Posted on October 25, 2023
“How can we best revive Lake Mitchell, and does it need to be dredged?”
That’s the multimillion-dollar question a panel of lake restoration experts and enthusiasts sought to answer Monday night during a debate held at Dakota Wesleyan University, moderated by professor Joel Allen.
The debate featured a panel of four who have different backgrounds on the subject of lake restoration work. Two panel members stood against the city’s proposed $25 million mechanical dredging project and laid out a cheaper alternative they believe would produce better results, while two dredging advocates made their case for mechanically dredging the lake bottom.
John Tucci, the founder and leader of a Michigan-based company that restores lakes through aeration methods and bio dredging, and Jordan Hanson, a Mitchell native who has conducted independent research on strategies to tackle Lake Mitchell’s algae woes, used a substantial amount of their allotted time seeking to poke holes in the proposed $25 million dredging project city leaders are seeking to pursue.
After reading through the hundreds of documents from city-funded lake studies over the past decade conducted by multiple engineering firms, Hanson said a common conclusion among them state the target phosphorus levels for a healthy Lake Mitchell is 90 parts per billion (ppb) or lower. In July, the lake saw phosphorus levels hovering as high as 900 ppb.
“One thing they mentioned a lot was that 90 parts per billion (ppb) of phosphorus levels was our target. Barr Engineering — who is not here tonight — says once we dredge our lake, at best we will have 560 ppb. That’s nowhere near the 90 ppb we need, so why would we spend $25 million to not reach our target?” Hanson said, noting the proposed dredging plan entails removing a little over 50% of the lake’s sediment.
“How many of you guys want to spend $25 million for an impaired body of water?” he asked the crowd of about 150 people.
Hanson pointed to the city’s past dredging project in the 1980s followed by alum treatments years later as a move that he said worsened Lake Mitchell. And he questioned why a similar strategy he believes caused environmental damage would be used again.
“The number one thing the Environmental Protection Agency (EPA) recommends is aeration. Do you think the EPA would like to see this?” Hanson asked, pointing to an enlarged photo on the monitor showing dead fish and decimated trees on the shorelines.
To produce an effective long-term lake restoration solution, Hanson suggests using a combination of aeration, floating wetlands and restoring the biological ecosystem — a plan he says would cost roughly $11 million. Lake aeration is a method that entails installing underwater aerator systems that provide oxygen and create steady movement aimed at reducing phosphorus concentrations.
In his third trip back to Mitchell, Tucci, who pitched an $11 million aeration and bio dredging project to city leaders a few years ago, opened up by declaring the proposed $25 million mechanical dredging project is “not a good solution” for Lake Mitchell.
Tucci provided an itemized rough cost estimate of the work proposed in the mechanical dredging project, which included $15 million in alum treatments and $14 million in interest on the loan the city is seeking to use for funding the project, and said roughly $13 million of the total project cost would be allocated for sediment removal work.
He claimed there hasn’t been any documented cases of a lake dredging project delivering a 10-year improvement on algae elimination. Tucci believes the proposed dredging plan would benefit engineers and bankers, not the taxpayers and wildlife in and around the lake.
Another concern Tucci echoed about mechanically dredging centered around the environmental impact it could have on the lake and its ecosystem.
“Is it worth a situation where you will have fish kills, frog kills and turtle kills to support the dredge project? We like to think of the lake as a living being and we like to treat everything in it with care,” Tucci said. “If you have a dried lake bed, what will the impact be on human health with winds blowing across the prairie?”
Dredging advocates reject aeration
The pro-dredging panel members were Charles Ikenberry, an engineer with Houston formerly named Fyra Engineering which analyzed the phosphorus sources entering and exiting Lake Mitchell, and Paula Mazzer, a Dakota Wesleyan University biochemistry professor with years of experience serving on the Lake Mitchell advisory committee who has led research projects on the lake.
Mazzer rejected aeration as an effective lake restoration strategy and claimed it would make the lake’s algae blooms worse.
Without removing the phosphorus-rich sediment that’s packed along the lake bottom, Mazzer said the lake’s algae woes would persist under any other restoration strategies that have been on the table.
“Just like putting sugar in my glass of ice tea, if something is dissolving slowly, you can make it dissolve faster by stirring it. We don’t want that. We don’t want more phosphate in the water, as it would make the algae blooms worse,” Mazzer said. “We have about a 10-ton reserve (of phosphorus sediment) down there (on the lake bottom), and that 10 tons can slowly dissolve out and replace whatever you remove. Whether you clean up the watershed, it doesn’t matter if that reserve is able to slowly dissolve out and replace it.”
Among all the methods discussed, Mazzer concluded mechanically dredging the lake — which was recommended to the city by Barr Engineering — would produce the best results. She deemed it the “only remaining scientifically viable option” for correcting the algae issues.
“Slowly draw down the lake water using the structure the city is going to build, scoop out that reserve and let the lake fill back up,” Mazzer said, noting it’s the only way the phosphorus sediment reserve can be eliminated without stirring.
From the perspective of an engineer, Ikenburry suggested a “multi-pronged” approach would be necessary for the city to drastically reduce the phosphorus that’s a key algae contributor.
During his time studying the phosphorus sources contributing to Lake Mitchell’s algae blooms, Ikenburry learned the 350,000-acre Firesteel watershed discharges enough water that it can refill the lake several times during an average precipitation year and more in a wet year. With the volume of water that flows into the lake on an annual basis, Ikenburry said adding anything into the lake such as a bacteria-eating algaecide Tucci’s company uses and alum, the chemical city officials are proposing to use post-dredging, would be flushed out quickly.
“We’ve got to reduce long-term sediment and nutrients entering into the lake from Firesteel Creek. However, we also believe that we have to get at that internal load for a couple reasons,” he said. “The old age of the lake has led to the fact that phosphorus has gotten very rich in that sediment. There is a lot of ferrous-bound and organic phosphorus in that sediment, and those two elements, if they’re subjected to aggressive aeration without that material being removed from the lake first, you really risk doing more harm than good.”
Ikenburry acknowledged the high price tag of the dredging project facing the city, but added doing nothing “also has a cost.”
While the entire panel agreed implementing an in-lake solution is a vital element to tackle the algae issues, Ikenburry emphasized the importance of reducing phosphorus loads and nutrients in the massive Firesteel watershed that drains into Lake Mitchell. He made clear that dredging alone would not “fix all problems overnight.”
“Lake management is an ongoing process that goes on as long as it’s there. It really all comes down to how much traction we can get in Firesteel Creek. Those are always going to be working against us until we can get those down to a more sustainable level,” Ikenburry said.
Audience weighs in
The debate provided audience members an opportunity to ask the panel questions and give brief speeches in support or against the dredging project. As he’s watched Lake Mitchell’s algae issues worsen over the years, Brian Klock is losing patience with the city leaders who haven’t committed to a restoration project. And he isn’t sold on aeration as the path forward for reversing the algae woes.
“Drive through the canal and realize aeration is not effectively working,” Klock said, noting he supports the city’s land purchase in the Firesteel watershed for future wetlands.
Klock backed dredging the lake and referenced nearby Lake Hanson as a body of water that was dredged in recent years and produced successful results. While Lake Hanson is much smaller than Lake Mitchell and had a much cheaper price tag to dredge, Klock said it resulted in a “clean lake” that now draws Mitchell residents. Considering the lake has reached what some city officials and experts say is the end of its life cycle, Klock said the time to invest in enhancing the 693-acre body of water is now.
“I’ve heard out forefathers who designed this lake designed it for 80 years. Well we made it 20 years past that, and yet we’re not willing to invest this money?” Klock said. “People use to talk about Lake Mitchell. Now my friends have cabins in Lake Madison and Okoboji.”
A self proclaimed “pro-Mitchell” advocate, Rich Darrington stood in support for dredging the lake and viewed aeration as a post-dredging algae management method. Darrington suggested the city dredge more sediment than what’s proposed in the design.