Lab tests hold hope for lakes | Rotorua News | Local News in Rotorua
Lab tests hold hope for lakes
Lake Okaro
By ALAN WILLIAMS in Whakatane
A two-pronged effort to reduce phosphorus levels in the Rotorua lakes has made a promising start in the laboratory.
The work now needs to be tested in the field as well as stacking up financially.
One test is a short-term answer in which a chemical is used to absorb phosphorus in the lake water, but using it is pointless if phosphorus levels being fed into the lakes are not also reduced in the long term.
Scientists have told Environment Bay of Plenty councillors that laboratory testing showed up to 100 percent absorption in lake water as well as good amounts through removal or "locking up" of the nutrient in streams feeding into Lake Rotorua.
Locking up means the chemical clings to the phosphorus so that it cannot be taken up by algae in the stream.
Nitrogen and phosphorus are the two nutrients doing most damage to the water in the Rotorua lakes.
Whereas nitrogen input is mostly from run-off from pastoral farming or sewage seeping into the lakes, the phosphorus occurs naturally, being picked up by rainwater as it soaks in through the volcanic rocks surrounding the lakes.
Mike van den Heuval, a scientist at Forest Research Institute in Rotorua, said the best results so far had come from zeolite, a mineral found at Ngakuru, which, with aluminium added to it, had been proved to absorb phosphorus. The regional council is seeking consents to conduct larger trials in Lake Okaro.
A health warning was placed on Lake Okaro on Friday, marking the start of the traditional algal bloom season on Rotorua lakes.
People have been advised not to swim in the lake or do any other recreational activities which involve significant contact with the water, and have been warned not to use it for drinking.
Okaro is the smallest of the region's lakes and is mostly used for boating and waterskiing.
Mr van den Heuval said the water in Lake Okaro already looked "like pea soup" but he hoped to be able to start the trials in December, with results expected to be known by July next year. He told councillors that if the results looked promising, the institute would find the money to commercialise the process.
The modified zeolite costs between $500 and $1000 a tonne.
Peter Brown, a scientist at engineering consultants URS, said alum had been shown to be the most effective chemical to remove or "lock up" phosphorus in the Hamurana, Utuhina and Puarenga streams feeding into Lake Rotorua.
Between them they put about 22 tonnes of phosphorus into the lake each year.
Mr Brown said low dose alum, using stream water in low dose lab tests, showed that the input level could be reduced by nearly 60 percent through the "lock up" process.
He said the capital costs would be about $500,000 for each stream, with operating costs of between $300,000 and $400,000 for each stream.
This compared with a total capital cost of about $20 million and operating costs of nearly $10 million a year for removal of phosphorus, for which tests had shown about a 70 percent success rate.
The regional council is seeking resource consent for further trials in the Utuhina and Puarenga streams.
A two-pronged effort to reduce phosphorus levels in the Rotorua lakes has made a promising start in the laboratory.
The work now needs to be tested in the field as well as stacking up financially.
One test is a short-term answer in which a chemical is used to absorb phosphorus in the lake water, but using it is pointless if phosphorus levels being fed into the lakes are not also reduced in the long term.
Scientists have told Environment Bay of Plenty councillors that laboratory testing showed up to 100 percent absorption in lake water as well as good amounts through removal or "locking up" of the nutrient in streams feeding into Lake Rotorua.
Locking up means the chemical clings to the phosphorus so that it cannot be taken up by algae in the stream.
Nitrogen and phosphorus are the two nutrients doing most damage to the water in the Rotorua lakes.
Whereas nitrogen input is mostly from run-off from pastoral farming or sewage seeping into the lakes, the phosphorus occurs naturally, being picked up by rainwater as it soaks in through the volcanic rocks surrounding the lakes.
Mike van den Heuval, a scientist at Forest Research Institute in Rotorua, said the best results so far had come from zeolite, a mineral found at Ngakuru, which, with aluminium added to it, had been proved to absorb phosphorus. The regional council is seeking consents to conduct larger trials in Lake Okaro.
A health warning was placed on Lake Okaro on Friday, marking the start of the traditional algal bloom season on Rotorua lakes.
People have been advised not to swim in the lake or do any other recreational activities which involve significant contact with the water, and have been warned not to use it for drinking.
Okaro is the smallest of the region's lakes and is mostly used for boating and waterskiing.
Mr van den Heuval said the water in Lake Okaro already looked "like pea soup" but he hoped to be able to start the trials in December, with results expected to be known by July next year. He told councillors that if the results looked promising, the institute would find the money to commercialise the process.
The modified zeolite costs between $500 and $1000 a tonne.
Peter Brown, a scientist at engineering consultants URS, said alum had been shown to be the most effective chemical to remove or "lock up" phosphorus in the Hamurana, Utuhina and Puarenga streams feeding into Lake Rotorua.
Between them they put about 22 tonnes of phosphorus into the lake each year.
Mr Brown said low dose alum, using stream water in low dose lab tests, showed that the input level could be reduced by nearly 60 percent through the "lock up" process.
He said the capital costs would be about $500,000 for each stream, with operating costs of between $300,000 and $400,000 for each stream.
This compared with a total capital cost of about $20 million and operating costs of nearly $10 million a year for removal of phosphorus, for which tests had shown about a 70 percent success rate.
The regional council is seeking resource consent for further trials in the Utuhina and Puarenga streams.
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