Environmental variability in Lake Naivasha Kenya

Authors: Kathleen R StoofLeichsenring Annett Junginger Lydia A Olaka Ralph Tiedemann Martin H Trauth

Publish Date: 2011/02/02

Volume: 45, Issue: 3, Pages: 353-367

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Abstract

Lake Naivasha Kenya is one of a number of freshwater lakes in the East African Rift System Since the beginning of the twentieth century it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee tea flowers and other horticultural crops within its catchment The waterlevel history of Lake Naivasha over the past 200 years was derived from a combination of instrumental records and sediment data In this study we analysed diatoms in a lake sediment core to infer past lacustrine conductivity and total phosphorus concentrations We also measured total nitrogen and carbon concentrations in the sediments Core chronology was established by 210Pb dating and covered a ~186year history of natural climatic and humaninduced environmental changes Three stratigraphic zones in the core were identified using diatom assemblages There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri which occurred during a prolonged dry period from ca 1820 to 1896 AD through a transition period to the present planktonic Aulacoseira sp that favors nutrientrich waters This marked change in the diatom assemblage was caused by climate change and later a strong anthropogenic overprint on the lake system Increases in sediment accumulation rates since 1928 from 001 to 008 g cm−2 year−1 correlate with an increase in diatominferred total phosphorus concentrations since the beginning of the twentieth century The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha This study identified two major periods in the lake’s history 1 the period from 1820 to 1950 AD during which the lake was affected mainly by natural climate variations and 2 the period since 1950 during which the effects of anthropogenic activity overprinted those of natural climate variationThis project was carried out through the Graduate School’s GRK 1364 research program on ‘Shaping Earth’s Surface in a Variable Environment’ funded by the German Research Foundation DFG We are grateful to the Government of Kenya Research Permits MOST13/001/30C 59/10 59/18 and 59/22 and the University of Nairobi for the research permits and their support We also thank Yannick Garcin and Laura Epp for the field support that they provided We are grateful to Antje Musiol for the TC and TN measurements and to Peter Appleby from the University of Liverpool for the 210Pb dating We would also like to thank Ulrike Herzschuh Andreas Bergner and all of the graduate school members and participants for inspiring discussions We also thank Ed Manning for professional proofreading of the manuscript

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