Baisden, a Waikato University lake and freshwater scientist, has experience studying major environmental issues across the globe including acid rain in the United States.
Early farmer meetings on the Government’s freshwater proposals package have raised concerns about setting dissolved nitrate level limits in waterways to 1 part per million.
Some catchments have been farming assuming they can work to limits of 6.9 ppm and concern has been raised about the ability of farms in those catchments to lower their nitrogen losses to meet the 1ppm limit.
Canterbury is one area experiencing the higher nitrogen levels in waterways.
Claims have been made by Federated Farmers an 80% reduction is required in nitrogen in parts of NZ.
But Baisden is concerned the debate confuses and distorts discussion about how agriculture’s nitrogen loss affects waterways.
“The value of 6.9ppm in old frameworks was precise but nearly meaningless.
“It corresponded to nitrate levels actually killing organisms due to direct toxicity.
“The new focus is on the water system’s ecological health.
“Too much nitrogen causes too much algal growth, somewhere between 0.5 and 1ppm, seen as slime in the water,” Baisden said.
However, the actual proportion of waterways exceeding 1ppm is relatively small, estimated at 10% outside the conservation estate.
“In many places, including Waikato River, nitrate levels are only just starting to exceed those ecological health levels and can still be brought back under control with good limit-setting. That needs to be done before we see more rapid exceedances over toxicity level limits like those in areas converted to irrigated dairying in Canterbury.”
Farms in the Manawatu-Wanganui (Horizons) catchment are already required to farm well below the 1ppm level, with the dissolved nitrogen level set at 0.4ppm of nitrogen. Ruataniwha in Hawke’s Bay is set at 0.8ppm.
While 1ppm of nitrogen does not define a pristine waterway it provides a limit to preserve some of the resident macro-invertebrate and fish populations.
A pristine waterway is defined in N terms as one that has levels of 0.2ppm.
“So, that dissolved nitrogen level of 1ppm leaves some room for leniency.”
Freshwater campaigner and agricultural science graduate Marnie Prickett said nitrogen won’t be the main focus in some farming catchments.
“It could be for some catchments where drystock farming is more common then it may be sediment that becomes their focus. The majority of the country is already below that 1ppm.”
She is concerned misinformation and emotion around one number in the proposals is causing farmers unnecessary stress.
“Nitrogen reduction is still likely to be a goal for some communities with catchments under 1ppm of nitrogen because their water quality is already good and they cannot degrade it further or they want it to be better.”
Massey University freshwater ecologist Professor Russell Death said he was frustrated in his attempt to explain the nitrogen limits to farmers at the Palmerston North meeting on the proposals.
“The fact is that anyone there farming in the Horizons catchment is already required to farm at a nitrogen limit lower than 1ppm, actually at 0.4ppm as set under the regional plan.
“I did try to explain this but they did not really seem to want to listen.”
The technical advisory group he was on advising the Government about the limits in the proposals had faced strong pressure from farming leaders to focus more, not less, on nitrogen limits than it already had.
“We were wanting to put in levels for fish and bugs and so on and they really pushed hard on us as scientists to set nitrogen limits.”
Both Death and Baisden said the proposals are valuable marketing tools for NZ’s food exports, where overseas markets expect standards to be clear around water quality.
“Australia have them, the United States have them, we need to have them as well,” Death said.
