Nitrate-nitrogen concentrations in New Zealand rivers

The term "nitrate nitrogen" is used to refer to the nitrogen present which is combined in the nitrate ion. This nomenclature is used to differentiate nitrate nitrogen from nitrogen in the form of ammonia (ammonia nitrogen), from nitrogen in the form of nitrite (nitrite nitrogen), etc.
It is highly soluble (dissolves in water) and can be readily used by plants and algae to help grow

Figure.NZ calculated the median, upper quartile, lower quartile, min and max clarity measures by land cover class. These calculations were undertaken to mirror the analysis undertaken for the Environmental Reporting Series (see http://stats.govt.nz/browse_for_stats/environment/environmental-reporting-series/environmental-indicators/Home/Fresh%20water/river-water-quality-nitrogen.aspx Figure 1)

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Small amounts of nitrogen are a natural component of healthy rivers. Nitrogen in rivers can vary due to differences in land use, climate, elevation, and geology. Nitrogen is transferred from land to water and is cycled through different forms, which can have different effects. Moderate concentrations of nitrate can cause weeds and algae to grow too fast. High concentrations of ammoniacal and nitrate nitrogen can be toxic to fish and other aquatic animals.

Regional councils monitor river water quality to manage environmental impacts. These sites tend to be in catchments dominated by agricultural land use. Rivers in low-lying and hilly areas in the North and South islands are well represented, while mountainous areas in the South Island and parts of the central North Island are not. For the analysis presented here, NIWA used nitrogen data from 587 sites monitored by them and regional councils with consistent time periods and comparable methods (Larned et al, 2015).

Sites are classified by dominant land cover in the upstream catchment. Lower values for nitrate-nitrogen concentration are better than higher values.