Total nitrogen concentrations in New Zealand rivers

Total nitrogen is the sum of all nitrogen forms found in a river water sample, including organic nitrogen from living and dead organic material

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 2)

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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. Too much total nitrogen can lead to excessive growth of algae.

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 354 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.