Plastic wetland to absorb nitrogen

While the Government gets a beating over water quality issues from the Cawthron Institute, a new initiative launched last week is making use of recycled plastic bottles to create an island that improves the water quality of Lake Rotoehu in Rotorua. 

Part of the Rotorua Lakes restoration programme, the 2800 square meter island has been constructed using no less than 364,000 recycled soft drink bottles that are covered in coconut matting. But the real pollution kicker comes from the native wetland plants species that have been planted in each of the bottles as a means of removing nitrogen from the lake waters. 

Screwed in place using 10 anchors, the island is also fully portable and can be moved in response to changes in the lake’s water level. 

The wetland has received 50 percent of its funding from the Crown through the Deed of Funding to clean up the four priority Rotorua lakes, Rotorua, Rotoehu, Rotoiti and Ōkāreka. It’s part of the Rotorua lakes restoration programme which is run by three partners: Bay of Plenty Regional Council, Rotorua District Council and Te Arawa Lakes Trust. 

Regional Council Chairman John Cronin says significant progress has been made in the clean up of the lakes. 

“This 800 hectare lake has become a very useful melting pot for testing lake restoration techniques that could be applied to other larger lakes in the programme. Weed harvesting has already removed up to 3500 tonnes of weed each year. This achieves the reduction in lake nutrients required to restore the lake, even before land use changes come into play.” 

But this is by no means the first initiative used to clean up Lake Rotoehu. Previous trials on the lake include bio-treatment in Otautu bay and de-nitrification of an in-flowing stream on the Tautara Matawhaura Māori Land Trust farm. Later this year a de-stratification project has been planned to prevent oxygen loss in the lake’s bottom waters over summer and autumn. 

And if you’re thinking an island made of recycled plastic is something new, it’s not quite. British artist Richard Sowa built this fully habitable plastic island a few years back after previous islands he’d constructed were wiped out by hurricanes. And while it hasn’t yet been actioned, “Recycled Island” is a proposal launched in March last year by Dutch conservationists. The aim is to create a fully habitable island using close to 44 million kilos of plastic waste from the North Pacific Gyre. The island could host around half a million people and would be powered by a mixture of solar and wave technology.