WATER-QUALITY OF DIFFERENT AQUIFERS IN SAUDI-ARABIA AND ITS PREDICTIVE EFFECTS ON SOIL PROPERTIES

Chemical composition data of different aquifers was used to classify g roundwaters in Saudi Arabia. For the mean water composition, different water quality parameter ranges were for EC, 1.56 to 8.24 dS m-1; tota l dissolved solids (TDS), 1200 to 4860 mg L-1; sodium adsorption ratio (SAR) 3.10 to 12.53; Ca2+/Mg2+ ratio, 0.80 to 3.15; and Cl-/SO42- rat io, 0.49 to 3.68. For the 90th percentile water composition, the water quality parameter ranges were for EC, 2.26 to 13.10 dS m-1; TDS, 1950 to 9800 mg L-1; SAR, 3.45 to 18.76; Ca2+/Mg2+ ratio, 0.58 to 3.49; an d Cl-/SO42- ratio 0.40 to 4.85. Sodium was found to be the most abunda nt cation, followed by Ca2+, and Mg2+. Cl- and SO42- were present in a balanced proportion, followed by HCO3-. The waters were classified as C3S1 to C4S4, i.e., a category of high to very high salinity and low to very high sodicity problem water. Other parameters such as adj. SAR , adj. R(Na+), and ESP were calculated, interrelated, and commented up on for possible salinity and sodicity hazards in soils if irrigated wi th these waters. The data showed a strong positive relationship betwee n EC and TDS (r values of 0.97 for mean chemical composition and 0.95 for 90th percentile samples) and a poor correlation between EC and SAR (r values of 0.49 for mean chemical composition and 0.25 for 90th per centile sampling). A leaching requirement of 15 to 20% in excess of cr op water requirements is suggested for safe use of these waters, provi ded proper soil, water, and crop management practices are followed und er a specific land use.