National water quality trends show macroinvertebrates are under pressure

Land, Air, Water Aotearoa (LAWA) has analysed and released 10-year trends for river macroinvertebrates for the first time and the results are publicly available on the LAWA website. The Macroinvertebrate Community Index (MCI) is an important biological indicator of freshwater quality and this year joins the eight other water quality parameters LAWA reports on annually, to produce the National River Water Quality 10-year Trend Summary (2008 – 2017). 

LAWA River Water Quality Lead Dr Tim Davie said the 10-year trends released today show the complexity of freshwater ecosystems.

“Looking at the trends, we see a mixed bag of improving and degrading sites across all water quality parameters. At the national level, for every parameter there are more sites showing signs of getting better than getting worse, except for the MCI trend which shows 2 out of 5 monitored sites are likely or very likely degrading,” said Dr Davie.

The MCI is used by scientists to monitor changes in macroinvertebrate populations because macroinvertebrates are responsive to multiple environmental changes such as flow, habitat, temperature, water quality and sediment. Macroinvertebrates are small animals (e.g. insects, worms, and snails) that live on or just below the stream-bed and are an important food source for fish.

“Macroinvertebrates are a good indicator of the wider health of waterways and have a high ecological value, so it’s disappointing to see they’re under pressure. 

“On the other hand, it’s positive to see improving trends for the eight chemical-physical water quality indicators as we know these are quicker to respond to change. It is particularly encouraging to see ammoniacal nitrogen improving at many sites given the work of councils in reducing point source discharge and farmers keeping stock out of waterways,” said Dr Davie.

LAWA Chair Stephen Woodhead hopes that by making this information freely available online, more New Zealanders will get involved with freshwater management and support efforts to improve the health of waterways. 

“We know from previous research that MCI is affected by human activity. Therefore, it’s important we keep focused on reducing our impact on waterways. This summer, LAWA will be sharing ways we can all do our bit to reduce run-off and improve river water quality. 

“In the meantime, we’ve made it easier for people to see at a glance if water quality is improving or degrading at their local rivers with an interactive map on the LAWA website showing thousands of water quality trends for sites across New Zealand,” said Mr Woodhead.

New Zealanders interested in river water quality can explore river trends and/or state across all nine water quality parameters using the map on www.LAWA.org.nz.

Cawthron Institute led the analysis and Cawthron Freshwater Ecologist Katharina Doehring said, “As the LAWA project continues to grow and innovate, so does our data analysis. This time, we’ve widened our reporting to produce 10-year trends for MCI alongside the other eight water quality parameters we report on.

“Producing the trends is a big team effort. The final dataset has close to a million data cases from river sites that are monitored by New Zealand’s 16 regional and unitary councils and the NIWA National River Water Quality Network,” said Mrs Doehring.

Regional councils are responsible for monitoring water quality in New Zealand and Chair of Local Government New Zealand Regional Sector Doug Leeder acknowledged the work of council science teams.

“There are hundreds of water quality scientists in the regional sector, working every day to ensure reliable monitoring, research, and implementation of solutions.

“I also want to recognise the efforts of iwi, farmers, businesses, and communities who work with our teams to help improve the quality of our freshwater. The trends released today show we’re not there yet, and our sustained, collective focus is required,” said Mr Leeder.

The parameters that LAWA has evaluated trends for are widely recognised indicators of water quality and include water clarityturbidityE. colitotal nitrogen (TN)total oxidised nitrogenammoniacal nitrogendissolved reactive phosphorus,  total phosphorus, and the Macroinvertebrate Community Index

Trend methodology evolves over time and this year the LAWA team adopted a new well-regarded trend evaluation method developed by Graham McBride (NIWA), and coded by Dr Ton Snelder and Caroline Fraser (LandWaterPeople).

LAWA is a collaboration between New Zealand’s 16 regional and unitary councils, Cawthron Institute, and the Ministry for the Environment.