Freshwater life lagging behind other water quality trends

Horizons Regional Council senior water quality scientist Logan Brown was recording river data in this 2012 photograph. Photo / Laurel Stowell

The freshwater life in some Whanganui waterways has been rated and added to the total picture of waterway health this year.

Land, Water, Air Aotearoa (LAWA) has released it latest findings, an analysis of trends in water quality across New Zealand for the last 10 years. This year for the first time it scored waterways on their MCI as well as qualities like clarity, E. coli and the nature and amount of nitrogen and phosphorous.

MCI is code for Macroinvertebrate Index, a measure of the insects, insect larvae, worms, snails and crustaceans that live in healthy freshwater. They eat algae and other water plants, as well as dead leaves and wood, or each other.

In the water they provide food for native fish. When the larvae hatch they provide food for birds, bats and spiders.

These little creatures are a very good indicator of the biological health of freshwater, LAWA river water quality lead Dr Tim Davie said. They respond to changed management more slowly than chemical indicators such as the presence of nitrogen and phosphorous.

An analysis of overall trends for water quality showed that for every other measure of water quality there was more improvement than decline. MCI was the exception. It was declining or likely to decline in two out of five waterways.

The LAWA website doesn't measure MCI for every waterway.

But it shows some healthy populations of macroinvertebrates in places like the Hautapu River and the Rangitīkei at Pukeokahu and Mangaweka.

In the Whanganui the MCI was only fair at Pipiriki.

In the Ruapehu District the Makotuku - Raetihi's water source - has an excellent MCI at State Highway 49 where it leaves Tongariro National Park. By the time it gets to Raetihi its MCI is rated poor.

The Turakina River's MCI is only assessed at one place, O'Neill's Bridge, where it is rated fair.

One waterway near Whanganui stands out as needing attention. It's a small stream that enters Lake Waipu, carrying wastewater from Ratana Pā's sewage treatment plant.

The unnamed stream is in the worst 25 per cent of all rural lowland sites for E. coli, turbidity, total nitrogen, ammoniacal nitrogen and two forms of phosphorous.

Its MCI is not measured, but likely to be poor as well. In the next few years it will get attention from a $1.8 million Freshwater Improvement Fund project.

LAWA is a combined effort by 16 regional and unitary councils, the Cawthron Institute, Niwa and the Ministry for the Environment.

Its chairman, Stephen Woodhead, says it is important for people to keep focused on reducing our impact on waterways.