Major and trace element geochemistry of Lake Bogoria and Lake Nakuru, Kenya, during extreme draught

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.

Algal communities of Kenyan soda lakes with a special focus on Arthrospira fusiformis

“…It is further enhanced by exceptionally high primary productivity (Talling et al 1973;melacK 1981;oDuor & Schagerl 2007a) resulting into the hyper-eutrophic nature of these systems. L. Nakuru and Bogoria are highly alkaline with a dominance of Na + in cations and HCO 3 -and CO 3 2-in anions (JirSa et al 2012). Both pH and sodium significantly influenced the plankton community structure.…”

“…The dependence on phytoplankton as driving force of productivity is even greater in these extreme habitats compared to freshwater systems since they have minimal macrophyte growth and low allochthonous organic carbon input due to limited surface run-off and river-inflows (Burian et al 2014). The dense phytoplankton, high amounts of dissolved organic matter (JirSa et al 2012) and increased particle loading significantly reduce the contribution of micro-phytobenthic community to overall productivity due to the resulting poor light climate in the water column (oDuor & Schagerl 2007b).…”

Cyanobacterial diversity in the hot spring, pelagic and benthic habitats of a tropical soda lake

“…() and Jirsa et al . (). Due to erosion from the alkaline volcanic rocks of the catchment area, sodium and hydrogen carbonates are the dominant salts in the waters of Lake Bogora National Reserve.…”

“…Lake Bogoria is located in the centre of the reserve. Its endorheic saline-alkaline basin has a surface area of about 34 km² and a maximum depth of about 10 m. Detailed characteristics of the lake and its catchment are provided by Harper et al (2003) and Jirsa et al (2012). Due to erosion from the alkaline volcanic rocks of the catchment area, sodium and hydrogen carbonates are the dominant salts in the waters of Lake Bogora National Reserve.…”

Assessing temporal and spatial variability of phytoplankton composition in a large reservoir in the Brazilian northeastern region under intense drought conditions

“…These changes, in turn, lead to shifts in phytoplankton attributes (Chellappa et al, 2009;Câmara et al, 2015), which reinforce the use of this community to evaluate the environmental status of these aquatic ecosystems. For example, high concentrations of nutrients, high conductivity and increased phytoplankton biomass could be expected in reservoirs and lakes located in semi-arid regions with reduced water volume (Naselli-Flores, 2003;Bouvy et al, 2003;Mosley et al, 2012;Jirsa et al, 2013). On the other hand, since the reduction of water volume occurs along with intensification in sediment resuspension and turbidity, a negative impact on phytoplankton biomass could also be expected (Braga et al, 2015).…”