博文
Land reclamation: tread carefully
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Land reclamation: tread carefully
Gaoming Jiang
Published in Chinadiologue on March 11, 2008
Reclaiming land from the sea has become a popular way to develop coastal regions in China. But destroying wetlands and mangrove forests leaves populations vulnerable to the ravages of the rising seas, says Gaoming Jiang.
The practice may be temporary solution to land shortages, but it means the destruction of ecosystems and a loss of security for China’s economy and society.
China’s coastal regions are suffering from a shortage of land; reclaiming land from the sea has become an ever more popular solution to the problem. Shanghai now has plans to build a “city on the sea” in northern Hangzhou Bay, according to a report in the Yangtze Evening Post, with a planned area of 6.5 square kilometres and a population of 50,000 to 80,000.
In 2006 Shanghai spent 40 billion yuan (around US$5.6 billion) on building Lingang New Town, of which 45% of its 133 square kilometres was reclaimed land. The city of Zhoushan, in Zhejiang province, invested 103 million yuan (US$14.5 million) in 2007 reclaiming 4.13 square kilometres of land. If this trend is not arrested, China’s coastal wetlands may be eradicated entirely.
Land reclamation is a popular option in countries facing land scarcity. The Netherlands was one of the first countries to practice land reclamation and are world leaders in the field. Japan, Singapore, Hong Kong and Macau have also reclaimed land from the sea. But reclamation takes meandering coastlines and replaces them with straight lines, destroying mangrove forests and shallows in the process. It may appear to bring benefits in the short term, but in the long term it can cause ecological disaster.
First, the loss of wetlands from land reclamation can worsen drought. Of course, it is the atmosphere that transports water from the oceans to the land, but diminishing wetlands mean less evaporation – and a reduction in rainfall. North China has suffered very dry weather in recent years, with levels of precipitation falling year on year, and this is related the many ponds and pools that dry out and are built over.
Second, land reclamation can mean the loss of biodiversity and fisheries. Coastal shallows, mangrove forests and intertidal zones are where the land and the sea meet. When artificially separated, nutrients from the land no longer flow into coastal waters, threatening crabs, shrimp, clams and other organisms, which rely on this source of food. This has an impact on the ocean food chain and the fishing industry, not to mention some land-dwelling animals. Salt and fresh water ecosystems are also intimately connected. For example, the Chinese sturgeon lays its eggs in the Jinsha River, a tributary of the Yangtze, but land reclamation can affect the migratory patterns of these important fish stocks.
Third, land reclamation causes flooding. Wetlands form a buffer between the ocean and the land, absorbing much of the ocean’s force. Land reclamation destroys this natural buffer, and can have potentially disastrous consequences.
On December 26, 2004, an earthquake in the Indian Ocean caused a series of tsunamis that killed more than 200,000 people in at least 13 countries and left many more homeless. In one place hit by a tsunami – Marina Beach in Chennai, India – houses had been built right up to the edge of the coast, some on reclaimed land. If natural vegetation – particularly mangrove forests – had been left in place, much of the energy of the tsunami would have been absorbed by the wetlands, reducing the deaths and injuries. In Thailand’s Ranong Mangrove Reserve, mangrove forests acted as a barrier, meaning homes were left untouched, unlike those only 70 kilometres away, which did not enjoy the same protection, and were flattened.
We can also look at China’s own experience. In the second half of the Qing Dynasty (1644-1912), the shallows of the Pearl River Delta were reclaimed for agriculture. First, rocks were thrown into the sea to trap sediment. Then a stone dam was built across the river mouth, causing the sediment to be deposited and the river channel to narrow. In the rainy season, however, water could not pass through fast enough, and flooding would occur. County records from the time record: “In 1839, Guo Jinxiang, a man in Panyu county, built a 10-kilometre dyke in the south of Nansha village and claimed the new land as his own. Since the artificial dyke blocked the flow of the river, there were floods every month for three months. Fields and houses in low-lying areas were completely inundated. With two rivers flooding, to the east and the north, the inundation continued for over a month, submerging large areas of fields and crops and causing a localised famine. As the crisis worsened the emperor forbade the creation of new agricultural land in the counties of Panyu, Shunde, Xiangshan and Xinhui.”
Fourth, land reclamation exacerbates the phenomenon of “red tides”, or harmful algal blooms. Restricting the tides artificially means nutrients accumulated in river deltas flow more quickly into the sea. Particularly if reclaimed land is used for aquaculture, large quantities of organic matter and nutrients will be carried by the tides to the ocean, triggering massive algal blooms, threatening ocean organisms and causing die-offs among fish and shellfish populations.
Lastly, land reclamation destroys natural landscapes. Over time, land is shaped and reshaped, and eventually reclaimed by the ocean. The process is a slow one that nature has time to adapt to, but if it takes place too quickly serious damage can be done – and coastal populations are left at risk.
Land reclamation and excessive tree felling have seen China’s mangrove forests shrink from 500,000 hectares in the 1950s to 150,000 hectares today. Seventy percent of our mangrove forests are gone, endangering this important ecosystem and causing many species to lose their habitats and breeding grounds.
The practice may be temporary solution to land shortages, but it means the destruction of ecosystems and a loss of security for China’s economy and society. The Netherlands is now returning its land to wetlands to avoid ecological damage caused by excessive human intervention.
Coastal wetlands are constantly threatened by the pressures of profit. Unregulated land reclamation should end; coastal shallows, wetlands and other natural ecosystems should have legal protection. It is difficult to restore large areas of wetlands that have been covered with tarmac, concrete or buildings, but we should not wait till nature punishes us with tidal waves, floods and red tides before we decide to give ecosystems their proper place. It is a lesson we cannot afford to learn.
Gaoming Jiang is a professor at the Chinese Academy of Sciences’ Institute of Botany. He is also vice secretary-general of the UNESCO China-MAB (Man and the Biosphere) Committee and a member of the UNESCO MAB Urban Group.
https://blog.sciencenet.cn/blog-475-18157.html
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