Earthshots: Satellite Images of Environmental Change

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» Huang He Delta, China

The Huang He River in China is a wanderer. Its lower reaches have changed course many times, moving the delta up and down the coast several hundred kilometers over the centuries.

The Huang He (Yellow) River is over 4,800 kilometers long. It’s the 2nd longest river in China and the 5th longest in the world. It’s also the muddiest river on Earth. On its long journey, the river crosses a soft plateau that’s covered with fine, wind-blown soil. The river carries away millions of tons of this delta-building material every year. The Huang He derives its yellow color from fine particles of mica, quartz, and feldspar.

The river shows up well in most of these Landsat images because of the high sediment load, which reflects light. The sediment even shows up in the water of many of these images where the river flows into the sea.

Map of the featured area.

The Huang He Delta has historically built up over a broad area because of its wandering ways. The river’s course in its lower reaches has shifted 11 times since 1855. The latest shift was in 1976. Before that, the river turned northward into the sea; in 1976, it took a different direction, heading east and carrying its sediment to build a new delta there.

The river now carries its sediment farther outward to create the beak-shaped delta that protrudes progressively into the sea.

While the river’s course and delta have changed naturally over time, people have also caused a lot of change. More water upstream is being used for irrigation. Dams and reservoirs on the river and its tributaries reduce the amount of sediment that reaches the delta. Seawalls have been built to reclaim land for the oil industry and for shrimp and salt farms. Additionally, levees now keep the main river from branching out at the delta.

People have caused the latest shift in the river that has affected the delta’s shape. In 1996, Chinese engineers blocked the main channel, making the river empty into the sea to the northeast instead of directly to the east. We see in the 1999 image where the new peninsula has formed from this shift, and where the old peninsula is beginning to retreat.

The city of Dongying is prominent in the 2010 image. Its current population is over 1.2 million. But you won’t find the city in the 1976 or 1979 images because it isn’t there. Dongying was established in 1983 with the opening of an oilfield on the northern delta.

Also noticeable in the time series images is the expansion of salt and shrimp farms, displayed by the dark geometric shapes along the coast. These farms were built on what were once tidal flats, a muddy coast that served as a buffer against storm erosion. Extensive development has degraded the tidal flats, resulting in increased coastal erosion.

The aquaculture development on the delta can have positive effects. While many of the shapes seen in the images are salt fields, many are shrimp farms that have recently moved toward culturing different seafood such as sea cucumber and crabs. These species have a lower carbon footprint, and shellfish also help clean the coastal waters. Another species beginning to be farmed is algae, which are at the very bottom of the food chain. Algae, often used as a nutritional supplement, are great at sequestering carbon dioxide from the atmosphere.

The rapid population growth in this area puts pressure on water resources and on the land, which has to grow increasing amounts of food. The region will need to plan carefully for the growth that accompanies economic development.


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