Revival of Sherman Park Lagoon

By Keith Gray, president, Integrated Lakes Management, Inc.

At the Chicago 60-acre Sherman Park Lake Park, contractor Integrated Lakes Management, Inc. used a Glyphosate product (Touchdown) to reduce the lake's unwanted wolffia and duckweed. Two applications were needed to insure that late-growing leaves missed in the first application were treated as well. Crews cleared the lake island, and seeded it with native plants. Photos: Keith Gray, president, Integrated Lakes Management, Inc.

Integrated Lakes Management, Inc. and Aramark Services bring one of Chicago's premiere park lakes back to life. Sherman Park's lake is a 60-acre jewel built in 1905-06 by the Olmsted Brothers and features a square mote-type arrangement covering more than 11 acres; on the island sits soccer and softball fields. Access to the athletic fields is over stone bridges at each corner.

Until recently, the entire water lagoon was covered with floating plants called wolffia (water meal) and duckweed, which created a monoculture, which gave the appearance of a flat putting green, not an inviting condition for anglers.

Attempts were made to control the unwanted aquatic growth chemically. However, not only was this approach costly and often ineffective, but the high chemical concentration needed to effectively control the hardy plants insured that no native or beneficial plants would survive. An alternative had to be found to bring this lagoon back to its former glory so that the tens of thousands of people who live in the vicinity could enjoy it.

Harvesting of the floating weeds is possible, but exceedingly difficult and labor intensive. The typical size of a floating duckweed plant is 5 millimeters and wolffia is 1-2 millimeters.

At the start of the project, nearly 100 percent of the 7,000-foot shoreline was bordered by cattails, which blocked any wind effect to move the water.

This detail shows the aerial view of the project, and details the planting scheme.

Challenges Faced

The target plants flourish in stagnant water with a high nutrient content. Since the pond serves a small 25.4-acre watershed, the water level is maintained using treated water from the city's water distribution system, which is high in phosphorus, a key nutrient to fuel the growth of the plants the contractors were trying to eliminate.

Nutrient deactivation and routing low phosphorus from a different source was cost prohibitive. Another option was to create water current movement.

As part of a 3-tiered approach to gain water movement, ILM staff worked with Otterbine Fountain representatives to evaluate the physical characteristics (length, variable width, depth, and resistance along the edges) of the looped lagoon to determine the sizes and number of underwater pumps needed to create a current fast enough to discourage the growth of the floating plants.

As with most projects, unforeseen obstacles made things interesting. The amount of power required to run these pumps was substantial, made even more difficult by the fact that the pumps would be spread out over the mile of waterway. In the end, it was a team effort by all contractors and the Chicago Park District Trades staff to come up with a solution that was safe and cost effective.

Thirteen 2-horsepower 230-volt, 1P Sub-Triton Mixer Industrial Aerator submersible pumps were installed on the lagoon bottom around the lagoon each of which pushes 5,000,000 gallons of water an hour to create a steady 'flow' throughout the waterway. Electrical power to the pumps comes from two transformers, which were wired to four control cabinet enclosures.

There remained a a substantial cattail seed bank in the soil that had to be dealt with in subsequent years. Broadcast herbicide application was no longer a viable method, as it would damage the recently installed native plants. Workers hand-wicked cattail sprouts for two seasons after the initial installation to insure that the slower growing native plants had sunlight and a chance to survive.

Increasing Water Current

Thirteen 2-horsepower submersible pumps were installed each influencing nearly five million gallons to create a steady flow throughout the waterway. But this was only the first phase. With more than a mile of shoreline with dense cattail growth, shielding the water surface from the benefits of wind action, something had to be done to open up the shorelines.

Cattails are prolific, and these plants also are not affected by chemical herbicide until the leaves reach approximately 36 inches in length, which usually occurs around the start of July.

Aramark Services, along with ILM, worked to apply herbicide to the thick stand of cattails using amphibious vehicles to gain access and high-pressure application to insure excellent coverage. Two applications were needed to insure that late growing leaves were treated as well.

After the herbicide was applied, a controlled burn was conducted to reduce the organic matter along the shoreline and make way for native plants in the spring.

Replanting The Shoreline

Aramark installed thousands of low growing native plants along the shoreline (various sedges, iris', reeds, rushes, lilies, and arrowhead).

Since this is a highly visible and highly used park, there was not time to step back and see if these two steps would be sufficient to rid the water of the unwanted plants.

To address the lagoon's high nutrient content, the contractor applied nutrient deactivation (aluminum sulfate) slurries twice annually using a Honda WX15 water pump. Aluminum sulfate's molecular structure binds with the phosphorus in the water and sinks to the bottom. Rooted plants that would enhance the eco-system can use the phosphorus, thus making it unavailable for the nuisance floating plants. The contractor analyzes the water to measure the orthophosphorus before and after the application to insure proper dosing. 3,200 pounds of dry aluminum sulfate material was used for each application.

Aramark Services, along with ILM, worked to apply herbicide to the thick stand of cattails using amphibious vehicles to gain access and high-pressure application to insure excellent coverage. Two applications were needed to insure that late growing leaves were treated also.

Nutrient Deactivation

It was decided to address the issue of the high nutrient content of the water by performing nutrient deactivation treatments twice annually with aluminum sulfate. The material is not harmful to plant or animal life. The molecular structure of aluminum sulfate is such that it wants to bind with the phosphorus in the water and sink it to the bottom where rooted plants that would enhance the eco-system can use it make it, but at the same time make it unavailable for the nuisance floating plants.

Conclusion

After two full seasons, the Sherman Park Lagoon has open water with aquatic herbicide used only in strategic areas to control small outbreaks of invasive plants. The habitat for the fishery has improved, and anglers have commented on the vast improvement of the lagoon's condition.

According to Integrated Lakes Management, ''The amount of herbicide used at this site has been reduced by 75 percent. Although there are marginal maintenance cost savings in chemicals and labor realized as a result of this initiative, the value in the improvement in the aesthetics and usability of this historic natural resource in a densely populated area; it can't be measured in dollars.''