Spatial and Seasonal Variation of the Water Quality of the Red Sea

Fatima Ali Mohamed Ahmed, Mukhtar Ahmed Mustafa


The quality of Red Sea water samples collected in winter and
summer from the shore at Dongonab, Arbaat, Port Sudan, Suakin and
Arim was assessed. Standard procedures were used for determining the
electrical conductivity (EC) of seawater, calcium plus magnesium,
sodium, potassium, bicarbonate, chloride and sulphate. Sodium
adsorption ratio (SAR) was calculated by the following equation: SAR =
Na+/[(Ca2++ Mg2+)/2], where the ionic concentration are expressed in
mmole+/l. In summer, the EC values of sea waters ranged from 52.3 dS/m
at Port Sudan to 60.7 dS/m at Arbaat with a mean of 55.4 dS/m and a
coefficient of variation (CV) of 6%. Statistically the EC values varied in
the following order: Arbaat > Dongonap = Arim = Suakin = Port Sudan.
Sodium ranged from 840.6 to 574.1 with a mean of 547.2 mmole+/l. and
a coefficient of variation (CV) of 12.9%. The percentage of mean Na+,
Ca++, Mg++, and K+ in the sea water were 64.8, 3.1, 17.0 and 15.1,
respectively. Sodium concentration increased significantly northwards
according to the following quadratic relationship:
[Na] = 0.0048 X2 – 0.9513 X + 545.45 (r2 = 0.8323)
where X is the distance (km) away from Arim. Chloride ranged from
600.1 to 850.0 with a mean of 747.2 mmole+/l. and a CV of 12.9%.
Chloride constituted, on the average, about 88.6% of the main three
anions. On the average, NaCl, KCl and (Ca-Mg)Cl2 constituted about 65,
* Part of an MSc thesis dersertification by the first author, University of khartoum
1 Former post graduate student in DADCSI and at present lecturer in the Department of
Environment and Natural Resources, Faculty of Applied Sciences, Red Sea
2 Professor of Soil Science/Desertification

15.1 and 8.6%, respectively. The SAR values ranged from 75.7 at
Dongonap to 50.0 at Suakin, with a mean of 59.9, a STDEV of 9.7 and a
CV of 16.1%. Thus, the spatial variation of SAR values was greater than
that of the EC values. The SAR values also increased northwards. The
winter data were slightly different from those of the summer indicating a
low seasonal variation. Both salinity and sodicity of the sea water
increased northwards.


Red Sea water; salinity; sodicity; spatial variation

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