Hydrochemical and isotopic investigation of the groundwater composition of an alluvial aquifer, Cap Bon Peninsula, Tunisia

Abstract

In the Grombalia region, Cap Bon Peninsula, northeastern Tunisia, increasing population and development of agricultural activity during the last few decades have engendered large expansion of groundwater pumping from the shallow, unconfined aquifer. Recently, the water table has displayed some signs of overexploitation such as decline in the water level in boreholes and considerable deterioration of water quality. Hydrochemical and isotopic data were used in conjunction with hydrogeological characteristics to investigate the groundwater composition in this aquifer. It has been demonstrated that groundwaters, recharged mainly in the surrounding foothills, acquire their mineralization principally by water-rock interaction, i.e., dissolution of evaporites and reverse cation exchange, and secondarily by return flow of irrigation waters. The isotopic signature of groundwaters permits identification of two different types. Water with depleted d 18 O and d 2 H contents is interpreted as recharge by non-evaporated rainfall, originating from a mixture of Atlantic and Mediterranean air masses. However, water with relatively enriched d 18 O and d 2 H contents is thought to reflect contamination by return flow of irrigation waters. Tritium contents, ranging between 1.2 and 4.5 TU indicate that groundwaters in an unconfined aquifer derive from post-nuclear recharge or contain a significant component of post-1950s water. The recent origin of these groundwaters is confirmed by the high carbon-14 activities, exceeding sometimes 100%, indicating the existence of a significant fraction of organic 14 C. This younger source of radiocarbon is, however, highlighted by the depleted d 13 C contents, corresponding to a system where CO 2 of C4 plants predominates.

Hydrogeochemistry and groundwater salinization in an ephemeral coastal flood plain: Cap Bon, Tunisia

“…10). Several previous studies in arid and semi-arid regions found the same result (Tsujimura et al 2007, Ben Moussa et al 2010, Diaw et al 2012): a decrease in d-excess is an indication that evaporation has occurred during the recharge process. Therefore, the decreasing values of d-excess for NaCl type shallow groundwater in Wadi Al Ayn plain suggest the role of wadi water in aquifer recharge, which again confirms the infiltrated oilfield brine in the groundwater near location AYR3.…”

“…6071500), the nearest GNIP (global network for isotopes in precipitation) station. The RMWL follows a linear regression: δ 2 H = 8δ 18 O + 12.4 (Maliki et al 2000, Ben Moussa et al 2010. The δ 18 O and δ 2 H contents of wadi water and groundwater in Wadi Al Ayn plain vary from -5.56‰ to -2.63‰ and from -32.71‰ to -20.04‰, respectively.…”

Combining boron isotopes and carbamazepine to trace sewage in salinized groundwater: A case study in Cap Bon, Tunisia

“…This is consistent with a meteoric recharge which was confirmed with stable isotopes (Ben Hamouda et al, 2011;Ben Moussa et al, 2009). It can also result from mixing with lowly mineralized groundwaters like in Piez 16 (2011) with a δ 11 B between 16‰ and 20‰ with very low B contents (3 µmol/L).…”

“…This hypothesis is supported by the evaporation identified in some groundwaters samples again with stable isotopes by Ben Moussa et al (2009).…”

Marine Eutrophication

“…Several isotopes such as B, O 2 , hydrogen (H), radon (Rn), and radium (Ra) are used as tracers for SGD (Cable et al 1996;Burnett and Dulaiova 2006;Burnett et al 2008;Ben Moussa et al 2010;Ben Hamouda et al 2011;Dimova et al 2013). …”