ON-GOING SEDIMENTOLOGICAL STUDY AROUND LAKE BARINGO, CENTRAL KENYAN RIFT VALLEY: IMPLICATION TO THE RECONSTRUCTION OF 20TH CENTURY ANTHROPOGENIC SOIL EROSION

Summery

Lake Baringo’s catchment is one of the most degraded landscapes in the central Kenyan Rift Valley. Increased soil erodibility together with drought and vegetation clearance by overgrazing resulted in severe soil erosion (Burnett and Rowntree, 1998). This long standing soil erosion resulted deposition of thick silt in the lake. The historical impact of human activities and past land-cover change on the process of widespread erosion and sedimentation is not well constrained. This poster presents an ongoing sediment based research to reconstruct soil erosion in the Lake Baringo basin over the past 200 yrs.

8 piston cores with lengths of 1.5-3m were recovered. Maximum sediment thickness 2.8-3m occurs in the south of the lake basin where the major Mollo and Prekerra rivers enter. The sediment lithostratigraphy exhibits similar trends with stiff compacted clay bottom unit U-1 with 9-13% OM, 43-52% average water content, and carbonate content 2.5-4%. This is overlain by U-2, 6-8cm thick compacted clay with 10-12% OM, water content of 44-57% and carbonate content of 2.5-4.5%. U-3 is peaty clay of variable thickness between 6-45cm, with water content of 60-80%, OM content of 9-13% and carbonate content of 2.3-4%. U-4 is the thickest sedimentary unit with alternating dark brown-dark grey colors, 7.3-8.5% OM, water content 71-83% and carbonate content 3.5-5.3%..

Sediments close to the main river entrance show double average MS χ, mean sedimentation rate ~ 0.65 g/ml, than sediments from the central and northern parts of the lake with lower average MS χ and sedimentation rate ~ 0.4 g/ml. Grain size results show bimodal size distribution. U-4B is dominated by fine silt-clay with specific laminations dominated by high MS medium-coarse sand size fraction. The possible source for the very fine silt and clay sediments is from the Holocene lacustrine sediments covering the gentle plain areas south of lake Baringo. Historically, severe land degradation started by the late 1920’s, when the area had been hit by severe droughts causing a shift in pastoral lifestyle and people started to accumulate goats. These stacking of browsing animals caused the removal of small shrubs and grasses leading to accelerated gully erosion. The coarse silt sediments which result in MS peaks could be transported from further upstream areas of the lake catchment.