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Journal of Environmental Hydrology
ISSN 1058-3912 |
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Electronic Journal of the International Association for
Environmental Hydrology
JEH Volume 17 (2009), Paper 31 Posted November 22, 2009 ENVIRONMENTAL TRACERS AS INDICATORS OF WATER FLUXES THROUGH THE UNSATURATED ZONE IN SEMIARID REGIONS: THE CASE OF GAFSA PLAIN (SOUTHERN TUNISIA)
Messaouda Yermani1 2Laboratory of Radio-Analysis and Environment, Department of Geography, Faculty of Arts and Humanities, Sfax, Tunisia 3Laboratory of Radio-Analysis and Environment, Department of Geology, National School of Engineers, Sfax, Tunisia 4UMR CNRS-UPS "IDES", Université Paris-Sud, Orsay, France 5Commissariat au Développement Agricole de Tozeur, Ministry of Agriculture and Water Resources, Tunisia ABSTRACT Isotopic and chloride investigations have been conducted to estimate local hydrologic processes taking place in the semiarid Gafsa Plain (Southern Tunisia). A sandy soil core has been sampled at one site where the water table is at about 6 m depth and where water level fluctuations indicate a direct recharge of the shallow aquifer. Oxygen 18 and chloride data have been interpreted using the model of Barnes and Allison to suggest that evaporation rates from groundwater average around 11 mm/y. The rates from the shallow aquifer level to the soil surface range from 7 to 22 mm/y. The model parameters highlight that evaporation mechanisms are increasingly dominated by vapor phase transfers as the thickness of the layer through which water evaporates increases. The recharge rates by direct rainfall infiltration have been estimated by chloride mass balance method to range from 3 to 5 mm/y, with a mean value of 3.9 mm/y. This represents about 2.4% of local rainfall (164 mm/year). The long residence time of 77.8 years shown by the 6m depth chloride profile indicates slow recharge processes. Reference: Yermani, M., N. Chkir, K. Zouari, J.L. Michelot, and L. Moumni. 2009. Environmental tracers as indicators of water fluxes through the unsaturated zone in semiarid regions: The case of Gafsa Plain (southern Tunisia). Journal of Environmental Hydrology, Vol. 17, Paper 31. CONTACT: Messaouda Yermani Departement de Biologie-Géologie Institut Préparatoire aux Etudes d’Ingénieurs de Bizerte Zarzouna 7021 Tunisia E-mail: yermanim@yahoo.fr |
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