The King Talal Reservoir (KTR) is partially recharged with sewage water effluent produced from the Khirbit-Es-Samra Treatment Plant. Because of the enrichment of the KTR water with nutrients, and the subsequent eutrophication, the effect of biochemical activity on the thermodynamic chemical equilibria of Cd(II) and Pb(II) was investigated. Twenty water samples were periodically collected from both surface and bottom waters of the KTR during the period 13/5/1986#x2014;9/11/1987. The water samples were analyzed for major chemical constituents, including Cd and Pb. Ionic speciation of each sample was carried out using the GEOCHEM program. The results indicated that surface and bottom waters were undersaturated with respect to CdCO3and Cd(OH)2. The surface water was in equilibrium with PbCO3for the samples having log {(H+)/(HCO3#x2212;)} lower than #x2014; 4.4. At values higher than #x2014; 4.4, Pb(II) was probably precipitated as lead phosphate. The bottom water was, in general, in equilibrium with PbCO3. However, some data points showed supersaturation. This was attributed to the unsteady state of the biochemical reactions affecting the (H+)/(HCO3#x2212;) ratio, which may well cause the apparent supersaturation with Pb(II).
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