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

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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

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