Study: Small streams have huge impact

Streams wider than a metre and deeper than 30cm must be fenced, but smaller unfenced streams have been found to cause most stock contamination of waterways. Photo / File

New research on keeping stock out of rivers and streams requires an urgent and radical rethink of the current national riparian fencing strategy, according to Fish & Game.

At present, streams wider than a metre and deeper than 30cm must be fenced to keep stock out of them, but this rule doesn't apply to smaller waterways. However, New Zealand scientific research just published in the international magazine Journal of Environmental Quality questions the current approach.

The research by Dr Richard McDowell found the smaller, exempt streams account for 77 per cent of the contamination load in a catchment. His research says not requiring smaller streams to be fenced may be undermining efforts to stop declining water quality.

Dr McDowell is the principal scientist for AgResearch-Invermay's Environment Group, Lincoln University Professor and Chief Scientist for the National Science Challenge.
Fish & Game chief executive Bryce Johnson says his research is extremely important.

"The current approach means small streams can be treated like farm drains."

"We now have the science to show what we have long suspected - small waterways are crucially important to the environment and need to be properly protected from contamination."

The research also calls into question the dairy industry's claim it is fencing 90 per cent of the country's waterways.

"The dairy industry is only talking about 90 per cent of larger waterways which have to be fenced anyway - not the critically important smaller ones where most of the pollution is occurring.

"These smaller streams are vital to the environment - they flow into the bigger streams and rivers and Dr McDowell's research shows that by the time they join up with bigger streams, much of the pollution has already occurred."

Mr Johnson says protecting these small steams needs to be an urgent priority.

"These smaller waterways are the capillaries of our lakes and rivers and provide essential habitat and breeding areas for a range of species. Yet the current approach means they can be treated like farm drains for animal effluent and farm run-off.

"This has to change. If the farming sector is serious about reducing its impact on water quality and restoring rivers to be swimmable then it has to exclude stock from all water bodies - regardless of size - and create more extensive riparian buffer zones."

Mr Johnson says there is now an emphatic public demand for better water quality.

"And New Zealand's wealth relies heavily on clean fresh water. The country's two biggest income earners - tourism and agriculture - cannot survive without it. This latest research shows urgent action is required to protect New Zealand's internationally unique point of difference and fencing all streams will play a significant role in preserving that heritage."

Dr McDowell's research paper can be found at:
https://dl.sciencesocieties.org/publications/jeq/articles/46/5/1038