The thousands of dead pigs floating in the Huangpu River in March shocked residents and raised questions about the quality and safety of drinking water resources in Shanghai.
All drinking water is treated and experts have pronounced the water safe. Most comes from the upper reaches of the Huangpu River and from reservoirs.
The 16,000 pigs fished from the Huangpu and tributaries were not a threat to human health, experts said. Farmers had improperly dumped carcasses in upstream tributaries because it was cheaper than proper disposal. Some pigs died of a porcine virus, not communicable to humans, and others from poor raising conditions.
The unsettling pig episode prompted a water quality investigation team in late May to check water quality in the upper reaches of the Huangpu River. Shanghai Daily joined the team, which was named the Think Blue 21st Century Climate Change Mission.
Along the way, the mission tested water quality, talked to farmers living by the streams that feed into the Huangpu River and investigated the nearby environment.
Among the mission were environment experts, students and media professionals.
Their findings highlighted the importance of reducing pollution and rebuilding ecosystem in the upstreams.
Because of its geographical location on the Huangpu River, a tributary of the Yangtze River, Shanghai is considered a "passive" recipient of pollution. Many streams outside Shanghai feed into the Huangpu River.
Shanghai faces the East China Sea, with the Yangtze River and Hangzhou Bay to the south, so it seems there's water everywhere. At one time, the city and its suburbs contained 23,000 rivers and creeks, including many small streams and ponds that have been filled in and used for development. The city gets an average 1,200 millimeters of rainfall.
Despite all that water, Shanghai is listed by the United Nations as one of the six-biggest cities facing a shortage of safe water in the future.
While the city has good water treatment technology, pollution in the area is increasing and some water is too polluted to be treated for drinking purposes.
Apart from ocean pollution, the biggest threat to Shanghai's water resources is polluted water upstream.
"Sitting at the lower reaches of Taihu Lake and the Yangtze River puts Shanghai in a very passive position, receiving pollution from all those towns and farms in the upper reaches," says Zhang Zhenjia, professor of environmental science and engineering at Shanghai Jiao Tong University, who is a member of the mission.
This makes it very difficult for the city to solve its water pollution problems, since unclean water from upstream aggravates the already poor water situation.
The Huangpu River, known as Shanghai's mother river, has been frequently questioned as a source of safe drinking water. The thousands of dead pigs entered the Huangpu River from rivers in Jiaxing in Zhejiang Province.
Expanding and unregulated farming and breeding industries lead directly to the problem of eutrophication, the excessive enrichment by nitrogen and phosphates from animal waste and fertilizers, especially in summer. This causes algae blooms, depleting oxygen, cutting off needed sunlight for aquatic plants and killing fish.
The increasing number of factories in the upper reaches of the river system makes the situation worse.
China uses a water quality ranking system of 1-5; only Levels 1 and 2 are drinkable after basic treatment. Level 1 is considered very good and requires only simple treatment; Level 2 is slightly polluted but still drinkable with treatment.
Nothing else is drinkable. Level 3 is for swimming pools and fish farming. Level 4 is for industrial use and artificial scenery - no human contact. Level 5 is for agriculture. Some water in Shanghai and the region is worse, off the scale.
With the use of quick water-quality examination kits, the team tested for Chemical Oxygen Demand (COD), nitrogen (N) and phosphorus (P). It found that much surface water in the area was Level 5 or worse.
High nitrogen and phosphorus content usually indicates eutrophication, typically from farming. COD is related to chemical pollution from factories.
Extremely high nitrogen and phosphorous (N>2 and P>10, the maximum that the examination kits can display) were found in Zhulin Village of Xinfeng Town where pig raising is the basis of the economy.
Though the offending pig farms were closed after the "floating dead pig" case, the air is still filled with the stench of manure.
Many red worms cover the surface of nearby water, indicating serious eutrophication, consistent with the test results.
For many years, pig farmers casually threw manure and dead pigs into nearby streams, according to one villager in his 50s. As the pig industry expanded greatly since 2007, the water quickly was polluted and smelled bad.
"What you see now is much better than it used to be, The local government banned pig-raising after the dead pig case and farmers are forced to find other jobs," he says.
High COD content - 90 out of the maximum 100 - is found in nearby Donghu Lake, which feeds into the Huangpu River as it enters Shanghai.
"This is not surprising, considering all the factories on the way from Xinfeng Town to here," says Ma Ji, a member of the investigation team.
The good news from the quick testing kit is that the tap water in Shanghai is quite positive, with nitrogen around 0.5, phosphates almost 0 and COD between 0-5.
Though modern water treatment helps ensure safe drinking water, there's much to be done to improve satisfaction with water quality, says Professor Zhang of Jiao Tong University.
Though tap water is supposed to be safe, even boiled tap water has a strange taste. Professor Zhang says quality and taste can be improved at home with simple treatment equipment available in many stores.
Many pollution control, treatment and quality improvement programs have been carried out in Shanghai. These include closing and relocating polluting factories and excavating polluted river sediment in Suzhou Creek, which used to be lined with factories.
Restoring ecosystems is a good way to help water purify itself.
One successful case is the restoration of nine hectares of wetland at Dalian Lake in the upper reaches of the Huangpu River. The demonstration project was carried out by the World Wildlife Fund and completed in 2008.
Within a year, the water quality improved from worse than Level 5 (not drinkable even with treatment) to Level 2, which is drinkable with simple treatment. The improved water quality has been maintained.
The major problem was eutrophication from intensive fish raising and farming. The restored ecosystem consumed excessive nutrition and purified water as natural wetlands do.
In the middle of a pond, a crescent-shape island was built to ensure long and twisting water currents. Another purifying "kidney" island was built of sediment and aquatic plants to collect and absorb excessive nutrition at the point where the pond connects with the polluted lake.
A layer of charcoal was spread over the sediment to ensure the nutrition was absorbed evenly and gradually to feed the plants. Aquatic plants and other vegetation on the crescent-shaped island also consume excess nutrition.
Every year withered plants must be removed and replaced with new ones on both islands to ensure the system is sustainable. Organic farming also contributes to better water quality.
"Helping water resources regain their self-purification function is crucial to improving quality," says Yang Aihui, manager of the Shanghai Conservation Program of the World Wildlife Fund. "Otherwise, it's absurd to talk about cleaning a water resource, since it won't stay clean for long."
Seeing the good results, the Qingpu District Government invested 270 million yuan (US$44 million) to expand the wetland model to the entire Dalian Lake.
"As a NGO, we can only suggest a possible solution. Participation by the government and public is what really can make a big change," says Yang.
Restoring wetlands is highly effective in improving water quality, but it can only be used where there are natural earth banks.
Many sections of river within the city of Shanghai have concrete banks, and in these cases aquatic plants can also be used to improve water quality, according to Wu Guohua, coach of the student technology innovation team of the Nanyang Model School in Xuhui District.
The team was awarded the Stockholm Junior Water Prize in 2006 for its project restoring the ecosystem of a section of Caoxi River in Xuhui District.
Since 2002 the team has been restoring ecosystems in eight sections of Huangpu River tributaries. Both filtration beds on the bottom and floating plants are used.
In some places water quality improved from less than 5 to Level 3. Fish, eel and shellfish can be found in some sections.
Using microorganism to purify water sustainably is the major principle.
"Everybody knows microorganism can purify water by reducing the pollution, but you can't just mechanically put microorganisms into the water for purification; that's not sustainable," says Wu. "A better way is to introduce suitable water plants - that's the key to the ecosystem restoration process. That's because microorganisms naturally grow around the water plants."
Different plants are needed in different phases. Though submerged plants like hornwort and pondweed are especially good beds for microorganisms, they cannot survive in Level 5 water. In these cases, filtration beds made of gangue, or waste rock from mining, are needed initially to clean the water.
When submerged plants get established in the river, an ecosystem will be restored and expand naturally to keep on purifying the water.
This is a cheap, effective and sustainable way to clean up river channels in downtown areas without much shipping, Wu says.
These underwater "forests" need regular trimming to ensure the best environment for microorganisms. From 200 to 500 plants in each square meter of water is optimum for purification, while too many plants will do the opposite, Wu says.
Though cutting submerged plants is very low-cost maintenance compared with other big water-cleaning programs, the local water department finds it creates too much workload. Last year the department stopped participating in the program and the water quality has subsequently degraded. Creating ecosystems helps clean up pollution Where Shanghai gets its water
SHANGHAI has three major drinking water sources, and next year there will be a fourth resource.
The three are the upper reaches of the Huangpu River, the Chenhang Reservoir in Baoshan District and the Qingcaosha Reservoir in Chongming County.
Next year the Xisha Reservoir in the southwestern part of Chongming Island will become operational.
Except for the upper reaches of the Huangpu River, the other three sources take water from the Yangtze River, which is considered safer than the Huangpu.
Before the Qingcaosha Reservoir was completed, around 70 percent of the city's drinking water came from the Huangpu River.
The Chenhang Reservoir, completed in 1992, supplies part of drinking water to northern districts, including Baoshan, Putuo, Zhabei, Yangpu and Hongkou District.
Qingcaosha Reservoir, which became operational in 2011, shares the supply burden with the upper reaches of the Huangpu River. It supplies drinking water for the downtown area, the Pudong New Area, and part of Minhang, Baoshan and Qingpu districts, supplying around 50 percent of the needs.
Xisha Reservoir is expected to supply water in Chongming County next year.
The quality of Huangpu River water has decreased greatly in recent years because of pollution in its upper reaches, as well as its own offshore pollution. This, in addition to population growth, made construction of the Qingcaosha and Xisha reservoirs necessary.
Though the water quality of the Yangtze River so far is better than that of the Huangpu River, the long-term use of the Qingcaosha Reservoir has been questioned. In 2012 water experts said pollution in the reservoir from eutrophication will increase greatly if it is not controlled, posing a threat to water quality.