Excessive nitrogen and phosphorus are the major water pollutants in the Three Gorges Dam area, the 2007 Yangtze Conservation and Development Report has said.
The report on the Three Gorges Dam, the largest hydro-power plant in the world, was released at the second Yangtze Forum held in Changsha, capital of central China's Hunan Province, over the weekend.
"Nitrogen and phosphorus, which come mainly from domestic disposals and fertilizers, account for 60-70 percent of the pollutants in the Three Gorges Dam area," said Weng Lida, of the Yangtze River Water Resources Protection Bureau under the Ministry of Water Resources.
"Such pollution from non-point sources is very hard to control," Weng said. "If the pollutants had been discharged by a few plants, they could have been moved out of the area. But nitrogen and phosphorus are used by millions of people living there, hence, it is difficult to ask them to stop using substances containing the pollutants."
The excessive amount of nitrogen and phosphorus has caused rampant growth of algae, which makes the water look like soy sauce, Weng said.
Statistics show that in 2004, over 75,000 tons of nitrogen-based and 25,000 tons of phosphorus-based fertilizer were used in the area. Added to that were large amounts of phosphorus in detergents used by millions of people living there.
There are no figures on the exact amounts of nitrogen and phosphorus that flow into the Yangtze River in the area.
"Pollution has worsened after the Three Gorges Hydro-power Plant started running," Weng said. "The water in the dam now flows at the speed of 1 or 2 centimeter a second, as a result it seems almost still. That to a large extent has weakened the river's self-purifying capability."
The report warns against point-source pollution, such as those from industrial plants, and floating-source pollution (from ships), too. In 2004, for instance, the Three Gorges Dam area received about 500 million tons of wastewater from industries, 2 million tons from domestic sources and another 2 millions from ships.
(China Daily April 16, 2007)