CHRIS CONROY

Te Waikoropupu Springs have some of the clearest waters in the world.

New evidence challenging a key witness has halted a hearing involving special protection for one of the world's clearest springs.

The Water Conservation Order hearing for Golden Bay's Te Waikoropupū Springs was adjourned on Friday after evidence questioning the validity of a key council scientist was tabled.

Dr John Gamlen, a retired mathematician now based in Golden Bay, made a submission criticising the Tasman District Council's freshwater hydrologist Andrew Fenemor's nitrate modelling at the springs. 

Environment Protection Agency senior communications advisor Mark Wardle said Gamlen and Andrew Fenemor would be called to reappear before the tribunal in late May or early June. Closing statements also still need to be heard.

The special tribunal hearing in Takaka has been running for nearly a month.

Environmental group Friends of Golden Bay submitted the evidence, on behalf of Gamlen, on Friday.

READ MORE:
* Soil scientist questions accuracy of Overseer modelling
* 'Public hysteria' fuelled over farming near Springs
* Ngāti Rārua stand united with other iwi to support Water Conservation Order

Fenemor had earlier presented evidence about how nitrate levels would affect the Springs if further irrigation was allowed.

He used nutrient-budgeting software programmes for findings, including one called Overseer.

Overseer is a software that enables farmers and growers to manage nutrient use on farms, and has become central to freshwater management around New Zealand.

But Gamlen called Fenemor's modelling "flawed", resulting in wrong conclusions.

"If this quality of analysis were to be submitted to a large team research project such as IPCC climate research programme, it would not even reach the peer review stage," he wrote.

Gamlen criticised the validity of such models and their role in forming public policy.

BRADEN FASTIER

Andrew Fenemor has been criticized by a retired mathematician over his nutrient modelling at the springs.

A member of the environmental group Friends of Golden Bay, Gordon Mather, said the new criticism presented by Gamlen was "damning".  

An accurate understanding of nitrogen inputs and outputs in the Arthur Marble Aquifer and related aquifers was a "cornerstone" of management decisions. 

"We need clarity, accuracy and reliability," he said.

"Nitrogen is a prime pollutant ... it's something we want and need clarity and reliability around.

"If we increase the nitrogen in the aquifers, there's a very real risk these organisms [responsible for the clarity] could be damaged or extinguished – it would have a catastrophic effect on the springs."

Freshwater scientists not involved in the hearing have conflicting views over Gamlen's claims.

Professor Troy Baisden from the University of Waikato, said Fenemor's modelling was widely accepted and commonly used by councils around the country.

He believed it represented a "consistent set of calculations". Gamlen may have been confused about geological evidence from one of the applicant's witnesses, Professor Williams.

Gamlen claimed "diffusion" was involved in the flow of water through the Arthur Marble Aquifer, and as a result Fenemor's calculations were flawed. 

However, Baisden said diffusion described what happened in a wet sponge.

"If water on one side of the sponge contains nitrate, then the nitrate will very slowly get to the other side. But Mt Arthur [marble] is more like a piece of wood that's had boring insects through it, making caves and interconnecting passages.

CHRIS CONROY

Te Waikoropupu Springs is considered sacred to local iwi.

"The water flows right through the cave system, and out. Nitrate and other contaminants go right along with it."

Marc Shallenberg, an Otago University professor and Freshwater Sciences Society president, said the type of catchment modelling used by Fenemor relied on a number of assumptions.

What Gamlen seemed to be emphasising was the uncertainties and assumptions behind such models.

There had been concerns raised in hearings on the Bay of Plenty Regional Council Land and Water Plan Change about Overseer's reliability in modelling nutrient loads to lakes.

He said "careful review" of the models and assumptions underpinning them were needed to fully understand how accurate the model prediction could be, especially when using them for setting nutrient limits for receiving waters.

Council communications adviser Chris Choat said it was important the tribunal had access to as much information as they needed for their decision.

"It is only right Mr Fenemor has the opportunity to discuss the criticism of his evidence with the tribunal as part of this process."

 - Stuff