Emily Peck, Conservation Science Program, WWF-US.
Jeppe Kolding, Department of Fisheries and Marine Biology, University of Bergen, Bergen, Norway
Major Habitat Type
Main rivers to other water bodies
Lake Turkana is the largest lake in the eastern portion of the Rift Valley and the fourth largest lake by volume in Africa (Beadle 1981). Lying in a low closed basin at approximately 365 m asl, the lake is situated primarily in northwestern Kenya, with only its northernmost end, the Omo Delta, inside Ethiopia. Of the twelve principal rivers that feed Lake Turkana, the River Omo is its only perennial tributary, supplying over 90% of the lake’s inflow (Beadle 1981). The Omo River drains the southwestern portion of the Ethiopian Massif and flows through the Rift Valley into Lake Turkana. Of the seasonal rivers that flow into the lake, the Turkwell and Kerio Rivers are the largest contributors and enter the lake along its western edge and in its southern half (Hughes & Hughes 1992).
Lake Abayaand LakeChamoare located in the northeastern portion of the ecoregion. Five major rivers feed Lake Abaya, the most important of which is the Bilate. During the rainy season, overspill from Lake Abaya is carried to Lake Chamo via the Ualo River (Hughes & Hughes 1992).
Encompassing much more than the immediate Lake Turkana environs, the Lake Turkana ecoregion reaches north to include Lakes Abaya and Chamo, as well as the headwaters of the Omo Riverin southwestern Ethiopia.
Lake Turkana is 260 km long, with an average width of 30 km, a mean depth of 31 m, and a maximum depth of 114 m. It has an area of approximately 7,560 km² and a volume of 237 km³ (Coulter et al. 1986). With no surface outlet, the water budget of the lake is a balance between river and groundwater inflow and evaporation. Evaporation rates are high, at around 2.3-2.8 m/yr. An influx of about 19 km3/yr is required to keep lake levels steady, and high inter- and intra-annual fluctuations in water level occur as a function of the rainfall in distant upland Ethiopia (Kolding 1992). Generally, the lake level fluctuates annually with an amplitude of about 1-1.5 m, but it also undergoes considerable long-term variations that exceed those of any other lake of natural origin (Butzer 1971). The mean retention time of water in the lake is a short 12.5 years (Kolding 1992).
The salinity of Lake Turkana is higher than that of any other large African lake. This is due to the fact that the lake has no outlet, and that it has contracted in volume over the last 7,500 years. Very recent volcanic activity in the basin has also contributed to the high salinity of the lake (Beadle 1981). Water samples taken between 1931 and 1975 record salinity as ranging from 1.7-2.7o/oo (Hughes & Hughes 1992; Spigel & Coulter 1996). The mean conductivity is about 3500 µS/cm, with an estimated rise of about 0.45 µS/cm/yr (Ferguson & Harbott 1982). Due to the volcanic origin of the catchment area the water chemistry is dominated by sodium (more than 95% of the cations by weight) and bicarbonate, which generate a high alkalinity (pH » 9.3).The seasonal inflow of water, coupled with strong diurnal wind patterns, keep the waters of Lake Turkana productive and well mixed. In fact, the oxygen content of Turkana’s deepest water is never less than 70% (Beadle 1981).
The most common emergent plants are the grasses Paspalidium geminatum and Sporobolus spicatus, with extensive beds of Potamogeton occurring in shallow bays (Hughes & Hughes 1992). The waters of Abaya and Chamo contain numerous submerged plants, such as Ceratophyllum demersum, Hydrocotyle sp., and Potamogeton spp., as well as floating plants like Lemna gibba, Nymphaea spp., and Ottelia ulvifolia (Hughes & Hughes 1992).
The evergreen bush and woodland of the Ethiopian Massif grade into deciduous bush in the Rift Valley. Extensive seasonal floodplains exist along the Omo River Delta, at the northern tip of
Description of endemic fishes
The endemic species nearly all live in the offshore demersal or pelagic zone (Lowe-McConnell 1987). Endemic chiclids include three halpochromine species adapted for deep water: Haplochromis macconneli, H. rudolfianus, and H. turkanae. Other species endemic to
Justification for delineation
Level of taxonomic exploration
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