Environmental Problems in Two Egyptian Shallow Lakes Subjected to Different Levels of Pollution

The two study areas are Lake Mariut and the Nozha Hydrodrome. The water of Lake Mariut is pumped to the Mediterranean Sea. It is the heavily polluted basin in Egypt receiving huge amounts of contaminated drainage waters and untreated domestic and industrial wastes. The Hydrodrome was separated in 1939 from Lake Mariut and became polluted in recent years from the feeding contaminated Nile water. The present study, a part of a research project on pollution of both lakes, deals with their limnological characteristics to illustrate the influence of developmental projects in their surroundings and to compare between their levels of pollution. The effect of thermal stratification was ignored in both lakes, due to their shallowness and the effect of prevailing winds. Seasonal variations of water temperatures followed those of the air. The chlorosity in Lake Mariut, affected mainly by drainage waters, was noticeably higher than that in the Hydrodrome. In Lake Mariut, chlorosity showed a highly significant positive correlation with dissolved oxygen (DO) and a highly significant negative correlation with hydrogen sulphide, confirming that the main source of this toxic gas is the heavily polluted Qalaa Drain. Except in some occasions, Lake Mariut water was nearly depleted from DO. The oxygenated region in this lake constituted about 10-15% of its area. The DO problem affects markedly fish survival. The DO average value in Umum Drain, partially supplying Lake Mariut with oxic waters, was nearly double that in the feeding water of the Hydrodrome. Hydrogen sulfide was found in most parts of Lake Mariut and was never detected in the Hydrodrome. This gas dissolved in the lake water caused anoxic conditions and thus destroyed the aquatic life. Significant positive correlations were found in Lake Mariut between temperature, pH and DO, possibly reflecting the high influence of pollution and intensity of photosynthesis. The temperature and pH correlation in the Hydrodrome was less significant. Poor correlations existed in both lakes between pH and chlorophyll-a. Based on above data and others, solutions have been suggested for restoration of Lake Mariut and returning of both lakes to their previous healthy conditions.