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

Persian Gulf - July 28th, 2009

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.

Tags: Algal Bloom Euphrates River Iran Iraq Persian Gulf Qatar Saudi Arabia Sediments Tigris River United Arab Emirates |  Print This Post |  Email This Post | | Leave a comment

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

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.

Tags: Africa Algal Bloom Democratic Republic of the Congo Fires Great Rift Valley Lake Mweru Wantipa Lake Rukwa Lake Tanganyika Tanzania Zambia |  Print This Post |  Email This Post | | Leave a comment

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

Caspian Sea - June 3rd, 2009

Volga 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

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.

Tags: Algal Bloom Asia Azerbaijan Bird's Foot Delta Caspian Depression Caspian Sea Digitate Delta Europe Gizil-Agach State Reserve Gyzylaghadj State Reserve Kazakhstan Kura River Oil Field Ramsar Wetland Russia Ryn Desert Sediments Tengiz Field Ural Delta Ural River Volga Delta Volga River Water Pollution |  Print This Post |  Email This Post | | Leave a comment

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

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.

Tags: Algal Bloom Belosaray Spit Dolgaya Spit Don River Kalmius River Mius River Russia Sandy Isles Sea of Azov Taganrog Bay Yeya River |  Print This Post |  Email This Post | | Leave a comment

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

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.

Tags: Algal Bloom Astrakhan Oblast Behr's Mounds Caspian Depression Caspian Sea Europe Kazakhstan Russia Volga Delta Volga River |  Print This Post |  Email This Post | | Comments (1)

April 19th, 2009 Category: Image of the day, Rivers

Caspian Sea - March 31st, 2009

The Volga Delta 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 Russia’s Astrakhan Oblast, north-east of the republic of Kalmykia. Although some clouds partially obstruct the view of the area, the delta is visible on the northwestern shores.

The Volga Delta has grown significantly in the past century because of changes in the level of the Caspian Sea. However, in recent years industrial and agricultural modification to the delta plain has resulted in significant wetland loss.

Between 1984 and 2001, the delta lost 277 km² of wetlands, or an average of approximately 16 km² per year, from natural and human-induced causes.

The Volga discharges large amounts of industrial waste and sediment into the relatively shallow northern part of the Caspian Sea. The added fertilizers nourish the algal blooms that grow on the surface of the sea, allowing them to grow larger.

This algae is responsible for the green color of the water immediately around the delta, and may also be contributing to the green color present in the rest of the sea’s northern section.

Tags: Algal Bloom Astrakhan Oblast Caspian Sea Kazakhstan Russia Sediments Volga Delta Volga River |  Print This Post |  Email This Post | | Leave a comment

April 1st, 2009 Category: Lakes

Kenya - March 24th, 2009

Lake Turkana, formerly known as Lake Rudolf, is a lake in the Great Rift Valley in Kenya, with its far northern end crossing into Ethiopia. It is the world’s largest permanent desert lake and the world’s largest alkaline lake.

The climate is hot and very dry. On-shore and off-shore winds can be extremely strong as the lake warms and cools more slowly than the land. Sudden, violent storms are frequent.

Three rivers (the Omo, Turkwel and Kerio) flow into the lake, but lacking outflow its only water loss is by evaporation. Lake volume and dimensions are variable. For example, its level fell by 10 meters between 1975 and 1993. The water is potable but not palatable.

Despite the barren surroundings, the lake itself is a surprisingly rich if somewhat limited habitat for life, which on the lowest level manifests itself in an immense bloom of soda-loving algae, which can change its color from sky blue to jade green. The algae, in turn, support large numbers of fish.

Here, the waters of the lake and the rivers flowing into it appear white due to sun glint. A greenish algal bloom is present in the southern part of the lake.

Tags: Algal Bloom Ethiopia Great Rift Valley Kenya Kerio River Lake Rudolf Lake Turkana Omo River Salt Lake Turkwel River |  Print This Post |  Email This Post | | Comments (1)

March 28th, 2009 Category: Lakes

Cahora Bassa Lake, Mozambique - March 24th, 2009

The Cahora Bassa lake is Africa’s fourth-largest artificial lake, situated in the Tete Province in Mozambique. Here, the western part of the lake appears tan from sediments, while the eastern part is green from phytoplankton growth, including various species of green and blue-green algae.

The lake has reached a maximum length and width of approximately 250 km and 38 km respectively, flooding an area of 2,700 km² with an average depth of 20.9 m.

In Africa, only Lake Volta in Ghana, Lake Kariba, on the Zambezi upstream of Cahora Bassa, and Egypt’s Aswan dam are bigger in terms of surface water.

The Cahora Bassa Dam system is the largest hydroelectric scheme in southern Africa with the powerhouse containing 5 x 415MW turbines.

It is one of the three major dams on the Zambezi river system, the others being Kariba and Itezhi-Tezhi (although the latter is not on the main stream of the Zambezi, but on its tributary the Kafue River).

Tags: Africa Algal Bloom Cahora Bassa Cahora Bassa Dam Mozambique Phytoplankton Sediments Tete Province Zambezi River |  Print This Post |  Email This Post | | Leave a comment

March 23rd, 2009 Category: Snapshots

Laguna Madre, Gulf of Mexico - March 19th, 2009

The Laguna Madre is the name of two long, shallow bays along the western coast of the Gulf of Mexico in the United States and Mexico; the two being separated by the outlet of the Rio Grande.

Meaning “mother lagoon” in Spanish, the Laguna Madre proper is 130 miles (209 km) long, the length of Padre Island. Its biological corridor, though, extends well into Mexico, to the mouth of the Río Soto la Marina in the state of Tamaulipas.

In the United States, the section visible here, Laguna Madre is separated from the Gulf of Mexico on the east by Padre Island, and bounded on the west by mainland Texas, and extends from Corpus Christi in the north to Port Isabel in the south.

In Mexico, Laguna Madre is separated from the Gulf of Mexico on the east by a number of barrier islands, including Barra Los Americanos, Barra Jesús María, and Barra Soto la Marina. It is bounded on the west by mainland Tamaulipas.

The Laguna Madre is very shallow, with an average depth of only 0.9 m. It is connected to the ocean by only two narrow inlets, so the tidal range – which is already minor in this part of the Gulf of Mexico – is negligible.

Oceanographically, the Laguna Madre is considered a hypersaline lagoon; this indicates that it is usually much saltier than the ocean, due to being nearly landlocked in a semiarid environment, and is one of only six hypersaline lagoons in the world. The Laguna Madre has been experiencing a persistent algal bloom (including drift algae) that may be partially caused by its hypersaline conditions, which favor algal growth.

Atmospheric effects are much more important than tides in its circulation; its weak currents generally follow the prevailing winds, and these winds can influence the water level by as much as a meter. Some such currents are visible to the South, their movements made visible by green algae.

Tags: Algal Bloom Corpus Christi Currents Gulf of Mexico Laguna Madre Mexico Padre Island Tamaulipas Texas USA |  Print This Post |  Email This Post | | Comments (1)