Physico - chemical changes in the two rift valley lakes Bogoria and Nakuru, Kenya, over a period of 16 months including an extreme drought.

Autor(en)

Franz Jirsa, Martin Gruber-Dorninger, Anja Stojanovic, Steve Omondi Oduor, Dieter Mader, Wilfried Körner, Michael Schagerl

Abstrakt

The physico-chemical properties of surface water samples from the two athalassic endorheic lakes Bogoria and Nakuru in Kenya were analysed in weekly intervals between July 2008 and October 2009. 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). In addition 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 elevated 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 ratio of low mass molecules to high mass molecules (E250/E365) in DOC was observed, contradicting the assumed positive correlation of salinity and this ratio, leading to the necessity for further investigations in this field. Anyway, the change in this DOC “quality” was followed by an almost complete depletion of dissolved Fe from the water phase, leading to the assumption that Fe(III) was released from chelating agents followed by hydroxide formation and then precipitation. In Lake Bogoria the evapoconcentration effects were far less pronounced (total salinity changed from about 40‰ to 48‰). The distributions of REE in the superficial sediments of Lake Nakuru and Lake Bogoria show a high abundance of the REE, corresponding to their volcanic geological background and a very distinct Eu depletion of Eu/Eu* = 0.33–0.45.

Organisation(en)

Institut für Anorganische Chemie, Department für Lithosphärenforschung, Department für Funktionelle und Evolutionäre Ökologie

Externe Organisation(en)

University of Johannesburg (UJ), Egerton University, Université de Ngaoundéré

Seiten

404

Publikationsdatum

07-2016

ÖFOS 2012

106020 Limnologie, 104023 Umweltchemie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/247890a7-50e3-4bef-8718-cc7b64e65dfd