The Pot at Levin - part of a Nationwide study

The pot field site

'The Pot' field site in Levin. Photo credit LEI

Two native NZ plants, mānuka and kānuka could soon join the battle to improve New Zealand's freshwater quality.

Scientists from the Centre for Integrated Biowaste Research (CIBR) are two years into a nationwide study to investigate the native trees ability to filter out freshwater harming nutrients and pathogens.

‘The Pot’ at Levin is the latest field site to be planted with an mānuka, kānuka dominated ecosystem. Other field sites include a plots of land on the shores of Lake Waikare, Lake Wairarapa, and Duvauchelle.

Lake Waikare - 4 hectares of mānuka dominated ecosystems

4 ha of mānuka dominated ecosystems planted at Lake Waikare, in the Waikato in collaboration with Waikato River Authority, Waikato Regional Council, Ngā Muka, and Nikau Trust Farm. 

Planting in the Wairarapa Moana

Planting in the Wairarapa Moana in collaboration with farm owners, Greater Wellington Regional Council, and Ngati Kahungunu ki Wairarapa

Trial at Duvauchelle , showing plant growth

The trial at Duvauchelle in year 1 (left) and year 3 (right), in collaboration with Christchurch City Council.

Funded by the Freshwater Improvement Fund from the Ministry for the Environment, and Horowhenua District Council, a 10 hectare trial at The Pot is underway.  Mānuka, kānuka and 12 other NZ-native species have replaced radiata pine at the Pot and over the next five years the team will investigate if this special plant can enhance the land treatment of wastewater.

Over the last six months, >70,000 native trees have been planted at the site and over 350 soil samples have been taken.  The soil sampling at this early stage will give the scientists a baseline to compare against once the trial is finished.   The natives largely consist of mānuka and kānuka, but also include more than 20 other native species.  The planting has been undertaken in a specially designed way to allow the scientists to compare the different species, with measurements of growth and drainage water.

harvesting, soil sampling and planting of the site

Harvesting, soil sampling and planting of the 'The Pot'

Next up is the installation of specialised scientific equipment, water flux meters, that will measure the drainage water flow around the roots of the mānuka, kānuka and other plants.   This will ultimately tell us what happens to different contaminants in the wastewater as they interact with the root systems of the plants.

Soil flux meters that will be installed at The Pot trial site

Soil flux meters that will be installed at The Pot trial site

The hope for this site is that the native ecosystem approach will significantly reduce contaminant leaching and will enhance biodiversity, protect vulnerable soils and improve water quality in the Waiwiri catchment.

This project poses a great opportunity for the researchers at CIBR for investigating the first full scale application of treated municipal watewater on NZ native vegetation in the country. The applied research component of this project is twofold, first we can provide validation of the benefits of mānuka/kānuka-dominated ecosystems to enhance the land treatment of land applied wastewater in an operational environment. Secondly, we will collate information on the accumulation, fate and effects of emerging organic contaminants in wastewater applied to land. This is a knowledge gap for both councils and communities and Horowhenua District Council have been asked to provide key stakeholders with information on the impacts of emerging organic contaminants in the environment. 

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