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FIG. 12. Flow diagram: Nile water to drainage water to the coastal zone.
eight effluents differs from the Nile flood in more than one aspect. The periodical pattern is replaced by a continuous one. While the impact of the Nile pulse was limited to three or four months, the drainage flux is continuous throughout the year.
Instead of two river outlets, the effluents are more or less equitably distributed from west to east along the coast. The level of dissolved nutrients is comparable, if not higher, but the total volume outflowing is smaller. Estimated at about 40% of the average pre-dam flow, it is devoid of suspended sediments.
A succession of localized bloom pulses throughout the year have replaced the massive autumn Nile bloom (Fig.14). As far as the fisheries are concerned, the post High Dam drainage pattern appears to have compensated the absence of the Nile input. The fisheries yield has recovered its pre High Dam level. These issues are also discussed by Nixon [7].
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FIG. 14. Surface salinity of the eastern Levantine Sea, integration of all available data (1965-2000, October only). Showing localized dilution off the Nile Delta.
FIG. 15 a. Vertical profile, Egypt to Cyprus.
5. Impact of the high dam on the hydrography of the levantine sea. The “levantine pump”
The Mediterranean basin is known to be a concentration basin in an arid zone, where evaporation exceeds precipitation and river runoff. This is one of the main driving forces for its hydrographic system.
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FIG. 15 b. The LIW, all available data 1900 to 1964 (end of winter).
FIG. 15 c. The LIW, all available data 1965 to 2000 (end of winter).
The control of the river Nile has accentuated this process. Since the High Dam became functional, the salt content of the Levantine Sea has been on the increase, as shown by the data. The cumulative fresh water deficit for the past forty years comes to about 880 km3, the drainage volume excluded. Winter vertical mixing is intensified by the rise in density that follows. A direct effect is to enhance the formation of the Levantine intermediate water, LIW. It is likely that several new source areas in the Levantine Sea contribute at present to its formation as already foreseen by Moreos [8]. The size of this water mass has actually been greatly magnified (Fig. 15 a, b, c).
It is not without interest to mention here the observation of Zore-Armanda [9]. She concluded that the increase in the Adriatic surface salinity is likely to be due to the deficit in the Nile fresh water input.
The consequences are far reaching. The direct consequence will be an increase in the rate of what can be termed the “Levantine pump”. The ultimate effect will be an acceleration of the rate of renewal of Mediterranean water. More Atlantic water will be pumped in and more Levantine Intermediate Water of higher salinity pumped out to the Atlantic ocean.
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It can be concluded therefore, that both during the pre- and post-High Dam eras, the Nile was and still is one of the driving forces for the Levantine oceanographic system and presumably beyond, although in different ways.
ACKNOWLEDGEMENTS
The author is indebted to his colleague Prof. Ahmed El-Guindy for the data of Figures 3, 14, and 15.
He is also very grateful to Miss Soha Shabaka who has given so much time and effort to produce the manuscript of this paper.
REFERENCES
[1] HALIM, Y., GUERGUESS, SH.K., SALEH, H.H., Hydrographic Conditions and Plankton in the Southeast Mediterranean during the Last Normal Nile Flood (1964), Int. Revue ges.
Hydrobiol. 52 3 (1967) 401-425.
[2] NIELSEN, J. N., Hydrography of the Mediterranean Sea and adjacent waters. Danish Oceanogr.
Exped., 1908-1910, Vol 1 (1912) 77-191.
[3] HALIM, Y., Observations on the Nile bloom of phytoplankton in the Mediterranean, J. Conseil Intern. Explor. de la Mer. 26 1 (1960) 59-67.
[4] HALIM, Y., MORCOS, S.A., RIZKALLA, S., EL-SAYED, M.KH., "The impact of the Nile and the Suez Canal on the living marine resources of the Egyptian Mediterranean waters (1958- 1986)" Effects of reverine inputs on coastal ecosystems and fisheries resources, FAO Fisheries Technical paper 349 (1995).
[5] HALIM, Y., MORCOS, S.A., Le role des particules en suspension dans l’eau du Nil en crue dans la repartition des sels nutritifs au large de ses embouchures, Rapp.et Proces-verb., Comm.
Int. Explor. Mer Medit., 28 (1966) 733-736.
[6] HALIM, Y., SAMAAN, A., ZAGHLOUL, F.A., Estuarine Plankton of the Nile and the Effect of Fresh-Water. Phytoplankton. In: Fresh-Water on the Sea. (Proc. Symp. Influence of Fresh- Water Outflow on Biological Processes in Fjords and Coastal Waters, 22-25 April 1974, Geilö, Norway), The Association of Norwegian Oceanographers, Oslo (1976).
[7] NIXON, S.W., Replacing the Nile: Are Anthropogenic Nutrients Providing the fertility once brought to the Mediterranean by a Great River? Ambio 321 (2003) 30-39.
[8] MORCOS, S.A., "Sources of Mediterranean intermediate water in the Levantine Sea", Studies in physical oceanography, a tribute to Georg Wüst on his 80th birthday, (GORDON, A.L., Ed.) 2, Gordon and Breach, New York (1972) 185-206.
[9] ZORE-ARMANDA, M., "Development of Mediterranean physical oceanography", Ocean Sciences Bridging the Millenia, A spectrum of historical accounts, UNESCO, Paris and China Ocean Press, Beijing (2004) 179-195.
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