Breaking new ground

Mary de Winton (centre), demonstrating the potting of macrophytes.

Mary de Winton (centre), demonstrating the potting of macrophytes.

When the massive beds of naturally-occurring macrophytes 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, to take up nutrients, to improve water quality and to 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, that 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 only macrophyte restoration project 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.

Hamilton-based NIWA freshwater ecologist Mary de Winton is leading the ground-breaking four-year project and 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 neighboring the lake.

“Finding that there were submerged macrophytes left in the lake system was a great boost. 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.”

Ruppia, one of the macrophyte species being raised at the Macrophyte culture facility.

Ruppia, one of the macrophyte species being raised at the Macrophyte culture facility.

Mary says the whole macrophyte project is challenging if only for the fact that 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 says.

“That”, she says, “is both daunting and exciting”.

“It’s a leap of faith. There are no examples for us to follow and no guarantees either. We’re tapping into local knowledge and we’re 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, ecosourced macrophytes have been split and planted three to a pot and put into the thirty 1800 litre tanks on site. Mary is confident up to 3000 macrophytes can be raised at the site and she 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.

Mary says working closely with iwi has been immensely valuable to the project.

Filming at the macrophyte culture facility at Taumutu.

Filming at the macrophyte culture facility at Taumutu.

“We’ve been very fortunate to have people like Dr Ian Hawes from the University of Canterbury working with us and by consulting with iwi, we’ve been able to bring our collective knowledge 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 looked for seeds and plants, they’ve been able to show us the best places to look. They gave us a steer and having access to that local knowledge of the lake systems has had huge benefits for us,” she says.

Another planting day at the macrophyte culture facility is planned for this summer and Mary says once the macrophytes are in the lake, a year of monitoring should indicate whether or not the plants will persist.

“We’ve chosen the sites we think will give the macrophytes the best chance of survival.

“The project has been a little daunting given we have no forerunners to this kind of restoration project but if we succeed and we can get macrophytes to re-establish successfully in Te Waihora, 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.