Researchers in Duluth turn streams purple to help measure effectiveness of restoration

Two people spread dye
Valerie Brady and Brad Evraets with the University of Minnesota Duluth watch as a purple dye spreads slowly down Mission Creek in western Duluth on Monday.
Dan Kraker | MPR News

It was an odd sight earlier this week along Mission Creek in far western Duluth. University of Minnesota Duluth researchers dumped two 5-gallon buckets of deep purple-colored water into the crystal clear stream.

Spectral shapes floated downstream as the dye slowly spread. The periwinkle water cascaded over rocks and swirled in pools.

“It's really cool watching those tendrils when it first starts,” said Brad Evraets, a graduate student in the water resources sciences program at UMD.

To be clear, the dye, called Resazurin, is non-toxic. And Evraets said they notified people who lived near the stream not to panic if they saw it suddenly change color. That’s something scientists failed to do in the Washington, D.C. area recently when they conducted a similar experiment.

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“And all of a sudden the cops showed up, and people were wondering, why is the creek all red!” he said.

A purple dye in a stream 5
A nontoxic purple dye is carried downstream in Mission Creek in western Duluth on Monday.
Dan Kraker | MPR News

The researchers on this trout stream about 12 miles southwest of downtown Duluth are using the dye to figure out how well the stream is connected to the groundwater beneath it. That connection is important to maintain cold water fish habitat.

It’s part of a much broader project to evaluate the effectiveness of stream restoration projects around the region.

In recent years Minnesota has spent millions of dollars to restore creeks and rivers that have been heavily damaged and eroded by major rain and flood events.

“So I think it's really important that we figure out if they're holding up,” said Valerie Brady, an aquatic ecologist with the Natural Resources Research Institute at UMD. “And is there any way to improve them as we're doing more and more of these?

A woman shows bugs she has found
Valerie Brady, an aquatic ecologist with the Natural Resources Research Institute at the University of Minnesota Duluth, shows tiny bugs she found in Mission Creek in western Duluth on Monday.
Dan Kraker | MPR News

Mission Creek is one of 16 designated trout streams in Duluth. They cascade down the steep hillside into the St. Louis River and Lake Superior. But many of those streams suffered major erosion and other damage from massive flooding in 2012.

Since then, the Minnesota Department of Natural Resources and other agencies have spent millions of dollars to try to restore those streams. Mission Creek's restoration was completed about five years ago.

“And they took it from a fairly straight channel, and they ‘re-meandered’ it, made it all curvy again, with nice riffles and runs and pools, to make it better fish habitat,” Brady said about the restoration.

Workers placed big rocks to help armor the stream banks. They planted trees to prevent erosion. Similar work has been completed on many other streams and rivers.

But beyond fish counts, and rough estimates of how much habitat was created, there hasn't been much research done to assess just how well the stream restorations are working, said Karen Gran, an environmental sciences professor at UMD.

“So some people would call it the ‘Field of Dreams’ approach, right? If you build it, everything will come. We're interested in trying to take a deeper dive and look into that more. If we are putting money into a stream, and changing the stream, we want to make sure that we're actually improving it.”

So Gran, Brady and other scientists received a $319,000 grant from the state’s Environment and Natural Resources Trust Fund to evaluate six recently restored Duluth area streams, to assess how well the stream restorations are working, and if anything can be done to improve them as more of them are done.

Two people mix dye
University of Minnesota graduate student Brad Evraets mixes nontoxic dye with Valerie Brady, aquatic ecologist with the Natural Resources Research Institute at UMD at Mission Creek in western Duluth on Monday.
Dan Kraker | MPR News

Broader look, deeper questions

The goal is to take a broader, ecosystem-level look at the functioning of the streams, to ask deeper questions about their restorations.

For example, “How much fish habitat is there?” said Brady. “How much habitat is there for bugs and how many bugs are there to feed the fish? How's it doing on basic water chemistry aspects?”

Then they will compare that with data they collect from similar but undamaged sections of streams. The study will also analyze different restoration designs, and look at how well different projects have held up in the face of large storm events.

Gran said a major restoration project on the East Branch of the Beaver River along the North Shore of Lake Superior was completely wiped out last year by major flooding during spring snowmelt.

She said part of the challenge is that there is a time of weakness in a stream channel shortly after restoration projects are done, when the vegetation hasn't had a chance to grow and stabilize the soil.

“So we're interested in documenting that and trying to understand how much erosion is increasing in the streams,” said Gran.

A purple dye in a stream 4
A nontoxic purple dye is carried downstream in Mission Creek in western Duluth on Monday.
Dan Kraker | MPR News

The use of non-toxic dye to measure a stream’s connection with groundwater was pioneered in sandy waterways in the American southwest, Brady said. To her knowledge, this is the first time it’s been used in rocky streams in the Midwest.

“To see it just turn the water purple, bank to bank, is great,” she said as she watched the dye slowly spread. “This is the fun part of science.”

The dye in the stream turns red when it mixes with cooler water seeping in from springs just below the surface. But she didn’t expect to be able to see it with her naked eye.

Researchers collected water samples to take back to the lab, where they will document changes in color with an instrument called a spectrophotometer.

“The more that the dye changes color, that will tell us how much more interaction there is,” she said.

That interaction with the groundwater is especially important for trout habitat, because that provides infusions of cold water to the streams, which trout need to survive.

“Anything that we can do to help streams stay connected to that cool groundwater is really going to help the trout in this area and help maintain these as trout streams. If they get too warm, the trout just can't handle it anymore,” said Brady.

A creek with water and rocks
Mission Creek, pictured here on Monday, is a designated trout stream that was damaged by major flooding in 2012. Crews restored the stream in 2018 to return it to more of its natural state.
Dan Kraker | MPR News

Conservation specialist Tim Beaster expects to learn some important lessons from the research. He works for South St. Louis Soil and Water Conservation District, which together with the city of Duluth and the DNR, implemented the Miller Creek restoration and several others in the area.

“Because we're not going to stop doing stream restoration. There’s a lot of need out there. We have a lot of degraded streams, which I think we have a more moral imperative to fix,” he said.

Many streams have been disconnected from their historic floodplains by roads, homes and other development. So instead of water gradually seeping into streams, it now often washes into stream beds in violent torrents.

Stream restoration is a fairly new and evolving field, Beaster said. The work is challenging and complex. They have to provide for a wide range in flow levels, create a wide variety of habitats and revegetate the stream banks.

That all has to be done in a 10 week window, because of restrictions on when work can be done on trout streams. They strive to make the restored streams look as natural and aesthetically pleasing as possible.

“So it's almost like we're performing surgery on a loved one. And so we want to take the best care as possible when we're restoring them,” he said.