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Methods - How we monitor

Where and how we collect the data

We do routine monitoring of river water quality under two main programmes. This monitoring provides information on the condition of the water so that we can assess its suitability for desired uses (for example, supporting healthy ecosystems, human recreation). The programmes are:

  1. Waikato River monitoring programme
  2. Regional rivers monitoring programme (which covers rivers throughout the region, other than the Waikato River).

Monitoring sites

We have 10 sites on the Waikato River and 105 sites on other rivers and streams (including three NIWA sites).

Sites are grouped into two river reaches (upper and lower reaches of the Waikato River) and seven zones.

Table 1: Water quality monitoring river reaches and zones

River reaches and zones Number of sites
Upper Waikato River 5
Lower Waikato River 5
Coromandel 11
Hauraki 13
Inflows to Lake Taupō 13
Upland tributaries of the Waikato River 12
Lowland tributaries of the Waikato River 26
Waipa River and tributaries 16
West Coast 14
Total 115

Monitoring frequency

Each site is visited at monthly intervals.

Monitoring history

The Waikato Regional Council began monitoring sites on the Waikato River between 1980 and 1987. The regional rivers programme started monitoring between 1993 and 1994.

Measurement technique

Water quality is measured by taking some measurements on site (for example, water temperature and water clarity) and taking samples of water back to the laboratory for analysis. More than 20 water quality variables are measured, including:

  1. physical variables (for example, temperature, pH, turbidity)
  2. chemical variables (for example, dissolved oxygen, arsenic, nitrogen and phosphorus)
  3. microbiological variables (for example, faecal coliforms, Escherichia coli).

How this indicator is compiled

Three categories of water quality for ecological health were developed: excellent, satisfactory and unsatisfactory. These were based on ‘critical values’ for seven water quality variables we identified as relevant to the suitability of river water for ecological health:

  1. dissolved oxygen
  2. pH
  3. turbidity
  4. ammonia
  5. temperature
  6. total phosphorus
  7. total nitrogen.

Check out the table below for critical values for the three categories that were derived from national or other standards and guidelines, and from expert opinion.

At each monitoring site, the proportions of all samples collected during 2014-2018 for a given water quality variable which met the standard for excellent water quality were determined. Similarly the proportions which met the standard for satisfactory and unsatisfactory water quality were determined. This process was undertaken for all seven variables.

At each site, the average value of the proportions found to be ‘excellent’ for each of the seven variables was calculated. Average proportions for the ‘satisfactory’ and ‘unsatisfactory’ categories were also calculated.

The results for the individual sites were then aggregated according to site location. Results from the Waikato River sites upstream of Lake Karapiro were aggregated into an ‘Upper River’ result, while the other sites were aggregated into a ‘Lower River’ result. The results for the other sites were aggregated into seven ‘water zones’.

Guidelines and standards

The table below lists the water quality guidelines and standards used.

Table 2: Guidelines and standards used to assess water quality for ecological health

Water quality variable (units) Relevance   Categories  
    Excellent Satisfactory Unsatisfactory
Dissolved oxygen (% of saturation) Oxygen for aquatic animals to breathe >90 80–90 <80
pH (acidity) Can affect plants and fish 7–8 6.5–7 or 8–9 <6.5 or >9
Turbidity (NTU) Can restrict plant growth <2 2–5 >5
Ammonia (g N/m3) Toxic to fish <0.1 0.1–0.88 >0.88
Temperature (°C) Fish spawning May-Sep <10 10–12 >12
  Fish health Oct-Apr <16 16–20 >20
Total phosphorus (g/m3) Causes nuisance plant growth <0.01 0.01–0.04 >0.04
Total nitrogen (g/m3) Causes nuisance plant growth <0.1 0.1–0.5 >0.5

Limitations

The aggregation of river water quality data within a zone or reach ignores any differences between the sites in a given zone or reach.

Quality control procedures

Tulagi, A. 2017. Waikato River Water Quality Monitoring Programme: Data Report 2016. Waikato Regional Council Technical Report 2017/14. Waikato Regional Council, Hamilton.