoreau retreated to live on Walden Pond, he wrote: "We can never have enough of nature."

But a study published Thursday in the journal PLOS One  has found that Thoreau's little lake outside Concord, Mass., may have more than enough of us.

The findings suggests that 150 years after Thoreau made the pristine natural landscape there famous, Walden Pond has become murkily human. 

As It Happens host Carol Off spoke to Paul Smith's College biology professor Curt Stager, the lead researcher on the study. Here is part of their conversation.

What are people doing to Walden Pond?

It seems like we may be on the verge of loving it to death, if we're not careful. Thoreau loved it for its clarity and beauty. People love it today for the same reasons, but we're changing the lake.

Since about the 1930s, Walden Pond has not only been a pilgrimage place for people who admired Thoreau, but also a swimming hole, basically, for the Greater Boston area.

Nowadays, the number of people coming to Walden Pond to swim is in the hundreds of thousands over the course of a year.

Some of Stager's students collecting a sample from Walden Pond. (Submitted by Curt Stager)

As you mention, Henry David Thoreau often described it, loved it, for its clarity, the colour of the water, the temperature. It was just a perfect environment. What's it like now?

I went there expecting to be disappointed and, frankly, I was not. It's still beautiful and inspiring.

Most of the crowds are on the far end of the lake, opposite the one that Thoreau was on. But there's a footpath you can follow back to the other end of this little secluded cove, called Thoreau's Cove, and his cabin site is right there in a grove of trees.

I found all kinds of people enjoying Walden in all kinds of ways — from swimming and fishing, to contemplating Thoreau and our place in nature.

The bottom-hugging weeds that help protect the lake. (Submitted by Curt Stager)

But you took a closer look, didn't you? You took some samples from the bottom. What did you find?

The layers of sediment accumulate, year by year, like pages in a book. Anything that lived in the lake is likely to leave some remains behind.

What my students and colleagues and I were looking at is the remains of the plankton, which determines how clear the water is.

We noticed that starting around the 1930s, a new kind of plankton developed that Thoreau would not have recognized. Basically, meaning that the water is not quite as clear as it was 150 years ago.

Stone pillars delineate the actual site of Henry David Throeau's cabin on the shores of Walden Pond. (Michael Dwyer/Associated Press)

And what contributions are the bathers, the swimmers, making to that?

That was a shocking discovery done by other scientists several years ago. It was U.S. Geological Survey and others. They measured the amount of phosphorus, which is a sort of fertilizer that lets the plankton grow that normally comes from soils and the ecosystem itself.

They found more of it in the water than you would otherwise expect. So they looked at the most likely source and it included erosion of shoreline from the trail and development of the shore.

But they also noticed hundreds of thousands of bathers and, being realistic, they realized that some people urinate while they are swimming.


I don't know how they got this percentage but they estimated how many people of those hundreds of thousands release their waste while they are swimming in Walden Pond and came up with a figure that suggests that as much as half the phosphorus budget of the entire lake now comes from swimmers.

Oh dear, so people are peeing in the lake — and I'm sure that Mr. Thoreau peed in the lake too.

[Laughs] But there was only one of him!

Exactly, so he's made his contribution. But the lake could have coped with that. There have been swim warnings on the lake in recent years haven't there?

Yes, and other lakes in the area have fared even worse. There was sort of a twin lake nearby called White Pond that Thoreau actually said he thought was even more beautiful than Walden Pond. They had some serious algae blooms just a few years ago.

Reclusive essayist, poet and naturalist, Henry David Thoreau. (Hulton Archive/Getty Images)

So the combination of a lot of recreation there, plus climate change — that's kind of a perfect storm unfortunately for the pond?

Exactly. I found it ironic as I've read more Thoreau because of this study. I found out that he and his contemporaries tended to see us as something maybe a little separate from nature.

But it's clear now, in that last century and a half, this kind of science shows that we've become a force of nature ourselves and are not only changing ponds and lakes wholesale, but the atmosphere itself.

It doesn't sound very transcendental does it?

No, it doesn't.

But the flipside of this, at first it may seem kind of depressing, but it really shows what power we have as a force of nature.

These kinds of changes happened unintentionally. And now, with studies like this, we can see what our impacts are and we can try to head them off before they get worse and that's one of the goals of this study.

Written by John McGill. Interview produced by Kevin Robertson. This Q&A was edited for length and clarity. 


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