695 square kilometers! Poyang Lake has become bigger, migratory birds and finless porpoises are happy →

Affected by the recent autumn rains in western China, the water level of the Yangtze River has gradually risen. Poyang Lake, China's largest freshwater lake, has seen backflow of Yangtze River water for the first time this year, and the water area has expanded by 695 square kilometers.

According to monitoring by the hydrological department on October 4 and 6, the outflow of Poyang Lake was -2.77 cubic meters per second and -531 cubic meters per second respectively, marking the first backflow of water from the Yangtze River this year. During the same period, the inflow of water from the five rivers into Poyang Lake was 1,720 cubic meters per second and 1,890 cubic meters per second respectively.

According to satellite data monitoring by the Jiangxi Provincial Ecological Meteorological Center, the main body of Poyang Lake and nearby waters area was 2,098 square kilometers on October 5, 2023, an increase of 695 square kilometers from the water area monitored on September 18 (1,403 square kilometers), an increase of 49.5%. Compared with the same period last year (600 square kilometers on October 2, 2022), it has doubled the smallest area in history since satellite remote sensing monitoring records were kept, but it is still slightly smaller than the same period in history (an average of 2,129 square kilometers).

Poyang Lake: East Asia's most important migratory bird habitat

Poyang Lake is the largest wintering ground for migratory birds in my country and even in East Asia, accommodating more than 100 species of migratory birds and a population of more than 700,000 birds each year. There are also some resident birds living here. These birds have different diets and preferred habitats, and the complex habitat of Poyang Lake in winter can meet their diverse choices.

Various ducks move on the water surface and look for seeds of various aquatic plants, white cranes dig up the roots and rhizomes of submerged plants for food, black-winged stilts prefer benthic invertebrates in mudflats, Oriental white storks are good at fishing in shallow water, and grey geese like to eat leaves of moss on the beach... Here, they can all find an ecological niche that suits them.

Why does Poyang Lake attract hundreds of thousands of migratory birds to spend the winter?

Due to uneven sediment deposition, some depressions naturally formed in the basin of Poyang Lake.

In the summer flood season, they are submerged under the vast lake surface. In the autumn and winter, when the lake water gradually retreats northward into the Yangtze River, these depressions become like shallow saucers, "holding" limited water for Poyang Lake, similar to the tidal pools that accumulate seawater in the depressions of the reef intertidal zone after the sea ebbs.

The locations of these "dish-shaped lakes" (also known as "sub-lakes") in Poyang Lake during the dry season are roughly fixed, and the total number is about 100.

Although most saucer-shaped lakes are small in area and shallow in water, they are complex wetland ecosystems that provide diverse habitats and food sources for migratory birds.

From the center of the lake to the lakeshore, the water gradually becomes shallower, and the habitat types are roughly arranged in the order of "open water surface - shallow swamp - mud flat - grass flat", forming a "concentric circle" structure.

The diets and feeding habits of various migratory birds vary greatly. The migratory birds that winter in the Poyang Lake area can be roughly divided into "aquatic plant seed group", "fish eating group", "tuber eating group", "benthic organism eating group" and "herbivorous group". Each has its own preferred habitat and ecological niche. No matter which category, they can find suitable food and habitat in the small saucer-shaped lake and its surrounding areas.

In the winter of 2022, the water in the famous Qianyan Bridge area of ​​Duchang County on the shore of Poyang Lake gradually receded, and the exposed lake bed was covered with cracks. In the summer of 2022, the severe drought in the Yangtze River Basin caused the water area of ​​Poyang Lake to shrink by 69% in just 40 days, and the exposed lake bed turned into grassland. People are worried that the early dry season in autumn and winter caused by drought will affect the wintering of migratory birds.

Poyang Lake: The main playground for finless porpoises

The Yangtze River dolphin is a freshwater whale species unique to my country. It is at the top of the Yangtze River aquatic food chain, an important component of the Yangtze River biodiversity, and an important indicator species of the Yangtze River's ecological environment. It has unique ecological, scientific, and social value. Protecting the Yangtze River dolphin is an important part of protecting the Yangtze River's aquatic biodiversity.

Yangtze River dolphins have always been known as beautiful smiling angels in the water for their intelligence, liveliness, cuteness and jubilation. They are very smart and can send out two types of sound signals: high-frequency pulse signals when detecting the environment and hunting; sometimes low-frequency continuous signals, like the sound of sheep or birds, are very pleasant to the ear. The lively Yangtze River dolphins often show their swimming nature in the water. They will swim upstream and dive, roll and jump constantly, and also make a series of movements such as nodding, spraying water, and turning suddenly. When swimming sideways, one leaf of its tail fin emerges from the water, sways from side to side, and crosses the air, looking very silly. What is very interesting is its "performance" of spitting water. When it wants to spray water, it will expose its head above the water, swim forward quickly, open and close its mouth, and spray water from its mouth from time to time, sometimes up to 60-70 cm away.

"Since the 1990s, the population of Yangtze finless porpoises has continued to decline, and the decline is accelerating." According to Mei Zhigang, assistant researcher at the Institute of Hydrobiology, Chinese Academy of Sciences, and leader of the scientific expedition team's visual group, after the Baiji dolphin was declared functionally extinct in 2006, the Yangtze finless porpoise became the only cetacean living in the Yangtze River. The results of the 2012 Yangtze River freshwater dolphin survey showed that the population of Yangtze finless porpoises was only 1,040, and the annual decline rate of the population in the mainstream of the Yangtze River was about 13.7%, and it was declining at an accelerated rate. Many small groups were forced to be isolated for a long time and live in some tributary waters. The protection situation is extremely critical.

The Yangtze River porpoise is only distributed in the middle and lower reaches of the Yangtze River, as well as in Dongting Lake and Poyang Lake, and occasionally appears at the Yangtze River estuary. The number of porpoises in Poyang Lake accounts for about half of the total population .

The migration season for wintering migratory birds has begun, and wintering migratory birds such as swan geese are migrating in one after another. The drastic changes in the hydrological situation have had a great impact on the habitat of flora and fauna in Poyang Lake. It is expected that the Poyang Lake area will be conducive to the habitat of finless porpoises and the foraging of migratory birds this year.

Comprehensive sources: Guangming.com, China National Geographic, China Science Expo, Beijing Aquatic Wildlife Rescue Center