The recent extinction of Azolla nilotica in the Nile Delta, Egypt

Azolla nilotica does not occur in Egypt today, reaching as far north as central Sudan. Its spores have been recorded in sediment cores from the Nile Delta near Manzala Lake up to ca. 550 AD. As part of the CASSARINA Project on recent changes in ecosystems of North African lakes, short sediment cores, covering up to the last two centuries, were taken from the open water of the large Delta lagoons, Lakes Edku, Burullus, and Manzala. Azolla nilotica megaspores were recovered from all three cores. Its most recent record at Manzala Lake was during the 19 century, at Edku Lake around 1920, and at Burullus Lake in the 1960s. A. nilotica is associated with fossil assemblages typical of high conductivity fresh-water and brackish conditions, all with a low nutrient content. It may have become locally extinct in Manzala Lake after a rise in sea-level destroyed its habitat of open water within reed-swamp vegetation. At Edku Lake it became extinct due to the decreased influence of sea-water combined with the increased input of fresh-water and nutrients as a result of Nile diversions to improve irrigation. Burullus Lake remains brackish today, and A. nilotica survived until the closure of the Aswan High Dam accelerated fresh-water and nutrient supply to the lake. In contrast, A. filiculoides was introduced as a bio-fertilizer in the 1970s and has subsequently become an aquatic weed. It has been able to flourish in the fresh, nutrient-rich water of Edku and Manzala Lakes, but so far seems to be absent from brackish Burullus Lake. A. nilotica persisted in the Nile Delta as long as nutrient levels were low. It seems to be intolerant of increased eutrophication by nitrate and phosphate supplied by agricultural runoff and sewage. As lake-water nutrient levels have steadily risen due to increasing irrigation by fresh-water and use of chemical fertilizers, and the increasing population, A. nilotica declined and became extinct in Egypt as recently as the 1960s.