Stoneflies in strange places: Glacier’s alpine streams and the Nyack aquifer

In 1974 an engineer walked into a Montana biologist's office with a complaint: "maggots," he said, were coming out of the pipes of a new water supply built into the floodplain aquifer of the Tobacco River for the town of Eureka. The biologist, Jack Stanford, recognized them at once. They were pale, long-legged insects with underdeveloped eyes, stoneflies that had lived all their lives in total darkness. This National Park Service feature by Renata Harrison follows those underground stoneflies and their alpine cousins in and around Glacier National Park.

Stoneflies at a glance

Stoneflies belong to the order Plecoptera. Most of a stonefly's one to two years of life is spent as a nymph, crawling on stones in fresh running water, scraping nutritious film off rocks, shredding leaves or preying on smaller bugs. To become adults, the nymphs climb out at the river bank and shed their skin one last time. The winged adults live about a week, long enough to mate before fish and birds eat them.

Stoneflies generally cannot tolerate low-oxygen water and need flowing water with spaces to crawl in, so finding them signals a high-quality freshwater ecosystem. They are also a link in the stream's food web.

A meltwater stonefly clings to a rock in a high mountain stream. NPS/Renata Harrison.

Stoneflies underground

Before the 1970s, scientists thought stream insects such as stoneflies stayed in the riverbed. Stanford had found more than 50 stonefly species in the main stem of the Flathead River, but could not find the nymphs of seven of them. The aquifer stoneflies were the missing piece. His later research showed a whole community of organisms living at least 4.2 meters below the surface and 50 meters from the river channel, with evidence that the stoneflies were eating other insects down there.

The discovery changed how river ecology is understood: a river ecosystem is three-dimensional, with water flowing along the channel, across it and up from deep in the floodplain. The stoneflies opened the door to a dark, cold dimension of the river that supports a surprising amount of life.

Pale stonefly larvae collected from an alluvial aquifer. NPS/Renata Harrison.

Much of this research takes place on the Nyack floodplain on the southwest boundary of Glacier National Park, a gravel-bed river floodplain about 7.5 miles long and 1.5 miles wide, studied extensively for its pristine condition and high biodiversity. A researcher at the Flathead Biological Station pumps nymphs out of wells drilled about 20 feet into the aquifer. She says Montana rivers hold 113 species of surface-dwelling macroinvertebrates, but the aquifer holds only about seven, and those seven are not found in the river. The floodplain's sediments differ in pore size, and although the water is generally well oxygenated, some pockets have very little oxygen. Stoneflies live even there. She is running laboratory experiments on how species whose relatives live in oxygen-rich river water have adapted underground, and she and her colleagues suspect that some populations complete their whole life cycle in the aquifer.

Stoneflies on the mountain

High in the park, a USGS aquatic entomologist searches for Lednia tumana, the meltwater stonefly. In 2009 the U.S. Fish and Wildlife Service asked him to document where this rare alpine stonefly and Zapada glacier, the western glacier stonefly, occur and what habitat they need. Both had been petitioned for protection under the Endangered Species Act because of habitat loss from climate change.

A meltwater stonefly (Lednia tumana) on a fingertip. NPS/Renata Harrison.

The alpine species eat moss and algae rather than leaves. No fish live in their streams, but adult stoneflies are eaten by spiders, birds and some small mammals. Both species have extremely small ranges and have been found at only a few sites inside and outside the park. As the climate warms they move to colder places, and the entomologist describes them as having worked their way upward into genetically isolated "sky islands."

For the aquifer's stoneflies, gravel mining and development on the floodplain sever the link between groundwater and the river. Stanford is quoted as saying that healthy river systems worldwide have intact floodplains in three dimensions, and encroaching on them reduces the resilience of the whole system.

Why a bug matters

The scientist's answers, as the article tells them, run from clean water for growing food, to the appeal of clean rivers for floating and fishing in the Flathead Valley, where stoneflies are an important food for trout, to biodiversity itself. The article says species are now going extinct at 1,000 times the natural rate, and asks what will happen as links in food webs disappear. Its suggestion: look at any one species and ask what it eats, what eats it and what it gives other organisms.

Sources

• National Park Service, Glacier National Park, “From Alpine to Aquifer: Stoneflies in Strange Places” by Renata Harrison (https://www.nps.gov/articles/alpine-to-aquifer.htm); rewritten in hubnx's own words.