NASA MODIS Image of the Day: March 27, 2012 – Sediment in the South China Sea
A thick curtain of sediment poured from the Yangtze River and spread across the East China Sea on March 26, 2012. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite captured this true-color image at 5:10 UTC (1:10 p.m. China Standard Time). In this image, both the Yangtze River and Hangzhou Bay, to the south, are filled with thick brown sediment. The sediment extends both to the north and the south along China’s coast, and is joined by sediment from smaller watercourses along the coast. As the sediment flows into the East China Sea, it begins to sink and the reflectance quality changes; as less light is reflected, the color becomes greenish, then blue. The Yangtze River, also called the Changjiang River, is Asia’s longest watercourse, flowing about 6300 kilometers from the Geladaindong Mountains of the Tibetan Plateau to empty in the East China Sea near the city of Shanghai. Below the Three Gorges Dam, the flow rate in middle and lower Yangtze reaches approximately one to two meters per second. At this rapid rate, sediment loading can become intense, especially combined with human activities which create debris or destroy vegetative land cover. The Yangtze River basin is home to approximately one-third of the population of China, and the land is steep, so land use easily affects water quality. The building of the Three Gorges Dam and related projects, including road grading and construction in the area, has been identified as a source of increased sediment deposition. On the triangular point of land just south of the milk-chocolate colored waters of the Yangtze, the city of Shanghai can be seen as a long gray blotch surrounded by green vegetation. Lake Taihu sits to the southeast of Shanghai, and also bears the creamy tan color which indicates sediment. A haze hangs over Shanghai, and in some areas is so thick it obscures the ground, especially southeast of Lake Taihu. A few clouds also hang over the land in this area. In true-color images, both thick haze and thin cloud can sometimes have a similar appearance.
