Environmental isotope characteristics of water sources in the Sokoto Basin – an evaluation of the role of meteoric recharge and residence time

The water sources of the Sokoto Basin are mainly of interrelated origin. The groundwater is composed of old water recharged in different climate regimes and of recent meteoric water. The recharge source is influenced by both local and regional moisture circulation given the lower slope and intercept of the local meteoric water line (LMWL) relative to those of the global meteoric water line (GMWL) and distribution of the deuterium excess d from -20 to +14 ‰. The identified interrelated water sources were confirmed by variations in tritium measured between 4.9 and <0.4 TU. The groundwater and surface water were identified to be of mixed origin, consisting of interrelated and recent types. This depicts active recharge taking place across the basin. The groundwater recharge was established to be renewable; however, rational water exploitation should be exercised considering growing water demand with the corresponding population rise.