Nitrate, ammonia and dissolved reactive phosphorus concentrations, NGMP sites, 2004–13

Source:
GNS Science

Method:
"Nitrogen concentration in groundwater is measured by taking a sample of water from a well, which is then sent to a laboratory for chemical analysis.
Nitrate is measured and reported as the elemental nitrogen equivalent, described as nitrate–nitrogen, or NO3–N. Concentrations of nitrate–nitrogen above 11.3 g/m3 can affect whether groundwater can be safely used for drinking water supply (Ministry of Health, 2008). Nitrate–nitrogen is also a plant nutrient which can contribute to excessive plant and algae growth, damaging the ecological health of rivers and lakes, if it enters surface water.
Ammoniacal nitrogen includes readily available forms of ammonia and ammonium. These are collectively reported as the elemental nitrogen equivalent; ammoniacal nitrogen, or NH4–N.

Dissolved reactive phosphorus concentration in groundwater is measured by taking a sample of water from a well, which is then sent to a laboratory for chemical analysis. The laboratory detection limit for DRP was either 0.004 g/m3 or 0.002 g/m3, depending on the site or laboratory used.
GNS Science manages a National Groundwater Monitoring Programme (NGMP). This involves quarterly sampling by regional council staff of over 100 groundwater monitoring sites around New Zealand.
Many of these sites monitored are for non–potable uses (e.g. irrigation and stock drinking water).
Sources of nitrogen include animal urine, sewage discharges, leaking septic tanks, dairy effluent and fertilizers.
The form that the nitrogen takes in the groundwater is influenced by the amount of oxygen available in the aquifer (underground water bearing rock or sediment). Aquifers rich in oxygen, often those which are shallow and have young water, store nitrogen as nitrate (NO3). Aquifers with low oxygen concentrations instead store nitrogen as ammoniacal nitrogen (NH4–N).


The accuracy of the data source is of high quality.



Reference:

Ministry of Health (2008). Drinking–water standards for New Zealand 2005 (revised 2008). Available from www.health.govt.nz."