5 μg g−1 y−1, reaching 258.8 μg g−1 y−1 in 2010. Cadmium concentrations are higher in the carbonate phase than in the other solid phases (Figure 3). The variation find more in the total cadmium concentrations (min = 6.5 μg g−1 y−1 in 1900, max = 43.8 μg g−1 y−1 in 2010) with time shows a different pattern. The average total cadmium concentration increased at a rate of 0.42 μg g−1 y−1 from 1900 to 1950, after which there followed a period of approximately no variation (constant concentrations of 26 μg g−1 y−1) from 1950 to 1970. After 1970 the average total cadmium concentrations in the sediments increased at a higher rate (0.53 μg g−1 y−1) than during

the period 1900–1950. The data also show that the vertical distribution Obeticholic Acid curves for both zinc and cadmium follow the same pattern for each metal separately. The data on the concentrations of total zinc and cadmium in the surface

sediments of Nozha Hydrodrome in 1977 (Ahdy 1982), 1987 (El-Rayis & Saad 1990) and 2004 (Ahdy & Saad 2006) well match those obtained in this study at depths in the sediment cores representing similar years (Figures 2 and 3). This indicates that the technique of dating the Nozha Hydrodrome sediment cores based on the sedimentation rate calculations used in this study is quite reliable. On the other hand, comparison of the average zinc (258 μg g−1) and cadmium (43 μg g−1) concentrations in the upper layer of the sediment cores with those in the surface sediments of the Nile Delta Lakes Maryut (zinc=508 μg g−1, cadmium=27 μg g−1) ( Saad & Ahdy 2006), Burullus (zinc=217 μg g−1, cadmium=5 μg g−1) and Manzala (zinc=432 μg g−1, cadmium=84 μg g−1) ( Saeed & Shaker 2008) shows that zinc in Nozha sediments is lower than in its mother Lakes Maryut and Manzala, whereas it is slightly higher than in L. Burullus;

the cadmium concentration is higher in Nozha sediments than in Lakes Maryut and Burullus but lower than in L. Manzala. These variations in the concentrations of both zinc and cadmium in the surface sediments of the Nile Delta lakes indicate their dependence on the source that supplies both metals to them. Rho The history of zinc and cadmium concentrations in the sediments of Nozha Hydrodrome shows that there was an increase in zinc from 1900 to 1990 followed by a decrease from 1990 to 2010. On the other hand, since 1900 cadmium concentrations in the sediments have been rising continuously. The zinc concentration in the natural sediments of aquatic environments is ~120 μg g−1 or less ( CEQG 1999, ANZECC & ARMCANZ 2000, WDNR 2003) and any increase over this value points to increased input due to human activities. In 1900 the total concentration of zinc in Nozha Hydrodrome sediments was 96.2 μg g−1. This value is below the level of zinc in natural aquatic sediments, and the Hydrodrome was considered a clean environment. At that time, there were no urban areas around the Hydrodrome and no untreated sewage was dumped into the pond.