Sediment flows offshore from the Yangtze River 

Today’s Image of the Day from NASA Earth Observatory features a large sediment plume from the Yangtze River that extends hundreds of kilometers off the coast of China.

“Brown, sediment-laden water is visible along this shallow, turbid stretch of coast year-round, but a vast plume like the one visible here is a characteristic feature of winter. Scientists have proposed several causes of this seasonal phenomenon,” said NASA.

“The ebb and flow of tides contain enough energy to stir up sediments from the seafloor, a 2017 study found. While there are also tides in the summer, the models used in the study showed that sediment only rises to the surface in the winter. That’s when temperatures and salinities at the sea surface and bottom are similar, allowing for vertical mixing to occur and for sediment to churn higher into the water column.”

Additional studies have suggested that the summer monsoon’s influence on currents impedes the eastward flow of sediment out of the estuaries, noted NASA.

“Despite what looks like a glut of suspended sediment in the water, the overall amount of it flowing from the Yangtze River has declined steadily over the past several decades. The construction of dams, including the Three Gorges Dam, has been the primary driver of this trend.”

It is important for scientists to track the movement of suspended sediment. This material can cause direct harm to marine life, as well as indirect harm by blocking sunlight.

The Yangtze River, also known as the Chang Jiang in Chinese, is the longest river in Asia and the third-longest in the world, following the Nile and the Amazon. It flows for over 6,300 kilometers (about 3,917 miles) from the glaciers of the Qinghai-Tibet Plateau in western China to the East China Sea at Shanghai. 

The Yangtze River basin is a key region for China’s agriculture, industry, and hydroelectric power production. The river’s waters are used for irrigation, navigation, and as a source of freshwater. The basin is home to diverse wildlife, including the critically endangered Yangtze river dolphin or Baiji, which may now be extinct.

The image was captured on February 12, 2024 by the Visible Infrared Imaging Radiometer Suite sensor on the NOAA-20 satellite.

Image Credit: NASA Earth Observatory

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