A Chinese scientist believes he has found a potential solution to China's growing problem of blue-green algae outbreaks in the country's lakes.

Yu Dan, Professor of Botany and Zoology with the College of Life Sciences at Wuhan University, said that growing more aquatic weeds could curb lake contamination.

Yu reached the conclusion after his research team succeeded in removing large swathes of algae from the Liangzi Lake, situated between the three industrial cities of Wuhan, Erzhou and Huangshi on the middle reaches of the Yangtze River, through the growth of aquatic weeds.

"Aquatic weeds and algae are the two primary kinds of lake-borne plants and are fighting against each other in the same environment," said Yu. "A good growth of aquatic weeds can absorb more nutrients such as nitrogen and phosphorus, depriving the algae and improving the quality of the lake water."

Blue-green algae grows easily in polluted water with a high concentration of nitrogen and phosphorous and a temperature of around 18 degrees Celsius. An excess of blue-green algae removes oxygen from the water, killing fish and other aquatic life.

Liangzi Lake, the second largest lake in Hubei Province, has a water area of 28,000 hectares. It fell victim to frequent algae outbreaks in the late 1980s as a result of unrestricted development of aquaculture on the lake, coupled with the emergence of a large number of industrial projects and mining businesses which directly discharged waste water into the lake, causing the ecological environment of the lake to deteriorate.

The local government has closed business ventures, dismantled 2,000 hectares of aquacultural grounds, improved the environment around the lake and introduced fishing bans to curb the lake's degradation.

In the meantime, Chinese scientists led by Professor Yu have grown 13,333 hectares of aquatic weeds in the Liangzi Lake since 1992. Aquatic weeds are now growing in 80 percent of the lake.

The efforts appear to have paid off. Local environmental protection organizations now monitor that the water in the LiangziLake has attained the I-category and II-category levels, which both meet drinking water standards.

The practice of planting weeds has also been implemented in Changtan Reservoir in Taizhou, east China's Zhejiang Province. The reservoir was crippled by an algae bloom from 1999 to 2001.

Yu brought waterweed seeds and propagating agents to Changtan Reservoir in 2002 and grew 666 hectares of aquatic weeds. The quality of water in the lake returned to the II-category level a year later.

Yu hopes to use the weed-planting technique to reduce pollution in other major lakes in China but there are no concrete plans at present and he is quick to recognize the scale of the task ahead.

"It is very hard to restore a damaged lake's ecological environment in a very short period of time, but success is not mission impossible if concerted efforts can be made over dozens of years, " said Yu.

The scientific team led by Yu has built a resource bank and a database of more than 150,000 aquatic weed samples collected in the past 25 years.

"I believe the growing of aquatic weeds is a cost efficient method to prevent ecological degradation of lakes and there are no technical barriers in this regard," said Yu.

There are more than 20,000 natural lakes across China, of which 2,800 measure at least one square kilometer. One thousand lakes have disappeared from Chinese territory in the past 50 years, according the State Environmental Protection Administration of China.

Many of the country's lakes have been ridden by pollution. The Taihu Lake drainage area is situated in one of the most densely populated regions in China and receives 56 billion tons of sewage discharge each year.

However, about 30 million people rely on Taihu Lake, China's third largest freshwater lake, for drinking water, including nine cities in the provinces of Jiangsu and Zhejiang as well as Shanghai Municipality.

A severe algae outbreak at the end of May rendered tap water undrinkable for a week for half of the 2.3 million residents in Wuxi, a city in eastern Jiangsu Province.

By mid-June, a second algae bloom appeared, covering 800 square kilometers and causing widespread concern in cities around the lake.

Blue-green algae outbreaks have also been reported in the Chaohu Lake in east China's Anhui Province and the Dianchi Lake in southwestern Yunnan Province since May, and have threatened the local tap water supply.

(Xinhua News Agency September 5, 2007)