What do we measure?
Water quality variables measured
A range of physical and chemical variables are measured in the NRWQN, covering four main categories:
Physico - chemical variables: dissolved oxygen, temperature, pH, conductivity
Optical variables: Visual clarity, turbidity, coloured dissolved organic matter
Nutrients: Total and dissolved forms of nitrogen and phosphorus
Microbial Indicator: E. coli (since 2005).
In addition, we also measure several biological indicators of water quality, specifically macroinvertebrates and periphyton. Dissolved oxygen, temperature and visual clarity are collected directly while in the field. Water samples are obtained from each site and freighted by overnight courier to the NIWA laboratory in Hamilton, where the remaining water quality variables are measured.
Flow at NRWQN sites
All NRWQN sites are located at, or close to, hydrometric stations from which flow is estimated for each sampling visit. These sites are managed by a variety of agencies.
Flow is crucial for interpreting river water quality. For example, data are routinely ‘flow-adjusted’ for trend analysis using the trend calculator.
Flow is also needed for estimating rates of delivery of materials (such as phosphorus) that are transported to the sea in river waters. Delivery rate in kg/s is calculated by multiplying concentration by flow.