Disruption of Lake Elementaita food chain may be the main cause of bird flight
Tuesday, March 02, 1999
The Nation (Nairobi, Kenya) by Michael Njuguna
Lake Elmentaita, lying 5,827 feet above sea level along a popular route for migratory birds may now be full to the brim but is almost deserted by the water fowls.
The soda lake, situated about 40 kilometres from Nakuru town, off the Nakuru Nairobi highway, is popular with flamingoes, pelicans and other water fowl that feed in the brackish water.
But when we visited Elmentaita last week, only a few herons were found in the northern part of the lake. Not a single flamingo was in sight despite the fact that there were more than 37,000 flamingoes there in 1996.
A conservationist, Mrs Fleur Ng'weno said recently during the Wetland Day celebrations in Nakuru that pelicans were now nesting in some of the islands within Lake Elmentaita.
But according to her, the pelicans fly off to Lake Nakuru every morning to feed on fish (the small tilapia grahami), before retreating to Elmentaita in the evening.
Mrs Ngw'eno said that a recent water fowl count at Lake Bogoria in the neighbouring Bogoria district established that more than a million flamingoes were residing there.
To many observers, the disruption of the food chain in the Rift Valley Lakes as a result of the vagaries of the weather could be the main cause of now unpredictable movement of flamingoes and other water fowls.
Some conservationists suspect that the depletion of spirulina platensis in Lake Nakuru as a result of the El Nino rains which completely filled up and diluted the brine waters of the lake last year, could have led to the migration of the flamingoes to Bogoria and other lakes where the effects of that rain phenomena were not as intense. The flamingoes feed on spirulina platensis a blue and green algae that thrives in the saline waters. The pelicans feed on fish and other small aquatic creatures.
A report by scientists from the Microbiology and Immunology Department of Leicester University in Britain, who carried out tests on the microbial diversity of soda lakes, says that the almost unlimited supply of carbon dioxide combined with high ambient temperatures and high daily light intensities in the tropics contribute to making East African Lakes among the most productive of the naturally aquatic environments in the world.
The photosynthetic primary productivity, mainly the result of the dense populations of cyanobacteria, presumably supports the rest of the microbial community.
According to the scientists, these blooms of cyanobacteria are usually dominated by Spirulina platensis but in different lakes, and also depending on seasonal factors, Cyanospira and unicellular forms which might be Synechococcus may also be common.
The report says further that the Rift Valley soda lakes maintain dense populations of nonphototropic, aerobic organotrophic bacteria which may be somewhat surprising considering that the lakes are eutrophic, rather shallow and presumably oxygen limited.
Although the cyanobacteria of the genus Cyanospira have been isolated from Lake Magadi, cyanobacterial blooms occur only occasionally after extensive rainfall causes dilution of the brine.
The Rift Valley is a volcanically active region and many of the soda lakes are fed by hot springs at temperatures of 45 - 96 degrees Celsius. These are complex habitats, often characterised by a variety of algal mat types whose true nature has never been investigated. These ecosystems provide some interesting gradients of pH, salinity and temperature.
From anaerobic sediments of hot springs of Lake Bogoria, the Leicester scientists isolated strictly anaerobic rod-shaped bacteria having a typical sheath - like structure and growing optimally at 70 degrees Celsius and pH 9.5.
Says the scientists, " Although we can try to construct some unifying theory to describe nutrient cycling and the microbial community structure in soda lakes, it can only be superficial.
In the East African Rift Valley, there is an obvious difference between the hypersaline lakes of the Magadi- Natron basin with salt concentration approaching saturation and the northern lakes which include lake Nakuru and Elmentaita, which are less saline."
The soda lakes are not entirely closed systems. They suffer considerable disturbance from wildlife, in particular the vast flocks of wading flamingoes that return their feaces to the nutrient cycle.
The flamingoes nest in the most inaccessible parts of Lake Natron and fly up and down the Rift Valley in search of lakes with cyanobacterial blooms on which to feed and fresh water to drink.