Dr Jacqueline Rowarth: Why NZ's waterways are like a supermodel

Photo / File

Comment: Although Land Air Water Aotearoa's latest report is all "doom and gloom", New Zealand's waterways are still something to be proud of. After all, a supermodel with a zit is still a supermodel, writes Dr Jacqueline Rowarth.

The LAWA (Land Air Water Aotearoa) report released on Sunday was presented with doom and gloom.

More rivers are deteriorating in New Zealand than improving. The news was extremely disappointing after the 2018 "cause for optimism" headline.

A large number of farmers have spent hundreds of thousands of dollars to reduce their environmental impact.

They have implemented the recommendations given to them by researchers and rural professionals: fence, plant, bridge, culvert, replace, retire ... identify your contaminant source, put in wetlands, storage ponds, upgrade the effluent …

So last year's report made sense. Everything being done was working, and when things are going well, it is easy to feel positive about doing more.

LAWA's 2019 report was a shock.

But the headline is based on a broad-brush analysis that doesn't differentiate land use, source of contaminant, geographical concentration of measurements, or starting point.

In addition, the state of a site is presented in comparison with the rest of New Zealand as being in the best 25 per cent, best 50 per cent, worst 50 per cent and worst 25 per cent.

This is similar to the old school exam system where 50 per cent always failed.

Dr Jacqueline Rowarth. Photo / Supplied

The "improving or deteriorating" trend is identified for each site generally over 10 years.

This means that a best site could be deteriorating… but is still "best". This is like achieving top of the class with a 90 per cent in an exam one year and being top of the class with 85 per cent the next.

You are still performing highly but have deteriorated. Or like a supermodel with a zit – would she still be a supermodel? (Note, the man in the house said he'd be prepared to do the research if it would help science).

LISTEN HERE
• Jamie Mackay interviews Dr Jacqueline Rowarth in The Country - Water Report edition.

The real problem with interpreting the data is the variable pass mark.

LAWA does give some bands in the explanatory notes. These show that New Zealand rivers are high quality in many parameters in comparison with anything overseas.

And though it is certainly true that New Zealand waters are "different", we need to think what differences matter.

In nitrate, Niwa has suggested that up to 1.5 mg/kg for the annual 95th percentile is unlikely to harm even the most sensitive of fish.

The LAWA report indicates that 75 per cent of river sites tested are below 0.8 for nitrate and nitrite (a very small component) combined. The Thames in the UK has a nitrate of about 7 and also has 125 species of fish.

For E. coli, the EU swimming directive gives a grade of "excellent" for a 95th percentile of coliform forming units of less than 540 cfu/100ml, and "good" for less than 1000.

No health problems seem to occur (note that the EU does not measure within two days of heavy rain, and also discards outliers). LAWA reports that 75 per cent of sites have E. coli of less than 288.

And the Macroinvertebrate Index thresholds are above 119 score for excellent, and less than 80 for poor. The LAWA report indicates 75 per cent of sites are above 92.

Further analysis shows that many of the declining sites are associated with human habitation.

This is partly a function of geographical concentration of sampling, but also reflects the difficulty of keeping human activity separate from the environment.

Leaking septic tanks and sewerage systems, runoff from roads (including zinc and copper), plus dogs, ducks and seagulls create problems. And so do earthworks and buildings.

There are few people in New Zealand who don't value the concept of clean rivers supporting wildlife, and they like the thought of swimming in the rivers when the weather suits.

It is known that native fish are struggling, and work is being done on how to assist their survival. It is the migratory species that are most at risk, but Minister Sage's proposal to limit whitebaiting caused uproar.

Other suggestions such as creating places for fish to hide by reducing sediment, allowing trees to fall into rivers, and building fish tunnels, have been implemented in various places; time will indicate whether they have or haven't been effective.

Fisherman on Ngaruroro River, whitebaiting. Photo / Ian Cooper

As for swimming, the LAWA data indicates that the problem is not as great as feared.

Furthermore, during the 1950s when some current people in power were children swimming in rivers in the long hot summers that always existed… the E. coli between Cambridge and Hamilton was measured at 500-600 cfu per 100ml. Downstream of Hamilton, 6000 to 110,000 was measured.

New Zealand rivers have improved since the 1950s and though a deterioration in some indicators has been recorded in the past decade, the overall quality is still good to excellent.

The latest LAWA report has used different measuring techniques from the last one, but shows that we have an excellent starting point from which improvements can be made, targeting the area of concern.

The Government's Freshwater Reforms, currently under discussion and inviting feedback, have indicated that we all have a part to play.

The LAWA website shows where we can focus. Change will require further investment – through increased rates for urban regions, through farm income in rural areas.

Before we make the commitment, we need to be very sure that what is being suggested will have the desired effect. And, perhaps, how bad the perceived problem really is.

Zits improve with the right treatment and a supermodel with a blemish is still a supermodel.

- Dr Jacqueline Rowarth has a PhD in Soil Science (nutrient cycling) and has been analysing agri-environment interaction for several decades.