Freshwater quality: Big picture is good picture

30 August 2012

The health of Taranaki’s rivers and streams is going from strength to strength and the pressures on them are stable or reducing, according to the latest scientific scorecards.

Two new Taranaki Regional Council reports examine the ecological health and the physical and chemical state of the region’s waterways. The reports are based on analyses of hundreds of samples taken from scores of sites across the region in 2010-2011, and comparisons with data from earlier years and decades. Their conclusions include:

Sites showing improvements in ecological health (assessed by examining the types of life forms found within the waterway) outnumber sites showing declines by 3.3 to one. In a similar comparison two years ago, the proportion was less than three to one.

In particular, there has been a marked improvement in the lower Waingongoro River since discharges ceased from the Eltham wastewater treatment plant.

Overall levels of nutrients (nitrogen and phosphorus) are mostly stable or reducing, particularly in the past seven years.

Overall bacteria levels and evidence of organic contamination are mostly stable or reducing.

“The reports also highlight a few aspects where there have been declines and improvements are needed, so there is no room for complacency,” says the Council’s Scientific Officer for State of the Environment Monitoring, Alex Connolly.

“But overall, the picture is very, very encouraging. We are seeing a lot of improvement, especially in the more recent data.”

Ecological health is regarded as the primary measure of freshwater quality, and the Taranaki Regional Council was a pioneer in developing an index based on the richness of the macroinvertebrate communities (tiny animals including insects, crustaceans, molluscs, worms and leeches) found in waterways. This system is now used nationwide.

“We’ve been doing this work since 1995, so we can be confident that the trends we’re seeing are statistically robust,” says Ms Connolly.

The Council’s Director-Environment Quality, Gary Bedford, says while much of the national discussion about water quality focuses on nutrient levels, these are only indicators of potential pressures. The ecological index measures what is actually happening in waterways.

“In terms of ecological health, we’re seeing our waterways going from strength to strength,” he says. “And overall, the pressures on them aren’t getting worse.”

He says one-off problem areas can crop up and generate headlines, but these reports present the big picture, which is important because it allows issues to be kept in perspective.

The reports were presented to the Council’s Policy and Planning Committee today. They are available online:

Freshwater Macroinvertebrate Fauna Biological Monitoring Report 2010-2011 (PDF, 4.5 MB) http://bit.ly/NVgKnb

Freshwater Physicochemical Monitoring Report 2010-2011 (PDF, 2.2 MB) http://bit.ly/TOqpNh

Technical details

Ecological health

• 57 sites surveyed on 25 rivers and streams.

• Improvements found at 40 sites.

• No site showed significant deterioration.

• Two years earlier, 38 sites showed improvement.

Physical and chemical state

• 11 sites sampled monthly and analysed for up to 22 parameters including organic contamination, bacteriological quality, appearance, nutrient levels, conductivity, pH and temperature.

• 16-year and seven-year data trends have been analysed – the shorter period allows assessment of the impact of the Regional Fresh Water Plan for Taranaki adopted in 2001.

• Over 16 years, 32 of 50 measures for nutrients at 10 sites (64%) show no trend of deterioration. Over the most recent seven years, 49 of 55 measures for nutrients at 10 sites (89%) show no trend of deterioration.

• Over 16 years, 19 of 20 measures of bacterial levels (95%) show no deterioration. Over the most recent seven years, 21 of 22 measures of bacterial levels (95.5%) show no deterioration.

• Over 16 years, nine of 10 measures of organic contamination (90%) show no deterioration. Over the most recent seven years, nine of 11 measures of organic contamination (82%) show no deterioration.

• Over 16 years, 46 of 50 other measures of water quality (92%) show no deterioration. Over the most recent seven years, 54 of 55 other measures of water quality (98%) show no deterioration.

ENDS

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