Distribution of the major ions Lake Nasser. I. Major anions

Abstract

      The completion of the Aswan High Dam in 1964 produced a permanent large impoundement; the High Dam Lake extending for 480 km, with the north­ern two thirds in Egypt (Lake Nasser) and the southern third in Sudan (Lake Nubia). Seasonal and regional distribution of major anions in Lake Nasser was investigated. The irregular vertical distribution of anions might be attributed to the effects of various physico-chemical and biological factors. The increase in the rate of evaporation in August was accompanied by the maximum seasonal average temperature value. The minimum and low seasonal average values of bicarbonate in May and August accompanied by the high and maximum se­asonal averages of carbonate coincided mainly with the decrease in solubility of carbonate by elevation of temperature those months. The highest evaporation rate in May and August was mainley responsible for the highest seasonal average concentractions of chloride those months. The maximum seasonal ave­rage sulphate value in April might be attributed to the increase in dissolved oxygen concentration from the high rate of photosynthesis in spring. The de­crease in the regional average values of sulphate and chloride in the southern region of the lake coincided possibly with dilution by the flood waters. The highest regional average bicarbonate concentrations accompanied by the lo­west regional average carbonate values in the northern area of the lake coin­cided in the main with the stagnation condition, where the CO₂ produced from decomposition of organic matter converted the carbonate into bicarbonate.