Water scarcity and water pollution are increasingly critical global issues. Water scarcity is driven not only by shortages of water, but also by rendering water unusable through pollution. New Zealand is no exception to these trends.
Demand for water has rapidly increased, and New Zealand now has the highest per capita take of water for agriculture among OECD countries. Regulatory failures have also led to over-allocation of many ground and surface water resources.
Some water sources are also well on the way to being unusable. Over the past few decades, nutrient and sediment emissions into waterways have increased, driven by agricultural and horticultural intensification.
Much is made of the environmental benefits of New Zealand’s “grass-fed” dairy systems. But a major downside of high-intensity outdoor farming systems is the nitrate leaching from animal waste and synthetic fertilisers that contaminates fresh water.
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Milk’s grey water footprint
Our new paper focuses on nitrate pollution in Canterbury. We comprehensively quantify, for the first time, the nitrate “grey water” footprint of milk production in the region.
A water footprint (WF) is a measure of the volume of fresh water used to produce a given mass or volume of product (in this case, milk).
It’s made up of both “consumptive” and “degradative” components. The consumption component is rainwater (green WF) and groundwater or surface water (blue WF) used in irrigation.
Most water footprint studies of food systems highlight the consumptive water component and often neglect the degradative component. However, we found Canterbury’s pasture-based systems mean grey water is the biggest component.