Total Nitrogen, 2009–2013

Source:
National Institute of Water and Atmospheric Research; regional councils

Method:
"Nitrogen is measured in laboratories. Samples are collected from the river at fixed locations once a month, and sent to a laboratory for chemical analysis.
Estimates of median nitrogen across New Zealand is based on measurements from the 16 regional councils (277, 510, and 288 river sites for total nitrogen, nitrate nitrogen, and ammoniacal nitrogen respectively), and 77 sites along 35 major rivers measured by the National Institute of Water and Atmospheric Research (NIWA).
Nitrogen occurs as several forms in the environment. The following forms are reported:
– Total Nitrogen (TN) is the sum of all nitrogen found in a river water sample, including organic nitrogen from plant tissue.
– Nitrate is highly soluble (dissolves in water) and so can readily be used by plants and algae to help them grow. Because of this solubility it can also leach through soils very easily, particularly where soils are sandy or after heavy rainfall (McDowell et al 2008). Sources include excessive application of inorganic fertilizer, stock urine, septic tanks and leaking sewage systems. It is measured and reported as the elemental nitrogen equivalent, described as nitrate–nitrogen (NO3–N).
– Ammoniacal nitrogen can be toxic at moderate to high concentrations. Elevated quantities in waterways are primarily from direct pollutant discharges such as untreated effluent. We are unable to reliably estimate trends in ammonia concentration prior to 1995 due to a subsequent change in laboratory procedures. Ammoniacal nitrogen includes readily available forms of ammonia and ammonium. These are collectively reported as the elemental nitrogen equivalent; ammoniacal nitrogen (NH4–N).
This is inferred from the predominant land cover in a catchment and the surrounding landscape characteristics, such as, climate, elevation, and geology.
The accuracy of the data source is of medium quality.

Reference:
McDowell, RW, Houlbrooke, DJ, Muirhead, RW, Müller, K, Shepherd, M, & Cuttle, SP (2008). Grazed pastures and surface water quality. New York: Nova Science Publishers."