The dynamics of Central Main Ethiopian Rift waters: evidence fron delta18O, deltaD and 87Sr/86Sr ratios

Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for dD, d18O and 87Sr/86Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show d18O _3.36 to +3.69 and dD _15.85 to +24.23, deep Aluto-Langano geothermal wells show d18O _4.65 to _1.24 and dD _12.39 to _9.31, groundwater wells show d18O _3.99 to +5.14 and dD _19.69 to +32.27, whereas the lakes show d18O and dD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: dD = 7 d18O + 11.2, R2 = 0.94, n = 42) and the Local Evaporation Line (LEL: dD = 5.63d18O + 8, n = 14, R2 = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (dD = _5.15 and d18