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Posts tagged Algal Bloom

Sediments and Algae in the Persian Gulf – August 15th, 2009

29.5N 49.5E

August 15th, 2009 Category: Image of the day, Rivers

Persian Gulf - July 28th, 2009

Persian Gulf - July 28th, 2009

Iraq shoreline

Iraq shoreline

The Tigris and Euphrates Rivers carry great quantities of silt into the Persian Gulf off the shores of Iraq. The entire area near the rivermouths is a river delta interlaced by the channels of the two rivers and by irrigation canals.

In the close-up, agricultural areas are visible towards the upper left border, while marshlands and channels can be observed near the rivermouths.

Upon opening the full version of the main image, greenish blooms of algae can be seen in the gulf as well, particularly along the southern shoreline, which belongs to Saudi Arabia (left), Qatar (center) and the United Arab Emirates (right). The shores of Iran (above), on the other hand, show no algal growth and are flanked only intermittently by sediments.

Because the waters of the Tigris and Euphrates above their confluence are heavily silt-laden, irrigation and fairly frequent flooding deposit large quantities of silty loam in much of the delta area. Windborne silt also contributes to the total deposit of sediments.

It has been estimated that the delta plains are built up at the rate of nearly twenty centimeters in a century. In some areas, major floods lead to the deposit in temporary lakes of as much as thirty centimeters of mud.

Colorful Lakes in Central Africa – July 25th, 2009

8S 32.2E

July 25th, 2009 Category: Fires, Image of the day, Lakes

Tanzania, DRC and Zambia - June 21st, 2009

Tanzania, DRC and Zambia - June 21st, 2009

Three lakes in Central Africa are easily identifiable by their differences in color: Lake Rukwa appears golden yellow, Lake Tanganyika dark blue, and Lake Mweru Wantipa burgundy. Also of note is a wild fire burning in the upper part of the image.

Lake Rukwa is an alkaline lake in southern Tanzania that lies at an elevation of about 800 metres, in a branch of the rift system. The lake has seen large fluctuations in its size over the years, due to varying inflow of streams.

In 1929 it was only about 30 miles (48 km) in length, but in 1939 it was approximately 80 miles (128 km) long and 25 miles wide (40 km). Currently it is about 180 km long and averages about 32 km wide, making it about 5760 square kilometres in size.

Lake Tanganyika is a large lake in central Africa. Its southern section, visible here, is shared by the Democratic Republic of the Congo (left), Zambia (below) and Tanzania (right). It is estimated to be the third largest freshwater lake in the world by volume, and the second deepest. Here, an S-shaped algal bloom can be observed in its waters.

Lake Mweru Wantipa is a lake and swamp system in the Northern Province of Zambia, lying in a branch of the Great Rift Valley. Its water is muddy in appearance, at times appearing reddish and ‘slightly oily’.

It has been regarded in the past as something of mystery, displaying fluctuations in water level and salinity which were not entirely explained by variation in rainfall levels; it has been known to dry out almost completely.

Deltas and Wetlands of the Caspian Sea – June 10th, 2009

43.0N 49.9E

June 10th, 2009 Category: Image of the day, Lakes, Rivers

Caspian Sea - June 3rd, 2009

Caspian Sea - June 3rd, 2009

Volga River Delta

Volga River Delta

Ural River Delta

Ural River Delta

Various types of wetland and delta areas can be found on the shores of the Caspian Sea. The northern section of this immense lake is encompassed by the Caspian Depression, a low-lying flatland region.

The depression, which covers approximately 200,000 kilometers² (77,220 miles²), lies at the southern end of the Ryn Desert, and is in both Kazakhstan and Russia.

The Volga River and the Ural River, which forms part of the traditional boundary between Europe and Asia, flow into the Caspian Sea through this region. The deltas of the Ural and Volga Rivers are extensive wetlands.

Both deltas can be observed in detail in their respective close-ups. The fan-shaped Volga River Delta has, unfortunately, experienced significant wetland loss due to industrial and agricultural modification to the delta plain. Much of the water in and around the delta appears bright green due to algal blooms, intensified by fertilizers carried in by the river.

Tengiz Field

Tengiz Field

Kura River and wetlands

Kura River and wetlands

In fact, studies have shown that water pollution, mostly coming from the Volga River, poses a serious threat to the biodiversity of the Caspian Depression. Water pollution is contributed mainly by industrial, agricultural, and household discharges.

The Ural River Delta in Kazakhstan has a different shape from that of the Volga: rather than a wide triangular or fan-shape, it is longer and thinner. This is called a “bird’s foot” or “digitate” delta. Such deltas are often seen on sediment-rich rivers flowing into lakes.

Much of the Caspian Depression is below the level of the sea; its lowest point is 28m (92 ft) below sea level. Its eastern region comprises large areas of marshlands. One such marshy area in western Kazakhstan is the location of the Tengiz Field (see close-up), a huge source of oil.

The final close-up focuses on the western shore of the Caspian Sea, in Azerbaijan. Here, the Kura River enters the sea, discharging sediments. Onland, the dark green area in the center near the coast is swampy Gyzylaghadj State Reserve. Also called the Gizil-Agach State Reserve, it is a Ramsar Wetland that is an important wintering and nesting area for migrant, swamp and wild birds.

Russia’s Taganrog Bay in the Sea of Azov – May 25th, 2009

47.0N 38.6E

May 25th, 2009 Category: Image of the day, Lakes

Taganrog Bay, Russia - May 17th, 2009

Taganrog Bay, Russia - May 17th, 2009

Taganrog Bay or Taganrog Gulf  is the northeastern arm of the Sea of Azov. At its northeast end is the mouth of the Don River. The bay is about 140 km long and 31 km wide at its mouth, with a median depth of about 5 m.

Its mouth is marked by the Dolgaya Spit to the south and the Belosaray Spit (Belosarayskaya Spit) to the north. It abounds in sandy spits that partly enclose shallow bays. The bay also contains the Sandy Isles.

It is generally frozen from December to May, although here it has already thawed completely. It is fed by the Don, Kalmius, Mius and Yeya Rivers.

Here, the waters of the bay appear greenish in color due to an algal bloom. Much of the Sea of Azov is characterized by intensive and rather long-term blooming periods. The tolerance of algae to salinity changes precisely defines the boundaries of their distribution in the sea and the Bay of Taganrog.

The Three Zones of the Volga Delta, Russia – May 20th, 2009

46.7N 47.8E

May 20th, 2009 Category: Image of the day, Lakes, Rivers

Volga Delta, Russia - May 17th, 2009

Volga Delta, Russia - May 17th, 2009

The Volga Delta is located in Russia’s Astrakhan Oblast. It is the largest inland river delta in Europe, and occurs where Europe’s largest river system, the Volga River, drains into the Caspian Sea in the Caspian Depression. The far eastern part of the delta extends into Kazakhstan.

The delta lies in the arid climate zone, characterized by very little rainfall. The region receives less than one inch of rainfall in January and in July in normal years.

Strong winds often sweep across the delta and form linear dunes. Along the front of the delta, one will find muddy sand shoals, mudflats, and coquina banks. Green algae, nourished by fertilizers, is present in the waters around the delta.

The Volga Delta has grown significantly in the past century because of changes in the level of the Caspian Sea. In 1880, the delta had an area of 3,222 km². Today the Volga Delta covers an area of 27,224 km² and is approximately 160 km across.

The changing level of the Caspian Sea has resulted in three distinct zones in the delta. The higher areas of the first zone are known as “Behr’s mounds,” which are linear ridges of clayey sands ranging from 400 m to 10 km in length, and averaging about eight meters in height. Between the Behr’s mounds are depressions that fill with water and become either fresh or saline bays.

The second zone, in the delta proper, generally has very little relief (usually less than one meter), and is the site of active and abandoned water channels, small dunes and algal flats.

The third zone is composed of a broad platform extending up to 60 km offshore, and is the submarine part of the delta.

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