Cedar Lake begins alum treatment to reduce algae blooms
The Cedar Lake Protection & Rehabilitation District realized an important part of its lake management plan on Wednesday, June 14, when it began the first of five alum treatments that will be used to combat phosphorus levels in the lake over the next 15 years.
Historical records and sediment samples collected as part of a three-year study of the lake and its watershed, confirmed that algae and the sometimes smelly and toxic blooms it can cause, have been a part of the lake's history since the 1930's. Core studies of sediment samples indicate that beginning with the clearing of the forest surrounding the lake for agricultural purposes in the 1880's, nutrients including phosphorus have been collecting in the lake basin at ever increasing rates until recently. Runoff management practices have begun to slow that loading process.
Several dozen residents attended a brief educational program about alum treatment followed by a question and answer session with John Holz, Ph.D., limnologist and owner of HAB Aquatic Solutions LLC, and consultant, Bill James, a Senior Researcher with the Discovery Center and Biology professor at the University of Wisconsin Stout. HAB was selected as the contractor to implement the alum treatment plan for Cedar Lake. According to Catherine Bosley, Director of Business Development for HAB, her firm has conducted alum treatments on more than 60 lakes.
"This is our 61st lake. We've worked on lakes all over the United States and just completed our first project in Canada," said Bosley.
Alum is used, as it is in many wastewater treatment applications, to bond with phosphorus in the water column. Once the alum is injected into the water, it appears as a milky white precipitate called a floc, which adheres itself to suspended phosphorus and sinks to the lake bottom where it forms a protective layer of alum between lake sediments and that water. That barrier prevents the larger concentration of phosphorus in the lake bottom sediment from leaching back into the water column. Removing the phosphorus from the water deprives algae of a primary food source thereby reducing algae and improving water quality.
"The first alum treatment in North America was in Wisconsin in the 1970's. We conducted scientific research between 2009 and 2012 where we monitored water quality on a number of lakes. We were able to determine that the sediment was recycling most (85 percent) of the phosphorus driving these algae blooms in the lakes. From there we moved into management. We estimated the amount of aluminum sulfate that would be needed to inactivate that recycling, that leaching. It's been a long process, nine years. I've been working on a lot of lakes. We have been perfecting the treatment approach and we are on the cusp of a lot treatments," said James.
The specific plan for Cedar Lake is to treat every three years for 15 years. The first application of approximately 280,000 gallons of alum was scheduled to be applied over two weeks starting June 13. The liquid alum is delivered by tanker truck and stored in a series of tanks located at the north landing on 10th Avenue. A specially equipped barge uses a boom outfitted with series of tube fed nozzles, much like a crop duster, to inject liquid alum about a foot below the surface of the water. At that depth, surface turbulence doesn't affect the distribution of the alum. The alum sinks to the bottom at a rate of about 8 feet every 20 minutes. The barge uses GPS guidance to distribute the alum in a dosage specifically measured to match the concentration of phosphorus in the bottom sediment. Using core samples, James created a prescription grid map to insure the correct dosage of alum is delivered to the correct locations.
"The injection process is conducted using GPS to document exactly how much alum is being distributed where. The alum is only applied at depths greater than 20 feet. When we surveyed the lake by collecting sediment all along a grid pattern, that's where we found the greatest concentration of phosphorus. Sediment is naturally funneled to the deeper basins of the lake. Shallow areas tend to be more sandy, have more activity, which re-suspends the finer sediments as they migrate to deeper water," explained James.
The alum treatment will be monitored daily. A container of water will be withdrawn from the lake each day to which the prescribed dosage of alum will be added. That water's pH level will be checked to insure the water quality and safety. The barge is also equipped with pH level monitoring instruments. Sediment samples will also be routinely collected and analyzed back at UW Stout.
Alum treatment is expensive. Seventy percent of funding for the initial treatment was provided by the Wisconsin Department of Natural Resources including a $200,000 Lake Protection Grant, $165,000 Targeted Runoff Management Grant, $50,000 in Lake Planning Grants and $1,000 from Star Prairie Fish and Game for Eurasian Milfoil Hand Removal. Thirty percent of the cost was paid for by a special assessment to lake residents. The special assessment is scheduled to last 10 years and is likely to rise depending on the availability of additional WDNR grants to help defray the costs of additional treatments. The assessment will also pay for administrative costs including bid solicitation and management, loan fees, supervising the treatment and development of the special assessment.
"We're going to use an adaptive management approach on Cedar Lake, meaning, we're going to monitor the effectiveness. If it needs more (alum) we can add more or move up the next treatment to two years rather than waiting three years. By in large, this approach has been very successful. It depends on putting on enough (alum) to reduce that sediment recycling. If successful, this treatment can be effective for decades," said James.
Significant to the decision to undertake alum treatment was the effect management of runoff from the external watershed.
"This has been the culmination of lots and lots of years of effort by an awful lot of people. First and foremost is the farmer-lead council. They are the folks who have been at the forefront, leading the way to make sure the water coming into Cedar Lake is clean. Our lake has been on the list of Wisconsin impaired lakes for a long time. This is just one step in the process that our board and all these people have gone through to clean up the lake. So we'd like to thank Buzz Sorge and the DNR, the farmer-lead council, and people like Bill James, our chief scientist. We owe so many people a debt of gratitude, so, thank you and bravo," said Alum Committee Chair Dan Early.
To learn more about the Cedar Lake management plan, visit the Lake District website at: cedarlake-wi.org.
For updates on the progress of the alum treatment, visit: cedarlakealum.com.