Lakes Naivasha and Sonachi (Eastern Rift, Kenya) together form a complex of four limnologically and sedimentologically distinct, but hydrologically interconnected shallow lake basins: the main basin of Lake Naivasha, Crescent Island Crater, Lake Oloidien, and Lake Sonachi. This system therefore constitutes a natural laboratory to study how basin hydrology, morphometry, mixing regime, and sedimentation patterns affect the formation and preservation of climate-proxy signatures in the lake-sediment record. This study calibrates climate-proxy signatures in 210 Pb-dated sediment profiles from each basin against documentary evidence of climatically driven lake-level and salinity change over the past century. The results demonstrate that the continuity and temporal resolution of a climate-proxy record strongly depend on the persistence and quality of the local depositional environment, as determined by the physical and chemical limnology of the particular lake basin. Further it is found that at all time scales gradual environmental change will be recorded as an apparent steplike event when change in the selected climate proxy is controlled by limnological or sedimentological thresholds. Calibration of the recent sediment record in all four basins is then used to interpret the lithostratigraphy of an 8.20-meter long sediment profile from Crescent Island Crater, representing the last 1500 years of climatic history in equatorial East Africa.

Ecological aspects of the dissertation focus on the potential of fossil assemblages of aquatic invertebrates to resolve past water-level fluctuations in African lakes on a time scale of decades. Analysis of the stratigraphic distribution of fossil Chironomidae, Ostracoda, and Cladocera in recent sediments of lakes Oloidien and Sonachi form the basis for an investigation of the mechanisms regulating aquatic-invertebrate communities of shallow fluctuating lakes in tropical Africa. The results indicate that in addition to salinity, also mixing regime and availability of preferred substrate are important ecological determinants controlling the immigration, expansion, and local extinction of individual invertebrate species. It is argued that analysis of fossil invertebrate assemblages can be a valuable complement to quantitative methods of paleosalinity inference because of its ability to reconstruct lake-level change independently from salinity change. Due to non-linearity in the relationship between the water level and salinity of fluctuating lakes at short time scales, this ability gains importance together with the need for increased temporal resolution and precision in the reconstruction of past climate.