Ob River

• Category: Inland Aquatic Biomes.
• Geographic Location: Eurasia.
• Summary: The Ob River watershed faces environmental issues including water diversion, nuclear waste, and oil and gas development.

The Ob River watershed is the fifth-largest drainage basin in the world, and the Ob is the westernmost of the three great Siberian Rivers, extending from northern Kazakhstan to the Arctic Ocean. The total river length is 2,300 miles (3,700 kilometers). Ob River drainage begins in the temperate grasslands and coniferous forests of the Altai Republic (near Lake Teletskoye) and flows northwestward, eventually entering the Kara Sea, part of the Arctic Ocean, through the Yamal-Nenets Autonomous Region of Russia in Arctic tundra. To the west of the catchment are the Ural Mountains, and to the east is the Central Siberian Plateau.

The largest tributary of the Ob is the Irtysh. Its drainage begins in the far western mountains of Mongolia and the Xinjiang Uyghur Autonomous Region of northwestern China, and flows northwest through the steppes of Kazakhstan to Omsk in Russia, where it enters the forests of western Siberia and eventually joins the Ob in the Khanty-Mantsi Autonomous Region.

Climate

The Ob crosses several climate zones. The lower reaches of the Ob are Arctic tundra, and the river is ice-bound 100 miles (160 kilometers) above its mouth from the end of October to the beginning of June each year. Mid-sections of the river flow through taiga, or boreal forest, while the upper reaches flow through the warmer temperate forest zones or steppe regions.

In general, the Ob basin has short, warm summers and long, cold winters. Average January temperatures range from minus 18 degrees F (minus 28 degrees C) on the shores of the Kara Sea to 3 degrees F (minus 16 degrees C) in the upper reaches of the Irtysh. July temperatures for the same locations, respectively, range from 40 degrees F (4 degrees C) to above 68 degrees F (20 degrees C).

Precipitation varies greatly in the Ob River watershed: less than 16 inches (40 centimeters) per year in the north, 20–24 inches (50–60 centimeters) in the taiga zone, and 12–16 inches (30–40 centimeters) on the steppes. The western slopes of the Altai Mountains receive as much as 62 inches (160 centimeters) per year.

Flora and Fauna

The Ob River estuary is a gulf that extends 500 miles (800 kilometers) north from where the river first enters the sea, making it the longest estuary in the world. The Taz River estuary here is a branch of the Ob River estuary, further extending its reach. The vast floodplain of the Ob River from Khanty-Mantsi north to the Gulf of Ob is one of the richest waterfowl habitats and nesting areas in the world. Three large wetlands of international importance, as designated under the Ramsar Convention, are present in this area. One of them, the Islands in Ob Estuary Ramsar Site (Nizhne-Obskiy Nature Reserve), is a vast delta consisting of numerous islands and temporary lakes used for duck migration.

Before reaching the sea, the river flows through a swampy taiga floodplain about 12–19 miles (20–30 kilometers) wide. A network of interconnected lakes and channels characterize the lower river within the extensive Western Siberian Lowland. This is a boggy area with belts of taiga, generally evergreen conifer, forests along rivers. Trees are widely spaced, with an understory of dwarf shrubs. Fish here include Arctic migratory species such as tugun, peled, muksun, and char; and boreal river species of pike, dace, and perch.

Of some 50 species of fish found in the river or in the gulf, the most valuable, economically speaking, are several varieties of sturgeon. Shallow floodplain water bodies called sors serve as major areas of feeding for migratory fish. Other, smaller river systems that are tributaries to the Kara Sea have a similar fish fauna. Lake Teletskoye, near the Ob River headwaters, has endemic (found nowhere else) species of whitefish.

The Turgay Plateau of Kazakhstan is the southern watershed boundary, separating north-flowing polar rivers from the temperate Volga or Caspian Sea drainage to the west. The steppe grassland habitats in this area contain patches of forests, and a narrow band of deciduous forest grows between the steppe and boreal forest. In the steppes in the southern part of the Ob River drainage, aspen, birch, and pine grow in small groves called koloks.

Within this steppe region are lakes used by migratory waterfowl; many of the lakes are saline and do not have connections with a river system. Thousands of lakes and wetlands dot the steppe and deciduous and conifer forests, providing vital habitat for waterfowl in this otherwise-dry region. There have been more than 170 bird species identified here.

Mammals of the Ob watershed include European and Siberian mole, Siberian and American mink, ermine, fox, wolf, elk, white hare, water rat, muskrat, otter, and beaver. Notably, the Siberian subsoil contains the remains of as many as 150 million mammoths, which have been frozen for thousands of years. Ivory tusks are found as more and more tundra melts away as the world warms. Common areas for exposure of these prehistoric fauna are along the eroding banks of rivers. Since the 19th century, about a dozen soft-tissue specimens of mammoths have been recovered. In May 2007, a complete, month-old baby mammoth corpse was found lying on a sandbar in the Yuribey River in Yamalia.

Human Impact

In the north, the river flows through the low-lying West Siberian Plain. It is the site of the world’s second-largest gas field, the Urengoy field, in Yamal-Nenets; it is also the home of most of Russia’s oil production, in Khanty-Mantsi. The Samotlor Oil Field is Russia’s largest. The Urengoy and Nadym gas fields extend southward from the Gulf of Ob and the Gulf of Taz. To the north of the Taz River, the Yamburg Gas field is the world’s third-largest gas field and Russia's second largest. And the Bovanenkovo Production Zone on the Yamal Peninsula is one of the newest and northernmost gas fields. In 2020 it produced 99 billion cubic meters. These oil and gas developments also include networks of pipelines and gravel roadbeds. Environmental management, including the prevention of chemical spills and its effects on indigenous peoples, are key issues.

In the southern parts of the Ob River watershed, water diversions have been discussed to provide water for drier southern areas. China is working on a project to divert the upper Irtysh River to provide water to drier parts of Xinjiang through an underground irrigation canal system. In 2023, it was reported that China diverted 21.5% of the runoff in the Irytish Basin, significantly decreasing the water level of the river and the amount that reaches other countries.

In the watershed in Chelyabinsk and Sverdlovsk Oblasts, are areas affected by the legacy of nuclear weapons production. At Ozersk (Chelyabinsk-65), a 1957 explosion in a radioactive-waste storage area dispersed radioactivity into Sverdlovsk and Tyumen Oblasts. In the southern watershed along the Irtysh River in Kazakhstan, the Semipalatinsky Test Site was where much of the former Soviet Union’s nuclear testing took place. Toxic remains from these activities remain a concern today.

Global climate change is now affecting the glacier melt in the Altai Mountains, and therefore water flow in the Ob River basin. Greenpeace reports that the melting permafrost soil not only affects the way of life of the indigenous nomadic Nenets people, but also adds burden to existing climate change because of the massive release of methane and carbon dioxide as decomposition is activated in the defrosting soil.

Bibliography

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Krickov, Ivan V., et al. "Sizable Carbon Emission from the Floodplain of Ob River." Ecological Indicators, vol. 131, 2021, doi.org/10.1016/j.ecolind.2021.108164. Accessed 31 Oct. 2024.

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