Nitrate-nitrogen

Nitrate-nitrogen Values for the Wairau Plain

The nutrients nitrogen, sulphate, potassium and phosphorus generally occur naturally in local groundwaters to varying degrees; but can also be added by manmade processes. These include decaying plant material, animal or human waste and agricultural fertilisers.

The latter is the most common non-point source of nutrients to groundwater. They are mostly found in low concentrations in Marlborough groundwaters with the exception of nitrogen and to some extent sulphate. Nitrate levels in local groundwater vary considerable both spatially and seasonally. Generally speaking groundwater nitrate concentrations of greater than 1 to 3 g/m usually point to man-made inputs. Concentrations above 11.3 g/m in drinking water can be harmful to human health.

Nitrate contamination is not a major problem in Marlborough aquifers, but historically there have been localised hotspots west of Renwick, at Rārangi, Lower Fairhall/Brancott Valley, Doctors Creek; and associated with the Wairau Fault in the Lower Waihopai Valley.