From Alpine to Aquifer: Stoneflies in Strange Places

By Renata Harrison

A meltwater stonefly clings to a rock in a high mountain stream.

NPS/Renata Harrison

I struggle to stay upright. A wave of vertigo hits me as I turn and confront the enormous valley below me. Flat shards of stone clatter under my boots. I try digging a spot to anchor myself on the slope, sending down a trickle of loose rocks. The distance in front of me seems impossibly huge, carving out space in huge bites from above and below. I feel like an insect standing on the jagged tooth of a shark’s open jaws.

Across the expanse of air, a crown of mountaintops rises above slopes dense with conifers. The cars on the road below look like toys. My head swims as I turn away from the vastness to rest on a rocky ledge. Incredibly, with no sign of where it’s coming from, a perfect stream flows out of a hole at the base of the ledge. I plunge my hand into the crystal water and within seconds it’s numb. If I could scan through this mountaintop with X-ray vision, I could see the glacier on the other side. I’m in Glacier National Park, high in the Northern Rocky Mountains—water towers of the continent.

The frigid water emanating mysteriously out of the mountain comes mostly from glaciers and snow fields melting above. Some of it surfaces from “mountain aquifers” underneath the rocks. Water flows down the mountain, joining creeks, flowing into rivers and lakes, ending up in oceans. Some of the water that flows into the nearby Flathead River will seep into the ground and recharge the Nyack aquifer. The aquifer exchanges water with the river, a vital ecological connection. The water’s path from the mountaintop down into the aquifer is like a corridor, or pathway. Following the corridor from top to bottom, water exchanges and interacts with the landscape. This flow and exchange creates a series of habitats populated by organisms adapted to their own specific niches.

One of these adapted organisms is the reason I’m battling gravity on this slope. I came here with Joe Giersch, Aquatic Entomologist for the U.S. Geological Survey. I drop my notebook and scramble for my voice recorder as he launches into a pre-departure presentation on his research. Giersch clearly has practice explaining to people why he does what he does.

Joe Giersch, Aquatic Entomologist for the USGS, searches for rare alpine stoneflies up above the Going-to-the-Sun Road.

NPS/Renata Harrison

Up high on the mountain slope, we look for a rather unassuming insect that spends most of its life crawling on rocks underwater. It’s of the order Plecoptera, commonly known as a stonefly. Most of a stonefly’s life, one to two years, is spent as an immature life stage known as a nymph. They roam around on stones in fresh, running water, scraping nutritious goo off the rocks, shredding leaves to eat, or preying on smaller bugs. When it’s time for adults to emerge, they’ll make their way to the river bank. Once out of the water, they’ll attach to a surface and shed their skin one last time, emerging as winged adults. They’ll exist for about a week as flying adults, long enough to mate before getting gobbled up by fish and birds.

Generally, stoneflies can’t tolerate low-oxygen environments, and they need flowing water with spaces to crawl around in. Because of this, their presence is known to indicate a high-quality, freshwater ecosystem. They’re an integral part of the stream’s food web, cycling the nutrients they consume through the things that consume them. Stoneflies are benchmarks of water quality. They are intimately tethered to the conditions they’ve evolved to live in. And, as I begin to learn on this mountainside, some of them live in very unique conditions.

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Pale stonefly larvae collected from an alluvial aquifer.

NPS/Renata Harrison

Scientists in northwest Montana have been looking at stoneflies in strange places with increasing scrutiny since the 1970s. In 1974, Dr. Jack Stanford, Professor of Ecology, was running the University of Montana’s Biological Station in Polson, Montana when a perturbed engineer showed up at his office. The engineer had built a water supply system to take water from the alluvial aquifer of the Tobacco River to the town of Eureka. “They thought maggots were coming up out of the pipes they’d drilled in the floodplain, and city managers weren’t too happy about it,” Stanford tells me. “But I knew immediately what they were.” These were no maggots. They were pale, long-legged insects with underdeveloped eyes that had been living in total darkness. And they happened to be the missing piece to a puzzle he had been trying to solve.

Up to this point, scientists thought that stream-dwelling macroinvertebrates like stoneflies stayed in the riverbed. “I was doing my dissertation at the time,” says Stanford. “I’d found over 50 species of stoneflies in the mainstem Flathead River, but for seven of them, I could not find their nymphs.” The day that engineer walked through the door, “maggots” in hand, changed everything. In later research, Stanford was able to show that there was an entire community of organisms living at least 4.2 meters below and 50 meters away from the river channel. The discovery of underground stoneflies so far from the river, and evidence that they were eating other bugs down there, was a remarkable find.

This discovery spurred a dramatic change in the understanding of river ecology, namely, the realization that river ecosystems are three-dimensional. To visualize this, think first of following the flow of the river, like you’re floating down it in a raft. Next, think of a river crossing. Picture yourself walking across the riverbank and fording the river. Finally, imagine digging a deep hole in the floodplain next to a river channel. Water starts to well up from underground, spilling over into the river itself. Discovering these stoneflies underground was like unlocking the door to another dimension of the river ecosystem—a dark, cold dimension fostering a surprising amount of life.

Since then, Stanford and other scientists working for the Flathead Biological Station have contributed exciting discoveries to the world of underground stoneflies. Much of this research takes place on the Nyack floodplain. The Nyack is a gravel-bed river floodplain about 7.5 miles long and 1.5 miles wide, located on the southwest boundary of Glacier National Park. It has been studied extensively due to its pristine condition and high biodiversity. To me, it resembles a pastoral setting, with tall grass meadows and a burbling river.

In contrast to my mountain excursion, I’m here to see some extremely different stoneflies. Standing in a field of tall grass where the flat ground is saturated and muddy, Dr. Rachel Malison, a researcher at the Biostation, explains how she pumps stonefly nymphs out of wells drilled into the floodplain. “There are 113 species of benthic (surface-dwelling) macroinvertebrates in Montana rivers, but only about seven in the aquifer. Those seven are not found in the river,” explains Malison. The wells go about 20 feet down into the aquifer. With the help of a gas-powered pump, researchers pump water out of the aquifer, filling their nets with the pale underground nymphs of stoneflies like Paraperla frontalis.

The requested video is no longer available.

“Think of the floodplain as a giant bathtub full of different cobbles and sediments with different pore sizes,” says Malison. “In general, the water is pretty well-oxygenated, but there are some places with really low oxygen.” Surprisingly, researchers at the Biostation have found stoneflies living in these low-oxygen pockets in the aquifer. Malison is conducting laboratory experiments to investigate how different species of the same insects that live in highly-oxygenated river water have adapted to low-oxygen environments underground. Malison and her colleagues also suspect that there are populations of stoneflies that complete their entire life cycle underground. Watching her pick pale nymphs off her nets, I wonder how many more secrets these humble creatures have in store.

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Duration:

2 minutes, 10 seconds

This is a short video showing Aquatic Entomologist Joe Giersch searching for rare alpine stoneflies in Glacier National Park. An Audio Described version of this video is also available.

Back on the mountainside with Joe Giersch, I watch him plunge his hands into the frigid water, flipping over stones. His boots planted solidly in the slippery rocks, he’s clearly at home here. He holds out a fingertip with a small brown blob on it. “This,” he says, “is Lednia tumana, the meltwater stonefly.” I feel like I’m meeting a celebrity—one I need a magnifying lens to see. It looks like a prehistoric underwater grasshopper crossed with a long-legged earwig. It’s unlike anything I’ve seen before, which endears me to it immediately.

In 2009, the U.S. Fish and Wildlife Service enlisted Giersch’s help to document the distribution of this rare alpine stonefly along with Zapada glacier, the western glacier stonefly. Both had been petitioned for protection under the Endangered Species Act due to climate-change induced habitat loss, and Giersch was tasked with investigating where they occur, and what their habitat requirements are. L. tumana and Z. glacier live in alpine streams sourced from glaciers, snow fields, ground springs, and seeps. They thrive in water between 33-45 degrees Fahrenheit. Their food base is composed of moss and algae, rather than leaves. Fish are absent from these streams, but adult stoneflies get gobbled up by spiders, birds, and even some small mammals. Both species have extremely small ranges and have only been found in several sites inside and outside the park. Due to their reliance on water from cold, alpine sources like glaciers and snowfields, these insects end up being excellent indicators of a changing climate.

Although alpine and aquifer stoneflies are specialized to live in extremely different environments, their biggest threats come from the same source—human actions. Alpine streams change temperature drastically as they tumble down the mountain. Air temperatures are warming, precipitation patterns are changing, and snow and ice are melting faster due to climate change. As this happens, cold-adapted species like L. tumana and Z. glacier migrate to where it’s colder. These frigid-water stoneflies, explains Giersch, have worked themselves upwards into genetically isolated sky islands.

Dr. Malison stands in a creek, explaining the importance of the floodplain ecosystem.

NPS/Renata Harrison

Down in the aquifer, temperatures stay stable in the insulated ground. Here, disturbances and development of river floodplains are the biggest threat. Gravel mining and human development on the floodplain severs the link between groundwater and the river. This directly impacts stoneflies and other groundwater organisms. “Healthy river systems worldwide have intact floodplains in three dimensions,” says Stanford. “If you encroach on floodplains, you reduce the resilience of the entire system.”

Peering through my lens at the tiny brown insect on Giersch’s finger, I can’t help but wonder: Why should I care? It’s just a bug. I put the question to him and he quickly lays out a few arguments. Sometimes the story is about industry and human health—we all need to eat food, and producing food requires good water. Clean water comes from healthy, unpolluted sources with intact ecosystems. Stoneflies in mountaintops and floodplains are integral parts of the freshwater pathway. They cycle and exchange nutrients, water, and organisms from the top of the mountain to the floodplains below, where food is grown.

Sometimes the story is about recreation. In the Flathead Valley, people come from all over the world to float and fish in clean rivers and lakes. A big part of the visitor experience is the appeal of being somewhere wild and pristine. I take pride in knowing the water is clean and that aquatic ecosystems are thriving. My friends who fish know that stoneflies are an important food source for trout. Talking to the researchers I’ve met, though, I get a sense that there’s something else going on. There’s another side to the story that isn’t as easily explained.

This is the story of biodiversity. Biodiversity is the variety of all forms of life on Earth—within species, between species, and among ecosystems. And in every parameter, it’s shrinking. Extinction of species is now happening at 1,000 times the natural rate. Human activity and population increase have sped up rates of change in the biosphere, creating a trickle-down effect of species loss throughout ecosystems.

As more species become threatened, endangered, and extinct, scientists sound the alarm about losing biodiversity. There are theories about what will happen as links in food webs disappear. Will other species be able to fill the gaps left behind by those that can’t survive? Or will the results be catastrophic? It’s hard to predict what will happen. Do we have the right to say which species matter and which don’t?

Perhaps the simplest way to explain why extinction at this rate matters is to look at any particular species and ask how it’s connected to its environment. What does it eat? What eats it? Does it provide any benefits to other organisms in that ecosystem? Chances are, as John Muir said, “"When one tugs at a single thing in nature, you find it attached to the rest of the world.“

A tiny, brown meltwater stonefly (Lednia tumana) clings to a fingertip.

NPS/Renata Harrison

Out here in Glacier, surrounded by powerful forces of nature, I sometimes feel like a vulnerable insect. It’s easy to feel small in this land of grizzly bears and ancient rocks; to sense one’s shortcomings in the wilderness. When I first arrived here, I was overwhelmed by this landscape. Learning about stoneflies, a small but important part of this ecosystem, helped connect me to these mountains and floodplains. When I’m in those places now, I think about the stoneflies. I look for them and wonder what they’re doing. Mere knowledge of their existence, and how unique they are, enriches my experience. I might feel small, but I know I am part of something larger. National parks are here in part to protect all things, even if they don’t have an obvious benefit to humans. What will we decide is the value of biodiversity? And will we realize it before it’s too late?