Effect of river outflow management on marine life

Abstract

Construction of the Aswan High Dam in Egypt, and subsequent cessation (since 1965) of surplus Nile Flood water (ca 35 billion m³ of water annually) from discharging into the Mediterranean Sea, has had an impact on marine life in coastal waters adjoining the Nile Delta and on brackish-water life in the lakes. Nutrient concentrations have fallen considerably in these waters; phytoplankton blooms associated with the Nile Flood have disappeared and, consequently, Sardinella catches have dropped from ca 15,000 tons in 1964 to 4,600 tons in 1965 and to 554 tons in 1966. Depletion of nutrients, reduction of organic matter and of mud and silt deposition, affect also benthic life on the Continental Shelf and in brackish-water lakes adjoining the sea. Lake fisheries have also suffered from reduction in potential area and abstruction of free connection with the sea, thus hindering spawning migrations of mugils, shirimp and eel. Marine erosion of the Delta Coast has speeded-up following the Dam construction, due to loss of mud and silt deposition and loss of Lake-Sea currents. This can result in transgression of the sea on these lakes, and calls for urgent measures for shore protection. On the other hand, the benefits of the Dam to Egypt and Sudan in terms of agricultural expansion, hydro-electric power generated, industrialization and rehabilitation of populations are apparent.