Way to go, Waiokura

12 June

Latest results from a long-running scientific study strongly suggest Taranaki is taking the right approach to protecting and improving the quality of its rivers and streams.

Location of Waiokura catchment. Marked improvements have been progressively obvious in the Waiokura catchment, near Manaia, in the past 15 years and especially since 2014 – with the credit going to farmers’ efforts in fencing and planting waterways on their properties, and switching to land-based disposal of dairy shed effluent.

“The Waiokura was originally chosen for this study because it wasn’t doing very well at the time,” says the Taranaki Regional Council’s Director-Environment Quality, Gary Bedford. “So seeing good results here means we can be sure of good results elsewhere across the ring plain.”

The Waiokura is part of a national project in which researchers from NIWA, AgResearch, DairyNZ and Regional Councils have been studying five ‘best practice dairy catchments’ – two in the north Island and three in the South Island – since the mid-1990s. 

Latest findings, published in the Journal of Marine and Freshwater Research, include strong improvements in the Waiokura that have become particularly evident since 2014 – across ecological health (assessed by monitoring the number and type of small creatures living in the river), nitrogen levels, suspended solids, bacteria levels and water clarity.

“Notably, improvements in (ecological health) were greatest at the Waiokura catchment where active planting of riparian vegetation was greatest,” says the report, which focuses on the effectiveness of environmental measures in all five catchments nationally.

Mr Bedford says that early on in the project, researchers and farmers had concluded that stream health could be improved by riparian (streamside) fencing and planting, and by disposing of dairy shed effluent by spreading it on land rather than treating and discharging it to waterways.

“Both these measures are key Council environmental requirements right across the ring plain,” says Mr Bedford. “Thousands of kilometres of streambank across the ring plain have been fenced and protected with millions of plants by farmers, working in partnership with the Council. And as consents for effluent treatment ponds expire, farmers are being required to switch to land-based disposal.”

Of the Waiokura catchment’s 115km of streambank, 90% is now protected with fences and almost 70% is protected with vegetation, and work is continuing to complete the job.

Meanwhile, 15 of the catchment’s 23 consented dairy discharges are to land or primarily to land, and conversions to land disposal will continue as consents expire. Over the study period, there has been a 67% reduction in the volume of treated farm dairy effluent discharged to the stream.

“It’s very clear that we’re now starting to see how these changes have led to a significant improvement in stream health and freshwater quality,” says Mr Bedford. “These latest research results can be seen as an independent validation of the Council’s approach, and a vindication of the investment and effort by farmers.”

Crucially, farm productivity in the catchment has increased at the same time as stream health, he says. In 10 years, milk solids per hectare are up 21% and milk solids per cow are up 31%, while nitrogen loss per kilogram of milk solids is down 11% and nitrous oxide emissions per kilogram of milk solids are down by 7%.

Mr Bedford says the Waiokura is unusual because it is fed by groundwater originating from beneath dairy pasture, rather than springs fed from Mt Taranaki. “We never put it up as being a typical ring-plain waterway – it has fewer natural advantages in its favour. Our thinking was that if ‘best practice’ could make a difference here, it could make a difference anywhere. These results suggest we’re on the right track.”

He also says it’s interesting to note that the research report’s authors caution against making too much of a correlation between ecological stream health and nitrogen levels.

“The results are too inconsistent. Yes, Waiokura is enjoying both improved ecological health and reduced nitrogen levels. But another catchment in the study, Toenepi in the Waikato, is seeing increases in both nitrogen and in ecological health. The relationship between nutrient levels and stream ecological health is a complex issue, and the report suggests seasonal factors may be a stronger influence.”

The latest report will feed into the current review of Taranaki’s Freshwater and Land Plan.

Doing the job ... riparian protection on the Waiokura.

Doing the job ... riparian protection on the Waiokura.