National River Water Quality Network (NRWQN)
The National River Water Quality Network (NRWQN) is New Zealand’s most comprehensive freshwater quality monitoring network.
The NRWQN is operated by NIWA. Monitoring commenced in January 1989. The NRWQN provides reliable scientific information on many important physical, chemical, and biological characteristics of a selection of the nation’s river waters.
The NRWQN consists of 77 sites on 35 rivers that are fairly evenly distributed over the two main islands of New Zealand. The sites and variables measured were carefully selected after reviews of networks in other countries and consideration of their relevance to New Zealand.
The NRWQN river catchments together drain about one half of New Zealands total land area. The catchments (of fairly large rivers) within the NRWQN are somewhat weighted towards the uplands. Therefore, the data from the NRWQN is usefully augmented by a study, published by Larned et al. (2004), specifically of lowland rivers in NZ - which have generally lower water quality. Collectively, these data provide an integrated picture of the nations water quality."
Sites were selected so that a national perspective of state and trends of water quality could be developed. On most rivers there are two or more sites representing an upstream ‘Baseline’ site (lightly impacted) and a downstream ‘Impact’ site (reflecting the impacts of humans on water quality).
The NRWQN sites are coded, denoting the locations of the 14 NIWA field stations where staff who do the water sampling are based.
Water samples are collected monthly and analysed for a range of physical and chemical variables (see 'What do we measure?', above). Periphyton is also assessed monthly. In addition, benthic invertebrate samples are collected on an annual basis (see 'Benthic biology', above).
The NRWQN is noteworthy internationally for its stability throughout its history. There have been essentially no changes to monitoring sites and methods of measurement.
Data generated from this network have many applications (see 'Applications', above).
1 In terms of length of record, data quality and assurance, range of variables, continuity, national coverage and data availability, since only one agency is responsible for data collection and management.