CCTV, China’s state broadcaster, looks at the use of remote sensing to monitor the country’s vanishing “kidneys” — wetlands that provide a range of invaluable ecosystem services that have become seriously under threat from rapid urbanization and modernization.
“Half Empty” is a 12-part series for China’s state-run China Central Television (CCTV) network that focuses on the country’s water crisis, its causes and the efforts underway to address problems ranging from urban water shortages, contamined groundwater to desertification in Inner Mongolia.
In episode five, reporter Han Bin tackles the challenges facing China’s wetlands and, in particular, Lake Poyang, China’s largest freshwater lake located on the southern bank of the Yangtze River in east China’s Jiangxi Province, and one of the most important wetlands in the world.
Lake Poyang was also the subject of a 2014 Probe International study that explored the link between the lake’s shocking dry-up and the disruption to a once thriving floodplain caused by the Three Gorges Dam, one thousand kilometres away on the Yangtze’s upper reaches.
According to Fan Xiao, a respected Sichuan geologist who has been monitoring the effect of the Three Gorges Dam on the hydrogeomorphology of the Yangtze River, by blocking the natural flow of sediment down the Yangtze and releasing only “clear water,” the Three Gorges Dam has caused the scouring and lowering of the Yangtze’s riverbed by a phenomenal 11 metres. With the Yangtze now so much lower, Lake Poyang inevitably drains into it, as if a plug had been pulled. [See: “Is the Three Gorges Dam to blame for extreme drought in the Lake Poyang area?“]
In “Half Empty: Remote sensing monitors wetland fluctuations,” Han Bin learns that satellite and remote sensing found Poyang had shrunk by 30 square kilometres every single year for the past decade. Similar to Probe International’s findings, the “Half Empty” report tracks the lake’s shrinkage to the dredging of Poyang’s lakebed for its premium quality sand — which, despite a seasonal ban, remote sensing has found still continues in secret — as well as the Three Gorges Dam which the CCTV news program says “likely” contributed to the lake’s drawdown “though scientific evidence is needed”.
Remote sensing reveals that since the 1970s, Lake Poyang has diminished from edge to center and is now overcome by encroaching marshland and risks vanishing altogether. A challenge Chen Xiaoling, a professor at Wuhan University’s State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing (LIESMARS), told Han Bin all of China’s wetlands faced.
“Wetlands are like kidneys,” he said. “More than 200 lakes with an area of over one square kilometre in China have disappeared over the past five years. We need to keep a wetland bottom line of 53 million hectares through 2020. Once this red line is crossed, the bottom line of ecological balance will be broken, which will push up the cost of wetland protection.”
Professor Chen said the management of the country’s wetlands could be improved by strengthened legislation and supervision, as well as greater public awareness.
1 The transitional areas between terrestrial and aquatic systems saturated with water, either permanently or seasonally — such as swamps, bogs and marshes — that provide a range of benefits including water purification, carbon sequestration, flood prevention or moderation, coastline protection, and habitats that support plant and animal diversity.