Leaves of trees for the healing of nations

Posted on July 28, 2017

New Zealand has 425,000 km of rivers and streams and 3,820 lakes, more than half of them are degraded, according to the recent report “Our Fresh Water 2017” by the New Zealand Ministry for Environment. Degradation in water quality is mainly due to high inputs of “the big three”: nutrients (mainly nitrogen and phosphorous), sediments and pathogens. Run-off from farming areas, livestock waste, fertilizers, pesticides, septic tanks, wastewater, and storm water are the main contributors of “the big three” into waterways and groundwater. In addition, the deforestation of many areas adjacent to waterways has increased the erosion of river banks, and removed the natural filters around rivers and lakes.

Over the last 10 years researchers from The Centre for Integrated Biowaste Research (CIBR) have been investigating the antimicrobial properties of mānuka and kānuka. The bioactive/antimicrobial compounds produced by these plants can inhibit the conversion of ammonia into nitrous oxide and nitrate, and at the same time, enhance the die-off of pathogenic organisms including Escherichia coli, and Salmonella sp. in the wastes that pass through their root systems [1-4].

Using this research, Dr’s Jacqui Horswell and Maria Gutierrez-Gines from the Institute of Environmental Science and Research (ESR) Ltd and Professor Brett Robinson from Lincoln University, have hypothesized that incorporating bioactive plants like mānuka and kānuka into biodiverse riparian planting schemes, has the potential to both filter nitrates and deactivate pollutants from intensive agriculture, leading to significant improvements in water quality. Along with decreasing the levels of nitrates and E. coli, they expect to decrease the erosion of river banks, increase biodiversity and ecosystem services, and provide economic return for farmers by the way of honey and essential oil production.

Initial trials involved growing pasture, mānuka and kānuka in containers and watering these plants with water that was contaminated with measured levels of nitrogen and E.coli. The water from the bottom of the containers was collected and remeasured for residual levels of nitrates and E.coli. The residual levels of these contaminants from the mānuka and kānuka containers was less than 10% of the residual levels from the pasture containers (click on the graphs icon above).

They are currently planting up working examples of mānuka dominated riparian plantations than can be used as flagship sites to collect data and develop farm models. This work will enable detailed plans to be drawn up for retirement and planting of riparian zones and critical source areas, which maximises the benefits to water quality, biodiversity, and cost off-sets, such as the production of natural products or browse supplements [5, 6].

For further information about these projects, please contact Maria Gutierrez-Gines: maria.gutierrez-gines@esr.cri.nz.


Research articles:

  1. Prosser, J.A., et al., Can manuka (Leptospermum scoparium) antimicrobial properties be utilised in the remediation of pathogen contaminated land? Soil Biology and Biochemistry, 2014. 75: p. 167-174.
  2. Prosser J A, et al., The potential in-situ antimicrobial ability of Myrtaceae plant species on pathogens in soil. Soil Biology & Biochemistry, 2016. 96: p. 1-3.
  3. Esperschuetz J, et al., The potential of L. scoparium, K. robusta and P. radiata to mitigate N-losses in silvopastural systems. Environmental Pollution, 2017. 225: p. 12-19.
  4. Esperschuetz J, et al., Response of Leptospermum scoparium, Kunzea robusta and Pinus radiata to contrasting biowastes. Science of the Total Environment, 2017. 587–588: p. 258–265.
  5. Hahner, J.L., et al., The Phytoremediation Potential of Native Plants on New Zealand Dairy Farms. International Journal of Phytoremediation, 2014. 16(7-8): p. 719-734.
  6. Dickinson, N., et al., Endemic Plants as Browse Crops in Agricultural Landscapes of New Zealand. Agroecology and Sustainable Food Systems, 2015. 39(2): p. 224-242.