Hydrochemical characterization and quality assessment of groundwater in Meki River Basin, Ethiopian Rift

Abstract

The present study was carried out in Meki River Basin (Ethiopian Rift) aiming at characterizing the hydrochemical composition of groundwater and evaluating the water quality status for drinking and irrigation uses. For this purpose, 63 primary groundwater samples from springs, hand-dug wells, and boreholes were collected and subjected to major ions analysis besides the in situ tests. The analysis result illustrates that Na+ and HCO3− are the principal cation and anion in the study area. The spatial investigation of the physiochemical parameters revealed that temperature, pH, TDS, EC, Na+, K+, HCO3−, Cl−, SO42−, and F− show a positive trend from the highland towards the rift floor along the groundwater flow direction. On the contrary, Ca2+ and Mg2+ show a negative tendency along the groundwater flow path. The groundwater of the study area generally evolves from predominantly fresh (TDS 750 mg/l) Na–HCO3 water type in the rift floor following the regional groundwater flow path. Gibbs diagram supported by ionic ratio (Na+ + K+/Ca2+ + Mg2+ vs total cations (TZ+) and Chloro-Alkaline Indices (CAIs) suggests that rock–water interaction (silicate hydrolysis and cation exchange) is the major hydrochemical processes controlling the evolution of the groundwater in the study area. 19% of TDS, 11% of EC, 83% of K+, 84% of HCO3−, and 52% of F− of the total water samples were unsuitable for the drinking uses compared with WHO water quality guideline. Spatial distribution maps of major ions (Ca2+, Mg2+, Na+, K+, Cl−, HCO3−, SO42−, and F−) and binary plots of physical parameters (temperature, pH, TDS, and EC) with elevation were produced. Both the spatial maps and binary plots generally show a water quality drop rift wards. Similarly, using multiple agriculture water quality criteria such as EC, SAR, RSC, PI, and Na%, the suitability of the groundwater for agricultural use was evaluated. Except a few samples in the rift floor, the majority of the water samples are found to be suitable for irrigation uses. As the study area is located where active geothermal activity and fluid circulation through fault systems, it is highly advised to carry out further toxic trace elements analysis to investigate the possible influence on the water quality.