This study is developed in the frame of the Project "Water harvesting and Agricultural techniques in Dry lands: an Integrated and Sustainable model in MAghreb Regions" (www.wadismar.eu). Among its objectives, the Project aims at increasing groundwater availability through managed aquifer recharge in two watersheds of the Maghreb Region: Oued Biskra in Algeria and Oum Zessar in Tunisia. Prior to the design of the recharge intervention and supporting the selection of suitable zone for the recharge systems, a detailed hydrogeochemical characterization of the study areas was carried out, including bulk chemistry and multi-isotopic analyses of water and solid samples. Results for the Tunisian case are presented here. The area of interest is located in the SE of Tunisia. The main aquifers of the region are included in two hydro-lithostratigraphic provinces: the northern Jeffarah, limited to the south by the monoclinal of Djebel Tebaga de Medenine of Permian age, and characterized by a large coastal aquifer made essentially of Senonian limestone and Mio-Pliocene sand; the southern Jeffarah with the occurrence of Triassic sandstone upstream of the Medenine fault, and with Lower Miocene sand downstream of the fault. Dissolved sulphate isotopic composition in the local aquifers indicates that, mainly, the origin of sulphate is natural, being a mixture of different existing natural sources related to evaporites (Triassic and Jurassic gypsums). Dissolved nitrate from the Triassic aquifer show values in the isotopic range of soil organic nitrogen. Nevertheless, higher NO3 contents (> 10 mg/L) points to an origin from ammonium fertilizers affected by volatilizations processes. Increasing values of delta15N-NO3 and delta18O-NO3 from nitrate in some wells in the sourthern Jeffara coupled with a decreasing of the correspondent NO3 concentrations, indicates that denitrification processes are occurring in the aquifer.
Environmental isotopes (N, S, C, O, D) applied to the hydrogeochemical characterization of the Oum Zessar watershed (Tunisia)
CARLETTI, ALBERTO;DA PELO, STEFANIA;GHIGLIERI, GIORGIO
2016-01-01
Abstract
This study is developed in the frame of the Project "Water harvesting and Agricultural techniques in Dry lands: an Integrated and Sustainable model in MAghreb Regions" (www.wadismar.eu). Among its objectives, the Project aims at increasing groundwater availability through managed aquifer recharge in two watersheds of the Maghreb Region: Oued Biskra in Algeria and Oum Zessar in Tunisia. Prior to the design of the recharge intervention and supporting the selection of suitable zone for the recharge systems, a detailed hydrogeochemical characterization of the study areas was carried out, including bulk chemistry and multi-isotopic analyses of water and solid samples. Results for the Tunisian case are presented here. The area of interest is located in the SE of Tunisia. The main aquifers of the region are included in two hydro-lithostratigraphic provinces: the northern Jeffarah, limited to the south by the monoclinal of Djebel Tebaga de Medenine of Permian age, and characterized by a large coastal aquifer made essentially of Senonian limestone and Mio-Pliocene sand; the southern Jeffarah with the occurrence of Triassic sandstone upstream of the Medenine fault, and with Lower Miocene sand downstream of the fault. Dissolved sulphate isotopic composition in the local aquifers indicates that, mainly, the origin of sulphate is natural, being a mixture of different existing natural sources related to evaporites (Triassic and Jurassic gypsums). Dissolved nitrate from the Triassic aquifer show values in the isotopic range of soil organic nitrogen. Nevertheless, higher NO3 contents (> 10 mg/L) points to an origin from ammonium fertilizers affected by volatilizations processes. Increasing values of delta15N-NO3 and delta18O-NO3 from nitrate in some wells in the sourthern Jeffara coupled with a decreasing of the correspondent NO3 concentrations, indicates that denitrification processes are occurring in the aquifer.
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