Groundwater nitrate-nitrogen concentrations
A key indicator of groundwater contamination typically arising from land use intensification and/or on-site wastewater disposal systems. Nitrate-nitrogen in groundwater can affect its quality for drinking-water supply. See the LAWA factsheet for more information.
Usage guide: switch tabs to look at different variables – drag and scroll on the map to move and zoom in on areas of interest – click on a site circle to see more information and subset the table below to that specific site – use the selection box on the map ( ) to subset table data to sites in that area.
Human health
Groundwater nitrate-nitrogen concentrations are evaluated below in terms of likely human influence, as excess concentrations can have negative health effects.
- A threshold of 3 mg/L has been adopted as a means of defining nitrate contamination from anthropogenic sources (Close et al. 2001);
- ‘Elevated’ nitrate-nitrogen concentrations are above 3 mg/L;
- ‘Highly elevated’ threshold was arbitrarily set at >7 mg/L, approximately mid-way between the ‘elevated’ threshold and the Drinking Water Standard New Zealand (DWSNZ) Maximum Acceptable Value (MAV) of 11.3 mg/L.
All calculations use nitrate-nitrogen (mg/L). Click on the +/- button at the end of a row to see the raw sample data and highlight that site on the map above. Click on a table header or the arrows ( ↓↑ ) next to it to sort the data by that column.
Ecosystem health
Groundwater discharges from aquifers into a number of surface water bodies throughout the region and there is the potential that groundwater high in nitrate-nitrogen could contribute to the decline of surface water quality.
The 2000 Australia New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC) define default guideline values (DGVs) for the 80th percentile of nitrate-nitrogen based on second-level River Environment Classification (REC) class reference conditions.
Groundwater within Connectivity Category A (direct) that has 80th percentile nitrate-nitrogen concentrations above the guideline is the highest risk to ecosystem health in the surface water system. See groundwater connectivity for more information on surface water connectivity categories.
All calculations use nitrate-nitrogen (mg/L). Click on the +/- button at the end of a row to see the raw sample data and highlight that site on the map above. Click on a table header or the arrows ( ↓↑ ) next to it to sort the data by that column.
Aquatic toxicity
The National Policy Statement on Freshwater Management (NPS-FM) requires regional councils to identify water quality limits to manage values of our aquatic ecosystems.
The nitrate toxicity (NT) threshold is calculated at 2.4 mg/L for annual median nitrate-nitrogen concentrations. This is within the guideline described by Hickey, 2013 as ‘Chronic - slightly to moderately disturbed systems (95% protection)’. Freshwater water systems connected to groundwater above this threshold are deemed unsafe for aquatic life.
Groundwater within Connectivity Category A (direct) that has median annual nitrate-nitrogen concentrations above the guideline is the highest risk to aquatic life in the surface water system. See groundwater connectivity for more information on surface water connectivity categories.
All calculations use nitrate-nitrogen (mg/L). Click on the +/- button at the end of a row to see the raw sample data and highlight that site on the map above. Click on a table header or the arrows ( ↓↑ ) next to it to sort the data by that column.
