Ancient poop provides clues to Yellowstone's past

Untold numbers of scientists have explored and analyzed the history of Yellowstone National Park's famous geology, flora and fauna. They've written books and papers, given talks and penned newspaper columns. Each account adds a bit more to the park's unique evolution above and below ground.

Now one of the newest sequences of the park's history is unfolding not in an Imax movie of a steaming caldera but in five feet of sediment from the bottom of a lake. And this one is layered like a parfait - but with traces of ancient wildlife poop steroids. 

The top layer, the mud closest to the water, reflects a recent rise in bison use of the area. Then there's the late 1980s when the historic Yellowstone fires ripped through and burned more than half a million acres of trees, willows and sagebrush steppe.

Go 2000 years back and it's a time of relative ecological stability, the mud reflecting few changes in either vegetation or the animals that munched on those plants.

The history as told through a mud layer cake shows not only which large herbivores occupied one portion of Yellowstone in the last couple millennia, but also how vegetation changed with their presence. It was published in late October in the prestigious PLOS One Journal. 

"This one record provides a baseline, at least for this small system. So if park managers are interested in understanding the baseline of large herbivore use, they could now compare modern levels to the long-term average and variability," said John Wendt, the paper's lead author and a post-doctoral fellow at Oklahoma State University. "As in, is what we're doing now outside of some historic range of variability?"

The groundbreaking technique also has the potential to create a more detailed, in-depth picture of landscapes across the West that, combined with historical human accounts from tribal members to trappers, can provide an increasingly accurate picture of what once existed. And at some point, this analysis of ancient poop could help us see what animals and plants lived across the landscape in various climate scenarios, providing more insight into how plants and animals will react as our climate continues to change.

Digging into the past

Analyzing sediment for the steroid remains of animal fecal matter is relatively new but not unfounded. European scientists have been using the technique for years to better understand prehistoric use of livestock, and anthropologists used it to study where early humans may have lived and at what densities.

But Wendt wasn't focused on the livestock that occupied Yellowstone. He was interested in what wildlife lived there throughout history.

Like most science fieldwork, the technique involved both fancy technology and more than a little playing in the mud. Five years ago, Wendt and colleagues drug pack rafts to the edge of Buffalo Ford Lake on the park's northern end and paddled out to the deepest part. 

There they dropped their three-inch-wide core sampler into the mud and drilled down about five feet, pulling up a layer cake of brown, loosely packed ooze. The team then took the samples back to the lab where they began dissecting them. 

And here's where it gets complicated. 

Before collecting the sediment samples, Wendt analyzed steroids found in bison, elk, pronghorn, mule deer and moose dung. Once he could isolate the unique steroid compounds in each, he took the sediment samples with 1000-year-old poop remains to a lab in Venice, Italy for analysis. There, he isolated steroids in the sediment and compared them to the known examples. 

The fecal samples likely came from when animals congregated on the lake's frozen surface in the winter as well as when they did their business around the edges and rain and snowmelt washed the feces into the lake where it settled on the bottom. 

"Because Yellowstone has such a well-documented history, we were able to compare the management practices and some of what is known about where animals were distributed at different points over the past 150 years to our observations," he said. "That gave us a lot more confidence in interpreting the record further down."

The stories poop can tell

For Rick Wallen, a former bison manager at Yellowstone National Park who was not involved in this study, the result proved that species like bison and elk did, in fact, roam across much of the park long before European settlers largely wiped the species out. 

But some people argue that Yellowstone now houses unnaturally high numbers of bison and elk and claim that while the species may have wandered through the park, they likely didn't occupy the area in large quantities.

"Everyone acknowledges there were a lot more animals in the lower country and as the colonization of the West occurred, they retreated back up into wherever they could get away from development and conflicts," Wallen said. "But bottom line, this shows bison and elk had been in that area of the high country for at least 2300 years."

Cathy Whitlock agrees. The Montana State University earth sciences professor is a co-author on the paper and has spent the past 40 years studying millennia of ecosystem changes in Yellowstone. Researchers like Whitlock have long looked at the park and wondered how more recent populations of animals like bison and elk have compared to historical levels. 

"Our lake studies are not like finding a bone in a cave," she said. "Sure, you can get a radiocarbon date and show how old the bone is, but that doesn't indicate sustained presence, it's a one off."

Wendt's test has the ability to show presence and prove where animals historically roamed. Essentially, this technique may be able to set the record straight.

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