Dissolved reactive phosphorus

Dissolved reactive phosphorus (DRP) is the amount of phosphorus dissolved in water and is most immediately and readily absorbable for plant and algae growth. It is one component of total phosphorus (TP), the other being phosphate that is stuck to sediment and is therefore unavailable for plants.

Current national state

Current water quality across the whole country is estimated using models, which are based on data collected from hundreds of monitoring sites over a five year period to 2012.

Modelling and site data indicate that higher DRP concentrations generally occur in the Waikato, through parts of the Hawke's Bay and the Manawatu regions and in Southland.

Average dissolved reactive phosphorus concentrations

Site Data

This map provides the site locations and value of the monitoring data, which was used to train the model.

Modelled Data

The map illustrates the modelled condition across the country from highest to lowest. The dots indicate the site location and value of the monitoring data, which was used to train the model.

Comparison Data

The map shows a comparison between modelled concentrations and actual monitoring site data. Symbols show where the site data was substantially (50%) better than the model predicts, or substantially (50%) worse.

Modelled national DRP concentrations for four different land-cover classes

The box plot below shows the modelled dissolved reactive phosphorus concentrations for four different land-cover classes.

Modelling predicts that median DRP concentrations in rivers draining urban, pasture and exotic forest land covers are 2-3 times higher than those draining catchments with predominately indigenous land-cover.

Rivers and streams draining pasture catchments have the widest range of concentrations, ranging from the highest in the country to some of the lowest. Such variability might be due to high variability in erosion, combined with a wide range of different pastoral farming practices and intensities.

Modelled national dissolved reactive phosphorus concentrations for four different land cover classes 

DRP State Boxplot

What is the trigger value? 
What is this type of graph? 

Recent national trends

Overall, across all land cover types, the number of monitoring sites where improving dissolved reactive phosphorus trends (DRP) were detected (40%) outweighed those that showed a deteriorating trend (11%). Because this pattern occurred over all land covers, it may be due to factors unrelated to management such as long term climate variation.

Percentage of river length nationwide with significant trends in DRP concentrations across four land-cover classes

DRP concentrations across land cover classes

What is this type of graph?

See also:

– Other nutrients: Total phosphorus and nitrate-nitrogen
Benthic macroinvertebrates
Faecal indicators (E. coli)