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Figure 10.4: Comparison of median nutrient levels in rivers and streams by catchment land use, 1997–2002

Return to the point in the document where this figure is located.

Nitrate Nitrogen

 

Dissolved Reactive Phosphorus

Ammoniacal Nitrogen

Notes:

(1) River environments have been defined using the River Environment Classification (see chapter 1, ‘Environmental reporting’). Catchments are defined as ‘natural’ unless pasture exceeds 25 per cent of the catchment area (in which case, it is classed as ‘pastoral’), or unless urban land use exceeds 15 per cent of the catchment area (in which case, it is classed as ‘urban’).

(2) The Australia and New Zealand Environment Committee Council guidelines provide ‘trigger values’ for the protection of ecosystems and the recreational and aesthetic values of waterways (Australia and New Zealand Environment Committee Council, 2000). If a trigger value is reached, it does not necessarily mean that ecosystem damage is occurring or that recreation is no longer possible, but it provides advance warning that a problem may be emerging.

(3) mg/L = milligrams per litre.

Data source: Adapted from Ministry for the Environment, in press a.

Text description of figure

Figure showing (1) map of all rivers in New Zealand (that appear on a 1:50,000 topographic map) colour-coded according to whether they are in catchments dominated by natural, pastoral or urban land use/cover, and (2) graphs of median nutrient trends across the network. 

Key message from the graphs is that medians for dissolved reactive phosphorus, nitrate-nitrogen and ammoniacal nitrogen in pastoral and urban catchments are higher than natural catchments and generally exceed ANZECC guidelines.

Nitrate Nitrogen

Year

Measure

Pastoral (mg/L)

Natural (mg/L)

Urban (mg/L)

ANZECC Guideline (mg/L)
(averaged for upland and lowland sites)

1997

Median

0.335

0.0775

0.93

0.306

1998

Median

0.31

0.08

0.82

0.306

1999

Median

0.366

0.0765

1

0.306

2000

Median

0.32

0.091

0.8825

0.306

2001

Median

0.355

0.0905

0.6675

0.306

2002

Median

0.394

0.07075

0.8

0.306

Ammoniacal nitrogen

Year

Measure

Pastoral (mg/L)

Natural (mg/L)

Urban (mg/L)

ANZECC Guideline (mg/L)
(averaged for upland and lowland sites)

1997

Median

0.02

0.008

0.05

0.0155

1998

Median

0.02

0.006

0.05

0.0155

1999

Median

0.02

0.0085

0.05

0.0155

2000

Median

0.018

0.0085

0.05

0.0155

2001

Median

0.02

0.01

0.05

0.0155

2002

Median

0.02

0.0095

0.05

0.0155

Dissolved reactive phosphorus

Year

Measure

Pastoral (mg/L)

Natural (mg/L)

Urban (mg/L)

ANZECC Guideline (mg/L)
(averaged for upland and lowland sites)

1997

Median

0.015

0.01

0.02

0.0095

1998

Median

0.013

0.01

0.02

0.0095

1999

Median

0.0135

0.008

0.02

0.0095

2000

Median

0.013

0.0075

0.015

0.0095

2001

Median

0.0155

0.00675

0.015

0.0095

2002

Median

0.0145

0.006

0.01025

0.0095