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 field study to investigate the ability of native trees to filter out freshwater harming nutrients and pathogens. The CIBR team from Lowe Environmental Impact (LEI), ESR, University of Canterbury and Northcott Research Associates, obtained funds from Horowhenua District Council (HDC) and the Freshwater Improvement Fund (Ministry for Environment) to carry out an exciting real world large-scale project of applying treated municipal wastewater (TMW) to mānuka and kānuka dominated ecosystems, to reduce the impacts of this land-application on the Waiwiri Stream in the Horowhenua region.
“The Pot” is the local name of a seven hectare (ha) pond where wastewater from the Levin wastewater treatment plant (WWTP) is stored in, before being used for irrigation of 40 ha of exotic pines. The resource consent for the irrigation scheme at the Pot required renewal and this offered the opportunity to revise the design of the irrigation scheme, with input from key stakeholders including local Iwi, DOC, Regional and District Councils. The revised design has the scope to incorporate the most up to date irrigation technology, including utilising recent research discoveries on the abilities of mānuka/kānuka native ecosystems to provide enhanced treatment of wastewater.
10 ha of pine forest will be replaced with native ecosystems comprised of 40-60 % mānuka and kānuka. The mānuka/kānuka will form a contiguous mosaic interspersed with other native species that were common or native in this area before the land clearing. Borders of the drains and wet areas within the site will be also be planted with mānuka/kānuka and other suitable riparian species to limit contaminants entering the drain and subsequently the Waiwri Stream. Existing links with mana whenua will facilitate advice on taonga species (species of interest/treasured) that can be re-established in these areas.
This project poses a great opportunity for the researchers at CIBR to investigate the first full scale application of TMW 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 with HDC asked to provide key stakeholders with information on the impacts of emerging organic contaminants in the environment.
New knowledge obtained from this project on the effects of native plant systems to mitigate emerging organic contaminants and pathogens in treated human wastewater will make a significant contribution to national and international research in the field of land treatment of biowaste.
In December 2017, the team at ESR conducted a large sampling campaign of the area at The Pot. Over 400 samples of soil were collected to cover the areas of pine plantation irrigated for 30 years, pine plantation non-irrigated, pasture irrigated, pasture non-irrigated, and an old kānuka stand as a control of native vegetation. Soil samples were collected at increasing depths down to 2 m with a large scale analysis performed on the samples. All the areas of pine were also harvested with site redvelopment.
In mid 2018 more than 70,000 native trees were planted at the site, with many gathered to help out and celebrate the first planting. Planting was completed in late 2018.
In early 2019, water flux meters were installed at the site this 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.