Region still riding wave of water-quality gains

Published: Tue 17 Jul 2018 01:30 PM
The rate and extent of Taranaki’s improvements in freshwater ecological health are defying assumptions – even among those working to make our waterways healthier.
Latest monitoring results from the Taranaki Regional Council show trends improving at 49 of the 57 monitored ring-plain sites at which changes can be determined – the most sites ever and surpassing record highs seen in the past two years.
“Statistically, any environmental trend can be expected to flatten out and reach a new equilibrium after a period of change,” says the Council’s Director-Environment Quality, Gary Bedford. “We’re surprised but delighted that we’re not yet seeing this here. We’re still riding the wave, so to speak.”
Ecological health is the Council’s prime measure of freshwater quality and is assessed by examining what sort of tiny creatures are living in waterways. The latest report is based on analyses of samples taken in the 2016-17 year at 59 sites on 26 rivers and streams across the region, and on trends derived from the results of all sampling since 1995.
Other findings include:
Sites showing improvements outnumber those showing declines by 6.1 to one, maintaining the continual increases in recent years and in sharp contrast to the 2008 ratio of 2.9 to one.
‘Statistically significant’ improvements are evident at 30 sites, maintaining the strong results of the previous three years and double the number 10 years ago.
The improvements in ecological health bear no relation to trends in nutrient levels.
Most of the improvements are being recorded in middle to lower catchments of the Taranaki ring plain where intensive farming occurs.
Sites showing the most improvement are the mid reaches of the Kaupokonui Stream, the lower Punehu Stream, the upper and mid Kapoaiaia Stream and the lower Mangati Stream.
The one significant negative trend is at the upper Katikara Stream, which has been affected by natural erosion events upstream in the recent past.
The state of ecological health at most sites is not much different from what could be expected for the altitude and distance of each from Egmont National Park.
Mr Bedford says the region is clearly seeing the benefits of the Council’s long-running Riparian Management Programme, under which farmers have fenced thousands of kilometres of streambanks and protected them with millions of native plants. Other factors behind the improvements include major investments in reducing and cleaning up major point-source discharges, and this is continuing with a move to land disposal of dairy effluent.
“One of the interesting aspects of our findings to date is that improvements in ecological health are largely taking place regardless of the nutrient trends at any particular site,” he says. “This needs to be borne in mind in discussions about environmental interventions and regulations.”
The technique of assessing the ecological health of waterways by looking at their populations of tiny insects and other creatures is based on a scoring system called the Macroinvertebrate Community Index (MCI), which is recognised internationally and which Council scientists helped to develop for New Zealand in the 1980s. It is regarded as giving the best picture of the aquatic health of waterways.
The Council’s other waterway monitoring programmes include a systematic series of surveys of periphyton (algae) at 21 sites in 10 regional catchments, measuring the extent of algal slime that occurs as thick streambed mats or as long, thread-like filaments.
A new report covering the 2016-2018 period has found little overall change from the previous two years in the amount of thick mats, and an overall reduction in amount of filaments. The biggest improvements were sites on the upper Kapoaiaia Stream and on the Patea River downstream of Stratford’s recently upgraded wastewater treatment plant.
The Council also runs monitoring programmes to measure the physical and chemical state of waterways and summer recreational water quality at popular swimming spots.

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