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

The report discusses the stable isotope values and major solute composition s 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 drinki ng water supplies discharge from local flow systems at scales of only tens of meters. The delta O-18 and deltaD values of waters unaffected by shallow evaporation form a local meteoric water line of deltaD = 8.1 delta O-18+19 .0, almost identical to that for the eastern Mediterranean area. The delta O-18 values show an altitude effect of -0.5% per 100-m elevation rise. Tota l dissolved nitrogen concentrations locally exceed 6 mg/L (as N), and phosp hate concentrations were elevated above background levels in some springs, exceeding 0.2 mgn PO4, probably due to agricultural practices upgradient of the springs. Modest well-head protection should be considered to protect p ublic health from the effects of pollution by agricultural waste, given the very local scale of the flow systems providing spring water to Ethiopian v illages.