| dc.description.abstract | Some aspects of water chemistry, vegetation structure and water level
fluctuations of the Lake Elementeita drainage basin in Kenya's Rift Valley
were studied. The analysis of water samples showed that the lake was highly
alkaline and saline. Total alkalinity and electrical conductivity of 3832 mg
CaCOs/land 12842 J..lS/cmrespectively in the lake was 60-70 times higher than
in rivers of the catchment and resembled conditions of other saline lakes in
the Rift Valley notably: Nakuru, Bogoria and Magadi.
In the vegetation analysis, mappingwas implemented from transect and
profile data. The Shannon-Weiner index together with arbitrary cover
abundance classes were used to estimate vegetation diversi ty and abWldance.
Over150different plant species were identified within the basin in nine major
plant associations. Dominantspecies in the catchment included Olea BIz-leana,
JlI11peruB ~, Acacia tartlllB and TarchananthuB~tua The lake
region exhibited some distinct plant communities notably the Acacia
zanthophloea woodlands, T.Jr.pha-~ swamps and Sporobolus spicatus
grasslands. The distribution of species around the lake was influenced by
water chemistry. Cyperrm PBPYrus for example was restricted to areas where
fluoride concentration was below 1.0 mall. This species was replaced by
Cyperus laevigatus and Cyperrm.i...sDBUB in areas where conducti vi ty exceeded
150J,JS/cm.
Climatic variations were found to be a major factor influencing water
level f luct.uat.ione at Lake Elementeita. Average annual rainfall has declined
in the recent past, rarely exceeding 900 mmwhile average annual temperature
appears to have risen from 140Cin the 1960s to 160C in the 1980s. Apart from
the influence of climatic cycles, rapid population growth in the watershed has
instigated significant landscape modifications. Colour Infra-red LANDSAT
imagerywas used to estimate the rate of forest and woodlanddepletion in the
watershed which was found to be between 11km2/yr (1973-76) and 4 km2/yr
(1976-84). mostly through conversion to agro-ecosystems.
Several conclusions were drawn from findings in this study. Lakewater
chemistry was found to be influenced by geology and thermal springs in the
region. Volcanic rocks in the area contribute to high mineralization
particularly with regard to sodium(Na+),potassium (K+)and fluoride (F-) ions.
Riverkariandus was found in this regard to form a major input of mineral salts
into the lake. The lake-bed springs south of the lake were also found to be a
prominent source of sodium(Na+),chloride (Ol") and sulphates (S04--) ions into
the lake.
The loss of forest andwoodlands in the drainage basin was found to have
been particularly rapid in the -1970s as a result of increased human
settlements. The study concluded that such depletion will result in declines
in water levels at Lake Elementeita particularly during periods of drought.
Waterlevel fluctuations were however. found to emanate mainly from changes
in climatic factors.
The study recommends conservation of remaining tracts of Olea-
Juniperus-Acacia forest and woodlands as essential ecosystems in the
watershed and rehabilitation of degraded areas through improved land
managementpractices. Several other recommendations have been advanced
mainlyfor further research and experiment. | en |
