The Stable Isotope Characteristics of Groundwater in the Voltaian Basin � An Evaluation of the Role of Meteoric Recharge in the Basin

The Stable Isotope Characteristics of Groundwater in the Voltaian Basin – An Evaluation of the Role of Meteoric Recharge in the Basin

This study finds that groundwater recharge in the shallow aquifer system of the Voltaian Basin is recent meteoric water which has undergone evaporative enrichment of the heavier isotopes of the main components of the water molecule as it transits the vadose zone. Apparently, low annual relative humidities and high temperatures in the basin have led to lower slope and intercept of the Local Meteoric Water Line than is observed in the Global Meteoric Water Line. This assertion is consistent with the observation that annual relative humidity variations in the basin are in the range of 65% – 85% even during the rainy season. Surface flows are considerably enriched in terms of the heavier stable isotopes of oxygen and hydrogen, suggesting severe evaporation. Using the stable isotope data of the surface flows and the estimated isotopic signature of the most probable source rainwater, this study finds that the rate of evaporative losses of water from the surface waterbodies ranges between 29.5% and 84.7%.