Groundwater age dating and recharge mechanism of Arusha aquifer, northern Tanzania: application of radioisotope and stable isotope techniques

Chacha, Nyamboge; Njau, Karoli N.; Lugomela, George V.; Muzuka, Alfred N. N.

Groundwater age dating and recharge mechanism of Arusha aquifer, northern Tanzania: application of radioisotope and stable isotope techniques | Datation des eaux souterraines et mécanisme de recharge de l’aquifère d’Arusha, Nord de la Tanzanie: application des techniques des radio isotopes et des isotopes stables Edad del agua subterránea y mecanismos de recarga del acuífero de Arusha, norte de Tanzania: aplicación de técnicas de radioisótopos e isótopos estables 坦桑尼亚北部Arusha含水层地下水测年及补给机理:放射同位素和稳定同位素技术的应用 Datação de águas subterrâneas e mecanismos de recarga do aquífero Arusha, norte da Tanzânia: aplicação de técnicas de radioisótopos e isótopos estáveis

2018

Chacha, Nyamboge | Njau, Karoli N. | Lugomela, George V. | Muzuka, Alfred N. N.

The continuous abstraction of groundwater from Arusha aquifers in northern Tanzania has resulted in a decline in water levels and subsequent yield reduction in most production wells. The situation is threatening sustainability of the aquifers and concise knowledge on the existing groundwater challenge is of utmost importance. To gain such knowledge, stable isotopes of hydrogen and oxygen, and radiocarbon dating on dissolved inorganic carbon (DIC), were employed to establish groundwater mean residence time and recharge mechanism.¹⁴C activity of DIC was measured in groundwater samples and corrected using a δ¹³C mixing method prior to groundwater age dating. The results indicated that groundwater ranging from 1,400 years BP to modern is being abstracted from deeper aquifers that are under intensive development. This implies that the groundwater system is continuously depleted due to over-pumping, as most of the sampled wells and springs revealed recently recharged groundwater. High ¹⁴C activities observed in spring water (98.1 ± 7.9 pMC) correspond with modern groundwater in the study area. The presence of modern groundwater suggests that shallow aquifers are actively recharged and respond positively to seasonal variations.

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