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Restoring impaired lakes through adaptive management

October 10, 2024
Restoring impaired lakes through adaptive management When applied to water, aluminum sulfate is visible as a white cloudy trail. As it settles, it removes phosphorus that would otherwise be used for algae growth. Photo credit: Jane McDonald-Black and the Bassett Creek Watershed Management Commission.

Removing a lake from a state impaired waters list is a challenging endeavor that can take many years. But the story of Sweeney Lake shows that by taking an adaptive management approach, conducting regular monitoring, and making purposeful partnerships, restoring impaired lakes is possible. Here, we get an insider’s perspective from Barr’s Greg Wilson, senior water resources engineer, on how watershed districts and municipalities can successfully achieve long-term water quality improvement.

A pivotal moment

On a spring afternoon in 2018, senior water resources engineer Greg Wilson stood at the edge of Schaper Pond in Golden Valley, Minnesota. He noticed something he had previously only suspected. The water surface was steadily rippled by dorsal fins—the fins of invasive carp. He snapped a few photos then proceeded to his meeting with the Bassett Creek Watershed Management Commission.

Since 2002, less than 10% of nearly 700 nutrient-impaired lakes have been delisted.

Greg had been helping the commission understand and address elevated phosphorus in neighboring Sweeney Lake, which had caused chronic algal blooms and poor water quality for decades. Previous studies attributed part of the problem to external sources of phosphorus: organic matter, fertilizer, and sediment in stormwater runoff that entered Schaper Pond before drifting into the lake through a pipe that connected them. The commission’s previous attempts to control those sources, however, did not perform as expected.

The flailing fins alerted Greg to the possibility that sources of phosphorus could be internal rather than external. But to know for sure, and to justify expenditures to address what was so far only a hunch, Greg and the commission would need to collect more data and adapt their efforts accordingly. It would take time, patience, and persistence to finally get the lake’s phosphorus levels under control.

Greg didn’t know it at the time, but his visit to Schaper Pond marked a pivotal moment in a success story of adaptive lake management—one that would lead to the removal of Sweeney Lake from the Minnesota Pollution Control Agency’s impaired waters list in November 2023. This is a significant achievement. Since 2002, less than 10% of nearly 700 nutrient-impaired lakes have been delisted.
 

Aerial view of Schaper Pond and Sweeney Lake
Schaper Pond collects stormwater runoff from nearby roads and neighborhoods before draining north into Sweeney Lake through a pipe.

A new approach

Adaptive management is an approach to pollution control that recognizes multiple pollutant sources. Rather than addressing individual sources based on minimal information, adaptive management applies a strategy that leverages consistent water quality monitoring and committed local partnerships to address multiple sources simultaneously. It is an informed approach focused on the long term and flexible in its ability to adjust pollution control efforts based on the outcomes of previous efforts, predicted or not. This was the approach Greg recommended to the commission.

Taking a step back to investigate the significance of internal sources and, if necessary, adapt to address them, Greg and the commission spent the next two years assessing the influences of invasive carp and another likely internal source: the phosphorus-laden sediment that had been gathering at the bottom of Sweeney Lake for decades, releasing phosphorus into the water during certain times of the year.
 

Graphic depicting the long path of targeted efforts to control phosphorus in Sweeney Lake.

The Total Maximum Daily Load (TMDL) study for Sweeney Lake, which established its water quality standards, was completed in 2011. Since then, the commission has embarked on a long path of targeted efforts to control phosphorus in Sweeney Lake.

Assessing the impact of invasive carp

Greg teamed with Carp Solutions, LLC, who tagged and tracked the movement of carp between the lake and Schaper Pond. The results were astonishing. Not only did the pond and the lake contain five to ten times the amount of carp biomass that would normally cause lake water quality problems, but the invasive carp were also using Schaper Pond as a nursery. The decomposition of carp fecal matter and disturbance of bottom sediment by carp were certainly a significant internal source of phosphorus. With this information, the commission implemented multiple carp removal campaigns and stocked the lake with natural predators to reduce carp biomass to roughly a tenth of its original amount.
 

Photo of carp being captured and removed from Schaper Pond and Sweeney Lake.
Carp Solutions, LLC, used baited box nets to capture and remove over 600 carp from Schaper Pond and Sweeney Lake. Photo credit: Carp Solutions, LLC.

Managing phosphorus levels

Simultaneously, Greg launched a series of aluminum sulfate injections—commonly referred to as alum treatment—into Sweeney Lake, which was recommended from a previous feasibility study. When injected directly by boat, aluminum sulfate binds permanently to phosphorus in the water and sediment to prevent it from being consumed by algae, which can trigger harmful algal blooms. Over time, this would lower the amount of phosphorus bound in lake sediment that was susceptible to release and consumption.

The result?

The results of both efforts were monitored closely with data collection by Greg, the commission, and volunteers—local residents who supplemented the commission’s monitoring program and proved to be a critical addition. The results showed that this iterative, two-pronged strategy of carp removal and alum treatment was working.

Sweeney Lake is now cleaner and more accessible for recreation than it has been since the 1970s.

External sources were not to be neglected. During this time, the commission engaged in committed partnerships with the City of Golden Valley, which maintains multiple stormwater ponds that feed into Sweeney Lake. These partnerships were critical in pooling funding for these efforts and for implementing targeted practices that would continue to limit external sources within the Sweeney Lake watershed.

After several years of alternating carp harvesting and alum treatments, followed by routine monitoring, Greg and the commission had assembled the body of data necessary to demonstrate to the Minnesota Pollution Control Agency that Sweeney Lake was no longer considered nutrient (phosphorus)-impaired by state standards. In November of 2023, Sweeney Lake was removed from the Minnesota Pollution Control Agency’s impaired waters list. The lake is now cleaner and more accessible for recreation than it has been since the 1970s.
 

Graphic depicting levels of total phosphorus in Sweeney Lake from 1972 to 2022.

Recent implementation of water quality improvements has resulted in a significant improving trend in total phosphorus concentrations as compared to state standards and the history of lake water quality impairment.

The lesson?

Greg’s lesson for lake managers? Delisting an impaired lake is not common, but it’s also not impossible. The path to delisting takes patience, persistence, and partnerships. It takes active pursuit of grant funding to sustain pollution control efforts. And importantly, it requires an adaptive management approach, which demands regular data collection and a willingness to adjust one’s strategy to new information.

Ready to implement cleanup and restoration plans for impaired water bodies? Connect with Barr’s water quality and lake ecology experts to take the next step toward improving lake water quality and envision strategies for delisting impaired waters.

About Greg Wilson

Greg Wilson, senior water resources engineer, has more than three decades of experience in the areas of hydrology and hydraulics, surface water quality, GIS, limnology, and watershed and lake management planning, including 1W1P and Nine Element Plans. He performs watershed and in-lake water quality modeling, recommends management actions, and facilitates technical advisory meetings for development of lake management plans. Greg has conducted water quality and water quantity monitoring and modeling and/or TMDL/WRAPS studies for more than 100 lakes. He also leads design, sediment analysis, chemical dose determination, and/or alternative treatment options for internal phosphorus control in lakes and ponds.

Tags:

Water quality Impaired Waters Adaptive Management Invasive Carp Phosphorus Pollution Control

 

Greg Wilson headshot
Greg Wilson
Senior Water Resources Engineer
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