Abstract
Sources of metals in the environment are widespread and data on typical concentrations in the various media and environmental settings exits worldwide. Distribution and comparative concentrations of some selected metals in surface sediments of two shallow tectonic freshwater basins were assessed, as useful indicators of the level or magnitude of anthropogenic influences, as well as other aquatic processes, considering the increasing challenges in management of waste disposal. Concentrations of Pb, Cd and Zn in the sediments were detectable in all sites, albeit there were relatively lower levels reported in the column of alkaline waters. In dry weight basis, and in increasing order, the levels were Cd<Pb<Zn in both basins. Cd, Pb and Zn elements are all chalcophiles. However, using a student t-test, the concentrations of Cd and Pb in the sediments showed significant differences (p<0.05) between the two basins. Using freshwater sediment quality guidelines (ISQG) values, all the three metal mean contents in L. Baringo were above these values. Average levels of Zn and Cd were also above the ISQG values. However, all the mean concentrations of Zn, Cd and Pb in surficial sediments were found to be below the probable effect level, and above normal concentrations ranges found in sedimentary and igneous formations. Concentrations of Pb and Zn found are comparable to other relatively large basins, with extensive drainage basins and urban influences. Cadmium sediment levels are a concern, as the evaluation shows increasing accumulation in sediments, with possible future exposure risks to aquatic organisms. Surface runoff, waste discharges and particulate deposition is thought to be significant in these basins, and to understand overall impacts from anthropogenic deposition, it is important that background metal levels are determined together with supporting chemical partitioning to reveal more information on available metal contents. Key words: Tectonic lake basins, surface sediments, concentrations, lead, zinc, cadmium.
Highlights
Sediments receive both autochthonous and allochthonous inputs in a lake ecosystem and contain records of contaminants over time
This study presents total concentrations of some of the priority metals, which were monitored in surficial sediments of two shallow freshwater lake basins to understand possible associated anthropogenic influences and processes
Lakes Naivasha and Baringo are important water bodies with a thriving commercial fishery based on introduced species (Muchiri and Hickley, 1991; Hickley et al, 2008; Ojuok et al, 2007), with the common carp Cyprinus carpio L. and the marbled lungfish Protopterus aethiopicus (Heckel, 1851) dominating the catches respectively
Summary
Sediments receive both autochthonous and allochthonous inputs in a lake ecosystem and contain records of contaminants over time. Kamau et al (2008, 2007), Mutia et al (2012), Ochieng et al (2007), Dharani et al (2010, 2007), Tarits et al (2006), Campbell et al (2003), Hakan Tarras-Wahlberg et al (2002), Bonzongo et al (1996) and Njenga et al (2009), provided very useful information on detectable levels of several metals in the rift valley lakes water, sediment and aquatic organisms, and soils of surrounding areas. High levels of Cd and Zn in soils and Acacia xanthophloea Berth., were reported in polluted sites around L Nakuru, another closed basin saline rift valley lake (Dharani et al, 2010, 2007). This study presents total concentrations of some of the priority metals, which were monitored in surficial sediments of two shallow freshwater lake basins to understand possible associated anthropogenic influences and processes
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