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World’s largest floating wetland to boost lake water quality

30 September 2011

World’s largest floating wetland to boost lake water quality while branding Rotorua

Rugby field-sized floating wetland on Lake Rotorua will help boost water quality

Anyone flying over Rotorua in the future will be in no doubt what part of the country lies below when they see the name ‘Rotorua’ spelled out in giant letters as part of a floating wetlands environmental initiative on the surface of Lake Rotorua.

What is believed to be the world’s largest manmade floating wetland should be ready to be launched on Lake Rotorua before the end of the year as a major environmental enhancement project to help restore the lake’s water quality.

It is estimated that the floating island will remove up to four tonnes of Nitrogen and over 1,000 kilograms of phosphorus from the lake every year.

Technology used in construction of the rugby field sized floating wetland will involve the recycling of more than half a million plastic soft drink bottles to be transformed into an expansive 5,100 square metre floating fibre mat.

Cut-outs in the densely planted wetland island surface will be formed in the shape of the word ‘Rotorua’ providing an extra marketing bonus for the district.

The $900,000 environmental initiative is a partnership of Rotorua District Council, Bay of Plenty Regional Council and Te Arawa Lakes Trust. It follows the successful development of a smaller scale floating wetland on another Rotorua lake, Rotoehu, earlier in the year.

Rotorua mayor Kevin Winters said the building of a large-scale wetland was an environmental consent requirement to compensate in part for reducing an area of land-based wetlands when the city’s airport runway was extended recently. Rotorua District Council's investment in the project would be $450,000.

“Because floating wetlands have proved substantially more effective as environmental remediation tools, this project’s key focus is on a lake-based wetland device rather than land-based wetlands.

“To maximise effectiveness it needs to have ‘cut out’ areas within the island so we are taking the opportunity to form these into the shape of the letters that make up the word ‘Rotorua’ – the name of both the district and the lake. To our knowledge this concept will be a world first, as well as the largest project of its type in the world.

“We expect it to capture attention worldwide as an innovative environmental improvement measure and we anticipate it will also become an intriguing addition to our region’s diverse tourism product.”

Bay of Plenty Regional Council chairman John Cronin said wetlands played an important role in filtering out water-based nutrients that otherwise impact on water quality and lead to intermittent outbreaks of algal bloom.

He said science showed that strategically located floating wetlands were at least four times more effective at stripping nutrients from water, like Nitrogen and Phosphorus, than conventional terrestrial wetlands.

“So we're pleased to be able to substantially support this proposal. The Regional Council is putting in $225,000 and we're supporting it with an additional $225,000 funding from the Crown via the Rotorua Lakes Funding Deed.

“The Regional Council is committed to the important partnership with both Rotorua District Council and Te Arawa Lakes Trust. This particular initiative complements an objective in our ten year plan to develop more wetlands, as well as our broader objectives around improving the water quality of Rotorua’s lakes.

Te Arawa Lakes Trust chairman Toby Curtis said the trust was right behind the initiative as it was a significant contributor to the future sustainability of the district’s largest lake.

“We know that there is no quick fix solution to the issues around lakes water quality degradation that have occurred over many years, but this innovative project will provide an important boost to improving Lake Rotorua’s water in the long term.

“It aligns with Te Arawa’s kaitiakitanga responsibilities and is a very worthy environmental improvement project in its own right, but it’s also a substantial waste recycling initiative and a great promotional opportunity for our district too. It’s a win-win-win project for our planet and for the Rotorua Community.”

The exact location for anchoring the floating wetlands in Lake Rotorua was yet to be finalised but a number of sites were currently being assessed for potential effectiveness with the support of local hapu Te ure o Uenukukopako.

Additional Information:

• The floating wetlands island concept works like a giant kidney taking in the lake’s poisons that affect the health of the water system.
• The island’s total footprint will be 5,100m square metres. The larger zone within, below and around the island is known as the ‘ecological influence area’ and this will create a new ecological habitat for aquatic and terrestrial flora, fauna and other life forms.
• Recycled plastic soft drink bottles used for constructing the floating island will be made into a non-toxic durable matrix of fibres. The material is dense, porous and stable with a UV-resistant resin coating that meets US Environmental Protection Agency irradiation accelerated degradation standards.
• Plants on the floating wetland will have root zones suspended beneath the island with extensive nutrient stripping qualities. The roots provide a large surface area for microbes and bacteria to grow and multiply in bio films that adhere to root hairs. These microbes and bacteria consume nitrogen and phosphorus and the plants also take up nutrients from the water to grow and survive.
• Bio films in the root zones are the base of life. Micro-invertebrates and bacteria feed on the bio film, and are in turn consumed by larger species in the food chain, including fish and bird species.
• Once the island is mature and established it will provide a ripple effect of water cleansing around it like concentric circles.


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