Shulou(Shulou.com)11/24 Report--

This article is from the official account of Wechat: Earth knowledge Bureau (ID:diqiuzhishiju), author: cold Night Cold Star

Author: cold Night Cold Star

Revised manuscript: gu Hanying / Editor: Fruit Chestnut

Perhaps you have wandered in the beautiful fragrance of the Liaozi Flower Sea and were reluctant to part; maybe you could not hide the joy of seeing the whole picture of Luoxingdun after the blue waves had faded; maybe you had immersed yourself in the joy and play on the beach prairie of Poyang Lake. But perhaps you do not know that behind these beauties and joys is the increasing shortage of the habitat of rare winter migratory birds such as white cranes, cranes and swans, the constant compression of the swimming space of the finless porpoise, and the helpless brows of farmers during spring ploughing.

Behind the beautiful scenery is the drying up of Poyang Lake and the shrinking habitat.

Since late February this year, the water level in Poyang Lake has continued to decline due to the reduction of water from the five rivers such as the Ganjiang River in Jiangxi Province and the receding of the water level in the mainstream of the Yangtze River. on February 27, the water level of Xingzi Station in Poyang Lake is 7.9 meters, which is lower than the extremely low water level of 8 meters. the water area of Tongjiang in the lake area is only 277 square kilometers, reaching the low water blue early warning standard. According to the analysis of the hydrological department, it is expected that the water level of Poyang Lake will continue to decline for a period of time in the future.

On March 2, the water level of Xingzi Station in Poyang Lake was as low as 7.47 meters.

Jiangxi Hydrological Monitoring Center upgraded and issued a low-water yellow warning on the same day.

(figure: xiaoyuka.com) ▼

Why is the problem of water shortage in Poyang Lake more and more prominent in recent years? If we want to explore the reasons for the ecological deterioration of Poyang Lake during the dry season, we have to start with the past life and this life of the largest freshwater lake in China.

The success of the Great Lake: Poyang Lake, the largest freshwater lake in China, is located in the north of Jiangxi Province, accounting for nearly 94% of the surface runoff in Jiangxi Province, and eventually converges into the lake, so Poyang Lake is affectionately called "Mother Lake" by Jiangxi people.

At the end of water resources in Jiangxi Province, many tributaries converge.

The lake area at low water level is about 1/8 ▼ of that at high water level.

Among the many tributaries of Poyang Lake, Xiushui, Ganjiang, Fuhe, Xinjiang and Raohe are the most important rivers. They are not only the backbone of Poyang Lake water system, but also the dense distribution area of population and regional economic center of Jiangxi Province.

Most of the larger cities in Jiangxi are ▼ along the river.

The waters of Poyang Lake are bounded by Songmenshan Island in the lake and can be roughly divided into two lakes in the north and south. The northern space is squeezed by the Lushan Mountain on the west and the hills on the east, and the lake is relatively narrow, which is very different from the broad waters where the rivers converge to the south of Songmen Island.

The southern part of Poyang Lake is the main lake area.

The narrow and long area in the north is the waterway into the river.

(figure: NASA) ▼

During the Yanshan movement 130 million years ago, during the uplift of Lushan Mountain, a large area of subsidence occurred in the southeast of Lushan Mountain, forming a graben lake basin, which laid the basic geological conditions for the formation of Poyang Lake.

About 6000 years ago, after the ancient Yangtze River came out of the Wu cave in Hubei Province, a fan-shaped delta-like bifurcated water system was formed on the north side of Jiangxi Province today. "Yugong" is called "Jiujiang", and this Jiujiang converges on Gupenglize.

▼

Ancient Penglize is the confluence of rivers, and its scope is equivalent to the riverside lakes in eastern Hubei and western Anhui on the north bank of the Yangtze River. After that, the area around Poyang Lake began to sink, and the lake gradually invaded to the south. During the Sui Dynasty, Peng Lize's lake expanded southward to near Poyang County.

The "Peng Li Ze" ▼ in the Western Han Dynasty

From the late Tang Dynasty to the early Northern Song Dynasty, the new Peng Lize rapidly expanded to the southeast plain, which established the scope and shape of Poyang Lake today.

After the opening of the Grand Canal, Poyang Lake became a life-and-death joint related to Jiangxi water transport and trade channels. Since the Ming Dynasty, the water transportation trunk line of the Grand Canal-Yangtze River-Poyang Lake-Ganjiang-Dayu Ridge-Pearl River (Beijiang)-Guangzhou has become the most important inland north-south waterway in the middle and later period of ancient China.

Schematic diagram of Jingguang waterway ▼

From the 13th century to the 16th century, the global geological plate activity was active, and due to frequent earthquakes and other factors, the sinking trend in the southeast of Poyang Lake was obvious. In addition, since the Qing Dynasty, China's climate is in a small ice age, resulting in more plum rain in the south, so the surface runoff into Poyang Lake continues to increase, Poyang Lake further expanded, entering the heyday of water area of 6000 square kilometers.

From the point of view of hydrological characteristics, Poyang Lake is a typical lake with the throughput of the Yangtze River. the so-called "swallowing" means that Poyang Lake, in addition to accommodating the flow of Xiushui, Ganjiang, Fuhe, Xinjiang and Raohe rivers, its swallowing position in the Yangtze River may also cause it to "swallow" part of the runoff of the Yangtze River; the so-called "spit" means that many of its confluent rivers will "spit" into the Yangtze River through Poyang Lake.

The huge throughput of Poyang Lake

It is the main reason for its "different lakes" in different seasons.

(figure: google map) ▼

When the flood season comes, the amount of water "swallowed" by Poyang Lake is far greater than that "spit", the scene of "flood" will appear, and the maximum water area of Poyang Lake in a year appears during this period. When the dry season comes, the amount of water that Poyang Lake "spits" into the Yangtze River is greater than its "swallowed" surface runoff. At this time, the water area of Poyang Lake shrinks greatly, and there is a scene of "low water".

There is a very close relationship between the water level of Poyang Lake and the amount of river water.

If the river runs out of water, Poyang Lake can be "thinned into a bolt of lightning" every minute.

(base: NASA) ▼

Thus it can be seen that the lake area of Poyang Lake varies greatly in flood season and low water season, and the water storage capacity of Poyang Lake is relatively limited because of the hydrological characteristics of its water quantity "spitting" into the Yangtze River.

The trap of the Great Lake: the reclamation of the lake and the aggravation of low water since the middle ages, the expanding agricultural production activities around Poyang Lake have made the trunk and tributaries of the Poyang Lake system silt up into the lake, especially since the middle of the Qing Dynasty. the intensification of land reclamation not only eroded the watershed space of Poyang Lake, but also accelerated the decline of its water storage capacity caused by soil and water loss.

The sediment deposited is more obvious in the dry season.

The water is divided into "small lakes" by sediment.

(figure: NASA) ▼

During the Southern Song Dynasty, with the completion of the southward shift of China's economic center and the surge of population in the southern region, large-scale agricultural development began in the vast hilly and lakeside areas.

In the upper reaches of many rivers in the Poyang Lake system, due to soil erosion caused by deforestation and opening up wasteland, the sediment content of the river increases continuously, and the slower downstream channels are silted up. Finally deposited in the Ganjiang River, Fuhe River, Xinjiang River, Raohe River, Xiushui and other rivers into the lake delta front.

This siltation makes the river not smooth in the flood season, flooding, and then force the river to change its course and run into other water systems, while the lower reaches of the five rivers gradually form bird claw tributaries into the lake due to continuous bifurcation.

However, the "tree of the earth" formed by the confluence of rivers into Poyang Lake is quite beautiful.

Since the middle of the Qing Dynasty, China's population growth has accelerated, and the siltation and expansion of the lake delta has provided conditions for reclaiming farmland from the lake and increasing arable land.

After these deltas are silted to a certain height, some farmers build dikes for reclamation, resulting in continued siltation outside the levees, which is higher than that inside the levees, that is, "Jiuwei into ponds". The more the siltation expands, the reclamation moves along with the advance, and gradually pushes to the center of the lake, resulting in the downward movement of the estuary of each river. As a result, the water area of Poyang Lake began to shrink and the water storage capacity decreased gradually.

Remote sensing monitoring shows that the delta of the middle branch of the Ganjiang River extends obviously into the lake mouth.

(photo: Jiangxi Academy of Water Conservancy) ▼

However, due to the compression of the hilly areas on both sides of Poyang Lake, the agricultural production land around Poyang Lake is relatively limited, and its scale is far less than that of Dongting Lake Plain in Hunan Province.

Although the barrier of Mount Lushan made the urban construction of Jiujiang not like that of Yueyang in Hunan Province, it also suppressed the momentum of farmland construction along the coast of Poyang Lake in previous dynasties. This situation is more obvious in the North Lake part of Poyang Lake.

After the 1970s

The reclamation area of Poyang Lake has not increased significantly.

(photo: Jiangxi Academy of Water Conservancy) ▼

At the beginning of the 20th century, when the sediment deposition in Dongting Lake became more and more serious, because the warlords and officials competed for land and profits with the people, they competed for reclamation when they saw the silt, which further aggravated the shrinking of the lake. By 1983, Dongting Lake had shrunk to 2691 square kilometers. As a result, Poyang Lake has surpassed Dongting Lake to become the largest freshwater lake in China.

Yun Mengze of Hao Tang Tang only stays in the records of history books.

(photo: atlas of Hunan Province) ▼

In the implementation of the development strategy of the green rise of Jiangxi, more attention has been paid to the ecological construction of Poyang Lake. However, in recent years, with the continuous construction of water conservancy facilities such as the trunk and tributaries of the Yangtze River and reservoirs in the upper reaches of Poyang Lake, Poyang Lake is facing a new ecological crisis.

In order to alleviate the problem of water shortage in agricultural and residential life in the local dry season, these reservoirs have carried out water storage at the end of the flood season.

In this way, in the dry season, not only the main tributaries of the Yangtze River and Xiushui, Ganjiang, Fushe, Xinjiang and Raohe and other rivers sharply reduce the amount of water discharged into Poyang Lake, but also the sediment content of these rivers is also greatly reduced due to the obstruction of the water control project. in this way, the discharge of clear water scours the downstream river, making the river continuously cut down.

Distribution of some dikes in Poyang Lake area since the Founding of the people's Republic of China

(base: NASA) ▼

As a result, although the water storage capacity of the downstream river has been increased, but at this time, the amount of water "swallowed" in Poyang Lake is not reduced, but the amount of water "spit" is increasing. Since then, the water level of Poyang Lake continues to decline in autumn and winter, and the dry season of Poyang Lake is getting earlier and earlier year by year.

The aggravation of the extremely dry state in the dry season of Poyang Lake has brought a series of ecological problems. Not only the contradiction of urban and rural water supply in Lushan City, Duchang County and other areas along the coast is aggravating, it is more and more difficult to obtain water for agricultural irrigation, but also the shipping traffic is blocked, and the capacity of ships decreases greatly in the dry season.

In the extremely dry state of Poyang Lake

It's not the boat but the man who can walk.

What is more worrying is that the wetland ecosystem of Poyang Lake has been degraded. As a result, fish resources and submerged plants in the lake area continue to decrease, while migratory birds can only transfer to constructed wetlands because they are unable to find enough food from natural wetlands, resulting in a reduction in population and population.

Finless porpoises, known as "giant pandas in the water", sometimes starve to death due to lack of food or injured by ship propellers because of the compression of mobile space.

If Poyang Lake does not want to lose the smile of the finless porpoise

We must pay attention to the current ecological problems.

Danger of the Great Lakes: extreme drought and water shortage from late June to mid-November 2022, Jiangxi Province experienced a historical extreme drought. Not only the number of days without rain was at an all-time high, but the average precipitation also decreased by 6.7%, reaching the lowest level in the same period in history. During this period, the average temperature and high temperature days in Jiangxi Province ranked the highest in the same period.

From drought in summer to winter

Jiangxi had a hard time in the second half of last year.

(photo: national Climate Center) ▼

Affected by this historical extreme drought, on September 23, 2022, the water level of Poyang Lake Xingzi Station fell to 7.10 meters, falling below the historical lowest water level; on November 17, the water level of Poyang Lake fell to 6.46 meters, setting another record for the lowest water level, and the water area of the main body of Poyang Lake and its vicinity repeatedly set new lows.

The water level process line of Xingzi Station moved obviously to the left in 2022.

And the water level has fallen very fast since the end of June ▼

Did it with Dongting Lake next door.

(photo: Jiangxi Hydrological Monitoring Center) ▼

By November 17, the water level was historically low.

(photo: Jiangxi Hydrological Monitoring Center) ▼

Due to the aggravation of the dry weather and the extension of the dry period of Poyang Lake, at the end of November and the beginning of December last year, under the influence of the winter northwest monsoon, the roaring north wind blew a large area of sediment from the bottom of Poyang Lake to Nanchang because of the low water. as a result, the southern provincial capital surrounded by the lake and wetlands encountered sand blowing weather for several days.

The rare air quality index in Nanchang is ▼.

On the eve of the Spring Festival in 2023, with several streams of cold air moving south and rain coming one after another, the drought warning in many parts of Jiangxi Province was lifted one after another. At one point, the water level of Poyang Lake rose again in mid-February, and its water area was significantly larger on February 15, which was about 57% larger than that on January 31, and the water shortage was alleviated to a certain extent.

Finally returned to the appearance of the lake.

(photo: CCTV) ▼

However, from the past February, the precipitation in Jiangxi Province is still on the low side, and shows a trend of more before and less after. In the coming week, most parts of Jiangxi Province will still have sunny or cloudy weather, the temperature will continue to be on the high side, and the precipitation will be significantly less than that of the same period of the year. Poyang Lake, which has not "recovered" from last year's drought, will face a new round of water shortage crisis.

Jiangxi will not be able to wait for heavy rain to quench its thirst in the short term.

(photo: central Meteorological Station) ▼

According to the FY-3D meteorological satellite monitoring of the National Satellite Meteorological Center, on February 27, the water area of Poyang Lake was about 1044 square kilometers. Compared with the average value of the same period in the past decade, the water area of Poyang Lake decreased by about 21.8 percent, and compared with the same period last year, the water area decreased by about 30.5 percent, reaching the lowest area for the same period in nearly 10 years.

(photo: national Satellite Meteorological Center) ▼

The persistence of drought and high temperature is the main reason for the aggravation and persistence of low water in Poyang Lake.

The Poyang Lake basin is the main area of population distribution in Jiangxi Province. In the face of continuous drought, many cities in the upper reaches of Poyang Lake can only use dams and other water conservancy facilities to store river water to ensure the safety of water supply. For example, in September last year, in order to ensure the safety of urban water supply, Nanchang City had to build a temporary water-lifting cofferdam in the Nanchang section of the Ganjiang River (which was demolished at the end of November last year) to raise the water level of the Ganjiang River to ensure water supply.

To ensure the use of water for residents

Carrying the cofferdam is only a last resort.

(photo: Jiangxi Network Radio and Television Station) ▼

The water storage and lifting of these water conservancy facilities in the upper reaches will inevitably aggravate the water shortage in Poyang Lake. On the other hand, not storing and carrying water will threaten the safety of water supply for nearly 20 million people. At present, spring sowing is being carried out one after another, which may further aggravate the drought and low water condition of Poyang Lake.

In the movie wandering the Earth, Ma Zhao once said: "without human civilization, there is no meaning." Similarly, not considering the ecological protection of human survival is a complete negation of the development of human existence and the progress of civilization.

In 2022, 2769 artificial precipitation increases in Jiangxi Province were negligible in the face of sudden drought. How to transfer the "flood" Poyang Lake to the "low water front line" Poyang Lake, this time-space storage problem is still urgent for researchers and builders to challenge and break through.

Reference:

1. Editorial Board of Poyang Lake Research: Poyang Lake Research, Shanghai Science and Technology Press, 1988.

two。 Zhong Qihuang: general History of Jiangxi, Jiangxi people's Publishing House, 2008.

3. Liu Zhigang, "the Development and Evolution of Poyang Lake and the influence of changes in the relationship between rivers and lakes", Journal of Environmental Science, No. 5, 2015.

4. Tang Guohua and Hu Zhenpeng: a study on the expansion and morphological Evolution of Poyang Lake during the Ming and Qing dynasties, Jiangxi Social Sciences, No. 7, 2017.

5. "Why is the Poyang Lake Water Control Project difficult to give birth", China Science Daily, March 21, 2021.

6. Wang Jianhua and Liu Huan: "6% of the world's water resources feed 20% of the world's population!" How much water resources are available in our country? Knowledge is Power, No. 3, 2021.

7. Li Qing: Poyang Lake and Jiangxi economy in History, Master's thesis of Jiangxi normal University in 2012.

8. The water area of Poyang Lake has shrunk to the smallest netizen in the same period of nearly 10 years: why is it withered again? China Weather Network.

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