Analysis carried out by the Institute for Governance and Policy Studies at Victoria University of Wellington and published in the Australasian Journal of Environmental Management, revealed the nitrate grey water footprint for Canterbury ranged from 433 to 11,110 litres of water per litre of milk, depending on the water standards applied.
Lead author Dr Mike Joy said: “This footprint is higher than many estimates for global milk production, and reveals that footprints are very dependent on inputs [such as feed and fertiliser] included in the analyses and on the water quality standards applied to the receiving water.”
The research also found that there are not sufficient volumes of rain and river water to dilute nitrate pollution in Canterbury to acceptable drinking standards. It warned Canterbury groundwater drinking supplies are on a trajectory to extreme levels of nitrate contamination of 21 mg/L – nearly double the allowable value for drinking water of 11.3mg/L – rendering much of it “undrinkable.”
Dr Joy claimed growing use of synthetic nitrogen fertiliser and imported feed such as Palm Kernel Expeller has “dramatically increased nitrate levels and the water pollution problems” in New Zealand.
“There isn’t enough water falling from the sky or pouring down Canterbury’s rivers to actually dilute the nitrate contamination produced by thousands of tonnes of synthetic nitrogen fertiliser and over a million dairy cows across the plains,” he said.
“The large footprint for milk in Canterbury indicates just how far the capacity of the environment has been overshot. To maintain that level of production and have healthy water would require either 12 times more rainfall in the region or a 12-fold reduction in cows.”
He went on to claim the extensive dairy farming in Canterbury is leading to significant pollution of the region’s groundwater, much of which is used for drinking water. “Dairy farming at this intensity is unsustainable and if not reduced could pose a significant risk to human health and the market perception of the sustainability of the New Zealand dairy industry and its products.”
The research concluded that large reductions of nutrients of around 96 per cent are needed to reduce elevated groundwater nitrate concentrations. “Unless this environmental degradation is reversed and current dairy farming significantly reduced and/or replaced by low-nitrate emission non-pasture grazed systems, dairy farming on the Canterbury Plains will remain unsustainable and seriously damaging to the local freshwater environment, including local drinking water sources. This degradation could continue to pose a significant human health risk and threat to our global market for dairy products.”
Greenpeace Senior Campaigner Steve Abel said: “This research starkly shows the need to phase out synthetic nitrogen fertiliser and reduce stocking rates if we are to protect people’s drinking water.”
Reference
The grey water footprint of milk due to nitrate leaching from dairy farms in Canterbury, New Zealand
Australasian Journal of Environmental Management
DOI: https://doi.org/10.1080/14486563.2022.2068685