Scientists studying the signature sounds of rivers

Imagine plunging under the surface of the North Fork of the Flathead River and floating for miles. What you would see would be very different from what was above the surface.

What you would hear would be very different as well. Rivers, it turns out, have unique underwater soundscapes as much as they do landscapes.

The sounds a river makes could also steer fish movements and impact the behavior of aquatic invertebrates, according to Mark Lorang, an associate research professor at the Flathead Lake Biological Station.

Over the past few years, Lorang has been studying the soundscapes of rivers with researchers Diego Tonolla, Kurt Huetschi and Kelement Tockner.

The work first began in a laboratory flume in Switzerland, comparing the sounds water made as it flowed over different substrates like gravel or boulders.

Through that work, the team refined their sound-recording techniques and tested their theories out on real rivers, including sections of the Middle Fork of the Flathead River, at Nyack, and the North Fork from Big Creek to Blankenship. They compared the Middle and North forks to a channelized river, the Thur, in Switzerland.

The North and Middle forks had far more diverse soundscapes than the Thur, they found. The sounds of a river are also likely directing the movements of fish. For example, Lorang explained, water rushing over some bouldered sections of a river like the Middle Fork can be as loud as a rock concert.

But there are also quiet zones tucked into pools, where fish also happen to have their greatest range of hearing. As Lorang explained, a steelhead that swims into a pool of water from a riffle will often head behind a boulder.

The soundscape behind the boulder is entirely different than the riffle. Fish have ears, and they likely find these safe structures through sound, not sight, Lorang notes.

Soundscapes can also play a greater role in river restoration, Lorang said. He has found the best way to describe a river's riffles, pools and runs is by its soundscape, not by visual and hydrological cues. Plotted on a graph, the sound signature of a riffle actually looks like a riffle, and a rapid looks like a rapid.

In future river restoration projects, structural designs could be made to mimic the soundscapes of healthy river systems, he suggested.

The group's research work also has artistic implications, Lorang said. He's been contacted by a composer who would like to assemble a piece of music based on Lorang's river recordings.