If you want to find out more about phosphorus, have a look at the phosphorus factsheet.
TP concentrations across the whole country are estimated using models, which are based on data collected from hundreds of monitoring sites over a five year period to 2012. View a factsheet on how the national picture current state is calculated.
TP concentrations vary across the country, as shown in the map below. Higher total phosphorus concentrations are widespread in the mid- to upper-North Island. In the South Island, the monitoring data indicates higher total phosphorus concentrations exist at sites along the east coast and southern parts of the Island:
The modelled total phosphorus results for four different land-cover classes. The data shows that the rivers that drain urban land use have five times the level of phosphorus than a typical reach draining predominantly indigenous land-cover.below shows the
Rivers draining pastoral land use have 3.5 times, and rivers that have their catchment in erosion, combined with a range of land-use types and intensities associated with different farming practises:, 2.5 times the levels of those in catchments associated with predominantly indigenous land-cover. Rivers and streams draining pasture catchments have the widest range of concentrations (which is shown by the ‘whiskers’ of the pasture box-plot), ranging from the highest in the country to some of the lowest. This might be due to different soil types, different levels of
Overall, improving trends were detected at 30% of monitoring sites, outweighing those that show a deteriorating trend (10%), across all land-cover types. This may reflect improving environmental management practices, such as wastewater treatment andplanting.
The graph below shows that total phosphorus concentrations improved in urban river sites (i.e. TP concentrations decreased). Urban rivers make up less than 1% of the total length of rivers nationwide, indicated graphically by the small size of the column in the graph below. For all other land covers, total phosphorus concentrations showed no evidence of a trend, or decreased (i.e., an improving water quality trend). It is interesting to see that although total phosphorus levels mostly improved in indigenous vegetation, there were also a small proportion of monitoring sites that showed a deteriorating trend (i.e., phosphorus levels increased).
View a factsheet on how national trends are calculated.