Over the last 50 years, there has been a 73% increase in pollution levels from hundreds of cities, in the main stem of the Yangtze River. The annual discharge of sewage and industrial waste in the river has reached about 25 billion tons, which is 42% of the country’s total sewage discharge, and 45% of its total industrial discharge.
In addition, the CCICED (China Council for International Cooperation on Environment and Development) Task Force on Reducing Non-Point Pollution from Crop Production concluded that 92% of the nitrogen discharged into the Yangtze is from agriculture.
Shipping discharges are also to blame for the river’s declining health. As well, the extensive loss of floodplain areas to agriculture has reduced the basin’s ability to detoxify pollutants.
The major pollutants in the Yangtze mainstem are suspended substances, oxidizing organic and inorganic compounds, and ammonia nitrogen. This has severely reduced drinking water quality and contributed to dramatic eutrophication.
In addition, shallow, slower water flowing in belts adjacent to the banks near urban areas, and in smaller lakes and tributaries off the main stem, suffer even worse eutrophication and higher concentrations of the pollutants.
In addition, the Yangtze is the 4th largest sediment carrier in the world due to the proportion of arable land in its catchment, damming and erosion from land conversion.
In the first 60 years of the 20th century, the Yangtze’s sediment yield increased by about 30%, which corresponds to a related increase in surface erosion area in the basin.
Since the 1960’s, the sediment yield in many areas of the basin has increased, while the suspended sediment flux has dramatically decreased as it has been trapped in dam reservoirs.
Lastly, hydropower developments impound reservoirs that severely affect water quality. After 13 years of construction, the Three Gorges Dam is now built and will be fully operational in 2008.
The Three Gorges Dam exacerbates water pollution by impounding waters, trapping sediment and increasing eutrophication. Chongqing Municipality, at the confluence of the Yangtze and Jialing rivers has become the largest economic centre in southwest China, but is the largest source of organic water pollution in the Yangtze upstream of the Three Gorges Dam.
Before the Three Gorges Dam, health impacts in the area were already substantial including intestinal infectious diseases such as hepatitis A, and dysentery incidence rates some 50% higher than the national average. E.coli bacteria is rampant in water sources, and as high as 15,000 E.coli/L in some parts of the city.
The Three Gorges Dam, about 660 Km downstream, reduces the velocity of the Yangtze River, increases its water depth, and alters the natural flow regime. In the huge reservoir behind the dam, eutrophication threatens surface water quality, and near water intakes.
Also, impounded water submerges existing urban water and sanitation infrastructure. In addition, construction for the Three Gorges Dam never included a budget to clean towns of toxic waste before submerging them.
In Wanxian, Wan County, the Three Gorges Dam submerges part of the sewer system and waste water treatment plant as well as dumpsites along the river. Garbage heaps, boat effluent, pig and animal waste, factories, hospitals, and mines containing hazardous and possibly radioactive waste on the bottom of the reservoir are creating serious pollution.
In addition, possible riverbank collapses and landslides as a result of damming will add even more stress to the water quality of the Yangtze.