Opinion: Measurable limits on nitrogen and phosphorus a must to protect waterways ecology

Waterways action: Waterways such as the Otautu Estuary Whangamata are popular for recreation and tourism. Photo / Supplied

In a recent survey 80 per cent of New Zealanders expressed concern about the declining state of our rivers, lakes, and wetlands.

It is no surprise that there has been a lot of interest in the Government's package of reform for our waterways.

It's a mixed bag. Most welcome is that here will be a cap on the input of nitrogen fertiliser to farms although the limit set is weak. Farmers will have to fence off waterways and adopt targeted farm environment plans. There will be a streamlined planning process and specialist freshwater panels that include regional council and tangata whenua appointees.

National models for 2013-17 estimated that 85 per cent of rivers in pasture-dominated catchment, which make up half of the country's waterways measured by length, exceeded nitrate level guidelines.

A quarter of nitrate–nitrogen leaching by livestock in New Zealand is in the Waikato, so it is a huge problem in our region.

If too much nitrogen enters waterways by leaching through the soil, algae can grow in large amounts. This triggers a cascade of problems and fuels toxic blooms, such as we saw on the Hauraki Plains this summer when thousands of fish and birds were killed.

So, it was a big disappointment that central government has deferred or ignored the majority of scientific advice which recommended the introduction of measurable limits on nitrogen and phosphorus to protect the ecology of our waterways.

Public health medical professionals strongly supported a low measurable limit for nitrogen pollution because of concerns for drinking water quality and human health especially around the link to bowel cancer which is disproportionately high in parts of New Zealand with elevated nitrate levels.

Our dependence on synthetic nitrogen fertiliser is unsustainable, and it is adding to New Zealand's greenhouse gas footprint through nitrous oxide emissions. Many farmers have shown they can make more profit by reducing their use of artificial fertilisers and by adopting regenerative agriculture methods.

The government has kicked the nitrogen pollution problem to touch for 12 months for a further review. To protect the health of our waterways and human health ultimately the science must prevail, just as it has done so successfully in our health response to the Covid 19 crisis.