State and Trends in the National River Water Quality Network (1989-2005)

• Executive Summary
• 1 Introduction
• 2 The National River Water Quality Network
• 3 Water Quality State (2005)
• 4 Changes in Water Quality State (1989-2005)
• 5 River Water Quality Trends (1989-2003)
• 6 Discussion
• 7 References

2 The National River Water Quality Network

The New Zealand National River Water Quality Network (NRWQN) commenced operation at the beginning of 1989, following an agreed design (Smith et al 1989; Smith and McBride 1990). The network design nominated two objectives: (i) to detect significant trends in water quality, and (ii) develop better understandings of the nature of the water resources and hence to better assist their management.

The Network includes 77 sites (Figure 1.1) distributed throughout the North Island (44 sites) and South Island (33 sites) at which river flow is measured continuously and 14 physical/ chemical parameters are measured monthly.

According to criteria given by Smith and McBride (1990), sites were selected to reflect both baseline conditions (32 upstream sites) and impact conditions (45 downstream sites). Where possible, sites were selected to have median flow >1 m³/s. Field work is carried out by NIWA's 14 regional hydrometric field teams; the first two letters of each site descriptor (see Figure 1.1) being taken from the location of the field party, eg, RO for a Rotorua party's site, GY for a Greymouth site. (There were originally 15 teams - GS is now amalgamated with HV.) Laboratory analyses are performed at NIWA's Hamilton laboratory.

At an individual site, sampling on each occasion is generally at the same time of day to remove the variance-inflation attributable to diurnal variability. Flow is measured or estimated on each sampling occasion. Other field measurements include dissolved oxygen (measured as percentage of saturation; % DO), temperature, and visual clarity (measured by horizontal black disc visibility). In the laboratory pH, conductivity, biochemical oxygen demand (five-day test with no inhibition for nitrification; hereafter BOD₅), oxidized-N (ie, NO_x-N = NO₂-N + NO₃-N), ammoniacal-N (ie, NH₄-N = NH₄+-N + NH₃-N), total N (TN), dissolved reactive P (DRP) and total P (TP) are measured. Analytical methods remained the same over the study period (January 1989-December 2005). See Smith and McBride (1990) for further details. Measurement of levels of E. coli, a faecal indicator bacteria, began in 2005.

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