Where the rivers flow

21:41, Aug 03 2012

Over the spring and summer months Taranaki Regional Council scientific officers Chris Fowles, Bart Jansma and Katrina Smith can be found knee deep in steams with nets in their hands.

But these are not your everyday net - they are a specific type with a mesh size of 0.5 of a millimetre.

They kick the stream bed to dislodge tiny animals, which they net. The collection method is simple but effective. The critters - freshwater macroinvertebrates - some of which are so small a number of them would fit on one thumbnail, are then put into 500 millilitre pottles. Each can fit several hundred invertebrates, which may represent up to 40 or more different species, called taxa.

Back in their Stratford lab the invertebrate samples are preserved. It can take four or five hours to sort and identify them under the microscope.

Collecting the invertebrates is a way of measuring water quality - it shows the degree of biological health. It is used alongside chemical testing that measures the concentration of pollutants in the water at the time of sampling.

The biomonitoring works by using a scoring system, the Macroinvertebrate Community Index (MCI), which was developed by a TRC biologist in 1985. Then there were close to 100 scoring taxa, now there are closer to 200.


The different invertebrates are scored according to their tolerance to organic pollution, one - very tolerant, 10 very sensitive. Those at the top end of the scale tend to be found in good quality water. At the bottom end the water is more polluted.

The number of animals and the variety of species is taken into account. The maximum possible score is 200 and the lowest is 20.

In or near the National Park, close to the mountain, the score is around 140 and drops to 90 or so as the ringplain streams get closer to the coast.

The further from the mountain the more deterioration there is in the biological health of the water, Chris Fowles says, "because [health] is related to habitat. Streams have good natural riparian cover in the National Park and as they flow downstream, this cover reduces or disappears. There are increases in temperatures and surface runoff enters the water. This results in increases in nutrients and sedimentation. These changes in habitat are reflected in the scores."

He tracks changes in the scores to see if the quality of the water gets better, stays the same or gets worse over time as part of the TRC's ongoing state of the environment activities.

An example is the monitoring that was done of two sites in the Kurapete Stream, one immediately upstream of the Inglewood wastewater treatment plant and the other 6km downstream. This was to measure the impact on the stream once treated wastewater was no longer discharged into it. The results showed an increase in taxa that are more sensitive to pollution and a decrease in the tolerant taxa, and therefore an increase in MCI scores.

The monitoring system was originally used for consent compliance work to see if discharges into the water had an impact on the streams.

The use of freshwater biomonitoring began to increase in the 1970s. Back then, when Fowles was at university, diagrams were drawn to assist with identifying the animals, he says.

"Identification wasn't easy. I wasn't particularly good at drawing, but you learnt to draw. That's all we had." There were a few books and scientific papers with sketches of the animals to help.

Then came two dimensional photos (produced by TRC biologists) and now there are three dimensional images available on Landcare Research's website.

The TRC sponsored part of the website project in recognition that some of the information came from Taranaki in the first place, Fowles says.

To some extent the TRC pioneered the biological method of testing water quality using the animals, and, as the TCC, was one of the first catchment boards to use it. (The 20 catchment boards around the country have now become 12 regional councils.) In the 1970s there were fewer than 100 sites surveyed. Now there are more than 9000 surveys from more than 1100 sites on the TRC database, the majority of which are in ringplain streams and rivers.

The method is designed to be used for stoney bottom waterways and shouldn't be used straight after a flood.

Flooding affects which animals are present, as this causes some to burrow into the bed of the stream to avoid the flood while others will be swept downstream, he says.

The greatest variety of animals are found in flowing water riffles, which are like rapids but not as ferocious. Those animals which indicate better water quality like well aerated water. Mayflies and stoneflies, for example, prefer cooler and well oxidated water.

Those animals are very diverse, Fowles says.

"Examples are caddisflies. Some have hard cases while others are free living. The variety of cases is incredible. The cases are comprised of material that are associated with their habitat. Often, they may be confused with the debris. When they move they carry their cases with them."

Over the spring and summer months primary school children can be found splashing around in streams with kitchen sieves in their hands. Rather than kick stones, they use a scrubbing brush to dislodge tiny animals into their sieve. They then lay out their find on white trays. At first it looks like all they have is debris, but then the animals start jumping.

Under the guidance of TRC education officer Kevin Archer the children try to identify the animals and put them into a bug box, which has pictures of the different species.

Archer taught at Frankley School for nearly 20 years and has been at TRC for eight years. He takes Taranaki school children, both primary and secondary, out to learn about the animals that inhabit the waterways. During the winter months he teaches about recycling, wetland studies and by the end of the term will have taken the New Zealand ShakeOut earthquake programme into 84 classrooms.

"In the past, most schools, when studying water tended to study ponds rather than streams or rivers. But the TRC and its stream and river monitoring programme seemed to offer more, and as a result we now have a popular and widely used stream health study programme in our schools."

The week before a field trip takes place he visits the class to give a lesson about the stream and the little animals they will be looking for.

As they don't have microscopes, they look for critters that are big enough for children to be able to see.

"Even five and six-year-olds can identify some of the larger ones. Finding 20 or 30 is pretty common. They like looking for toebiters."

The toebiter, or dobsonfly, is, at 30mm, one of bigger invertebrates and is scored a seven on the MCI.

It curls up when scared and then it will open up in front of the children.

Archer always tells the children he can't catch a darting mayfly, which makes the kids determined they will.

The children know if they find mayflies or stoneflies then the water is good, he says.

"If they find worms, then the water is not of such a high standard."

The majority of the animals are still at the larvae stage. Once they hatch they fly off, living only a few days.

School children also take a thermometer to take the water temperature. If it is good at 10 to 15 degrees Celsius, plus clear water, the kids can work out what sort of animals they will find, Archer says.

"The kids love doing that. It adds credibility to what they are doing."

BY THE NUMBERS In Taranaki 286 primary river systems 530 named streams 300 of them on the ringplain 17,500km stream banks on the ringplain.

Taranaki Daily News