Te Waihora restoration project a New Zealand first

When the massive beds of naturally-occurring macrophytes (karepō seed beds) disappeared from Te Waihora/Lake Ellesmere in the 1960s, it was a turning point for the quality of the lake’s water.

Known for their ability to buffer wave action, take up nutrients, improve water quality and provide diverse habitats for fish and wildlife, submerged macrophyte systems in many New Zealand lowland lakes collapsed at about that time and never returned.

In Te Waihora, the decline was exacerbated by the Wahine storm of 1968 that literally tore them out of the lake.

Today, in what is thought to be one of the few restoration projects of its type in the world, NIWA and the University of Canterbury are working with Whakaora Te Waihora partners to restore the Te Waihora macrophyte beds. Whakaora Te Waihora is the joint restoration programme led by Ngāi Tahu and Environment Canterbury – see www.tewaihora.org

Hamilton-based NIWA freshwater ecologist Mary de Winton is leading the ground-breaking four-year project. Two years into it, she is pleased with progress and delighted that the team has been able to eco-source a good supply of macrophyte species within the Halswell River system neighbouring the lake.

“Finding that there were submerged macrophytes left in the lake system was a great boost,” she said. “We found six different species including two key species – Ruppia and Sago pondweed – that we know were part of the lake’s historical macrophyte beds. We also found two rare species – a brackish water charophyte and Lepilaena – both considered to be threatened plants in New Zealand.

“Although we’re not working with the latter two species, we were very pleased to see they have survived in Te Waihora. Their presence gives me hope. That they’re managing to persist in the lake is very pleasing.”

Ms de Winton said the macrophyte project was particularly challenging because it is the first time anything like it has been trialled in New Zealand.

“I’m not aware of anyone working internationally to restore submerged macrophyte beds on this scale either,” she said. “That is both daunting and exciting. There are no examples for us to follow and no guarantees.

“We’re tapping into local knowledge and taking it one step at a time. Even if the beds fail to re-establish long term, we hope we may better understand why they never recovered naturally and why they struggle to survive in current conditions. We’re aiming to learn as much as we possibly can about the lake system and how it works.”

The restoration plan has included the establishment of a macrophyte culture facility at Taumutu. Land has been leased from a local landowner, who also acts as the facility caretaker.

With the help of Taumutu whānau and tamariki on school holiday programmes, eco-sourced macrophytes have been split, planted and placed into the 30 1800 litre tanks on site. Ms de Winton is confident up to 3000 macrophytes can be raised and hopes to have them transplanted into three approved sites around Te Waihora by late 2015.

The Te Waihora Management Board has approved the first site and resource consent has been gained for the first trial wave barrier that will be installed at the planting site to reduce wave action and help the macrophytes establish.

Ms de Winton said working closely with iwi and the University of Canterbury has been immensely valuable to the project.

“The Te Waihora Management Board and the whānau from Taumutu Marae have been great at introducing us to the right people with extensive knowledge of the lake. When we’ve needed seeds and plants, they’ve been able to show us the best places to look,” she said.

Another planting day at the macrophyte culture facility is planned for this summer and Ms de Winton said once the macrophytes are in the lake, a year of monitoring should indicate whether the plants will persist.

“We’ve chosen the sites we think will give the macrophytes the best chance of survival. If we succeed we are confident they will have significant benefits for the future of the lake.

“And of course we’ll be following up with ongoing monitoring of water quality, fish habitats and improved cultural values.”

The macrophyte trials will end in early 2017. On Tuesday 18 November 2014, Māori Television features the project as part of its Project Whenua (“Real life people, Real life science”) series.

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