The Ministry for Primary Industries (MPI) opposed introducing a tough bottom line for nitrogen levels in rivers over concerns the economic impact would outweigh the environmental benefit, documents show.
MPI repeatedly clashed with the Ministry for the Environment (MfE), even though scientific experts said a Dissolved Organic Nitrogen (DIN) level of 1 mg/L was the best way to protect rivers.
Emails obtained under the Official Information Act show MPI staff wanted the economic cost of introducing a bottom line pushed more prominently in a cabinet paper about nitrogen level options put to ministers in May 2020.
It's the first time MPI's influence on the issue has been revealed.
The government eventually abandoned the idea of a DIN bottom line because its panel of experts were divided on the issue and instead adopted stronger nitrogen toxicity targets favoured by farmers.
The emails show MPI and Ministry for the Environment staff discussing what evidence should be presented in the Cabinet paper.
Despite scientific experts supporting a nitrogen bottom line, MPI officials were unconvinced.
"There is some concern that the likely negative socio-economic impact of a DIN bottom line set at 1.0mg/L could outweigh the environmental benefits," it wrote in a document about how Horowhenua and Kapiti's vegetable growing sector would be hit by such a rule.
MPI modelling also showed the stronger nitrogen toxicity targets if applied to Lake Horowhenua and Pukekohe, which are key vegetable growing areas, could only be met if there was "extensive land use change" out of vegetable production.
Vegetable prices would rise, people would have less access to fresh produce and their health could suffer, MPI warned in its analysis.
It proposed Lake Horowhenua and Pukekohe should be exempt from the nitrogen toxicity targets, which the government agreed to.
Before that decision was taken and the DIN bottom line was still being considered, an MPI staffer wrote to Environment Ministry counterparts that not enough emphasis was being given to the economic impacts if it were adopted.
"I am still very concerned we have not yet landed the impacts section in particular. Happy to discuss further with you ... and land this asap."
MPI wanted to highlight DairyNZ's modelling in the Cabinet paper, which emphasised the impact of a nitrogen bottom line on farmers, but an Environment Ministry staffer was unimpressed.
She responded: "I personally wouldn't single out DairyNZ's modelling as I think other submitters included useful modelling also."
Dairy NZ wanted the nitrogen bottom line idea abandoned in favour of a higher nitrogen toxicity level for rivers - which the government eventually did.
Another MPI staffer later wrote asking for "more discussion around the economic impact modelling".
Just before the Cabinet paper was finalised, an MPI policy analyst wrote to an Environment Ministry colleague about suggested changes.
They were "important as they even the tone and ensure Minister O'Connor's voice is throughout."
Damien O'Connor, a former farmer, is the Minister of Agriculture.
Forest and Bird spokesperson Tom Kay said the emails were disappointing and showed why more weight was given to MPI's advice in the cabinet paper over other experts.
"The correspondence clearly shows that the Freshwater Leaders' Group, Kaahui Wai Māori, the Science and Technical Advisory Group, Ministry for the Environment, and even the Regional Sector Group all recommended a nitrate bottom line.
"But MPI opposed it and that advice mattered most."
He was concerned the environmental bottom line was not the priority.
"It clearly shows that one ministry's advice is being prioritised over the advice of others, which arguably have more expertise on this subject," Kay said.
In a statement, MPI said its job was to provide advice on how policy affects the primary sector.
"MPI together with MfE gave the government advice about the trade-offs in the proposed Essential Freshwater package, including information to allow the government to weigh up the economic impacts alongside the environmental benefits."
"It's wrong to say that DairyNZ's submission was highlighted over other analysis by MPI. Rather, it was noted as a document (which is publicly available) within a large set of information considered, to ensure wide views were considered to support decision-making, including understanding impacts on farmers and communities," MPI deputy director-general of policy and trade Julie Collins said.
DairyNZ said it opposed a nitrogen bottom line because it disagreed with the science.
"We felt the evidence base for the DIN metric was not rigorous," DairyNZ strategy and investment leader for responsible dairy David Burger said.
"DairyNZ proposed an alternative nitrate toxicity measure to achieve the environmental outcomes with less economic and social disruption."
Its modelling forecast GDP would fall by $6 million annually and exports would decline 5.2 percent by 2050, with Southland, Taranaki, Marlborough and West Coast most affected.
The government's decision to drop the DIN bottom line idea surprised many.
Victoria University freshwater ecologist Mike Joy, who was on the Scientific and Technical Advisory Group, said it was a misnomer the group couldn't agree on it.
"There wasn't disagreement on the day, in the room. The disagreement happened afterwards ... when the scientists went back to their organisations, and the disagreers pretty much came from one organisation."
However, even then only five of the 19 experts disagreed with the idea of introducing a bottom line. They were three NIWA scientists, a University of Waikato water ecology professor and a Horizons Regional Council water scientist.
Environment Minister David Parker originally said the nitrogen bottom line would be reviewed in 12 months' time, but in a U-turn now says the review would not be necessary as the industry needed "stability".
Joy said MPI employed many staff from the agriculture sector so they had a natural bias towards the industry when it came to providing advice to the government.