Paper No. 8
Presentation Time: 3:30 PM
CHANGES IN OSTRACOD ASSEMBLAGES AND THEIR IMPLICATIONS FOR INTERPRETATIONS OF RECENT LAKE-LEVEL FLUCTUATIONS IN FERGUSON'S GULF, LAKE TURKANA, KENYA
Lake Turkana is a closed-basin lake located in an arid region of northern Kenya. Lake level in the basin is primarily controlled by a balance of fluvial inputs from the perennial Omo River, which flows southward from the Ethiopian Highlands, and output via evaporation from the surface of the lake. Because Lake Turkana is hydrologically closed, changes in lake level affect the water chemistry and thereby the ecosystems that depend upon in. Ferguson’s Gulf is a ~ 13 km2, shallow embayment located on the western shore of Lake Turkana. The gulf is connected to the rest of the lake by a narrow mouth on its northern end which is ~1 m deep. Therefore, relatively minor drops in lake level have the potential to restrict flow from Lake Turkana into Ferguson’s Gulf, creating localized evaporative water chemistry, which should effect the suitability of this area for sustaining various benthic populations. Six short cores collected in 2011 and 2012 were picked for ostracods at 5 cm intervals to study the changes in assemblages through 83 cm of sediment. These results were then compared with modern lake level curves to look for systematic changes in both ostracod speciation and total abundance. There was an overall decrease in ostracods abundances up core, with a significant drop in total abundances above 23 cm. Potamocypris worthingtoni was the most common ostracod species found in Ferguson’s Gulf sediments. Therefore, this species was used in conjunction with Plesiocypridopsis newtoni to generate a Potamo/Plesio ratio in order to quantitative fluctuations in ostracod assemblages. Pb-210 analysis was used to establish a chronology for these cores. Because changes in lake level are tied to suitability of the gulf’s water chemistry for sustaining various species of ostracods, changes in ostracod assemblages may reflect changes in lake levels. Tying this record to satellite altimetry data from the past 20 years, will allow from high-resolution reconstructions of how lake level fluctuations affect benthic communities. This in turn will help us understand how future anthropogenic impacts on Lake Turkana’s water budget will impact ecosystems in the basin.