Nitrates 'still increasing' in three-quarters of Canterbury's groundwater bores

Friday, 8 April 2022

A new analysis of long-term trends for Canterbury’s groundwater has found nitrate levels are still increasing in three-quarters of bores tested – and measures to reverse the decline in water quality are yet to pay off.

Environment Canterbury (ECan) staff found that despite many years of work to find ways to reverse increasing nitrate concentrations in groundwater, there had been “no clear reversal of the trends”.

ECan runs rolling 10-year analyses of groundwater quality, but the new data covers 30 years and paints a broader picture of water quality decline.

Over the past decade, nitrate levels were ‘likely’ or ‘very likely’ increasing in 51 per cent of the wells tested, and showed a decrease in only 24 per cent.

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When 30 years of data was analysed, 73 per cent of wells tested showed increasing nitrate levels, while only 12 per cent showed an improvement.

In most cases, the report said it took five to 10 years to see improvements after land use changed.

“If widespread changes to land use management have been happening around the region over the past five to 10 years, we would expect to be seeing some improvements in groundwater quality, even if the full effects of the changes might take decades to come through.

“The fact that we haven’t seen these improvements suggests that either the changes have not been enough to bring about widespread changes in groundwater quality, or they have not yet been fully implemented.”

The paper also showed nitrates in Canterbury’s groundwater were a long-term problem, with levels increasing “since farming began in the region”.

“Even by the 1970s [and] 1980s, concentrations were well above natural levels.”

The earliest picture the regional council had of nitrate-nitrogen concentrations in Canterbury’s groundwater came from the period between 1975 and 1984.

Many of the concentrations found were low, but some wells had concentrations above 11.3 mg/L, the maximum limit set out in New Zealand’s drinking-water standards.

The report showed that in 1992, just one per cent of wells measured had nitrate levels over 11.3mg/L. But by 2021, eight per cent failed to meet drinking-water standards.

Councillor Lan Pham – also a freshwater ecologist – said using 10-year data sets, which is generally the standard for regional council reporting, tended to mask the real extent of pollution.

This could lead to an inaccurate picture of the scale of damage done, she said, while using 30 years “fool-proofs” the data from shifting baselines.

Pham said she was lost for words to see “evidence this bleak”.

“I think we should be shocked and ashamed by these results. It's clearly documenting the fact that over the last few decades our rules and regulations have failed to protect our precious freshwater ecosystems.”

The report highlighted just how urgent new freshwater legislation was to give effect to Te Mana o Te Wai – or the concept the health and wellbeing of water has legal primacy above economic needs – she said.

ECan is currently working on a three-year, $20 million programme to design an integrated “mountains to sea” planning framework to address this, alongside Ngāi Tahu partners.

“I'd love to think damning reports like this will be a relic of our past, and I guess my hope is that we're at a turning point,” Pham said.

“A future that protects and regenerates our environment first is the only way forward if we are serious about giving younger and future generations a shot at a liveable future.”

Forest & Bird freshwater advocate Tom Kay said the new data reinforced what they had known for a long time.

“Intensive agriculture has destroyed the health of our rivers, lakes, and aquifers in Canterbury. It builds on a pile of other reports that have effectively concluded the same thing – things are getting worse.

“There are too many cows. We’re using too much fertiliser. We have to stop. Animal agriculture is not our future – at least not like this.”

Canterbury’s groundwater systems are connected to its rivers, Kay said, and freshwater ecosystems suffer when nitrate levels rise above 1.0 mg/L.

There is evidence human health is also affected.

Levels as low as 0.87 mg/L were linked to increased bowel cancer risk in a major Danish study published in 2018, and last year two new studies linked nitrates in drinking water with pre-term births.

“I can’t help but hear the words of the UN Secretary General again and again when I see more reports like this about nature – we’re digging our own graves.

“Climate change is going to make water issues much more pronounced, so [we] need to make big changes now to reduce nitrogen pollution.”

North Canterbury Federated Farmers president Caroline Amyes said a lot of work was being done in the region to optimise irrigation efficiency, apply fertiliser in the right amounts, and to fence off waterways and plant them out.

But she said it was a complex challenge and the sector was looking for more tools to deal with it.

She said there was exciting research that would “give us more tools in the toolbox”.

Amyes said she would be interested to know the location of sites where groundwater was improving. “We could learn off that and then hopefully replicate that in other places.

“We all want good quality water,” she said.

ECan is currently in the process of developing analysis tools and data-viewers to better share long-term surface water trends.

Those tools are nearly complete, and will be presented to the natural environment committee at its next meeting on May 18.

- Additional reporting by Steven Walton.