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Floating wetlands

Two of the largest floating wetlands have been constructed for Lake Rotorua and Lake Rotoehu.

Lake Rotoehu now boasts a 2,800 m2 floating wetland.  The wetland was built from more than 364,000 recycled plastic bottles and planted in native wetland species sourced from around the district. The roots of the plants reach into the water, removing nitrogen as the plants grow.

The Lake Rotorua wetland is about the size of one-and-a-half rugby fields and spells out ‘Rotorua’ in giant floating letters.  More than 20,000 native plants have been sewn into the constructed wetland.  Lake Rotorua’s wetland is currently moored at Sulphur Point and once fully established it will be towed out to its final spot near the airport.

Floating wetlands have a design lifespan, they are not a permanent solution to nutrient reduction and that is why more long term solutions are favoured such as land use change. Based on the most relevant research available, the ‘ROTORUA’ floating wetland is reported to achieve 73kg N/year.   However as this research undertaken by NIWA (Sukius et al 2010) related to wetland trials in streams, the above figure is likely to be an overestimation of the actual uptake of the Lake Rotorua floating wetland as the available nitrogen concentrations in the lake are much lower than those found in streams or at points where streams exit into the lake.

Once established floating wetlands will reduce nitrogen and phosphorus in the lake.  Floating wetlands also provide additional benefits such as a nursery for koura, nesting options for birds, enhanced fisheries and wave dampening.

Read the following reports on floating wetlands and their role in reducing nutrients in our lakes.

  • Floating treatment wetlands: a new tool for nutrient management in lakes and waterways

 

Report title  Author Summary Date

Floating treatment wetlands: a new tool for nutrient management in lakes and waterways

 

Chris C. Tanner, James Sukias, Jason Park, Charlotte Yates and Tom Headley

Floating treatment wetlands (FTWs) employing emergent aquatic plants growing on a buoyant mat are an innovative new tool for nutrient management in ponds, lakes and slowflowing waters. They are currently being trialled or applied for water quality enhancement in a wide range of situations in New Zealand and around the world. Trials were held to record areal TP removal rates.

2011

Floating treatment wetlands (FTWs) employing emergent aquatic plants growing on a buoyant mat are an innovative new tool for nutrient management in ponds, lakes and slowflowing waters

J.P.S Sukias

C.R Yates

C.C Tanner

Trials were undertaken to provide information on the effectiveness of floating treatment wetlands to reduce nutrients from stream inflows to Lake Rotoehu.

2010