METAL CHEMISTRY OF IRRIGATION AND DRAINAGE WATERS OF AL-AHSA OASIS OF SAUDI-ARABIA AND ITS EFFECTS ON SOIL PROPERTIES

Water samples from 18 springs and 13 drainage canals and subcanals were collected from Al-Ahsa Oasis. Concentrations of total dissolved salts, Cl, SO4, HCO3, B, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, V, Ti, and Zn were determined. The soil salinity development (SSD), the adjusted Na ratio (adj. SAR), the adjusted Na adsorption ratio (adj. RNa), and exchangeable Na percentage (ESP) were calculated. Sodium was the most abundant cation in all water samples followed by Ca, Mg, Sr, and K in descending order. Concentrations of all other metals were below 0.1 mg L-1. Chloride was the most abundant anion, followed by SO4 and HCO3 in these waters. A significant correlation (P < 0.05) between Na and Cl in water samples was found. Thermodynamic calculations revealed that an appreciable fraction of Ca and Mg in spring and drainage waters were associated with SO4 and HCO3 ions. Calcium increased from less than 10 meq L-1 in spring waters to > 16 meq L-1, Mg was doubled, and Na and Cl increased several times in the drainage waters. The salinity and sodicity hazards of the spring and drainage waters were classified as C4S2 i.e. high salinity with medium sodicity problems.