Danielle Wain, 7 Lakes Alliance Science Director
In summer 2018, the largest alum treatment to date in New England was conducted on East Pond (Smithfield, ME) in two phases in June and October 2018 to address the recurrent algal blooms of the past 20+ years. East Pond was a prime candidate for an alum treatment because a detailed watershed loading analysis indicated that 50% of the phosphorus available to algae came from lake sediments, not predominantly from new phosphorus entering the lake from the watershed. Additionally, property owners had already made significant improvements to try and reduce runoff to only 25% of phosphorus load.
Prior to the treatment, partners 7 Lakes Alliance and Colby College had conducted extensive water quality and sediment analyses to determine the proper dose for the alum treatment, in collaboration with Maine DEP, US EPA, and an outside consultant. 7 Lakes Alliance successfully secured permits based on this scientific approach. In total, 676 acres of lake sediment were treated with 800,000 lbs of aluminum hydroxide with a total cost of $1.1M. Throughout the treatment, our team monitored pH, alkalinity, and dissolved aluminum to ensure the treatment did not significantly impact lake chemistry and ecology.
This summer, after the first phase of the treatment, East Pond had excellent water quality (Secchi depth > 5 meters). The next benchmark will be if the same water quality continues in 2019. If the benchmark is achieved, 7 Lakes Alliance and its partners are confident that the alum treatment will be effective for many years. East Pond will continue to be monitored as part of the 7 Lakes Alliance/Colby College Water Quality Initiative with the assistance of the East Pond Association.
The East Pond alum treatment was the culmination of years of work investigating the sources of phosphorus in the lake, acting to reduce the external load, and carefully measuring the sediment properties to determine a proper dosage. Each one of our Belgrade Lakes is unique in terms of size, shape, and watershed characteristics, and in-lake remediation methods that work well in one lake may not work well in another. Alum treatments are another tool in our toolbox for managing our lakes but reducing phosphorus inputs from the watershed through erosion control including through Youth Conservation Corps and LakeSmart, is key to ensuring such tools work long term.