Aquatic biodiversity and saline lakes: Lake Bogoria National Reserve, Kenya

Abstract

Lake Bogoria, in the Rift Valley of Kenya is an extreme saline lake (conductivity 40-80 mS cm −1 , alkalinity 1500 m equ l −1 ). It is hydrologically more stable than the other, endorheic lakes in Kenya, because it is deepmaximum depth at present just over 10 m in an area of 3000 ha -and so does not have periods when it is dry. It is ecologically simple, with only one species dominating the phytoplankton -the cyanobacterium 'spirulina', Arthrospira fusiformis. Its biomass and productivity were very high -biomass between 38 and 365 µg l −1 chlorophyll 'a' and 3.4-21 × 10 3 coils ml −1 and net production between 0.24 and 1 gm C m 3 h, the latter in a narrow zone of less than a metre. There were no macro-zooplankton in the plankton and the only grazer of A. fusiformis was the lesser flamingo, Phoeniconaias minor, which occurred irregularly in very high concentrations (in excess of 1 × 10 6 ). Detritivory in the benthos was effected by a single chironomid species, Paratendipes sp., at a maximum density of 4 × 10 4 m −2 . The mean daily emergence of adult chironomids was estimated to be 1 × 10 3 m −2 , the maximum 3. There was no littoral plant community within the lake but 44 dicotyledonous and 31 monocotyledonous plant species in the drawn-down zone and adjacent to it. A diverse draw-down terrestrial invertebrate fauna, only superficially described here, processed the flamingo feathers and carcasses, with other detritus such as chironomid pupal exuviae and decaying A. fusiformis scum. About 50 bird species depended upon the chironomids, either as they emerged through the water column as flying adults or later on the shoreline as floating pupal exuvia and dead adults. The lake has high conservation value because of three bird species in particular -lesser flamingo, Cape teal and black-necked grebe. The former provides real economic value in a region otherwise impoverished, because of the spectacle of tens of thousands of flamingos set against the landscape of hot springs and fumaroles at the lake edge, which draws 15 000 visitors per annum. P. minor has experienced three periods during the past ten years when major mortalities have occurred, the last of which killed 700 birds day −1 . This could have involved as many as 200 000 birds (about 1/5th of the maximum population at this lake) if mortality was at a constant rate for the nine months it was observed. Causes of mortality have been suggested as avian tuberculosis, poisoning from cyanobacterial toxins or from heavy metal contamination at Lake Nakuru, but it is still not yet clear what contribution each makes to the problem.

Microzooplankton feeding behaviour: grazing on the microbial and the classical food web of African soda lakes

“…All animals used for grazing experiments were isolated from lake water, starved for 6 h and acclimated stepwise to conductivity levels in case experimental conditions differed from natural conditions (change rate of 5 mS cm -1 h -1 ). Experiments were conducted in complete darkness with a constant conductivity of 45 mS cm -1 at 22°C, which is close to the average lake temperature (Vareschi, 1982;Harper et al, 2003) and the recommended temperature of 25°C for grazing experiments of B. plicatilis (Montagnes et al, 2001).…”

“…Both lakes represent typical examples of hypersaline tropical soda lakes and have been used as model systems before (Vareschi & Jacobs, 1985;Harper et al, 2003). For a detailed description of their physical and chemical properties refer to Oduor & Schagerl (2007a, b).…”

Vanishing world: alkaline, saline lakes in Central Europe and their diatom assemblages

“…The high nutrient availability of these lakes is not necessarily the consequence of anthropogenic pollution; however, most are surrounded by agricultural areas and tilled down to their shorelines. Even so, because of the tens of thousands of birds that populate these lakes during migration (Harper et al 2003, Boros et al 2006, Horváth et al 2013c) and the active maintenance of endemic beef cattle (Bos primigenius) and buffalo (Bubalus bubalis) farms in the regions, mammal and bird populations substantially increase plant nutrient levels through their droppings (Oduor and Schagerl 2007). The average TP concentration is 8 times higher (1989 µg L ) exceed twice that of freshwater concentrations (based on the database of the University of Pannonia, unpublished data).…”

Die Nahrungsprobleme des Zwergflamingos. Rätselhafte Massensterben an den Salzseen

“…Wenn es zu Regenfällen kommt, führen diese zu starker Erosion und schwemmen den Boden des Umlandes in die Salzseen ein. Seit Mitte der 1990er Jahre wurde eine erhöhte Mortalität des Zwergflamingos in Ostafrika beobachtet [6]. So kam es 1993,1995,1999,2001, 2006 und 2008 zu Massensterben mit jeweils mehreren Zehntausend toten Vögeln.…”