Prof. Samir M. Nasr *, Mohamed A. Okbah**, s. res. w. Yuri. N. Gursky***
*Institute of Graduate Studies and Research, University of Alexandria, Egypt
** National Institute of Oceanography and Fisheries, Alexandria, Egypt
*** Faculty of Geology, Dept. Geochemistry, Moscow University,Russia
Lake Burullus is one of the protected areas of the Mediterranean Sea of Egypt. The lake is a shallow brackish water basin. The lake lies in the north of the Nile Delta, along the Mediterranean Coast of Egypt between Long. 30o 30` & 31o 10` E and Lat. 31o 35` N (Figure 1).
It covers an area of about 35.000 hectare with an average depth of 90 cm. The length of the lake is about 65 km., and its width varies between 6 and 16 km, with an average of about 11 km. The depth of the lake ranges between 0.42 and 2.07 m. The eastern sector of the lake is the shallowest, showing an average depth of 0.8m. The lake is connected to the Mediterranean Sea at the northern side through Boughaz El-Burg. The capacity of the lake is about 330 million cubic meters. The lake serves as reservoirs for drainage waters, which are contaminated, with anthropogenic materials. It receives drainage waters from agricultural areas through seven drains in addition to the fresh water from Brembal Canal situated in the western part of the lake. Sea water may also enter the lake during winter period. Saline water enters the lake from the sea through El-Boughaz.
It is subjected to several anthropogenic pollutants such as trace elements and other wastes. The previous work demonstrate that Al-organic matter complexes may be solubilzed in the pH range of 5 to 7 and thereby become available to plant and account for Al toxicity effects at pH values near neutrality. Element may be essential in a particular organism, while being toxic at the same or higher concentration in other organisms.
The objecte of this study is to identify the geochemical forms of aluminum (Al) in core sediments from Lake Burullus. Also, to study the distribution mapping of aluminum content of the surface and subsurface sediments of different fractions. The sediments in the area are mainly composed of Sand (11.3 to 35.4%) and Mud constitutes (88.7 to 64.6%). Generally, the sediment type changes from Clay, Silty Clay and Clay Loam. The carbonate content reached from 19.85 % to 37.82 %. The total organic matter content of the sediments ranged from 2.14% to 3.86%. It is obvious that there is an accumulation of organic matter in the surface layer and then tends to decrease with the increase of depth.
The total Al content varied between 2.65 and 3.23% with a mean of 2.97%. Considerable variability has been detected in the content of Al mobile forms. The lowest content of Al is recorded in the carbonate and exchangeable fractions. The ranges and average content of Al (μg/g) in the study area for the different fractions were; from 2.94 to 15.21 (8.99 ± 5.17) for exchangeable; from 1.17 to 13.26(5.10 ± 4.33) for carbonate fraction; from 8.00 to 187.28 (104.99 ± 55.46) bound to Fe-Mn oxides; from 99.58 to 995.00 (622.8 ± 302.09) in the organic fraction and from 25350 to 30745(28080 ± 2003) as residual.
The results of the vertical distribution of Al-exchangeable fraction revealed irregular variations through the four cores in the present study. Generally, the residual fraction is the first highest percentage reached to more than 90% of the total aluminum and followed by the organic fraction which has Al content more than 2% for most intervals of the four cores. The relative percentage of Al bound to the five fractions from the total concentrations can be arranged as the following: carbonate (0.01 √ 0.05%) < Exchangeable (0.01 √ 0.41%) < Fe-Mn oxides (0.03 √ 0.58%) < organic (0.41 √ 3.12%) < Residual (more than 90%).