Sedimentological, palynological and charcoal analyses of the hydric palustrine sediments from the Lielerai-Kimana wetlands, Kajiado, southern Kenya

Abstract

: Intermittent and sometimes ephemeral wetlands found in savannah ecosystems are subject to complex hydrological and geomorphological processes that influence vegetation and fire patterns, and their use by humans, cattle and wildlife. Today these wetlands are impacted by changes in land use, climate, and wildlife use. Small wetlands in semi-arid climates are dynamic ecosystems that respond rapidly to biological, physical and chemical processes and accumu-late sedimentary deposits making them excellent archives of past environmental changes. The Lielerai-Kimana wetlands in the Greater Amboseli Ecosystem of southern Kenya are located within the current protected area network. A 384 cm long palustrine sediment core was recovered from the Lielerai-Kimana wetlands, radiometrically dated, and used for sedimentological, palynological and charcoal analyses. The 210 Pb (n = 16 ages) and 14 C (n = 10 ages) results suggest a complex depositional pattern covering c . 1500 years.The mismatches between 210 Pb and 14 C date estimatessuggestsomedegreeofsedimentmixingwhichmaypreventcentennial-scaleinterpreta-tionofthepalaeoenvironmentalrecord.Thesedimentsarecharacterisedbyahighsiltcontentfrom 1500–600 cal yr BP with the organic content increasing from 600 cal yr BP to the present. The pollen data show little changes in vegetation composition, suggesting a mosaic of savannah, woody savannah, riparian, and montane forest persisted throughout the period of deposition. Charcoal and organic content suggest the continuous presence of herbaceous fuels at the coring site from 600 cal yr BP to the present. The results highlight the spatiotemporal heterogene-ity and complexity of wetland records across the semi-arid landscapes of Amboseli during the Late Holocene. Further studies on hydroclimate and vegetation change, disturbance ecology (fire, erosion, bioturbation), and human-environment interactions would further develop our understanding of the environmental history and drivers of environmental change across these ecosystems that are increasingly under human land use pressures.