Groundwater evolutions in the semi-arid aquifers of Dodoma City, Tanzania using stable isotopes of water and hydrogeological facies

Abstract

The recent influx of people into Dodoma City, Tanzania has greatly increased pressure on freshwater sources. To manage such stressed water resources, an assessment of evolutions of various groundwater masses using stable isotopes (SI) and hydrogeochemical facies was performed. The major groundwater types were found to be NaHCO3 and NaCl. The groundwater in some areas was polluted with up to 223.7 ppm of nitrate-NO3- . The majority of water masses were found to be of meteoric origin and deep aquifers were mostly replenished by heavy rains, which are more depleted in SI (δ2H and δ18O). Further, δ2H and δ18O from Hombolo Dam (HD) and Matumbulu Dam (MD) were highly enriched by evaporation, with average δ2H and δ18O values, of 5.76 & 39.69 and 2.37 & 16.34 ‰ compared to average rain values of 5.52 and 32.99 ‰, respectively. The contributions of highly enriched HD and MD waters to respective shallow groundwater systems were 57.52 and 22.2%. Yet, it was found that 75.4% of groundwater in the Hombolo suburb originates from the Makutupora aquifer, and this is the first time the contribution is quantified. Generally, this study offers a robust tool for adapting a local groundwater management strategy impacted by climate change, pollution, and overabstraction.