Lake Natron's very alkaline water has a pH of around 10.5 - too high for many animals Image: picture-alliance/dpa/Mary Evans Picture Library/A. Ol Doinyo Lengai, an active volcano, lies not far from the lake. It owes its unusual chemistry to the surrounding volcanic geology: the minerals, particularly sodium carbonate, and salts created by volcanic processes flow into the lake from the surrounding hills. The lake's extremely alkaline water has a pH as high as 10.5, similar to milk of magnesia, a treatment used to neutralize stomach acid. But when coupled with the sight of dead animals seemingly turned to stone, the lake appears even more eerie. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.The scarlet waters of Lake Natron in northern Tanzania are eye-catching enough by themselves. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. The image in this article has been cropped and enhanced to improve contrast. Patterns of these sub-environments therefore appear different across the span of a few years.Īstronaut photograph ISS012-E-20456 was acquired March 15, 2006, with a Kodak 760C digital camera using a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The area and shape of the open water and salt-raft zones depend on lake levels, controlled mainly by local rainfall and evaporation. Images of Lake Natron from four other dates can be seen on the Earth Observatory and associated links. The government of Tanzania recognized both the threat and the uniqueness of the habitat in 2001, when it placed Lake Natron on the list of Wetlands of International Importance as part of the Ramsar Convention, an intergovernmental treaty meant to protect wetlands. Although development plans include construction of a dike at the north end of the lake to contain the fresh water, the threat of dilution to this breeding ground may still be serious.
Threats to the salinity balance from increased fresh water influxes will come from projected logging in Natron watersheds and a planned hydroelectric power plant. As salinity increases, so do the number of cyanobacteria, and the lake can support more nests. The flamingoes feed on the nutrient-rich cyanobacteria. Vast numbers of the pink Lesser Flamingo (2.5 million by one calculation) rely on Lake Natron as their only breeding ground in the Rift Valley. Open water, salt flats with salt crusts, and mud flats succeed each other in a west-to-east progression towards the shallow side of the lake. The delta of one of two dominant streams that flow into the lake (top left) shows where fresh water enters the basin. The four main environments typical of salt (alkali) lakes in East Africa are illustrated well in the image. Also part of the rift system is Gelai Volcano, the slopes of which appear in the lower right corner. Called fault scarps, these lines are the steep, step-like slopes created when the land was pushed up during earthquakes along faults in the Great Rift Valley system of East Africa. Tan lines run north-south, parallel to the eastern lake shore on the right side of the image. In this image, the lake is about ten kilometers wide. The lake is quite shallow, less than three meters deep, and varies in width depending on its water level. Bright white clouds are also visible just right of center and on the top margin. In the inset, numerous, near-white salt-crust “rafts” pepper the shallowest parts of the lake. The red pigment in the cyanobacteria produce the deep reds of the open water of the lake, and orange colors of the shallow parts of the lake. Salt-loving organisms include some cyanobacteria, tiny bacteria that grow in water and make their own food with photosynthesis as plants do. As water evaporates during the dry season, salinity levels increase to the point that salt-loving organisms begin to thrive. This image of the southern half of Lake Natron shows the characteristic colors of lakes where very high evaporation occurs.
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