Eutrophication in Lake Mariut, Egypt PDF

Keywords

eutrophication, nutrients, chlorophyll-a, dissolved oxygen, hydrogen sulphide

Abstract

Eutrophication is the most serious problem in Lake Mariut. Lake Mariut is one of the North Nile Delta lakes. It is closed and unconnected directly with the sea. Its waters are discharged into the sea via El-Mex pumping station. Its area has been reduced due to land reclamation and the construction of some fish farms. Hydrographical and nutrient salts studies covering five seasons from January 1996 (winter) to April 1997 (spring) showed increasing quantities of inorganic and organic nutrients, which led to pronounced change in the quantitative and qualitative structure of Lake Mariut. Originally, Lake Mariut had a basin of quite different biological properties, one part mostly covered by Potamogeton pectinatus (macrophytes), while another part that recieved discharge from Alexandria city was plankton dominated and of extremely high productivity. Primary production measured as chlorophyll-a ranged between 0.78 and 1.91 g m-3. As a result of the extensive input of nutrients from Alexandria city, the enclosed nature of the lake and the shallowness of the water, heavy algal blooms and domination of plankton existed. The lake receives heavy industrial, domestic and agricultural wastewaters from different sources. The chlorosity values showed a narrow range variation between 1.139 and 2.009 g/l. The most affected part of the lake is its north western sector (lake proper). The state of deterioration of this basin is so bad that the intensive production led to remarkable reduction of dissolved oxygen (~1 mg/l) and the appearance of hydrogen sulphide up to 14.4 mg l-1. The study of hydrochemical variables was supported by hydrographical data (temperatures, pH, Eh and transparency). Very high values of phosphate (18.3 mol/l) , polyphosphate (11 mol/l) , ammonia (41 mol/l), nitrite (2.4 mol/l), nitrate (36 mol/l), and silicates (157 mol/l) were recorded.