Yalu River ecosystem

Category: Inland Aquatic Biomes.

Geographic Location: Asia.

Summary: The Yalu River is the border river between China and North Korea, an area rich in biodiversity and vital to migrating raptors and waterfowl.

The Yalu River is located on the border between China and North Korea. It was known as the Ma Zi River during the Han Dynasty. Starting in the Tang Dynasty, it became known as the Yalu River. The word yalu in Chinese means “duck green,” and the name is thought to originate from the fact that the clear waters of the river appear the same color as the feathers on a duck’s head. Another possible source of the name is the combination of two river names, the Ya River and Lu River, which do come together to form the Yalu.

The Yalu River originates in the Changbai Mountains in northeastern China, then flows southwest through the cities of Changbai, Linjiang, Kuandian, and Dandong along the border between China and North Korea. As the various tributary branches of the Yalu combine, the river’s southward flow takes it into the Yellow Sea. Approximately 493 miles (795 kilometers) long, the Yalu covers an area of over 39,767 square miles (64,000 square kilometers). The river ranges 459–1,279 feet (140–390 meters) wide in various sections; at its estuary, the Yalu is 3 miles (5 kilometers) wide.

Except for small areas of basalt in the upper portions, the entire riverbed of is mostly Precambrian rock formations; the river flows through deep river valleys in rugged mountainous terrain in most places. There are many waterfalls and hidden reefs. The lower part of the Yalu has slow-running water; it is often used for timber transportation. Alluvial sediment is plentiful in this segment, and the water is very shallow in winter. In some places, even a raft cannot float downriver easily.

South of Ji’an City, the river opens onto a coastal plain; the water runs deep and swiftly in this area. It is a spot conducive to hydroelectric plants, and several have been built there. The water then slows once more, depositing more alluvial sediment to form many large deltas and islands along the estuary to the Yellow Sea. The rate of sedimentation assures that the delta grows, and that the alluvial area of the river becomes more shallow, with mudflats and reed islands growing.

The annual precipitation in the Yalu River area is 34–43 inches (870–1,100 millimeters), and is higher in the downstream region than upstream. Summer floods occur annually starting in mid-June, and the monthly flow reaches its highest point in August. The summer water flow makes up about 60 percent of the total water flow in an entire year, with the average annual flow rate at around 3,038 cubic feet (926 cubic meters) per second. The water volume decreases in the fall, and the river enters its dry season in October. A series of reservoirs have changed the character of these natural seasonal flows to a great extent, however.

Biodiversity

The Yalu River area is considered a humid, temperate climate zone. The winter is very cold and the summer is warm. There are vast differences in terms of natural conditions between the upper and lower parts of the Yalu River. The river surface is usually frozen from December to April.

The ample precipitation encourages the growth of conifer and deciduous trees, and vast forests cover much of the landscape. Forests provide ideal habitats for various wildlife; commonly found mammals along the river banks include the wild hog, wolves, tigers, leopards, bears, and foxes. Birds such as the pheasant and many others are found here. In Liaoning Province, a major migration route and resting place for waterfowl and raptors, at least 163 species of water birds and 46 species of shorebirds have been recorded among the more than 400 total avian species cataloged here.

Some 90 fish species in the Yalu River give proof of a fairly robust riparian habitat. Most are native species, including types of carp and eel. They must contend, however, with a number of introduced fish species, such as silver carp, bighead carp, blue fish, grass carp, Changchun bream, and triangular bream. Each of these is considered a favorable type for subsistence or commercial fisheries.

Threats

Threats to the Yalu River include human-induced changes, such as the addition of hydroelectric plants that change the nature of the river and destroy habitatable areas, as well as the increased pressure upon farmlands to produce more and more food. Climate change threats include greater chances of floods. A 2020 study published in the journal Hydrology and Earth System Sciences, found that flooding on the river steadily increased from the year 1000 to 1940. Following a decrease during the latter half of the twentieth century, flooding on the Yalu is once again rising as of the 2010s—the last decade for which data was available. Combined atmospheric changes and direct human intervention, in the forms of logging and land-clearance for more cropland, are degrading the capacity of some ecosystems along the Yalu River to keep pace. Flora and fauna that cannot adapt must move to higher ground in some cases, or find shelter and sustenance in the expanding estuary area in others.

Bibliography

Alpine Birding. “Liaoning Province.” http://www.alpinebirding.com/lview.asp?id=64.

Gao, Jian-hua, Shu Gao, Yan Cheng, Li-xian Dong and Jing Zhang. “Sediment Transport in Yalu River Estuary.” Chinese Geographical Science 13, no. 2 (2002).

Sheng, Hui, et al. “Frequency and Magnitude Variability of Yalu River Flooding: Numerical Analyses for the Last 1000 Years.” Hydrology and Earth System Sciences, vol. 24, 2020, pp. 4743–4761, doi.org/10.5194/hess-24-4743-2020. Accessed 18 Aug. 2022.