Talking on Water 7: The gen on nitrogen

Nitrogen is the focus of much of the discussion about water quality, but it's good to understand the bigger picture.

Talking on Water cartoon 7.

While nitrogen can lead to problems under some circumstances, monitoring in Taranaki and elsewhere shows that there are times when there is no association between nitrogen levels and the ecological health of waterways. Our waterways are showing encouraging signs of stability and improvement, thanks to efforts aimed at maintaining and enhancing their ecological health.

Nitrogen levels have not been increasing in Taranaki waterways or groundwater.

Crisis? What crisis?

Is nitrogen the curse of our waterways?

Widespread dairy conversions in some regions have led to increased concentrations of nitrogen in streams, from fertilisers and animal wastes. Depending on weather, water temperature and other factors, this can bring an increase in periphyton, also known as algae or slime.

Some people want national restrictions on the use of nitrogen fertiliser (urea) or reductions in the number of cows that dairy farmers are grazing on their land. There are also suggestions that categories of water quality should be based on the amount of nitrogen in the water.

But it’s important to understand the whole picture before assuming that water-quality problems are all about nitrogen. Internationally, ecological measures (such as directly assessing the state of macroinvertebrate communities) are regarded as much more meaningful indicators of stream health than concentrations of nutrients. The UK has determined that there’s not sufficient scientific confidence in the association between the level of nitrogen and ecological health to support regulation.

Monitoring data from Taranaki shows negligible association between nitrogen levels and ecological health - and in any case, nitrogen has not increased in Taranaki’s streams, nor in our groundwater. In our region, there is a continuing trend of widespread ecological improvement. So we are not facing a ‘nitrogen’ crisis. But the Council does promote nutrient budgeting and management tools to ensure efficient and effective use of nitrogen.

An analysis by an independent expert suggests that in Taranaki, the completion of riparian (streamside) fencing and planting and ceasing dairy effluent discharges to streams would have far greater environmental benefits than restricting nitrogen application by farmers.

They are far more practical and less costly than imposing limits on nitrogen fertiliser. According to one estimate, the latter would cost the region more than $1 billion in lost production but without enriching in-stream habitat, reducing water temperatures, intercepting sediment, phosphorus or bacteria, or providing shade and food sources. Riparian planting does all of this, and is already taking place in the dairying areas of our region.