A geochemical survey of spring water from the main Ethiopian rift valley, southern Ethiopia: implications for well-head protection

Abstract

The report discusses the stable isotope values and major solute compositions of 16 springs and river-water samples along a topographic gradient in the main rift valley of southern Ethiopia. Most of the springs used for drinking water supplies discharge from local flow systems at scales of only tens of meters. The δ18O and δD values of waters unaffected by shallow evaporation form a local meteoric water line of δD=8.1δ18O+19.0, almost identical to that for the eastern Mediterranean area. The δ18O values show an altitude effect of –0.5‰ per 100-m elevation rise. Total dissolved nitrogen concentrations locally exceed 6 mg/L (as N), and phosphate concentrations were elevated above background levels in some springs, exceeding 0.2 mg/L PO4, probably due to agricultural practices upgradient of the springs. Modest well-head protection should be considered to protect public health from the effects of pollution by agricultural waste, given the very local scale of the flow systems providing spring water to Ethiopian villages.