Major and trace element geochemistry of Lake Bogoria and Lake Nakuru,Kenya, during extreme draught |
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| Authors: | Franz Jirsa Martin Gruber Anja Stojanovic Steve Odour Omondi Dieter Mader Wilfried Körner Michael Schagerl |
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| Institution: | 1. University of Vienna, Institute of Inorganic Chemistry, Währingerstrasse 42, A-1090 Vienna, Austria;2. University of Vienna, Department of Limnology, Althanstrasse 14, 1090 Vienna, Austria;3. Egerton University, Department of Biological Sciences, P.O. Box 536, Njoro, Kenya;4. University of Vienna, Department of Lithospheric Research, Althanstrasse 14, 1090 Vienna, Austria;5. University of Vienna, Department of Environmental Geosciences, Althanstrasse 14, 1090 Vienna, Austria |
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| Abstract: | The physico-chemical properties of water samples from the two athalassic endorheic lakes Bogoria and Nakuru in Kenya were analysed. Surface water samples were taken between July 2008 and October 2009 in weekly intervals from each lake. The following parameters were determined: pH, salinity, electric conductivity, dissolved organic carbon (DOC), the major cations (FAAS and ICP-OES) and the major anions (IC), as well as certain trace elements (ICP-OES). Samples of superficial sediments were taken in October 2009 and examined using Instrumental Neutron Activation Analysis (INAA) for their major and trace element content including rare earth elements (REE). Both lakes are highly alkaline with a dominance of Na > K > Si > Ca in cations and HCO3 > CO3 > Cl > F > SO4 in anions. Both lakes also exhibited high concentrations of Mo, As and fluoride. Due to an extreme draught from March to October 2009, the water level of Lake Nakuru dropped significantly. This created drastic evapoconcentration, with the total salinity rising from about 20‰ up to 63‰. Most parameters (DOC, Na, K, Ca, F, Mo and As) increased with falling water levels. A clear change in the quality of DOC was observed, followed by an almost complete depletion of dissolved Fe from the water phase. In Lake Bogoria the evapoconcentration effects were less pronounced (total salinity changed from about 40‰ to 48‰). The distributions of REE in the superficial sediments of Lake Nakuru and Lake Bogoria are presented here for the first time. The results show a high abundance of the REE and a very distinct Eu depletion of Eu/Eu* = 0.33–0.45. |
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| Keywords: | Lake Nakuru Lake Bogoria Saline lakes REE DOC Molybdenum Arsenic Iron |
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