“What is that floating out in the lake?!”

It’s one of the most asked questions we get while on-site at lakes with floating treatment wetlands or floating treatments islands.
So for World Water Day 2018, we thought we would take a moment and do a rundown of the top seven questions about floating treatment islands.

Happy World Water Day!
Kat

1) What is it?

This is a Floating Treatment Wetland (FTW). They can also be referred to as Floating Islands.

A 350 sqft floating treatment wetland at RedHill Community Park

Floating Treatment Wetlands are islands of buoyant artificial mats containing emergent plants. They are planted with sod, garden or wetland plants and launched onto a water body. The plants are allowed to grow naturally, and as they develop, their roots grow through the matrix and into the water below.

They are an excellent example of biomimicry, using nature’s processes and systems to tackle environmental issues, such as poor water quality.

A cross-sectional diagram of the matrix, biofilm and plants in an established Floating Treatment Wetland.

The matrix, is made from 100% recycled plastic, mainly derived from drinking bottles, which use the most inert plastic available. This plastic is melted then extruded into a matrix of fibers, (with carbon added for UV protection) which look like a pot-scrub or loofah. Layers of matrix are bonded together with foam to provide extra buoyancy.

The fibers that make up the floating treatment wetland matrix come exclusively from plastic drinking bottles.

They are used to improve water quality. Specifically to reduce excess nutrients, suspended solids, heavy metals and other pollutants, which are degrading the water quality at this site.

The wetlands and the plants that grow through them, provide an extensive surface area for bacteria to thrive, otherwise known as a biofilm. These bacteria are able to remove nitrogen and phosphorus from the system through a variety of ways.

Also, the roots entrap fine suspended particulates, and as the plants roots are in direct contact of the water column they can uptake nutrients in the water (to a small degree), contributing to the overall water body clean up.

Climate will dictate what species of plants are used. Here in California the following types of plants have been used and tested:

  • Native riparian, bog, and aquatic plants
  • Trees
  • Sedges (bulrush)
  • Juncus
  • Vetiver grass
  • Water Irises
  • Fairy Lilies
  • Water Cana

Artificial grass is also used around the perimeter of the island as it withstands abuse from waterfowl and turtles best.

The majority of urban lakes and water bodies have a residential population of waterfowl and other birds associated with it. To allow for the plants to establish both on top of the island, and the roots to grow within the matrix and into the water below, birds and turtles have to stay off the Floating Treatment Wetlands. Therefore, “bird spiders” and bird spikes are used for the first season. The bird spiders are covered in shiny tape and spikes are placed all around the island to act as a deterrent so the birds do not land or get onto the lake and decimate the newly planted foliage.

Floating treatment wetlands come in all sizes and shapes depending on the need and location. They can be specifically designed for a number of different uses, including:

  • Domestic wastewater treatment
  • Stormwater run-off treatment
  • Agricultural waste
  • Wave mitigation
  • Floating vegetable gardens
  • Creating habitat
  • Tourism