Scientists seek answers to toxic algal blooms in NZ, China
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E-mail Xinhua, April 24, 2014
New Zealand scientists believe they might be closer to forecasting toxic algal blooms like those that have made water from sources such as China's third largest lake, Lake Taihu, undrinkable.
A study of one of New Zealand's most toxic lakes, the South Island's Lake Rotorua, has shown that the cyanobacteria algae accelerates production of toxins as it becomes more concentrated, and scientists are trying to figure out why this reaction is triggered.
The algae often form a greenish slick of scum on the water surface and the water becomes unsafe to drink.
Waikato University Professor David Hamilton, who has also worked with the Chinese Academy of Sciences' Nanjing Institute of Geography and Limnology (NIGLAS) in studying Lake Taihu for the last 10 years, said a monitoring buoy in Lake Taihu had been gathering data on temperature and oxygen there since 2007.
There were two aspects to the study of the algal blooms and the toxins: first was what triggered the algae to accumulate in a bloom and second was what triggered them to produce toxins, Hamilton told Xinhua in an e-mail interview Thursday.
"It seems that high concentrations of the algae provide a trigger for toxin production, but we are unsure of the exact mechanism. We are also using models to try to predict when and where the blooms will occur. Developing a good predictive model will help management and allow targeted efforts to reduce concentrations," Hamilton said.
Cyanobacteria tended to proliferate most when they had adequate nutrient supply, warm water temperatures and calm conditions that allowed them to float to the surface to form blooms, and the toxins could spread through the food chain, including fish that ate the algae or ate zooplankton that consumed the algae.
Once in the water, the toxins could persist for days and become a major problem in water supplies.
"They are not necessarily removed by conventional filtration methods and boiling water doesn't remove the toxins. Advanced treatment methods are required to remove algal toxins, such as activated carbon filters," said Hamilton.
"Filtering lake water will also certainly be unsuccessful in natural lakes because they grow faster than the rate of removal from filtration."
Once algal blooms began, it could take many years to deal with the problem going right back to source nutrients coming off the land and protect water quality.
"The fundamental solution is to better retain nutrients on land: better agricultural practices, improved treatment of human and industrial wastes, and better protect the natural vegetation around lakes, which serves an important ecosystem service of protecting lake water quality," he said.
"There are other technological solutions, but these will only go so far and will increasingly impose major costs, such as costs of water treatment, if we are not dealing with keeping nutrients on land first of all."
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