Using New Zealand native vegetation to improve water quality

According to the report Our Fresh Water 2017(external link) by the New Zealand Ministry for the Environment, the continuous degradation of water quality is the main environmental issue that needs urgent consideration.

The three main drivers of degradation of water quality are the nutrients (mainly nitrogen, N and phosphorous, P), pathogens, and sediments. Run-off from farming areas, livestock waste, fertilizers, pesticides, septic tanks, wastewater, and stormwater are the main contributors of nitrogen, phosphorous and pathogens into waterways and groundwater. In addition to this, the deforestation of many areas adjacent to waterways has increased the erosion of river banks, and removed the natural barrier that reduced the inputs of nutrients, sediments and pathogens to streams from agricultural and urban areas.

ESR is working on the potential of New Zealand native vegetation to improve water quality. Over the last 10 years, working with colleagues at Lincoln University New Zealand, we have demonstrated that the antimicrobial properties of mānuka and kānuka (usually recorded in honey and essential oils) are also present in root systems. This means that microbial contaminants (measured by E. coli as an indicator) die-off is much faster under mānuka and kānuka than under pasture (8 days against 83 days)[1]. These properties are also extended to soil bacteria related to the nitrogen cycle, making mānuka and kānuka root systems able to significantly reduce the leaching of nitrate compared with pasture or radiata pine.

These properties open the gates to numerous uses and applied research, based on using these plants to reduce the main drivers of water pollution. The current projects that we are undertaking are based on the following questions:

Can we demonstrate in real conditions the properties of mānuka and kānuka to reduce pathogens and nutrients?

ESR hypothesizes that restoring native vegetation where mānuka and kānuka are included in the margins of waterways, would reduce the amount of nutrients, sediments and pathogens that arrive from farming lands. In the same way, plantations of mānuka and kānuka could be used to safely land-treat biowastes such as municipal wastewater or biosolids.

ESR is leading projects around Lake Waikare and Lake Wairarapa to demonstrate and quantify the potential of mānuka and kānuka dominated native vegetation, to increase the water quality affected by farming activities. These projects are funded by the Waikato River Authority, Waikato Regional Council, Greater Wellington Regional Council, and ESR Strategic Science Investment Funding, and count on numerous collaborators: Ngā Muka Ltd, Te Riu o Waikato Ltd, Matahuru Marae / Nikau Farm Trust, Ecoquest, Rangitane, Kahungunu ki Wairarapa and Manuka Farms.

A drain that flows to Lake Waikare in the Nikau Farm, where one of the experimental riparian plantations will take place.

ESR scientists working the in the experimental plots in Lake Wairarapa Project.

Are there other native plants with the same properties?

Current projects are seeking to find other native plants with similar properties as mānuka and kānuka. As a first step, we are screening a list of potential native plants for their antimicrobial properties. For this, plant extracts of 15 native species from North Island and South Island are being tested against important pathogens such as Staphylococcus aureus, and Campylobacter jejuni. With this results we expect to increase the knowledge about potential native plants for reducing pathogen and nitrogen loads into waterways, as well as to provide incentives for increasing the biodiversity in riparian plantations.

Jacqui Horswell,

Maria Gutierrez-Gines,

[1] Prosser J, Anderson CWN, Horswell J, Speir TW. 2014. Can mānuka (Leptospermum scoparium) antimicrobial properties be utilised in the remediation of pathogen contaminated land? Soil Biology and Biochemistry 75: 167–174.

Prosser JA, Woods RR, Horswell J, Robinson BH. 2016. The potential in-situ antimicrobial ability of Myrtaceae plant species on pathogens in soil. Soil Biology and Biochemistry 96: 1–3