A Description of the Nile Basin, and a Synopsis of Its History, Ecology, Biogeography, Hydrology, and Natural Resources

Abstract

Following a description of the Nile, the longest river of the world (ca 6,800 km) and its basin (2.9 × 106 km2), including its various “source” lakes, some brief notes on its main neighbours (Congo and Logone-Chari) and their history are given. The biota of the basin are moderately diverse, and endemism tends to be low, except in some of the “old” source lakes. The situation is complicated by the fact that at least two of these lakes (Victoria and Tana) dried out around or slightly before the beginning of the Holocene, and thereafter, speciation (especially of cichlid fish) may have happened at an unusually great speed. In general, the Nile offers a pathway for African species to extend from the tropics to a Mediterranean climate and spill over into the Levant and Arabia. Such incursions may have happened many times across history, with some of the older “waves” using the Red Sea (before its opening to the Indian Ocean) rather than the Nile. Currently, as elsewhere in the world, invasive species in the Nile are becoming more and more common, although the oldest cases (some Ponto-Caspian cnidarians) may date back to the end of the nineteenth century. The water hyacinth Eichhornia has invaded the Nile basin in at least three different zones. Since early pharaonic times, man has interfered with the river and its flow regime, in an effort to control the yearly “flood of a hundred days”, but large-scale damming only started in the nineteenth century, and culminated with the construction of the Aswan High Dam in the 1960s, reducing the river to a giant irrigation canal. More recent developments include the construction of the Toshka lakes diverticle to Lake Nasser, a project with an uncertain future. The river and its lakes are important fisheries resources; the various dams are generating large amounts of power, and fossil hydrocarbon deposits are under development in at least three zones of the basin. This may contribute to river pollution, which is still a local phenomenon, except in Lake Victoria, which suffers from eutrophication, and in Egypt, that combines a population explosion (almost four doublings in the last century) with a substantial industrial development.