2009) The surplus water of the Hydrodrome is discharged via an o

2009). The surplus water of the Hydrodrome is discharged via an outlet located at its south-western limit to the see more El-Amlak drain that pours into Lake Maryut (Ahdy & Saad 2006). A hand auger equipped with a polyethylene tube was used by SCUBA divers to collect seven sediment core samples,

each approximately 75 cm in length, from the bottom of Nozha Hydrodrome (Figure 1). The polyethylene tubes containing the sediments were kept in ice boxes and transferred to the laboratory for analysis. Based on the average sedimentation rate (0.65 cm y−1) in Nozha Hydrodrome (determined by Ahdy (1982) using in situ sedimentary traps) the core samples were split into subsamples, each one representing ~5 years of sedimentation (approximately 3.25 cm). A total of 23 sediment subsamples were obtained for each core. The concentrations of zinc and cadmium in the bulk sediment subsamples were extracted using a technique modified from Tessier et al. (1979), Steinberg & Tayarani-Dastmalian (1993) and Perin et al. (1997). Measurements of zinc and cadmium concentrations were carried out using an Atomic Absorption Spectrophotometer selleck chemicals (Perkin Elmer Analyst 800, equipped with Zeman background correction). To ensure the accuracy of these concentrations, the above procedure was

conducted 5 times on standard reference material. The recoveries were 90% for Cd and 110% for Zn. The precision of the technique was tested by replicate analysis of the studied metals, using IAEA-SL-1 Standard Reference Material (International Atomic Energy Agency), as shown in Table 1. To test the reliability of the dating calculation using the sedimentation rate, the data on the total concentrations of zinc and cadmium in the sediments in the years 1977 (1982, Ahdy 1987, El-Rayis & Saad 1990) and 2004 (Ahdy & Saad 2006) were plotted on the vertical distribution curves together with the data of the present study. Because of the homogeneity and similarity of the sediment core lithology, the data of the seven cores have

been averaged to obtain an overview of the variation of zinc and cadmium concentrations with time for the entire Hydrodrome. The average vertical distributions of zinc and cadmium concentrations in the solid phases (exchangeable, bound to carbonate, bound Verteporfin mouse to Fe-Mn oxides, bound to organic matter, and residual) and the average total concentrations in core sediments of Nozha Hydrodrome are presented in Figures 2 and 3 respectively. Zinc concentrations in the exchangeable and carbonate phases in the sediment core are much lower than those in the other phases, whereas the oxide-phase concentrations are the highest (Figure 2). The zinc concentration in the sediments was at a minimum (96.2 μg g−1) in 1900 and reached a maximum (280 μg g−1) in 1990. The rate of increase in the total zinc concentrations with time was 2.5 μg g−1 y−1 from 1900 to 1950, decreasing to 1.5 μg g−1 y−1 from 1950 to 1990.

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