The seasonal and spatial variations of labile copper, iron, manganese, lead and zinc sediment fractions in Lake Naivasha, Kenya

Abstract

Lake Naivasha is a freshwater lake with no surface outlet, lying within a closed basin of the Kenyan Rift Valley. It is perceived to be a lake undergoing anthropogenic stresses. This study is intended to determine the speciation of some selected heavy metals in the sediments of Lake Naivasha, as an indicator of potential pollution of the lake. Sediment and water sampling of the lake was conducted in March and May 2003, during the dry and wet seasons, respectively. Analyses of the speciation of heavy metals in sediment samples (<63 µm faction) were performed on sediment samples collected from five sites within the lake. The study results obtained indicated that influent Malewa River was not a source of labile copper (Cu), lead (Pb) or zinc, despite the river having the highest percentage clay content during the wet season (86%). Copper was highly distributed in the residual sediment fraction (average of 90%). Among the labile sediment factions, the highest quantity of Cu was in the oxidizable phase (3.58 and 2.30 µg g -1 during the dry and wet season, respectively). Carbonate-bound Cu was sparingly distributed during both the dry and the wet seasons, ranging between 0.74 and 1.81 µg g -1 . Iron was highly distributed in the oxidizable sediment phase, exhibiting concentrations ranging between 2.0 and 6.0 (×10 3 ) µg g -1 . Relative to the other heavy metals, manganese was distributed in lower proportions in the residual sediment fraction. High concentrations of Pb were observed in the oxidizable phase from most of the sampling sites along the lake shore. Zinc was distributed largely in the oxidizable phase, being highest at sampling site SS, which was located near a municipal sewage input to the lake. The sediments collected at the sampling sites located in the deep portion of the lake exhibited the highest concentrations of labile heavy metals.

Trace metal concentration in water and sediments of satellite lakes within Lake Victoria (Kenya) basin

“…Although other authors have provided data on metal speciation in sediments (Tessier et al. 1979; Cloutier & Dube 1998; Kamau et al. 2007), there are no studies on the element associations in sediments in satellite lakes in this area.…”

Comparative spatial metal concentrations and partitioning in bottom sediments of two tropical freshwater lake basins, Kenya

“…Metal partitioning data from L. Naivasha in this study indicates metal concentrations of similar magnitude to that from a study by Kamau et al . (), which was performed using different extractants and conditions. The mean range concentrations (dry wt) of exchangeable, carbonate, reducible and oxidizable fractions for Cu (nd to 6.87 μ g g −1 ) and Pb (5.62 to 8.75 μ g g −1 ) were similar, with variable levels of Fe (33.1 to 4,884.5 μ g g −1 ), Mn (65.0 to 210.6 μ g g −1 ) and Zn (nd to 15 μ g g −1 ).…”

“…Kamau et al . () reported mean range concentrations (dry wt) of exchangeable, carbonate, reducible and oxidizable fractions for Cu (0.6 to 4.6 μ g g −1 ), Fe (3.1 to 5,569 μ g g −1 ), Mn (19 to 847 μ g g −1 ), Zn (0.9 to 51 μ g g −1 ) and Pb (nd to 10.0 μ g g −1 ). More differences are evident when the residual fractions and total sum of all fractions data (47 to 64 μ g Cu g −1 ; 3,085 to 52,897 μ g Fe g −1 ; 532 to 1,106 μ g Mn g −1 ; 67 to 129 μ g Pb g −1 ; and 151 to 228 μ g Zn g −1 , as residual Cu, Fe, Mn, Pb and Zn respectively) are compared.…”

“…Only a few studies, however, have incorporated information on the speciation or geochemical partitioning of metals (Kamau et al . ; Njenga et al . ; Mbabazi et al .…”

Heavy metals in surface sediments of Lake Naivasha, Kenya: spatial distribution, source identification and ecological risk assessment

“…However, ecological changes in the lake in the last two decades coincide with increase in horticultural farming [29][30][31][32][33]. Earlier, increase in sediment load to the lake is linked to commercial farming during British colonization [34], and subsequent, high concentrations of heavy metals in sediments, water and fishes have been reported [35][36][37][38]. The methodologies employed in these studies were diverse in terms of sampling, depth, density, toxic metals detected and risk assessment.…”