Hydrochemical and Isotopic Assessment of Groundwater in the Goda Mountains Range System. Republic of Djibouti (Horn of Africa)

Abstract

The hydrogeological system of the Goda Mountains Range (GMR) in the Republic of Djibouti (Horn of Africa), hosted by volcanic and sedimentary formations, is the only water resource in the Tadjourah region for more than 85,000 inhabitants. Water needs are expected to drastically increase in the coming years, due to fast socio-economic development of the region. Accordingly, this system is under high pressure and should sustainably be exploited. However, little is known about the hydrogeology of this system. This study aims to improve the understanding of the hydrochemistry and the recharge processes of this system. The study is based on the combined interpretation of major ions, stable isotopes (18O, 2H), and radiogenic isotopes (3H, 14C). The interpretation of major ions contents using classical hydrochemical methods and principal component analysis highlighted that alteration of volcanic rocks minerals, coastal rainfall infiltration, and evaporation are the main processes from which groundwater acquires mineralization. Stable isotopes revealed that groundwater is of meteoric origin and has undergone high evaporation during infiltration. Radiogenic isotopes showed that groundwater in the basalts is mostly submodern to old, in relation with low hydraulic conductivity of the rocks and/or longer pathways through fissures from outcrop to subsurface. Groundwater in the rhyolites is much younger compared to the basalts due to faster infiltration. The sedimentary part, in connection with the rhyolites, has younger waters compared to the basalts, but older compared to the rhyolites. The overall results show that GMR is a fairly complex hydrogeological system, containing a resource made up of a mixture of waters of different ages. This study has made significant progress in understanding this system and is an initial step towards the sustainable exploitation of resources.

The Characteristics and Distribution of Deep Groundwater in Djibouti

“…With this background, groundwater studies in Djibouti have been intensified in recent years with respect to groundwater quality, age, and flow systems. In Tadjoura area, the northern part of the country, previous study using stable isotope and radioisotope analyses to estimate groundwater recharge systems and ages [2]. The results indicate that the groundwater in the area is mixed with different geological formations, such as rhyolite, basalt, and alluvium, indicating that the area may have a complex hydrogeological system.…”

“…150 mm yr-1 ), in this region and only occurs irregularly short-time localized rainfall. Hence, rivers are not formed regularly in this region, and groundwater has been used as the main water resource for humans and livestock [2].…”

“…In recent years, however, as the lifestyle of nomads as most of the population living in the suburbs has shifted from pastoralism to a combined agro-pastoralism [3] [4], the increased demand for groundwater resources, mainly for irrigation, and the pollution of groundwater quality due to rapid social development have become problems [2] [5]. Previous study using nitrogen stable isotope ratio and oxygen stable isotope ratio of nitrate in groundwater at Djibouti indicated that the high concentrations of nitrate in groundwater may have originated from livestock manure used mainly as organic fertilizer in agricultural activities [6].…”

Isotopic Assessment of Groundwater Salinity: A Case Study of the Southwest (SW) Region of Punjab, India

“…The value of d-excess varies due to evaporation at various stages [28]. The use of stable isotopes can be extremely useful in identifying various hydrological processes [6,29]; mechanisms [11]; sources [21,30]; characteristics of surface-groundwater interactions [22]; and depth-wise salinity variations [19] in India. In view of the above, the present study is carried out to (i) assess the present-day waterlogging and groundwater saline in aquifers at different depths in the southwest (SW) parts of Punjab and (ii) identify depth-wise saline water and freshwater zones in the aquifers using isotopes.…”

Abacus to Predict Groundwater Recharge at Non-Instrumented Hydrographic Basins

“…According to Scanlon et al [12] and Singh et al [13], there is no universal approach to study groundwater recharge and that is why the amount of methods reported in scientific literature is high. Amongst these methods, it can be highlighted: (i) the ones based on measuring the water table level [14][15][16]; (ii) the ones that use chemical tracers [17][18][19][20][21]; (iii) the ones based on direct Regardless of the issue, the intention, for the most part, is to provide tools for information gathering, in a way that water management may be more rational and efficient. According to Bortolin et al [1], for surface water a lot has been accomplished in that sense, but there is still a huge gap to bridge when it comes to groundwater.…”