Oct. 28 (Bloomberg) -- Chinese farmers should stop using fertilizer during the flood season and fishermen experiment with fish-net systems to mitigate damage from the Three Gorges Dam.

Ohio State University researchers say if farmers in the flooded area that extends 410 miles (660 kilometers) behind the dam, longer than the U.S.'s Lake Superior, don't avoid fertilizers, the waters will be fouled with excessive nutrients and cause algae blooms in standing water covering fields along the Yangtze River.

Harnessing the Yangtze's energy has been a longstanding dream of the Chinese, originally envisioned by Sun Yat-sen almost 90 years ago. But since construction began on the dam in 1994, and power generation started in 2003, the project has been fraught with warnings from scientists of a burgeoning environmental nightmare.

The Three Gorges Dam, set to become the world's biggest hydroelectric power station when fully operational by 2012, has already forced about 1.5 million people to relocate. Damming Asia's longest river has led as well to the extinction of the Yangtze river dolphin as scientists foresee further ecological fallout.

``Nature is going to see something it's never seen before,'' said William Mitsch, an Ohio State University wetlands expert and natural resources professor. ``There is no ecosystem that has such an exaggerated change in flooding levels, even the Amazon River.''

Ecological Engineering

The scientist proposed altering farming methods and fishing practices to prevent further environmental damage to the region in an Oct. 24 letter co-written with four colleagues from Ohio State and China to the journal Science, which published an Aug. 1 report detailing the environmental dangers.

``If done properly, ecological engineering can minimize some of the impact,'' Mitsch wrote.

The reservoir floods a 244-square-mile (632 square kilometers) area, half that of Itaipu Dam on the Brazil-Paraguay border. If fully operational now, China's milestone project would provide 22,500 megawatts of power generation, about 3 percent of the nation's total consumption.

Three Gorges was designed foremost to control floods on the Yangtze. An overflow in 1954 killed more than 33,000 people and forced 18 million to move. The deluge covered Wuhan, then a city of 8 million residents, for more than three months.

Father of China

Construction began 14 years ago on a dam first envisioned almost a century earlier by Sun Yat-sen, sometimes called the father of modern China. The project, coaxed forward by Chiang Kai-shek and supported by Mao Zedong, has ended up flooding 1,300 archaeological sites and caused landslides that killed 44 people.

Deforestation, soil erosion and water pollution issues cropped up. Sedimentation from run-off was higher than expected, leading scientists to fear excessive buildup could block dam sluice gates.

Environmental woes from the project extended as well to the critically endangered Siberian crane, most of which winter in the wetlands being destroyed by the dam, Peter Matthiessen has written.

Scientists say the reservoir contributed not only to the disappearance of rare, nearly blind white river dolphin but the Yangtze's sturgeon have been affected as the river's flushing capacity suffered. As water quality fell, pollution levels rose.

China's agriculture industry must adopt new practices to minimize the ecological fallout from the project, scientists have proposed. ``We're saying everyone has to think outside the box,'' Mitsch wrote.

Terraced Ponds

Farmers in the now-flooded region should construct cascading terraced ponds to retain water as they seek to continue harvesting in a new ecosystem created by an annual cycle of flooding that lasts up to six months and draining.

The Three Gorges project is entering its final stage this winter as water levels behind the dam reach their peak of 575 feet (175 meters) and then are lowered about 100 feet during the flood season.

Creating a reservoir that stretches more than 400 miles back, equivalent to the land area of Hong Kong, extending to the city of Chongqing, meant that entire towns and villages were relocated as previously dry areas became submerged.

``Former cities, homes and farm fields of about 1.5 million people will be seasonally under water and a set of new unique ecosystems will develop,'' Mitsch and his colleagues wrote.

No Fertilizers

Farmers will be able to continue cultivating land covered by the reservoir during periods of low water. But they must eliminate the use of fertilizers to prevent the buildup of nutrients in the water, the scientists said. An imbalance, called eutrophication, can cause algae blooms that choke fish.

``Fertilizers actually won't be needed,'' Mitsch said, because the sediment left behind by flooding will be rich in nutrients, especially phosphorus, beneficial to many crops.

The group of scientists recommended building cascading terraces and wetlands along the border of the reservoir to trap water as it recedes and to reduce the loss of nutrients to the pulsing river system.

Another option would be to use net systems to capture fish at the end of the flooding season as water levels diminish. Mitsch's proposals noted that mudflats at or near the river system in the summer may also provide an ideal habitat for birds.

China, the world's largest electricity consumer after the U.S., has been building power plants to prevent shortages during peak demand periods. The country relies on coal for two-thirds of its energy needs. The government is encouraging the use of cleaner-burning fuel, such as natural gas, and renewable energy including water, as an alternative to coal.

China Three Gorges Project Corp., the parent of Shanghai- listed China Yangtze Power Co., is developing the Three Gorges Dam, whose costs when completed may reach an estimated $24 billion. The finished project will generate eight times the power of the U.S.'s Hoover Dam, according to a report in Scientific American.

To contact the reporters on this story: Randall Hackley in Zurich at rhackley@bloomberg.net; Gareth Gore in Madrid at ggore1@bloomberg.net

Last Updated: October 28, 2008 09:43 EDT