In June 2013, 2 Floating Treatment Wetlands (FTWs) were assembled and installed in Tamarack Lake in hopes of reducing nutrient levels in the lake. Together, the islands are a total of 324 square feet, with about 200 plants.
The project was funded by VLAWMO as part of its SLMP implementation program. A grant for work from the Conservation Corp of Minnesota was also awarded to help with the construction and deployment of the islands, providing a majority of the physical labor.
Reason for project:
Because Tamarack Lake is impaired for nutrients, projects were being explored to decrease nutrients and to work towards removing the lake from the state Impaired Waters list. Floating Treatment Wetlands were identified as a project that could reduce nutrient levels by means of drawing nutrients out of the water, as well as other chemicals, with plants and microbes. The goal is to reduce phosphorus levels, the main limiting factor of excess algae growth in water bodies, with the end goal of increasing water clarity. Additional benefits also include uptake of other chemicals and nutrients, such as heavy metals and nitrates, as well as added wildlife habitat and aesthetic appeal.
The islands are composed of recycled plastic pop/water bottles injected with an inert foam to provide buoyancy. These islands are planted with vegetation, promoting vegetation habitat above water, and microbial habitat below to take up nutrients and sequester them from the water. Installation of the island itself was no small feat, and required significant physical labor, much of which was provided by a Conservation Corps of Minnesota crew. The installation process started with covering the island in a shallow peat/soil mix, and wrapping it with erosion blanket to protect the material from UV rays. Next, the island was planted with native flowers and grasses followed by the erection of a small fence to prevent geese from tearing up the plants. Finally, the island was launched by canoe into the water. The island is anchored to the bottom of the lake to be stationary.
After 3 years of monitoring data that studied nutrients and lake conditions, the floating islands have not shown to decrease nutrients in any measurable amount for Tamarack Lake. Nutrient samples are taken both, right next to the island, and by the dock every month during the monitoring season. Every sample taken next to the FTW has been nearly identical in nutrient amounts as the sample taken from the Lake’s dock. With no measurable differences in nutrients, it is hypothesized that the islands were undersized for the Tamarack Lake basin.