Dog and Cranberry Lake Association Floating Treatment Wetlands Platforms

Jeff Green | Aug 03, 2022

In 2021, South Frontenac Township launched the lake ecosystems community grant program, and one of those grants went to the Dog and Cranberry Lake Association, for an experimental citizen science program to both monitor and mitigate phosphorus levels in the lake.

Since high phosphorus concentrations are an essential element in the periodic outbreak of toxic blue-green algae blooms that have been a major issue on both lakes, the association is keen to develop strategies.

The plan, which was implemented this spring, was to launch platforms, the size of a small floating dock, in order to expose cattail roots to the water in Milburn Bay on Dog Lake.

“We launched our first of three, experimental Floating Treatment Wetlands platforms (FTWs) on Friday,

May 13th, then we launched another two a few weeks later. Each platform holds 120 phosphorus

loving cattails which will be busy all summer absorbing excess nutrients from Milburn Bay. Nutrient

levels in the plant tissues will be harvested and analyzed at specific points during the season and

compared to those of plants from a lower nutrient location,” said Shirley French, a biologist and Milburn Bay resident who put this experimental project together.

“The community grant in 2021 allowed us to purchase the materials for the platforms which we built that year. The more time-consuming aspect of the project was the time it took to get permits from both Transport Canada and Parks Canada,” she added

She said that before embarking on the project, her and her small team looked at 20 years of data from the “Lake Partner Program'' that the Dog and Cranberry Association participates in, and saw a gradual increase in total phosphorus over time, especially in the south end of Dog Lake.” There have been two major blue green algae events on Milburn Bay over the last 6 years.

“Phosphorus is a nutrient that is prominent in the production of cyanobacterial blooms (aka BGA, blue green algae). The goal with this pilot study is to determine if the cattails will perform the task of taking up phosphorus comparable to levels measured in the Experimental Lakes Area (ELA) experiments. The cattail roots are the important uptake region of the plant. By keeping the roots suspended in the water and not rooted to the sediment, we can cut the roots and monitor phosphorus uptake over time. An important step in the FTW process is to remove the phosphorus by composting the cattails away from the wetland at the end of the growing season. We will report back next year with our results.”

She said that the impact on phosphorus levels from two platforms, each with 120 cattails, will be modest and 1mcg/litre of phosphorus per year in Milburn Bay, although the impacts will accumulate over time. The target upper limit for phosphorus in lake water is 20 mcg/litre.

If the pilot project with two platforms is successful, she hopes that individual property owners may want to get involved, and a landscaping business might be able to use the cattails for shoreline naturalisation planning programs.