Title: Major and Trace Elements Geochemistry of Natural Waters in Meru, Tanzania

Abstract

The geochemistry of major and trace elements and stable isotopes of surface and groundwaters in the upper flanks of Mt. Meru volcano was assessed. The study area is in the volcanic province of northern Tanzania, in the Gregory Rift of the East Africa Rift System. This study involved spring-, stream-, river-, lake-, and groundwaters. PHREEQC was used for the calculation of aqueous speciation and mineral saturation indices.
The studied waters are of meteoric origin as indicated by δ2H-H2O and δ18O-H2O, with Na-HCO3 composition. The chemistry of the studied waters is mainly controlled by progressive dissolution of rocks at low temperatures as indicated by the correlation between major constituents (Na, K, Mg, SO4, and Cl). Two possible end-member water compositions, non-reacted rainwater and reacted water have been identified, and other spring-, river- and groundwaters fall between these two end members. The saline lakes are formed by evaporation of waters sourced at higher altitudes. Dissolution of carbonates, mixing with biogenic and atmospheric CO2, and input of deep volatiles are suggested based on δ13C-CO2.
The element mobility relative to Na is generally low in the studied waters, suggesting that many elements are incorporated into weathering minerals. Multiple mineral equilibria geothermometry suggests a possible low-temperature (<100 °C) geothermal system on the Eastern flank of Mt. Meru. The concentrations of As, Fe, Hg, Mn, Mo, U, Na, Cl, SO4, and NO3 in some samples and F in nearly all samples are higher than the permissible limits defined by local and international health guidelines.