eDNA as a holistic measure of pastoral landscape effects on taonga species

Freshwater quality is measured with key indicators such as faecal indicator bacteria (E. coli), nitrates and phosphates. For communities, such indicators are vague and somewhat abstract. Our objective was to increase commitment to action in catchments by demonstrating a new approach to assessing freshwater quality. This was done by using tiny traces of genetic material, or environmental DNA (eDNA), as novel indicators that provide a living context for understanding the ecological health of waterways.

Our case study site area was the upper reaches of the Manawatū River encompassing native bush, a hill country sheep and beef farm, and a dairy farm where freshwater samples were obtained from five separate sites for eDNA analysis. Freshwater sites were sampled for eDNA detection on four occasions, two before and two after Cyclone Gabrielle in 2023.

Taonga species identified using eDNA included whio/blue duck, ruru/morepork, kōtare/kingfisher, tuna, kaharore bully, dwarf galaxias and kōura.

Conventional water quality assessment attributes were also measured and compared to eDNA reads. Using E. coli, physico-chemical data, eDNA reads from invasive/pastoral species (possum, deer, cattle and sheep) and local knowledge, likely inferences were made on contamination sources and potential mitigations.