In 2007, aquaculture businesses around Taihu Lake were devastated by an outbreak of algae that ruined the companies' reputations. Eight years later, the water quality has improved dramatically thanks to the use of a raft of organic cleaning measures, Cang Wei reports from Wuxi, Jiangsu province.

Sun Chu knew his dream was coming true when he watched flocks of wild ducks flying over his local lake in Jiangsu province in search of food.

Sun, manager of Yixing Aquaculture Co in Wuxi, Jiangsu, cherishes an ambition to restore the reputation of aquatic produce from Taihu Lake in markets across Southeast Asia, Japan and South Korea, after sales plummeted in the wake of a massive outbreak of blue-green algae that devastated the flora and fauna, and led many customers to cancel their orders.

"In March 2007, two-thirds of the clam larvae in our 20-kilometer-long, 10-kilometer-wide aquaculture farm died suddenly," Sun said.

The lake had been affected by industrial eutrophication, a form of water pollution caused by large quantities of external nutrients entering the water, which results in massive outbreaks of algae that deplete oxygen levels and kill aquatic life forms.

"The company's direct economic losses totaled 13 million yuan ($2 million). The local environmental protection department later found that clams were killed by water pollution. Before the outbreak, we exported nearly 10,000 metric tons of high-protein, low-fat clams annually, but afterward all our foreign customers ended their relationships with us almost immediately."

Yixing Aquaculture, established in 1995, was forced to relocate its underwater farm to Hongze Lake, about 500 kilometers away.

The outbreak attracted national attention because of the lake's location, its size and the 40 million people who live within its watershed. Covering 2,428 square kilometers and stretching across two provinces, the lake is situated in the densely populated Yangtze River Delta, and experts said the pollution was mainly caused by the excessive discharge of agricultural fertilizers and chemicals used in household cleaning products.

Exports start again

"It was a hard time for aquaculture companies and governments in the Taihu area," Sun said. "Seven years later, tests were conducted by the environmental protection department and we were delighted to find that the condition of the water had improved dramatically."

Sun moved the farm back to Taihu Lake in 2013, and the company started exporting clams again the following year. "In January, we put 1,100 tons of clam larvae into the lake, double the number of last year. We believe the water quality will continue to improve, and that will allow us to put in more clams next year," Sun said.

According to the Jiangsu General Office of Taihu Lake Water Pollution Prevention and Control, the quality of the water in China's third-largest freshwater lake has improved because of the measures imposed by the government and the efforts of local residents and business owners.

"Last year, we investigated nine sources of water and waterworks, which all met or exceeded the national water quality standard," Zhang Limin, deputy director of the general office, said. "The number of blue-green algae blooms and the density of algae in the lake declined in 2014, compared with the previous year, which made it possible to supply 700 million tons of clean water to Jiangsu and neighboring provinces during the year."

According to Mao Ying, director of Aquatic Animal Husbandry in Yixing, a county-level city under the jurisdiction of Wuxi, putting clam larvae into the lake is one of many natural ways of improving the water quality.

"The clams spend a year growing in the lake. They eat algae, which helps to lower the levels of nitrogen and phosphorus in the water," Mao said, adding that cities in the region also provide millions of silver carp, which eat about 42 kilograms of algae for every kilogram of weight they gain.

"Experts are now reviewing the types of plants in the lake in an attempt to lower the pollution level, but although the plants help to purify the water by absorbing some pollutants, their decomposition, especially in summer, lowers the water quality," Mao said.

The Suzhou Office of Taihu Lake Water Pollution Prevention and Control said experiments have been carried out in about 350 hectares of water near the city to control the growth of aquatic plants and identify a suitable mix of different types.

Physically removing the algae from the lake has also proved an effective way of reducing pollution, according to the Wuxi government, which has removed 6.72 million tons since 2007, equal to the removal of 1,794 tons of nitrogen and 450 tons of phosphorus.

Last year, the pollution office investigated 223 lakeside businesses and closed 59 of them for failing to treat wastewater properly.

Since 2007, the provincial government has allocated 2 billion yuan annually to manage water pollution in the lake. By the end of 2013, it had invested more than 106 billion yuan to set up 1,450 projects to deal with the heavily polluted water.

Wuxi has also partnered with other lakeside cities, including Suzhou and Changzhou, to implement pollution-control measures.

Yixing, a county-level city under the jurisdiction of Wuxi, has invested more than 5 billion yuan to establish a sewage collection and disposal system, plus a garbage-treatment system that serves the whole city. It has also closed about 600 chemical factories and related businesses as well as more than 400 glazed-tile enterprises that were thought to have adversely affected the local environment.

Despite these achievements, pollution remains a major problem. "The industrial wastewater and sewage discharged into the lake, although treated, often fails to meet the national standards," Zhu Tiejun, director of the general office, said.

Lakeside farms

In addition to problems caused by industry, livestock and poultry farms along the lakeside are also significant sources of pollution.

According to Zhang, the annual waste from the farms equals that of 6.4 million pigs, and as one pig daily produces seven times more waste than a human being, the sewage discharged into the lake annually is equal to that generated by more than 40 million people.

When the office investigated 15 rivers that feed the lake last year, it discovered 114 illegal livestock farms along their banks; only 12 had been fitted with facilities for treating sewage, and only nine of them functioned well.

However, local governments say they can't close the farms because they are unable to compensate the farmers for their losses. Last year, the Yixing government paid more than 100 million yuan to close farms around just one river.

"We understand that the farmers need to run the farms to support their families," said Wang Yunxian, director of the Changzhou branch of the general office. "We also understand that local governments will come under great financial pressure if they close the farms, so sometimes we feel that successful pollution control is extremely hard to achieve."

Zhu said short-term economic considerations often outweigh long-term ambitions: "The provincial government ordered that 10 to 20 percent of increased annual revenue must be allocated to treat water pollution in the lake, but some local governments are reluctant to follow orders, let alone close businesses and farms. They complain that closing the businesses would affect local economic development, and they refuse to launch more treatment projects."

According to a 2013 survey conducted by the Chinese Academy of Sciences, the level of nitrogen in wastewater discharged into the lake was 3.3 times higher than national standards, and phosphorus levels were 2.5 times the standard.

"The eutrophication of the waters of the lake will continue for a long time, as will the outbreaks of algae," Zhang said. "We can never be too careful about controlling water pollution in the lake, and we must make great efforts to make it work."

Contact the writer at cangwei@chinadaily.com.cn

(China Daily 05/08/2015 page6)