Lake Uvs Nuur

Category: Inland Aquatic Biomes.

Geographic Location: Asia.

Summary: A salty lake located between desert and tundra, Uvs Nuur is important to many migrating birds and supports some unique fish species.

Lake Uvs Nuur is a highly saline lake in an arid, high-altitude basin located mostly in Mongolia and partly in Russia. The largest lake in Mongolia, at 1,300 square miles (3,350 square kilometers), Uvs Nuur has a surface elevation of 2,490 feet (759 meters). The lake averages a depth of just 20 feet (6 meters). Uvs Nuur is a remnant of an ancient lake that covered 35,500 square miles (92,000 square kilometers) and plunged 2,430 feet (740 meters) deep. Ancient mountain uplift separated the present Uvs Nuur basin from the Khirgis Nuur basin to its south, causing major depletion of these waters. Glacial action, winds, and fluid erosion processes molded the present lake basin. The lake’s surface level was more than 130 feet (40 meters) higher in the last ice age, but evaporation has steadily reduced it to the current state, with high groundwater salinity part of the proof.

The lake is fed by several rivers that originate at the edges of the basin, either in the Altai Mountains to the west or the Khangai Mountains in the east. There is no outlet; the basin is endorheic, meaning draining to the interior. This contributes to the degree of salinity, which is roughly half that of ocean water. The basin spans the geoclimatic boundary between Siberia and central Asia, making for extreme variance in temperatures. From a high of 117 degrees (47 degrees C) in summer, the temperature can reach minus 72 degrees F (minus 58 degrees C) in winter. The water temperature gradient responds to these changes; for instance, in summer a surface temperature of 77 degrees F (25 degrees C) can decrease to 66 degrees F (19 degrees C) at the bottom. Uvs Nuur is ice-covered from October to May, despite its high salinity.

Between 1999 and 2020, water salinity shifted and conditions changed from low algal production and nutrient content, accompanied by clear and oxygenated waters, to grey-colored, somewhat turbid waters with medium levels of nutrients and an intermediate level of productivity.

Flora

Uvs Nuur contains diverse flora communities. Its shallow shore habitats are occupied by species-poor spreads of reed marshes. These are often severely and continuously disturbed by cattle; their grazing and trampling results in the development of annual mudbank communities. The region also includes low reedbeds of mare’s tail and spike-rush that develop in shallow water bodies. Aquatic vegetation is primarily represented by fennel pondweed, with water milfoil, stoneworts, and gutweed present. In addition, free-floating duckweed communities appear in several oxbow lakes and pools around the fringe.

At times when the water level drops, short-living stands of dwarf rushes establish themselves on the moist mudbanks, alongside alkali seepweed. Celery-leaved buttercup appears in places, along with oak-leaved goosefoot.

Some salt-tolerant plants grow in shallow depressions that have been cut off from Uvs Nuur, such as glasswort around the bare central part of salt pans with a thick salt crust, followed by stands of alkali seepweed. The transition areas from this groundwater-dependent, halophytic vegetation to the steppe and semidesert are often inhabited by belts consisting of tall and coarse tussocks of Mongolian derris and its associated species.

Fauna

Uvs Nuur is home to 49 species of phytoplankton, 83 types of phytobenthic algae, 45 kinds of aquatic macrophytes, 66 different zooplankton, and 118 species of zoobenthos. The littoral invertebrate community includes scuds, small waterfleas, oar-feet crustaceans, seed shrimp, and insect larvae.

Uvs Nuur is an important habitat for 46 resident waterfowl species, as well as 215 different kinds of birds migrating south from Siberia. At the northernmost area of central Asia, Lake Uvs Nuur and a few smaller neighboring lakes are key nesting sites for many birds, including at least 10 species that overwinter here. Altogether, an estimated 20,000–50,000 waterfowl per year utilize the 24-mile (40-kilometer)-wide delta of the Tes-Khem River, a major lake tributary that meanders through an extensive wetland complex. The Uvs Nuur is critical for waterfowl conservation for such endangered species as the white-headed duck and swan goose.

A few dozen mammal species live or pass through the Uvs Nuur biome, including the globally endangered snow leopard.

The lake supports several fish species from genus Oreoleuciscus, which is considered near-endemic to the region, meaning it is found scarcely anywhere else in the world. Because of the relative isolation of Uvs Nuur, many of its fish species are endemic or near-endemic. Altai osman, Mongolian grayling, and various species of the ray-finned genus Triplophysa also inhabit the lake.

Environmental Issues

As a moist, if salty, oasis in a high basin sited between tundra and desert, Uvs Nuur has not been polluted or developed by industrial or commercial interests. Much of its human interaction takes the shape of pastoral and nomadic activity. The area is generally one of low population density, although livestock herd size in the province has expanded in recent years. There has also been some diversion of water from tributaries, which at times makes fish migration difficult. As environmental protection actions increase in Mongolia, some attention has been paid to Uvs Nuur, which the government classifies as a Strictly Protected Area. Nearby, a national park is located on one of the lake’s tributaries. Various international designations have been conferred on the lake and its basin, such as Biosphere Reserve, Ramsar Site, and Important Bird Area. In 2003, the lake and the surrounding basin were named a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Site

Bibliography

Alonso, Miguel. Limnological Catalog of Mongolian Lakes. Barcelona, Spain: Endesa, 2011.

Batima, Punsalmaa, Nyamsuren Batnasan, and Bernhard Lehner. Freshwater Systems of the Great Lakes Basin, Mongolia: Opportunities and Challenges in the Face of Climate Change. Ulan Bator: Mongolia Programme Office, World Wildlife Federation, 2004.

Dulma, Auyur. “Hydrobiological Outline of the Mongolian Lakes.” Internationale Revue der Gesamten Hydrobiologie und Hydrographie 64, no. 6 (1979).

Fernández-Giménez, María E. “Spatial and Social Boundaries and the Paradox of Pastoral Land Tenure: A Case Study from Postsocialist Mongolia.” Human Ecology 30, no. 1 (2002).

Hilbig, Werner. “The Distribution of the Vegetation in the Uvs-Nuur Basin and its Surrounding Mountain Ranges.” Feddes Repertorium 114, nos. 7–8 (2003).

Shinneman, Avery L. C., James E. Almendinger, Charles E. Umbanhowar, Mark B. Edlund, and Soninkhishig Nergui. “Paleolimnologic Evidence for Recent Eutrophication in the Valley of the Great Lakes (Mongolia).” Ecosystems 12 (2009).

“Uvs Nuur Basin.” UNESCO, 2022, whc.unesco.org/en/list/769/. Accessed 19 Aug. 2022.