20 years of monitoring provides insight into New Zealand`s river water quality

Two decades of monitoring of river water quality by NIWA has provided important information that is helping to care for New Zealand’s iconic rivers. More than 18 000 river water samples have been collected by New Zealand’s National Rivers Water Quality Network (NRWQN) over the past 20 years to monitor river conditions. The Network, which was set up to detect trends and conditions in water quality, as well as providing advice to government on the management of water resources, is now celebrating its 20th birthday.

Every month since 1989, NIWA field staff have visited 77 sites, (mostly upstream and downstream), on 35 of New Zealand’s larger rivers to take measurements and collect samples for assessing water quality. This complements monitoring on smaller waterways carried out by regional authorities.

Our staff measure the dissolved oxygen concentration in the water, its temperature, and visual clarity while on site. They also assess the algae growing on the river bed (known as ‘periphyton’).

A sample of water is collected for laboratory analysis of pH, salt content, water cloudiness, coloured dissolved organic matter, nitrogen, and phosphorus. A separate sample is tested for E. coli (a bacterium that is usually harmless, but indicates faecal contamination).

The monitoring shows:

  • overall New Zealand’s river water quality is in good condition by international standards, especially rivers in native forest and high country areas
  • however rivers running through pastoral areas are degraded by nutrient enrichment, fine sediment reducing visual clarity, and contamination by faecal microbes.

The microbial pollution is of particular concern for reducing suitability of our rivers for swimming.

Trend analysis also shows that pollution of New Zealand rivers from point sources (such as discharges of wastewater from towns and industries) has reduced appreciably since the late 1980s.

However, nitrogen and phosphorus levels have increased at many sites due largely to ‘diffuse pollution’ from pastoral farming – with increased stocking rates and use of fertilisers, and conversion of land used for sheep/beef farming to dairy or deer farms.

Dr Rob Davies-Colley, Principal Scientist, Aquatic Pollution, NIWA, says the NRWQN has been crucial for calibrating models for predicting how future land uses and climate might affect water quality.

“We’re pleased the NRWQN has been useful for a wide range of other scientific research. For example we have used the Network to measure carbon travelling down New Zealand rivers – and found that this flow to the sea of carbon, coming ultimately from soils, is the equivalent of about 40% of New Zealand’s fossil fuel carbon emissions. We’ve also recently combined river quality data with satellite images of coastal areas to track river plumes. These can affect coastal water quality and could impact on marine reefs and shellfish aquaculture,” Dr Davies-Colley says.

Data collected over the last 20 years has also provided important information that is helping the Government agencies manage and protect New Zealand rivers.

Mike Thompson, senior adviser at the Ministry for the Environment (MfE) describes the NRWQN as one of the “cornerstones” of the Ministry’s freshwater State of the Environment reporting programme.

“The coverage, continuity and consistency of the NRWQN monitoring is unique in New Zealand, and invaluable for national reporting purposes. It allows us to determine with confidence the quality of water in our larger rivers, and how they are changing over time.”

“While the monitoring of these rivers does not tell us everything about the health of our waterways, it gives us the best collective indication of the pollution impacts of land use on river water quality at a national scale. This information is crucial to help understand how widespread pollution problems are and what management actions are needed.”

The monitoring has also increased scientific knowledge of New Zealand river ecosystems and assisted in environmental work, here and overseas.

New Zealand has about 425 000 kilometres of rivers and streams, which are highly valued for recreational activities such as swimming and boating, and provide essential services such as drinking water supply, irrigation, and hydro-electricity.

The NRWQN is mainly funded by the New Zealand Foundation for Research, Science and Technology (FRST), and operated by the National Institute for Water & Atmospheric Research (NIWA).

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