According to one veterinarian, farmer and ecologist, agriculture needs a paradigm shift towards optimising wellbeing.

Dr Alison Dewes, who spoke at the recent water symposium in Havelock North, said as health professionals there was a responsibility to safeguard people, animals and ecosystems for present and future generations.

"Economic models have driven farmers more to growth (output) but the think big and more hasn't delivered the wellbeing that it purported to do."

"The model assumes continued output without environmental effects or resource degradation."

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The critical source areas in the catchments were the areas where there was the highest loss risk of phosphorus, sediments and pathogens. These were the points that needed to be targeted, but there was also the risk of diffuse loss that could occur through leaky soils such as gravels or peats.

The increased amount of nitrogen across the country and this increase in fresh water monitoring sites via intensification such as large scale irrigation schemes has had a significant effect.

Dr Dewes said nitrate travels through the land and one female cow's urine patch alone delivered 1000kg of nitrogen to the hectare. This was too much for the soil, so the nitrogen, which was transferred to nitrate in the soil, ran through to the groundwater.

"The nitrogen bomb" was also influenced by the feed given to stock with 30 per cent more protein than what animals needed. This meant there was a spill over into their urine and then the environment.

"If we have to start constraining nitrogen in our systems we have to ask is grass the best feed for our stock or should we diversify?"

Phosphorus runs across the land like soil run-off, it gets attached to particles or things on farms that run off on storm events.

Meanwhile, pathogens go through and across the land.

Dr Dewes said irrigation and intensification on vulnerable soils, linked to drains, wetlands, rivers, lakes, and eventually coastal food collection environments, meant there was a fully linked system where the paddock pathogens such as cow faeces could find a pathway to the swimming hole or plate.

She said a common zoonotic pathogen would be hosted by the animal and could be transferred from the animal via contact, food, faeces or vehicles such as water.

To have clean recreational and drinking water sources, bugs needed to be stopped at the source, sediment needed to be kept out, nutrients that grew algae and sucked oxygen needed to be kept away and there needed to be clarity, not turbidity.

To do this Dr Dewes said there needed to be a clear vision for pasture and agriculture in New Zealand.

"We need to stop converting vulnerable soils or there will be a train of damage. We can get more from less and leading farmers have worked this out.

"Several farmers have dropped their stocking rate and are not making any less money."

Dr Dewes said there could be a win-win for rivers and climate if people do a combination of things with a farm system shift.

"We could lower protein in the diet, lower intensity of the system, reduce winter cropping, reduce nitrogen fertiliser and move to more mixed systems with cereal.

"This would give a 30-40 per cent drop in the nitrogen spill over in to the environment and probably pathogens as well."

Looking specifically at pathogens, Dr Dewes said people needed to stop doing "dumb stuff" in "dumb places" like feedlots on gravely, leaky soils.

"Contaminants get directly in contact with sub surface water and we need to get these animals back out of these concentrated points."

Dr Dewes said nationally there needed to be freshwater limits, which were around ecosystem health and not nitrogen and pathogen enriched.