Nitrogen leaches through soil mainly from concentrated urine patches and flows through to arteisan groundwater supplies. At high levels, nitrogen can be harmful to humans. Babies are most at risk and may suffer from a disease known as ‘blue baby syndrome – where there is not enough oxygen in their blood. Babies are at risk when in the womb and when fed with contaminated water (from being bottle fed with formula mixed with contaminated water). Water from public supplies is thought to be safe to drink as it will be treated if it exceeds safe nitrogen levels. However, private artesian supplies are more at risk of having elevated nitrate levels.
Elevated nitrogen levels are becoming a threat in Canterbury because of the increasing expansion of dairy farming and the relatively free draining soils present there – more nitrogen leaches through the soil before it has a chance to be taken up by pasture.
In the past decade, nitrate concentrations have been increasing in about 37 per cent of tested wells in the Canterbury region . Monitoring of these wells in 2013 showed that 9 per cent were above the nitrate maximum allowable value (MAV) for drinking water. This was a decrease from 11 per cent in 2012, but has increased since 2011 from 7 per cent.