In 1988, a national survey of nitrate contamination of groundwater found some of the highest nitrate concentrations in parts of the Waikato region1.
Nitrate moves down into groundwater from land use activities at the surface. Concentrations are generally highest in shallow, vulnerable aquifers and lowest in very deep or iron-rich waters.
Nitrate is the most widespread contaminant in groundwater. Nitrate is an environmental and health indicator of land use affects as excessive nitrate is a concern for both human health and the environment.
Excessive nitrate concentrations are linked to a blood disorder in bottle-fed babies known as ‘blue baby syndrome’ (methaemoglobinaemia). Nitrate seepage from groundwater into streams and lakes can also result in nutrient enrichment of these waterways and coastal waters.
Elevated nitrate concentrations typically indicate pollution from land use activities such as applying farm dairy effluent to land, use of nitrogen fertilisers, waste and domestic sewage disposal.
High nitrate concentrations are also a concern because of potential barriers to market access with trading nations.
This indicator measures nitrate concentrations in the Waikato region’s groundwater supplies. Waikato Regional Council collects groundwater information from two monitoring networks. We use this information to tell us about the quality of the region’s groundwater supplies for human and environmental health.
In our region, higher nitrate concentrations are generally found in areas of market gardening (such as Pukekohe) and intensive dairy farming (such as Hamilton). In the Hauraki Plains there is a general trend of decreasing nitrate concentration northward with progressively low-lying, finer and peaty sediments. This is associated with a change from recharge to discharge flow regimes and reducing groundwater conditions such as lower redox.
We have few records to indicate long-term nitrate trends, but long-term information from some schools supplies (since 1950s) indicates a steady increase in nitrate at these sites. Pressures on groundwater quality are generally increasing as land-use intensifies. The total volume of wastewater consented to discharge to land has increased steadily. In 1997 the total volume was 540,000 m3 d-1.
Geological and Nuclear Sciences – groundwater and geothermal database (external link)
You can order any of these documents from our library. Most documents will incur a charge.
Bird, G.A. 1987: A study of the groundwater resources of the Tokoroa region. Waikato Valley Authority Technical Publication No. 47, ISSN 01107615.
Hadfield, J.C. 1993: Groundwater Chemistry of the Piako Catchment, Hauraki Plains. Environment Waikato Technical Report 1993/7, Environment Waikato, Hamilton.
Hadfield, J.C. and Nicole, D. 2000: School and Community Groundwater Supply Protection. Environment Waikato Technical Report 2000/10, Environment Waikato, Hamilton.
Marshall, T.W. 1986: Groundwater Quality Characteristics of the Mangaonua-Mangaone Catchments. Waikato Valley Authority Technical Report 86/2, Environment Waikato, Hamilton.
Eco-Link Ltd. 2000: Sustainable Resource Management: agriculture and forestry - implications of groundwater nitrate standards for agricultural management. Prepared for Ministry of Agriculture and Forestry Policy. Technical Paper 2000/15.
Ringham, K.L.; Cochrane, P.R. and Petch, R.A. 1990:Groundwater Chemistry of the Northern Waikato District. Waikato Regional Council Technical Report 1990/5, Environment Waikato, Hamilton.
Environment Waikato. 1998: Waikato State of Environment Report 1998. Environment Waikato, Hamilton.
The nitrate indicator is updated every two years. It will next be updated in 2017.
Hydrogeologist - Science and Strategy Directorate
Rosen, M. R., S. G. Cameron, C. B. Taylor and R. R. Reeves. 1999: New Zealand Guidelines for the Collection of Ground Water Samples for Chemical and Isotopic Analyses. The Institute of Geological and Nuclear Sciences. Lower Hutt. 1999/9.
Updated June 2015